This study presents the design and structural analysis of a bridge to protect two natural gas pipelines against static and dynamic loads resulting from a new railway line to be constructed above them. Structural analyses were conducted considering earthquake effects, particularly using the load combinations and coefficients recommended by AASHTO LRFD [2017]. The railway bridge is not designed to span any crossings. However, since the existing railroad is situated directly on the ground, a train load is transferred to the pipelines through the ground. To reduce this load transfer, a 25-30cm gap is maintained between the deck and the ground in this protective bridge design proposal. The maximum anticipated displacement of the bridge was considered in the analysis. Site-Specific Earthquake Hazard Analysis was first performed for the proposed bridge due to the critical implications of the pipelines. In the second stage, the structure underwent nonlinear dynamic displacement loading and bridge-pile-soil interaction was analyzed using both linear and nonlinear methods. The performance targets - Uninterrupted Use for DD2a class ground motion and Controlled Damage for DD1 earthquake) - stipulated by the Turkish Bridge Design Standards [TBDS, 2020] were evaluated using strength-based linear and strain-based nonlinear analyses. The results confirmed that the proposed bridge satisfied all target safety levels. In conclusion, this study aims to guide both designers and practitioners, as it is among the first to address the newly enacted TBDS-2020 regulation in Turkiye and serves as an exemplary engineering solution for similar protective bridge designs.

The compressive bearing capacity of a new type of concrete-expanded plate pile (NT-CEP pile) is significantly affected by the size of the bearing platform; however, research in this area remains limited. Therefore, this study investigates the effect of bearing platform size on the compressive bearing capacity of an NT-CEP pile foundation under combined vertical and horizontal loads. Using ANSYS finite element software, a four-pile model was established to analyze the failure behavior of the bearing platform and surrounding soil under these loads. The findings indicate that in an NT-CEP four-pile foundation, the bearing capacity of piles with a bearing platform increased by 66.67% compared with those without one. However, although the bearing capacity increased with platform size, this increase reduced after reaching a certain threshold. Optimal bearing performance was achieved when the platform size was 1.5 times the pile diameter from the edge to the pile center. High shear stress at the junction between the lower part of the platform and pile body suggested a potential stress concentration. The findings emphasize the importance of maintaining the optimal bearing platform size and reinforcing the connection between the platform and pile body to prevent local damage from affecting the overall bearing capacity.

Liquefaction and earthquake damage to coral sand sites can cause engineering structure failure. Both testing and analyzing the seismic response characteristics of pile groups on coral sand sites are highly important for the seismic design of engineering structures. To address the lack of research on the seismic dynamic response of group pile foundations in coral sand sites, this study analyzes the characteristics of the seismic dynamic response of vertical and batter pile foundations for bridges in coral sand liquefaction foundations via the shaking table model test and investigates the variation patterns of acceleration, excess pore water pressure (EPWP), and the bending moment and displacement of foundations, soil, and superstructures under different vibration intensities. Results show that the excitation wave type significantly affects liquefaction: at 0.1 g of peak acceleration, only high-frequency sine wave tests liquefied, with small EPWP ratios, while at 0.2 g, all tests liquefied. Vertical pile foundations had lower soil acceleration than batter piles due to differences in bearing mechanisms. Before liquefaction, batter piles had smaller EPWP ratios but experienced greater bending moments under the same horizontal force. Overall, batter piles showed higher dynamic stability and anti-tilt capabilities but endured larger bending moments compared to vertical piles in coral sand foundations. In conclusion, batter pile foundations demonstrate superior seismic performance in coral sand sites, offering enhanced stability and resistance to liquefaction-induced failures.