Basic Design Parameters Analysis And Optimal Design For A Five-span Continuous Rigid Frame Bridge

With the development of high-speed transportation project and the enhancement of the traffic speed, it is important to improve the comfort in vehicle-driving. It is an effective way to increase the total length of superstructure of continuous rigid frame bridge. Under the circumstances multi-span continuous rigid frame bridge is used continually, but the ratio of spans of multi-span is relatively various. The choosing of a suitable ratio with thinking of static behavior of the structure is worthy of study. Because continuous rigid frame bridge is a kind of multi-degree indeterminate structure, large internal force will be produced in the bridge structure due to the temperature effect. Therefore, it is necessary to design the flexible pier with small lateral displacement rigidity, which calls for the decision of a reasonable ratio of beam bending rigidity to pier lateral displacement rigidity.Based on a practical engineering, the basic FEM model of a five-span continuous rigid frame bridge is built, and with which the static behavior of the basic bridge under dead load and annual temperature change and sunshine temperature differential is analyzed. After changing the ratio of spans and the thickness of the walls of the double thin-wall pier, parameter analysis is processed under dead load and annual temperature change and sunshine temperature differential. In the end, two simple object functions are built based on the results of parameter analysis, with which to search the optimum ratio of spans by the grid searching method. The static behavior is also compared between the optimized bridge and the basic bridge. The basic conclusions are as follows:(1) Under the common effects of dead load and temperature, the internal forces of two intermediate piers are obviously larger than those of two side piers of five-span continuous rigid frame bridge.(2) The change of ratio of spans has a great effect on the whole bridge under dead load and sunshine temperature differential. On the contrary, it has a smaller effect on the bridge under annual temperature change.Increasing the ratio of side span to second middle span does good to the static behavior of the whole bridge. It is highly recommended that the ratio of side span to second middle span had better be chosen as 0.7 or so. And the ratio of second middle span to middle span had better be chosen more than 0.9. The gap of intermediate spans of other(3) multi-span continuous rigid frame bridges also should small for proper.(4) Decreasing the thickness of double thin-wall pier wall has a small effect on the main beam of the continuous rigid frame bridge, while it can greatly reduce the internal force of the piers caused by temperature, especially that of the side piers. Consequently, in order to guarantee the stability of construction and service, the lateral displacement rigidity of the piers should be decreased as much as possible. (5) For five-span continuous rigid frame bridge, to increase lateral displacement rigidity of two intermediate piers and reduce lateral displacement rigidity of two side piers can reduce internal force of two side piers and make four piers suffer even internal force. When the height of four piers is near, the ratio of the thickness of two intermediate piers to that of two side piers may adopt 1.8 or so for proper.