Simulation And Prediction Of Long-term Deformation Of Prestressed Concrete Bridges Under Environmental Thermal And Vehicle Loads

Prestressed concrete bridges expose to the external environment for a long time and bear increasing traffic loads,which leads to the degeneration of long-term performance.With real-time acquisition of long-term performance of bridges,maintenance can be realized in time,so that the costs are greatly reduced and the effectiveness of maintenance measures is improved.However,the prediction of longterm performance of bridges are mainly on the experimental or empirical level at present.It is impossible to obtain the degradation law of long-term performance only rely on existing prediction methods,which leads more and more bridges to miss the optimal maintenance.Therefore,the rapid and accurate prediction of long-term performance by means of numerical simulation has become a hot topic for researchers all over the world.There are many factors affecting the evolution of long-term performance,so that the existing simulation technology can not accurately predict it.In recent years,with the improvement of computer hardware and the innovation of numerical analysis platform,it is possible to realize the fine modeling and accurate prediction of long-term performance for long-span bridges.In order to analyze the longterm performance of bridges quickly and accurately,the long-term deformation of prestressed concrete bridges under thermal and vehicle loads is studied in this paper.The main innovations and achievements are as follows:(1)A fine and effective themral analysis for bridges in natural environment is proposed,aiming to obtain the distribution of temperature,thermal stress and deformation quickly and accurately.The sheltering of components under sunshine is divided into permanent sheltering,self-sheltering and mutual sheltering,so that a threedimensional(3D)ray sheltering algorithm suitable for space structure is proposed.A multi-scale modeling method for predicting the spatial distribution of temperature in cable structure is proposed,by which the equivalent thermal physical parameters,temperature distribution of cable cross-section and space cable can be obtained.A heat transfer analysis between concrete and air in enclosed space is proposed,in which both convection and radiation heat transfer can be considered at the same time.Based on computational fluid dynamics(CFD)method,the heat transfer coefficients on the surface of concrete structure can be solved,and the non-uniform distributions of heat transfer coefficients on the surface can be obtained.A substructure method suitable for bridge structures is proposed and the calculation efficiency is improved.The case studies show that the non-uniformity of temperature and thermal stress distribution of bridges can be obtained with the consideration of 3D sunshine shielding.The maximum thermal stress is usually accompanied by traffic,so the effect of overlapping of live loads and thermal stress on fatigue life of components should be considered.Based on the fine temperature analysis of a suspension bridge,it is found that the thermal dynamic properties of long-span suspension bridges under solar radiation are mainly caused by the thermal stress stiffening effect.(2)Based on the long-term and random characteristic of environmental themmal and vehicle loads,a random traffic model,a prediction method for long-term fine temperature distribution of bridges and an equivalent method for random thermal loads are proposed.Based on the video data of vehicle types and weight in motion(WIM)data,a random traffic model is established.The generated random vehicle loads can be equivalent to uniform loads,which can be applied directly on the pavement.The tedious data transfer between different softwares is avoided.In order to solve the problem that the thermal analysis is limited to several days through the fine temperature analysis in(1),a prediction method for long-term fine temperature distribution of bridges is proposed.By interpolating the fine temperature distribution of bridges within limited days,the long-term fine temperature distribution within one year or several years can be obtained.The equivalence method of random thermal loads is proposed and its feasibility is verified theoretically.Based on the weather type and direct radiation factor generated randomly,the distribution of temperature in bridges under clear sky radiations can be directly corrected,so that the random temperature distribution can be obtained.The calculation of the fine temperature distribution of bridges under random weather conditions is avoided.(3)With the consideration of the coupling mechanism of fatigue,concrete plastic damage,concrete shrinkage and creep,a concrete creep model under cyclic loads is established.The fatigue creep strain is redefined in the model,and the physical meaning of the parameters in the expression is more clear.Subsequently,a long-term deformation analysis for prestressed concrete bridges under random traffic loads is proposed.In order to analyze the prestress loss under variable amplitude loads,a differential expression of prestress loss is derivated.Case studies show that the longterm deformation of prestressed concrete bridges can be greatly increased by vehicle loads(especially heavy vehicles).Influence of randomness of vehicles on long-term deformation is increasing with years.The longitudinal cracks observed in the bottom slab can be caused by the combination of concrete static damage in the pre-stressed anchorage area with the tension fatigue damage under vehicle loads.The cracks on the surfaces of diaphragm and passing hole can be caused by the concrete static damage during excessive deflection.(4)Based on(1),(2)and(3),a concrete creep model under cyclic thermal and vehicle loads is established and a long-term deformation analysis for prestressed concrete bridges under cyclic thermal and vehicle loads is proposed.The temperature dependence of long-term deformation of prestressed concrete bridges is also studied.Case studies show that the coupling effect of concrete time-varying behavior and prestress loss can be affected under temperature-varying conditions.The acceleration of prestress loss and the decrease of elastic modulus of materials in higher temperature conditions lead to the increase in initial deformation.Applying different temperature distribution mode leads to different long-term deformations.The direction of long-term deformation for a span caused by temperature gradient is opposite to that caused by instantaneous elastic thermal deformation.The long-term deformation of continuous girder bridge is related to the residual stress after one day's sunshine.If only the longterm deformation is concerned,the influence of random weather can be ignored.The cracks on webs can be from the difference of heating rate between inside and outside webs and the prestress loss inside webs.