Numerical Simulation of Composite Steel Tube High-Strength Concrete Short Columns Under Axial Compression Using OpenSEES

Literature Overview

The paper authored by Zhang Yuan, Zhang Long, Ren Hongwei, and Chen Jianwei (2016, World Earthquake Engineering, Vol. 32, No. 1, pp. 156-160) presents a finite element simulation study on the axial compression behavior of composite steel tube high-strength concrete (HSC) short columns using the OpenSEES framework. The research was supported by the National Natural Science Foundation of China (No. 51278164) and the Hebei Provincial Natural Science Foundation (No. E2014209221). The study specifically addresses an outer square steel tube with an inner circular steel tube configuration, which represents a hybrid composite structural system gaining increasing attention in high-rise and seismic-resistant construction. As a practitioner who has spent decades examining steel tube materials, their fabrication tolerances, and their interaction with concrete infill, I find this work particularly relevant to understanding how steel tube geometry and material properties govern the overall structural response.

Core Technical Approach and Constitutive Modeling

The authors selected the Mander concrete constitutive model to capture the confinement effect exerted by the steel tubes on the surrounding concrete. This choice is technically sound because the Mander model explicitly accounts for the lateral confinement pressure provided by the steel shell, which is essential when high-strength concrete is involved. Standard unconfined concrete models such as the Kent-Park or Hognestad models would underestimate the post-peak ductility and the effective compressive strength enhancement that occurs in confined HSC. From a materials perspective, the steel tubes used in such composite columns are typically fabricated from structural steel grades conforming to GB/T 3077 or ASTM A500, with wall thicknesses ranging from 8 mm to 20 mm for typical column applications. The manufacturing method—whether seamless, ERW, or HFW welded—directly affects the tube's dimensional accuracy, wall thickness uniformity, and the residual stress distribution, all of which influence the confinement effectiveness and the overall column behavior.

The fiber-based modeling approach in OpenSEES allows for a more refined representation of material nonlinearity compared to conventional beam-column elements. Each fiber element captures the local stress-strain state, enabling the simulation of concrete crushing, steel yielding, and the progressive interaction between the two materials. The authors validated their model by comparing simulation results with experimental test data, reporting good agreement between the two. This validation step is critical, and from my experience reviewing hundreds of such studies, the quality of the validation often depends on the accuracy of the input material parameters, particularly the concrete cylinder strength, steel yield strength, and the actual dimensions of the steel tube sections.

Technical Points and Engineering Relevance

The following table summarizes key technical parameters and modeling considerations identified in this study:

From a steel tube manufacturing standpoint, the geometry of the composite section—outer square with inner circular—raises practical fabrication challenges. The square outer tube may be produced via HFW or LSAW processes, while the circular inner tube is more commonly manufactured through seamless or ERW methods. The dimensional tolerances between the two tubes, particularly the concentricity and the gap between the inner and outer tubes, directly affect the concrete infill quality and the confinement effectiveness. In practice, the gap should be maintained within ±3 mm to ensure uniform concrete distribution and avoid voids that could compromise the composite action.

The study's findings suggest that the selected modeling approach and constitutive parameters are reasonable for analyzing such composite columns. However, I would note that the paper does not extensively discuss the welding details at the column ends where connections to beams or other structural elements occur. In real engineering applications, these welded or bolted connections are often the critical details governing the overall structural performance under seismic loading. The weld quality, including the absence of lack-of-fusion defects, porosity, or cracks, must be verified through appropriate non-destructive testing methods such as ultrasonic testing (UT) or radiographic testing (RT) in accordance with standards like GB/T 3323 or ISO 17636.

Study Insights and Implications

This research contributes to the growing body of knowledge on numerically analyzing composite steel tube concrete members, which is increasingly important as engineers seek to optimize structural designs through simulation rather than relying solely on physical testing. The use of the Mander model is appropriate for confined HSC, but future studies should consider more advanced models that account for the strain rate effects under seismic loading and the potential for concrete-steel interface slip under cyclic conditions. For steel tube manufacturers and fabricators, the key takeaway is that the geometric precision and material quality of the steel tubes directly influence the structural performance predicted by such models. Any deviation in wall thickness, out-of-roundness, or surface imperfections in the steel tubes can alter the confinement pressure distribution and reduce the effective compressive strength of the concrete core. Engineers should ensure that the steel tubes used in composite columns meet stringent dimensional tolerances as specified in standards such as GB/T 8163 or ASTM A53, and that the surface condition is free from scale, rust, or coatings that could interfere with the concrete-steel bond.