CLADDING TECHNOLOGY SHANXI CO., LTDStudy Note on Tensile Performance of Weld Overlay Grouted Sleeve Connections
Literature Overview
This paper by Gao Qiang from the School of Civil Engineering at Shenyang Jianzhu University and Zhao Weijian from the School of Civil Engineering at Zhejiang University, published in the Journal of Building Structures in 2022 under the National Science and Technology Support Program (2011BAJ10B04) and National Natural Science Foundation (51278312), investigates the mechanical performance of grouted sleeve connections incorporating weld overlay features under unidirectional tensile loading. This research is significant for structural engineers working on bolted and mechanical connections in steel structures, particularly in applications where corrosion resistance or enhanced load transfer capacity is required at connection interfaces. The study contributes to the understanding of how weld overlay modifications affect the load-bearing capacity, ductility, and failure modes of grouted sleeve connections used in prefabricated steel construction.
Core Technical Viewpoints
The research addresses several important aspects of weld overlay grouted sleeve connection performance:
- Connection configuration: The grouted sleeve connection consists of an inner reinforcing steel bar inserted into an outer steel sleeve, with the annular gap filled with high-strength non-shrink grout. Weld overlay is applied to the inner surface of the sleeve to enhance bond strength and corrosion resistance.
- Load transfer mechanism: Under tensile loading, load is transferred from the reinforcing bar through the grout-sleeve interface via friction and mechanical interlock. The weld overlay layer modifies the interface friction characteristics and provides additional mechanical keying.
- Failure modes: The study identifies several potential failure modes including grout-sleeve interface slip, sleeve yielding, reinforcing bar yielding, and weld overlay spalling, with the dominant failure mode depending on the overlay thickness, grout properties, and connection geometry.
- Parametric influence: Key parameters affecting connection performance include sleeve inner diameter, sleeve wall thickness, overlay thickness, grout compressive strength, and reinforcing bar yield strength.
Experimental Test Results and Key Parameters
| Test Variable | Range Tested | Effect on Tensile Capacity |
|---|---|---|
| Sleeve inner diameter | 80–120 mm | Larger diameter increases capacity proportionally |
| Sleeve wall thickness | 6–10 mm | Thicker walls delay sleeve yielding |
| Overlay thickness | 0, 1.5, 3.0 mm | 1.5–3.0 mm overlay increases capacity by 15–25% |
| Grout compressive strength | 40–80 MPa | Higher strength increases bond capacity |
| Reinforcing bar yield strength | 400–600 MPa | Higher grade bars increase overall capacity |
| Sleeve length | 10d–20d (d = bar diameter) | Longer sleeves improve load transfer efficiency |
Failure Mode Analysis
The study classified the observed failure modes as follows:
| Failure Mode | Description | Critical Parameter | Design Implication |
|---|---|---|---|
| Interface slip | Grout-sleeve relative displacement exceeds threshold | Overlay surface roughness; grout friction coefficient | Ensure adequate overlay roughness; use high-friction grout |
| Sleeve yielding | Sleeve wall reaches yield stress | Sleeve wall thickness; overlay contribution to section modulus | Design sleeve thickness considering overlay section |
| Bar yielding | Reinforcing bar reaches yield strength | Bar cross-sectional area; connection length | Ensure connection capacity exceeds bar yield capacity |
| Overlay spalling | Weld overlay separates from sleeve substrate | Bond strength; thermal cycling; residual stress | Control overlay process parameters; verify bond strength |
| Grout crushing | Grout fails in bearing under concentrated load | Grout compressive strength; bearing area | Use high-strength grout; ensure uniform grout fill |
Engineering Design Recommendations
Based on the experimental findings, the following design recommendations are proposed for practical application:
- Overlay thickness optimization: An overlay thickness of 1.5–3.0 mm provides the optimal balance between bond enhancement and cost, with diminishing returns beyond 3.0 mm due to increased risk of overlay spalling.
- Grout selection: Non-shrink grout with compressive strength of at least 60 MPa is recommended for critical connections, as it provides adequate bearing capacity and dimensional stability.
- Connection length: A minimum sleeve length of 15d (where d is the reinforcing bar diameter) is recommended to ensure adequate load transfer and prevent interface slip under service loading.
- Overlay surface preparation: The overlay surface should be prepared with a controlled roughness profile (Ra 12.5–25 μm) to maximize mechanical interlock with the grout without introducing stress concentration sites.
- Quality verification: Post-installation inspection should include ultrasonic testing of the grout fill to detect voids, pull-out testing of sample connections to verify bond strength, and visual inspection of the overlay surface for defects.
Study Insights and Implications
This research makes a valuable contribution to the field of structural connection design by demonstrating that weld overlay can significantly enhance the tensile performance of grouted sleeve connections without requiring changes to the fundamental connection geometry. The practical implication for structural engineers is that existing connection designs can be upgraded through overlay modification, providing a cost-effective retrofit solution for aging infrastructure. A critical consideration that emerges from the study is the long-term durability of the overlay layer under cyclic loading conditions, which is not fully addressed in the static tensile tests presented. Engineers should note that the weld overlay process introduces residual stresses at the sleeve-overlay interface, which may interact with the grout stresses during service loading and potentially accelerate fatigue damage at the interface. Future research should investigate the fatigue performance of overlay-modified grouted sleeve connections under cyclic loading, as well as the effects of environmental exposure (chloride ingress, carbonation, and freeze-thaw cycling) on the long-term bond strength of the overlay-grout interface. The findings of this study provide a solid foundation for the development of design guidelines for weld overlay enhanced structural connections in seismic and wind-resistant design applications.