Compressive Stability Bearing Capacity of Disc-Lock Steel Pipe Supports: Experimental and Finite Element Study

Literature Overview

This paper presents experimental tests and finite element analysis of disc-lock steel pipe support systems used in construction shoring and temporary support applications. Disc-lock systems (also known as ring-lock or disc-lock scaffolding) are modular steel pipe support structures that utilize disc-shaped connectors for rapid assembly and adjustment. The study focuses on the compressive stability bearing capacity, examining failure modes, buckling behavior, and the accuracy of finite element predictions.

System Configuration and Test Setup

Disc-lock steel pipe supports consist of vertical standards connected by horizontal ledgers at each disc level, with diagonal braces providing lateral stability. The disc connectors allow for multiple connection angles and heights, making the system highly adaptable to various support geometries. The test specimens represent typical construction applications with varying slenderness ratios and brace configurations.

Test Parameter	Specimen A	Specimen B	Specimen C
Standard diameter	48.3 mm	48.3 mm	48.3 mm
Wall thickness	3.0 mm	3.0 mm	3.0 mm
Height	3.0 m	4.0 m	5.0 m
Slenderness ratio	100	133	167
Brace configuration	Single diagonal	Cross diagonal	Cross diagonal
Disc spacing	1.5 m	1.5 m	1.5 m
Steel grade	Q235	Q235	Q235

Buckling Behavior and Failure Modes

The experimental results demonstrate that the compressive stability capacity is governed by overall column buckling rather than local buckling of individual members. For low slenderness ratios (below 100), the failure mode is characterized by lateral-torsional buckling of the entire support frame. As slenderness increases, the buckling mode transitions to a more localized instability involving the buckling of individual standards between disc connection points.

The disc connectors play a crucial role in defining the effective buckling length. The rotational stiffness provided by the disc connections is neither fully rigid nor fully pinned, but rather semi-rigid. This semi-rigid behavior significantly influences the critical buckling load, and simplified design assumptions of either fully pinned or fully fixed ends can lead to inaccurate predictions.

Finite Element Model Validation

The finite element model employs shell elements for the steel tubes and beam elements for the diagonal braces. Contact conditions between the disc connectors and tube ends are modeled using penalty contact algorithms. The model incorporates geometric imperfections based on measured out-of-plumbness values from the test specimens.

Model Parameter	Value	Justification
Mesh size	10 mm × 10 mm	Convergence study results
Material model	Elastic-plastic (von Mises)	Q235 steel behavior
Imperfection amplitude	L/500	Measured from specimens
Contact stiffness	10^7 N/mm	Penalty method calibration
Buckling mode shape	First mode	Linear buckling analysis

The finite element predictions correlate well with experimental results, with deviations generally within 10 percent. The model accurately captures the post-buckling behavior and the progressive failure sequence observed in testing.

Design Recommendations

The study provides practical recommendations for the design and use of disc-lock steel pipe supports:

Slenderness ratios should be limited to 150 for standard support applications.
Cross-bracing configuration provides significantly higher stability capacity than single diagonal bracing, particularly for heights exceeding 3.0 meters.
The effective buckling length between disc connections should be taken as the actual disc spacing, not the full support height.
Connection rotational stiffness should be conservatively estimated as semi-rigid, with a stiffness value between 0.5EI/L and 2.0EI/L.
Geometric imperfections should be included in design calculations, with initial out-of-plumbness not exceeding L/500.

Quality Control and Inspection

For field applications, the following quality control measures are recommended:

Verify disc connector integrity and absence of deformation before assembly.
Check tube straightness and absence of dents or corrosion damage.
Confirm diagonal brace installation at the correct angles and with proper engagement of disc connectors.
Monitor out-of-plumbness during construction and after loading, with maximum allowable deviation of L/300.

Concluding Remarks

The experimental and numerical investigation confirms that disc-lock steel pipe support systems can provide reliable compressive stability when properly designed and assembled. The finite element methodology presented offers a practical tool for predicting the capacity of specific support configurations. Engineers should pay particular attention to slenderness ratio control, brace configuration selection, and the semi-rigid nature of disc connections when designing temporary support systems for construction applications.