# Influence of Lower Lateral Bracing on the Seismic Pounding Damage to Slab-On-Girder Steel Bridges
## 5 Conclusions  
In this paper, a multiscale fine numerical simulation of continuous slab-on-girder steel bridges with and without lower lateral bracing is carried out to discuss their response and damage under seismic action. El Centro seismic recordings were selected and the peak acceleration amplitude was adjusted to 0.4 g as the input acceleration boundary condition for the finite element model. Focusing on the lateral seismic response of bridges, the following conclusions can be drawn:  
1. Under transverse seismic actions, the steel beams on both sides will experience seismic bounding and be damaged. For steel bridges with lower lateral bracing, the lateral collision damage of the steel beam is significantly reduced due to the sharing and transmission of the bounding force by the lower lateral bracing. The lower lateral bracing can share about 1/3 of the bounding action and reduce the displacement angle of the steel beam by 40%. 2. Under horizontal two-way seismic actions, the seismic response and damage of the steel beams on both sides are significantly amplified. Although the lower lateral bracing only slightly reduces the stress at the key, it significantly reduces the stress on other parts of the steel beam. The lower lateral bracing only elastically bends vertically under the full action of the earthquake. 3. The lower lateral bracing connection with discontinuous vertical stiffness will bend and deform in the area of sudden stiffness; that is, connection failure will occur. After the connection fails, the lower lateral bracing will lose the lateral support effect on the steel beam. The novelty of this paper is paying attention to the previously neglected lower lateral bracing structure and confirming that it plays an important role in controlling the seismic bounding damage to steel beams. Although this phenomenon has been hinted at by the actual seismic damage to steel bridges, few studies have been refined to analyze it. The possible failure modes and engineering design recommendations for the lower lateral bracing are further proposed in this paper. In summary, lower lateral bracing should be considered in the design of slab-on-girder steel bridges. It significantly improves the lateral seismic performance of the bridge and reduces the seismic bounding damage to steel beams. In addition, attention must be paid to the design of the connection between the lower lateral bracing and the steel beam to avoid connection failure. On the basis of this research study, the research on the seismic bounding problem of steel bridges can be further improved from the perspective of an analysis model and algorithm development. In terms of analytical models, many existing beam dynamics analysis models focus on the beams' dynamic vibration characteristics [24; 25; 26; 27]. The research content of this paper is based on the three-dimensional finite element analysis of an entire bridge and its components. In fact, it is also necessary to propose a theoretical analysis model of steel girder bridges that can consider the seismic bounding effect from the perspective of simplifying the model and improving its practicality. The seismic response of steel girder bridges can be obtained accurately without using complex finite element models. In terms of algorithm development, deep learning and artificial intelligence have a significant impact on bridge and structural engineering and are widely used in the field of numerical modeling and prediction [28; 29; 30]. Therefore, in future work, the method of deep learning can be considered to assist in the decision-making of the form and quantity of the lower lateral bracings so as to avoid a large number of numerical model optimization work. **Author Contributions:** Data curation, F.S. ; funding acquisition, D.W.; investigation, J.D. ; methodology, F.S. ; project administration, D.W.; resources, J.D. ; validation, L.T. ; visualization, L.T. ; writing--original draft, F.S. ; writing--review and editing, D.W. All authors have read and agreed to the published version of the manuscript.