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1
Rudman, Chantal. "Investigation into the structural behaviour of portal frames." Thesis, Stellenbosch : University of Stellenbosch, 2009. http://hdl.handle.net/10019.1/1853.
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Sanchez, Escalera Victor M. "ENHANCING PROGRESSIVE COLLAPSE RESISTANCE OF STEEL BUILDING FRAMES USING THIN INFILL STEEL PANELS." DigitalCommons@CalPoly, 2011. https://digitalcommons.calpoly.edu/theses/499.
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Progressive collapse occurs when damage from a localized first failure spreads in a domino effect manner resulting in a total damage disproportionate to the initial failure. Recent building failures (e.g., World Trade Center twin towers) highlight the catastrophic outcome of progressive collapse. This research proposes a reliable and realistic retrofit technology which installs thin steel panels into steel building structural frames to enhance the system progressive collapse resistance.
The steel frames with simple beam-to-column connections, under different boundary conditions (i.e., sidesway uninhibited and sidesway inhibited, respectively), and the loss of one bottom story column were retrofitted using the proposed technology (i.e. installing thin steel panels in the structural frames). Performance of these frames was investigated. Two Finite Element (FE) models which require different modeling efforts were developed to capture the system behavior. The first model explicitly models the infill plates to capture the plate buckling behavior. The second model known as strip model represents the infill panels as diagonal strips. In addition to the FE models, a plastic analysis model derived from the prior research on seismically designed Steel Plate Shear Walls (SPSWs) was considered. The system progressive collapse resistance obtained from the two FE models and the plastic analysis procedure were compared and good agreements were observed. It was observed that installing infill plates to steel structural frames can be an effective approach for enhancing the system progressive collapse resistance.
Beyond the strength of the overall system, the Dynamic Increase Factor (DIF) which may be used to amplify the static force on the system to better capture the dynamic nature of progressive collapse demand was evaluated for the retrofitted system. Furthermore, the demands including axial force, shear force and bending moment on individual frame components (i.e., beams and columns) in the retrofitted system were quantified via the nonlinear FE models and a simplified procedure based on free body diagrams (FBDs). Finally, the impact of premature beam-to-column connection failures on the system performance was investigated and it was observed that the retrofitted system is able to provide stable resistance even when connection failures occur in all beams.
3
Wong, Shao Young. "The structural response of industrial portal frame structures in fire." Thesis, University of Sheffield, 2001. http://etheses.whiterose.ac.uk/3005/.
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A number of recent fires in single-storey warehouses have drawn attention to a current lack of understanding about the structural response of industrial portal frame structures to elevated temperatures. This research project has investigated the subject by conducting fire tests on a scaled model and by computer modelling using the non-linear finite element program VULCAN. This program has been developed in-house by the University of Sheffield and is capable of modelling the behaviour of three-dimensional steel and composite frames at elevated temperatures. It has been validated throughout its development. An initial investigation was conducted to validate the program for analysing inclined members, which form part of a pitched- roof portal frame, but for which it was not initially developed. Additional features were implemented into the program where necessary. A series of indicative fire tests was conducted at the Health and Safety Laboratories, Buxton. A scaled portal frame model was designed and built, and three major fire tests were conducted in this structure. In the third of these tests the heated rafters experienced a snap-through failure mechanism, in which fire hinges could clearly be identified. The experimental results were then used for validating the numerical results produced by VULCAN analyses. The correlations were relatively close, both for predictions of displacements and failure temperatures. This gave increased confidence in using VULCAN to conduct a series of parametric studies. The parametric studies included two- and three-dimensional analyses, and a number of parameters were investigated, including the effects of vertical and horizontal load, frame geometry, heating profiles and base rotational stiffness. The influence of secondary members was investigated in the three-dimensional studies using different fire scenarios. A simplified calculation method has been developed for estimating the critical temperatures of portal frames in fire. The results compare well with predictions from VULCAN. The current guidance document for portal frames in boundary conditions has been reviewed, and the concept of performance-based design for portal frame structures has been discussed.
4
Bourahla, Nouredine. "Knee bracing system for earthquake resisting steel frames." Thesis, University of Bristol, 1990. http://hdl.handle.net/1983/d4ba97ab-0a65-4469-8a69-776a009514d9.
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Atlayan, Ozgur. "Hybrid Steel Frames." Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/50562.
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The buildings that are designed according to the building codes generally perform well at severe performance objectives (like life safety) under high earthquake hazard levels. However, the building performance at low performance objectives (like immediate occupancy) under low earthquake hazards is uncertain. The motivation of this research is to modify the design and detailing rules to make the traditional systems perform better at multi-level hazards.<br /><br />This research introduces two new structural steel systems: hybrid Buckling Restrained Braced Frames (BRBF) and hybrid steel Moment Frames (MF). The "hybrid" term for the BRBF system comes from the use of different steel material including carbon steel (A36), high-performance steel (HPS) and low yield point (LYP) steel. The hybridity of the moment frames is related to the sequence in the plastification of the system which is provided by using weaker and stronger girder sections. Alternative moment frame connections incorporating the use of LYP steel plates are also investigated. <br /><br />The hybrid BRBF approach was evaluated on seventeen regular (standard) frames with different story heights, seismic design categories and building plans. By varying the steel areas and materials in the BRB cores, three hybrid BRBFs were developed for each regular (standard) frame and their behavior was compared against each other through pushover and incremental dynamic analyses. The benefits of the hybridity were presented using different damage measures such as story accelerations, interstory drifts, and residual displacements. Collapse performance evaluation was also provided.<br /><br />The performance of hybrid moment frames was investigated on a design space including forty-two moment frame archetypes. Two different hybrid combinations were implemented in the designs with different column sections and different strong column-weak beam (SC/WB) ratios. The efficiency of the hybrid moment frame in which only the girder sizes were changed to control the plastification was compared with regular moment frame designs with higher SC/WB ratios. As side studies, the effect of shallow and deep column sections and SC/WB ratios on the moment frame behavior were also investigated. <br /><br />In order to provide adequate ductility in the reduced capacity bays with special detailing, alternative hybrid moment frame connections adapting the use of low strength steel were also studied.<br>PhD
6
Davison, John Buick. "Strength of beam-columns in flexibly connected steel frames." Thesis, University of Sheffield, 1987. http://etheses.whiterose.ac.uk/1866/.
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This thesis describes an experimental study undertaken to examine the influence of joint resistance to in-plane moments on the performance of steel columns and complete frames. The principal objective of the tests was to provide experimental data against Which sophisticated computer analysis programs may be verified. Details of the experimental study of 22 joint tests, eight column subassemblages, and two three storey, two bay steel frames are reported. It is demonstrated that all beam to column connections have an inherent degree of stiffness and that their moment-rotation characteristics are non-linear. The load carrying capacity of columns, confined to buckle in-plane, is shown to be enhanced considerably by the resistance to rotation provided by simple beam to column connections. In frames incorporating flange cleat connections the beams and columns can sustain greater loading and deflect less than is predicted by current design models. The assumptions of pin-ended columns and simply supported beams are shown to be conservative. Comparisons of the results of the column and frame tests with two finite element analysis programs are presented. The use of computer programs for semi-rigid design as well as the development of a simple approach are discussed.
