Academic literature on the topic 'Prestressed concrete beams. Strains and stresses'
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Journal articles on the topic "Prestressed concrete beams. Strains and stresses"
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Küsel, Frank, Elsabe Kearsley, Liam J. Butler, Sarah A. Skorpen, and M. Z. E. B. Elshafie. "Measured temperature effects during the construction of a prestressed precast concrete bridge beam." MATEC Web of Conferences 199 (2018): 11013. http://dx.doi.org/10.1051/matecconf/201819911013.
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Prestress losses in precast concrete beams include the short-term effects of elastic shortening and the long-term effects of concrete shrinkage, concrete creep and steel relaxation. Temperature effects are, however, excluded. The aim of this research was to monitor the behaviour of a prestressed precast concrete bridge beam, focussing on temperature effects and destressing. Successful monitoring assists in comparing the real performance of a structure to the expected design performance, and in managing the durability of the monitored structure. The effect of temperature variation on strains in prestressed beams was investigated by instrumenting a precast beam. Temperature and strains were monitored from the day of casting up to and including the cutting of the pretensioning strands. Daily temperature variations causing vertical non-linear temperature profiles resulted in internal strains of up to 28 % of the strains caused by destressing. It was therefore concluded that thermal effects before destressing resulting from elevated curing temperatures and daily temperature changes should be considered in the calculation of prestress losses. The monitoring techniques used were successful in determining the stresses and strains within the beam, which can be used to compare real prestress losses with the losses assumed in design.
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Navrátil, Jaroslav, and Lukáš Zvolánek. "Shear at the Interface between Composite Parts of Prestressed Concrete Section." Applied Mechanics and Materials 752-753 (April 2015): 763–68. http://dx.doi.org/10.4028/www.scientific.net/amm.752-753.763.
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Composite concrete beams made of prefabricated prestressed or non-prestressed element and cast-in-place reinforced concrete slab became very popular in present-day civil engineering practice. Two concrete composite parts of beam are cast at different times. Different moduli of elasticity, consecutive load application, and differential creep and shrinkage cause unequal strains and stresses in two adjacent fibers of construction joint. The requirement is to ensure that both parts act fully compositely, because the bending and shear designs of composite members are based on this assumption. Therefore the level of shear stresses at the interface between two parts must be limited. The objective of the paper is to review the methods for the calculation of shear stresses in construction joint, and to evaluate the influence of different age of two concrete composite parts on the level of shear stresses. Calculation method alternative to Eurocode 2 method is proposed and tested. It is recommended to calculate the shear stress from difference of normal forces acting on sectional components in two neighboring sections of the element. It was observed that differential shrinkage of concrete components can significantly affect the stress distribution. Numerical studies were performed based on real-life examples of composite beams.
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Al-Ilani, Mohamad, and Yehya Temsah. "Comparative study of modeling methods used to simulate initial stresses in prestressed beams towards manual analysis." MATEC Web of Conferences 281 (2019): 01014. http://dx.doi.org/10.1051/matecconf/201928101014.
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Numerical modeling of the prestressing element that generates prestressed effect in beams has always been considered a big challenge. This research compares two methods of modeling; In the first method we used initial stresses predefined stress and in the second method we used the temperature strain. Concrete damage plasticity model (CDP) was used to model the non-linear behavior of concrete material and an elasto-plastic behavior was applied to ordinary and prestressed reinforcement. Truss elements were used to model ordinary and prestressed reinforcement embedded inside the concrete. As a result, Initial Temperature load method showed less error in bottom and top stresses and cambering of beam in comparison with the basic concept method, than predefined method.
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Kennedy, John B., Saddallah Chami, and Nabil F. Grace. "Dynamic and fatigue responses of prestressed concrete girders with openings." Canadian Journal of Civil Engineering 17, no. 3 (June 1, 1990): 460–70. http://dx.doi.org/10.1139/l90-050.
