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1
Carvajal, Juan-Carlos, William D. Liam Finn, and Carlos Estuardo Ventura. "Response spectrum-based seismic response of bridge embankments." Canadian Geotechnical Journal 57, no. 11 (2020): 1639–51. http://dx.doi.org/10.1139/cgj-2018-0674.
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A single degree of freedom model is presented for calculating the free-field seismic response of bridge embankments due to horizontal ground shaking using equivalent linear analysis and a design response spectrum. The shear wave velocity profile, base flexibility, 2D shape, and damping ratio of the embankment are accounted for in the model. A step-by-step procedure is presented for calculating the effective cyclic shear strain of the embankment, equivalent homogeneous shear modulus and damping ratio, fundamental period of vibration, peak crest acceleration, peak shear stress profile, peak shear strain profile, equivalent linear shear modulus profile, and peak relative displacement profile. Model calibration and verification of the proposed procedure is carried out with linear, equivalent linear, and nonlinear finite element analysis for embankments with fundamental periods of vibration between 0.1 and 1.0 s. The proposed model is simple, rational, and suitable for practical implementation using spreadsheets for a preliminary design phase of bridge embankments.
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Lui, Mathew, Elizabeth E. Gardiner, Jane F. Arthur, et al. "Novel Stenotic Microchannels to Study Thrombus Formation in Shear Gradients: Influence of Shear Forces and Human Platelet-Related Factors." International Journal of Molecular Sciences 20, no. 12 (2019): 2967. http://dx.doi.org/10.3390/ijms20122967.
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Thrombus formation in hemostasis or thrombotic disease is initiated by the rapid adhesion, activation, and aggregation of circulating platelets in flowing blood. At arterial or pathological shear rates, for example due to vascular stenosis or circulatory support devices, platelets may be exposed to highly pulsatile blood flow, while even under constant flow platelets are exposed to pulsation due to thrombus growth or changes in vessel geometry. The aim of this study is to investigate platelet thrombus formation dynamics within flow conditions consisting of either constant or variable shear. Human platelets in anticoagulated whole blood were exposed ex vivo to collagen type I-coated microchannels subjected to constant shear in straight channels or variable shear gradients using different stenosis geometries (50%, 70%, and 90% by area). Base wall shears between 1800 and 6600 s−1, and peak wall shears of 3700 to 29,000 s−1 within stenoses were investigated, representing arterial-pathological shear conditions. Computational flow-field simulations and stenosis platelet thrombi total volume, average volume, and surface coverage were analysed. Interestingly, shear gradients dramatically changed platelet thrombi formation compared to constant base shear alone. Such shear gradients extended the range of shear at which thrombi were formed, that is, platelets became hyperthrombotic within shear gradients. Furthermore, individual healthy donors displayed quantifiable differences in extent/formation of thrombi within shear gradients, with implications for future development and testing of antiplatelet agents. In conclusion, here, we demonstrate a specific contribution of blood flow shear gradients to thrombus formation, and provide a novel platform for platelet functional testing under shear conditions.
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Johnston, T. M. Shaun, and Daniel L. Rudnick. "Observations of the Transition Layer." Journal of Physical Oceanography 39, no. 3 (2009): 780–97. http://dx.doi.org/10.1175/2008jpo3824.1.
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Abstract The transition layer is the poorly understood interface between the stratified, weakly turbulent interior and the strongly turbulent surface mixed layer. The transition layer displays elevated thermohaline variance compared to the interior and maxima in current shear, vertical stratification, and potential vorticity. A database of 91 916 km or 25 426 vertical profiles of temperature and salinity from SeaSoar, a towed vehicle, is used to define the transition layer thickness. Acoustic Doppler current measurements are also used, when available. Statistics of the transition layer thickness are compared for 232 straight SeaSoar sections, which range in length from 65 to 1129 km with typical horizontal resolution of ∼4 km and vertical resolution of 8 m. Transition layer thicknesses are calculated in three groups from 1) vertical displacements of the mixed layer base and of interior isopycnals into the mixed layer; 2) the depths below the mixed layer depth of peaks in shear, stratification, and potential vorticity and their widths; and 3) the depths below or above the mixed layer depth of extrema in thermohaline variance, density ratio, and isopycnal slope. From each SeaSoar section, the authors compile either a single value or a median value for each of the above measures. Each definition yields a median transition layer thickness from 8 to 24 m below the mixed layer depth. The only exception is the median depth of the maximum isopycnal slope, which is 37 m above the mixed layer base, but its mode is 15–25 m above the mixed layer base. Although the depths of the stratification, shear, and potential vorticity peaks below the mixed layer are not correlated with the mixed layer depth, the widths of the shear and potential vorticity peaks are. Transition layer thicknesses from displacements and the full width at half maximum of the shear and potential vorticity peak give transition layer thicknesses from 0.11× to 0.22× the mean depth of the mixed layer. From individual profiles, the depth of the shear peak below the stratification peak has a median value of 6 m, which shows that momentum fluxes penetrate farther than buoyancy fluxes. A typical horizontal scale of 5–10 km for the transition layer comes from the product of the isopycnal slope and a transition layer thickness suggesting the importance of submesoscale processes in forming the transition layer. Two possible parameterizations for transition layer thickness are 1) a constant of 11–24 m below the mixed layer depth as found for the shear, stratification, potential vorticity, and thermohaline variance maxima and the density ratio extrema; and 2) a linear function of mixed layer depth as found for isopycnal displacements and the widths of the shear and potential vorticity peaks.
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Shrestha, Ram Krishna, Mukil Alagirisamy, Purushottam Dangol, Binod Pradhananga, and Om Prakash Giri. "Impact of irregular masonry infill walls on the seismic response of reinforced concrete frame buildings using linear dynamic analysis." International Journal of ADVANCED AND APPLIED SCIENCES 11, no. 8 (2024): 98–110. http://dx.doi.org/10.21833/ijaas.2024.08.011.
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This paper aimed to investigate the seismic response of reinforced concrete (RC) frame buildings using linear dynamic analysis. The study focused on the effects of irregular distributions of masonry infill walls both in elevation (soft story at different levels) and in horizontal (plan) distribution on seismic behavior. Seventeen models were analyzed, including infill frame models with soft stories, models with infill panels only in certain bays, and bare frame models. All models were analyzed using the linear response spectrum (RS) dynamic analysis method. Structural design typically focuses on peak response values, and response spectrum analysis examines the structure's behavior and performance through these peak values. The analysis results indicate that masonry infill walls significantly affect the building's fundamental time period, base shear, story shear, and inter-story drift.
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Skempton, A. W., D. Norbury, D. J. Petley, and T. W. Spink. "Solifluction shears at Carsington, Derbyshire." Geological Society, London, Engineering Geology Special Publications 7, no. 1 (1991): 381–87. http://dx.doi.org/10.1144/gsl.eng.1991.007.01.34.
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AbstractA clayey solifluction deposit of Devensian age on the lower slopes of a broad valley in Namurian mudstone is about 1.2 m thick and near its base are shear surfaces, gently undulating and occupying on average 40% of the length (56 m) examined in trial pits. Within a shear zone up to 2 mm in thickness the clay mineral aggregates are aligned sub-parallel to the shear surface; otherwise the aggregates are in random orientation. Tests show that strength on the shear surface falls to the residual value (c′ = 0, φr′ = 12°) after small displacements. The resultant peak strength parameters of the deposit, allowing for the undulating and discontinuous nature of the shears, are c′ = 6 kPa and φ′ = 18°; as compared to c′ = 10 kPa and φ′ = 20° for the intact clay. Average index properties are w = 40, LL = 75, PL = 32 and clay fraction = 62%.
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El Ouardani, Adil, and Taoufik Tbatou. "Seismic Isolators Layout Optimization Using Genetic Algorithm Within the Pymoo Framework." Civil Engineering Journal 10, no. 8 (2024): 2517–35. http://dx.doi.org/10.28991/cej-2024-010-08-07.
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In most previous studies, seismic base isolation system optimization has mainly focused on determining isolation layer parameters. However, the subsequent steps of isolator device selection and positioning can significantly impact overall system performance. To address these shortcomings, we propose an alternative optimization approach demonstrated through two models: regular and irregular 8-storey reinforced concrete structures. This approach utilizes the Pymoo framework and commercially available isolators to find optimal isolator layout configurations in two steps. First, using the equivalent lateral force (ELF) procedure, an initial population of seismic isolators meeting shear strain, base shear coefficient, and buckling requirements was randomly selected from suppliers' elastomeric bearing catalogs. Second, the Non-dominated Sorting Genetic Algorithm II (NSGA-II) was used to improve the seismic response of the models under the fast nonlinear analysis (FNA) method by minimizing peak roof acceleration, inter-story drift ratio, displacement of the isolated base layer, as well as maximizing the fundamental period. The results underscore the effectiveness of this approach in improving seismic response. Compared to fixed-base structures, the optimal solutions achieved more than double the fundamental period, reduced peak roof acceleration by over 70%, and diminished base shear force by approximately 50%. This methodology can serve as a reference for future research across various structure types, including hybrid isolation systems and steel structures. Doi: 10.28991/CEJ-2024-010-08-07 Full Text: PDF
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Song, Liang-Long, Tong Guo, and Xin Shi. "Seismic Analysis of Low-Rise Self-Centering Prestressed Concrete Frames considering Soil-Structure Interaction." Shock and Vibration 2019 (December 11, 2019): 1–13. http://dx.doi.org/10.1155/2019/2586452.