7
Kameshki, Esmat Saleh. "Stability of steel frames by the transfer matrix method." Thesis, University of Southampton, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.315349.
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Hoang, Ha. "Structural Continuity Effects in Steel Frames under Fire Conditions." Digital WPI, 2010. https://digitalcommons.wpi.edu/etd-theses/420.
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Fire has always been one of the most serious threats of collapse to structural building frames. The September 11 incident has stimulated significant interests in analyzing and understanding the behavior of the structures under fire events. The strength of the material decreases due to the elevated temperature caused by fire, and this reduction in strength leads to the failure of the member. Frames that do not have sufficient ductility can suffer progressive collapse of the entire structure if one member fails during a fire event. Such collapse could result in loss of human life and serious economic consequences. The motivation for this thesis is to provide an understanding of the continuity effects in steel frames under fire conditions. The continuity effects of the structure can provide additional strength to the system to sustain the loads under fire event. Different scenarios of the frame and beam structures which include changes to member sizes, fire locations, and bay size, are investigated with the assistance of SAP2000 and ANSYS. These programs can provide the collapse analysis for each scenario at different temperature. The continuity effect was investigated from the strength point of view of the structure. Ultimately, the thesis presents a design tool for aiding member design under fire conditions. The design tool consists of different graphs that maybe use to determine the collapse load capacity of a continuous structure at elevated temperature based on the analysis of a simpler, determinate structure.
9
Kim, Yoon Duk. "Behavior and design of metal building frames using general prismatic and web-tapered steel I-section members." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/33965.
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Metal building frames are typically designed using welded prismatic and web-tapered members with doubly-symmetric and/or singly-symmetric cross sections. Until recently, the base U.S. provisions for design of frames with web-tapered members were provided in the AISC ASD (1989) and LRFD (1999) Specifications. Unfortunately, these previous AISC provisions address only a small range of practical designs. As a result, metal building manufacturers have tended to develop their own methods for design of the wide range of nonprismatic member geometries and configurations encountered in practice.
This research develops new design procedures for design of frames using general prismatic members and web-tapered members. An equivalent prismatic member concept utilized in prior research and the prior AISC provisions is generalized to accommodate the broad range of member types and configurations commonly used in metal building industry. Furthermore, the new design procedures incorporate many of the improvements achieved in the AISC (2005&2010) Specifications to metal building frame design. These improvements include a new stability design method, the direct analysis method, more complete considerations of different column buckling limit states (flexural, torsional and flexural-torsional buckling), and improved axial load and flexural resistance provisions. This research develops practical design-based procedures for simplified calculation of the elastic buckling resistances of prismatic and web-tapered members to facilitate the application of the proposed design methods. In addition, this research performs a relatively comprehensive assessment of beam lateral torsional buckling (LTB) behavior and strength of prismatic and web-tapered members using refined virtual test simulation. It is demonstrated that web-tapered members behave in a comparable fashion to prismatic members. Based on the virtual simulation study, recommendations for potential improvement of the AISC LTB resistance equations are provided. Lastly, the strength behavior of several representative metal building frames is studied in detail using the same virtual test simulation capabilities developed and applied for the assessment of the beam LTB resistances.
10
Najjar, Samer Rida. "Three-dimensional analysis of steel frames and subframes in fire." Thesis, University of Sheffield, 1994. http://etheses.whiterose.ac.uk/1861/.
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The aim of the present work is to develop a sophisticated analytical model for columns within three-dimensional assemblies in fire conditions. A preliminary investigation into this problem resulted in the development of a simplified approach for the analysis of isolated columns in fire. This model is based on the Perry-Robertson approach to defining critical loads of imperfect columns at ambient temperature. It takes into account uniform and gradient temperature distributions across the section of an isolated pin-ended column. It also accounts for initial out-of-straightness, load eccentricity and equal end-moments. A three-dimensional finite element model has subsequently been developed for the analysis of frames in fire conditions. This model is based on a beam finite element with a single node at each end of the element. At each node eight degrees of freedom are introduced. The finite element solution of the problem is obtained using an incremental iterative procedure based on the Newton-Raphson method, adapted to account for elevated temperature effects. The developed procedure offers a unique treatment of the thermal effects which allows solutions to be arrived at regardless of the problem's boundary conditions. The finite element formulation takes into consideration geometrical and material nonlinearities, initial out-of-straightness and residual stresses. It allows for virtually any temperature distribution across and along the structural members, and the analysis can handle any three-dimensional skeletal steel structure. The developed model allows the material mechanical properties to be expressed either as trilinear or continuous functions which vary with temperature. A computer program, 3DFIRE, has been developed based on the above-mentioned formulation and validated extensively against a wide range of previous analytical and experimental work. This program has then been used to perform parametric studies to establish the most prominent features of column behaviour in fire whether as isolated members or as part of structural assemblies. These studies have yielded a large amount of data from which generalised conclusions have been made. The analysis has been extended recently to include composite beams within the structural assembly. This development was undertaken to enable analytical studies on the test building at Cardington, in which fire tests are planned to take place in the near future.
11
Li, Guzhao. "Bracing design requirements for inelastic members." Access restricted to users with UT Austin EID, 2002. http://www.lib.utexas.edu/etd/r/d/2002/guzhaol022/guzhaol022.pdf#page=4.
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Filiatrault, André. "Performance evaluation of friction damped braced steel frames under simulated earthquake loads." Thesis, University of British Columbia, 1985. http://hdl.handle.net/2429/25091.
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This thesis presents the results obtained from qualification tests of a new friction damping system, which has been proposed in order to improve the response of Moment Resisting Frames and Braced Moment Resisting Frames during severe earthquakes. The system basically consists of a special inexpensive mechanism containing friction brake lining pads introduced at the intersection of frame cross-braces. The main objective is to study the performance of a 3 storey Friction Damped Braced Frame model under simulated
earthquake loads.
The main members of the test frame were chosen from available hot-rolled sections and the mass selected to provide the expected fundamental frequency of a three storey Moment Resisting Frame. The seismic testing was performed on an earthquake simulator table. The experimental results are compared with the findings of an inelastic time-history dynamic analysis. Two different computer models were used for this purpose. The first one is based on an equivalent hysteretic model and is only approximate,
since it does not take into account the complete behaviour of the friction devices. A more refined computer model was then developed and the results from the two models are compared. It is found that the simpler approximate model overestimates the energy dissipated by the devices, but the inaccuracy is relatively small (10-20% in resulting member forces).
To quantify the performance of the Friction Damped Braced Frame relative
to conventional aseismic systems, an equivalent viscous damping study is made. Viscous damping is added to the Moment Resisting Frame and the Braced Moment Resisting Frame until their responses become similar to the response of the Friction Damped Braced Frame. The results show that for this purpose 38% of critical damping must be added to the Moment Resisting Frame and 12% to the Braced Moment Resisting Frame. The new system becomes more efficient as the intensity of the earthquake increases.
