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1.
The performance of different nonlinear modelling strategies to simulate the response of RC columns subjected to axial load combined with cyclic biaxial horizontal loading is compared. The models studied are classified into two categories according to the nonlinearity distribution assumed in the elements: lumped-plasticity and distributed inelasticity. For this study, results of tests on 24 columns subjected to cyclic uniaxial and biaxial lateral displacements were numerically reproduced. The analyses show that the global envelope response is satisfactorily represented with the three modelling strategies, but significant differences were found in the strength degradation for higher drift demands and energy dissipation. 相似文献
2.
Shake table test of soil-pile groups-bridge structure interaction in liquefiable ground 总被引：2，自引：1，他引：1
<正>This paper describes a shake table test study on the seismic response of low-cap pile groups and a bridge structure in liquefiable ground.The soil profile,contained in a large-scale laminar shear box,consisted of a horizontally saturated sand layer overlaid with a silty clay layer,with the simulated low-cap pile groups embedded.The container was excited in three E1 Centra earthquake events of different levels.Test results indicate that excessive pore pressure(EPP) during slight shaking only slightly accumulated,and the accumulation mainly occurred during strong shaking.The EPP was gradually enhanced as the amplitude and duration of the input acceleration increased.The acceleration response of the sand was remarkably influenced by soil liquefaction.As soil liquefaction occurred,the peak sand displacement gradually lagged behind the input acceleration;meanwhile,the sand displacement exhibited an increasing effect on the bending moment of the pile,and acceleration responses of the pile and the sand layer gradually changed from decreasing to increasing in the vertical direction from the bottom to the top.A jump variation of the bending moment on the pile was observed near the soil interface in all three input earthquake events.It is thought that the shake table tests could provide the groundwork for further seismic performance studies of low-cap pile groups used in bridges located on liquefiable groun. 相似文献
3.
Topography effects on the vertical vibration responses of pile group are revealed though numerical analysis and model tests.First,a series of model tests with different topography of ground and bedrock are conducted.The results indicate that displacement amplitude of the pile head in sloping ground topography is larger than in horizontal ground.Differential displacement at various positions of the pile cap is observed in non-horizontal topography.Afterwards,a numerical algorithm is employed to further explore the essential response characteristics in group piles of different topography configurations,which has been verified by the test results.The lengths of the exposed and frictional segment,together with the thickness of the subsoil layer,are the dominant factors which cause non-axisymmetric vibration at the pile cap. 相似文献
4.
Construction of seaside and underground wall bracing often uses stiffened deep cement mixed columns (SDCM). This research investigates methods used to improve the level of bearing capacity of these SDCM when subjected to cyclic lateral loading via various types of stiffer cores. Eight piles, two deep cement mixed piles and six stiffened deep cement mixing piles with three different types of cores, H shape cross section prestressed concrete, steel pipe, and H-beam steel, were embedded though soft clay into medium-hard clay on site in Thailand. Cyclic horizontal loading was gradually applied until pile failure and the hysteresis loops of lateral load vs. lateral deformation were recorded. The lateral carrying capacities of the SDCM piles with an H-beam steel core increased by 3-4 times that of the DCM piles. This field research clearly shows that using H-beam steel as a stiffer core for SDCM piles is the best method to improve its lateral carrying capacity, ductility and energy dissipation capacity. 相似文献
5.
This paper presents a substructure online hybrid test system that is extensible for geographically distributed tests.This system consists of a set of devices conventionally used for cyclic tests to load the tested substructures onto the target displacement or the target force.Due to their robustness and portability,individual sets of conventional loading devices can be transported and reconfigured to realize physical loading in geographically remote laboratories.Another appealing feature is the flexible displacement-force mixed control that is particularly suitable for specimens having large disparities in stiffness during various performance stages.To conduct a substructure online hybrid test,an extensible framework is developed,which is equipped with a generalized interface to encapsulate each substructure.Multiple tested substructures and analyzed substructures using various structural program codes can be accommodated within the single framework,simply interfaced with the boundary displacements and forces.A coordinator program is developed to keep the boundaries among all substructures compatible and equilibrated.An Internet-based data exchange scheme is also devised to transfer data among computers equipped with different software environments.A series of online hybrid tests are introduced,and the portability,flexibility,and extensibility of the online hybrid test system are demonstrated. 相似文献
6.