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In this study, the seismic behavior of low-rise self-centering (SC) prestressed concrete frames considering soil-structure interaction (SSI) is presented. For this purpose, a typical 4-story SC concrete frame, with and without flexible foundations, is analyzed through nonlinear dynamic analysis. Ground motion sets with two hazard levels are selected for analysis. A conventional reinforced concrete (RC) frame is also studied, and the structural demands of the RC and SC frames are compared in terms of peak and residual drifts, base shear, residual settlement, and rotation of foundation. The analysis results show that considering soil-structure interaction generally increases the peak and residual drift demands and reduces the base shear and connection rotation demands when compared to fixed base conditions. For the cases with and without flexible foundations, the SC frame is found to have comparable peak story drifts with the RC frame and have the inherent potential of significantly reducing the residual drifts. The seismic analysis results of the frames with flexible bases show that the RC and SC frames can experience foundation damage due to excessive residual foundation rotations after the maximum considered earthquake (MCE).
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Heidebrecht, A. C., N. Naumoski, and A. Rutenberg. "Towards a new base shear format in future NBCC seismic provisions." Canadian Journal of Civil Engineering 21, no. 4 (1994): 682–95. http://dx.doi.org/10.1139/l94-068.
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Recent trends in the specifications of earthquake design forces are moving away from spectral amplification of ground motion towards direct evaluation of spectral values. Also, the 1988 Saguenay earthquake produced strong evidence for the need to modify the present provisions for low period structures in eastern North America. A new database consisting of 75 time histories was assembled and an extensive parametric study was undertaken to prepare new seismic response factors (S curves) for the National Building Code of Canada (NBCC). These time histories were divided into five categories (15 time histories each) on the basis of their frequency content as measured by their peak ground acceleration to peak ground velocity ratios, ranging from very high (≈3) to very low (≈0.5). Mean and mean + one standard deviation response spectra for one-degree-of-freedom and multi-degree-of-freedom systems were computed for the five categories using several normalizing (scaling) rules for the time histories. The results were compared and spectral amplification factors are presented. Spectra based on peak spectral velocity scaling were compared with spectra based on the present peak ground velocity scaling approach, and some differences are noted. Also, comparisons with the design spectra given in the 1991 edition of the National Earthquake Hazard Reduction Program provisions are presented. On the basis of this study, new S curves are proposed for consideration in the development of future editions of the NBCC. Key words: earthquake engineering, design spectra, building codes, amplification, ground motion, acceleration, velocity, ratio.
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Li, Sheng Сai. "Experimental Research on Restoring Force Characteristics of Light Composite Structure." Advanced Materials Research 261-263 (May 2011): 130–36. http://dx.doi.org/10.4028/www.scientific.net/amr.261-263.130.
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Pseudo dynamic test and pseudo static test were carried out on 1/2 scale model of light composite structure. By experimental research, hysteretic curves of base shear force and top displacement of the model structure were got, which come from various sections of pseudo dynamic test and pseudo static test, and through hysteretic curves of base shear force and top displacement of the model structure, skeleton curve of base shear force and top displacement of the model structure can be got. Outside line of all skeleton curves was skeleton curve of the light composite structure model. By analyzing and simplifying of the skeleton curve, finally restoring force model of the model structure was obtained, so reasonable dynamic analysis method of seismic design of the model structure can be offered. Research shows that as peak acceleration of inputting seismic wave continuously grows, especially when the peak acceleration reaching 800 gal, after the model structure reached plastic stage and in the stage of pseudo static test, the hysteretic curves become fuller and fuller, which shows that, with continuous emerging and propagation of crack, the structural rigidity losses gradually, and its energy dissipation capacity increases gradually. So earthquake fortification level of not collapse when hit by rarely occurred earthquake will achieve.
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Thompson, Richard B., Ian Paterson, Kelvin Chow, et al. "Characterization of the relationship between systolic shear strain and early diastolic shear strain rates: insights into torsional recoil." American Journal of Physiology-Heart and Circulatory Physiology 299, no. 3 (2010): H898—H907. http://dx.doi.org/10.1152/ajpheart.00353.2010.
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Early diastolic left ventricular (LV) untwisting has been evaluated as a manifestation of LV recoil, reflecting the release of elastic energy stored during systole. The primary goal of this study was to characterize the relationship between systolic strain (e.g., circumferential strain and the shear strains that comprise twist) with the resulting early diastolic shear strain rates, including the rate of untwisting. A further goal was to characterize these relationships regionally from apical to basal locations. Cardiac magnetic resonance imaging tissue tagging was used to measure circumferential strain, global and regional (apex, mid, basal) twist (θ), and circumferential-longitudinal (ϵCL) and circumferential-radial (ϵCR) shear strains along with the corresponding untwisting rates (dθ/d t) and diastolic shear strain rates (dϵ/d t) in 32 healthy males (33 ± 7 yr). LV untwisting rates and shear strain rates measured during early diastole varied significantly with the measurement location from apex to base ( P < 0.001) but demonstrated significant linear correlation with their corresponding preceding systolic strains ( P < 0.001). Untwisting rates and diastolic shear strain rates were not significantly correlated with circumferential systolic strain or end-systolic volume ( P > 0.05). Normalization of the untwisting rates to the peak twist (dθ/d tNorm = −13.6 ± 2.1 s−1) or shear strain rates to peak systolic shear strain (dϵCL/d tNorm = −15.0 ± 5.4 s−1, and dϵCR/d tNorm = −14.2 ± 7.7 s−1) yielded a uniform measure of early diastolic function that was similar for all shear strain and twist components and for all locations from apex to base. These findings support a linear model of torsional recoil in the healthy heart, where diastolic shear strain rates (e.g., untwisting rates) are linearly related to the corresponding preceding systolic shear stain component. Furthermore, these findings suggest that torsional recoil is uncoupled from end-systolic volumes or the associated strains, such as circumferential strain.
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Li, Hai Bo, Hai Peng Feng, Bo Liu, and Jun Ru Li. "Experimental Studies on Mechanical Properties of Rock Joints under Dynamic Loading." Key Engineering Materials 326-328 (December 2006): 1709–12. http://dx.doi.org/10.4028/www.scientific.net/kem.326-328.1709.
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In order to study the strength and deformation properties of rock joint under different shear velocities, normal stresses and undulation angles, series testes are conducted by a RMT-150C testing machines with artificial concrete rock joint samples in the present paper. Base on the experimental results, it can be found that the peak shear strengths decrease with the increment of shear velocity, and the decreasing rates tend to decrease with the increasing shear velocity. The shear strength of rock joints increase with the increasing undulation angles, and linearly increase with the increment of normal stress. It is also indicated that the shear stiffness increase with the increasing normal stress, undulation angle as well as the shear velocity with a decreasing tendency.
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Srinivas, Arjun, Bryson Robertson, Jonah Benjamin Gadasi, Barbara Gwynne Simpson, Pedro Lomónaco, and Jesús María Blanco Ilzarbe. "Impact of Limited Degree of Freedom Drag Coefficients on a Floating Offshore Wind Turbine Simulation." Journal of Marine Science and Engineering 11, no. 1 (2023): 139. http://dx.doi.org/10.3390/jmse11010139.
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The worldwide effort to design and commission floating offshore wind turbines (FOWT) is motivating the need for reliable numerical models that adequately represent their physical behavior under realistic sea states. However, properly representing the hydrodynamic quadratic damping for FOWT remains uncertain, because of its dependency on the choice of drag coefficients (dimensionless or not). It is hypothesized that the limited degree of freedom (DoF) drag coefficient formulation that uses only translational drag coefficients causes mischaracterization of the rotational DoF drag, leading to underestimation of FOWT global loads, such as tower base fore-aft shear. To address these hydrodynamic modeling uncertainties, different quadratic drag models implemented in the open-source mid-fidelity simulation tool, OpenFAST, were investigated and compared with the experimental data from the Offshore Code Comparison Collaboration, Continued, with Correlation (OC5) project. The tower base fore-aft shear and up-wave mooring line tension were compared under an irregular wave loading condition to demonstrate the effects of the different damping models. Two types of hydrodynamic quadratic drag formulations were considered: (1) member-based dimensionless drag coefficients applied only at the translational DoF (namely limited-DoF drag model) and (2) quadratic drag matrix model (in dimensional form). Based on the results, the former consistently underestimated the 95th percentile peak loads and spectral responses when compared to the OC5 experimental data. In contrast, the drag matrix models reduced errors in estimates of the tower base shear peak load by 7–10% compared to the limited-DoF drag model. The underestimation in the tower base fore-aft shear was thus inferred be related to mischaracterization of the rotational pitch drag and the heave motion/drag by the limited-DoF model.
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Lythe, G. R., and D. Surry. "Wind-induced torsional loads on buildings." Canadian Journal of Civil Engineering 19, no. 4 (1992): 711–23. http://dx.doi.org/10.1139/l92-079.
