Mechanical Performance of Prefabricated Wall-Column Connections with CFST Key Joints

Literature Overview

This research by Wu Qian et al. (2019), published in Industrial Construction (Vol. 49, No. 11, pp. 138-143), investigates the mechanical performance of prefabricated reinforced concrete (RC) columns and shear walls connected through CFST (concrete-filled steel tube) key joints. The study was funded by the National Key R&D Program (2017YFC0703805), Liaoning Provincial Natural Science Foundation (20180550288), and Shenyang Science and Technology Support Program (18-013-0-29). Three specimens were subjected to shear tests to compare the performance of different connection configurations.

Connection Configurations and Test Programme

The study compares three connection approaches:

CFST key with RC block insertion: A reinforced concrete block is placed between the CFST key and the mating surface.
CFST key without RC block: The CFST key directly contacts the mating surface without an intermediate RC block.
Cast-in-place structure: A conventional cast-in-place connection as a reference.

The shear tests evaluated load-displacement curves, failure modes, and stress distributions for each configuration.

Core Technical Findings

Connection Type	Load Capacity	Ductility	Initial Stiffness	Failure Mode	Seismic Performance
CFST key + RC block	Higher than cast-in-place	Higher than cast-in-place	Comparable to cast-in-place	Distinct failure stages	Excellent
CFST key without RC block	Higher than cast-in-place	Higher than cast-in-place	Lower than cast-in-place	Less distinct failure stages	Good
Cast-in-place (reference)	Baseline	Baseline	Highest	Gradual	Baseline

The results demonstrate that both CFST key connection types exhibit superior load capacity and ductility compared with the cast-in-place reference. However, the configuration without the RC block shows reduced initial stiffness relative to the cast-in-place structure, while the configuration with the RC block maintains comparable initial stiffness and exhibits more distinct failure stages, indicating better energy dissipation characteristics.

Engineering Practice Implications

From a steel pipe manufacturing and structural engineering perspective, several important considerations emerge:

Prefabrication advantages: The CFST key connection method enables significant benefits in construction speed, quality control, and reduced on-site labour. The mechanical performance data demonstrates that these prefabricated connections can match or exceed the performance of cast-in-place alternatives.
RC block insertion significance: The inclusion of an RC block between the CFST key and the mating surface is critical for maintaining initial stiffness and achieving distinct failure stages. This finding has direct implications for connection design and detailing.
Seismic performance: The superior ductility of both CFST key configurations suggests enhanced seismic resilience. The RC block configuration, with its more distinct failure stages, offers better predictability of failure behaviour under cyclic loading.

Welding and Fabrication Considerations

The CFST key joints involve critical welding operations that must be carefully controlled:

Pipe-to-flange welding: The connection between the steel tube and the key joint flange requires full-penetration welds with strict quality control. Welding procedures should comply with applicable standards such as GB 50661 or AWS D1.1.
Residual stress management: The welding process introduces residual stresses that can affect the connection's load-bearing capacity and fatigue performance. Pre-welding heat treatment or post-weld stress relief may be necessary for high-strength steel applications.
Dimensional accuracy: The CFST key geometry must be precisely controlled to ensure proper fit-up with the mating surface. Tolerances for key dimensions should be tightly specified to prevent gaps that could compromise load transfer.

Key Reflections and Critical Analysis

The finding that both CFST key configurations outperform the cast-in-place reference in terms of load capacity and ductility is noteworthy. This challenges the conventional assumption that cast-in-place connections inherently provide superior mechanical performance. The enhanced ductility of the CFST key connections can be attributed to the steel tube's ability to deform plastically and redistribute stresses, providing a more ductile failure mode compared with the brittle cracking typical of cast-in-place concrete connections.

However, the reduced initial stiffness of the CFST key configuration without the RC block raises concerns about serviceability performance. In structures subject to frequent seismic events or wind loading, excessive initial deformations may lead to non-structural damage or occupant discomfort. The RC block configuration appears to be the preferred solution for most practical applications.

The study's emphasis on seismic performance is particularly relevant given the increasing adoption of prefabricated construction in seismically active regions. The demonstrated ductility advantages of CFST key connections could significantly improve the overall seismic resilience of prefabricated structures.

Summary

This study provides compelling evidence that CFST key connections for prefabricated wall-column systems can achieve mechanical performance equal to or better than cast-in-place alternatives. The inclusion of an RC block between the CFST key and the mating surface is recommended to maintain initial stiffness and achieve distinct failure stages. These findings support the continued development and standardisation of prefabricated construction methods that leverage steel pipe components for enhanced structural performance and construction efficiency.