The results of recent research on the dynamic response, failure mechanism, and changes in the load-transfer paths of a half-scale three-story, three-bay, and three-span reinforced concrete frame ...subjected to a series of sudden column removals are presented. Three phases of testing were carried out, including the removal of a corner column and a column adjacent to the corner column along the short span direction, two middle exterior columns along the long span direction, and one interior column. The column removal was enabled by using a gas cannon. The dynamic response at critical locations after the imposed failure of the respective columns was observed. The removal of the corner column followed by the adjacent column resulted in only an essentially elastic response of the structure. The removal of an interior column resulted in only small deflections. The removal of the two first-story exterior columns resulted in significant vertical deflections of the middle exterior columns and significant yielding at adjacent beams that framed into the two middle exterior columns.
AbstractAn experimental study was conducted to investigate the mechanical behavior and residual capacity of concrete-filled steel tubular (CFST) columns subjected to a post-earthquake fire. Nine ...circular cantilever CFST columns, including two control specimens, were tested to investigate their post-earthquake fire resistance time. The residual seismic behavior and load carrying capacity of an additional four columns were also studied following post-earthquake fire. All specimens were first subjected to a reversed cyclic or simulated earthquake loading (to induce initial seismic damage) and were then heated to obtain the fire resistance time or were subjected to additional cyclic reversed loading after a post-earthquake fire. The experimental results indicate that the CFST columns generally performed well after a post-earthquake fire. Specimens with high compressive strength concrete exhibited longer post-earthquake fire resistance times, whereas the increase in tube wall thickness only had a marginal effect on improving post-earthquake fire resistance. More importantly, the presence of residual lateral drift at the end of the earthquake loading had a much more significant effect on the post-earthquake fire performance than specimens without residual deformation. Finally, it is recommended that the failure criterion for fire loading should possibly take into consideration lateral deformation limits during fire testing.
A series of experiments on 14 square cantilevered columns under constant axial load was conducted to investigate the fire resistance time and residual seismic capacity of reinforced concrete columns ...subjected to a post-earthquake fire. All specimens were first subjected to a reversed cyclic loading or a simulated earthquake loading, and then exposed to a simulated fire endurance test (wherein high temperature representative of fire loading was imposed on the specimens), or they were subjected to cyclic reversed loading following a post-earthquake fire. The experimental results indicate that the tested specimens satisfied the fire protection requirements of ISO 834 and the Chinese Design Code after moderate earthquake damage, represented in this study by reversed cyclic loading up to a peak drift of 2% and simulated seismic displacement history with a peak drift of 3.5%. Residual drift had a more significant impact than the maximum lateral drift for post-earthquake fire resistance. The seismic response of columns subjected to post-earthquake fire exhibited reduced lateral load capacity, effective stiffness, and ductility. Results from the present study indicate that the lateral drift should be monitored during a fire test, and that lateral drift limits be incorporated into the criteria for post-earthquake fire loading. Keywords: earthquake loading; experimental testing; fire resistance; reinforced concrete (RC) column; residual seismic performance.
► A meshfree method for nonlinear analysis of RC structures is presented. ► Maximum-entropy basis functions are adopted to discretize the two-dimensional domain. ► The presented methodology is used ...to study the behavior of RC shear walls. ► Comparisons with experimental data and finite element analysis are included.
A meshfree method for nonlinear analysis of two-dimensional reinforced concrete structures subjected to monotonic static loading is presented. The concrete model is implemented in the context of the smeared rotating crack approach. The stress–strain relationship for steel bars accounts for the surrounding concrete bonded to the bar (tension stiffening effect). The principle of virtual work (variational form) is used to setup the nonlinear system of equations. Maximum-entropy basis functions are used to discretize the two-dimensional domain and background cells are adopted to facilitate the numerical integration. The generalized displacement control method is implemented to solve the nonlinear system of equations and to obtain the softened structural response beyond the maximum load capacity. The proposed meshfree methodology is used to study the nonlinear behavior of reinforced concrete shear walls. Comparisons with experimental data and finite element analysis indicate that the proposed maximum-entropy meshfree method is a viable approach for nonlinear simulations of planar RC structures.