In this study the stress–strain characteristics of sand-ground rubber mixtures are investigated in the sandlike zone,at different confining pressures,using hollow cylinder specimens subjected to torsional monotonic and cyclic loading.Under monotonic loading a mixture of sand-ground rubber with 10% and 25% rubber content show more contraction behaviour than that observed in a pure sand specimen.Phase transformation point in these mixtures are located on a larger shear strain.As expected,the shear strength of specimens decreases with increase of ground rubber content.However,with increasing of effective confining pressure,the loss in shear strength of the mixture is decreased.In addition,a mixture with 25% ground rubber shows a smaller loss in shear strength compared to a mixture with 10% ground rubber mixture.Under cyclic loading mixtures with 10% and 25% ground rubber have similar liquefaction resistance,especially at confining pressures of 110 k Pa and 260 k Pa.Therefore,by using of the mixture with 25% ground rubber,a larger volume of scrap tires could be recycled.The addition of ground rubber to sand would affect the shear strain variation and excess pore water pressure trends,and this effect was further intensified with increasing ground rubber percentage. 相似文献
7.
C.V.R.Murty JayantaDutta S.K.Agrawal 《地震工程与工程振动(英文版)》2004,3(2):215-222
A single-room, single-storey full-scale brick masonry building with precast RC roofing system was tested thric eunder displacement controlled lateral cyclic loading, to assess the effectiveness of the basic repair and seismic strengthening techniques. Initially, the virgin building specimen was loaded laterally to failure, In the second stage, the damaged building was repaired by stitching across the cracks, and tested under the same lateral loading. In the third stage, the twice-damaged structure was repaired once more by stitching and strengthened by twin lintel belt in steel and vertical corner reinforcement,and re-tested. The building strengthened by twin lintel belt in steel showed about 28% higher strength under lateral loading than the virgin building. 相似文献
8.
To study the dynamic response of vertical and batter pile groups in saturated sand,dynamic tests of these pile groups in saturated sand were carried out using the ZJU400 geotechnical centrifuge at Zhejiang University.The following results were obtained.(1)As the motion intensity increased,the peak acceleration in soil layers at different depths significantly decreased,indicating that the soil stiffness was significantly reduced.(2)During the motion process,the instantaneous bending moment of the vertical and batter pile groups at different depths changed continuously,which had a strong relationship with the saturated sand liquefaction.In the process of sand liquefaction,the residual bending moment generated by the batter pile was more obvious than that of the vertical pile.(3)With the liquefaction of the saturated sand,the distribution of the maximum bending moment of the vertical pile group changed,and the bending moment near the pile cap of the vertical and batter pile groups was always large.(4)In certain cases,the horizontal acceleration and dynamic displacement of the vertical pile cap were amplified.When the motion intensity was large,residual displacement of the batter pile cap occurred. 相似文献
9.