The economical potential of the new damping system is investigated by designing a reduced size Friction Damped Braced Frame having response characteristics which are similar to those of conventional structural systems with heavier members. For the model frames studied, the results show that if the effects of wind, live and torsion loads are neglected, it is possible to reduce the members sizes of the Friction Damped Braced Frame by 47% and still achieve a superior performance under strong earthquake, in comparison to the seismic response of the two other conventional frames with their original, heavier members.
The results, both analytical and experimental, clearly indicate the superior performance of the friction damped braced frame compared to conventional building systems. Even an earthquake record with a peak acceleration of 0.9 g causes no damage to the Friction Damped Braced Frame, while the Moment Resisting Frame and the Braced Moment Resisting frame undergo large inelastic deformations.<br>Applied Science, Faculty of<br>Civil Engineering, Department of<br>Graduate
13
Shakya, Anuj Man. "P-DELTA EFFECTS ON STEEL MOMENT FRAMES WITH REDUCED BEAM SECTION CONNECTION." OpenSIUC, 2011. https://opensiuc.lib.siu.edu/theses/702.
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The P-delta effect is a second order effect experienced by any structure when subjected to lateral loads like earthquake or wind loads, and is originated by an additional destabilizing moment generated due to the gravity acting on the laterally deflected member further displacing it. For the purpose of this research, displacement is considered as the study parameter to analyze the second order P-Delta effects. The main objective of this study is to investigate effects of forces causing P-Delta effects on Single Story Single Bay Steel Moment Frames with Reduced Beam Section Connection (RBS). FEMA-350 and AISC Seismic Design Manual suggest that, if the specified conditions are satisfied, there is no need to provide additional panel zone reinforcements as continuity and doubler plates. This study makes an effort to observe the effects of panel zone strength in formation of plastic hinges and in shifting fracture zone away from the column face on frames with RBS connections under P-Delta effects and find whether further increasing the stiffness of panel zone will have beneficial outcome or not.
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Ozcelik, Ramazan. "Seismic Upgrading Of Reinforced Concrete Frames With Structural Steel Elements." Phd thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613450/index.pdf.
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This thesis examines the seismic internal retrofitting of existing deficient reinforced concrete
(RC) structures by using structural steel members. Both experimental and numerical studies
were performed. The strengthening methods utilized with the scope of this work are chevron
braces, internal steel frames (ISFs), X-braces and column with shear plate. For this purpose,
thirteen strengthened and two as built reference one bay one story portal frame specimens
having 1/3 scales were tested under constant gravity load and increasing cyclic lateral
displacement excursions. In addition, two ½<br>scaled three bay-two story frame specimens
strengthened with chevron brace and ISF were tested by employing continuous pseudo
dynamic testing methods. The test results indicated that the cyclic performance of the Xbrace
and column with shear plate assemblage technique were unsatisfactory. On the other
hand, both chevron brace and ISF had acceptable cyclic performance and these two
techniques were found to be candidate solutions for seismic retrofitting of deficient RC
structures. The numerical simulations by conducting nonlinear static and dynamic analysis
were used to estimate performance limits of the RC frame and steel members. Suggested
strengthening approaches, chevron brace and ISF, were also employed to an existing five
story case study RC building to demonstrate the performance efficiency. Finally, design
approaches by using existing strengthening guidelines in Turkish Earthquake Code and
ASCE/SEI 41 (2007) documents were suggested.
15
Saab, Hassan A. "Non-linear finite element analysis of steel frames in fire conditions." Thesis, University of Sheffield, 1990. http://etheses.whiterose.ac.uk/1868/.
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The present work is concerned with the development of a finite element approach and its subsequent use for behavioural studies on steel frames in fire conditions. The nonlinear structural analysis is based on a tangent stiffness formulation using large deformation theory. Deterioration in material strength and stiffness at increasing temperature is represented by a set of nonlinear stress-straintemperature relationships using a Ramberg-Osgood equation in which creep effects are implicitly included. The clearly nonlinear form of steel material properties at elevated temperatures is better represented as a set of continuous stressstrain relationship than in a bilinear form although provision is made for any form of relationship to be included. Structures subject to increasing loads or temperatures are analysed using an incremental Newton-Raphson iterative procedure. The analysis permits collapse load or critical temperature to be calculated at a specified temperature or load level respectively, and provides a complete load-deformation and temperature-deformation history for two-dimensional multistorey steel frames. A nonlinear method of frame analysis, based on largedeformation theory, has been used which includes the effect of geometric nonlinearity, temperature-dependent nonlinear material behaviour and variation in temperature distribution both along and across the section. The effects of thermal strains, residual stresses and thermal bowing are also included and different values of the elastic stiffnesses of the support conditions can be considered. A beam element with two nodes and three degrees of freedom at each node is used in the analysis. Gradual penetration of yielding through the cross-section is accounted for using the transformed area approach. The validity of this method is tested by comparing with experimental and analytical data covering as wide a range of problem parameters as possible. The comparisons show good agreement with this data. The method has been used to study a number of aspects of frame behaviour in fire. The influence of slenderness ratio, stress-strain representation and material models, various forms of protection, magnitude of residual stress and thermal gradient along and across the section of a frame are investigated. An approximate curve based on statistical analysis of the derived results is suggested as a simple means of predicting the critical temperature or collapse load of a uniformly heated steel frame. Further examples are presented which illustrate the special form of moment redistribution that occurs at elevated temperatures for frames that contain partially heated elements. Finally, general conclusions and recommendations for future work are presented.
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Akpinar, Ugur. "Nonlinear Analysis Of Rc Frames Retrofitted With Structural Steel Elements." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612380/index.pdf.
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Deficient concrete structures are serious danger in seismic zones. In order to minimize economical and human loss, these structures should be retrofitted. Selecting suitable retrofitting schemes requires detailed investigation of these systems. Considering these facts, this study aims to calibrate analytical models of systems with chevron braces and internal steel frames<br>and evaluate their seismic performances. First, analytical models of the frames with braces and internal steel frames were prepared and then their responses were compared with cyclic responses of experimental studies. Results of these models were used to determine performance limits by the methods proposed by TEC2007 and ASCE/SEI-41. Then, calibrated models were employed for time history analyses with various scales of Duzce ground motion and analytical results were compared with experimental findings. Seismic performance of these systems was also evaluated by using aforementioned codes. Finally, evaluated retrofitting schemes were applied to a 4-story 3-bay reinforced concrete frame that was obtained from an existing deficient structure and effectiveness of applied retrofitting schemes was investigated in detail.
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Yoo, Jung Han. "Analytical investigation on the seismic performance of special concentrically braced frames /." Thesis, Connect to this title online; UW restricted, 2006. http://hdl.handle.net/1773/10115.
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Taylor, Joshua Michael. "Nonlinear analysis of steel frames with partially restrained composite connections and full or partially composite girders." Thesis, Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/19272.
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Abdel-Rahman, Nabil Mahmoud. "Cold-formed steel compression members with perforations." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ30065.pdf.
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Hunt, Stephen J. "Semi-active smart-dampers and resetable actuators for multi-level seismic hazard mitigation of steel moment resisting frames." Thesis, University of Canterbury. Mechanical Engineering, 2002. http://hdl.handle.net/10092/1256.
