جستجوی مقالات مرتبط با کلیدواژه « مدل هایپربولیک » در نشریات گروه « عمران »

Because of non-linear and settlement dependent behavior of soil and effect of the interactions, understanding the behavior of piles and raft and the load sharing mechanism in piled rafts is a key issue. Recently, researchers have introduced few normalized hyperbolic models according to numerical analysis to estimate the load-sharing ratio of piles in piled raft foundations. These models are based on experimental results and considering different interaction effects between pile-raft-soil, raft, and pile dimensions and the amount of settlement. The aim of this research is to investigate the behavior of piled raft foundation and to estimate the load-sharing ratio of piles experimentally. So, various tests have been conducted on piled rafts, group piles, and unpiled rafts under vertical loading by changing the number and length of piles and density of bed sand. For this purpose, an innovative combined loading system, instrumented by measuring devices, is designed and constructed; then the load-sharing ratio of piles from the total load with a novel method is estimated by measuring soil pressure underneath the raft at any settlement. According to the results, bearing capacity of piled raft foundation in analogous conditions is more than unpiled raft and twice group piles approximately. Also increasing the number of piles in piled rafts and group piles increases bearing capacity and reduces raft settlement. The load sharing ratio of piles shows downward trend by increasing settlement and it increases with increasing the number of piles in the same conditions. In this study, the ultimate bearing capacity of group piles which have been experimentally obtained is compared with the ultimate criterion of the hyperbolic model proposed by other researchers. Then, the model is modified by mathematical analysis methods indicating good agreement between experimental and analytical results.

Nonlinear site response analysis gives a more detailed description of soil behavior than the linear elastic or equivalent linear methods, but application of nonlinear codes in practice has been limited because of its greater number of parameters. In addition, there are some diculties in calibration and adjustment of parameters in nonlinear codes. There are two main approaches for studying the response of soil deposits subjected to earthquake loading, including total stress and eective stress methods. The major de ciency of the total stress method is that it is unable to take into account the progressive stiness degradation caused by pore pressure buidup in soil. Only the eective stress method can model the gradual loss of soil strength and stiness due to the build-up of pore water pressure. In this study, a loosely coupled nonlinear model is presented to predict the undrained behavior of sand subjected to cyclic loading. A modi ed Kondner - Zelasko (MKZ) model, which is coupled with a pore water pressure generation model based on strain energy, is used for eective stress analysis. There are a couple of methods for the eective stress analysis and modeling of liquefaction, but these methods often require many parameters, and their determination requires greater time and cost. The numerical method presented in this paper is simple and needs a few and determinable parameters. It also provides accurate and acceptable predictions in triaxial condition. Although the proposed model is unable to account for the cyclic mobility and uctuation of pore water pressure during cyclic loading, it accurately predicts peak points of pore pressure history during cyclic loading. Modeling of cyclic undrained triaxial tests conducted on Toyoura and Frazer River sands con rms that the proposed approach predicts the onset of liquefaction very well, and it can be used in nonlinear site response analysis to evaluate liquefaction occurrence.