Finite Element Study on Axial Compression Mechanical Properties of Square Steel Tube Recycled Aggregate Concrete Under Acid Rain Environment

Literature Overview

This paper by Chen Mengcheng, Wang Chao, Huang Hong, and Liu Jingjian (2016), published in Concrete (No. 12, pp. 1-4), investigates the axial compression behavior of square steel tube recycled aggregate concrete (RAC) short columns subjected to acid rain corrosion. Using ABAQUS finite element software, the authors simulated the axial compression tests of 11 specimens and compared two modeling approaches for representing the acid rain corrosion effects: one considering wall thickness reduction and the other considering degradation of steel yield strength and elastic modulus. The research was supported by multiple national and provincial funding sources.

Core Technical Approach

The study adopts a dual-method approach to model the acid rain corrosion effects on square steel tube RAC columns. Method 1 accounts for the geometric degradation caused by corrosion, specifically the reduction in steel tube wall thickness. Method 2 accounts for the material property degradation, specifically the reduction in steel yield strength and elastic modulus due to corrosion. Both methods were implemented in ABAQUS and compared against experimental test results.

The simulation results show that both methods achieve an average deviation of approximately 5% from experimental values. However, Method 1 tends to overpredict the axial compression capacity, while Method 2 provides results that are on the conservative side and better matches the load-deformation relationship observed in experiments.

Technical Parameters and Modeling Comparison

Corrosion Mechanism Analysis

Acid rain corrosion of steel tubes involves both uniform corrosion and localized pitting corrosion. The uniform corrosion component reduces the wall thickness uniformly, which is captured by Method 1. The localized pitting corrosion creates stress concentrations and initiates cracks, while the chemical attack on the steel matrix reduces the effective yield strength and elastic modulus, which is captured by Method 2. The experimental results suggest that the material property degradation mechanism plays a more dominant role in the load-deformation behavior than the geometric reduction alone.

From a steel pipe manufacturing perspective, the corrosion resistance of the steel tube is influenced by the steel grade, surface treatment, and the welding quality of the tube. For square steel tube RAC columns, the weld seams at the corners are particularly vulnerable to acid rain corrosion because the weld metal typically has different corrosion resistance compared to the base metal. The heat-affected zone of the weld may exhibit reduced corrosion resistance due to microstructural changes induced by the welding thermal cycle.

Finite Element Model Development Considerations

The finite element model must accurately capture the following aspects: the nonlinear behavior of the recycled aggregate concrete, which typically exhibits lower strength and stiffness compared to natural aggregate concrete; the confinement effect of the square steel tube on the concrete core; the interaction between the steel tube and the concrete surface; and the corrosion-induced degradation of the steel tube properties. The contact formulation between the steel tube and the concrete is critical for accurately simulating the confinement effect, particularly as the column undergoes lateral expansion under axial compression.

The recycled aggregate concrete introduces additional complexity because the recycled aggregate typically has higher porosity and weaker interfacial transition zones compared to natural aggregate. This results in lower concrete strength, reduced elastic modulus, and potentially different failure modes compared to conventional concrete-filled steel tube columns.

Key Reflections and Engineering Implications

The finding that Method 2 provides more conservative and accurate predictions is significant for engineering design. It suggests that the material degradation effect of acid rain corrosion is more influential on the structural behavior than the geometric reduction effect. This has important implications for the corrosion protection strategy: rather than focusing solely on maintaining the original wall thickness through protective coatings, engineers should also consider the material property degradation and design with appropriate safety factors that account for the reduced steel strength and stiffness.

For the manufacturing of square steel tube RAC columns, the welding process must be carefully controlled to minimize the corrosion susceptibility of the weld zone. Post-weld heat treatment may be necessary to restore the corrosion resistance of the heat-affected zone. Additionally, the surface finish of the steel tube should be optimized to reduce the susceptibility to localized corrosion initiation.

Study Insights and Practical Recommendations

This research provides valuable guidance for the design and assessment of square steel tube RAC columns in corrosive environments. Engineers should adopt Method 2 for finite element analysis of acid rain-corroded CFST columns to ensure conservative and accurate predictions. The 5% average deviation achieved by both methods indicates that finite element analysis is a reliable tool for this application, provided that the corrosion model is properly calibrated. For long-term durability, a combined approach that addresses both geometric and material degradation should be adopted in the design process, supplemented by appropriate corrosion protection measures during fabrication and maintenance throughout the service life.