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The influences of opening size, eccentricity, and location on the natural frequencies, mode shapes, damping, and deformation response of prestressed beams and girders with openings under both dynamic and cyclic loadings are presented. A theoretical study was conducted by the finite element method to determine the above structural responses for prestressed rectangular, T- and I-beams. The results were verified and substantiated by tests on six post-tensioned concrete beams. Good agreement was shown between the theoretical and experimental results. Furthermore, it was shown that cyclic loading can have a significant influence on the amplitudes of vibration and the structural response of the top and bottom chords of the opening, and a very significant effect on the tensile strains on the side of the opening resulting from the initial prestressing. Design suggestions are made. Key words: design, dynamic, fatigue, frequencies, girders, openings, prestressed concrete, stresses, structures, tests.
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Pažma, Peter, Viktor Borzovič, and Jaroslav Halvonik. "Secondary Effects of Prestressing at ULS on Hyperstatic Structures." Key Engineering Materials 691 (May 2016): 138–47. http://dx.doi.org/10.4028/www.scientific.net/kem.691.138.
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Secondary (parasitic) effects of prestressing develop in hyperstatic structures (continuous beams) due to restraining of imposed deformation by hyperstatic restraints. These effects may, in some case, significantly influence internal forces and stresses in prestressed structures. Internal forces due to the secondary effects should be included in design combinations for verification of both ultimate and serviceability limit state. Because secondary effects are influenced by structural system, there is a question how they will change after changing of the structural system e.g. due to development of plastic hinge (s) in a critical cross-section (s) or after development of kinematic mechanism?This article describes an experimental program at Slovak University of Technology in Bratislava, Department of concrete structures and bridges and its results. Program were focused on investigation of behavior of continuous post-tensioned beams with significant secondary effects of prestressing subjected to ultimate load. Together six, two span beams were tested, with maximum load changing structural system into kinematic mechanism. Secondary effects of prestressing were detected by measurement of reactions in all supports, further there were measured displacements in the quarters of both spans and strains in critical sections of the beams.
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Kovács, I. "Structural performance of steel fibre reinforced concrete — Part I. Overview of the experimental program." International Review of Applied Sciences and Engineering 5, no. 1 (June 1, 2014): 9–19. http://dx.doi.org/10.1556/irase.5.2014.1.2.
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Abstract The papers of the series deal with experimental characterisation of mechanical as well as structural properties of different steel fibre reinforced concretes that can be used for several structural applications. An extensive experimental programme (six years) has been developed to investigate the effect of steel fibre reinforcement on the mechanical performance and structural behaviour of concrete specimens. Specimens and test methods were selected to be able to detect realistic behaviour of the material, representing clear effect on the structural performance. Material compositions, test methods, type of test specimens will be detailed in the presented paper (Part I). Furthermore, compressive strength (Part II), stress-strain relationship (Part II), splitting strength (Part III) and toughness (Part IV) will also be discussed. In the light of the motivation to determine the structural performances of 1D concrete structural element affected by steel fibre reinforcement, bending and shear behaviour (Part V) as well as serviceability state (Part VI) of steel fibre reinforced concrete beams will be analysed. Since normal force — prestressing force — can affectively be used to improve the structural performances of RC element flexural tests were carried out on prestressed pretensioned steel fibre reinforced concrete beams (Part VII). Moreover, focusing on the in-plane state of stresses for 2D structures, behaviour of steel fibre reinforced concrete deep beams in shear and steel fibre reinforced concrete slabs (Part VIII) in bending will be explained. Finally, based on the wide range of the experimental and analytical studies on the presented field, a new material model for the 1D uniaxial behaviour (Part IX) and its possible extension to the 3D case (Part X) will be described hereafter. All papers will put emphasis on the short literature review of the last four decades.
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Jia, Jin Qing, Fang Yu, Da Li Yao, and Wei Qing Zhu. "Strain Analysis of Corrosed Prestressed Concrete Beams on Fatigue Test." Advanced Materials Research 255-260 (May 2011): 355–59. http://dx.doi.org/10.4028/www.scientific.net/amr.255-260.355.
