Seismic Analysis of Protected Elements in Monorail Guideway Structures

Abstract

Monorail guideway structures (MGWS) exhibit distinct performance characteristics compared to traditional bridges due to the flexibility of their guideway beams. Therefore, a comprehensive study of the seismic behavior of MGWS is imperative to ensure their ductility and flexibility through seismic events. Shear and torsion failures are brittle modes of structural failure, necessitating that elements designed for seismic protection possess sufficient resistance capacity to ensure safety and integrity during extreme ground motions. While design codes have addressed shear over-strength ratios for bridges, they do not offer specific guidance for determining the over-strength ratio necessary to safeguard the shear and torsion capacity of MGWS elements. This paper presents a methodology for establishing the shear and torsion over-strength ratio required to protect MGWS elements from brittle failure and to achieve ductile failure. This in research was developed using displacement-controlled pushover analysis (PA) conducted with SAP2000 software. The finite element model created for this study was calibrated based on experimental test results from the existing literature. Shear and torsion over-strength ratios were determined according to the 2022 publication of AASHTO Guide Specifications for LRFD Seismic Bridge Design and were compared to the values calculated from the SAP2000 model. This comparison was conducted in both longitudinal and transverse directions, considering various parameters such as span length, pier height, pier cross-section, reinforcement ratio, confining stirrups, and concrete compressive strength. Ultimately, proposed over-strength ratios for structural members of the MGWS are provided to maintain ductility and prevent brittle failures, both in terms of shear and torsion.