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This thesis explores the creation and assessment of semi-active control algorithms for both squat shear buildings and tall flexible structures. If cost-effective, practicable, semi-active structural control systems can be developed, the potential reduction in loss of both property and lives due to seismic events is significant. Semi-active controllers offer many of the benefits of active systems, but have power requirements orders of magnitude smaller, and do not introduce energy to the structural system. Previous research into semi-active controllers has shown their potential in linear simulations with single earthquake excitations. The distinguishing feature of this investigation is the use of appropriate non-linear modelling techniques and realistic suites of seismic excitations in the statistical assessment of the semi-active control systems developed. Finite element time-history analysis techniques are used in the performance assessment of the control algorithms developed for three and nine story structural models. The models include non-linear effects due to structural plasticity, yielding, hysteretic behaviour, and P-delta effects. Realistic suites of earthquake records, representing seismic excitations with specific return period probability, are utilised, with lognormal statistical analysis used to represent the response distribution. In addition to displacement focused control laws, acceleration and jerk regulation control methods are developed, showing that potential damage reduction benefits can be obtained from these new control approaches. A statistical assessment of control architecture is developed and undertaken, examining the distribution of constant maximum actuator authority for both squat shear buildings, and tall slender structures, highlighting the need to consider non-linear structural response characteristics when implementing semi-active control systems. Finally, statistical analysis of all results and normalised values shows the efficacy of each control law and actuator type relative to different magnitude seismic events. As a result, this research clearly presents, for the first time, explicit tradeoffs between control law, architecture type, non-linear structural effects, and seismic input characteristics for the semi-active control of civil structures.
21
Alemdar, Bulent Nedim. "Distributed plasticity analysis of steel building structural systems." Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/22220.
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Gibbons, Craig. "The strength of biaxially loaded beam-columns in flexibly connected steel frames." Thesis, University of Sheffield, 1991. http://etheses.whiterose.ac.uk/14765/.
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This thesis describes the experimental appraisal of a series of 10 'non-sway' steel column subassemblages, each comprising a 6m long column with up to three 1.5m long beams, together with two full-scale 3 storey, 2 bay, single span, non-sway steel frames (typical overall dimensions 9m x 10m x 3.5m). The subassemblages tests were conducted in the Department of Civil and Structural Engineering at the University of Sheffield whilst the much larger frame tests were carried out at the Building Research Establishment. In all cases, the beam and column elements were connected using 'simple' bolted steelwork connections. The aim was to investigate the effect of the inherent rotational stiffness (semi-rigid characteristics) of such connections on the behaviour of steel frames in which the columns were loaded biaxially and were not restricted to in-plane deformation. The appraisal of the results from these experiments clearly shows that the stiffness of even the most modest connection can have a significant influence on the distribution of bending moments, the ultimate column capacity and deflection of frame members. The experimental data were subsequently used to validate the predictions of a sophisticated finite-element computer program which was developed specifically to analyse 3-dimensional column subassemblages employing semi-rigid connections. This thesis documents this validation and reports the findings of an extensive parametric study which was then conducted to investigate the influence of semi-rigid connection behaviour on a wide range of subassemblage configurations. Comparisons with the experimentally observed and analytically predicted ultimate capacities of the subassemblage and frame tests showed that 'commonly used' methods of frame design are unduly conservative. The author has therefore proposed a number of design approaches for both ultimate and serviceability limit state loading conditions which take into account the inherent benefits of semi-rigid joint action.
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Clément, Denis Emile. "Seismic analysis of knee elements for steel frames." Thesis, University of Oxford, 2002. http://ora.ox.ac.uk/objects/uuid:c69aee93-4489-486c-a5fe-11685728e903.
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The 1994 Northridge and 1995 Kobe earthquakes, which were moderate in seismological terms, showed that many buildings were subjected to demolition or very expensive repairs because of severe damage in principle members, mainly in the column-beam connections. As a result, the development of dissipative systems was encouraged, which limit the damage parts to easily replaceable elements, in case of moderate earthquakes. One such system is the knee braced frame. Knee braced frames are a modified form of cross bracing in which the brace is cut short and connected to the mid point of a knee element spanning between the adjacent beam and column. The key component is the knee element, which controls both the initial elastic stiffness of the frame, and the onset of yield and subsequent energy dissipation. The knee elements are required to ensure energy absorption through repeated large deformations without suffering collapse or instability. This thesis describes the development of different knee element designs and their performance assessments. It is shown that the dissipative mechanism of the web yielding in shear is advantageous because it is independent of the moment distribution and it does not affect the connections and extends the dissipative zones to all its lengths. Extensive finite element modelling and experimental testing have been undertaken. In the shear yielding mode excellent performance was achieved using standard hot rolled sections, modified by the addition of web stiffeners to prevent localised buckling failure. Weakening of the knee element's webs so that it yields very early in an earthquake has potential benefit, but is shown to be unsafe as it promotes premature failure of the element. A knee element model for non-linear dynamic analysis of an entire building has been developed. Time history analyses showed that knee braced frames with the developed knee element have a large global ductility and an outstanding performance. Results obtained with different pushover analysis methods (Eurocode 8, FEMA-356 and ATC-40) have been compared to those obtained wit the time history analyses. Moreover FEMA-356 method, which includes a more accurate representation of the structure's significant post-yield stiffness, gave the closest agreement with the time history analyses and is recommended for the design of knee braced frames.
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Abou-Elfath, Hamdy Mohamed. "Rehabilitation of nonductile reinforced concrete buildings using steel systems /." *McMaster only, 1998.
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Kizilkan, Melisa. "Investigating The Effect Of Column Orientations On Minimum Weight Design Of Steel Frames." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/3/12611431/index.pdf.
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Steel has become widespread and now it can be accepted as the candidate of being main material for the structural systems with its excellent properties. Its high quality, durability, stability, low maintenance costs and opportunity of fast construction are the advantages of steel. The correct use of the material is important for steel&rsquo<br>s bright prospects. The need for weight optimization becomes important at this point. Available sources are used economically through optimization. Optimization brings material savings and at last economy. Optimization can be achieved with different ways. This thesis investigates the effect of the appropriate choice of column orientation on minimum weight design of steel frames. Evolution strategies (ESs) method, which is one of the three mainstreams of evolutionary algorithms, is used as the optimizer in this study to deal with the current problem of interest. A new evolution strategy (ES) algorithm is proposed, where design variables are considered simultaneously as cross-sectional dimensions (size variables) and orientation of column members (orientation variables). The resulting algorithm is computerized in a design optimization software called OFES. This software has many capabilities addressing to issues encountered in practical applications, such as producing designs according to TS-648 and ASD-AISC design provisions. The effect of column orientations is numerically studied using six examples with practical design considerations. In these examples, first steel structures are sized for minimum weight considering the size variables only, where orientations of the column members are initially assigned and kept constant during optimization process. Next, the weight optimum design of structures are implemented using both size and orientation design variables. It is shown that the inclusion of column orientations produces designs which are generally 4 to 8 % lesser in weight than the cases where only size variables are employed.
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Sanchez-Zamora, Francisco. "Seismic Rehabilitation of Steel Concentrically Braced Frames Vulnerable to Soft-Story Failure through Implementation of Rocking Cores." DigitalCommons@CalPoly, 2013. https://digitalcommons.calpoly.edu/theses/995.
