Stiffness And Load-Carrying Capacity Evaluations Of Short-and Medium Span Bridges Based On Influence Coefficients

There are huge amount of short and medium-span bridges in transportation system.During their service,their stiffness will be degraded due to the coupling effect of unfavorable factors,which will eventually lead to their insufficient load-carring capacity and collapse.Therefore,it is of great significance to evaluate the stiffness and load-carring capacity of short and mediumspan bridges in a timely manner.The influence coefficient is a static property of the bridge.It can be tested by moving a single calibration truck and collecting the single point responses simutanously.It contains the stiffness and internal force information of each bridge section,and provides a basis for the rapid evaluation of bridge performance degradation.This paper foucus on the evaluation of stiffness and load carrying-capacity base on influence coefficients,aming to solve the problems in under-determined boundary reconstruction of influence coefficients,quantifying local stiffness degradation without reference,and considering bridge degradation differences in bridge load-carrying capacity evaluation.The proposed methods are finally integrated into an applicable engineering software.The main contents are as follows:(1)In the process of bridge infleunce coefficients testing and identification,movement of the loading trucks are limited at the edge of the bridge deck,which leads to a high degree of under-determination of the infleunce coefficients.This under-determination cause distortion and loss of the identified influence coeffcients.For this reason,a dynamic disturbance elimintaion method based on empirical mode decomposition is introduced.Based on the superposition principle of structural response under static loads,a mathematical model that can completely describe the relationship between vehicle-induced bridge responses and influence coefficients is established,and an iterative regularization method is introduced.The model and method are then extended to the two-dimensional influence surface identification problem,and the truck routines that can reduce the underdetermined degree of the influence coefficients is planned.The illustrative example show that the proposed method realizes the accurate identification of the influence coefficients of the bridge deck edge under various vehicle-bridge relation and different test dimensions.(2)In the process of influence coefficients-based bridge stiffness evaluation,the stiffness of the bridge supports and the main girder are coupled with each other,which causes the quantification of the stiffness degradation of the elastically supported beam bridge to depend on the reference of the intact state.For this reason,the relation between the influence coefficients of the elastically supported beam bridge and the stiffness of the main girder and the supports is derived,and a method of converting the beam bridge support constraints into additional couples is proposed to evaluate the support stiffness.According to the bending moment-curvature relation of the beam structure and Betti’s law,the relation between various influence lines and the structural deformation curves under the force system is established.A method for estimating the stiffness distribution of the girder bridge main girder based on the influence coefficient is proposed.The unrealiable intervals of the stiffness evaluation results are defined,and the sensor placement recommendations for structural stiffness evaluation are given.The numerical example shows that the proposed method realizes reference-free estimation of the girder bridge support rotation stiffness and the main girder flexural stiffness distribution.(3)In the process of influence coefficients-based load-carring capacity evaluation method,the degradations of actual structure are not consistent in different limite states,and ignoring the difference will lead to the conservative evaluation result.To this end,this paper compares and analyzes the bridge load-carrying capacity evaluation formulas and load testing methods in Chinese and American codes,plans a multi-level truck moving rotines that can test the influence coefficients of each section.The corresponding relation between the key points of the influence coefficients and the structure positions is given,and the influence coefficients calibration process is established based on the realation.Through virtual loading of the measured influence coefficients,the direct calculation method of the structure virtual responses and the correction method of the resistance-load effect relationship based on the structure check coefficient are proposed,which are respectively used for the rapid evaluation of bridge load carrying capacities for service and ultimate limite states.The bridge testing example shows that the proposed method only needs to interrupt the traffic for a short time to realize the evaluation of bridge load-carring capacity of each limte state.(4)Considering that the bridge performance evaluation methods are difficult for the onsite engineers to apply,this paper integrates the series of proposed methods and developed a bridge rapid service performance evaluation software based on the Matlab platform: Bridge Rapid Evaluation System(BRE).A logical interactive mode and a view area that can display three dimensions bridge model are established.Some practical functions are developed such as automatic generations of load testing trucks layout and evaluation report.An evaluation example is presented at the end of this section to illustrate the utilization of basic functions and effectiveness of the software.The software is closely integrated with the current bridge evaluation codes,and is expected to provide an effective solution for the rapid evaluation of short and medium-span bridges.