Zhuojin Pipe Fitting Co., LtdConstruction Technology Study of Large-Span Steel Pipe Trusses at Hangzhou International Expo Center
Literature Overview
This study, authored by Ge Jie, Wang Guiling, Wang Yuling, and Zhang Xiaoyong from China Construction Eighth Engineering Division Corporation Limited, was published in the journal Steel Structure (Volume 31, Issue 8, 2016, pages 81-84). The project under investigation involves Zone V of the Hangzhou International Expo Center, where the third-floor column-free exhibition hall features 14 sets of 72-meter-span shuttle-shaped steel pipe trusses. The core engineering challenge lies in the exceptionally large span, which introduces significant uncertainties in deflection behavior, construction sequencing, and overall structural response. The adopted construction scheme is "ground assembly followed by integrated lifting," which demands precise control of pre-camber values, member fabrication tolerances, and lifting coordination. This literature provides valuable engineering methodology for large-span space truss construction that is directly relevant to our practice in steel pipe and pipe fitting fabrication and installation.
Core Technical Content and Analysis
The fundamental problem addressed in this study is the discrepancy between the structural response under the construction completion state and the original design state. In a 72-meter-span truss, even small deviations in member length, joint geometry, or erection sequence can produce measurable deflections that compromise both serviceability and safety. The authors conducted simulation analysis of the truss construction process to quantify these differences and to provide a scientific basis for determining the pre-camber values that must be applied to individual members before installation.
The shuttle-shaped (fusiform) truss geometry is notable because its cross-sectional depth varies along the span, which creates non-uniform stiffness distribution and complex load paths. This geometry is common in large-span exhibition halls where column-free clear spans are required, but it also complicates fabrication and erection. From a pipe fitting perspective, the varying member cross-sections and the complex joint configurations demand careful attention to fit-up tolerances, welding sequence, and residual stress management during fabrication.
Pre-Camber Determination Methodology
The pre-camber strategy is the central technical contribution of this paper. In large-span trusses, the dead load alone can produce deflections that exceed the design allowable limits. By pre-cambering the truss upward during fabrication, the structure is designed to deflect downward under its own weight until it reaches the intended geometric profile at the construction completion state. The key steps in determining the pre-camber value include:
- Finite element modeling of the truss under the design state to obtain the target deflection profile.
- Simulation of the construction process, including member-by-member assembly, lifting, and sequential loading.
- Comparison of the construction completion state with the design state to identify the residual deflection difference.
- Allocation of the required pre-camber to individual members based on their contribution to the overall deflection.
The following table summarizes the key parameters and considerations:
| Parameter | Typical Value / Range | Engineering Significance |
|---|---|---|
| Truss span | 72 m | Governs deflection magnitude and lifting equipment requirements |
| Number of trusses | 14 sets | Requires batch fabrication and coordinated erection |
| Truss type | Shuttle-shaped (fusiform) | Variable depth creates non-uniform stiffness |
| Construction method | Ground assembly + integrated lifting | Minimizes working-at-height but demands large crane capacity |
| Pre-camber range | Typically 1/300 to 1/500 of span | Must be calibrated through simulation |
| Member fabrication tolerance | ±1.5 mm (typical for large truss members) | Directly affects joint fit-up and overall geometry |
Welding and Fabrication Quality Control Considerations
From the perspective of pipe fitting fabrication and welding quality control, several critical aspects emerge from this study. The large-span truss members are typically fabricated from steel pipe sections (seamless or longitudinally welded), and the quality of the welds at gusset plates, splice joints, and end connections directly determines the structural integrity of the truss.
Welding Process Selection and Quality Requirements
For truss members of this scale, the primary welding processes include submerged arc welding (SAW) for longitudinal seams in pipe fabrication, gas metal arc welding (GMAW) or gas tungsten arc welding (GTAW) for gusset plate attachment and end connection welds, and flux-cored arc welding (FCAW) for field splices. The welding procedure specifications (WPS) must be qualified in accordance with relevant standards such as GB/T 985, AWS D1.1, or EN 1090-2, depending on the project specification.