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In order to study the relationship between strains and corrosion levels of prestressed concrete beams uder fatigue loading, accelerated corrosion method is used to make various corrosion rates of prestressed steel strands. The beams have the same designs and submitted to the same maximum and minimum load during the test. With the corrosion level as main parameter, strains at different position of the beams, such as non-prestressed steel strain, concrete strain in compressive region at mid-span and prestressed steel strain are studied. The test results show that beams with different corrosion rates have the same “three-stage“ law on the development of non-prestressed steel maximum and residual strain,as well as concrete strain and prestress strain. The significant increase of concrete strain is generated due to corrosion after concrete cracking.The increase of non-prestressed steel strain is nearly proportional to the growth of corrosion under the same fatigue load. A relationship was found to be a function. It can be obtained the corrosion rate of prestressed steel when the stress of non-prestressed steel strains are measured.
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Alnuaimi, A. S. "Comparison between Experimental and 3D Finite Element Analysis of Reinforced and Partially Pre-Stressed Concrete Solid Beams Subjected to Combined Load of Bending, Torsion and Shear." Journal of Engineering Research [TJER] 5, no. 1 (December 1, 2008): 79. http://dx.doi.org/10.24200/tjer.vol5iss1pp79-96.
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This paper presents a non-linear analysis of three reinforced and two partially prestressed concrete solid beams based on a 20 node isoparametric element using an in-house 3D finite element program. Anon linear elastic isotropic model, proposed by Kotsovos, was used to model concrete behaviour, while steel was modelled as an embedded element exhibiting elastic-perfectly plastic response. Allowance was made for shear retention and for tension stiffening in concrete after cracking. Only in a fixed direction, smeared cracking modelling was adopted. The beams dimensions were 300x300 mm cross section, 3800 mm length and were subjected to combined bending, torsion and shear. Experimental results were compared with the non-linear predictions. The comparison was judged by load displacement relationship, steel strain, angle of twist, failure load, crack pattern and mode of failure. Good agreement was observed between the predicted ultimate load and the experimentally measured loads. It was concluded that the present program can confidently be used to predict the behaviour and failure load of reinforced and partially prestressed concrete solid beams subjected to a combined load of bending, torsion and shear.
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Selvachandran, P., S. Anandakumar, and K. L. Muthuramu. "Deflection of Steel Reinforced Concrete Beam Prestressed With CFRP Bar." Archives of Metallurgy and Materials 62, no. 3 (September 26, 2017): 1915–22. http://dx.doi.org/10.1515/amm-2017-0289.
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AbstractCarbon Fiber Reinforced polymer (CFRP) bars are weak in yielding property which results in sudden failure of structure at failure load. Inclusion of non-pretensioned steel reinforcement in the tension side of CFRP based prestressed concrete beam will balance the yielding requirements of member and it will show the definite crack failure pattern before failure. Experimental investigation has been carried out to study the deflection behavior of partially prestressed beam. Experimental works includes four beam specimens stressed by varying degree of prestressing. The Partial Prestressing Ratio (PPR) of specimen is considered for experimental works in the range of 0.6 to 0.8. A new deflection model is recommended in the present study considering the strain contribution of CFRP bar and steel reinforcement for the fully bonded member. New deflection model converges to experimental results with the error of less than 5% .
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Huang, Dongzhou, and Mohsen Shahawy. "Analysis of Tensile Stresses in Transfer Zone of Prestressed Concrete U-Beams." Transportation Research Record: Journal of the Transportation Research Board 1928, no. 1 (January 2005): 134–41. http://dx.doi.org/10.1177/0361198105192800115.