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Recent research reports that steel Concentrically Braced Frames (CBFs) (even the code-compliant ones) may be susceptible to soft-story failures during strong earthquakes. Such a failure mode causes catastrophic outcomes and should be definitely avoided in practice. This thesis focuses on development and validation of a seismic retrofit strategy for low-rise and mid-rise steel CBFs vulnerable to soft-story failures. The considered retrofit strategy consists of a sufficiently stiff rocking core (RC) pinned to foundation and connected to the existing frame. For demonstration purpose, two representative benchmark steel CBF buildings, which are the three-and six-story CBFs designed forLos Angelesin the SAC Steel Project, are considered. Finite element (FE) models of the benchmark buildings are validated using the published results and explicitly take into account gusset plates, member yielding, brace buckling, brace rupture, and P-Delta effect. Eigenvalue analyses are first conducted to investigate the effect of RC on system modal properties. It is found that the added RC generally does not significantly change the fundamental period and therefore does not attract excessive earthquake force to the system. Additionally, nonlinear static pushover analyses are performed to address the beneficial contribution of RC to the system under the performance objectives including immediate occupancy, life safety, and collapse prevention. The Monte-Carlo simulation technique is used to take into account uncertainty in lateral force distribution and its effect in system seismic performance. It is found that sufficiently stiff RC creates more uniform inter-story distribution along the vertical direction in all considered scenarios. Furthermore, nonlinear dynamic analyses are conducted using three different ground motion suites. It is shown that the systems with properly selected RC can achieve the Best Safety Objective defined in FEMA 356 and ensure the collapse prevention performance under near-fault earthquakes.
27
Dogan, Erkan. "Optimum Design Of Rigid And Semi-rigid Steel Sway Frames Including Soil-structure Interaction." Phd thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612281/index.pdf.
Full textAbstract:
In this study, weight optimization of two dimensional steel frames is carried out in
which the flexibility of beam-to-column connections and the soil-structure
interaction are considered. In the analysis and design of steel frames, beam-tocolumn
connections are assumed to be either fully rigid or perfectly pinned.
However, the real behavior of beam-to-column connections is actually between
these extremes. Namely, even the simple connections used in practice possess some
stiffness falling between these two cases mentioned above. Moreover, it is found
that there exists a nonlinear relationship between the moment and beam-to-column
rotation when a moment is applied to a flexible connection. These partially
restrained connections influence the drift (P- effect) of whole structure as well as
the moment distribution in beams and columns. Use of a direct nonlinear inelastic
analysis is one way to account for all these effects in frame design. To be able to
implement such analysis, beam-to-column connections should be assumed and
modeled as semi-rigid connections. In the present study, beam-to-column
connections are modeled as &ldquo<br>end plate without column stiffeners&rdquo<br>and &ldquo<br>top and seat
angle with web angles&rdquo<br>. Soil-structure interaction is also included in the analysis.
Frames are assumed to be resting on nonlinear soil, which is represented by a set of
axial elements. Particle swarm optimization method is used to develop the optimum
design algorithm. The Particle Swarm method is a numerical optimization technique
that simulates the social behavior of birds, fishes and bugs. In nature fish school,
birds flock and bugs swarm not only for reproduction but for other reasons such as
finding food and escaping predators. Similar to birds seek to find food, the optimum
design process seeks to find the optimum solution. In the particle swarm
optimization each particle in the swarm represents a candidate solution of the
optimum design problem. The design algorithm presented selects sections for the
members of steel frame from the complete list of sections given in LRFD- AISC
(Load and Resistance Factor Design, American Institute of Steel Construction).
Besides, the design constraints are implemented from the specifications of the same
code which covers serviceability and strength limitations. The optimum design
algorithm developed is used to design number of rigid and semi-rigid steel frames.
28
Biddah, Aiman Mahmoud Samy. "Evaluation of the seismic level of protection of steel moment resisting frame building structures." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0007/NQ42833.pdf.
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Lokkas, Philotheos. "A consistent approach to the buckling design analysis of rigid jointed steel-frames subject to sidesway." Thesis, University College London (University of London), 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336448.
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Buell, Grant. "Comparison of structural steel lateral force resisting systems for a theoretical hospital grid system." Manhattan, Kan. : Kansas State University, 2009. http://hdl.handle.net/2097/2321.
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Agar, Mehmet. "Strengthening Of Reinforced Concrete Frames By Using Steel Bracings." Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609664/index.pdf.
Full textAbstract:
Structures in high seismic risk areas may be susceptible to severe damage in a major earthquake. Structures designed to meet older code requirements may be at even greater risk. When these structures are evaluated with respect to current code criteria, it is observed that they lack of lateral strength and/or ductility. Since safety and economic considerations are major problems, these structures become viable candidates for retrofit and seismic strengthening.
For the variety of structures and possible deficiencies that arise, several retrofitting techniques can be considered. Diagonal bracing system is one of the retrofitting techniques and it provides an excellent approach for strengthening and stiffening existing building for lateral forces. Also, another potential advantage of this system is the comparatively small increase in mass associated with the retrofitting scheme since this is a great problem for several retrofitting techniques.
In this study, the use of steel bracing for the strengthening of low, intermediate, and relatively high rise reinforced concrete frames are investigated analytically. The ultimate lateral load capacities of the strengthened frames are determined by a load controlled push-over analysis. The post-tensioning effect of preloading is also investigated.
32
Gunaydin, Egemen. "Natural Periods Of Braced Steel Frames Designed To Ec8." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614032/index.pdf.
Full textAbstract:
A two-phase study was undertaken to investigate the fundamental period of concentrically braced steel frames (CBFs) designed according to Eurocode 8. In the first phase, typical office buildings were studied by conducting two types of designs which are called as iterative and non-iterative. Non-iterative design is composed of obtaining final period by designing the structure with lower bound expression in Eurocode 8 while iterative design is similar to the non-iterative one but an updating of periods was considered in order to converge assumed and final periods. Different overstrength provisions are considered in the study. Lower bound expression in Eurocode 8 results in shorter periods which indicates that this expression can be safely utilized. The lower bound represented by Tremblay (2005) is also admissible except for some cases including shorter periods. In the second phase, a simple expression is derived for estimating the design base acceleration for braced frames proportioned according to Eurocode 8. This method requires inelastic top story drift values which were obtained from structures designed in the first phase using iterative method. These drifts were represented by simple expressions utilizing data fitting techniques. The method gives suitable first order estimate for the design base acceleration.
33
Tahir, Mahmood Md. "Structural and economic aspects of the use of semi-rigid joints in steel frames." Thesis, University of Warwick, 1997. http://wrap.warwick.ac.uk/4192/.