Key quality control checkpoints include:
- Pre-weld preparation: Surface cleanliness, fit-up gap control (typically 2-4 mm for SAW, 1-2 mm for GTAW root pass), and root preparation geometry.
- Welding sequence control: Symmetric welding sequence to minimize angular distortion in gusset plates and to control residual stress distribution.
- Heat input management: Controlled heat input (typically 1.5-3.0 kJ/mm for structural steel) to limit the heat-affected zone (HAZ) microstructure changes and to prevent excessive residual stress.
- Post-weld treatment: For high-strength steel grades (Q345, Q390, Q420), controlled cooling rates and, where specified, post-weld heat treatment (PWHT) to relieve residual stresses.
Defect Analysis and Countermeasures
Common welding defects encountered in large truss fabrication include:
| Defect Type | Typical Cause | Detection Method | Countermeasure |
|---|---|---|---|
| Porosity | Inadequate shielding, contaminated base metal | RT, UT | Improve gas flow, clean base metal, use dry electrodes |
| Undercut | Excessive travel speed, improper current | Visual, MT | Reduce travel speed, adjust current, use proper weave pattern |
| Lack of fusion | Insufficient heat input, poor fit-up | UT, TOFD | Increase current, ensure proper gap, use proper electrode angle |
| Cracking (cold/hot) | High carbon equivalent, excessive restraint | MT, PT | Preheat, control interpass temperature, use low-hydrogen consumables |
| Excessive distortion | Asymmetric welding sequence | Visual, measurement | Symmetric welding, use back-gouging, apply clamps and fixtures |
Integration with Engineering Practice
In practical engineering, the lessons from this study extend beyond the specific project at Hangzhou to any large-span steel pipe truss construction. The methodology of comparing construction state with design state through simulation is a powerful tool that should be applied routinely. The following engineering practice recommendations are derived from the study:
- Early-stage simulation: Structural simulation should be initiated during the detailed design phase, not deferred until after fabrication. This allows for adjustments to member sizes, connection details, and pre-camber values while design changes are still economical.
- Fabrication tolerance coordination: The fabrication tolerances specified in the shop drawings must be consistent with the erection tolerances required by the construction method. For ground-assembly and integrated lifting, the overall truss geometry tolerance (typically ±10 mm for a 72 m span) must be achievable through cumulative member tolerances.
- Lifting equipment verification: The lifting equipment and rigging system must be verified for the actual weight and center of gravity of the assembled truss, including the effects of pre-camber and any temporary bracing.
- Monitoring during erection: Real-time monitoring of deflection, strain, and temperature during the lifting and erection process provides valuable feedback that can be compared with simulation predictions to validate the analysis model.
Key Questions and Reflections
Several questions arise from this study that warrant further investigation:
- How sensitive is the pre-camber requirement to variations in steel grade and yield strength? A shift from Q345 to Q390 steel, for example, would change the elastic modulus and the dead load deflection profile.
- What is the impact of construction sequence on the final geometry? If the 14 trusses are erected in a specific sequence, the cumulative effect of truss-to-truss connections and lateral bracing on the individual truss geometry should be quantified.
- How should wind loading during the lifting and erection phase be accounted for? A 72-meter-span truss presents a significant wind load area during lifting, and the dynamic effects of wind on the suspended truss can induce additional deflections.
Study Insights and Implications
This literature reinforces the principle that large-span steel pipe truss construction is as much a matter of process control and simulation as it is of structural design. The pre-camber methodology presented here is a practical example of how computational analysis can be integrated with fabrication and erection practice to achieve geometric accuracy. For engineers involved in pipe fitting fabrication and welding quality control, the key takeaway is that the quality of individual welds and member dimensions directly influences the overall structural performance and must be managed with a systems-level perspective rather than an isolated component approach. The study also highlights the importance of cross-disciplinary communication between structural designers, fabrication engineers, and construction teams to ensure that the intended structural behavior is achieved at every stage of the project lifecycle.