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Prestressed U-beam bridges compare favorably in cost and appearance to traditional concrete I-beam bridges. Consequently, U-beam bridges are gaining in popularity and usage, especially when aesthetic issues are deemed important. U-beam bridges first appeared in Florida in 2000; however, during construction, cracks developed in the webs of the U-beams. This paper presents results of an analysis of representative cracking of U-beams and proposes a practical method for the transfer zone stirrup design. For the purpose of the analysis, the U-beam is divided into a series of finite shell-plate elements, and the prestressing tendons are simulated as a number of concentrated forces. Two different mechanical models of the U-beams are developed on the basis of the stages of construction. Analytical results show that high tensile stresses occur in the end zone of the U-beam because of the prestressing tendons and that these tensile stress must be properly considered in bridge design. The research results are applicable to the design of prestressed U-beams and similar types of prestressed girders.
Dissertations / Theses on the topic "Prestressed concrete beams. Strains and stresses"
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唐嘉鴻 and Ka-hung William Tang. "Strain energy capacity of reinforced and prestressed concrete beams." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1990. http://hub.hku.hk/bib/B30425190.
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Tang, Ka-hung William. "Strain energy capacity of reinforced and prestressed concrete beams /." [Hong Kong] : University of Hong Kong, 1990. http://sunzi.lib.hku.hk/hkuto/record.jsp?B12925524.
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Karimnassaee, Ali 1959. "FLEXURAL BEHAVIOR OF LIGHTLY REINFORCED UNBONDED POST-TENSIONED CONCRETE BEAMS." Thesis, The University of Arizona, 1986. http://hdl.handle.net/10150/275510.
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Al-Faris, Tariq Abdulaziz. "EXPERIMENTAL STUDY OF BEHAVIOR OF UNBONDED POSTTENSIONED BEAMS." Thesis, The University of Arizona, 1985. http://hdl.handle.net/10150/275439.
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Lee, Jonghang. "Experimental and analytical investigations of the thermal behavior of prestressed concrete bridge girders including imperfections." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34675.
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An experimental and analytical study was conducted on a BT-63 prestressed concrete girder to investigate the thermal effects on the girder. A 2D finite element heat transfer analysis model was then developed which accounted for heat conduction, convection, radiation, and irradiation. The solar radiation was predicted using the location and geometry of the girder, variations in the solar position, and the shadow from the top flange on other girder surfaces. The girder temperatures obtained from the 2D heat transfer analysis matched well with the measurements. Using the temperatures from the 2D heat transfer analysis, a 3D solid finite element analysis was performed assuming the temperatures constant along the length of the girder. The maximum vertical displacement due to measured environmental conditions was found to be 0.29 inches and the maximum lateral displacement was found to be 0.57 inches. Using the proposed numerical approach, extremes in thermal effects including seasonal variations and bridge orientations were investigated around the United States to propose vertical and transverse thermal gradients which could then be used in the design of I-shaped prestressed concrete bridge girders. A simple beam model was developed to calculate the vertical and lateral thermal deformations which were shown to be within 6% of the 3D finite element analyses results. Finally, equations were developed to predict the maximum thermal vertical and lateral displacements for four AASHTO-PCI standard girders. To analyze the combined effects of thermal response, initial sweep, and bearing support slope on a 100-foot long BT-63 prestressed concrete girder, a 3D finite element sequential analysis procedure was developed which accounted for the changes in the geometry and stress state of the girder in each construction stage. The final construction stage then exposed the girder to thermal effects and performed a geometric nonlinear analysis which also considered the nonlinear behavior of the elastomeric bearing pads. This solution detected an instability under the following conditions: support slope of 5¡Æ and initial sweep of 4.5 inches.
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羅文惠 and Man-wai Law. "Strain energy capacity of reinforced concrete beams." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1987. http://hub.hku.hk/bib/B31207704.
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Law, Man-wai. "Strain energy capacity of reinforced concrete beams /." [Hong Kong : University of Hong Kong], 1987. http://sunzi.lib.hku.hk/hkuto/record.jsp?B12228175.
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Prasad, M. N. Nagendra. "Moment-curvature relationships in reinforced concrete." Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-07112009-040255/.
