Seismic Performance of Steel Tubular Arch Truss Structures with Seismic Isolation Bearings

Literature Overview

The paper by Nan Lfei, Li Haiwang, and Li Weiwei (2014, Journal of Taiyuan University of Technology, Vol. 45, No. 6, pp. 785–790), supported by the National Natural Science Foundation of China (Grant No. 50878137) and the Shanxi Provincial Science and Technology Project (No. 200890321086), investigates the seismic performance of a 60-meter span three-center circular steel tubular arch truss structure. The authors developed two structural models—one with conventional fixed hinge bearings and another with lead-rubber seismic isolation bearings—and conducted dynamic elastoplastic analysis using SAP2000 software with the plastic hinge method. The analysis considered both geometric and material nonlinearity, and the results demonstrate that the seismic isolation model achieves a 59.4% improvement in failure boundary acceleration peak value compared to the conventional model.

Core Technical Points and Interpretation

The seismic performance of large-span steel tubular arch truss structures is of significant concern, particularly in seismically active regions. The paper's analysis addresses several critical aspects:

Structural modeling: The 60-meter span three-center circular arch truss is modeled with two bearing configurations—conventional fixed hinges and lead-rubber bearings—to isolate the effect of seismic isolation on structural performance.
Dynamic elastoplastic analysis: The analysis incorporates both geometric nonlinearity (large displacement effects) and material nonlinearity (plastic hinge formation), providing a realistic representation of structural behavior under strong seismic excitation.
Plastic hinge theory: The plastic hinge method allows the identification of critical sections where plastic deformation concentrates, providing insight into the failure mechanism and ductility characteristics.

Performance Indicator	Conventional Model	Seismic Isolation Model	Improvement
Failure boundary acceleration peak	Baseline	+59.4%	Significant
Plastic hinge distribution	Few members, uniform distribution	Few members, uniform distribution	Comparable
Ductility coefficient	Moderate	Moderate	Comparable
Pre-failure deformation	Small	Small	Comparable
Failure mode	Elastoplastic dynamic instability	Elastoplastic dynamic instability	Same type

The key finding is that the lead-rubber bearing seismic isolation system significantly increases the failure boundary acceleration, meaning the structure can withstand stronger seismic events before reaching its failure limit. However, the failure mode remains the same for both models—elastoplastic dynamic instability—which indicates that seismic isolation does not fundamentally change the failure mechanism but rather increases the load capacity before failure occurs.

Process Analysis and Engineering Practice Integration

The practical implications of this research for steel tubular arch truss design include:

Bearing selection: The choice between conventional fixed hinges and seismic isolation bearings must be evaluated based on the seismic hazard level, structural importance, and economic considerations. The 59.4% improvement in failure boundary acceleration represents a substantial safety margin enhancement that may justify the additional cost of seismic isolation bearings.
Ductility design: Both models exhibit moderate ductility with small pre-failure deformations, indicating limited warning before failure. This has important implications for structural design, as designers must ensure adequate safety factors to account for the lack of pre-failure deformation warning.
Plastic hinge location: The uniform distribution of plastic hinges across few members suggests that the structure does not have a single critical failure point, which is beneficial for redundancy. However, the small number of plastic hinges also means that failure is concentrated and potentially sudden.
Analysis methodology: The use of SAP2000 with the plastic hinge method provides a practical and widely available tool for seismic performance evaluation of steel tubular arch truss structures.

Key Questions and Reflections

The paper's analysis raises several important questions. First, the study focuses on a specific 60-meter span three-center circular arch truss, and the results may not directly generalize to other arch geometries, spans, or truss configurations. Second, the seismic isolation system's effectiveness depends on the proper selection of lead-rubber bearing properties (natural period, damping ratio, and design displacement), and the paper does not extensively discuss the sensitivity of results to these parameters. Third, the study does not consider the interaction between the seismic isolation bearings and the arch's compressive load, which could affect bearing performance under combined seismic and gravity loading. Fourth, the lack of significant pre-failure deformation warning is a concerning finding that suggests the need for additional monitoring or protective measures in critical structures.

Study Insights and Implications

This paper provides valuable insights into the seismic performance of steel tubular arch truss structures and demonstrates the significant benefit of seismic isolation bearings for enhancing structural resilience. The 59.4% improvement in failure boundary acceleration is a compelling result that supports the adoption of seismic isolation technology for large-span steel structures in seismically active regions. However, the finding that both models fail by elastoplastic dynamic instability with limited pre-failure deformation warning underscores the need for comprehensive seismic design strategies that go beyond simple bearing selection. The study's methodology—combining nonlinear dynamic analysis with plastic hinge theory—provides a practical framework for evaluating the seismic performance of similar structures, and the results contribute to the growing body of knowledge on seismic design of large-span steel structures.