# Influence of Lower Lateral Bracing on the Seismic Pounding Damage to Slab-On-Girder Steel Bridges
## 1 Introduction  
During strong seismic events, adjacent structures tend to pound with each other, and the large bounding force significantly alters the dynamic behavior of the adjacent structures. Whether to buildings [1] or bridges [2], seismic-induced bounding can cause structural damage (even serious damage under large seismic activity). Some new characteristics were observed in the steel bridges' seismic damage in the 2016 Kumamoto earthquake [3]. As shown in Figure 1, typical seismic damage to steel bridges includes steel beam damage and lower lateral bracing buckling. Seismic-induced bounding is closely related to these seismic damages, and the lower lateral bracing influences the beam's damage. Figure 1: Damages of slab-on-girder steel bridges in Kumamoto earthquake. (**a**) Steel beam damage; (**b**) lower lateral bracing buckling. Some scholars have paid attention to the seismic bounding effects of bridges. [PERSON] et al. [4] studied the combined effects of ground motion spatial variation, local site amplification, and soil-structure interaction on the seismic-induced bounding failure of bridges and estimated the separation distance that expansion joints need to provide. [PERSON] [5] studied the bounding between the superstructure segments of an elevated highway bridge with a three-span continuous deck under three-dimensional nonuniform earthquake excitation. [PERSON] et al. [6] studied the adjacent bounding effect of a midspan curved bridge with a longitudinal slope and analyzed the influence of connection parameters such as gap size and longitudinal slope. These studies analyzed the influencing factors of the seismic bounding response of bridges from the perspectives of different bridge structural forms and seismic effects. However, the models used in these studies are simplified, making it difficult to determine the damage caused by seismic poundings. In recent years, the study of the seismic pounding response of bridges has developed in a more refined direction. [PERSON] and [PERSON] [7], for example, used a refined 3D finite element model to study the seismic pounding damage to a two-span bridge model without or with shear keys and concluded that neglecting shear keys in bridge seismic response analysis may lead to inaccurate predictions. [PERSON] et al. [8] presented an experimental study on the transverse pounding reduction of a high-speed railway simple-supported girder bridge. [PERSON] et al. [9] proposed a new type of shear key for the retrofit of existing highway bridges and further studied their seismic pounding damage under repeated monotonic loading. [PERSON] et al. [10] studied the performance of steel keys in seismic pounding events of bridges via shake table experiments and discussed the influence of gap size. These studies further discussed the problem of bridge pounding damage in further detail through refined finite element models and experiments. The lateral seismic pounding effect must be transmitted from the shear keys to the beam and bracing, and a detailed consideration of the shear keys is conducive to a more accurate calculation of the beam's damage. However, the above studies still ignore the damage to the lower lateral bracing under the action of seismic pounding and do not realize the natural advantages of lower lateral bracing in controlling the damage to steel beams. Some scholars have proposed different measures to reduce the beam's pounding damage from the perspective of increasing damping devices, such as placing hard rubber bumpers [11], magnetorheological dampers [12], and rotational friction hinge dampers [13]. These measures have proven effective, but placing many dampers will inevitably significantly increase the seismic design cost of the bridge and also bring inconvenience in long-term maintenance. In fact, from the perspective of seismic damage to steel bridges, well-designed lower lateral bracing has the characteristics of reducing the pounding damage to steel beams.