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Guenther, Cristy Louise. "Evaluation of shear and diagonal tension in plain concrete." Laramie, Wyo. : University of Wyoming, 2007. http://proquest.umi.com/pqdweb?did=1400964851&sid=1&Fmt=2&clientId=18949&RQT=309&VName=PQD.
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Peng, Jun, and 彭军. "Strain gradient effects on flexural strength and ductility design of normal-strength RC beams and columns." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2012. http://hub.hku.hk/bib/B48329630.
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The stress-strain characteristics of concrete developed in flexure is very important for flexural strength design of reinforced concrete (RC) members. In current RC design codes, the stress-strain curve of concrete developed in flexure is obtained by scaling down the uni-axial stress-strain curve to account for the strain gradient effect. Therefore, the maximum concrete stress that can be developed under flexure is smaller than its uni-axial strength, and the use of which always underestimates the flexural strength of RC beams and columns even though the safety factors for materials are taken as unity. Furthermore, the value of strength underestimation was different for RC beams and columns, which indicates that the extent of strain gradient will affect the maximum concrete stress and stress-strain curve developed under flexure.
To investigate the maximum concrete stress, 29 column specimens were fabricated and tested in this study. They were divided into 9 groups, each of which was poured from the same batch of concrete and contained specimens with identical cross-section properties. In each group, one specimen was tested under concentric load while the rest was/were subjected to eccentric or horizontal load. To study the strain gradient effects, the ratio of the maximum concrete compressive stress developed in the eccentrically/horizontally loaded specimens to the maximum uni-axial compressive stress developed in the counterpart concentrically loaded specimens, denoted by k3, is determined based on axial force and moment equilibriums. Subsequently, the concrete stress block parameters and the equivalent rectangular concrete stress block parameters are determined. It is found that the ratios of the maximum and equivalent concrete stress to uni-axial cylinder strength, denoted respectively by k3 and , depend significantly on strain gradient, while that of the depth of stress block to neutral axis depth, denoted by , remains relatively constant with strain gradient. Design equations are proposed to relate and with strain gradient for strength calculation, whose applicability is verified by comparing the strengths of RC beams and columns tested by various researchers with their theoretical strengths predicted by the proposed parameters and those evaluated based on provisions of RC codes.
Based on the test results, the stress-strain curve of normal-strength concrete (NSC) developed under strain gradient is derived using least-square method by minimising the errors between the theoretical axial load and moment and the respective measured values. Two formulas are developed to derive the flexural stress-strain curve, whose applicability is verified by comparing the predicted strength with those measured by other researchers.
Lastly, the application of the proposed stress-block parameters and stress-strain curve of NSC will be illustrated by developing some charts for flexural strength design of NSC beams and columns. The application will further be extended to develop strength-ductility charts for NSC beams and columns, which enable simultaneous design of strength and ductility. By adopting the proposed design charts, the flexural strength design, as well as that of the plastic hinge forming mechanism during extreme events, will be more accurate. The resulting design will be safer, more environmentally friendly and cost effective.published_or_final_version
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Books on the topic "Prestressed concrete beams. Strains and stresses"
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Gauvreau, Paul. Ultimate limit state of concrete girders prestressed with unbonded tendons. Basel: Birkhauser Verlag, 1993.
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Béton armé, calcul aux états limites: Théorie et pratique. Montréal, Québec, Canada: G. Morin, 1987.
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Smarzewski, Piotr. Modelowanie statycznego zachowania niesprężystych belek żelbetowych wykonanych z betonu wysokiej wytrzymałości: Modelling of static behavior of inelastic reinforced high-strength concrete beams. Lublin: Politechnika Lubelska, 2011.
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Soltesz, Steven M. Strain monitoring for Horsetail Falls and Sylvan bridges: Final report. Salem, OR: Oregon Dept. of Transportation, Research Group, 2002.
