| With the expeditious development of our civil traffic projects, plenty of oversize bridges have constantly rushed. The number of new bridges and old bridges has been increased. In order to insure safety and security of the people's health and wealth, it is the focus of current bridge project to detect fleetly and effectively structural damaged position and extent likely occurring and to command the health status of bridge in commonly using state in time.Actuality of damage identification for structures is expatiated firstly and comments are made on the methods of them. These methods include natural frequency, strain mode, COMAC, flexibility matrix, wavelet analysis, nerve network and genetic algorithms etc.However, actual damage detection method ubiquitously exists the problem of error orientation. And in order to solve this problem, we should need to probe damage reason. On generally, structures in course of using not only get the effect of certainty load, but also get the disturbance of uncertainty random circumstance factor. In some special conditions, dynamic loads indeed play so dominant effect as to result in unsteady or damage of structure. However, structures designed in general static state put up of a sort dynamical character in practical application and prematurely invalidate or are damaged beyond people's anticipation. The aim of this paper is to relate structural inherent characteristic with exterior excitation, to wield experimental mode analysis technique and structure intension theory in order to separate structural leading mode under practical work state on base of spectrum analysis of exterior excitation and identification each rank mode parameter of structure. Sequentially, the issue of space complex stress state in effect of static and dynamic coupling transforms into the issue of simple stress state (under mode form) in reciprocal effect of each rank mode in order to analyze structural dynamical intensity.The paper (in chapter 4) will combine the principle of experimental modalanalysis with the theory of structure intensity; utilize theories in existence; regard static issue as dynamic special issue; decompose dynamic force issue to static force issue in mode of each rank; realize consolidation of static and dynamic issue.In chapter 5, by number value simulation calculation and experiment of one simple support beam, we will compare the magnitude of the coupling static and dynamic stress at each point on the girder under harmonic excitation, and so find conclusions such as:(1) There are so much correlations between structure damage and environmental effect and exterior excitation leads dominant effects in structure damage that we should consider static and dynamic stress together.(2) New intension design rules should be set up, according which the range of structure possible damage position should be estimated in advance. And consequently, theory would be provided for correct orientations of structure damage. |
