Ductility a seismic performance of reinforced concrete box piers
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In order to obtain the ductility a seismic performance of reinforced concrete box piers,the equivalent plastic hinge length and ultimate displacement calculation methods for reinforced concrete box piers were discussed based on bi-axial quasi-static tests of 14 piers and moment curvature analyses of reinforced concrete box cross-section under action of bi-axial load. The results showed that the piers with larger height-width ratio have bigger plastic damage area, meanwhile their ultimate curvature drops obviously; the calculated yielding displacement and ultimate displacement are close to the actual measured ones,so the ultimate displacement calculation method can be used in ductility a seismic analysis for reinforced concrete box piers.Keywords:
Plastic hinge
Ductility (Earth science)
Seismic loading
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Three Dimensional nonlinear finite element analysis was carried out to verify the enhancement of seismic performance of reinforced concrete bridge piers such as shear strength and ductility by controlling bond of longitudinal reinforcement. Proposed analytical method was found to model the global hysteretic behavior and failure mode of unbonded RC piers producing an excellent correlation with that of experimental results. The enhancement of seismic performance and alteration of the failure mode of unbonded pier was found to be due to the change in internal mechanism to the one resembling a tied arch.
Ductility (Earth science)
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A new finite element procedure is developed to study the ultimate strength and ductility behavior of the concrete piers up to softening stage. In the computer code, a degenerate isoparametric curved shell element with layered model is adopted. The arc-length algorithm combined with line search acceleration is employed to overcome the numerical difficulties near and beyond the failure stage. The structural responses of the concrete piers are simulated and compared with experimental results, which shows the efficiency and reliability of the computer code. The stiffening efficiency with different stiffening lengths is discussed, and other two practical stepped concrete piers are also studied. For the covering abstract see ITRD E111699.
Stiffening
Ductility (Earth science)
Slab
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A research project into the ductility of bridge piers is described covering the post-elastic ductile behaviour of reinforced concrete bridge piers particularly the influence of aspect ratio on such behaviour. The units tested, two octagonal and two square sections, were designed according to the second draft of the concrete design code DZ 3101, for differential axial load levels. The testing procedure included slow static incremental loading followed by fast dynamic cyclic loading. Results are presented in the form of load-displacement hysteresis curves, curvature profiles and transverse steel strain distribution. A discussion deals with the comparison of ultimate moment capacities, measured ductilities, equivalent plastic hinge lengths, maxiumum concrete compression strains, ultimate shear forces, enhancement of concrete strength by confinement, and idealised stress-strain curves for confined concrete. Comparisons with previous projects are made and it is concluded that that the influence of aspect ratio is insignificant for piers confined in accordance with present New Zealand code provisions. (TRRL)
Plastic hinge
Ductility (Earth science)
Precast concrete
Seismic loading
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A large number of experimental curvatures in plastic hinges of concrete members are used alongside analytical moment-curvature relations to backestimate strains in the bars, the extreme concrete fibers of a section, or its confined core at the ultimate conditions of concrete sections in flexure with axial loads. Strain limits derived from these ultimate strains can support fiber models for prismatic members or models with finite-length plastic hinges at the ends. The measurements come from circular or rectangular columns (some tested diagonally), walls, or beams. The ultimate strains derived for steel bars and concrete are not local material properties (especially for cyclic loading): they depend on the geometric features of the section as a whole and of the immediate vicinity of the most critical point in the section. The size effects are clear: (1) concrete ultimate strains increase in a small compression zone, (2) the monotonic ultimate strain of tension bars increases with decreasing number of bars in the tension zone, (3) the ultimate strain of steel in cyclic tests increases with the increasing number of bars in the compression zone, and (4) the ultimate strain of confined concrete is larger at a section corner in biaxial bending than along the full side of a rectangular compression zone in uniaxial flexure, while at the perimeter of a circular section, it is in between these two extremes. The cyclic ultimate strain of steel in tension increases as the bar diameter–to–stirrup spacing ratio increases, thanks to the delay of bar buckling in previous compression half-cycles. The ultimate strains derived apply both as mean values in a plastic hinge and at the end section of prismatic members. Compared to experimental ultimate curvatures, those computed from the proposed ultimate strains do not have bias and exhibit much less scatter than those obtained from arbitrary ultimate strains specified in some codes. These code predictions are, in general, unsafe.