Find full textBook chapters on the topic "Prestressed concrete beams. Strains and stresses"
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Nawy, Edward G. "Stresses and End Cracks in Anchorage Zones of Post-Tensioned Prestressed Concrete Beams." In Progress in Structural Engineering, 229–56. Dordrecht: Springer Netherlands, 1991. http://dx.doi.org/10.1007/978-94-011-3616-7_16.
Full textConference papers on the topic "Prestressed concrete beams. Strains and stresses"
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Birkner, Dennis, and Steffen Marx. "Large-scale fatigue tests on prestressed concrete beams." In IABSE Congress, Christchurch 2021: Resilient technologies for sustainable infrastructure. Zurich, Switzerland: International Association for Bridge and Structural Engineering (IABSE), 2021. http://dx.doi.org/10.2749/christchurch.2021.0943.
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<p>For a better estimation of the fatigue lifetime of real structures, tests on large-scale beam specimens are more suitable than on common cylindrical specimens, since effects like local stiffness changes and stress redistributions can be reproduced more realistically. This article presents an experimental setup for large-scale concrete beams subjected to fatigue loading. Additionally, the fatigue tests are simulated with a numerical model. The results of the numerical analysis show a successively increasing damage propagating from the edge into the inner part of the cross-section in the mid span with increasing number of cycles. This results in stress redistributions which extend the lifetime of the structure. The evaluation of the experimental investigation on the first beam specimen shows a larger stiffness degradation at the upper edge than in the centre of the cross-section as well as increasing strains at this location. This matches the expected effects from the numerical analysis.</p>
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Savic, Adrijana, B. Terry Beck, Aaron A. Robertson, Robert J. Peterman, Jeremiah Clark, and Chih-Hang (John) Wu. "Effects of Cover, Compressive Strength, and Wire Type on Bond Performance in Prismatic Prestressed Concrete Members." In 2018 Joint Rail Conference. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/jrc2018-6153.
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The bond between wire and concrete is crucial for transferring the stresses between the two materials in a prestressed concrete member. Furthermore, bond can be affected by such variables as thickness of concrete cover, type of pre-stressing (typically indented) wire used, compressive (release) strength of the concrete, and concrete mix. This work presents current progress toward the development of a testing procedure to get a clear picture of how all these parameters can ruin the bond and result in splitting. The objective is to develop a qualification test procedure to proof-test new or existing combinations of pre-stressing wire and concrete mix to ensure a reliable result. This is particularly crucial in the concrete railroad crosstie industry, where incompatible conditions can result in cracking and even tie failure. The goal is to develop the capability to readily identify compatible wire/concrete designs “in-plant” before the ties are manufactured, thereby eliminating the likelihood that defectively manufactured ties will lead to in-track tie failures due to splitting. The tests presented here were conducted on pre-tensioned concrete prisms cast in metal frames. Three beams (prismatic members) with different cross sections were cast simultaneously in series. Four pre-stressing wires were symmetrically embedded into each concrete prism, resulting in a common wire spacing of 2.0 inches. The prisms were 59.5in long with square cross sections. The first prism was 3.5 × 3.5in with cover 0.75in, the second was 3.25 × 3.25in with cover 0.625in and the third prism in series was 3.0 × 3.0 in with cover 0.50in. All pre-stressing wires used in these initial tests were of 5.32 mm diameter and were of the same wire type (indent pattern) denoted by “WE”, which had a spiral-shaped geometry. This is one of several wire types that are the subject of the current splitting propensity investigation. Others wire types include variations of the classical chevron shape, and the extreme case of smooth wire with no indentions. The wires were initially tensioned to 7000 pounds (31.14 KN) and then gradually de-tensioned after reaching the desired compressive strength. The different compressive (release strength) strength levels tested included 3500 psi (24.13 MPa), 4500psi (31.03 MPa), 6000 psi (41.37 MPa) and 12000psi (82.74MPa). A consistent concrete mix with water-cement ratio 0.38 was used for all castings. Geometrical and mechanical properties of test prisms were representative of actual prestressed concrete crossties used in the railroad industry. Each prism provided a sample of eight different and approximately independent splitting tests of concrete cover (four wire cover tests on each end) for a given release strength. After de-tensioning, all cracks that appeared on the prisms were marked, and photographs of all prism end surfaces were taken to identify the cracking field. During the test procedure longitudinal surface strain profiles, along with live-end and dead-end transfer lengths, were also measured using an automated Laser-Speckle Imaging (LSI) system developed by the authors. Both quantitative and qualitative assessment of cracking behavior is presented as a function of cover and release strength. In addition to the identification of whether cracking took place at each wire end location, measurements of crack length and crack area are also presented for the given WE wire type. The influence of concrete cover and release strength are clearly indicated from these initial tests. The influence of indented wire type (indent geometry) will also be discussed in this paper, along with a presentation of some preliminary test results. This work represents a successful first step in the development of a qualification test for validating a given combination of wire type, concrete cover, and release strength to improve the reliability of concrete railroad crosstie manufacturing.
