Fire Resistance Performance Analysis of Steel Tube Concrete Composite Column-RC Beam Spatial Joints

Literature Overview

This paper by Zhang Bo et al., published in the Journal of Shenyang Jianzhu University (Natural Science Edition) (2024, Volume 40, Issue 2, pp. 259-266), investigates the fire resistance performance of steel tube concrete composite column-reinforced concrete (RC) beam spatial joints under ISO-834 standard fire conditions. The research was conducted at Shenyang Jianzhu University's School of Civil Engineering, Liaoning Transportation Polytechnic College's Department of Architectural Engineering, China Construction Eighth Engineering Division's Northeast Branch, and Foshan University of Science and Technology's School of Transportation and Civil Architecture, supported by the National Natural Science Foundation of China (51808351) and the Shenyang Science and Technology Program (21-108-9-34).

Problem Statement and Technical Background

Fire resistance is a critical design consideration for structural components, particularly for composite structures that combine steel and concrete elements. The steel tube concrete composite column-RC beam spatial joint is a complex connection that must maintain structural integrity under elevated temperatures for a specified duration. The interaction between the steel tube, concrete core, and RC beam creates a multi-material system with complex thermal and mechanical behavior under fire conditions.

The numerical analysis was conducted using ABAQUS, with separate temperature field and mechanical models established for the ISO-834 standard fire scenario. The temperature field model accounts for heat transfer through conduction, convection, and radiation, while the mechanical model captures the temperature-dependent material properties and structural response. The models were validated against experimental test data, ensuring the accuracy of the numerical predictions.

Key Technical Parameters and Analysis Results

The numerical results reveal that the spatial joint exhibits excellent fire resistance performance, meeting practical engineering requirements. The joint zone temperature is significantly lower than the non-joint zone due to the protective effect of the beams and slabs, which shield the joint from direct flame impingement and reduce heat transfer to the critical connection region.

A notable finding is the increase in internal steel tube concrete load sharing from 43.27% at room temperature to 52.9% at 180 minutes of fire exposure. This counterintuitive result is explained by the differential thermal degradation of the materials: the concrete core retains more of its compressive strength at elevated temperatures compared to the surrounding steel, which loses strength more rapidly. As a result, the concrete core assumes a larger share of the internal force as the temperature increases.

Interpretation of Technical Points

The fire resistance behavior of the spatial joint is governed by several competing mechanisms. The steel tube provides initial structural integrity but loses strength rapidly at temperatures above 550°C. The concrete core, while more fire-resistant, may spall at high temperatures, reducing its load-bearing capacity. The RC beam and slab provide thermal protection to the joint zone, creating a temperature gradient that favors the structural integrity of the connection.

The reduction in fire resistance with increasing beam count is attributed to the increased thermal load on the joint. More beams create additional heat transfer paths to the joint zone, raising the local temperature and accelerating the degradation of connection materials. This finding has important implications for the design of multi-beam connections in fire-prone environments.

The load-sharing analysis provides insight into the internal force redistribution under fire conditions. The increase in concrete core load sharing suggests that the composite action between the steel tube and concrete core becomes more important as the fire progresses. This has implications for the design of fire-resistant composite columns, where the interaction between the steel tube and concrete core should be considered in fire resistance calculations.

Engineering Practice and Quality Control

In practical engineering applications, several fire resistance considerations must be addressed for steel tube concrete composite column-RC beam spatial joints. First, the fire resistance rating of the joint must be verified through numerical analysis or experimental testing, with the design fire resistance duration typically ranging from 60 to 180 minutes depending on the building occupancy and structural importance. Second, the thermal protection of the joint zone should be considered in the design, with appropriate fire-resistant coatings or insulation applied to the steel tube and connection plates. Third, the fire resistance of the concrete core should be verified through thermal analysis, ensuring that the concrete does not spall prematurely under fire conditions.

Quality control for fire-resistant composite joints should include inspection of fire-resistant coatings, verification of concrete cover thickness, and testing of connection welds for thermal stability. The numerical analysis should be used to guide the design of fire protection measures, with particular attention to the joint zone where temperature gradients are most severe.

Study Insights and Implications

This research contributes to the understanding of fire resistance behavior in composite steel-concrete structures, providing quantitative data that can inform fire safety design. The identification of the joint zone as a relatively protected region due to beam-slab shielding is a valuable finding for fire engineering practice. The load-sharing analysis provides insight into the internal force redistribution under fire conditions, which can be used to improve fire resistance calculations for composite structures.

A key implication is the potential for developing simplified fire resistance design methods based on the numerical results. The identified trends regarding beam count, joint temperature, and load sharing can be incorporated into parametric design equations that provide initial estimates for joint fire resistance. Future research should address the long-term fire resistance of these joints under repeated fire exposure, as well as the interaction between fire resistance and seismic performance in composite structures.