Mechanical Performance of Overlay-Welded Sleeve Grouting Connections Under Uniaxial Tension

Literature Overview

The paper by Gao Qiang and Zhao Weijian, published in the China Civil Engineering Journal (2022, Vol. 43, No. 4, pp. 208–219), investigates the mechanical behavior of sleeve grouting connections formed by overlay welding under uniaxial tensile loading. The study is funded by the National Science and Technology Support Program (2011BAJ10B04) and the National Natural Science Foundation of China (51278312). Twenty-one specimens with varying parameters were fabricated and tested, providing a comprehensive dataset on the influence of anchor length, ring rib spacing, and sleeve inner diameter on connection performance. This research is highly relevant to the construction industry, particularly for applications in high-rise buildings, bridges, and seismic-resistant structures where reliable mechanical connections are critical.

Experimental Design and Specimen Configuration

The experimental program involved the fabrication of 21 joint specimens using overlay-welded sleeves and slotted reinforcement bars. The overlay welding process was used to form the internal ring ribs within the sleeve, providing mechanical interlock with the slotted bars. The key geometric parameters varied across specimens included:

The overlay welding process used to form the ring ribs is a specialized application of the technique, requiring precise control of deposition geometry, penetration depth, and metallurgical bond strength. The internal ribs created by overlay welding provide a mechanical interlock mechanism that transfers tensile forces from the reinforcement bar to the surrounding grout material and ultimately to the sleeve.

Test Results and Failure Mechanisms

The uniaxial tension tests revealed two distinct failure modes depending on the anchor length relative to a critical threshold value. When the anchor length was below the critical value (approximately 5d to 6d, where d is the reinforcement bar diameter), the failure mode was characterized as a scraping-out or plowing failure, where the reinforcement bar was pulled out of the sleeve with damage to the grout and sleeve material. When the anchor length exceeded the critical value, the failure mode was tensile fracture of the reinforcement bar itself, indicating that the connection was stronger than the bar.

The strain distribution analysis provided valuable insights into the load transfer mechanism. The reinforcement bar strain decreased from the sleeve end toward the mid-section, indicating that the majority of the tensile force was transferred near the sleeve end where the ring ribs provide the primary mechanical interlock. Conversely, the axial strain in the sleeve increased from the end toward the mid-section, reflecting the progressive development of hoop stress as the bar expands radially under tension.

The sleeve deformation pattern showed expansion at the end section and radial contraction at the mid-section, consistent with the Poisson effect and the non-uniform load distribution along the anchor length. This deformation behavior has important implications for the design of overlay-welded sleeve connections, as it indicates that the end regions of the sleeve experience the highest stresses and should be designed accordingly.

Parametric Analysis and Design Recommendations

The parametric study yielded several important design conclusions:

1. The critical anchor length for preventing bar pullout is in the range of 5d to 6d, providing a clear design criterion for engineers.
2. Reducing the number of internal ring ribs causes stress redistribution, with a larger proportion of the tensile force transferred at the sleeve end where ribs remain.
3. Decreasing ring rib spacing increases the connection capacity up to a certain threshold, beyond which further reduction provides diminishing returns.
4. The sleeve inner diameter has no significant influence on connection capacity, simplifying the design process.

These findings have direct implications for the design of overlay-welded sleeve grouting connections. The following design recommendations are derived from the study:

Study Insights and Engineering Implications

The research by Gao Qiang and Zhao Weijian provides a rigorous experimental foundation for the design of overlay-welded sleeve grouting connections. The identification of the critical anchor length as a key design parameter is particularly valuable, as it enables engineers to establish clear acceptance criteria for connection design. The strain distribution data also provides insight into the load transfer mechanism, which is essential for understanding the connection behavior under complex loading conditions.

One notable observation is the effectiveness of overlay welding in forming internal ribs within sleeves. This technique offers advantages over traditional machining or casting methods, including the ability to create complex internal geometries and the potential for localized reinforcement. However, the quality of the overlay weld is critical, as any defects in the rib geometry or bond strength would compromise the connection performance. Engineers should ensure that overlay welding processes are qualified through appropriate welding procedure qualification (WPQ) and that in-process inspections are conducted to verify rib geometry and weld quality.

The study also raises important questions about the behavior of these connections under cyclic or seismic loading, which is addressed in the companion study by the same authors (Topic 5 below). The combination of both studies provides a comprehensive understanding of the connection performance under both monotonic and cyclic loading conditions.