高阶振型在山地掉层结构中的影响研究

设置不同掉层层数、掉层跨数和坎上楼层层数的模型,对比分析各模型在不同振型数下结构响应值的误差,根据分析结果来验证常用振型数量控制方法的适用性和差异性。结果表明,高阶振型对山地结构中掉层部分的内力响应影响显著。不同的掉层结构布置对振型数的选择有重要影响,掉层层数的增加使层剪力误差超限的楼层位置从顶层转移到掉层部分,致使掉层部分对高阶振型更加敏感。伴随着掉层跨数的减少,最大层剪力误差及误差超限的楼层数均呈先增大后减小趋势,即存在最不利的掉层跨数比,此时各内力响应误差均最大。坎上楼层的增加会提高掉层部分的剪力误差值。相对于层剪力,层间位移更易于通过提高振型数来控制精度。振型位移控制法的精度较高,但会增加大量结构计算和分析成本。振型质量参与系数法仅在个别结构中的层间剪力误差较小,总体来说其控制效果较差。解决这一问题,还需进一步研究以便提出一种新的振型控制方法。

On the effect of the higher modes on the structures supported by the stepped graduate foundations in a mountainous city

This paper sets up frame structures with different quantities of the dropped stories,dropped spans and the upper story numbers and analyzes the errors of structurally graduate responses in every model under the different mode numbers in hoping to verify the applicability and difference of the general mode control methods.The results of our study show that there exists a significant effect of higher modes on the inherent force response at the dropped stories.What is more,the contributions of the second and third order are potentially in excess of the first mode,which proves to be greatly different from the regular frame structures.On the other hand,the mode number may also be affected by the different layouts of the structures supported by the stepped foundations quite heavily.For example,as the number of the dropped stories increases,it would be possible for the story whose shear force error to exceed the maximal limit and then to transfer the said error from the top to the dropped stories,and then to make the dropped stories more sensitive to the higher modes.In so doing,with the decrease of the number of dropped spans,it would be also possible for the error of the maximum story's shear force and the number of stories whose shear force story error to go beyond the limit may eventually tend to rise first and then drop,That is,there may exist the response of the maximum error of the internal force under the case to the most negative dropped spans ratio.What is more,the increased number of the upper stories tends naturally to lead to the increase of the error of storey shear force at the dropped stories.Thus far,as compared with the story shear force,the error of story drifting liability can be easily controlled by increasing the mode numbers.The accuracy of the mode displacement control method proves better than that of the modal participating mass ratio method.Nevertheless,the former method can probably prove to be more expensive for it has to spend more money on the increase of the structural calculation and analysis,whereas the error of story shear force in the modal participating mass ratio method can be smaller just at the local stories.In spite of this,the control effect of this method turns,in general,rather meager.Hence,a newer and better control approach to the problem solving can only be expected to be worked out in the near future.