Railway ballast forms a major component of a conventional rail track and is used to distribute the load to the subgrade, providing a smooth running surface for trains. It plays a significant role in providing support for the rail track base and distributing the load to the weaker layer underneath. Ballast also helps with drainage, which is an important factor for any type of transportation structure, including railroads. Over time, ballast progressively deforms and degrades under dynamic loading and loses its strength. In this study, extensive laboratory tests were conducted to investigate the effect of load amplitude, geogrid position, and number of geogrid layers, thickness of ballast layer and clay stiffness on the behavior of the reinforced ballast layer and induced strains in a geogrid. A half full-scale railway was constructed for carrying out the tests, which consisted of two rails 800 mm in length with three wooden sleepers(900 mm × 10 mm × 10 mm). Three ballast thicknesses of 200, 300 and 400 mm were used in the tests. The ballast was overlying 500 mm thickness clay in two states, soft and stiff. The tests were carried out with and without geogrid reinforcement; the tests were performed in a well-tied steel box of 1.5 m length ×1 m width ×1 m height. Laboratory tests were conducted to investigate the response of the ballast and the clay layers where the ballast was reinforced by a geogrid. Settlement in ballast and clay, soil pressure and pore water pressure induced in the clay were measured in reinforced and unreinforced ballast cases. It was concluded that the amount of settlement increased as the simulated train load amplitude increased, and there was a sharp increase in settlement up to cycle 500. After that, there was a gradual increase that leveled out between, 2500 to 4500 cycles depending on the frequency used. There was a slight increase in the induced settlement when the load amplitude increased from 0.5 to 1 ton but it was higher when the load amplitude increased to 2 tons. The increased amount in settlement depended on the existence of the geogrid and other parameters studied. The transmitted average vertical stress for ballast thicknesses of 30 cm and 40 cm increased as the load amplitude increased, regardless of the ballast reinforcement for both soft and stiff clay. The position of the geogrid had no significant effect on the transmitted stresses. The value of the soil pressure and pore water pressure on ballast thicknesses of 20 cm was higher than for 30 cm and 40 cm thicknesses. This meant that the ballast attenuated the induced waves. The soil pressure and pore water pressure for reinforced and unreinforced ballast was higher in stiff clay than in soft clay. 相似文献
10.
Sandwich masonry walls are widely used as energy-saving panels since the interlayer between the outer leaves can act as an insulation layer.New types of sandwich walls are continually being introduced in research and applications,and due to their unique bond patterns,experimental studies have been performed to investigate their mechanical properties,especially with regard to their seismic performance.In this study,three new types of sandwich masonry wall have been designed,and cyclic lateral loading tests were carried out on five specimens.The results showed that the specimens failed mainly due to slippage along the bottom cracks or the development of diagonal cracks,and the failure patterns were considerably influenced by the aspect ratio.Analysis was undertaken on the seismic response of the new walls,which included ductility,stiffness degradation and energy dissipation capacity,and no obvious difference was observed between the seismic performance of the new walls and traditional walls.Comparisons were made between the experimental results and the calculated results of the shear capacity.It is concluded that the formulas in the two Chinese codes(GB 50011 and GB 50003) are suitable for the calculation of the shear capacity for the new types of walls,and the formula in GB 50011 tends to be more conservative. 相似文献
11.
Emmanouil Rovithis Emmanouil Kirtas Kyriazis Pitilakis 《Bulletin of Earthquake Engineering》2009,7(3):719-736
Seismic soil-pile interaction is evaluated in this study based on back-calculated p-y loops constructed from sampled data
of pile bending moments. Fundamental properties of p-y loops are implemented to derive distributed springs and dashpots, thereby
quantifying soil-pile interaction in the realm of a Beam on Dynamic Winkler Foundation modeling. The procedure is validated
by means of well-documented centrifuge tests of a single pile supported structure founded on a two-layer soil profile that
comprises of soft clay overlying dense sand. Two shaking levels of a real earthquake motion applied at the base of the soil
profile were examined and the generated seismic p-y loops were compared to cyclic p-y curves commonly used in pile design
practice. The results demonstrate the strong influence of intensity of the input motion on seismic p-y loops while cyclic
p-y curves established for soft clays tend to overestimate soil stiffness under strong excitation. Typical sets of recorded
and computed structural response are presented, denoting the ability of the BDWF model related to p-y loops in reproducing
adequately fundamental aspects of seismic soil-pile interaction. 相似文献
12.
