Ultimate Bearing Capacity of Prefabricated Circular Semi-Continuous Steel Tube Concrete Columns

Literature Overview

This paper by Qian Huashan and colleagues, published in the Journal of Anhui Polytechnic University in 2025, presents an experimental and analytical investigation of the eccentric compression behavior of prefabricated circular semi-continuous steel tube concrete (SC) columns. Funded by the Anhui Provincial Natural Science Foundation (2408085ME122) and the Anhui Provincial Key University Natural Science Research Program (KJ2021A0504), the study conducts ten eccentric compression tests and develops a multi-component coupled system analysis method to predict the ultimate bearing capacity. The work addresses a growing need in the construction industry for prefabricated structural systems that combine the speed of assembly with the structural performance of conventional monolithic construction.

Core Technical Content

The prefabricated circular semi-continuous SC column system comprises an upper steel tube segment, a lower steel tube segment, an outer sleeve tube, and connecting bolts, with concrete core fill. The "semi-continuous" designation indicates that the steel tube is not fully continuous at the joint but is instead connected through mechanical fastening (bolts) and an outer sleeve, while the concrete core provides the primary load-bearing continuity.

Multi-Component Coupled System Analysis Method

The authors introduce a multi-component coupled system analysis method that decomposes the column into core and secondary components. The core concrete is identified as the primary load-bearing component, while the upper (lower) steel tube, outer sleeve tube, and bolts are classified as secondary components. The load transfer path is traced from the upper steel tube through the bolts to the outer sleeve tube and then to the lower steel tube. This decomposition allows for a systematic evaluation of the failure mode of each component and its interaction with adjacent components.

The following table summarizes the component classification and their respective roles:

Three Primary Failure Modes

The experimental results identify three dominant failure modes:

1. Local buckling: Occurs at low slenderness ratios where the steel tube wall buckles inward due to the lateral pressure from the surrounding concrete. The buckling initiates at the location of maximum bending moment, typically near the mid-height of the column.
2. Overall buckling accompanied by local buckling: At intermediate slenderness ratios, the column experiences lateral displacement leading to overall flexural buckling, with local buckling of the steel tube occurring at the inflection points of the deflected shape.
3. Instability failure: At high slenderness ratios, the column fails by elastic or inelastic overall buckling before significant local deformation develops. The failure is characterized by a sudden lateral displacement with limited energy dissipation.

Welding and Fabrication Implications

Although the prefabricated system relies primarily on bolted connections rather than field welding, the fabrication of the individual components—steel tubes, outer sleeves, and bolted splices—requires careful attention to welding quality. The steel tubes are typically manufactured by electric resistance welding (ERW) or high-frequency welding (HFW) processes, and the outer sleeve tubes may be longitudinally submerged-arc welded (LSAW) for larger diameters. The weld quality of these components directly affects the structural performance of the assembled column.

For the bolted splice connections, the contact surfaces between the upper tube end and the outer sleeve must be machined to a flatness tolerance of ±0.5 mm to ensure full bearing contact. Any surface irregularity creates a stress concentration that can initiate fatigue cracking under cyclic loading. The bolt pre-tensioning force must be calibrated to achieve the specified friction grip capacity, typically 70–80% of the bolt's proof load per GB/T 1231 or ASTM A325.

The following table presents typical fabrication parameters for the components of a prefabricated SC column:

Prediction Method and Validation

The proposed prediction method considers the dimensions, failure modes, and ultimate bearing capacities of individual components to derive the overall eccentric compression capacity of the column. The validation results show that the ratio of predicted to experimental ultimate load (P_pre-u / P_u) has a mean value of 0.970 and a variance of 0.0005, indicating that the predictions are slightly conservative and highly consistent. This level of accuracy is comparable to established design methods in GB 50010 or ACI 318 for conventional SC columns.

Study Insights and Engineering Practice

The multi-component coupled system analysis method represents a significant advancement in the analytical treatment of prefabricated SC columns. By explicitly accounting for the interaction between primary and secondary components, the method captures the progressive failure mechanism that occurs when one component yields and redistributes load to adjacent components. This is particularly important for the bolted splice connections, where the load redistribution from the upper tube to the outer sleeve through the bolts creates a complex stress state that is not captured by simple superposition models.

From a quality control perspective, the prefabricated SC column system demands rigorous inspection of both the individual components and the assembled joint. The concrete core must be placed without voids, as void defects significantly reduce the bearing capacity and ductility of the column, as demonstrated in related research on void-defective SC columns. The bolted connections must be inspected for proper pre-tensioning using magnetic flux leakage (MFL) or ultrasonic bolt tension measurement techniques. The outer sleeve tube must be verified for dimensional accuracy to ensure proper fit with the inner tube segments.

The practical significance of this work lies in its potential to accelerate the adoption of prefabricated SC columns in multi-story industrial and commercial buildings. The combination of factory-controlled fabrication quality and field assembly speed offers a compelling alternative to conventional monolithic construction, provided that the analytical methods for predicting structural performance are sufficiently accurate and reliable. The proposed prediction method, with its demonstrated accuracy and conservative bias, provides the analytical foundation necessary for code acceptance of this structural system.