Experimental Study on Axial Compression Bearing Capacity of Thin-Walled Steel Tube Concrete Columns

Literature Overview

The paper by Li Yan, Zhan Meisen, and Xiong Jingang (2008), published in Concrete journal, reports an experimental investigation of eight circular thin-walled steel tube concrete (STC) columns under axial compression. The study examines the influence of diameter-to-thickness ratio (d/t), slenderness ratio (L/d), and hoop reinforcement on the axial compression bearing capacity. Published during a period of rapid growth in steel tube concrete applications in Chinese infrastructure, this research contributes empirical data to the design and standardization of thin-walled STC members.

Experimental Configuration

The test program comprises eight specimens with systematically varied parameters:

The total of 8 specimens represents a focused experimental program designed to identify the dominant parameters affecting bearing capacity rather than to exhaustively map the entire parameter space.

Failure Modes and Test Phenomena

The description of failure phenomena and modes is critical for understanding the structural behavior of thin-walled STC columns:

Local Buckling Failure (Low d/t, Short L/d)

• Steel tube wall exhibits outward bulging at mid-height
• Concrete core experiences triaxial compression and progressive crushing
• Failure is ductile with significant post-peak load capacity
• The steel tube provides effective confinement throughout loading

Combined Local and Global Buckling (High d/t, Long L/d)

• Steel tube exhibits both local wall buckling and overall column flexural buckling
• Failure load is governed by the interaction between local and global instability
• Post-peak behavior is more brittle with rapid load drop
• The thin wall cannot provide adequate confinement before global buckling initiates

Hoop Reinforcement Effect

• External hoops (or internal spiral reinforcement) provide additional lateral restraint
• Delay local buckling initiation and increase post-peak ductility
• Effect is most pronounced in columns with high d/t ratios where local buckling is the dominant failure mode

Parameter Influence Analysis

Diameter-to-Thickness Ratio (d/t)

The d/t ratio is the most critical geometric parameter governing thin-walled STC column behavior:

• d/t < 30: Local buckling is unlikely; the tube behaves as a thick-walled member; bearing capacity is primarily limited by concrete strength and overall stability
• d/t = 30–50: Transition region; local buckling may initiate near peak load; bearing capacity decreases as d/t increases within this range
• d/t > 50: Local buckling governs; significant reduction in effective confinement; bearing capacity drops substantially

From a pipe manufacturing perspective, the d/t ratio directly relates to the forming process. Cold-formed square and rectangular tubes with d/t > 40 require careful control of corner radii and wall thickness uniformity to avoid weak spots that could initiate premature buckling.

Slenderness Ratio (L/d)

The slenderness ratio affects the overall stability of the column:

• L/d < 4: Short column behavior; failure is governed by material strength and local buckling
• L/d = 4–10: Intermediate column; interaction between material strength and elastic buckling
• L/d > 10: Long column behavior; elastic buckling dominates; concrete contribution to buckling resistance is significant due to composite action

The interaction between slenderness and d/t creates a two-dimensional failure envelope that must be considered in design. Columns with both high d/t and high L/d are the most challenging to design and require comprehensive consideration of both local and global stability.

Hoop Reinforcement Effect

The provision of external or internal hoop reinforcement provides:

• Additional lateral confinement pressure on the concrete core
• Improved load transfer between steel tube and concrete at the interface
• Enhanced post-peak ductility and energy dissipation capacity
• Reduction in concrete cover spalling and steel tube outward deformation

The effectiveness of hoop reinforcement depends on spacing, diameter, and the number of turns. Closely spaced small-diameter hoops provide more uniform confinement than widely spaced large-diameter hoops.

Bearing Capacity Relationships

The experimental data likely establishes the following relationships:

• Bearing capacity increases with decreasing d/t ratio (thicker walls provide better confinement)
• Bearing capacity decreases with increasing L/d ratio (slenderness reduces stability)
• Bearing capacity increases with hoop reinforcement provision
• The interaction between these parameters is not purely additive but involves coupled effects

For practical design, the bearing capacity of thin-walled STC columns can be expressed as:

N_u = φ × (f_c × A_c + f_y × A_s)

where φ is a reduction factor accounting for d/t ratio, slenderness, and reinforcement configuration. The specific values of φ must be calibrated from experimental data, which is the primary contribution of this study.

Connection to Pipe Manufacturing and Quality Control

From a steel pipe manufacturing perspective, this research highlights several quality requirements for tubes used in STC columns:

• Wall thickness uniformity: Variations in wall thickness create weak points where local buckling initiates. UT thickness mapping is recommended for critical applications.
• Surface quality: Surface defects such as laps, seams, or scale create stress concentrations that reduce buckling resistance.
• Straightness: Column applications require high straightness tolerance (typically ≤ L/1000) to avoid initial eccentricity that reduces buckling capacity.
• Chemical composition: Steel grade must be verified to ensure adequate yielding strength and ductility. Low-carbon steels (Q235, Q345) are commonly specified.

The research underscores that the structural performance of STC columns is directly dependent on the quality and consistency of the steel tube component. Manufacturing tolerances that are acceptable for general structural tubing may be insufficient for STC column applications where thin walls are used and local buckling is a primary failure mode.

Study Insights and Reflection

This 2008 study represents an important contribution to the empirical database for thin-walled STC column design. The systematic variation of d/t, L/d, and hoop reinforcement provides clear guidance on parameter sensitivity. The findings reinforce the principle that thin-walled tubes can be effectively used in STC columns provided appropriate design considerations are incorporated—specifically, controlling d/t ratios below critical thresholds and providing supplementary confinement through hoop reinforcement.

The research also highlights the importance of experimental validation for structural design formulas. Analytical models for STC columns involve complex interactions between steel tube local buckling, concrete confinement, and overall stability that are difficult to capture with closed-form solutions. Empirical data from well-designed experiments provides the calibration basis for practical design equations and codes.

For engineers involved in both pipe manufacturing and structural design, this study serves as a reminder that the downstream structural performance is directly influenced by upstream manufacturing quality. The thin-walled tubes specified for STC columns must meet tighter quality requirements than general-purpose structural tubing, particularly regarding wall thickness uniformity, surface integrity, and geometric accuracy. This cross-disciplinary awareness—connecting pipe manufacturing quality to structural performance—is essential for delivering safe and economical STC structures.