Zhuojin Pipe Fitting Co., LtdConcrete Lateral Pressure During Jacking Construction of Rectangular Concrete-Filled Steel Tube Columns
Literature Overview
The paper by Wu Honggang and colleagues from Qingdao Urban Construction Group, Shandong University, and Shandong Huayi Steel Structure Co., published in Cement magazine (2025, Issue 8, pp. 151-153), investigates the concrete lateral pressure during the jacking construction of rectangular concrete-filled steel tube (CFST) columns. The study employs field measurement methods to examine the lateral pressure variation patterns and column wall deformation during jacking, considering the influence of internal cross diaphragms, and proposes a calculation formula for the maximum dynamic lateral pressure.
Core Technical Content
Jacking construction of CFST columns is a specialized construction technique used in projects where columns must be erected through existing structures or in confined spaces. The process involves placing a steel tube in position, injecting concrete into the tube to form a composite column, and then jacking the column vertically to its final position. During this process, the fresh or partially hardened concrete inside the steel tube exerts lateral pressure on the tube walls, which can lead to tube deformation, buckling, or even failure if not properly accounted for.
The presence of internal cross diaphragms (horizontal stiffeners) inside the steel tube complicates the lateral pressure behavior. These diaphragms provide local support to the tube walls but also create discontinuities in the pressure distribution. The authors conducted field measurements to capture the dynamic lateral pressure variations during the jacking process and analyzed the relationship between jacking height and lateral pressure.
Field Measurement Parameters
| Measurement Parameter | Instrumentation | Purpose |
|---|---|---|
| Lateral pressure | Pressure sensors on tube inner walls | Quantify concrete pressure |
| Tube wall deformation | Displacement sensors or LVDTs | Monitor buckling risk |
| Jacking height | Position sensors | Correlate with pressure |
| Concrete temperature | Thermocouples | Account for thermal effects |
| Concrete slump | Slump test | Characterize workability |
The field measurements revealed that the lateral pressure is not uniform along the column height and varies dynamically during the jacking process. The presence of cross diaphragms creates localized pressure concentrations at the diaphragm locations, while the pressure between diaphragms follows a different distribution pattern. The maximum dynamic lateral pressure occurs at specific jacking stages and is influenced by the concrete's rheological properties, the jacking speed, and the diaphragm spacing.
Lateral Pressure Analysis
The authors propose a calculation formula for the maximum dynamic lateral pressure considering the obstruction effect of cross diaphragms. The formula accounts for the hydrostatic pressure component due to the concrete column height, the dynamic pressure component due to jacking movement, and the confinement effect of the diaphragms. The derivation considers the concrete as a non-Newtonian fluid with time-dependent rheological properties, transitioning from fluid-like behavior when freshly placed to solid-like behavior as it hardens.
The lateral pressure distribution can be characterized by the following components:
- Hydrostatic pressure: p_h = rho g h, where rho is the concrete density, g is gravitational acceleration, and h is the concrete height.
- Dynamic pressure: p_d = C_d rho v^2, where C_d is a drag coefficient and v is the jacking velocity.
- Diaphragm confinement: The diaphragms redistribute pressure, creating higher pressures at the diaphragm locations and lower pressures between diaphragms.
The combined effect results in a non-uniform pressure distribution that peaks at specific locations and times during the jacking process. The maximum dynamic lateral pressure is critical for determining the required steel tube thickness and the spacing of cross diaphragms.
Engineering Practice Integration
In practical jacking construction of CFST columns, the lateral pressure must be carefully managed to prevent tube deformation and ensure structural integrity. The field measurement data and calculation formula provided by the authors offer practical guidance for engineers designing jacking operations. Key engineering considerations include:
- Steel tube design: The tube wall thickness must be sufficient to resist the maximum dynamic lateral pressure without excessive deformation. The Eurocode 3 and relevant Chinese standards (GB 50017) provide design formulas for cylindrical shells under external pressure, but the dynamic nature of jacking-induced pressure requires additional safety factors.
- Diaphragm design: Cross diaphragms must be designed to provide adequate support to the tube walls while not obstructing the jacking process. The spacing of diaphragms should be optimized to minimize the unsupported length of the tube wall.
- Concrete placement: The concrete mix design must balance workability (for proper filling) with setting time (to prevent excessive pressure buildup). The slump and flowability of the concrete directly affect the lateral pressure magnitude.
- Jacking speed: The jacking velocity influences the dynamic pressure component. Slower jacking reduces dynamic pressure but increases the time during which the concrete is in a fluid-like state.
Design Recommendations Based on Study Findings
| Design Parameter | Recommendation | Rationale |
|---|---|---|
| Tube wall thickness | Based on maximum dynamic pressure | Prevent buckling and deformation |
| Diaphragm spacing | Optimized based on pressure distribution | Minimize unsupported tube length |
| Concrete slump | Controlled to limit pressure | Balance workability and pressure |
| Jacking speed | Limited to reduce dynamic effects | Control dynamic pressure component |
| Monitoring | Real-time pressure and deformation | Ensure safety during jacking |
Key Questions and Reflections
The study raises important questions about the applicability of the proposed formula to different column geometries and concrete types. The formula is derived from field measurements on rectangular CFST columns with specific cross diaphragm configurations. Its applicability to circular columns, columns without diaphragms, or columns with different diaphragm spacing requires further validation.
Another consideration is the effect of concrete hardening on the lateral pressure behavior. As the concrete transitions from a fluid to a solid, the pressure distribution changes fundamentally. The formula must account for this time-dependent behavior, which is challenging to model accurately. The field measurements provide valuable data, but the transition from fluid to solid behavior introduces complexity that may require numerical simulation for more accurate predictions.
Study Insights and Implications
The study provides valuable practical insights into the lateral pressure behavior during jacking construction of rectangular CFST columns. The field measurement approach, combined with analytical modeling, offers a practical methodology for engineers to predict and manage lateral pressures during jacking operations.
For engineering practice, the key implication is that jacking construction of CFST columns requires careful attention to lateral pressure management. The proposed calculation formula provides a quantitative tool for design verification, but engineers should also consider implementing real-time monitoring during jacking operations to ensure that actual pressures remain within design limits.
The research also highlights the importance of considering dynamic effects in the design of temporary and construction-stage structural systems. Traditional design approaches often focus on static loading conditions, but construction processes such as jacking introduce dynamic pressures that can significantly affect structural behavior. Incorporating these dynamic effects into design calculations improves safety and reliability.
The findings have broader applicability to other construction processes involving concrete-filled tubes, such as post-tensioned CFST columns or columns constructed using the slip-form method. The principles of lateral pressure management and dynamic effect consideration are transferable across different construction techniques.