Seismic Performance of Steel Tube Concrete Composite Column with Embedded Steel Truss Core Tube

Literature Overview

This study by Dong Hongying et al. (2011), published in Journal of Earthquake Engineering and Engineering Vibration (Vol. 31, No. 1, pp. 41-47), investigates the seismic behavior of a novel composite core tube system that integrates steel tube concrete (CFST) composite columns with an embedded steel truss within the frame border. The research was conducted at Beijing University of Technology's School of Civil and Architectural Engineering and the Key Laboratory of Urban and Engineering Safety and Disaster Prevention, and was supported by multiple national and municipal research funding programs.

Structural Configuration and Test Setup

The study proposed a hybrid structural system where the conventional reinforced concrete core tube is combined with a CFST composite column frame border and an internal steel truss. Two 1/6 scale models were tested under low-cycle reversed loading to simulate seismic conditions:

The 1/6 scale factor was selected to balance structural representativeness with practical testing constraints. Low-cycle reversed loading was applied to evaluate the hysteretic behavior, energy dissipation capacity, and ductility of both models under simulated seismic loading.

Key Test Results

The comparative analysis revealed several important findings regarding the seismic performance of the two configurations:

The embedded steel truss played a critical role in improving the overall seismic response. The truss effectively distributed the seismic forces more uniformly across the core tube structure, reducing localized stress concentrations that typically lead to premature failure in conventional RC core tubes. The CFST composite columns at the frame border provided additional strength and ductility, while the steel truss within the core tube enhanced the overall system integrity and energy dissipation capacity.

Bearing Capacity Calculation Model

A significant contribution of this study is the development of a bearing capacity calculation model for the proposed composite system. The authors derived analytical expressions that account for the interaction between the CFST columns, the steel truss, and the RC core tube. The calculation results showed good agreement with the measured values, validating the theoretical model. This is particularly important for practical engineering application, as it provides structural engineers with a reliable design tool for this novel system.

Engineering Practice Implications

For steel pipe and structural engineering professionals, this study has several important implications. First, it demonstrates that CFST columns — which are fabricated from steel pipes filled with concrete — can serve as effective structural elements in seismic-resistant building systems. The steel tubes used in CFST applications must meet specific requirements for formability, weldability, and mechanical properties, typically conforming to standards such as GB/T 8163, EN 10216-1, or ASTM A53/A106.

Second, the steel truss embedded within the core tube introduces additional fabrication and erection challenges. The truss members, typically fabricated from steel pipes or structural sections, require precise welding and connection details. From a welding perspective, the truss connections must be designed to accommodate the complex stress states that develop during seismic loading, including cyclic tension-compression reversals. Weld quality and connection detailing are therefore critical to the overall seismic performance.

Third, the study highlights the importance of system-level thinking in structural design. Rather than optimizing individual components in isolation, the proposed system achieves superior performance through the synergistic interaction of multiple structural elements. This systems approach is consistent with modern seismic design philosophy, which emphasizes ductility, redundancy, and progressive collapse resistance.

Key Reflections

The integration of steel trusses within reinforced concrete core tubes represents an innovative approach to improving seismic performance. From a practical standpoint, the fabrication and installation of such trusses within a concrete core tube presents significant construction challenges. The truss must be erected within the confined space of the core tube, which may require careful planning of reinforcement layout, concrete placement sequence, and access for inspection.

The study's use of 1/6 scale models is a practical approach, but it is important to acknowledge the scale effects that may influence the test results. The material properties, particularly the concrete strength and steel yield stress, may behave differently at full scale compared to the 1/6 scale models. Additionally, the boundary conditions applied in the test may not perfectly replicate the actual structural behavior of a full-scale core tube system. These limitations should be considered when applying the findings to real engineering projects.

The bearing capacity calculation model developed in this study provides a valuable design tool, but its accuracy should be verified against full-scale test data before widespread adoption in practice. The good agreement between calculated and measured values at the 1/6 scale is encouraging, but full-scale validation would provide greater confidence in the model's predictive capability.

This study makes a meaningful contribution to the field of seismic-resistant structural engineering by demonstrating the effectiveness of a hybrid CFST-steel truss-RC core tube system. The proposed system offers a promising solution for improving the seismic performance of high-rise buildings with core tube structural systems, and the associated calculation model provides a practical basis for design application.