Cyclic Tension-Compression Performance of Overlay-Welded Grout-Filled Sleeve Connections

Literature Overview

This companion paper by Gao Qiang and Zhao Weijian (2022, Journal of Building Structures, Vol. 43, No. 4, pp. 220-227) extends the uniaxial tensile study to investigate the behavior of overlay-welded grout-filled sleeve connections under high-stress cyclic tension-compression loading. Four specimens were subjected to cyclic loading protocols, with results compared against uniaxial tension tests to evaluate connection durability and seismic performance potential.

Technical Motivation and Seismic Context

In seismic regions, steel structures must withstand repeated cyclic loading without progressive damage accumulation. Grout-filled sleeve connections are widely used in steel structures for field splicing of reinforcing bars, and their cyclic performance directly affects seismic resilience. The overlay-welded sleeve manufacturing technique, while promising in static loading (as shown in the companion study), requires validation under fatigue and cyclic conditions.

Experimental Protocol

The cyclic loading protocol applies 20 repeated cycles at high stress levels (approaching yield), simulating seismic loading conditions.

Key Experimental Results

Residual Deformation

After 20 cycles of high-stress tension-compression loading, the residual deformation of the connection specimens was approximately 0.1 mm. This value is remarkably small and indicates:

The negligible residual deformation confirms that the connection maintains its geometric integrity and functional capacity after repeated loading.

Effect on Load Capacity and Failure Mode

The high-stress cyclic loading does not alter the failure mode or significantly reduce the ultimate load capacity. This is a critical finding indicating that the connection mechanism—mechanical interlock between ribs and grout—remains intact after repeated loading.

Stiffness and Ductility Changes

The 40% reduction in pre-yield stiffness indicates that the connection experiences some degree of damage accumulation in the elastic range, likely due to micro-cracking in the grout or slight loosening of the bar-grout interface. However, the 26% increase in elongation suggests that the connection retains—and even enhances—its ductility, which is favorable for seismic performance.

Strain Distribution Under Cyclic Loading

The strain distribution measurements reveal important behavioral differences between tension and compression phases:

• Tension phase: Strain concentrates at the sleeve end region, with progressive load transfer toward the middle—similar to static tension behavior.
• Compression phase: Strain distribution differs markedly, with more uniform distribution along the bar length.
• After 20 cycles: The strain values at the sleeve end during peak tension converge toward a consistent value, indicating stabilization of the load transfer mechanism.

Sleeve Strain Behavior

The sleeve itself shows no significant degradation under cyclic loading, confirming that the overlay-welded ribs maintain their structural integrity. The constraint effect of the sleeve on the bar is minimal before bar yielding, which has implications for connection design philosophy.

Design Implications and Performance Assessment

Seismic Performance Classification

Based on the experimental results, the overlay-welded grout-filled sleeve connection can be classified as:

Design Recommendations

1. For seismic applications: The connection demonstrates adequate cyclic performance for moderate seismic zones. The small residual deformation and stable failure mode are particularly favorable.
2. Stiffness consideration: The 40% stiffness reduction in the elastic range should be accounted for in structural analysis, particularly for connections subjected to frequent small-amplitude cycles (e.g., wind loading).
3. Cycle capacity: Only 20 cycles were tested; for high-seismicity regions requiring greater cycle capacity (50-100 cycles), additional testing is recommended.
4. Weld quality criticality: The internal overlay-welded ribs must be manufactured to high quality standards, as any weld defect could initiate progressive damage under cyclic loading.

Comparative Analysis with Traditional Connections

The overlay-welded connection shows competitive or superior cyclic performance compared to traditional machined connections, while offering manufacturing advantages.

Study Insights and Engineering Outlook

This research provides critical validation of the overlay-welded grout-filled sleeve connection under cyclic loading conditions. The most significant finding is the combination of negligible residual deformation (0.1 mm) and maintained load capacity (>95%) after 20 high-stress cycles, which strongly suggests suitability for seismic applications. The stiffness reduction of 40% in the elastic range is the primary concern and warrants further investigation through fatigue testing at lower stress levels. The convergence of strain distribution after multiple cycles indicates that the connection reaches a stabilized load-transfer state—a behavior that could be leveraged in performance-based design approaches. Engineers considering this technology for seismic structures should ensure comprehensive weld quality inspection of internal ribs and conduct connection-level cyclic testing as part of the qualification process before deployment in critical applications.