Full textAbstract:
This thesis reports on five main areas as follows: 1. Braced steel frames designed for semi-continuous construction were studied to determine savings in both cost and weight. Various frame parameters such as the number of bays, use of grade S355 steel, beam spans, types of connection, and selection of beam size were investigated. The investigation confirmed that semicontinuous construction contributes to worthwhile percentage savings on both cost and weight. 2. Analysis and design of steel unbraced frames bending on both axes were performed with emphasis on stability and deflection checks. Rules are proposed to improve the stability and stiffness. For connections to the minor axis, a proposed joint detail is presented. The performance of the frames was checked for collapse load level at ULS; deflection limits at SLS were also checked; in both cases using first and second order analysis. The investigation demonstrated that the frames should be restricted to less than four storeys. 3. A study on minor axis joints was carried out for flush end plate connections connected to the column web. Previous experimental results of moment and stiffness were compared with predicted values. Moment values were predicted using Gomes' formulae. The stiffness due to the column web was predicted using finite element analysis. The results showed good agreement between experimental and predicted values. The study on the connections was extended to their suitability in steel frames bending about the minor axis; the investigation confirmed that the connections were not suitable for unbraced wind-moment frames. An equation for prediction of initial stiffness was nevertheless established for the connection. 4. Steel frames with composite beams designed for minimum wind combined with maximum gravity load were studied for their performance, taking into account cracking along the beams. The investigation showed that the frames meet the requirements of deflection and sustain a load level of 1.0 for ULS. For frames studied for maximum wind combined with minimum gravity load, the moment capacity of the joints governed the design which resulted in a deeper beam section. 5. Seven tests were carried out for a new type of shear connector system installed by compressed air. The aim of the tests was to study the shear capacity and ductility of the studs. The tests showed that the pins fail due to fracture and the stud systems needs some improvements to increase the key structural properties.
34
Coy, Bradly B. "Buckling-Restrained Braced Frame Connection Design and Testing." Diss., CLICK HERE for online access, 2007. http://contentdm.lib.byu.edu/ETD/image/etd2030.pdf.
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Lopes, Arlindo Pires. "Seismic Behavior and Design of the Linked Column Steel Frame System for Rapid Return to Occupancy." PDXScholar, 2016. http://pdxscholar.library.pdx.edu/open_access_etds/3012.
Full textAbstract:
The Linked Column Frame (LCF) is a new brace-free lateral structural steel system intended for rapid return to occupancy performance level. LCF is more resilient under a design level earthquake than the conventional approaches. The structural system consists of moment frames for gravity that combines with closely spaced dual columns (LC) interconnected with bolted links for the lateral system. The LC links are sacrificial and intended to be replaced following a design level earthquake. The centerpiece of this work was a unique full-scale experiment using hybrid simulation testing; a combination of physical test of a critical sub-system tied to a numerical model of the building frame. Hybrid simulation testing allows for full scale study at the system level accounting for the uncertainties via experimental component and having the ability to model more conventional behavior through numerical simulation. The experimental subsystem consisted of a two story LCF frame with a single bay while the remainder of the building was numerically modeled. Two actuators per story were connected to the specimen. The LC links have been designed to be short and plastically shear dominated and the LCF met the design intent of 2.5% inter-story drift limits. For evaluating the LCF response, hybrid testing was performed for ground motion at three different intensities; 50%, 10% and 2% probability of exceedence in 50 years for Seattle, Washington ground motions. The system overall had exhibited three distinct performance levels; linearly elastic, rapid return to occupancy where only the replaceable links would yield, and collapse prevention where the gravity beam components also became damaged. Results demonstrated a viable lateral system under cyclic and seismic loading, offering a ductile structural system with the ability to rapidly return to occupancy.
36
Abu, Sha'ari. "Analysis of steel frame structures in fire." Thesis, University of Sheffield, 1991. http://etheses.whiterose.ac.uk/3065/.
Full textAbstract:
The main aim of the present research is to develop a method of analysis for structural frames exposed to fire including the effects of material and geometric non-linearities. A matrix stiffness method based on a secant stiffness approach is used providing a full temperature deformation history. The approach has previously been used for the analysis of continuous beams and is extended in the present work to include axial forces. These not only affect the longitudinal displacement, but also reduce the member stiffness and create secondary moments due to the p-delta effect. The influence of material unloading on the moment-axial force-curvature relationship is studied by examining a cross-section subjected to different combinations of bending moment and axial force at both ambient temperature and in fire. A computer program, based on the method is used to conduct a limited parametric study. This includes the influence of slenderness ratio, the magnitude of axial load and moment, the size of cross-section and grade of steel. Both uniform and non-uniform temperature profiles are considered for isolated beams, columns and simple portal frame. The importance of the p-delta effect is also investigated.
37
Maleck, Andrea Eden. "Second-order inelastic and modified elastic analysis and design evaluation of planar steel frames." Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/19610.
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Tuna, Mehmet. "Inelastic Panel Zone Deformation Demands In Steel Moment Resisting Frames." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614329/index.pdf.
Full textAbstract:
Panel zone is one of the significant parts of beam-column connections in steel structures. Until the 1994 Northridge Earthquake, a few experimental research and parametric studies had been carried out to understand the behavior of the panel zones. However, after the Northridge Earthquake, it was observed that beam-column connections were unable to show presumed seismic performance. Therefore, current design codes needed to be revised to improve seismic performance of connections in general and panel zones in particular. In this research, panel zone deformation demands are examined using explicit three dimensional finite element models and considering different parameters. For this purpose, a frame model with two different beam-column configurations was developed in order to observe the effects of beam depth, the axial load level and the level of seismicity. The frame models were analyzed under twenty different ground motion records. Local strain demands at the panel zones as well as the global frame deformation demands are evaluated. Analysis results revealed that AISC Specification designs allowed panel zone yielding<br>however, panel zones designed according to FEMA 355D showed minimal yielding for both shallow and deep beam configurations. Based on the analysis results, local shear strain demands in panel zones were expressed as a function of interstory drifts and normalized panel zone thicknesses.
39
Adams, Scott Michael. "Performance-Based Analysis of Steel Buildings: Special Concentric Braced Frame." DigitalCommons@CalPoly, 2010. https://digitalcommons.calpoly.edu/theses/389.
Full textAbstract:
The performance-based analysis methods and evaluation criteria in ASCE 41-06 were used to evaluate a special concentric braced frame building based on the design standards in ASCE 7-05. A rectangular, six-story office building was evaluated using linear static, linear dynamic, nonlinear static, and nonlinear dynamic procedures. The results showed that the linear procedures underestimated damage compared to the nonlinear procedures, with the building performing to Life Safety for the linear procedures, and the nonlinear procedures indicating component damage beyond the intended Life Safety limit for the 2/3 maximum considered earthquake (MCE) hazard. This trend continued to the maximum considered earthquake hazard as well, under which the overall building performance for the linear procedures did not reach the Collapse Prevention level, which occurred in the nonlinear procedures.
40
Williamson, Conner F. F. "SEISMIC PERFORMANCE OF SYMMETRIC STEEL MOMENT FRAMES WITH RANDOM REACTIVE WEIGHT DISTRIBUTIONS." DigitalCommons@CalPoly, 2012. https://digitalcommons.calpoly.edu/theses/890.
