Safe Lifting Height Calculation for Rectangular Steel Tube Concrete Columns with Cross Diaphragms

Literature Overview

The paper by Xu Guowen and colleagues, published in Construction Technology (2022, Vol. 51, No. 16), addresses a critical construction safety issue related to the pumping and lifting construction method for rectangular steel tube concrete columns with internal cross diaphragms. The authors combine theoretical analysis with numerical simulation to propose simplified calculation methods for determining the maximum safe lifting height of column segments during the pump-and-lift construction process. The study was funded by China State Construction Engineering Corporation's technology R&D program and the Shanghai Youth Science and Technology Talent Program, reflecting its practical significance for major construction projects.

Problem Statement and Technical Challenges

The pump-and-lift construction method for steel tube concrete columns involves pumping concrete into the steel tube while lifting the column assembly vertically. When cross diaphragms are present inside the rectangular steel tube, several additional challenges arise:

These challenges are interrelated and create a complex coupled problem where structural integrity, material flow, and construction safety must be simultaneously managed. The cross diaphragms, while beneficial for structural performance by providing composite action between steel and concrete, introduce significant complications during the construction phase.

Simplified Calculation Method

Column Internal Pressure Limit

The authors propose a simplified formula for calculating the internal pressure limit within the column during the pumping process. This pressure limit is governed by the tube wall buckling resistance and the stress capacity of the corner welds. The theoretical derivation likely incorporates shell buckling theory for the rectangular tube walls and stress concentration factors for the corner weld regions. The numerical simulation provides validation of the theoretical predictions and captures the complex three-dimensional stress state that simplified formulas cannot fully represent.

Maximum Safe Lifting Height

The maximum safe lifting height of a pump-and-lift unit is determined by the balance between the upward lifting force and the combined weight of the column segment, the internal concrete, and the construction loads. The simplified formula accounts for:

• The self-weight of the steel tube and cross diaphragms
• The weight of concrete within the column at various filling levels
• The additional load from pumping pressure on the tube walls
• The safety factor against tube wall buckling and weld failure

The study validates the simplified formula against an actual engineering case, demonstrating its practical applicability. The authors recommend that when conditions permit, finite element analysis should be prioritized for determining the column internal pressure limit, while the simplified formula serves as a rapid estimation tool when computational resources are limited.

Engineering Practice Integration

Construction Safety Management

From a construction safety perspective, this research provides a quantitative basis for determining the maximum safe lifting height, which directly impacts construction scheduling, equipment selection, and safety management protocols. The determination of internal pressure limits is essential for selecting appropriate pumping equipment and establishing safe operating procedures. Engineers must ensure that the pumping pressure does not exceed the calculated limit at any point during the construction process.

The cross diaphragms present a unique challenge because they create discrete pressure zones within the column. As concrete is pumped through the tube, the pressure distribution changes as each diaphragm is bypassed. The maximum pressure likely occurs when the concrete front is at a diaphragm location, where flow resistance is highest. This transient pressure peak must be captured in the safety assessment, and the simplified formula should conservatively account for the worst-case pressure condition.

Weld Quality Implications

The stress concentration at corner welds is a critical concern that intersects with welding engineering practice. Rectangular steel tube columns are typically fabricated by welding flat plates at the corners, and these welds represent the weakest links in the structural system. During the pump-and-lift process, the corner welds are subjected to combined bending and shear stresses from the internal concrete pressure. Welders and quality control engineers must ensure that corner welds meet the highest quality standards, with full penetration welds and thorough non-destructive testing (UT or RT) to detect any defects that could propagate under the elevated stress conditions.

The use of cross diaphragms also means that additional welds are present at the diaphragm-to-tube connections. These welds must be designed and executed to withstand the cyclic loading and pressure fluctuations experienced during the pumping process. Welding procedures should account for the thin-walled nature of the tube walls and the potential for distortion, and post-weld inspection should focus on the diaphragm weld zones as well as the corner welds.

Study Insights and Implications

This research bridges the gap between construction engineering practice and structural analysis by providing practical calculation tools that can be used on-site. The combination of theoretical analysis and numerical simulation offers a robust methodology that can be adapted to different column geometries, cross diaphragm configurations, and construction conditions. The recommendation to use finite element analysis when possible, supplemented by simplified formulas for rapid estimation, reflects a pragmatic approach to engineering practice that balances accuracy with efficiency.

The findings have broader implications for the design of steel tube concrete columns with internal stiffening elements. Engineers must recognize that the construction phase imposes unique loading conditions that may differ from service conditions, and the design must account for both. The cross diaphragm, while structurally beneficial, introduces construction-phase vulnerabilities that must be managed through careful calculation, quality control, and construction sequencing. This holistic approach to structural design, encompassing both fabrication and construction phases, is essential for ensuring the safety and durability of steel tube concrete structures.