# Influence of Lower Lateral Bracing on the Seismic Pounding Damage to Slab-On-Girder Steel Bridges
## 4 Discussion  
The numerical simulation results show that for slab-on-ginder steel bridges, lower lateral bracing has a good seismic rounding damage control effect. From the perspective of steel beam deformation, the lower lateral bracing increases the lateral stiffness of the steel beam, thereby reducing the lateral deformation of the steel beam by about half at the location of the bounding (Figure 11). From the perspective of impact action, the lower lateral bracing shares about 1/3 of the impact force (Figure 12), thereby effectively reducing the bounding stress of the steel beam. Therefore, the lower lateral bracing reduces the bounding damage to the steel beam. Although severe buckling damage can occur in the lower lateral bracing under seismic action, it must be noted that the lower lateral bracing acts as a \"fuse\" in terms of seismic damage to steel beam webs. This \"fuse\" function is reflected in the fact that the bracing and the steel beam jointly bear the bounding effect, which protects the steel beam from serious local impact damage under the action of a transverse earthquake. When a large bounding occurs, the bracing fails before the steel beam and shows bending failure, which can consume energy in this process, reflecting the seismic design idea of multi-fortification. It can be confirmed that it is very inappropriate to ignore the role of the lower lateral bracing when analyzing seismic damage to steel bridges, especially in relation to seismic bounding damage. In previous studies [16; 17], the lower lateral bracing was also considered in the simulations, albeit simplified to ancillary components. Simplification of the bracing is generally considered only as beam elements in the finite element model, rather than refined plate elements. It is difficult to reasonably reflect the cross-sectional form and connection details of the lower lateral bracing in the beam element model, and the damage state and failure mode cannot be obtained. In fact, the interaction between the bracing and  
Figure 19: Vertical displacement and stress time history of the lower lateral bracing with truncated stiffener. the steel beam is complex in the case of seismic pounding, and it is necessary to adopt a refined model with plate elements to consider the seismic damage to the beam and the bracing. In order to clarify the importance of lower lateral bracing in the seismic analysis of steel bridges, the results of this paper are further explained from the perspective of previous studies. [PERSON] et al. [16] discussed the damage survey of the Tawarayama Bridge affected by the 2016 Kumamoto earthquake. Tawarayama Bridge is a typical slab-on-girder steel bridge in which the lower lateral bracing was severely damaged by the earthquake. The authors used the B31 beam element to build the entire finite element model, including the steel beam and all lateral bracings. Under the design earthquake, 4% of the lateral bracings exceed the \(\sigma/\sigma_{\rm y}\) value of 1. The lower lateral bracing has the maximum \(\sigma/\sigma_{\rm y}\). In addition, there is no lateral bracing buckling under one-way seismic actions, while the lateral bracing at the piers has a clear buckling tendency under two-way seismic actions. Overall, the above views are consistent with the results of Section 3. However, the finite element model is composed entirely of beam elements, which means that the lateral bracing and steel beams are directly connected by two beams. Since the cross-sectional area and stiffness of the steel beam are much larger than the lateral bracing, the simulation results of the beam element can only indicate that the lateral bracing has been damaged under seismic action. This result may create a potential misconception that steel beams do not suffer seismic damage and that the lateral bracing should be removed to avoid seismic failure. In fact, according to the results of Figure 11, the importance of the lower lateral bracing is self-evident.