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This paper examines the mean and peak torsional wind loads on tall buildings using two data bases of torsion measured experimentally in wind tunnel tests: the first, a large data base of mean torsional loads; and the second, a smaller data base of peak torsions. Although the mean load constitutes only a part of the total peak load required for design, it provides considerable insight into the aerodynamics of torsion, while improvement in its estimation also improves the estimation of the total peak load, using empirical gust factor methods. Comparisons between experimental results and the corresponding provisions of the 1985 National Building Code of Canada and Commentary indicate that, while the NBCC is a good estimator of mean shear loads, it significantly underestimates the mean torsional loads on tall buildings. The experimental data are further analysed to provide an improved estimation method for both the mean and the peak torsion. For mean torsion, this involves evaluating various definitions of the torsion coefficient and classifying building shapes in order to decrease the variability of the associated coefficients. This process leads to some notion of those shapes susceptible to large torsional loads and the most important building parameters on which to base predictions. This insight, along with the data base of peak torsion, is used to simplify and improve an existing method for estimating peak torsion, which was developed using a smaller data base. Key words: torsion, wind loading, codes, wind tunnel tests, tall buildings.
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Pouranvari, Majid, and Pirooz Marashi. "Resistance Spot Welding of Unequal Thickness Low Carbon Steel Sheets." Advanced Materials Research 83-86 (December 2009): 1205–11. http://dx.doi.org/10.4028/www.scientific.net/amr.83-86.1205.
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Resistance spot welding is the dominant process for joining sheet metals in automotive industry. Even-thickness combinations are rarely used in practice; therefore, there is clearly a practical need for failure behaviour investigation of uneven-thickness resistance spot welds. The aim of this paper is to investigate and analyze the failure mode and failure mechanism of dissimilar thickness low carbon steel resistance spot welds during tensile-shear overload test. Microstructural investigations, microhardness tests and tensile-shear tests were conducted. Mechanical properties of the joint were described in terms of peak load, energy absorption and failure mode. It was concluded that weld nugget size and the strength of the thinner base metal are the controlling factors of the peak load and energy absorption of dissimilar thickness spot welds.
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Hussain, Majid, and Ajanta Sachan. "Effect of Inter-granular Void Ratio on Volume Compressibility and Undrained Shear Response of Base-sand and Natural Silty-sand of Kutch." E3S Web of Conferences 92 (2019): 06002. http://dx.doi.org/10.1051/e3sconf/20199206002.
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In this article, effect of inter-granular void ratio (eg) on the volume compressibility and undrained shear strength behaviour of a natural silty-sand and base-sand is explored. Natural silty-sand sample was collected from Fatehgarh dam in Kutch region of India and the specimens prepared were subjected to isotropically consolidated undrained compression (CIUC) triaxial tests under two scenarios. In scenario one, silty-sand collected from Fatehgarh dam was used to perform CIUC triaxial tests at in-situ density. However, scenario two was based on CIUC triaxial tests on base-sand, which was extracted from Fatehgarh dam silty-sand soil by removing fines. It was ensured that the two specimens (silty-sand, base-sand) had the same void ratio (e = 0.704) but different inter-granular void ratios (eg-silty-sand = 1.156 and eg-base-sand = 0.704). Volume compressibility during isotropic consolidation phase of specimens was strongly reduced in the base-sand as compared to silty-sand. The undrained shear response of base-sand showed an increase in peak deviatoric stress by a factor of 1.8, 1.6 and 1.7 as compared to silty-sand at an initial effective confining pressure of 100 kPa, 200 kPa and 300 kPa respectively. The angle of friction mobilized at peak deviatoric stress and the work done per unit volume increased with the decrease in the inter-granular void ratio (eg), although the void ratio (e) was same.
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Yuan, Ying, Ai Hong Zhou, and Yan Li Gao. "Effect of Friction Bearing Ratio on Isolation Performance and Nonlinear Property in Parallel Composite Isolation System." Advanced Materials Research 639-640 (January 2013): 896–900. http://dx.doi.org/10.4028/www.scientific.net/amr.639-640.896.
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Different friction bearing ratios have effects on the base isolation property of parallel composite isolation system subjected to the seismic excitation. In order to deeply investigate how the friction bearing ratio affect the isolation property, the numerical simulation was carried out by the time-history analysis method, in which the seismic response of parallel composite isolation system with different friction bearing ratios under different acceleration peak values were calculated. Then, the effects of different friction bearing ratios on the base maximum shear coefficients and base maximum displacements; the hysteretic characteristics and nonlinear properties were analyzed and discussed. The results show that, for the parallel composite isolation system, friction bearing ratio is a key factor affecting the isolation property and the nonlinear properties are tightly related to the friction bearing ratio and acceleration peak values.
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A. Krishnamoorthy. "Effects of Damping Ratio of Restoring force Device on Response of a Structure Resting on Sliding Supports with Restoring Force Device." Electronic Journal of Structural Engineering 5 (January 1, 2005): 55–68. http://dx.doi.org/10.56748/ejse.550.
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Effects of damping ratio of the restoring force device on the response of a space frame structure resting on sliding type of bearing with restoring force device is studied. The NS component of the El – Centro earthquake and harmonic ground acceleration is considered for earthquake excitation. The structure is modeled considering six-degrees of freedom (three translations and three rotations) at each node. The sliding support is modeled as a fictitious spring with two horizontal degrees of freedom. The response quantities considered for the study are the top floor acceleration, base shear, bending moment and base displacement. It is concluded from the study that the displacement of the structure reduces as the damping of the restoring force device increases. Also, the peak values of acceleration, bending moment and base shear decreases as the damping of the restoring force device increases.
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Griffith, Michael C., Ian D. Aiken, and James M. Kelly. "Comparison of Earthquake Simulator Test Results with the SEAONC Tentative Seismic Isolation Design Requirements." Earthquake Spectra 6, no. 2 (1990): 403–17. http://dx.doi.org/10.1193/1.1585577.
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Earthquake simulator tests were performed on a 1/5-scale, 6-story reinforced concrete shear-wall structure and a 1/4-scale, 9-story braced steel frame structure. The structures were supported by five different base isolation systems which consisted of various types and combinations of elastomeric bearings. The main objective of this study was to compare the peak experimental displacements of the base isolation systems tested with values given by the tentative base isolation design provisions proposed by the Seismology Committee of the Structural Engineers Association of Northern California (SEAONC). Comparisons of experimental results and values from the SEAONC base isolation design formula for displacements indicated that the formula is generally conservative, even for predominantly low frequency earthquake motions, provided the ground motion coefficient Av (based on the effective peak velocity as defined by ATC 3-06) is used in the design equation for base-isolated structures with periods greater than 1 second.
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Nelson, M. A., E. R. Pardyjak, M. J. Brown, and J. C. Klewicki. "Properties of the Wind Field within the Oklahoma City Park Avenue Street Canyon. Part II: Spectra, Cospectra, and Quadrant Analyses." Journal of Applied Meteorology and Climatology 46, no. 12 (2007): 2055–73. http://dx.doi.org/10.1175/2006jamc1290.1.
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Abstract Velocity data were obtained within Park Avenue in Oklahoma City, Oklahoma, using three-dimensional sonic anemometers under unstable atmospheric conditions. These data are used to produce velocity spectra, cospectra, and weighted joint probability density functions at various heights and horizontal locations in the street canyon. This analysis has helped to describe a number of physically interesting urban flow phenomena. Previous research has shown that the ratio of Reynolds shear stresses to normal stresses is typically much smaller deep within the canopy than those ratios found at the top of canopy and in the roughness sublayer. The turbulence in this region exhibits significant contributions to all four quadrants of a weighted joint-probability density function of horizontal and vertical velocity fluctuations, yielding the characteristic small Reynolds shear stresses in the flow. The velocity cospectra measured at the base of the canopy show evidence of discrete frequency bands of both positive and negative correlation that yield a small correlation, as indicated by the Reynolds shear stresses. Two major peaks were often observed in the spectra and cospectra: a low-frequency peak that appears to be associated with vortex shedding off the buildings and a midfrequency peak generally associated with canyon geometry. The low-frequency peak was found to produce a countergradient contribution to the along-wind vertical velocity covariance. Standard spectral tests for local isotropy indicate that isotropic conditions occur at different frequencies depending on spatial location, demonstrating the need to be thorough when testing for local isotropy with the urban canopy.
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Hazaveh, Nikoo K., Ali A. Rad, Geoffrey W. Rodgers, J. Geoffrey Chase, Stefano Pampanin, and Quincy T. Ma. "Shake Table Testing of a Low Damage Steel Building with 2-4 Displacement Dependent (D3) Viscous Damper." Key Engineering Materials 763 (February 2018): 331–38. http://dx.doi.org/10.4028/www.scientific.net/kem.763.331.
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To improve seismic structural performance, supplemental damping devices can be incorporated to absorb seismic response energy. The viscous fluid damper is a well-known solution. However, while they reduce displacement demand, they can increase overall base shear demand in nonlinear structures as they provide resistive forces in all four quadrants of force-displacement response. In contrast, Direction and Displacement Dependent (D3) viscous fluid dampers offer the opportunity to simultaneously reduce structural displacements and the total base-shear force as they only produce resistive forces in the second and fourth quadrants of a structural hysteresis plot. The research experimentally examines the response of a half-scale, 2-storey moment frame steel structure fitted with a 2-4 configuration D3 viscous fluid damper. The structure is also tested with conventional viscous dampers to establish a baseline response and enable comparison of results. Dynamic experimental tests are used to assesses the base shear, maximum drift and residual deformation under 5 different earthquakes (Northridge, Kobe, Christchurch (CCCC), Christchurch (CHHC), and Bam ground motion). Response metrics including base shear, the maximum structural displacement, and peak structural accelerations are used to quantify performance and to assess the response reductions achieved through the addition of dampers. It is concluded that only the 2-4 device is capable of providing concurrent reductions in all three of these structural response metrics.