Performance of laterally loaded H-piles in sand Guo, P.X.; Xiao, Y.; Kunnath, S.K.
Soil dynamics and earthquake engineering (1984),
December 2014, 2014-12-00, 20141201, Letnik:
67
Journal Article
Recenzirano
Results from experimental testing of four approximately one-third scale laterally loaded H-piles, subjected to monotonic and cyclic loading are presented. The test setups were designed to prevent ...torsion in the pile during testing and to eliminate the self-weight of the hydraulic actuator that could otherwise induce moment on the model piles. The tests were conducted in compacted medium dense sand and all the piles were extensively instrumented. Test results indicate that the lateral force–displacement responses under cyclic loading exhibited slight pinching behavior due to the gap that opened at the top of the soil-pile interface. Numerical simulations show that p–y curves based on the American Petroleum Institute (API) recommendations and that proposed by Reese et al. can reasonably predict the lateral response of the piles though slightly underestimate the ultimate capacities. The general pile behavior such as force–displacement response and moment distributions along the pile depth show slight sensitivity to the subgrade reaction modulus at large displacements.
•Four 1/3 scale H-piles were tested under monotonic and cyclic lateral loading.•Hysteresis curves showed slight pinching due to the gap at soil-pile interface.•API model reasonably predicts lateral force–displacement response envelope.•Reese model resulted in a lower lateral stiffness than observed during testing.
An important issue in seismic design of concrete buildings concerns the stability of structural walls when subjected to intense earthquake ground motions. Large tensile strains, developed as a result ...of significant yielding in the wall, are a cause for concern since the stability of the wall depends on the magnitude of the tensile strain imposed on the wall. A critical condition exists where excessive out-of-plane displacement may occur upon load reversal prior to crack closure causing the wall to buckle. The potential for instability can be mitigated by requiring a minimum wall thickness to ensure that the in-plane lateral strength can be fully developed in the reversed direction. A methodology for assessing the minimum wall thickness is outlined in this paper and results are presented for a number of parameters including the ground motion intensity, longitudinal reinforcement ratio, floor weight, wall-to-floor area ratio and number of stories. The minimum wall thickness is compared with recommendations in current building codes.
Under seismic actions, the induced damage in critical regions of a concrete-filled steel tube (CFT) column could be attributed to cumulative damage of the steel tube caused by repeated cyclic loading ...in the post-yield strain range. An experimental study was undertaken to develop an analytical model of cumulative damage for circular CFT columns subjected to cyclic loading. The low-cycle fatigue behavior of CFT columns was investigated and a relationship between fatigue life and normalized displacement amplitude was established for typical controlling parameters. A total of 12 large-scale model column specimens, representing two types of circular CFT columns with different steel tube diameter-to-thickness ratios were tested under quasistatic loading with either constant drift amplitude or standard cyclic loading histories with increasing peak drift displacement. Test results indicate that the low cycle fatigue behavior of CFT columns depends on the thickness of the steel tube. Fatigue life expressions useful for application in damage-based seismic design are developed and used to predict the damage index for additional CFT columns based on experimental data reported in the literature. PUBLICATION ABSTRACT
Using the internet-based network platform NetSLab, the seismic response of bridge pier and precast concrete pile foundation was investigated in this study. NetSLab was developed based on ...client/server concept along with a data model and communication protocols, and is capable of transferring control and feedback data and signals among geographically distributed laboratories or computers connected by the Internet. In this study, the bridge column was simulated numerically whereas the full-scale prestressed/precast pile model was tested physically with predetermined moment distribution along the pile model and neglecting pile group effects. The hybrid experimental results indicate that the sudden spalling of the thick concrete cover of the precast pile may cause unstable response of the bridge pier and pile foundation system under simulated earthquake loading, particularly when the bridge is subjected to near fault ground motions. The research also demonstrated the enhanced testing capabilities of the networked pseudo dynamic testing concept.
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