Full textAbstract:
When a structure undergoes seismic excitation, the intensities and spatial distributions of the reactive weights on the structure may not be the same as those assumed in original design. Such a difference is inevitable due to many facts with the random nature (e.g., redistribution of live load), resulting in accidental eccentricity and consequently torsional response in the system. The added torsion can cause excessive deformation and premature failure of the lateral force resisting system and its detrimental effect is typically accounted for in most building design codes with an arbitrarily specified accidental eccentricity value. While it tends to amplify drift response of buildings under earthquake excitations, it is unclear whether the code specified accidental eccentricity is quantitatively adequate or not in seismic fragility assessment of steel moment frames (including low-rise, mid-rise and high-rise frames) with random reactive weight distributions. This thesis applies surveyed dead and live load intensities and distributions to three representative steel moment resisting frame structures that have been widely investigated in a series of projects under the collaboration of the Structural Engineers Association of California (SEAOC), the Applied Technology Council (ATC), and Consortium of Universities for Research in Earthquake Engineering (CUREE), known as SAC. Based on an extensive parametric study and incremental nonlinear dynamic analyses, it is found that variable load intensity and eccentricity had negligible impacts on the inter-story drifts of the low- and high-rise steel moment frames. However, they affect to a higher degree the performance of the mid-rise steel moment frames. Moreover, it is found that under the maximum considered earthquake (MCE) event, the actual drifts in steel moment frames with random reactive weight distributions can be conservatively captured through consideration of the code specified accidental eccentricities.
41
Olmez, Harun Deniz. "A Numerical Study On Special Truss Moment Frames." Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/12611322/index.pdf.
Full textAbstract:
A three-phase numerical study was undertaken to address some design issues related with special truss moment frames (STMFs). In the first phase, the design approaches for distribution of shear strength among stories were examined. Multistory STMFs sized based on elastic and inelastic behavior were evaluated from a performance point of view. A set of time history analysis was conducted to investigate performance parameters such as the interstory drift ratio and the plastic rotation at chord member ends. The results of the analysis reveal that the maximum interstory drifts are not significantly influenced by the adopted design philosophy while considerable differences are observed for plastic rotations. In the second phase, the expected shear strength at vierendeel openings was studied through three dimensional finite element modeling. The results from finite element analysis reveal that the expected shear strength formulation presented in the AISC Seismic Provisions for Structural Steel Buildings is overly conservative. Based on the analysis results, an expected shear strength formula was developed and is presented herein. In the third phase, the effects of the load share and slenderness of X-diagonals in the special segment on the performance of the system were evaluated. Lateral drift, curvature at chord member ends, axial strain at X-diagonals and base shear were the investigated parameters obtained from a set of time history analysis. The results illustrate that as the load share of X-diagonals increases, the deformations decreases. Moreover, the slenderness of X-diagonals is not significantly effective on
the system performance.
42
Sanchez, Juan Carlos. "Seismic Rehabilitation of Steel Moment Frames Vulnerable to Soft-Story Failures Through Implementation of Rocking Cores." DigitalCommons@CalPoly, 2013. https://digitalcommons.calpoly.edu/theses/1029.
Full textAbstract:
During seismic events, inefficient steel moment frame building systems may exhibit soft-story failures. This thesis focuses on development and validation of a seismic retrofit strategy for avoiding soft-story failures in low-rise and mid-rise steel moment frame buildings. The considered retrofit strategy consists of a sufficiently stiff Rocking Core (RC) pinned to the foundation and pin connected to the existing frame. For demonstration purposes, two representative benchmark steel moment frames, which are modified from the three- and nine-story pre-Northridge steel moment frames designed for Los Angeles in the SAC Steel Project, are considered. Finite Element (FE) models of the benchmark buildings are developed with consideration of member yielding, connection rupture, and P-Delta effect, and validated using published results. Eigenvalue analyses are conducted to investigate the effect of the RC on system modal properties. It is found that in general the added RC with practical stiffness value does not significantly change the fundamental period and therefore does not attract excessive earthquake force to the system. In addition, nonlinear static pushover analyses are performed to address the beneficial contribution of the RC to the system under the performance objectives including immediate occupancy, life safety, and collapse prevention. The Monte-Carlo simulation technique is used to generate the random lateral force distribution required in the nonlinear static pushover analysis. It is found that RC works as expected in all considered scenarios and creates more uniform inter-story distribution along the vertical direction when it is sufficiently stiff. Furthermore, nonlinear dynamic analyses are conducted using three different ground motion suites (including two suites with ground motions having probabilities of exceedance of 2% and 10% in 50 years, and one suite with near-fault ground motions). It is shown that the systems with properly selected RC can achieve the Best Safety Objective defined in FEMA 356 and exhibit collapse prevention performance under near-fault earthquakes.
43
Warrior, David Alexander. "The effects of longwall mining subsidence on steel framed buildings." Thesis, University of Bradford, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.281133.
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Sevil, Tugce. "Seismic Strengthening Of Masonry Infilled R/c Frames With Steel Fiber Reinforcement." Phd thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/3/12611516/index.pdf.
Full textAbstract:
Seismic resistance of many buildings in Turkey is insufficient. Strengthening using R/C infills requires huge construction work. Feasible, easy strengthening techniques are being studied in Structural Mechanics Laboratory of METU.
In this project, it was aimed to develop an economical strengthening method. This method is based on addition of steel fibers and/or PP fibers in mortar and application of mortar on masonry wall. Project was sponsored by the Scientific and Technical Research Council of Turkey (TÜ<br>BiTAK).
Physical properties of cement, aggregate, and mortar used in tests were determined by material tests. After performing flexural strength and compressive strength tests, optimum mortar was obtained. R/C frames strengthened by applying the mortar to brick infilled walls were tested under reversed cyclic loads. Before the frame tests, two series of panel tests were performed to correctly model strengthened infill walls and to gather information about behavior of walls under load. Totally 10 frame tests were done. 4 tests were done as reference tests, and other 6 were done as strengthened frame tests.
In the analytical part of study, the plastered hollow brick infill wall strengthened by FRM was modeled as two separate compression struts. First strut was used to model the plastered hollow brick infill wall. Second strut was used to model the FRM.
This technique is effective in improving seismic behavior by increasing strength, initial stiffness, energy dissipation, and ductility. Moreover, the method provides strengthening of the buildings without evacuating the structure.
45
Saver, A. K. B. "The reliability of standard design methods for steel frame structures." Thesis, University of Bath, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333024.
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Bailey, Colin Gareth. "Simulation of the structural behaviour of steel-framed buildings in fire." Thesis, University of Sheffield, 1995. http://etheses.whiterose.ac.uk/2990/.