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Motra, Gokarna Bahadur, Wrik Mallik, and Naresh K. Chandiramani. "Semi-active vibration control of connected buildings using magnetorheological dampers." Journal of Intelligent Material Systems and Structures 22, no. 16 (2011): 1811–27. http://dx.doi.org/10.1177/1045389x11412640.
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Response attenuation of seismically excited adjacent buildings connected by a MR damper is studied using semi-active LQR controller design. The modified Bouc–Wen model relating damper force to input voltage/states is considered. Thus, obtaining the input voltage to realize a desired control force is a non-trivial task. The desired control force is obtained using LQR control, and desired voltage predicted based on either a RNN model or a CVL. Results for the 5-storey and 3-storey interconnected buildings (B5–B3) are obtained in terms of peak and RMS responses. These are compared with passive-on control for which a constant saturation voltage is applied to the damper. Percentage reduction in maximum peak[RMS] response, when using LQR–CVL instead of passive on control, is 24[20] for interstorey drift, 18[23] for displacement, and 17[26] for accelerations. Corresponding further percentage reductions of 6[5], 5[5], and −5[4], and reductions in base shear, occur when considering LQR–RNN vis-á-vis LQR–CVL control. Peak accelerations for B5[B3] attenuate[increase] significantly, resulting in a re-distribution and reduction of base shear, when comparing semi-active versus passive-on control. Results show that connection of adjacent buildings using MR damper driven by a LQR–RNN controller provides a promising means of response attenuation.
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Chai, Shaoqiang, Yong Chen, Dongbo Cai, Wei Wang, Qihao Chen, and Jinhao Liu. "Study on the Influence of a Rubber-Modified Soil Isolation Layer on the Isolation Performance of Frame Structures with Different Foundation Forms." Buildings 13, no. 10 (2023): 2584. http://dx.doi.org/10.3390/buildings13102584.
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In order to investigate the seismic performance of a rubber-modified soil isolation layer, a three-dimensional finite element model was constructed using finite element analysis software, utilizing a two-story frame structure as the engineering background. Nonlinear dynamic time history analysis and comparisons were performed against the seismic performance of the structure. The evaluation was based on several parameters, including the contact area of the base, the thickness of the rubber-particle-modified soil isolation layer, ground motion records with varying amplitudes, and seismic frequency spectrum characteristics. The research findings indicate that the implementation of a rubber-modified soil isolation layer effectively mitigates the peak acceleration, horizontal displacement, and shear stress of the frame structure. This not only enhances the seismic performance of the structure but also enlarges the contact area of the base. Increasing the thickness of the rubber-modified soil isolation layer will effectively decrease the peak acceleration, horizontal displacement, and shear stress of the structure during seismic events. The effectiveness of the isolation provided by the rubber-modified soil layer improves as the intensity of the ground motion record increases.
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Pratama, M. Mirza Abdillah, Septiana Dyah Sugmana Putri, and Edi Santoso. "Analisis Kinerja Bangunan Gedung Tinggi Dengan Penambahan Dinding Geser (Studi Kasus: Bangunan 8 Lantai)." Siklus : Jurnal Teknik Sipil 7, no. 2 (2021): 119–30. http://dx.doi.org/10.31849/siklus.v7i2.6922.
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Shear walls in high-rise buildings serve to increase the resistance of high-rise buildings to lateral loads. This study aims to compare the structural performance of an existing 8 (eight) storey building designed as a special moment resisting frame structure against a building designed as a dual system, which consists of: structural vibration time, base shear force, displacement, and drift. Three configurations for shear walls are designed, as follows: (1) L-shaped located at the corner of one side of the building, totaling 2 (two) units (SW1); (2) L-shaped located at the four corners of the building totaling 4 (four) units (SW2); and 3) I-shaped located along the side of the building totaling 6 (six) units (SW3). Simulations are run using the Etabs by taking into account dead loads, live loads, and earthquake loads. The results show that the addition of shear walls can: (1) reduce the vibration period of the structure up to 62,55% in SW3, (2) increase the base shear force up to 86,34% in SW3, (3) reduce peak displacement up to 84,86% in SW3, and (4) reduce the drift between floors up to 89,58% in SW3. However, the SW2 is considered to be better applied to the building by taking into account the structural performance, effectiveness and efficiency factors.
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Wang, Yougang, Zhengchao Bi, Sheng Luo, and Jian Wang. "Experimental Study on the Mechanical Properties of Squat RC Shear Walls with Corrosion Along the Base." Buildings 14, no. 11 (2024): 3409. http://dx.doi.org/10.3390/buildings14113409.
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In corrosive environments containing chloride and sulfate, the corrosion of steel bars is common along the base of squat RC shear walls (SRCSW) due to problems such as construction quality, concrete stress concentration, local defects, and accumulation of water and corrosive media. In this paper, three SRCSWs are designed and constructed and their mechanical properties assessed. One side of each SRCSW was exposed to a corrosive environment for 70 days, while the other side was subject to the same conditions over different corrosion times (i.e., 0 day, 42 days, and 70 days). Then, the corrosion-induced cracking process, the mechanical properties of SRCSWs corroded along the base, the relationship between the mass loss of total steel bars (MLTSB) in the corroded area and the wall mechanical properties, and the relationship between the average width of corrosion-induced cracks (CICs) and the wall mechanical properties were studied through an accelerated corrosion test and a loading failure test. The results indicate that the area of corrosion-induced cracking on SRCSWs increased with the corrosion time, and the cracking area on the different SRCSWs was approximately identical when the SRCSWs were exposed to the same corrosion time. When the degree of corrosion was different, the loading failure characteristics of the SRCSWs were obviously different, but the failure mode always corresponded to shear failure. The load–displacement curves of the SRCSWs with different degrees of corrosion along the base basically coincided and were linear when the loading was in the elastic stage. Compared to SW-1, the peak load of SW-2 decreased by 4.0%, but that of SW-3 increased by 2.7%. Compared to SW-1, the yield loads of SW-2 and SW-3 decreased by 22.4% and 11.8%, respectively. When the MLTSB increased from 13.05% to 16.71%, the crack, yield, and peak loads of the SRCSWs corroded along the base decreased by 8.8%, 22.4%, and 6.8%, respectively. The cracking, yield, and peak loads of the SRCSWs corroded along the base decreased linearly with the increase in MLTSB and the average width of the CICs, and the corresponding fitting relations were established. The results of this study can serve as a reference for the durability design of SRCSWs in corrosive environments.
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Davids, William G., Zongmu Wang, George Turkiyyah, Joe P. Mahoney, and David Bush. "Three-Dimensional Finite Element Analysis of Jointed Plain Concrete Pavement with EverFE2.2." Transportation Research Record: Journal of the Transportation Research Board 1853, no. 1 (2003): 92–99. http://dx.doi.org/10.3141/1853-11.
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The features and concepts underlying EverFE2.2, a freely available three-dimensional finite element program for the analysis of jointed plain concrete pavements, are detailed. The functionality of EverFE has been greatly extended since its original release: multiple tied slab or shoulder units can be modeled, dowel misalignment or mislocation can be specified per dowel, nonlinear thermal or shrinkage gradients can be treated, and nonlinear horizontal shear stress transfer between the slabs and base can be simulated. Improvements have been made to the user interface, including easier load creation, user-specified mesh refinement, and expanded visualization capabilities. These new features are detailed, and the concepts behind the implementation of EverFE2.2 are explained. In addition, the results of two parametric studies are reported. The first study considers the effects of dowel locking and slab-base shear transfer and demonstrates that these factors can significantly affect the stresses in slabs subjected to both uniform shrinkage and thermal gradients. The second study examines transverse joint mislocation and dowel looseness on joint load transfer. As expected, joint load transfer is greatly reduced by dowel looseness. However, while transverse joint mislocation can significantly reduce peak dowel shears, it has relatively little effect on total load transferred across the joint for the models considered.
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Jeffery, Nicole, and Beth Wingate. "The Effect of Tilted Rotation on Shear Instabilities at Low Stratifications." Journal of Physical Oceanography 39, no. 12 (2009): 3147–61. http://dx.doi.org/10.1175/2009jpo4138.1.
