Axial Compression Performance of Anti-Debonding Prefabricated Square Steel Pipe Concrete Column with Finite Element Analysis

Literature Overview

This study addresses a well-recognized weakness in concrete-filled steel tube (CFST) columns: the tendency for the concrete core to debond from the steel tube walls under high compressive loads, particularly in square or rectangular sections where the stress distribution is inherently non-uniform. The research proposes a novel anti-debonding mechanism in a prefabricated square CFST column and validates its effectiveness through both axial compression tests and three-dimensional finite element analysis.

Core Technical Content

The anti-debonding mechanism typically involves one or more of the following approaches:

Internal shear studs or ribs: Welded to the inner surface of the steel tube to mechanically interlock with the concrete.
Surface roughening: Thermal cutting or shot blasting of the tube interior to increase frictional bond.
Preliminary concrete layer: A thin, high-strength concrete layer applied to the tube interior before the main concrete pour to create a keying effect.
Geometric interlock: Internal corrugations or protrusions formed during tube manufacturing.

Key Technical Parameters

Parameter	Specification
Square tube cross-section	300 × 300 mm to 500 × 500 mm
Wall thickness	8–14 mm
Steel grade	Q345B / Q355B
Concrete strength	C40–C60
Height-to-width ratio	3.0–4.5
Shear stud diameter (if used)	12–16 mm
Shear stud spacing	100–200 mm

Finite Element Modeling Approach

The finite element analysis (FEA) typically employs the following modeling strategy:

Element selection: 8-node solid elements (C3D8R) for concrete and shell elements (S4R) for the steel tube.
Concrete model: Concrete Damaged Plasticity (CDP) model calibrated with uniaxial and triaxial compression test data.
Steel model: Von Mises yield criterion with isotropic hardening, using the true stress-strain curve obtained from coupon tests.
Interface modeling: Cohesive zone elements or penalty-based contact with friction coefficient of 0.3–0.5 to simulate bond behavior.
Anti-debonding representation: Shear studs modeled as embedded reinforcement or as discrete spring elements connecting the tube interior to the concrete.

FEA vs. Experimental Results Comparison

Parameter	Experimental	FEA	Deviation
Ultimate load	100%	95–105%	±5%
Peak displacement	100%	90–100%	±10%
Initial stiffness	100%	95–100%	±5%
Failure mode	Consistent	Consistent	Qualitative match

Engineering Practice Implications

The prefabricated nature of the column system has significant implications for construction methodology:

Factory fabrication: The square steel tube with anti-debonding features can be manufactured and quality-inspected in a controlled workshop environment.
Transport and erection: Prefabricated segments are transported to site and erected using crane-assisted methods, reducing on-site labor and weather exposure.
Concrete placement: In prefabricated systems, the concrete is often cast in a vertical mold around the erected tube, or the tube is prefilled in the factory. The latter is preferred for quality consistency.
Segment joint design: Field-welded butt joints between prefabricated segments must maintain structural continuity. The weld design should follow ASME B31.3 or GB/T 19421, with full-penetration groove welds and 100% radiographic testing for critical connections.

Defect Analysis and Quality Control

Using a FMEA (Failure Mode and Effects Analysis) approach, the following potential failure modes are identified:

Failure Mode	Severity	Occurrence	Detection	RPN	Mitigation
Incomplete concrete fill	8	3	5	120	Ultrasonic testing during curing
Debonding at corners	7	4	4	112	Anti-debonding studs at corners
Weld defect at segment joint	9	2	3	54	100% RT of all butt welds
Tube wall thinning	6	3	4	72	UT thickness survey pre-fabrication
Concrete shrinkage cracking	5	4	5	100	Controlled curing and low-shrinkage mix

Study Insights and Reflections

The anti-debonding concept is particularly important for square and rectangular CFST columns because the stress concentration at internal corners creates preferential debonding paths. In circular CFST columns, the uniform radial confinement naturally resists debonding, but in square sections, the corners experience significantly higher radial pressure gradients.

The integration of FEA with experimental validation provides a robust design methodology. However, engineers should recognize that FEA results are only as good as the input material models. The concrete damaged plasticity model parameters (tension stiffening, dilation angle, fracture energy) must be calibrated against experimental data for the specific concrete mix used.

From a fabrication standpoint, the anti-debonding features (studs, ribs, corrugations) add complexity to the steel tube manufacturing process. If welded studs are used, the welding sequence must be planned to minimize residual stress distortion of the square tube. Post-weld stress relief or controlled cooling may be necessary for thick-walled sections.