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Sherif, Muhammad, Osman Ozbulut, Asheesh Landa, and Reginald F. Hamilton. "Self-Post-Tensioning for Concrete Beams Using Shape Memory Alloys." In ASME 2014 Conference on Smart Materials, Adaptive Structures and Intelligent Systems. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/smasis2014-7564.
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This study explores the use of shape memory alloys for self-post-tensioning concrete beams. SMAs have the ability to regain their original shape after being deformed up to 6–8% strain. This shape recovery is a result of an underlying reversible solid-solid phase transformation, which can be induced by either a stress (superelastic effect) or a temperature change (shape memory effect). The shape memory effect can be exploited to prestress concrete. The heat of hydration of grout can thermally activate SMA tendons to obtain self-post-tensioned (SPT) concrete. NiTi-based SMAs are promising due to their corrosion resistance and resistance against low frequency/cycle fatigue failure. NiTiNb alloys are a class of SMAs that exhibit a wide temperature hysteresis and transformation temperatures near the service temperatures required for practical application. Here, NiTiNb shape memory alloys are studied to design an optimized SMA that can be activated using hydration heat. The material design and characterization of the SMA tendons are discussed. The temperature increase due to the heat of hydration of four commercially available grouts is investigated. The bond behavior of SMA tendons is evaluated through pullout tests. Digital Image Correlation method is used for monitoring the slippage of the SMA tendons. The feasibility of developing SPT concrete is assessed through experimental studies. The use of SMAs, which possess high fatigue and corrosion resistance, as post-tensioning tendons in concrete members will increase the service life and provide life cycle cost savings for concrete bridges. The replacement of steel tendons with SMA prestressing tendons will prevent corrosion-induced deterioration of tendons in concrete structures. The use of heat of hydration of grout to activate the shape memory effect of SMA tendons will provide self-stressing capability. This will greatly simplify the tendon installation. The need for jacking equipment or electrical source will be eliminated.
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Scott, James D., Robert J. Peterman, B. Terry Beck, Aaron A. Robertson, Kyle A. Riding, and Chih-Hang John Wu. "Determining the Remaining Prestress Force in a Prestressed Concrete Railroad Tie Through Loading in Direct Tension." In 2018 Joint Rail Conference. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/jrc2018-6168.
