Lateral Nonlinear Deformation Analysis of Super-Tall SRC Stiffened Pier Continuous Rigid Frame Bridge During Construction

Literature Overview

This 2010 paper by Xu Tengfei, Zhao Renda, and Zhan Yulin from Southwest Jiaotong University, published in China Foreign Highway (Vol. 30, No. 4), presents a nonlinear finite element analysis of the lateral deformation behavior during the construction of a super-tall pier continuous rigid frame bridge with steel tube concrete (SRC) stiffening skeleton. Funded by Sichuan Transportation Science and Technology Project (2006A24-602) and Southwest Jiaotong University Science Development Fund (2007A06), the study addresses a critical construction-phase stability concern that has become increasingly relevant as bridge designs push toward taller piers and more complex geometries.

Core Technical Content

Structural System Description

The bridge studied features super-tall piers constructed with SRC stiffening skeleton technology, supporting a continuous rigid frame bridge with a curved main girder. The SRC stiffening skeleton piers consist of:

• Outer steel tubes (typically square or circular cross-section) forming the primary load-bearing structure
• Internal concrete infill providing compressive strength and fire protection
• Internal steel stiffeners (cross-diaphragms and horizontal ribs) enhancing the tube's resistance to local buckling
• Reinforced concrete infill that composites with the steel skeleton

The continuous rigid frame configuration means the piers and deck are monolithically connected, creating a structurally continuous system that transfers loads through both axial compression in the piers and bending in the deck-pier composite members.

Nonlinear Analysis Methodology

The authors established a nonlinear finite element model that accounts for:

• Geometric nonlinearity: Large displacements and rotations during construction stages, particularly relevant for tall slender piers where P-Δ effects become significant
• Material nonlinearity: Concrete cracking, steel yielding, and the composite action between steel tubes and concrete infill
• Construction sequence effects: The progressive erection of deck segments and the sequential placement of concrete in the SRC piers

Key Findings

1. Geometric nonlinearity has a pronounced effect on lateral deflection: The lateral displacement at the pier top under construction loads is significantly amplified by P-Δ effects, particularly during the maximum cantilever stage when the deck overhang creates the largest eccentric moment on the pier.
2. Lateral diaphragms (cross-bracing) should be installed before the main deck: The study demonstrates that installing lateral connecting beams between adjacent piers before the main deck construction significantly improves overall lateral stiffness and reduces geometric nonlinear effects. This is a crucial construction sequencing recommendation.
3. The curved main girder introduces additional torsional components: The curvature of the deck creates torsional moments that interact with the lateral bending of the piers, requiring three-dimensional nonlinear analysis rather than simplified two-dimensional models.
4. Maximum lateral displacement occurs at the maximum cantilever stage: The construction stage with the longest cantilever overhang produces the most critical lateral deformation, and this stage should be the design-basis condition for construction monitoring.

Construction Sequence Optimization

Based on the nonlinear analysis results, the following construction sequence optimization is recommended:

1. Construct pier foundations and lower pier sections first
2. Install lateral diaphragms and cross-bracing between piers at early stages
3. Erect the deck from the center span outward (or from the longest span outward, depending on the specific design)
4. Monitor pier top lateral displacement continuously during deck erection
5. Apply temporary supports or prestressing to control excessive lateral deflection during critical stages
6. Complete deck closure and release construction constraints in a controlled sequence

Implications for Steel Tube Fabrication and Welding

The SRC stiffening skeleton piers described in this study impose demanding requirements on steel tube fabrication and welding:

• Large-diameter square or rectangular tubes: These are typically fabricated from thick plate sections (16–40 mm) welded into box shapes. The welds must achieve full penetration and full-strength joints, requiring qualified welding procedures with appropriate preheat temperatures (150–250°C for thick sections) and post-weld heat treatment.
• Internal stiffener welding: The cross-diaphragms and stiffener plates welded internally to the steel tube walls must be designed to prevent local buckling of the tube walls between stiffener points. The welding sequence should be planned to minimize residual stresses and distortion, using techniques such as symmetric welding, back-step welding, and stress-relief welding.
• Welding residual stress management: In SRC piers, the welding residual stresses in the steel skeleton are partially relieved by the concrete infill, but uncontrolled residual stresses can lead to premature local buckling under compressive loads. Stress-relief heat treatment or vibration stress relief may be applied to critical welds.
• Concrete placement coordination: The concrete infill must be placed in stages to avoid excessive hydrostatic pressure on the steel tube walls during placement. The steel tube must be designed to resist the concrete placement pressure (typically 15–25 kPa per meter of concrete head) without excessive deformation.

Engineering Practice Recommendations

For projects involving super-tall SRC stiffened skeleton piers, the following engineering practice recommendations emerge from this study:

• Conduct nonlinear finite element analysis at all construction stages, not just the final service condition
• Implement real-time monitoring of pier top lateral displacement, inclination, and strain during construction
• Establish acceptable displacement thresholds and define corrective actions for exceeding these thresholds
• Design the lateral diaphragm system with adequate stiffness to provide effective cross-bracing between piers
• Consider the interaction between the SRC pier behavior and the deck construction sequence in the overall construction planning
• Perform wind load analysis for the construction stages, as tall piers under construction are vulnerable to wind-induced lateral forces before the full deck system provides aerodynamic stability

This research underscores the importance of construction-phase analysis in modern bridge engineering, particularly for complex structural systems where the construction sequence significantly influences the final structural performance and safety.