Structural damage identification is a vital part of the monitoring and maintaining of structural systems during their service life.Damage identification of structures based on dynamic test and measurement techniques has been a hot topic in recent years.Damage identification is an inverse problem in structural engineering.There are three main questions in the structural damage identification: the presence

location and extent of the structural damage.An improved genetic algorithm（GA） for the structural damage identification is presented in the present paper.The improvements include the adoption of real-valued representation

normalized geometric ranking operator

elitist model

arithmetical crossover operator and non-uniform mutation operator.Based on the conventional modal analysis theory

a new formulation of the objective function for GA

formulated by the residual forces at the nodes

is presented.Firstly

the residual forces method is employed to localize the damage

which can accurately locate the structural damage using one of any order of the modal data without noise.Noise

however

can not be avoided during the dynamic measurement

which makes the identification of the structural damage completely impossible.Considering this problem

the localization and quantification of the extent of the structural damage with noise is further performed with GA implemented by the objective function formulated by the residual forces at the node which is based on the conventional modal analysis theory.Unlike the conventional optimization methods

such as the gradient methods

which are easily trapped into local minima for the damage detection problem

GA has the capacity of locating global minima for function optimization with multiple local minima.Most importantly

GA can treat the noise-polluted problems effectively and is especially applicable to damage detection.Finally

an illustrative example of a plane truss model is used to perform a numerical simulation.The results show that the presented methods can localize and quantify the structural damage simultaneously and has good performance to deal with noise.Some problems encountered in this method are discussed in detail and some concluding remarks are given.