Zhuojin Pipe Fitting Co., LtdStatic Load Testing of a Concrete-Filled Steel Tube Tie-Arch Bridge
Literature Overview
This paper by Wang Hongnan, Liu Huabo, and Song Shuang, published in Journal of Highway and Transportation Research (2005, Vol. 22, No. 5, pp. 100–103), reports on the static load testing of a CFST tie-arch bridge with a 52-meter main span. The bridge was subjected to load testing due to concerns about its exterior quality, and the test program included measurement of load lateral distribution coefficients, strain influence lines, and deflection under static loading. The authors are affiliated with Shanghai Normal University, Shanghai Research Institute of Building Sciences, and Shandong University.
Core Technical Content
The bridge in question is a tie-arch configuration, where the arch ribs are concrete-filled steel tubes and the deck is suspended by vertical hangers connected to a tie beam. The main span of 52 meters is moderate for a CFST arch bridge, but the structural behavior is sensitive to the quality of the steel tube fabrication, welding, and concrete infilling.
Test Program Design
The static load test was designed using three identical container trucks as loading vehicles. The test program included:
| Test Item | Location | Purpose |
|---|---|---|
| Load lateral distribution coefficient | Mid-span and quarter-span | Verify load sharing between arch ribs |
| Strain influence lines | Key control sections | Characterize structural response under moving loads |
| Strain measurement | Control sections under basic loading | Compare measured vs. calculated stresses |
| Deflection measurement | Mid-span and other critical points | Verify serviceability under design loads |
Measurement Setup
Strain gauges were installed at critical sections of the steel tubes, including at weld joints, at the arch crown, springing, and quarter-span points. Displacement sensors measured deflection at mid-span and at the deck level. The measurement points were selected to capture the maximum stresses and deformations expected under the test loading.
Interpretation of Technical Points
The decision to perform load testing was triggered by concerns about exterior quality. In CFST bridge construction, exterior quality issues often indicate deeper problems, such as incomplete concrete infilling, poor welding quality, or inadequate surface preparation. The static load test serves as a verification of structural capacity, but the results must be interpreted in the context of the construction quality.
From a steel pipe engineering standpoint, the strain measurements at weld joints are particularly informative. If the measured strains at weld locations significantly exceed the calculated values, it may indicate stress concentrations due to weld geometry or residual stresses. The strain influence lines provide insight into how the structure distributes loads, which is critical for assessing the effectiveness of the composite action between steel and concrete.
Defect Analysis
| Observation | Possible Cause | Implication |
|---|---|---|
| Higher-than-expected strain at weld joints | Stress concentration at weld toes | Potential fatigue concern under cyclic loading |
| Asymmetric deflection between arch ribs | Differential concrete fill quality | Indicates incomplete infilling in one rib |
| Higher lateral distribution coefficient than predicted | Stiffer deck than assumed | May indicate over-conservative design |
| Strain at arch crown exceeds code limit | Concrete-steel interface slip | Composite action not fully developed |
Integration with Engineering Practice
The load test results provide valuable data for calibrating analytical models of CFST arch bridges. However, the results should be interpreted with awareness of the steel pipe manufacturing and welding history. For example, if the steel tubes were manufactured using spiral welding rather than longitudinal welding, the stress distribution at the weld seam would differ, potentially affecting the strain measurements. The welding procedure specification (WPS) and the weld quality records should be reviewed alongside the test results to form a complete picture of structural performance.
The static load test is a form of structural verification that complements non-destructive testing (NDT) of welds. While NDT identifies local defects in welds, load testing reveals the global structural response, including the effects of defects that may have escaped NDT detection. Engineers should use both approaches in a complementary manner: NDT for local quality assurance and load testing for global performance verification.
Key Reflections
This case underscores the importance of construction quality in CFST structures. A bridge that appears deficient in exterior quality may still possess adequate structural capacity, as confirmed by load testing, but the appearance issues may indicate systematic problems in the construction process. The load test results should be used not only to verify capacity but also to diagnose construction quality issues that may affect long-term durability. For steel pipe engineers, the lesson is that the quality of the final structure is the product of manufacturing quality, welding quality, concrete quality, and construction workmanship, and any weakness in one area can compromise the whole.