Influence on dynamic behavior of I-girder due to constructing transverse floor beams at different positions

The floor beam, or diaphragm, is a transverse strengthening element positioned between the main beams or girders of a bridge. It is essential for maintaining the structural integrity of the section, stabilizing the bridge girders, and distributing vertical and axial loads effectively. This study explores the effects of positioning transverse floor beams, or diaphragms, at different locations between I-girders on the dynamic behavior of I-girder bridge structures. The analysis considers three distinct configurations: the first featuring floor beams situated at the bottom portion of the girder, the second with floor beams positioned in the middle of the web, and the third with floor beams located at the top portion of the web. Dynamic responses are determined using the eigenvalue extraction method via finite element analysis in STAAD Pro V8i. The eigenvalue problem is addressed to evaluate the structure's frequencies and mode shapes, incorporating a diagonal lumped mass matrix that accounts for all active degrees of freedom. The analysis reveals that relocating the floor beam from the bottom to the top of the I-girder significantly influences the natural frequency of the bridge. Consequently, to prevent resonance, it is recommended that dynamic analysis be performed before implementing semi-through girders, where the floor beams are located at the bottom of the I-girder.