Cyclic Performance of Overlay-Welded Sleeve Grouting Connections Under High-Stress Repeated Tension-Compression

Literature Overview

The paper by Gao Qiang and Zhao Weijian, published in the China Civil Engineering Journal (2022, Vol. 43, No. 4, pp. 220–227), investigates the performance of overlay-welded sleeve grouting connections under high-stress cyclic tension-compression loading. This companion study to the uniaxial tension research (Topic 3) addresses the critical question of connection durability under repeated loading, which is particularly relevant for seismic design and fatigue-critical applications. Four joint specimens were tested under cyclic loading protocols, and the results were compared with monotonic tension test results. The study is funded by the National Science and Technology Support Program (2011BAJ10B04) and the National Natural Science Foundation of China (51278312).

Experimental Program and Loading Protocol

The experimental program involved the fabrication of four joint specimens using overlay-welded sleeves and slotted reinforcement bars, identical in geometry to those used in the monotonic tension study. The cyclic loading protocol consisted of 20 cycles of high-stress tension-compression, with the stress levels calibrated to ensure that the reinforcement bars experienced significant plastic deformation. The following table summarizes the test parameters:

The loading protocol was designed to simulate the type of repeated loading that connections may experience in seismic events or under fatigue-critical service conditions. The high stress levels ensure that the connection is subjected to significant plastic deformation, which is the most demanding condition for evaluating connection durability.

Test Results and Performance Evaluation

The cyclic loading tests revealed several important findings regarding the connection performance:

1. Residual Deformation: After 20 cycles of high-stress loading, the residual deformation of the connections was approximately 0.1 mm, indicating stable and reliable performance with minimal accumulated damage.
2. Failure Mode: The cyclic loading did not significantly alter the failure mode or ultimate capacity of the connections compared to monotonic loading. The connections maintained their structural integrity throughout the cyclic loading.
3. Stiffness Degradation: The stiffness of the connections decreased by approximately 40% before reinforcement bar yielding, indicating some degree of damage accumulation during cyclic loading.
4. Ductility Enhancement: The elongation at fracture increased by approximately 26% compared to monotonic loading, suggesting that cyclic loading may have a beneficial effect on the ductility of the connection.
5. Strain Distribution: The strain distribution in the reinforcement bars at the sleeve end showed distinct differences between tension and compression phases. After 20 cycles, the strain values at maximum tension converged to consistent values, indicating stabilization of the connection behavior.
6. Sleeve Strains: The axial and hoop strains in the sleeve were not significantly affected by the cyclic loading, suggesting that the sleeve material maintained its structural integrity.

Engineering Implications and Design Considerations

The findings of this study have important implications for the design of overlay-welded sleeve grouting connections in applications subject to cyclic or seismic loading:

• The residual deformation of approximately 0.1 mm after 20 high-stress cycles is acceptable for most structural applications, indicating that the connections can withstand repeated loading without significant degradation.
• The 40% stiffness reduction before yielding suggests that the connections may exhibit some degree of slip or damage accumulation during cyclic loading. Engineers should consider this in their design calculations, particularly for applications where stiffness is a critical design parameter.
• The 26% increase in elongation at fracture is a positive finding, as it suggests that the connections retain their ductility under cyclic loading. This is particularly important for seismic design, where ductile behavior is essential for energy dissipation and damage control.
• The stability of the failure mode and ultimate capacity under cyclic loading indicates that the connections are reliable under repeated loading conditions.

The following design recommendations are derived from the study:

Study Insights and Comparative Analysis

The comparison between the monotonic and cyclic loading results provides valuable insight into the connection behavior under different loading conditions. The relatively small residual deformation and stable failure mode under cyclic loading are encouraging findings, suggesting that overlay-welded sleeve grouting connections are suitable for applications subject to repeated loading. However, the stiffness degradation observed during cyclic loading should be carefully considered in design, as it may affect the overall structural response under seismic or fatigue loading.

The strain distribution data reveals an interesting phenomenon: the convergence of strain values at the sleeve end after 20 cycles suggests that the connection reaches a stable state where the load transfer mechanism has fully developed. This stabilization behavior is important for understanding the long-term performance of the connections and for predicting their behavior under more severe loading conditions.

The observation that the sleeve strains are not significantly affected by cyclic loading is particularly important, as it indicates that the overlay-welded sleeve material maintains its structural integrity under repeated loading. This is a critical finding for the design of overlay-welded connections, as it confirms that the overlay welds are capable of withstanding the stresses induced by cyclic loading without cracking or degradation.

The study also raises important questions about the long-term behavior of these connections under more severe cyclic loading conditions, such as those encountered in major seismic events. While the current study demonstrates adequate performance for 20 high-stress cycles, further investigation is needed to establish the fatigue life of the connections under more demanding loading protocols. Engineers should also consider the potential effects of environmental factors, such as temperature variations and corrosion, on the long-term performance of overlay-welded sleeve connections.

Concluding Remarks

The research by Gao Qiang and Zhao Weijian provides valuable experimental data on the cyclic performance of overlay-welded sleeve grouting connections. The findings demonstrate that these connections are capable of withstanding high-stress cyclic loading with minimal residual deformation and stable failure modes. The stiffness degradation and ductility enhancement observed during cyclic loading provide important design parameters for engineers. The quality of the overlay weld is critical for connection performance, and engineers should ensure that appropriate welding procedure qualification and in-process inspection are implemented. The combination of monotonic and cyclic loading studies provides a comprehensive understanding of the connection behavior and supports the use of overlay-welded sleeve grouting connections in a wide range of structural applications, including those subject to seismic or fatigue loading.