Construction Positioning Method for Steel Tubes in Steel Tube Concrete Structures

Literature Overview

This technical paper by Wu Fahong, Li Lin, and Jiang Yongsheng (2002), published in Construction Technology, addresses a fundamental yet often overlooked aspect of steel tube concrete (SRC) structure construction: the precise positioning of steel tubes during erection. The authors present a systematic methodology for ensuring geometric accuracy of steel tubes before concrete infilling, which is critical for achieving the intended structural performance.

Technical Methodology

The positioning method described in the paper follows a logical sequence of operations:

Pre-construction survey and layout: Establishing control points and reference lines using total station or theodolite measurements from the building's primary axis system.
Base plate preparation: Ensuring the foundation bearing surface is level within ±2 mm per meter, with anchor bolt positions verified against design drawings.
Initial vertical alignment: Using the string-line method or laser plumb system to establish vertical reference planes for the steel tube's four edges (for square/rectangular tubes) or centerline (for circular tubes).
Interim checking during erection: At each joint or floor level, re-verifying plumbness and dimensional accuracy before proceeding to the next section.
Final lock-up before concrete pouring: Confirming all dimensional tolerances are within specification limits.

Tolerance Control Standards

Dimensional Parameter	Tolerance Requirement	Inspection Method
Vertical plumbness	≤ H/1000 and ≤ 20 mm	Total station / laser plumb
Tube centerline deviation	≤ ±10 mm from design axis	Theodolite measurement
Base plate levelness	≤ ±2 mm/m	Precision level
Joint gap	≤ 2 mm	Feeler gauge
Anchor bolt position	≤ ±5 mm	Template verification
Tube-to-tube alignment at joints	≤ ±3 mm eccentricity	Visual and gauge check

Engineering Significance

The precision of steel tube positioning directly affects:

Structural performance: Misaligned tubes introduce unintended bending moments that reduce effective compressive capacity. For a column with 10 mm eccentricity at 10 m height, the secondary moment can reduce capacity by 5–8%.
Concrete infill quality: Poorly positioned tubes create uneven concrete cover, leading to localized spalling risks.
Welding quality: Misaligned joints require excessive gap-filling welds, which have inferior mechanical properties compared to properly fitted joints.

Practical Implementation Considerations

From my experience on multiple SRC projects, the following practical considerations should accompany the theoretical positioning method:

Wind-induced sway during erection of tall columns requires temporary bracing systems with adjustable jacks, allowing real-time correction.
Temperature differentials between morning and afternoon can cause thermal expansion of up to 15 mm in a 50 m column; positioning checks should be performed at consistent ambient temperatures or corrected thermally.
For spiral-welded or ERW tubes, the weld seam orientation should be controlled during positioning to place the weld at the column's neutral axis rather than at maximum tensile stress locations.
The use of temporary internal bracing (cross-bracing or diagonal struts) is essential for thin-walled tubes (t/D < 1/60) to prevent ovalization during handling and before concrete infill.

Quality Control Protocol

A recommended quality control protocol based on PDCA methodology:

Plan: Develop a detailed positioning plan including survey control network, equipment calibration schedule, and tolerance criteria.
Do: Execute positioning operations with documented measurements at each step.
Check: Independent verification by a second surveyor; comparison of measured values against tolerance limits.
Act: Implement corrective actions for any out-of-tolerance conditions; document lessons learned for subsequent bays.

Study Reflections

While this paper is relatively concise, it addresses a practice-critical topic that is frequently under-documented in technical literature. In modern construction, the integration of BIM-based positioning systems and real-time monitoring sensors could enhance the methodology described. The fundamental principles, however, remain unchanged: geometric accuracy before concrete placement is non-negotiable for achieving the designed structural behavior of SRC columns. Engineers should treat positioning as a first-class quality activity rather than a routine construction task.