浅埋条形基础抗震承载力拟动力分析

采用拟动力法推导出基岩至地表之间不同深度土层地震加速度时程，在此基础上针对砂性土地基，利用极限分析上限定理推导了地震作用下地基极限承载力系数N_γE的求解方法，并进一步分析了地震动向地表传播过程中，不同深度土层振动相位差与地震加速度幅值放大效应对N_γE的影响。研究结果表明:采用拟动力法计算出的N_γE随地震加速度和地基土内摩擦角的变化关系呈现出与拟静力计算结果相同的趋势，但振动相位差的影响导致前者明显高于后者，且地震波长越短，二者差异越明显；地表地震加速度是N_γE的主要影响因素，其在地基发生极限破坏时总是达到幅值；幅值放大效应由于放大了地表地震加速度幅值而导致N_γE显著降低。

Pseudo-dynamic Analysis of Seismic Bearing Capacity of Shallow Strip Footing

Calculating seismic bearing capacity of foundation is an important part in earthquake resistant design of engineering. Herein by pseudo-dynamic method the time history of earthquake acceleration in each soil layer at different depths from bedrock to ground was derived and on this basis, for sandy soil foundation, the solution to the ultimate bearing capacity factor N_γE of foundation under the action of earthquake was derived by upper-bound theorem of limit analysis, moreover how the oscillation phase difference of soil layers in different depths and the magnification effect of earthquake acceleration amplitude affect this factor N_γE during the propagation of seismic ground motion to the ground surface was analyzed. The result shows that, the N_γE calculated by pseudo-dynamic method changing with the earthquake acceleration and the internal friction angle of foundation soil tends to be the same as the result of pseudo-static calculation; however, the effect of oscillation phase difference causes the former higher than the latter obviously and, the shorter the seismic wave length, the obvious the difference between the both; the earthquake acceleration of ground surface is the main factor affecting the NγE which will reach the value of amplitude when the foundation is subject to ultimate failure; the magnification effect of amplitude, due to magnify the amplitude of surface earthquake acceleration, causes the N_γE to be decreased significantly.