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Abstract A linear stability analysis of the inviscid stratified Boussinesq equations is presented given a steady zonal flow with constant vertical shear in a tilted f plane. Full nonhydrostatic terms are included: 1) acceleration of vertical velocity and 2) Coriolis force terms arising from the meridional component of earth’s rotation vector. Calculations of growth rates, critical wavenumbers, and dominance regimes for baroclinic and symmetric instabilities are compared with results from the traditional nonhydrostatic equations, which include a strictly vertical rotation vector, as well as results from the hydrostatic equations. The authors find that for positive zonal z shear, tilted rotation enhances the dominance regime of symmetric instabilities at the expense of baroclinic instabilities and maintains symmetric instabilities at larger scales than previously indicated. Furthermore, in contrast to former studies, it is determined that hydrostatic growth rates for both instabilities are not maximal. Rather, growth rates peak in the fully nonhydrostatic equations for parameter regimes physically relevant and consistent with abyssal ocean stratifications and weak zonal z shears and oceanic measurements of the Labrador Sea and Southern Ocean. In addition, the authors find that zonal shear modifies the frequency range of subinertial inertio–gravity waves. Tilted rotation effects break the base flow shear reflection symmetry present in the traditional and hydrostatic models. Thus, only in the fully nonhydrostatic model does weak negative zonal z shear stabilize the flow and decrease the subinertial frequency range.
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Zhu, T. J., W. K. Tso, and A. C. Heidebrecht. "Evaluation of base shear provisions in the 1985 edition of the National Building Code of Canada." Canadian Journal of Civil Engineering 16, no. 1 (1989): 22–35. http://dx.doi.org/10.1139/l89-004.
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A statistical analysis is performed to evaluate the base shear provisions in the 1985 edition of the National Building Code of Canada (NBCC 1985). Three sets of real earthquake records are selected to represent seismic ground motions with low, normal, and high peak acceleration to velocity (a/v) ratios. Single degree of freedom stiffness degrading systems are used as structural models; three damage indicators are employed to measure structural damage. The yield strength of the systems is specified in two different ways: (a) a single seismic response factor is used, irrespective of the a/v ratios of the input ground motions; (b) three different seismic response factors are used in the short-period range, depending upon the a/v ratios of the input ground motions, as suggested in NBCC 1985. A comparison of the statistical results of the three damage parameters for the systems designed with these two methods of strength specification indicates that the NBCC 1985 base shear provisions provide consistent control over structural damage when the structural systems are subjected to ground motions with different a/v ratios. Key words: earthquakes, ground motions, response spectra, stiffness degrading systems, seismic design, base shear, yield strength, inelastic response, damage parameters.
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Ngo, Van-thuyet. "ЭФФЕКТИВНОСТЬ КВАДРАТНОГО АРМИРОВАННОГО ВОЛОКНОМ ЭЛАСТОМЕРНОГО ИЗОЛЯТОРА ДЛЯ ЖЕЛЕЗОБЕТОННОГО ЗДАНИЯ ПРИ ЗЕМЛЯТРЕСЕНИЯХ". International Journal for Computational Civil and Structural Engineering 19, № 4 (2023): 182–95. http://dx.doi.org/10.22337/2587-9618-2023-19-4-182-195.
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Un-bonded fiber reinforced elastomeric isolator (U-FREI) is a relatively new type of multi-layer elastomeric isolator in which fiber layers are used as reinforcement to replace steel sheets in conventional steel reinforced elastomeric isolators. It is installed directly between the substructure and superstructure without any connection at the interfaces. Most of the previous studies on the U-FREIs supported to the base-isolated buildings are masonry or stone structures. In this study, the dynamic responses of a reinforced concrete (RC) building supported on square U-FREIs under the action of recorded real time-history ground motions of earthquakes are investigated by finite element analysis using SAP2000 software. A hypothetical 4-storey reinforced concrete building constructed in Vietnam is selected for the study. Comparison of the dynamic responses of the base-isolated building and corresponding fixed-base building is carried out to evaluate the seismic vulnerability of the base-isolated building under earthquakes. Finite element analysis results show that peak values of floor acceleration and inter-storey drifts at different floor levels, and peak value of base shear of the base-isolated building are lower than those of the corresponding fixed-base building. The U-FREIs are found to be very effective in reducing seismic vulnerability of low and mid-rise RC buildings.
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Dehghani, Ehsan, Maryam Najafi Zadeh, and Azam Nabizadeh. "Evaluation of seismic behaviour of railway bridges considering track-bridge interaction." Roads and Bridges - Drogi i Mosty 18, no. 1 (2019): 51–66. http://dx.doi.org/10.7409/rabdim.019.004.
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Railway bridges have historically performed well in the previous earthquakes. Although this performance has qualitatively been studied in some references such as AREMA code, no quantitative criteria has been proposed for it. Thus, this study aims to present quantitative criteria for railway bridge performance under seismic loads. In the paper, seismic behaviour of railway bridges, with and without track-bridge interaction (TBI), is calculated through finite element modeling. Pushover and incremental dynamic analyses, are utilized to assess the proposed method, considering fourteen records of the past earthquakes. The results clearly show superior performance of the proposed model with track system, in which the deck displacement, base shear, and plastic rotation decrease by 70%-90%, 20%-83%, and 85%-100%, respectively. Finally, two equations are proposed to calculate deck displacement and base shear of railway bridges without performing track-bridge interaction (TBI) by Peak Ground Acceleration (PGA) of the applied record approximately.
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Ivarsson, J., D. C. Viano, and P. Lo¨vsund. "Influence of the Lateral Ventricles and Irregular Skull Base on Brain Kinematics due to Sagittal Plane Head Rotation." Journal of Biomechanical Engineering 124, no. 4 (2002): 422–31. http://dx.doi.org/10.1115/1.1485752.
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Two-dimensional physical models of the human head were used to investigate how the lateral ventricles and irregular skull base influence kinematics in the medial brain during sagittal angular head dynamics. Silicone gel simulated the brain and was separated from the surrounding skull vessel by paraffin that provided a slip interface between the gel and vessel. A humanlike skull base model (HSB) included a surrogate skull base mimicking the irregular geometry of the human. An HSBV model added an elliptical inclusion filled with liquid paraffin simulating the lateral ventricles to the HSB model. A simplified skull base model (SSBV) included ventricle substitute but approximated the anterior and middle cranial fossae by a flat and slightly angled surface. The models were exposed to 7600 rad/s2 peak angular acceleration with 6 ms pulse duration and 5 deg forced rotation. After 90 deg free rotation, the models were decelerated during 30 ms. Rigid body displacement, shear strain and principal strains were determined from high-speed video recorded trajectories of grid markers in the surrogate brains. Peak values of inferior brain surface displacement and strains were up to 10.9X (times) and 3.3X higher in SSBV than in HSBV. Peak strain was up to 2.7X higher in HSB than in HSBV. The results indicate that the irregular skull base protects nerves and vessels passing through the cranial floor by reducing brain displacement and that the intraventricular cerebrospinal fluid relieves strain in regions inferior and superior to the ventricles. The ventricles and irregular skull base are necessary in modeling head impact and understanding brain injury mechanisms.
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Tan, Junkun, Jiaqi Guo, Shifan Qiao, Changrui Dong, Ziyong Cai, and Gang Wang. "Experimental Study on the Shearing Behaviour on the Interface between Coarse Sand and Concrete under High Stress." Geofluids 2021 (August 14, 2021): 1–12. http://dx.doi.org/10.1155/2021/9982235.
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The shear behaviour on the interface between soil and structure is a research hot point. Based on the RMT-150B rock mechanics test system, a series of high-stress direct tests were performed on the coarse sand under the condition of different moisture contents and concrete substrates with different rough and hardness. The results showed that the shear stress-displacement curve and volumetric strain-displacement curve of the interface under high stress could be fitted by a hyperbolic model; the ultimate shear strength and initial shear stiffness of the interface both increased with the normal stress while the shear stiffness decreased with the shear displacement. The crushing rate of the coarse sand particles on the interface increased with the normal stress. After the range analysis for the influencing factors of the interface’s shearing behaviour, it was shown that for the ultimate shear strength, their sequence of influencing degree was normal stress, the roughness of interface, moisture content, and hardness of concrete base; for the initial shear strength, the sequence was normal stress, moisture content, interface roughness, and basal hardness. As for dry sand, the possibility of relative particle crushing was higher than that of sand with a moisture content of 8%, and a peak of crushing occurred when the moisture content was 16%.
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Banerjee, Debargha, Debasish Das, Uddipta Ghosh, et al. "Response Spectrum Analysis of a RC Building Based on Complete Quadratic Combination (CQC) Method." IOP Conference Series: Earth and Environmental Science 1084, no. 1 (2022): 012080. http://dx.doi.org/10.1088/1755-1315/1084/1/012080.
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Abstract In the realm of structural design, Seismic Analysis is crucial. Many structures have collapsed because of earthquakes; as a result of numerous studies, different methods for analysing and determining vibration modes of a structure have been created. Seismic analysis can be done in two ways: static analysis and dynamic analysis. The basic mode of vibration dominates the response in the static technique of seismic analysis, and the mass and stiffness of the structures are evenly distributed, resulting in a regular shape, however this assumption fails for irregular buildings. As a result, dynamic methods are used to solve this issue. Response spectrum is one such dynamic method that is relatively simple to utilize compared to others. The benefit of employing the seismic response spectrum method is that it aids in the prediction of displacement and member forces in structural systems. As a result, this method aids in determining peak structural responses within a linear range, which can then be used to calculate lateral forces created in structures due to earthquakes, allowing for more earthquake-resistant building design. Although this method is approximate, it is a cost-effective and beneficial method for preliminary design research. The response spectrum method is used on STAAD.PRO V8i software to design a G+4 residential structure in our study. The building’s measurements are 16 meters long, 12 meters wide and 15 meters tall. The foundation was built to a depth of 1.5 meters. The structure was built to withstand earthquakes in seismic zone III on medium-density soil. Dead load (IS 875 Part I), Live load (IS 875 Part II), Seismic Load (IS 1893 Part I), and Wind Load are some of the load instances that were presented based on Indian Standard code (IS 875 Part III). To acquire the best response, the response spectrum modal combination Complete Quadratic Combination (CQC) is used. Various parameters like wind intensity, seismic parameters, dynamic weight, modal participation factors, base shear and peak storey shear are calculated. Base shear and peak storey shear are found to maximum in Mode 2 and between 5th and 6th respectively.
