Temperature Monitoring And Temperature Stress Analysis Of Concrete Highway T-girder Bridge

Temperature action is one of the main loads which should be considered in the design of highway Bridges. Its distribution form and magnitude are directly related to the safety, serviceability and durability of the bridge structure. The currently-existing China specification "General Code for Design of Highway Bridges and Culverts" JTJ D60-2004directly follows American AASHTO specification on the calculation of temperature action, and has not yet considered the effects of geographical differences and the thickness of the concrete pavement on the vertical temperature gradient distribution and the maximum temperature difference. With this reason, combined with the project of revision of bridge general specification "Vertical Temperature Gradient Model Research of Highway Bridge ", the temperature field observation and temperature stress analysis of concrete highway T-girder bridge were carried out in the present thesis, covering the following major contents and conclusions:(1) The differences between domestic and international specifications regarding temperature action were summarized.(2) Two concrete T-girders with50mm and100mm asphalt concrete pavement and two concrete T-girders with150mm and200mm plain concrete pavement were made. The temperatures at146monitoring points distributed on8cross-sections of girders were acquired continuously from April2013to February2014. The results showed that, the girders had small lateral and longitudinal maximum temperature differences but the bigger vertical temperature differences. Vertical temperature differences of concrete T-girders with two types of pavement layer were nearly14℃and5℃. Compared with "General Code for Design of Highway Bridges and Culverts", the maximum vertical temperature differences of the tested girder with asphalt concrete pavement were lower than the specified values for50mm and100mm thickness pavement (respectively20℃and14℃). The girder with concrete pavement presented a greatly-reduced the maximum vertical temperature differences. Also, the results showed that, for the vertical temperature gradient of the girder with asphalt concrete pavement, a logarithmical or bilinear model was followed, which distinguished from the currently-existing code where the vertical temperature gradient adopts bilinear model. The turning point of the bilinear model proposed in this thesis was0.1m distance from the top surface of girder. While for the bridge with concrete pavement layer, the vertical temperature gradient follows an exponential or three fold line law. Also, it was showed that the turning points of the three fold line law were0.25m and0.6m distance from the top surface of concrete girder. Statistics of the maximum temperatures within each unit (10days) indicated that the annual daily maximum temperature differences over time followed a sine wave.(3) Combined with finite element theory of temperature field, integrated temperature, heat transfer coefficient and concrete thermal physical properties were determined in terms of the measured data and meteorological data. Numerical simulation of transient temperature field in concrete T-girder was performed using ANSYS finite element software and compared with measured values of temperature field. The results showed that the simulated values were close to the measured ones and the vertical temperature gradients between them were generally consistent, which verified the rationality of the input parameter values.(4) The temperature stresses of the tested girders were calculated based on the seven temperature gradient models using both theoretical formula and finite element software MIDAS/Civil. The results showed that the temperature stress along the vertical direction calculated according to the different temperature gradient models presented the almost same developing trend, namely, the top and bottom slabs of girder were compressed and web was tensioned. Also, it was found that the zone of0.1m below the flange had a bigger tensile stress and therefore the more attention should be paid to this potential cracking zone in the practical engineering design.