Stirrup
Tension (geology)
Plastic hinge
Neutral axis
Bar (unit)
Section (typography)
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Ductility (Earth science)
Constant (computer programming)
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While the high-pier bridges with large-span are widely used,the seismic problems of high-pier bridges become extremely prominent.In this study,bi-directional quasi-static testing on 6 scaled models of high hollow piers was conducted,and the nonlinear finite element(FE) model was established to simulate the seismic behavior of high hollow reinforced concrete pier under bi-directional cycle loading,in which,two factors,namely axial compression ratio and slenderness ratio were considered.The main conclusions drawn from the testing and analysis are as follows:(1) The high-hollow reinforced concrete piers under the axial loading and bi-directional cycle loading mainly result in typical flexural failure and the plastic hinge occurs at the bottom of the pier.Meanwhile,the shear effect can′t be neglected.(2) Mutual coupling occurs while the high hollow pier undertakes the bi-directional horizontal loading.The damage to the high piers may be caused under the mutual coupling effects.Especially,in the direction of to smaller rigidity the piers may be damaged seriously.The cracking may occur and the piers may step into the plastic stage in advance.(3) The proposed nonlinear FE model can predict the cracking and the failure of the high piers under bi-directional reversed low-cycle loading.The results from the FE model may accord well with those from the testing,such as the hysteresis characteristics and skeleton curves.(4) The proposed multi-dimensional model of loaddisplacement restoring force can reflect the seismic performance of reinforced concrete thin-walled high hollow piers and can be referenced in the seismic design and dynamic analysis of the high piers.
Plastic hinge
Structural load
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In order to relieve seismic damage and enhance restoring capability of bridge piers, the concept of arranging partial high strength steel bars replacing the corresponding longitudinal and hooped ordinary strength steel bars was presented. Compare to the ordinary steel bars, the high strength steel bars has the closeable elastic modulus and higher strength, which can be used to reduce deformation of bridge piers during strong earthquake movement. Through experimental study on four high- strength concrete columns subjected to low cyclic reversed loading, the failure patterns, hysteretic curves and skeleton curves were obtained. The influence of longitudinal high-strength reinforcement ratio upon the hysteretic characteristics, ductile behavior and ability of energy dissipation were analyzed. The results show that the main failure pattern was bending failure; and with the increscent of the longitudinal high-strength reinforcing steel bar ratio, the columns can endure larger seismic loads and displacement; the seismic performance of the whole bridge piers can be effectively improved by arranging reasonable high-strength reinforcing steel bars.
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To study the seismic behavior of frames with T-shaped steel reinforced concrete columns and steel beams, a pseudo-static test of a 1/3 scaled, 3-story 2-bay specimen was carried out. The main results such as the failure pattern, hysteretic and skeleton curves were obtained. The ductility, energy dissipation capacity and degradation of stiffness and strength of the specimen were analyzed. Numerical simulations were conducted with the fiber model to study the effects of different design parameters such as the axial compression ratio, steel ratio and concrete strength on the seismic performance of the frame. It was demonstrated that the specimen exhibited a beam-hinge failure mode under the condition of horizontal cyclic loading. The specimen had good ductility and energy dissipation capacity and it met the seismic design requirements of strong column-weak beam, strong shear-weak bending and strong joint-weak pole. The axial compression ratio has great influence on the performance of the specimen after yielding. With the increase of the axial compression ratio, the strength and ductility of the structure will decrease. It is necessary to control the axial compression ratio in a reasonable range in the design. The steel ratio mainly affects the initial stiffness and ultimate strength, while its increase can effectively improve the seismic performance of the frame. The increase of concrete strength can increase the ultimate strength of the structure, but reduce the ductility slightly. It is of great significance to consider concrete strength comprehensively in the design. The research results can provide reliable support for the design of this kind of structures.
Ductility (Earth science)
Strength reduction
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Steel fiber is one of the most widely used reinforcements to improve the performance of concrete members. However, few studies have been proposed to study the seismic performance of bridge piers constructed with steel fiber reinforced concrete. This paper presents the collapse vulnerability assessment of typical single bridge piers constructed with steel fibers. Fiber element models of RC bridge piers with and without steel fibers are firstly built by selecting suitable cyclic constitutive laws of steel fiber reinforced concrete, and then calibrated using the experimental results. The seismic capacity and inelastic demand of RC piers with steel fibers are quantified using both nonlinear static pushover analyses and nonlinear incremental dynamic analyses (IDA). In order to conduct the IDA, a suite of 20 earthquake ground motions are selected and scaled to different levels of peak ground acceleration (PGA). Collapse fragility curves are then generated using the maximum drift ratio of piers as the engineering demand parameter (EDP). In order to investigate the impact of various parameters on the collapse fragility curves, six parameters are considered in the parametric study: peak compressive strength of concrete, yield strength of steel, longitudinal reinforcement ratio, axial load ratio, transverse hoops ratio and steel fiber content. It was observed that the concrete strength, longitudinal reinforcement ratio and steel fiber content could significantly affect the collapse fragility curve of the bridge piers with steel fibers.
Fiber Reinforced Concrete
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