Structural Behaviors Of Three-tower Cable Stayed Bridges Under Action Of Temperature Changes

Besides their own weights and the repeated application of vehicle loads,bridge structures will also sustain the long term effects of atmosphere temperature and sunshine etc.as been exposed to natural circumstances.Temperature loadsare corresponding to the above thermal factors.Practice and calculation have indicated that sometimes displacements and internal forcescaused by temperature loads could be very large that they can't be ignored during the process of design and erection.Since cable stayed bridgesare multiply redundant structures,when subjected to temperature loadstheywill produce not only displacements but also thermal secondary forces.So it's necessary to study the temperature effects of cable stayed bridges.Temporary temperature effects analysis of cable stayed bridges mainly focus on two-tower cable stayed bridges.However,three-tower cable stayed bridges have lower integral rigidities compared to two-tower cable stayed bridges for lack of supports of middle auxiliary piers and transitional pier.Thustheir mechanical behavior will change inevitably.So it's also necessary to study the temperature effects of three-tower cable stayed bridges.ThispapertookWuhanErqi Yangtze River Bridge as the background to establish its single-girder finite element model.Referring to specifications and the bridge design documents,temperature loads were specified directly.Using the famous general finite element program ANSYS to analyze the temperature effects of a three-tower cable stayed bridge.The overall structural system temperature change,the positive and negative temperature difference between cables and the main girder,the positive and negative temperature gradient of both the main tower and the main girder were considered to see the structural behavior of it.Based on the resultdata,the sensitivity of different components under various temperature loads has been summarized.Here are the main conclusions:(1)Compared to the axial forces in the main girder and pylons caused by self-weight,the axial forces change caused bytemperature loadsare less than 2%,so they can be neglected.(2)Compared to the bending momentin the main girdercaused by self-weight,the bending moment change caused by the overall temperature difference andthe temperature gradient of the main girderare bigger than 5%,so they can't be ignored.Among the total bending momentcaused by temperature loads,the temperature gradient of the main girder takes the largest percentage.Compared tothe mid-span deflection of the main girder caused by self-weight,all temperature effectschange are bigger than 10%,so none of them can be ignored.When temperature loads are positive,the overall temperature change and the temperature difference between cables and the main girder will increase the mid-span deflection while the temperature gradient of the tower and the main girder will decrease it.However,When temperature loads are negative,the temperature effect will be the opposite.Among the total temperature effect,the temperature difference between cables and the main girder is the main factor of the mid-span deflection change of the main girder.While the overall temperature changeis the main factor of the horizontal displacement change of the beam-end.(3)Below thebifurcationof the side towers,compared to its self-weight internal forces,when temperature loads are positive,temperature difference between cables and the main girder will increase its shear force and bending moment,the temperature gradient of the tower and the main girder will decrease them.When temperature loadsare negative,temperature difference between cables and the main girder will decrease its shear force and bending moment while other temperature loads will increase them.Among the amplification effect,the negative overall temperature change is the strongest,the negative temperature gradient of the tower is in the middle while the negative temperature gradient of the main girder is the weakest.The overall temperature changeis the main factor of the horizontal displacement change of the side towers with a percentage over 80% among all the temperature effects.(4)Compared to the internal forces in the middle tower caused by self-weight,the temperature difference between cables and the main girder and the temperature gradient of the main girder almost have no impact on its shear force andbending moment with a percentage slightly over 0%,while the change of shear force and bending moment caused by the overall temperature change and the temperature gradient of the towerare way over 10%,so they can't be neglected.Among the total temperature effect,the temperature gradientof the tower has the most significanteffect on the horizontal displacement of the middle tower with a percentage over 100%.(5)Compared to the cable forces induced by self-weight,the positions of the maximum and minimum increments of cable forcescaused by temperature loadsare usually somewhere near the mid-span or tower or auxiliary pier(transitional pier),and the change of cable forcesare less than 8%.