Construction Load Analysis of Empty Steel Tubes in Steel-Concrete Frame Structures

Literature Overview

The paper by Yu Qing, Sun Guohui, and Tao Zhong, published in Industrial Construction (2009, Vol. 39, No. 4, pp. 33-36), focuses on the structural behavior of empty steel tubes during the construction phase of steel-concrete composite frame buildings. This research was supported by the Ministry of Railways-Tsinghua University Science and Technology Research Fund (Grant No. J2008G011) and conducted at the Department of Construction Management, Tsinghua University, and the College of Civil Engineering, Fuzhou University. The study establishes a finite element model for analyzing the load-bearing capacity of empty steel tubes in multi-story steel-concrete frames during construction, using a 12-story frame as a case study.

Core Technical Content

During the construction of steel-concrete composite frames, the steel tubes serve as temporary load-bearing elements before the concrete is poured and cured. This construction phase is often neglected in design, despite the fact that the empty steel tubes may be subjected to significant loads including self-weight, construction loads, equipment loads, and asymmetric loading due to sequential floor construction. The authors developed a finite element model to analyze the stress and deformation characteristics of empty steel tubes under construction loads, studied the development patterns of steel tube stresses and deformations, and preliminarily discussed the influence of different construction sequences.

The finite element model likely incorporated the geometric and material properties of the steel tubes, the connection details between steel tubes and floor slabs, and the boundary conditions representing the foundation and previously constructed floors. The construction loads considered would include the weight of wet concrete, formwork, construction equipment, and worker loads. The model would have been solved using a nonlinear finite element analysis to capture the geometric nonlinearity associated with large deformations and potential local buckling of the steel tube walls.

Technical Parameter Analysis

Engineering Practice Integration

This research addresses a critical gap in the design of steel-concrete composite structures. Many engineers focus on the final service condition of the structure but overlook the construction phase, where the steel tubes may be the sole load-bearing elements. The consequences of neglecting construction-phase analysis can be severe, including excessive deformation, local buckling of steel tube walls, connection failure, and even catastrophic collapse.

In practice, the construction phase analysis should be conducted as part of the structural design process. The finite element model developed in this study can serve as a template for analyzing specific construction scenarios. Key design considerations include:

• Determining the maximum construction loads at each construction stage
• Verifying the global stability of the steel tube frame under construction loads
• Checking local buckling resistance of steel tube walls under combined axial and bending stresses
• Evaluating the adequacy of temporary support systems
• Ensuring connection details can transfer construction loads safely

The study's finding that different construction sequences significantly affect the stress and deformation of empty steel tubes has direct implications for construction planning. Engineers should coordinate with construction managers to develop an optimal construction sequence that minimizes peak stresses in the steel tubes. This may involve staggering concrete pours, using temporary bracing, or implementing a specific sequence of floor construction.

Key Questions and Reflections

A significant question arising from this research is the adequacy of current design codes to address construction-phase loading. Most structural codes are focused on the service condition and do not provide explicit guidance for construction-phase analysis. The finite element approach presented in this paper offers a practical solution, but it requires significant computational effort and expertise. There is a need for simplified design methods or code provisions that can be easily applied by practicing engineers.

Another important consideration is the interaction between the construction-phase analysis and the final structural design. The stresses and deformations induced during construction may affect the final structural behavior, particularly if residual stresses or permanent deformations are introduced. The analysis should therefore be integrated with the service-condition design to ensure that the structure performs adequately throughout its entire lifecycle.

The research also highlights the importance of construction monitoring. While finite element analysis provides predicted stresses and deformations, actual construction conditions may differ from the model assumptions. Instrumentation of critical steel tubes during construction can provide real-time data to verify the analysis and identify potential issues early.

Study Insights and Implications

This paper makes an important contribution to the understanding of steel-concrete composite structure construction. The finite element model developed provides a practical tool for analyzing construction-phase loads, and the parametric study of construction sequences offers valuable guidance for construction planning. For contemporary practice, the principles established here should be incorporated into the structural design process, with construction-phase analysis becoming a standard part of the design documentation. The research underscores the importance of considering all phases of a structure's lifecycle, not just the final service condition, and emphasizes the need for close coordination between structural engineers and construction managers.