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Ma, Qinyong, and Hanyan Wang. "Analysis of the Direct Shear Test and Microstructure of the Lunar Soil Simulant Solidified by Sodium Silicate." Advances in Materials Science and Engineering 2022 (July 30, 2022): 1–11. http://dx.doi.org/10.1155/2022/7654781.
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The lunar soil is an ideal building material for future lunar base construction. In order to improve the strength of lunar soil, basalt with similar composition to lunar soil was used to simulate lunar soil due to lack of real lunar soil, and the simulated lunar soil was reinforced with sodium silicate. In order to study the direct shear mechanical properties of the simulated lunar soil by sodium silicate solidification, a series of direct shear tests and SEM microstructure tests were carried out, and the shear stress-displacement whole process curve was obtained. Influence law of mechanical characteristic parameters such as shear strength, shear deformation modulus, peak deformation and energy dissipation was studied. The results of the direct shear test show that the shear stress-shear displacement curve of the sample changes from hardening to softening with the increase of sodium silicate content. The shear strength and shear deformation modulus of simulated lunar soil increased first and then decreased. When the sodium silicate content was 5%, the shear strength and shear deformation modulus reached the maximum, which were 560 kPa and 7224 kPa, respectively. The addition of 5% sodium silicate increases the energy dissipation coefficient of the simulated lunar soil by about 12%. The microscopic test results show that the N-A-S-H gel and AFt formed by the alkali excitation and adsorption of the sodium silicate will connect the lunar soil simulant particles into a whole network structure, thereby improving the shear strength.
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Xie, Yunfei, Chenyang Yuan, and Weifeng Bai. "A Simplified Analysis Method for Seismic Response of Pile Foundation." Applied Sciences 13, no. 22 (2023): 12398. http://dx.doi.org/10.3390/app132212398.
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A simplified analysis method based on three-dimensional finite element analysis is proposed for the dynamic response of pile foundations under the action of vertically propagating SV waves. This method considers the impact of upper structure inertia force and free field deformation on the internal force of the pile separately. The former is considered using the Equivalent Base Shear Method, while the latter is analyzed using a finite element response acceleration method for underground structures. This study selected three seismic waves and their average values as loads to calculate the dynamic response of pile raft foundations. Through trial calculations, the seismic effect reduction coefficient range (0.35–0.4) of the representative values of the horizontal seismic inertia force corresponding to the upper structure was obtained. The error between the peak shear stress of the pile top obtained by the quasi-static method and the time history analysis results was less than 10%. The research results indicate that the proposed simplified analysis method can accurately obtain the peak shear stress and its distribution pattern of the pile body under horizontal seismic action while significantly improving the analysis efficiency. This method has high accuracy and efficiency in conducting seismic design comparison and analysis of multiple foundation schemes.
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Su, Dong, and Xiang Song Li. "Observed Soil-Water Interaction in the Centrifuge Dynamic Test." Advanced Materials Research 243-249 (May 2011): 2978–84. http://dx.doi.org/10.4028/www.scientific.net/amr.243-249.2978.
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Centrifuge physical modeling technique has been increasingly used in geotechnical earthquake engineering. A centrifuge dynamic model test has been conducted on the centrifuge on a saturated sand deposit model. The input motion at the base of the model was a strong earthquake waveform with a peak acceleration of 0.55 g in prototype. Some interesting phenomena, which include disappearance and reappearance of acceleration in soils during the shaking event, and existence of double plateaus or one plateau and one peak in the time histories of excess pore pressure, were recorded. The mechanism behind the phenomena was investigated by comparing the time history of excess pore pressure with the time history of acceleration, and with the derived shear modulus.
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Hoecker-Martínez, Martín S., William D. Smyth, and Eric D. Skyllingstad. "Oceanic Turbulent Energy Budget using Large-Eddy Simulation of a Wind Event during DYNAMO." Journal of Physical Oceanography 46, no. 3 (2016): 827–40. http://dx.doi.org/10.1175/jpo-d-15-0057.1.
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AbstractThe dominant processes governing ocean mixing during an active phase of the Madden–Julian oscillation are identified. Air–sea fluxes and upper-ocean currents and hydrography, measured aboard the R/V Revelle during boreal fall 2011 in the Indian Ocean at 0°, 80.5°E, are integrated by means of a large-eddy simulation (LES) to infer mixing mechanisms and quantify the resulting vertical property fluxes. In the simulation, wind accelerates the mixed layer, and shear mixes the momentum downward, causing the mixed layer base to descend. Turbulent kinetic energy gains due to shear production and Langmuir circulations are opposed by stirring gravity and frictional losses. The strongest stirring of buoyancy follows precipitation events and penetrates to the base of the mixed layer. The focus here is on the initial 24 h of an unusually strong wind burst that began on 24 November 2011. The model shows that Langmuir turbulence influences only the uppermost few meters of the ocean. Below the wave-energized region, shear instability responds to the integrated momentum flux into the mixed layer, lagging the initial onset of the storm. Shear below the mixed layer persists after the storm has weakened and decelerates the surface jet slowly (compared with the acceleration at the peak of the storm). Slow loss of momentum from the mixed layer extends the effect of the surface wind burst by energizing the fluid at the base of the mixed layer, thereby prolonging heat uptake due to the storm. Ocean turbulence and air–sea fluxes contribute to the cooling of the mixed layer approximately in the ratio 1:3, consistent with observations.
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Rodgers, Geoffrey W., J. Geoffrey Chase, Kerry J. Mulligan, John B. Mander, and Rodney B. Elliott. "Customising semi-active resetable device behaviour for abating seismic structural response." Bulletin of the New Zealand Society for Earthquake Engineering 42, no. 3 (2009): 147–56. http://dx.doi.org/10.5459/bnzsee.42.3.147-156.
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Semi-active resetable actuators have been shown to be capable of significantly improving seismic structural response and customising structural hysteresis loops to reduce both displacement and base shear demands. Hence, device behaviour and dynamics can be tailored to the application. However, the maximum forces produced, in particular with air as the working fluid, can be a limiting factor to avoid extreme device sizes. This investigation incorporates an actively controlled (stored) high-pressure air source to enhance the capabilities of such resetable devices. The devices are designed using a validated non-linear model incorporating the dynamics and non-linearities of the working fluid, valves, sensor lags and computational limitations. Initial simulations show 100-600% increases in the peak device forces, with 100% obtained when the initial pressure is doubled. In addition, the high pressure source allows greater manipulation of the device behaviour and response. This additional flexibility enables, for example, devices that are more resistant or resist differently in opposing directions. The impact of device enhancements over standard resetable devices is then demonstrated experimentally. This paper extends these novel resetable devices to create more flexible and actively controlled devices for semi-active structural control. Finally, a “net-zero base shear design” concept is presented, where the added damping reaction forces are exactly offset by structural response reductions to give large displacement reductions with no overall change to base shear forces – maximising control with no impact on the foundations.
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Herrada, Miguel A., Vladimir N. Shtern, and M. M. Torregrosa. "The instability nature of the Vogel–Escudier flow." Journal of Fluid Mechanics 766 (February 9, 2015): 590–610. http://dx.doi.org/10.1017/jfm.2015.34.
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AbstractThe instability of the steady axisymmetric flow in a sealed elongated cylinder, driven by a rotating end disk, is studied with the help of numerical simulations. It is argued that this instability is of the shear-layer type, being caused by the presence of an inflection point in the radial distribution of axial velocity of the base circulatory flow. The disturbance kinetic energy is localized in both the radial and axial directions, reaching its peak near the rotating disk, where the magnitude of base-flow axial velocity is close to its maximum. The critical Reynolds number, $\mathit{Re}_{cr}$, is found to be nearly $h$-independent for $h>5$; $h$ is the cylinder length-to-radius ratio. It is shown that the sidewall co-rotation suppresses the instability. As the co-rotation increases, the centrifugal instability becomes the most dangerous, i.e. determines $\mathit{Re}_{cr}$. Physical explanations are given for the stabilizing effect of the co-rotation, which is stronger (weaker) for the shear-layer (centrifugal) instability.
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FOSS, JUDITH K., and K. B. M. Q. ZAMAN. "Large- and small-scale vortical motions in a shear layer perturbed by tabs." Journal of Fluid Mechanics 382 (March 10, 1999): 307–29. http://dx.doi.org/10.1017/s0022112098003887.
