Seismic Performance of Conical Hollow Sandwich Steel Tube Concrete Compression-Bending Members

Literature Overview

This paper by Shi Yanli and colleagues from Lanzhou University of Technology, published in the Journal of Architecture and Civil Engineering in 2019 (Volume 36, Issue 5, pages 80-88), investigates the seismic behavior of conical hollow sandwich steel tube concrete (CHSC-SC) compression-bending members through numerical analysis. The research was supported by the National Natural Science Foundation of China (Project 51768038) and the Gansu Provincial University Collaborative Innovation Team Project (2018C-08). The authors employed ABAQUS finite element software to establish numerical models, validated against existing experimental data, and then conducted parametric studies on axial compression ratio, hollow rate, and slenderness ratio.

Core Technical Content

The conical hollow sandwich steel tube concrete section represents an innovative structural configuration that combines the advantages of steel tube confinement with the weight-reduction benefits of a hollow core. The conical geometry provides a gradual transition in cross-sectional properties, which is particularly advantageous for compression-bending members subjected to varying internal forces along their length.

Material Constitutive Models and Damage Criteria

The selection of appropriate material constitutive models is critical to the accuracy of any finite element analysis of composite steel-concrete members. The authors selected material models that account for the confined concrete behavior within the steel tube, considering the triaxial stress state that develops under lateral confinement. The concrete damage index was carefully chosen to reflect the progressive cracking and crushing behavior observed in experimental tests.

Parametric Analysis Results

The parametric study revealed several important trends regarding the seismic performance indicators, including hysteresis curve ultimate bearing capacity, ductility coefficient, and energy dissipation capacity.

The finding that hollow rate improvement enhances energy dissipation is somewhat counterintuitive at first glance, as one would expect a reduction in cross-sectional area to diminish overall capacity. However, the hollow core promotes a more uniform distribution of inelastic deformation along the member length, preventing premature localized crushing and thereby extending the effective plastic hinge length. This results in better overall energy dissipation despite the reduced section area.

Failure Modes Observed

The failure modes described in the paper follow the typical progression for steel tube concrete compression-bending members under cyclic loading. Initial cracking occurs in the concrete at the mid-span region where bending moments are maximum. As loading cycles accumulate, the steel tube begins to yield locally at the compression fiber, followed by progressive concrete crushing. The hollow core plays a role in redistributing the internal forces and delaying the onset of global instability.

Standards and Engineering Practice Integration

From a standards perspective, this research contributes to the understanding of non-uniform steel tube concrete members, which are not explicitly covered in most current design codes such as GB 50011-2010 (Code for Seismic Design of Buildings) or GB 50935-2014 (Technical Specification for Concrete-Filled Steel Tubular Structures). The conical geometry introduces additional complexity in terms of stress concentration at the geometric transition regions and potential buckling of the hollow core walls.

In engineering practice, conical steel tube concrete members are typically found in transmission towers, bridge piers with variable cross-sections, and certain industrial structures where weight optimization is critical. The numerical approach adopted in this study is directly applicable to the design verification of such members under seismic loading, provided the material models and damage criteria are properly calibrated.

Key Reflections and Study Insights

The equivalence finding is particularly noteworthy: the seismic performance of a conical hollow sandwich steel tube concrete member is equivalent to that of a circular hollow sandwich steel tube concrete member with a cross-section taken at one-quarter of the height from the base. This provides a practical design shortcut, allowing engineers to use existing design methodologies for uniform circular sections when evaluating conical members. However, this equivalence should be applied with caution, as it represents an average behavior and may not capture local effects at the geometric transition.

The parametric study confirms that all three investigated parameters must remain within defined limits to ensure satisfactory seismic performance. The interaction between axial compression ratio and hollow rate is particularly important: a high axial compression ratio combined with a large hollow rate may lead to premature concrete crushing in the compression zone, while an excessively large hollow rate with low axial compression ratio may result in insufficient stiffness and excessive drift.

The numerical validation approach using existing experimental data is appropriate for this type of research, though future work should ideally include dedicated experimental programs specifically designed for conical hollow sandwich members to further validate the numerical models and design recommendations.

Summary

This study provides valuable numerical insights into the seismic behavior of conical hollow sandwich steel tube concrete compression-bending members, establishing parametric trends for axial compression ratio, hollow rate, and slenderness ratio. The practical equivalence relationship with uniform circular sections offers a useful design tool, while the identified failure modes and performance degradation patterns inform limit state design considerations. The research fills an important gap in the understanding of non-uniform steel tube concrete members and should be considered in the development of future design provisions for such innovative structural configurations.