Theoretical Study Of Alternative Diaphragms For Concrete Bridges

The rapid development of China’s economy, demands higher requirements for the construction of infrastructures, such as highway, tunnel and bridge. In particular, in order to minimize the adverse impact on the maintenance of bridge, bridge inspection and maintenance has become a key issue in a place like Shanxi Province as heavy trucks carrying coals prevail there. Traditionally, diaphragm have been used in concrete bridges. Over time, these concrete diaphragms have been found to be prone to deterioration and damage, thus requiring costly and longtime repairs. In this paper, the feasibility of an alternative diaphragm utilizing the structural steel is discussed analytically.The majority of theoretical studies done on diaphragms have been focused on the load bearing capability of diaphragms. Virtually, no detailed research was made in terms of diaphragm spacing. In this study, the theoretical basis for diaphragm design is proposed first, followed by the reasonable diaphragm spacing based on numerical analysis results. In addition, a complete steel diaphragm design process is proposed in accordance with the current regulatory requirements. Three T-girder bridges and three box-girder bridges are selected to demonstrate the feasibility of the proposed design process and calculation method, as well as the comparison with the draft Code for Design of Steel Bridges. Lastly, relevant static and dynamic test plans are suggested. The main research achievement are as follows.1. By stress analysis after modeling, prove that due to the presence of diaphragm the overall load-bearing capacity of main bridge girders is increased and loads are distributed to the main girders more uniformly. For the 35 m box girder bridge, three intermediate diaphragms will result in favorable support reactions, moments and deflections.2. In the diaphragm study theoretical basis derived steel diaphragm calculation process. The diaphragm structural strengths can be calculated according to the information of the existing concrete diaphragms(including bending, shear, axial force). Then, the required sizes of steel diaphragms and the connections between the proposed steel diaphragms and the existing concrete girders can be determined. The whole diaphragm design is checked against the current design specifications including the draft steel bridge design code. Design examples are used to demonstrate the steel diaphragm design approach and its feasibility. The alternative steel diaphragms offer the following advantages: faster construction, lower construction cost, lighter total diaphragm weight(thus higher live-load capacity), short time consuming, and virtually no interruption to traffic.3. This study focuses on 30 m long(a common span in Shanxi Province) concrete box girders. The relevant static and dynamic load test plans are suggested, where load testing process, loading method, equipment setup, and required data to be measured are described in detail. For field test and laboratory test of two different test environments, proposed different trail design. So as to verify the validity of steel diaphragms made possible test program.