Seismic resistance of continuous monolithic bridges, considering the tension of post-tensioning reinforcement tendons during support-soil interaction

Ensuring the seismic stability of transport structures is a high-priority task in modern engineering design, especially in the seismically active regions of Central Asia. This paper examines the features of the numerical analysis of the seismic stability of a continuous monolithic highway overpass, considering the prestressing of post-tensioning reinforcement strands and the interaction between the piers and the soil foundation. The object of study is a three-span continuous monolithic reinforced concrete overpass with a 35+ 50 + 35 m span arrangement, located in the city of Jizzakh in a seismic intensity zone of 8 points, over the Tashkent-Samarkand high-speed railway line (Republic of Uzbekistan). The intermediate piers are double-column, 12 m in height; the cross-section of the superstructure slab includes 19 ducts with post-tensioning reinforcement strands. The analyses were performed using two software packages: SHARK (the direct step-by-step dynamic integration method using accelerograms from the actual 1976 Gazli earthquake, with an intensity exceeding 9 points on the MSK-64 scale) and MIDAS Civil (the response spectrum method). The soil foundation was modeled according to the Winkler model using viscoelastic links, the parameters of which were determined from the characteristics of Category III loess-like loams based on their seismic properties (KMK 2.01.03-19). The results of the normal stress calculations in the upper and lower parts of the overpass superstructure are presented. The maximum compressive stress in the upper part of the superstructure was -10.10 MPa (MIDAS Civil) and -3.30 MPa (SHARK); the tensile stress in the lower part was 2.32 and 2.25 MPa, respectively. The identified discrepancy in the results is due to the fundamental difference between the analysis methods: the response spectrum method provides a conservative (overestimated) assessment, whereas direct dynamic integration reproduces a more realistic picture of the stress-strain state. The analyses established that all stress values do not exceed the permissible limits set by SHNK 2.05.03-2022, indicating that the overpass maintains its operational performance during an earthquake with an intensity of more than 9 points on the MSK-64 scale.

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