The separate finite element model is established for the healthy reinforced concrete beam（RCB） and the RCB with perfect crack in this paper

and stiffness matrix for sticking unit in the model with 4 nodes is deduced.The parameters of vibration characteristic are able to be calculated for the healthy and damage RCB with the model.The relationship between the damage and the parameters is able to be studied by using this model.The numerical result tallies with the outcome from testing.After the numerical calculation and testing

three conclusions can be drawn.Firstly

the nature frequency is important guideline to determine the nature of the damage

such as the cracks

in the RCB.Secondly

the curvature mode shape and the strain mode shape are the sensitive parameters of the local damage in the RCB and the location of crack can be distinguished exactly by using the mode absolute residual vector in testing. Thirdly

the relationship is monotone between the norm of absolute residual vector of curvature mode shape and strain mode shape and the damage severity

and the damage severity can be evaluated based on the norm.