The present study aims to obtain p-y curves(Winkler spring properties for lateral pile-soil interaction) for liquefied soil from 12 comprehensive centrifuge test cases where pile groups were embedded in liquefiable soil. The p-y curve for fully liquefied soil is back-calculated from the dynamic centrifuge test data using a numerical procedure from the recorded soil response and strain records from the instrumented pile. The p-y curves were obtained for two ground conditions:(a) lateral spreading of liquefied soil, and(b) liquefied soil in level ground. These ground conditions are simulated in the model by having collapsing and non-collapsing intermittent boundaries, which are modelled as quay walls. The p-y curves back-calculated from the centrifuge tests are compared with representative reduced API p-y curves for liquefied soils(known as p-multiplier). The response of p-y curves at full liquefaction is presented and critical observations of lateral pile-soil interaction are discussed. Based on the results of these model tests, guidance for the construction of p-y curves for use in engineering practice is also provided. 相似文献
13.
Owing to their simplicity and reasonable accuracy, Beam on Nonlinear Winkler Foundation (BNWF) models are widely used for the analysis of laterally loaded piles. Their main drawback is idealizing the soil continuum with discrete uncoupled springs representing the soil reactions to pile movement. Static p–y curves, obtained from limited full-scaled field tests, are generally used as a backbone curve of the model. However, these empirically derived p–y curves could not incorporate the effects of various pile properties and soil continuity. The strain wedge method (SWM) has been improved to assess the nonlinear p–y curve response of laterally loaded piles based on a three-dimensional soil–pile interaction through a passive wedge developed in front of the pile. In this paper, the SWM based p–y curve is implemented as the backbone curves of developed BNWF model to study the nonlinear response of single pile under cyclic lateral loading. The developed nonlinear model is capable of accounting for various important soil–pile interaction response features such as soil and pile yielding, cyclic degradation of soil stiffness and strength under generalized loading, soil–pile gap formation with soil cave-in and recompression, and energy dissipation. Some experimental tests are studied to verify the BNWF model and examine the effect of each factor on the response of laterally loaded pile embedded in sand and clay. The experimental data and computed results agree well, confirming the model ability to predict the response of piles under one-way and two-way cyclic loading. The results show that the developed model can satisfactorily simulate the pile stiffness hardening due to soil cave in and sand densification as observed in the experiment. It is also concluded from the results that the gap formation and soil degradation have significant effects on the increase of lateral pile-head deflection and maximum bending moment of the pile in cohesive soils. 相似文献
14.
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. 相似文献
15.
This paper presents a procedure to compute the values of degradation factors of p-y curves in the pseudo-static analysis of piles in liquefiable soils. Three-dimensional finite-element model was used for the computation of p and y values using OpenSees computer package. The piles were modeled using beam-column elements and elastic section. The soil continuum was modeled using brick elements and a two-surface plasticity model. By comparing the results of models in two cases of liquefiable and non-liquefiable, values of degradation factors were obtained. Validation of the degradation factors computed was conducted through the centrifuge test results. The simulation results showed a similar trend between degradation factor variation in different densities and sands. With increasing depth, the degradation factor increased. By comparing the results of pseudo-static analysis with the centrifuge test results, it was concluded that the use of the p-y curves with computed degradation factors in liquefiable sand gave reasonable results. 相似文献
16.
Werasak Raongjant 《地震工程与工程振动(英文版)》2011,10(3)
This paper describes a quasi-static test program featuring lateral cyclic loading on single piles in sandy soil. The tests were conducted on 18 aluminum model piles with different cross sections and lateral load eccentricity ratios, e/d, (e is the lateral load eccentricity and d is the diameter of pile) of 0, 4 and 8, embedded in sand with a relative density of 30% and 70%. The experimental results include lateral load-displacement hysteresis loops, skeleton curves and energy dissipation curves. Lateral cap... 相似文献
17.
