Zhuojin Pipe Fitting Co., LtdSeismic Performance Test of Rectangular Steel Tube Concrete Planar Frame Structure
Overview and Research Significance
The experimental study by Li Bin and colleagues, published in the Journal of Inner Mongolia University of Science and Technology (2012, Vol. 31, Issue 1), presents low-cycle reversed loading tests on four full-scale single-story, single-bay frame specimens composed of square steel tube concrete columns and rectangular steel tube concrete beams. The study investigates the effects of column axial compression ratio and slenderness ratio on the hysteresis behavior, ductility, failure mechanisms, and seismic performance of fully rectangular steel tube concrete (SRC) frame structures.
Specimen Configuration and Test Parameters
Four specimens were designed with varying column axial compression ratios and slenderness ratios to systematically evaluate the influence of these parameters on structural response. The frames were tested under displacement-controlled low-cycle reversed loading protocols that simulate the inelastic deformation demands imposed by seismic loading.
| Parameter | Range Tested | Effect on Performance |
|---|---|---|
| Column axial compression ratio | Multiple levels | Higher ratio increases capacity but reduces ductility |
| Slenderness ratio | Multiple levels | Higher ratio reduces stiffness and capacity but increases displacement capacity |
| Displacement ductility coefficient | 3.05–3.49 | Meets ductile frame requirements |
Key Experimental Results
The hysteresis curves of all specimens were plump and exhibited no significant pinching, which indicates good energy dissipation capacity and stable inelastic behavior throughout the loading history. The displacement ductility coefficients ranged from 3.05 to 3.49, satisfying the requirements for ductile frame structures as specified in seismic design codes such as GB 50011.
The parametric study revealed clear trends: as the column axial compression ratio increased, the load-bearing capacity of the specimens increased while the displacement ductility decreased and the stiffness degradation became more pronounced. As the slenderness ratio increased, the initial stiffness decreased, the horizontal load-bearing capacity dropped significantly, and both the yield displacement and ultimate displacement increased substantially. The slenderness ratio influenced not only the numerical values of the response curves but also their overall shape.
Welding and Fabrication Considerations
The construction of rectangular steel tube concrete frame specimens involves critical welding operations at the beam-column joints. The steel tubes must be fabricated from high-quality structural steel plates, typically Q345 or Q355 grade, with longitudinal and circumferential welds inspected by ultrasonic testing (UT) in accordance with GB/T 11345. The connection details at the joints, whether bolted, welded, or hybrid, must be designed to ensure that the failure mode is ductile yielding of the steel tubes rather than brittle weld fracture.
The concrete infilling process within the rectangular steel tubes requires careful attention to compaction quality. Insufficient compaction can lead to voids that reduce the effective confinement of the concrete and compromise the composite action between the steel tube and the concrete core. The use of self-compacting concrete or carefully designed vibration protocols is recommended to ensure full filling of the steel tubes.
Engineering Application Assessment
The test results demonstrate that rectangular steel tube concrete frame structures possess good seismic performance characteristics, including plump hysteresis curves, adequate ductility, and stable energy dissipation capacity. The parametric study provides valuable design guidance: column axial compression ratios should be controlled to maintain sufficient ductility, and slenderness ratios should be selected to balance stiffness requirements against displacement capacity. These findings support the further research and practical application of fully rectangular SRC frame systems in seismic regions.
Study Reflections
The confirmation that rectangular SRC frames can achieve displacement ductility coefficients of 3.05 to 3.49 is encouraging for their application in medium-rise structures. However, the study was limited to single-story specimens, and the behavior of multi-story frames with cumulative deformation demands may differ. Future research should extend to multi-story specimens and incorporate the effects of P-Δ second-order effects, which become more significant in taller structures. The study also provides a foundation for developing simplified analytical models that can be used for practical seismic design of rectangular SRC frames.