Full textAbstract:
A three-dimensional finite element computer program has been developed which can predict the behaviour of steel-framed buildings, including the supported floor system, in any specified fire scenario. The developed software provides a more realistic prediction of structural behaviour at elevated temperatures, than is possible with models which are limited to frame analysis, since the building structure is considered as a more complete entity. Confidence in the software is strengthened by comparison with test results to the extent that different structural and fire scenarios may in future be investigated very cheaply. This could lead to a better understanding of the behaviour of steel, framed structures during fires and to more rational approaches to specification of fire protection requirements, which are currently rather expensive in terms of material and fixing costs. The steel beam-column members are represented by one-dimensional two-noded elements which incorporate both material and geometrical non-linearities. These can model three-dimensional steel member behaviour including lateral-torsional buckling. Temperature gradients can be specified through the steel cross-section and also along its length. Spring elements, of zero length, have been introduced to represent semi-rigid joints. These degrade in stiffness and strength with rise in temperature and are represented by any specified moment-rotation-temperature relationship. Unloading from an inelastic state has been modelled for both the steel members and connections, allowing the behaviour of the frame during the cooling phase of a fire to be investigated. This will enable the repairability of the frame to be assessed after a fire has occurred. The flooring system is represented by shell finite elements, which are linear elastic and include thermal strains, although the temperature distribution through the slab's thickness must be assumed uniform. A simplified method of representing cracking in the concrete has been introduced by placing a limit on its maximum bending stress. The node position of the steel one-dimensional finite elements can be displaced to allow connection to the two-dimensional shell elements at a common point. This allows composite action between the beam and supported slab to be modelled. Comparison has been made between computer simulations and fire tests on the full-scale test frame at Cardington. It has been shown that modelling isolated members is highly unrealistic. However models which incorporate a significant amount of the structure surrounding the heated zone, including the membrane action of the flooring system, perform far better when compared to actual tests. These comparisons indicate that the future development of design methods for fire safety of structures needs to be steered away from its traditional emphasis on isolated member behaviour, and towards considering the interaction of the whole building structure with the aim of avoiding disproportionate collapse.
47
Aydogdu, Ibrahim. "Optimum Design Of 3-d Irregular Steel Frames Using Ant Colony Optimization And Harmony Search Algorithms." Phd thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612285/index.pdf.
Full textAbstract:
Steel space frames having irregular shapes when subjected to lateral loads caused
by wind or earthquakes undergo twisting as a result of their unsymmetrical
topology. As a result, torsional moment comes out which is required to be resisted
by the three dimensional frame system. The members of such frame are generally
made out of steel I sections which are thin walled open sections. The simple beam
theory is not adequate to predict behavior of such thin-walled sections under
torsional moments due to the fact that the large warping deformations occur in the
cross section of the member. Therefore, it is necessary to consider the effect of
warping in the design of the steel space frames having members of thin walled
steel sections is significant. In this study the optimum design problem of steel
space frames is formulated according to the provisions of LRFD-AISC (Load and
Resistance factor design of American Institute of Steel Construction) in which the
effect of warping is also taken into account. Ant colony optimization and harmony
search techniques two of the recent methods in stochastic search techniques are
used to obtain the solution of the design problem. Number of space frame examples is designed by the algorithms developed in order to demonstrate the
effect of warping in the optimum design.
48
Berding, Daniel Christopher. "Wind Drift Design of Steel Framed Buildings: An Analytical Study and a Survey of the Practice." Thesis, Virginia Tech, 2006. http://hdl.handle.net/10919/33901.
Full textAbstract:
<p>The design of steel framed buildings must take into consideration the lateral drift of the structure due to wind loading and any serviceability issues that may arise from this lateral movement. This thesis focuses on one of these issues, damage to nonstructural components.
</p><p>
Although there are no specific requirements in the United States governing the effects of wind drift, it is an important issue which may significantly impact the buildings structural performance and economy. Furthermore, because these serviceability issues are not codified, there is a wide variation among design firms in how they are dealt with, leading to a greater economic disparity.
</p><p>
This thesis begins with a comprehensive review of the literature that covers all pertinent aspects of wind drift in steel framed buildings. Next an analytical study of the variations in modeling parameters is performed to demonstrate how simple assumptions can affect the overall buildings stiffness and lateral displacements. A study is then carried out to illustrate the different sources of elastic deformation in a variety of laterally loaded steel frames. The different modeling variables demonstrate how deformation sources vary with bay width, the number of bays and the number of stories, providing a useful set of comparisons.
</p><p>
To ascertain how serviceability issues are dealt with from firm to firm, a survey of the practice is developed to update the one conducted in 1988 (ASCE). In effect, the thesis is presented with the intention of suggesting and establishing a comprehensive, performance based approach to the wind drift design of steel framed buildings.</p><br>Master of Science
49
Means, Daniel Eric. "Identification of Physical Changes to a Steel Frame." DigitalCommons@CalPoly, 2010. https://digitalcommons.calpoly.edu/theses/246.
Full textAbstract:
The thesis utilized physical testing and computer modeling to determine the feasibility of identifying a change to the mass or stiffness of a steel frame. Physical testing was performed using an accelerometer, linear shaker, and arbitrary function generator. Two methods of laboratory testing were developed: ambient vibration testing (AVT) and forced vibration testing (FVT). AVT was able to preliminarily identify the natural frequencies and mode shapes of the frame. FVT was able to precisely identify four distinct natural frequencies, mode shapes, and damping ratios. The baseline frame then underwent two physical changes: the addition of mass to its roof, and the addition of braces along one of its sides. FVT was used again to determine the natural frequencies, mode shapes, and damping ratios of the newly changed structure.
An ETABS computer model was developed to represent the frame. This baseline model produced natural frequencies and mode shapes that closely matched the values determined by FVT. The mass and stiffness of this baseline model were then changed multiple times through the addition of mass and braces at various locations on the model. The frequencies and mode shapes were recorded for each change.
Two methods were developed to identify the changes to the steel frame. The first method was able to determine which one of the models best represented a single change to the structure (adding mass to its roof). The second method was able to determine the combination of models that best represented the two concurrent changes to the structure (adding mass to its roof and braces to its sides). Both methods utilized the percent differences of each altered computer model relative to the original, and each method satisfactorily identified its respective physical alteration.
50
Chatterjee, Aritra. "Structural System Reliability with Application to Light Steel-Framed Buildings." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/74879.
Full textAbstract:
A general framework to design structural systems for a system-reliability goal is proposed.
Component-based structural design proceeds on a member to member basis, insuring acceptable failure probabilities for every single structural member without explicitly assessing
the overall system safety, whereas structural failure consequences are related to the whole
system performance (the cost of a building or a bridge destroyed by an earthquake) rather
than a single beam or column failure. Engineering intuition tells us that the system is
safer than each individual component due to the likelihood of load redistribution and al-
ternate load paths, however such conservatism cannot be guaranteed without an explicit
system-level safety check. As a result, component-based structural designs can lead to both
over-conservative components and a less-than-anticipated system reliability.
System performance depends on component properties as well as the load-sharing network,
which can possess a wide range of behaviors varying from a dense redundant system with
scope for load redistribution after failure initiates, to a weakest-link type network that fails as
soon as the first member exceeds its capacity. The load-sharing network is characterized by
its overall system reliability and the system-reliability sensitivity, which quantifies the change in system safety due to component reliability modifications. A general algorithm is proposed
to calculate modified component reliabilities using the sensitivity vector for the load-sharing
network. The modifications represent an improvement on the structural properties of more
critical components (more capacity, better ductility), and provide savings on less important
members which do not play a significant role.
The general methodology is applied to light steel-framed buildings under seismic loads.
The building is modeled with non-linear spring elements representing its subsystems. The
stochastic response of this model under seismic ground motions provides load-sharing, system
reliability and sensitivity information, which are used to propose target diaphragm and shear
wall reliability to meet a building reliability goal. Finally, diaphragm target reliability is
used to propose modified component designs using stochastic simulations on geometric and
materially non-linear finite-element models including every individual component.<br>Ph. D.