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The large- and small-scale vortical motions produced by ‘delta tabs’ in a two-stream shear layer have been studied experimentally. An increase in mixing was observed when the base of the triangular shaped tab was affixed to the trailing edge of the splitter plate and the apex was pitched at some angle with respect to the flow axis. Such an arrangement produced a pair of counter-rotating streamwise vortices. Hot-wire measurements detailed the velocity, time-averaged vorticity (Ωx) and small-scale turbulence features in the three-dimensional space downstream of the tabs. The small-scale structures, whose scale corresponds to that of the peak in the dissipation spectrum, were identified and counted using the peak-valley-counting technique. The optimal pitch angle, θ, for a single tab and the optimal spanwise spacing, S, for a multiple tab array were identified. Since the goal was to increase mixing, the optimal tab configuration was determined from two properties of the flow field: (i) the large-scale motions with the maximum Ωx, and (ii) the largest number of small-scale motions in a given time period. The peak streamwise vorticity magnitude [mid ]Ωx−max[mid ] was found to have a unique relationship with the tab pitch angle. Furthermore, for all cases examined, the overall small-scale population was found to correlate directly with [mid ]Ωx−max[mid ]. Both quantities peaked at θ≈±45°. It is interesting to note that the peak magnitude of the corresponding circulation in the cross-sectional plane occurred for θ≈±90°. For an array of tabs, the two quantities also depended on the tab spacing. An array of contiguous tabs acted as a solid deflector producing the weakest streamwise vortices and the least small-scale population. For the measurement range covered, the optimal spacing was found to be S≈1.5 tab widths.
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Chandler, A. M. "Combined seismic base shear and torsional loading provisions in the 1990 edition of the National Building Code of Canada." Canadian Journal of Civil Engineering 18, no. 6 (1991): 945–53. http://dx.doi.org/10.1139/l91-117.
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This paper evaluates the earthquake-resistant design provisions of the 1990 edition of the National Building Code of Canada (NBCC 1990) for asymmetric building structures subjected to combined lateral shear and torsional dynamic loadings arising from earthquake base excitation. A detailed parametric study is presented, evaluating the dynamic edge displacement response in the elastic range, for the side of the building which is adversely affected by lateral–torsional coupling. A series of buildings is studied, with realistic ranges of the fundamental natural period, structural eccentricity, and uncoupled frequency ratio. These buildings are evaluated under base loadings arising from a total of 45 strong motion records taken from earthquakes in North America, Mexico, Europe, the Middle East, and Southern Pacific, categorized according to site soil conditions and the ratio a/v of peak ground acceleration to velocity. The latter parameter together with the uncoupled lateral period are found to influence strongly the combined dynamic edge response, with the greatest forces on edge members arising from earthquakes with high a/v ratio in structures with natural periods below 0.8 s. In this case the NBCC 1990 loading provisions significantly underestimate the elastic dynamic response. For buildings with periods longer than 0.8 s, the conservatism of the base shear provisions leads to overestimation of combined dynamic edge response in asymmetric systems, and this is also true in the short-period range for buildings subjected to ground motions with low a/v ratio. The NBCC 1990 provisions are reasonably conservative for short-period systems subjected to ground motions with intermediate a/v ratio. Key words: earthquakes, seismic, design, response, spectra, base, shear, torsional, provisions.
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Rangwani, Kiran, Gregory MacRae, and Geoffrey Rodgers. "Performance of rocking frames with friction tension-only devices." Bulletin of the New Zealand Society for Earthquake Engineering 56, no. 2 (2023): 71–90. http://dx.doi.org/10.5459/bnzsee.1583.
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The implementation of a new friction tension-only “GripNGrab” device attached to a rocking steel frame is described. The device, when subject to significant tension dissipates energy via sliding in the frictional component. When the device is loaded in the compression direction, almost no compressive force is carried, but displacement occurs in the ratchetting component. This absence of any significant compressive force within the dissipative system means that the rocking frame will always recentre after uplift from earthquake shaking. A 9 m tall 4.75m wide 3-storey steel concentrically braced rocking frame is designed for low-damage seismic performance. Restoring forces are provided by (i) gravity, (ii) friction “GripNGrab” (GNG) tension-only dissipation devices at the base, and (iii) beam-slab effects. The initial fundamental period of the structure was 0.16s. The initial structure used a 10mm GNG ratchet pitch, and had a GNG strength to not slide under serviceability level shaking. Elastic, pushover, cyclic pushover, as well as time history analyses, with different shaking intensities are conducted using OpenSEES software. The scope of work is limited to a single building and a single ground motion. Parameters varied included the presence of beam-slab effects, and the GNG device stiffness, strength and tooth pitch. It is shown that the full behaviour of the frame could be understood considering cyclic pushover analysis. The peak uplift displacement was conservatively estimated from the peak roof displacement using rigid body mechanics and the tension-only device provided no resistance to full frame recentring. For the frames considered, cumulative uplift displacements, necessary to determine the inelastic displacement capacity of the tension only device, were up to 28 times the peak uplift displacement, not necessarily occurring at the maximum shaking intensity. Maximum frame base shear force demands were up to 1.43 times that from pushover analysis. When the beam-slab, connecting the rocking frame to the rest of the structure, increased the lateral force resistance, the base shear increased significantly, reduced peak roof displacements, and increased the effective number of peak uplift displacement cycles (NPUDc). For large shaking intensities, yielding of the beam-slab occurred resulting in permanent peak roof and uplift displacements. The GNG device strength, stiffness and tooth pitch variations for the cases studied did not significantly affect the response. Initial stiffness, and secant stiffness, based methods to predict the response of rocking frames were non-conservative for these short-period structures with small energy dissipation, and a simple improvement to match the behaviour was developed for the case studied based on the R-T-m relationship for a range of shaking intensity.
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Song, Peng-Cheng, Guo-Xin Chen, and Ying-Jie Chen. "Optimizing the Utilization of Steel Slag in Cement-Stabilized Base Layers: Insights from Freeze–Thaw and Fatigue Testing." Materials 17, no. 11 (2024): 2576. http://dx.doi.org/10.3390/ma17112576.
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This paper presents a study on the mechanical properties of cement-stabilized steel-slag-based materials under freeze–thaw cycles for a highway project in Xinjiang. Using 3D scanning technology the specimen model conforming to the real steel slag shape was established. The objectives of the study are as follows: to explore the sensitivity between the macro- and micro-parameters of the specimen and to establish a non-linear regression equation; and to study the changes in mechanical properties of materials under freeze–thaw cycles, fatigue loading, and coupled freeze–thaw cycle–fatigue loading. The results show that there are three stages of compression damage of the specimen, namely, linear elasticity, peak plasticity, and post-peak decline. Maximum contact forces between cracks and particles occur mainly in the shear zone region within the specimen. The compression damage of the specimen is a mixed tensile–shear damage dominated by shear damage. When freeze–thaw cycles or fatigue loads are applied alone, the flexural strength and fatigue life of the specimens show a linear relationship of decline. The decrease in flexural modulus at low stress is divided into the following: a period of rapid decline, a relatively smooth period, and a period of fracture, with a tendency to change towards linear decay with increasing stress. In the case of freeze–thaw–fatigue coupling, the flexural modulus of the specimen decreases drastically by about 50% in the first 2 years, and then enters a period of steady decrease in flexural modulus in the 3rd–5th years.
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Sharma, Ajay, and Sudhir Soni. "Seismic Performance of Irregular Building with different Variable sliding isolators and Semi active Dampers." Proceedings of the 12th Structural Engineering Convention, SEC 2022: Themes 1-2 1, no. 1 (2022): 659–71. http://dx.doi.org/10.38208/acp.v1.567.
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The comparative performances of semiactive friction and stiffness dampers with different control laws in the base-isolated Irregular building subjected to bi-directionally acting strong earthquakes have been studied. The Irregular building is hybridly isolated with rubber bearings and friction pendulum system (FPS) or variable frequency pendulum isolator (VFPI) or variable curvature friction pendulum system (VCFPS). The shear type base-isolated Irregular building is modeled as three-dimensional linear elastic structure having three degrees-of-freedom at each floor level. Time domain dynamic analysis of the building has been carried out with the help of constant average acceleration Newmark-Beta method and non-linear isolation forces has been taken care by fourth-order Runge-Kutta method. The effects of variation of characteristic properties of semiactive dampers on their hysteresis loops and on the structural response of Irregular building is studied through parametric study. Comparative performances of different semiactive dampers with sliding isolation systems for seismic control of Irregular building have been observed through time history plots and peak response performance indices. It has been found that semiactive electromagnetic friction damper work efficiently with VFPI and VCFPS in comparison FPS for the Irregular building for near field earthquakes as it not only reduces base displacement at lower control force but also give lower base shear and story drift in base-isolated Irregular building. The control laws based on modulated homogeneous friction control semiactive friction dampers better than the predictive control law.
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Zhang, Bingbing, Fei Song, and Weiguang Li. "Stability Analysis of Retaining Walls with Geocell-Reinforced Road Milling Materials." Sustainability 15, no. 5 (2023): 4297. http://dx.doi.org/10.3390/su15054297.
