Construction Technology and Load-Bearing Capacity Testing of Large-Span Steel Pipe Structures

Literature Overview

This 2006 study by Yao Jiangfeng, Tang Xingrong, and Gong Changyi documents the construction technology and load-bearing capacity verification of a large-span steel pipe truss structure on the roof of the Suzhou Municipal Government Comprehensive Office Building. The paper covers measurement, installation, welding procedures, and post-construction load testing.

Core Technical Content

Project Background and Structural Characteristics

Large-span steel pipe truss structures are widely used in public buildings due to their high strength-to-weight ratio, aesthetic appeal, and construction flexibility. The Suzhou project involved a roof structure with significant span, requiring careful planning of fabrication, erection, and verification.

Construction Process and Quality Control Measures

Process Step	Key Technical Measures	Quality Criteria
Pre-fabrication	CNC cutting and bending of steel pipes; factory welding of sub-assemblies	Dimensional tolerance ±2 mm; weld quality per GB 50661
Transportation	Protective packaging; secure fastening to prevent deformation	No visible deformation or damage
On-site measurement	Total station and laser level for positioning; temperature compensation	Position accuracy within ±5 mm
Assembly and alignment	Temporary bracing; sequential installation from supports to midspan	Alignment within ±3 mm
Welding	Pre-qualified WPS; interpass temperature control; post-weld inspection	100% UT inspection on full-penetration welds
Load testing	Incremental loading to 1.0× and 1.5× design load; deflection monitoring	Deflection ≤ L/400 at service load; ≤ L/300 at test load

Welding Quality Assurance

The welding of large-diameter steel pipes requires particular attention to:

Weld procedure qualification (WPQ): Each joint configuration (tee, cross, lap) must have a qualified procedure
Residual stress management: Sequential welding from free edges inward; symmetric welding to minimize distortion
Heat input control: Limit heat input to prevent grain coarsening in the HAZ, particularly for high-strength steels
Post-weld treatment: Stress relief or vibration stress relief (VSR) may be applied for critical joints

Load-Bearing Capacity Verification

The post-construction load test is a critical verification step. The procedure typically involves:

Installing displacement transducers and strain gauges at critical locations (midspan, supports, joints)
Applying loads in increments (typically 20% of test load per step)
Recording deflections, strains, and any visible distress at each increment
Unloading and checking for residual deformation
Comparing measured responses with predicted values from structural analysis

Engineering Practice Implications

FMEA for construction processes: A Failure Mode and Effects Analysis should be conducted for each construction phase. For example:

Failure mode: Weld cracking during erection → Effect: Structural failure → Countermeasure: Pre-heat and controlled cooling rate
Failure mode: Bolt under-tensioning → Effect: Joint slippage → Countermeasure: Calibrated torque wrenches with witness marks

Temperature effects: Steel pipe structures are sensitive to temperature changes. During summer construction in Suzhou (hot and humid climate), thermal expansion can cause significant dimensional changes. The analysis should account for temperature differentials between the erected structure and the ambient environment.
Connection design: The load test results confirm that the connections (welded and bolted) perform adequately. However, engineers should note that the test verifies strength but not fatigue or long-term behavior. For cyclic loading environments (e.g., near airports or with vibrating equipment), fatigue assessment per GB 50017 is essential.
As-built documentation: Complete as-built drawings, including actual weld maps, bolt locations, and material certificates, should be maintained for future maintenance and modification planning.

Critical Reflections

The paper provides a practical case study that confirms the feasibility of large-span steel pipe structures when proper construction technology is applied. The successful load test validates both the design and the construction quality.

However, the study is limited in scope: it does not address long-term performance monitoring, maintenance requirements, or the impact of environmental factors (corrosion, UV degradation of coatings, thermal cycling). For a government building with a design life of 50 years, a comprehensive maintenance and inspection plan should be established, including periodic NDT of critical welds and corrosion thickness measurements.

The construction approach documented here—factory fabrication of sub-assemblies followed by on-site assembly—is a best practice that should be adopted for similar projects. The emphasis on measurement accuracy and weld quality control is commendable and reflects a mature quality management system.