Mechanical Performance Analysis of Steel-Concrete Composite Structures During Construction Stage

Literature Overview

This study by Wang Wenda and Han Linhai (2004, Industrial Construction, Vol. 34, No. 6) addresses a critical yet often overlooked aspect of steel-concrete composite (CFST) structure engineering: the mechanical behavior during the construction phase. The authors, affiliated with Fuzhou University, examine how empty steel pipes function as vertical support skeletons before concrete infill, and how they subsequently act as formwork during concrete placement. This work was supported by the Fujian Provincial Major Science and Technology Project (2002H007) and the Gansu Provincial Natural Science Foundation (ZS022-A25-010).

Core Technical Arguments

The fundamental premise of this paper is that CFST structures require a two-stage design approach. During construction, the hollow steel pipe must independently bear vertical construction loads before any concrete is poured, which induces initial stresses in the steel tube. When concrete is subsequently placed, the steel pipe transitions from a load-bearing structural element to a formwork component, now subject to lateral hydrostatic pressure from the wet concrete mass. This dual role creates a complex stress state that conventional single-stage design methods fail to capture.

The authors argue that neglecting the construction phase can lead to underestimation of cumulative stresses in the steel tube, potentially resulting in local buckling or yielding before the composite action is fully developed. The hydrostatic pressure exerted by wet concrete follows the formula P = ρgh, where ρ is the concrete density (approximately 2400 kg/m³), g is gravitational acceleration, and h is the depth of the concrete pour. For typical high-rise construction with pour heights exceeding 3 meters per lift, this lateral pressure can reach significant magnitudes that must be accounted for in the steel tube wall thickness design.

Two-Stage Design Methodology

The two-stage design methodology proposed in this paper separates the structural analysis into distinct phases:

The finite element analysis (FEA) conducted in this study models the construction-stage behavior using a shell element formulation for the steel tube, with appropriate boundary conditions representing the progressive loading sequence. The initial stress state from Stage 1 is mapped onto the Stage 2 model, ensuring continuity of the stress field throughout the construction process.

Engineering Practice Implications

From a practical standpoint, this research has several implications for steel pipe manufacturing and construction:

• Wall thickness selection: The steel pipe wall thickness must be adequate not only for service loads but also for construction-stage demands, particularly the hydrostatic pressure during concrete placement.
• Pour rate control: The rate of concrete placement directly influences the lateral pressure on the steel formwork. Slower placement rates reduce the effective unit weight of wet concrete but increase the total pour duration.
• Support spacing: The spacing between vertical supports for the empty steel pipe must account for the maximum expected construction load, which may include formwork, reinforcement, and construction equipment.
• Residual stress management: The initial stresses developed during Stage 1 become residual stresses in the final composite member, potentially affecting long-term fatigue performance and creep behavior.

The study also discusses the broader concept of construction mechanics in civil engineering, advocating for a systematic approach that treats the construction phase as an integral part of structural design rather than a transient condition to be neglected. This perspective aligns with modern construction engineering practices that emphasize constructability and construction-phase safety.

Key Insights and Reflections

This paper raises an important question that resonates throughout steel pipe engineering: how do we ensure that the manufacturing tolerances and material properties of steel pipes are compatible with the demands of the construction phase? For instance, a steel pipe manufactured to API 5L or GB/T 9711 specifications may be perfectly adequate for service loads but potentially insufficient for the construction-stage hydrostatic pressure if the pour height is not properly controlled. The interaction between manufacturing quality, construction sequencing, and structural performance forms a complex engineering problem that requires interdisciplinary coordination.

The concept of initial stress mapping from construction to service is particularly relevant for welded steel pipes, where welding residual stresses already exist. The superposition of construction-stage stresses with manufacturing residual stresses creates a complex stress state that warrants careful attention in quality control protocols. Engineers should consider whether pre-stress relief procedures are necessary for CFST applications where significant construction-stage loads are expected.

Reference Value and Outlook

This 2004 publication remains highly relevant as CFST structures continue to gain popularity in high-rise construction, particularly in China where steel-concrete composite technology has seen rapid adoption. The two-stage design philosophy has been incorporated into subsequent Chinese design codes, including GB 50936-2014 for steel-concrete composite structures. Future research should extend this work to include dynamic construction loads, temperature effects during concrete curing, and the interaction between construction-stage behavior and long-term durability, particularly for corrosion-prone environments where steel pipe quality is paramount.