Seismic Damage Analysis of Flying-Swallow Steel Tube Concrete Arch Bridges Under Traveling Wave Effect

Literature Overview

The paper by Liu Zhen, Han Xiaoyu, and Zhang Zhe from Dalian University of Technology investigates the seismic damage behavior of a large-span flying-swallow steel tube concrete (STC) arch bridge subjected to traveling wave effects. The study is funded by the National Natural Science Foundation of China (Grant No. 51178080) and published in the Journal of Sichuan University (Engineering Science Edition), Volume 47, Issue 6, 2015. The research employs numerical simulation methods using a 280 m main-span flying-swallow STC arch bridge as the structural sample and the Jiji earthquake record from Taiwan as the seismic input. The selection of a near-fault earthquake record containing higher long-period pulse components is a deliberate choice to amplify the traveling wave effect on the bridge structure.

Core Findings and Technical Analysis

The central finding of this research is that while the bridge satisfies seismic design requirements under uniform (synchronous) ground motion, the inclusion of traveling wave effects causes the structure to fail to fully comply with the "small earthquake, no damage" design principle. The overall damage increase due to traveling wave effects is approximately 21%. This is a critically important finding for the design of long-span bridges where the spatial variation of ground motion becomes significant.

Traveling Wave Effect Mechanism

The traveling wave effect arises because seismic waves propagate across the bridge length with a time delay, causing different bridge piers and supports to experience ground motion at different phases. For a 280 m span bridge, even at typical apparent wave velocities of 300–500 m/s, the time delay between supports can reach 0.56–0.93 seconds, which is significant relative to the fundamental period of the structure. The Jiji earthquake record was specifically chosen because it contains strong long-period pulse components that interact constructively with the traveling wave phase differences.

Key Technical Parameters

Implications for Steel Tube Concrete Design

From a materials and fabrication standpoint, the 21% damage increase has direct implications for the design of the steel tubes forming the arch ribs. The steel tubes in STC arch bridges must be designed not only for gravity and thermal loads but also for the additional cyclic stresses induced by traveling wave effects. The steel tubes typically used in such applications are made from low-carbon structural steel conforming to GB/T 1591 or ASTM A572, with wall thicknesses ranging from 20 to 60 mm depending on the span and load conditions. The additional damage implies that fatigue life assessment of the steel tube-to-concrete interface and the weld connections between steel tube segments must incorporate the traveling wave-induced stress cycles.

Engineering Practice Implications

For engineers involved in the fabrication and welding of steel tubes for large-span STC bridges, this research underscores several practical considerations. First, the steel tube segments and their butt-welded or TIG-welded joints must be designed with adequate fatigue margins to accommodate the additional cyclic loading from traveling wave effects. Second, the internal concrete filling of the steel tubes must be designed to maintain bond integrity under the combined action of axial compression and the additional bending moments induced by spatially varying ground motion. Third, quality control of the steel tube manufacturing process, including hydrostatic testing and non-destructive examination of welds, must be maintained to the highest standards because any pre-existing defects could be exacerbated by the additional damage mechanisms identified in this study.

Study Insights and Reflections

This paper is significant because it bridges the gap between structural dynamics research and practical bridge engineering. The 21% damage increase is not merely an academic number; it translates into real requirements for material selection, weld quality, and inspection protocols in the fabrication of steel tubes for long-span bridges. Engineers should recognize that the traveling wave effect is not a rare phenomenon but a systematic consideration for any bridge exceeding approximately 100 m in span. The research methodology, using near-fault earthquake records with pronounced long-period pulses, represents a conservative but appropriate approach for design verification. Future work should extend these findings to include the effects of soil-structure interaction and the specific contribution of different bridge components, including the steel tube arch ribs, to the overall seismic damage.