Modern seismic design codes stipulate that the response analysis should be conducted by considering the complete structural system including superstructure, foundation, and ground. However, for the development of seismic response analysis method for a complete structural system, it is first imperative to clarify the behavior of the soil and piles during earthquakes. In this study, full‐scale monotonic and reversed cyclic lateral loading tests were carried out on concrete piles embedded into the ground. The test piles were hollow, precast, prestressed concrete piles with an outer diameter of 300 mm and a thickness of 60 mm. The test piles were 26 m long. Three‐dimensional (3D) finite element analysis was then performed to study the behavior of the experimental specimens analytically. The study revealed that the lateral load‐carrying capacity of the piles degrades when subjected to cyclic loading compared with monotonic loading. The effect of the use of an interface element between the soil and pile surface in the analysis was also investigated. With proper consideration of the constitutive models of soil and pile, an interface element between the pile surface and the soil, and the degradation of soil stiffness under cyclic loading, a 3D analysis was found to simulate well the actual behavior of pile and soil. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
18.
Chung-Jung Lee Wen-Yi Hung Chen-Hui Tsai Ting Chen Yichun Tu Chin-Cheng Huang 《Bulletin of Earthquake Engineering》2014,12(2):717-734
This paper presents a pre-shaking technique for measuring the $V_{s}$ profile of sand deposits and determining the natural frequencies of the sand bed and soil-structure system in a centrifuge model at an acceleration of 80 g. The pre-shaking technique is a non-destructive test. It uses a shaker as a wave generation source and a vertical array of accelerometers embedded in the sand bed and the accelerometers attached to the pile head as receivers. The pre-shaking method can be easily used for in-flight subsurface exploration ( $V_{s}$ profile measurements) and in-flight system identification of soil-structure systems (natural frequency measurements). A soil–pile centrifuge model is used to demonstrate the versatility of pre-shaking during a routine centrifuge shaking table test. This paper discusses the testing setup, testing procedures, related SI techniques, and signal processing for the soil–pile system. The natural frequencies measured by the pre-shaking tests are consistent with theory-based results. This technique can be conducted at any time before and after major earthquake events occur in a test. 相似文献
19.
基于OpenSees数值分析平台，建立了群桩-土-桥墩非线性数值分析模型。模型中桩-土水平向相互作用和桩-土竖向相互作用、桩底-土竖向相互作用分别通过p-y、t-z与q-z零长度弹簧单元模拟。模型中同时考虑了群桩效应与纵筋在墩底的应变渗透和粘结滑移的影响。结合群桩基础拟静力试验结果，对数值模型的准确性进行了验证，在此基础上对土体参数特性对桩基滞回性能的影响规律进行了分析。结果表明:所建立的数值分析模型可对群桩基础滞回曲线和骨架曲线进行较为准确的模拟分析，验证了模型的可靠性。反复荷载作用下，前桩处土体的反应明显大于中桩处；土体由软黏土变为硬黏土时，墩顶侧向承载力与刚度显著增加，但土体的非线性反应减弱。 相似文献
20.
Multi-layered soil profiles, where one or more layers consist of loose liquefiable material, most commonly require pile foundations extending beyond the liquefiable layer to competent material. Under seismic loads, if the loose layer liquefies, then large localized plastic demands may be generated in the piles. To study this behavior and provide detailed data to validate numerical models, a 1-g shaking table experiment was conducted considering a single reinforced concrete pile embedded in a three-layer soil system. The model pile of 25 cm diameter was tested under increasing amplitude earthquake excitation in a sloped laminar soil box. The test specimen was designed at the lower bound of typical design to promote yielding, per ATC-32 (Applied Technology Council, 1996) [1]. The pile penetrated 7D (D=pile diameter) into a multi-layered soil configuration composed of a stiff uppermost crust overlying a saturated loose sand layer and a lower dense layer of sand. Plastic demands in the pile were characterized using curvature profiles coupled with back-calculation of the plastic hinge length and post-test physical observations. Results from this test quantify the post-yield behavior of the pile and serve as a complement to previously conducted centrifuge tests. 相似文献