Seismic Response Performance of Large-Span Steel Tube Concrete Arch Bridge

Literature Overview

The paper by Zheng Shixiong, Zhou Shuhua, and Ding Guibao from Southwest Jiaotong University, published in the Journal of Southwest Jiaotong University in 1999, examines the seismic response of a large-span steel tube concrete (STC) tied arch bridge with a span configuration of (76 + 360 + 76) meters. This research is particularly significant given the growing number of long-span bridges constructed in seismic regions worldwide, and the specific focus on traveling wave effects, which are often neglected in conventional seismic design procedures.

Core Technical Content

The study establishes a detailed analysis model for the specific bridge and examines its dynamic characteristics and seismic response under earthquake excitation. A key finding is that the seismic response internal forces at the mid-span section of the main arch rib are relatively small, while the internal forces at the arch foot section and sections at l/4 to 3l/8 locations are comparatively larger. This distribution pattern has important implications for the seismic design of arch bridges, as it suggests that the most critical sections for seismic detailing are not at the mid-span but rather at the supports and intermediate locations.

The traveling wave effect was investigated by varying the wave propagation velocity. The results indicate that considering the traveling wave effect generally increases vertical displacement and axial force while reducing lateral displacement. This is a counterintuitive finding that challenges conventional assumptions about seismic response amplification.

Key Technical Parameters and Findings

Analysis Aspect	Finding	Engineering Implication
Mid-span section forces	Relatively small seismic internal forces	Less critical for seismic detailing
Arch foot section forces	Relatively large seismic internal forces	Requires robust seismic design and detailing
l/4 to 3l/8 sections	Relatively large seismic internal forces	Important intermediate locations for design consideration
Traveling wave effect on vertical displacement	Increased	Must be considered in design for vertical response
Traveling wave effect on axial force	Increased	Affects compression members and connection design
Traveling wave effect on lateral displacement	Decreased	May provide some benefit in lateral response

The traveling wave effect refers to the phenomenon where seismic waves do not arrive simultaneously at all supports of a long-span structure. For bridges with spans exceeding several hundred meters, this effect becomes significant because the time difference in wave arrival can induce additional internal forces and deformations. The study demonstrates that neglecting this effect can lead to inaccurate predictions of seismic response.

Engineering Practice Implications

For the fabrication and welding of steel tube concrete arch bridges, the findings have direct implications for connection design. The arch foot sections, which experience the largest seismic internal forces, require particularly robust welded or bolted connections between the arch rib segments. In steel tube concrete arch construction, the arch ribs are typically fabricated in segments and erected using incremental launching or cable-stayed methods. The segment joints must be designed to accommodate both the gravity loads and the seismic forces identified in this study.

The welding quality at segment splices is critical because these locations experience high stress concentrations under seismic loading. Full-penetration groove welds with appropriate preheat and post-weld heat treatment are essential to ensure adequate toughness and fatigue resistance. Non-destructive testing, including ultrasonic testing (UT) and magnetic particle testing (MT), should be performed on all critical welds to detect any volumetric or surface defects that could initiate fracture under cyclic seismic loading.

Study Insights and Reflections

This research highlights an important gap in conventional seismic design practice, which often assumes synchronous ground motion at all supports. For long-span bridges, the traveling wave effect can significantly alter the seismic demand, and designers should consider site-specific wave propagation characteristics. The finding that mid-span sections experience smaller seismic forces is somewhat reassuring, as these sections are typically more difficult to access for inspection and repair. However, the emphasis on arch foot sections reinforces the importance of robust foundation design and detailed seismic connection design at the supports. The study provides a valuable analytical framework that can be adapted for other long-span steel tube concrete arch bridges in seismic regions.