Load history-based model for prestressed concrete beam damage evaluation

The residual capability of a damaged structure to resist further load is essential in optimal seismic design and post-earthquake strengthening. An experimental study on the hysteretic characteristics of prestressed concrete frame beams under different loading histories was performed to explore the influence of load history on energy dissipation and failure characteristics of the member. Based on the test results, the failure of the beam is defined, and the relationship between the failure moment under cyclic load and from the skeleton curve is formulated. Finally, based on displacement and energy dissipation, a model for prestressed concrete beam damage-failure evaluation is developed. In this model, the effect of deformation level, cumulative dissipated energy, and loading history on prestressed concrete beam damage-failure is incorporated, thus it is applicable to stochastic earthquake forces.

Modification of Wirsching’s Model for Fatigue Reliability Analysis

First, Wirsching's model, which is widely employed in fatigue reliability anlysis of marine and offshore structures, is analysed systematically. It is found that the very important random variable A in Wirsching's model can not be directly determined from fatigue experiment because of the irreversibility of fatigue test, and in fact, what Wirsching studied from testing results is not A but a of the statistical Miner's rule. Second, by use of the statistical Miner's rule, a modified Wirsching's model is proposed. Thirdly and more importantly, based on the two-dimensional probabilistic Miner's rule, a new model is established for fatigue reliability analysis of structural components subjected to specified cyclic loading of variable amplitude or stochastic time history. In the end, an example is presented, from which it will be seen that this new model is very convenient to use and feasible to engineering practice.

Analysis of rail-bridge interaction of a high-speed railway suspension bridge under near-fault pulse-type earthquakes

Due to the limitations of railway route selection,some high-speed railways are inevitably built near or across fault zones.To study the distribution of rail-bridge interaction under different load history states of suspension bridges under three types of near-fault pulse-type earthquakes,this paper takes China’s longest high-speed railway suspension bridge—Wufengshan Yangtze River Bridge-as the background and establishes a spatial model of the rail-bridge interaction of a suspension bridge.The results show that:under the constant load state,the distribution of additional force under three types of pulse-type earthquakes is generally consistent,and pulse-type earthquakes produce more significant responses than non-pulse-type earthquakes;with fling-step pulse being the largest,it is advised to specifically consider the influence of the fling-step pulse in the calculation.Under the initial condition of the main beam temperature loading history,all rail-bridge additional forces increase significantly,particularly affecting the steel rail system.The value of the rail-bridge interaction additional force under the near-fault earthquake in the initial state of the suspension bridge when the train deflection load is loaded from the tower to the mid-span is more significant and particularly unfavourable.The initial effect of the braking load will weaken the effect of the deflection load loading history.The results of the study indicate that the effect of the initial state of suspension bridges is an important factor influencing the rail-bridge interaction under near-fault pulse-type earthquakes,which needs to be considered in future seismic design.