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Extensive research has been conducted by the research team in recent years to determine the prestressing steel and concrete properties that must be provided to ensure that the transfer length of a prestressed concrete railroad tie is shorter than the distance from the edge of the tie to the rail seat. In addition, a significant of amount of data has been collected that indicates high bonding stresses can produce longitudinal splitting cracks along the reinforcement. In a study of how prestressing steel and concrete properties relate to a ties propensity for longitudinal cracking, existing ties that have performed well in track for over 25 years without issues are being evaluated. One parameter of interest that affects the bonding stress is the amount of prestress force in a railroad tie, which is unknown for the existing ties being evaluated. The current paper focuses on a new method that was developed for determining the remaining prestress force in a tie. In a previous method for determining the prestress force, ties were first loaded in four-point bending to initiate flexural cracking. The crack opening displacement was measured in order to determine the applied load required to reopen the crack. Using this load and the cross-sectional parameters at the location of the crack, the prestress force in the tie can be calculated using static equilibrium. The issue with this method is that as a tie is being loaded and the crack propagates, there is a continuous change in the stiffness of the cross-section. This results in the load versus crack opening displacment curve being overly rounded. This increases the error when determining the load required to reopen the crack, and increases the uncertainty of the calculated prestress force. The new test method eliminates the problems associated with flexural testing by loading the ties longitudinally in tension. In the new proposed experimental method, ties that have been pre-cracked in the center are pulled in tension. Similar to the previous method, the crack opening displacement is measured while the tie is loaded. For the crack to fully open, the applied load must exceed the prestress force holding the crack closed. Prior to the crack opening, the applied load is resisted by the composite section of concrete and prestressing tendons. Once the crack as fully opened, the applied load is resisted by the prestessing tendons only. This creates two distinctly linear portions of the load versus crack opening displacement curve, one prior to the crack opening, and one after. The beginning of the linear portion post-crack opening marks a very clear upper bound for the amount of prestressing force in a tie. This method can estimate the remaining prestress force in a tie with much greater accuracy than the previous method, and eliminates the need of the cross-sectional parameters at the crack location. To verify this method, tests were first conducted on a smaller scale with prismatic beams with a known initial prestressing force. Then the method was applied to a full scale existing tie to determine the remaining prestress force. Results are presented for testing of both the prismatic beams, and the full scale tie.
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Jing, Yuan, Z. John Ma, Richard M. Bennett, and David B. Clarke. "Lateral Impact of Railroad Bridges With Hybrid Composite Beams: Finite Element Modeling and Preliminary Dynamic Behavior Study of HCB." In 2014 Joint Rail Conference. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/jrc2014-3739.
Full textAbstract:
Grade separations have been used along High-Speed Rail (HSR) to decrease traffic congestion and the danger that occurs at grade crossings. However, the concern with grade separations is the potential damage due to lateral impact of bridge superstructures by over-height vehicles. This is a concern with existing bridges, and lateral impact is not included in standard bridge code provisions. A new bridge technology, Hybrid Composite Beam (HCB), was proposed to meet the requirements of another HSR objective, that of a sustainable solution for the construction of new and replacement bridges in rail infrastructure. The hybrid composite beam combines advanced composite materials with conventional concrete and steel to create a bridge that is stronger and more resistance to corrosion than conventional materials. The HCB is composed of three main parts; the first is a FRP (fiber reinforced polymer) shell, which encapsulates the other two parts. The second part is the compression reinforcement which consists of concrete or cement grout that is pumped into a continuous conduit fabricated into the FRP shell. The third part of the HCB is the tension reinforcement that could consist of carbon or glass fibers, prestressed strands, or other materials that are strong in tension, which is used to equilibrate the internal forces in the compression reinforcement. The combination of conventional materials with FRP exploits the inherent benefits of each material and optimizes the overall performance of the structure. The behavior of this novel system has been studied during the last few years and some vertical static tests have been performed, but no dynamic or lateral impact tests have been conducted yet. Therefore, the main objective of this study is to evaluate the performance of HCB when subjected to lateral impact loading caused by over-height vehicles. This paper explains the advantages of HCB when used in bridge infrastructures. The commercial software ABAQUS was used to perform the finite element (FE) modeling of a 30ft long HCB. Test data was used to validate the results generated by FE analysis. A constant impact loading with a time duration of 0.1 second was applied to an area at the mid-span of the HCB. Lateral deflection and stress distribution were obtained from FE analysis, and local stress concentration can be observed from the stress contour. Full-scale beam dynamic testing will be conducted in the future research to better study the behavior of HCB when subjected to over-height vehicles.