Influence of Structural Measures on Seismic Performance of Irregular Multi-Chamber Steel Tube Concrete Columns

Literature Overview

This paper by Zhang Jianwei, Hu Jianhua, Qiao Zhiyun, Yang Guang, and Cao Wanlin from Beijing University of Technology (published in the Journal of Beijing University of Technology, Vol. 41, No. 8, 2015, pp. 1172-1178) addresses a critical structural engineering challenge: how internal structural measures affect the seismic behavior of irregular cross-section multi-chamber steel tube concrete (SC) mega-columns. The research was funded by the National Natural Science Foundation of China (Grants 51408017 and 51421005). The authors conducted finite element analysis on five octagonal multi-chamber SC mega-column models with different structural measures to compare their seismic performance, stress distribution, and cost-effectiveness.

Core Technical Findings

The study systematically evaluated four types of internal structural measures within octagonal multi-chamber steel tube concrete columns:

The key finding is that compartment plates, vertical rib plates, and angle steel placed at plastic hinge zones produce clearly beneficial effects on seismic resistance, while horizontal rib plates show negligible influence. This distinction is critical for engineering design decisions.

Technical Interpretation and Engineering Significance

Role of Compartment Plates

From a structural engineering perspective, compartment plates within multi-chamber SC columns serve multiple functions. They prevent concrete spalling and lateral buckling of the infill concrete, particularly under cyclic lateral loading. The dividing plates create independent concrete chambers that constrain each other, enhancing the confinement effect on the core concrete. In terms of steel pipe fabrication, the welding of these internal compartment plates to the outer steel shell presents challenges regarding weld access, weld quality control, and residual stress distribution. The welds connecting compartment plates to the outer octagonal tube are typically fillet welds or partial-penetration groove welds, and their integrity directly governs the overall seismic performance.

Vertical Rib Plates and Angle Steel at Plastic Hinge Zones

Vertical rib plates increase the local bending stiffness of the steel shell, delaying the onset of local buckling under combined axial and lateral loads. This is particularly important for mega-columns where the slenderness ratio of individual walls between chambers can be high. The angle steel placed at plastic hinge zones acts as a localized reinforcement, ensuring that plastic deformation is confined to the designated region and preventing premature failure at weak cross-sections. From a welding and fabrication standpoint, the introduction of angle steel at plastic hinge zones requires careful consideration of the weld geometry to avoid stress concentrations that could initiate cracks under cyclic loading.

Limitations of Horizontal Rib Plates

The finding that horizontal rib plates have minimal effect is technically rational. In columns subjected primarily to axial compression with lateral displacement demand, the horizontal ribs do not significantly increase the column's resistance to flexural deformation. They primarily contribute to local plate buckling resistance, which is already adequately addressed by the multi-chamber configuration itself. This insight helps engineers avoid unnecessary material and fabrication costs.

Connection to Steel Pipe Fabrication and Welding Practice

The fabrication of irregular cross-section multi-chamber SC columns involves several critical welding and forming operations:

1. Octagonal tube forming: The outer shell is typically formed from rolled steel plates using ERW or submerged arc welding processes, followed by bending to achieve the octagonal geometry. The corner welds require special attention to ensure uniform wall thickness and avoid geometric imperfections.
2. Internal compartment plate welding: These are typically welded inside the assembled shell, requiring access through the top opening. The welding process (SMAW or GTAW) must be selected to minimize distortion while ensuring full fusion. Post-weld inspection by MT or PT is essential.
3. Plastic hinge zone reinforcement: The angle steel installation involves both longitudinal and transverse welds. The weld design should follow the principles outlined in GB 50011 and relevant seismic design codes, ensuring adequate ductility of the welds themselves.

Key Questions and Reflections

A critical question arises: how do these structural measures interact with the material properties of the steel tube and concrete under prolonged cyclic loading? The finite element analysis assumes idealized material behavior, but in practice, low-cycle fatigue, strain aging, and progressive microcracking at weld interfaces may reduce the effectiveness of these measures over time. Another consideration is the interaction between the internal structural measures and the fire resistance of the column, particularly when compartment plates partition the concrete core into isolated chambers with different thermal gradients.

Study Insights and Implications

This research provides valuable guidance for the design of mega-columns in high-rise buildings and long-span structures. The conclusion that compartment plates, vertical ribs, and angle steel at plastic hinge zones represent cost-effective seismic enhancement measures has direct implications for structural optimization. Engineers should prioritize these measures in seismic design while avoiding unnecessary horizontal ribs. From a fabrication and quality assurance perspective, the focus should be on ensuring weld quality at the critical interfaces where these structural measures connect to the main steel shell, as the overall seismic performance depends heavily on the integrity of these connections.