桩锤冲击动力响应的解析法分析

采用解析法,建立了锤击过程中桩—锤系统的动力响应.对于桩锤与砧铁采用集中质量块模拟,砧铁垫、桩顶的桩帽采用弹簧表示,桩作为阻尼器,砧座质量与桩帽垫分别考虑,桩锤与铁砧垫的质量分别考虑,分析了桩垫对锤击时桩顶所受最大冲击效果的影响.数值结果表明,随砧铁刚度增加,锤击发生反弹时间减小.当砧铁刚度增大到一定程度时,再增加砧铁刚度对桩所受最大冲击力大小几乎不产生影响;而随桩垫的刚度增加,锤击引起桩所受最大冲击力大小增大.另外随砧铁质量增加,桩所受最大冲击力大小有所减小.

Analyzing dynamic responses of pile hammer impact with analytical methods

The drivability study of piling requires modeling of the hammer impact to calculate the input force wave at the pile head.In this paper,analytical solutions are presented for hammer impact using a model which uses lumped masses for the ram and anvil,a spring for the anvil cushion,and another spring for the cap cushion on the top of a pile.The pile is modeled as a dashpot.The solutions account for the separation of the anvil mass from the pile cap cushion as well as the separation of the ram mass from the anvil cushion.The developed solutions are used to perform a parametric study to illustrate the influence of the pile cushion on the maximum force transmitted to the pile head.Numeric results show that an increase in hammer cushion stiffness will generally reduce the time at which hammer bounce occurs.For certain combinations of hammer and pile cushion stiffness,the pile cushion stiffness could be taken as infinite for the approximation of the peak transmitted to the pile.However,at higher hammer cushion stiffness values,the effect of the additional cushion must be taken into account in the impact model.In general,within the practical ranges of cushion stiffness values,there is a considerable reduction in the maximum force transmitted to the pile with an increase in anvil mass.