Bending and Shear Tests of Steel Pipe Interlocking Rigid Joints in Prefabricated Diaphragm Walls

Literature Overview

This study investigates the mechanical performance of steel pipe interlocking rigid joints used in prefabricated underground diaphragm walls. Prefabricated diaphragm walls are increasingly used in deep foundation engineering for their advantages in construction speed, environmental friendliness, and quality control compared to traditional in-situ diaphragm walls. The steel pipe interlocking joint is a critical connection element that transfers bending moments and shear forces between prefabricated wall panels.

Core Technical Content

Joint Configuration and Loading Conditions

The steel pipe interlocking rigid joint typically consists of steel pipes embedded at the edges of prefabricated concrete wall panels. During installation, the steel pipes of adjacent panels are interlocked or welded together to create a continuous diaphragm wall. The joint must resist both bending moments and shear forces that develop during excavation support and subsequent structural loading.

Test Parameter	Typical Values	Testing Standard
Steel pipe diameter	89-219 mm	GB/T 8163
Steel pipe wall thickness	6-12 mm	GB/T 8163
Concrete strength	C30-C50	GB/T 50081
Bending moment capacity	Design-dependent	GB 50011
Shear capacity	Design-dependent	GB 50011

Bending Performance Analysis

The bending behavior of the steel pipe interlocking joint is governed by several factors:

The yield strength and ductility of the steel pipe material.
The concrete cover thickness around the embedded steel pipe.
The connection method between adjacent steel pipes (welding, bolted, or friction fit).
The strain hardening characteristics of the steel pipe under cyclic loading.

The joint typically exhibits a bilinear moment-rotation relationship, with initial elastic behavior followed by plastic deformation at the pipe connection zone. The ultimate bending capacity is reached when the steel pipe cross-section achieves full plastic moment resistance.

Shear Performance Analysis

Shear resistance in the steel pipe interlocking joint depends on:

The friction and interlock between adjacent steel pipes.
The shear capacity of the concrete in the joint zone.
The weld strength if welded connections are used.
The confinement effect of surrounding concrete on the steel pipe.

The shear failure mode may involve steel pipe yielding, concrete crushing, or weld fracture, depending on the relative strengths of these components.

Defect Analysis Using FMEA Approach

Applying Failure Mode and Effects Analysis to the steel pipe interlocking joint reveals several critical failure modes:

Failure Mode	Severity	Occurrence	Detection	RPN
Weld cracking	10	3	4	120
Steel pipe yielding	8	2	3	48
Concrete crushing	6	4	3	72
Interlock slip	7	3	2	42
Corrosion at interface	5	5	2	50

Engineering Practice Implications

For engineers designing prefabricated diaphragm walls with steel pipe interlocking joints, the test results provide essential data for structural design calculations. The following practical recommendations emerge:

Weld quality at the steel pipe connections must be strictly controlled through non-destructive testing, particularly ultrasonic testing for subsurface defects.
The concrete strength in the joint zone should be at least equal to the wall panel concrete strength to ensure that failure occurs in the steel pipe rather than in the concrete.
Proper detailing of steel pipe embedment depth and spacing is critical for achieving the designed load transfer capacity.
Construction tolerances for steel pipe alignment must be tightly controlled to prevent eccentric loading that could reduce joint capacity.

Study Insights and Reflections

The study of steel pipe interlocking joints in prefabricated diaphragm walls addresses a practical and increasingly important engineering challenge. As urban construction becomes more constrained by space and environmental regulations, prefabricated wall systems offer significant advantages, but the connection details must be rigorously verified through testing.

One important insight from this type of testing is that the joint performance is often governed by the weakest link in the load transfer chain, which may not be the steel pipe itself but rather the concrete-steel interface or the weld connection. This emphasizes the need for integrated joint design rather than isolated component design.

The application of systematic testing approaches such as bending and shear tests under controlled laboratory conditions provides reliable data that cannot be obtained from field observations alone. For engineers responsible for quality assurance in deep foundation projects, understanding the test results and their implications for design and construction is essential for ensuring structural safety and serviceability.