Abstract: The joint faulting and poor quality of overhead casting may result in cracking of concrete diaphragm. The utilization of steel diaphragms can effectively address these issues, offering benefits such as improved uniformity in box girder formwork and accelerated bridge construction. An innovative triangular steel diaphragm with bolt-connection and its assembly process are proposed in this paper. Based on existing four-span continuous concrete box-girder bridges, a finite element model was developed using Abaqus 2021 to investigate the influence of the novel steel diaphragms. Both static and dynamic analyses were conducted on the numerical model. And in-situ tests were performed to validate the model. The results show that transverse distribution factor of the bridge enhanced by steel diaphragms is nearly 90% of that of the bridge using concrete ones under static load. And similar transverse distribution factors were observed in both bridges. Considering road surface roughness and vehicle-bridge dynamic interaction, the vertical deflection in the steel-diaphragm bridge is 95.01% at 20 km/h and 96.46% at 30 km/h of that of the concrete-diaphragm bridge, while the deflection ratio is 93.49% under static load. And the results also indicate a better dynamic performance of steel diaphragms with lower impact factor compared with concrete ones. Moreover, the application of triangular steel diaphragms leads to a 7.89% decrease in the local shear stress of the wet joint due to the support at the top point.