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A series of triaxial compression tests with different confining pressures were conducted for gravels, road surface milling materials, and surface–base milling mixtures to investigate the stress–strain relationships of these three kinds of materials. On the basis of the analysis of the test results, the strength and the deformation of the geocell-reinforced surface milling materials and the geocell-encased surface–base milling mixtures were predicted and compared with those of the gravels via the constitutive model of geocell–soil composites. The effects of the geocell pocket size, tensile stiffness, and the peak internal frictional angle on the stress–strain responses of the geocell-reinforced surface–base milling mixtures were examined. Moreover, by employing the finite element strength reduction technique, stability analysis was conducted on the geocell-reinforced retaining wall with the surface–base milling mixtures to investigate the factor of safety and the failure mechanism of the structure. The study results indicated that the surface milling materials exhibited strain hardening, while the gravels and the surface–base milling mixtures exhibited strain softening. The surface milling materials displayed evident shear contraction characteristics, whereas the gravels and surface–base milling mixtures first displayed shear contraction and later dilatancy features. In addition, the strength of the geocell-reinforced surface milling materials is smaller than that of the gravels, but the strength of the geocell-encased surface–base milling mixtures is larger than that of the gravels. Thus, the geocell-reinforced surface–base milling mixtures can be used to replace the gravels in engineering practices. Additionally, the size of the sliding wedge and the factor of safety of the retaining walls increase significantly with reductions in the geocell pocket size.
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Ouyang, Xiao, Zhiqiang Zhang, Hongjie Jia, Mingwen Ren, and Yaping Sun. "Study on the Effect of Heat Treatment on Microstructures and High Temperature Mechanical Properties of Welding Spots of Hot Stamped Ultra-High Strength Steel Patchwork Blanks." Metals 11, no. 7 (2021): 1033. http://dx.doi.org/10.3390/met11071033.
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Insufficient strength of welding spots is a common problem in the hot stamping process of ultra-high strength steel patchwork blanks (UHSSP). In this paper, the welding spots of 22MnB5 boron steel with thicknesses of 1.2 and 1.5 mm were austenitized and then air-cooled to 650–850 °C for high temperature tensile shear tests and high temperature cross-tension tests, respectively. To study the mechanical properties of the welding spots at room temperature after heat treatment, the austenitized welding spots were quenched in cold water to room temperature, and microhardness tests and microstructure observations were performed. The results indicated that compared to the original welding spots, the heat-affected softening zone disappeared after heat treatment, and the hardness values of the fusion zone, heat-affected zone and base material were basically the same, at about 500 HV. After heat treatment, the welding spots were mainly martensite. With the increase in deformation temperature, the peak loads of the tensile shear and the cross tension of the welding spots decreased. At 750 °C, the peak loads of the welding spots decreased less, energy absorption was larger, and the welding spots had the comprehensive mechanical properties of strength and ductility.
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Kang, Fu Wei, Xue Min Zhang, Jian Fei Sun, and Jun Ling Zhao. "Hot Deformation Behavior and Processing Map of a Nickel-Base Superalloy GH4169." Advanced Materials Research 834-836 (October 2013): 432–36. http://dx.doi.org/10.4028/www.scientific.net/amr.834-836.432.
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The hot deformation behaviors of the nickel-base superalloy GH4169 have been studied by isothermal constant true strain rate compression testing at 950°C-1150°C, 0.01s-1-10s-1and the height reduction 50%. The processing maps of GH4169 alloy have been constructed at different strains on the basis of testing data using a dynamic materials modeling. The maps exhibited two domains: the first at 950°C - 1100°C and strain rate higher than 0.1s-1, with a peak efficiency of power dissipation of 0.1, and the second at 950°C-1100°C and strain rate lower than 1s-1, with a peak efficiency of power dissipation of 0.4 and the strain rate of 0.01s-1. On the basis of microstructure observations, the first exhibits adiabatic shear bands, which called instability domain, the second represents fine recrystallized grain structures, which called stability domain. The optimal hot-working parameters are at 1050°C, 0.01s-1.
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Vibhute, A. S., S. D. Bharti, M. K. Shrimali, and S. Vern. "Seismic Performance of Elastomeric and Sliding Friction Isolation System." Proceedings of the 12th Structural Engineering Convention, SEC 2022: Themes 1-2 1, no. 1 (2022): 815–19. http://dx.doi.org/10.38208/acp.v1.588.
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The base isolation technique is widely used in the isolation of structures for providing efficient protection to structures concerning different loadings. This study aims to evaluate comparative performance and inelastic responses of the base-isolated structure for two types of isolation systems under the Far-field and Near-field earthquake. For this purpose, seismic response quantities like base shear, peak ?oor displacement, absolute acceleration, and isolator displacement for ten-story reinforced concrete building frame base isolated by lead rubber bearings (LRBs) are evaluated and compared with the seismic response of the same structure base isolated by Friction Pendulum Bearing Isolator. Nonlinear time history analysis is carried out to investigate the inelastic behavior of the base-isolated structure. The building frame was designed according to IS1893:2016 seismic code and IS 456:2000. To represent a wide range of assessments, a 10 storey building frame taking identical isolation parameters for elastomeric and sliding isolation system was analyzed in SAP 2000. It was observed that the responses of both the isolation system are nearly the same for all the three earthquakes.
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Lai, Chi-Ming, Ching-Yu Yeh, Sin-Yu Kang, and Heui-Yung Chang. "Effects of Shear Tabs and High-Strength Bolts in Seismic Performance of Steel Moment Connections." Buildings 11, no. 9 (2021): 415. http://dx.doi.org/10.3390/buildings11090415.
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A shear tab and high-strength bolts are often used to connect a steel H-beam to a column. The design demand and capacity of these elements vary from one standard to the other. To investigate the effect, this study applied a finite element method (FEM) to develop models for two steel moment connections and validated the effectiveness by test data. The connections were characteristic of bolted-web-and-welded-flange details. The FEM models were then used to study the design of shear tabs and high-strength bolts in accordance with the U.S. and Japan standards and compared to the Taiwan practice. The result showed a small difference in the peak loads of the connections. However, the U.S. direct welded flange connection had flange buckling and strength degradation at a relatively smaller drift. The connection had a thinner shear tab and fewer high-strength bolts. The other two connections had very similar design results and loading responses. The increase in shear-tab thickness reduced the stress concentration and fracture potential of the connections. It is, therefore, recommended to design a shear tab with moment capacity greater than the beam web. This will reduce the stress concentration of the base metal surrounding the beam-flange groove welds, increasing the connection ductility.
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Zhao, Zhuo, Xiaowei Lu, Yu Guo, and Xiaofeng Zhao. "Seismic Fragility Assessment of Base-Isolated Steel Water Storage Tank." Shock and Vibration 2020 (October 28, 2020): 1–13. http://dx.doi.org/10.1155/2020/8835943.
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Steel water storage tanks (WSTs) are among the important components of water treatment industry facilities that are expected to remain functional and applicable after strong earthquakes. In this study, the seismic vulnerability of base-isolated steel WST is investigated. A three-dimensional finite element stick model of the targeted tank is created using OpenSees. This model is capable of reproducing convective, impulsive, and rigid responses of fluid-tank systems. Time-history responses of convective displacement, bearing displacement, and base shear force for base-isolated tank subjected to a typical ground motion are compared. Furthermore, time-history analysis based on a suite of 80 ground motions is conducted. The seismic demand models for various responses are established and the most efficient intensity measure (IM) is determined based on the dispersion and coefficient of determination. Seismic fragility curves for different responses are derived for all three damage states using cloud analysis. The results from this study reveal that (i) the convective displacement is significantly greater than bearing displacement; (ii) peak ground displacement (PGD) is the most efficient and sufficient IM for the targeted tank; and (iii) the characteristic of isolation bearing significantly influences the seismic fragilities of convective displacement and bearing displacement and has a little impact on base shear force, which makes the selection of the proper characteristic parameters for isolation bearing very essential. The analysis technique and procedure mentioned above as well as derived insights are of significance to general liquid storage tank system configuration.
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Admane, Harshal, and Pranesh Murnal. "Response Prediction of VFPI Through Equivalent Long Period Wavelet of Near-Fault Ground Motion." Electronic Journal of Structural Engineering 22, no. 2 (2022): 53–67. http://dx.doi.org/10.56748/ejse.222982.
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Past research has revealed that a Variable Frequency Pendulum Isolator (VFPI) effectively controls the structural responses such as base shear and structural acceleration under far and near fault earthquakes and the VFPI may show excessive sliding displacement under some earthquakes having 4-6 s time-period long waves. But, the impact of the amplitude of the long period wave on the sliding displacement of VFPI is missing in past research due to difficulty in finding out the amplitude of long period wave of an earthquake. Therefore, the present study considered the amplitude of the long period wave of an earthquake to analyse the behaviour of the structure isolated by VFPI. For this, the most dangerous long period wave of earthquakes has been extracted in the form of noise free wavelets by using Mavroeidis and Papageorgiou proposed numerical approach. The results indicate that the noise free long period wavelet effectively represent the low frequency earthquake for the structure isolated by VFPI. It is also found out that, the VFPI shows the excessive sliding displacement for only those earthquakes which contains peak ground displacement of long period wave more than 0.40 m. The variation in the base shear and structural acceleration of structure isolated by VFPI under various value of Frequency Variation Factor (FVF) obey the exponential and cubic form respectively. According to this, the present research provides empirical formulas, chart, and tables to predict the structural and isolator responses by using the peak ground velocity (PGV) and dominating low frequency (fd) of a near fault earthquake.