Shake Table Test of Steel-Concrete Filled Steel Tube Frame Structure

Literature Overview

The paper by Du Guofeng, Xu Chengxiang, and Jiang Chuxiong, published in the Journal of Chongqing University (Natural Science Edition) in 2008, reports a systematic shake table test on a 1:10 scaled steel-concrete filled steel tube (CFST) column-H steel beam frame model. The research was supported by the Hubei Provincial Natural Science Foundation (2003ABA059). The study aims to evaluate the seismic response, dynamic characteristics, and seismic performance of CFST frame structures under simulated earthquake excitations, which is of direct relevance to the design and assessment of steel pipe-based structural systems in seismic zones.

Core Technical Findings

The test specimen was a single-bay frame model constructed at a 1:10 geometric scale, consisting of CFST columns and H-section steel beams. Three earthquake wave inputs were applied: El Centro wave, Tianjin wave (N-S component), and a Wuhan artificial wave. The measured responses included acceleration, displacement, and strain at critical locations.

Interpretation of Dynamic Characteristics

The first three natural frequencies of the model (9.51, 10.91, and 17.75 Hz) correspond to prototype periods of 1.05, 0.92, and 0.56 seconds, which fall within the typical range for medium-rise steel-concrete composite frames. The torsion-to-translation period ratios of 0.53 (Y-direction) and 0.61 (X-direction) are both below 0.7, satisfying the Chinese seismic code requirement (GB 50011) that torsional coupling should not dominate the structural response. This indicates that the frame possesses adequate torsional stiffness and that the structural layout is reasonably symmetric.

The acceleration amplification factor of 3.35 is notably high, suggesting significant dynamic amplification at the top of the structure. This is consistent with the expected behavior of a structure whose fundamental period is close to the dominant frequency content of the El Centro wave. Engineers should note that this amplification factor has direct implications for the design of non-structural components and connection detailing at beam-column joints.

Seismic Performance Assessment

Under an 8.5-degree frequent earthquake scenario, the prototype structure remained entirely within the elastic range. The maximum elastic total displacement angle of 1/750 and the inter-story drift angle of 1/318 both comply with the code-specified limits (1/550 for total displacement angle and 1/250 for inter-story drift angle under frequent earthquakes per GB 50011-2010). This confirms that the CFST frame system provides sufficient elastic deformation capacity and energy dissipation for seismic resistance at the frequent earthquake level.

Engineering Practice Implications

From a steel pipe manufacturing and structural engineering perspective, this study reinforces the value of CFST columns as seismic-resistant structural elements. The key insight is that the composite action between the steel tube and the infill concrete provides superior ductility and energy dissipation compared to hollow steel tube columns. For engineers specifying steel pipes for such applications, the following considerations are relevant:

• The steel tube should be fabricated with high dimensional accuracy to ensure proper concrete placement and composite action.
• Welding quality at tube-to-beam connections is critical, as these joints govern the overall seismic performance.
• The steel grade typically used (Q345 or Q355 per GB/T 1591) must meet the elongation and toughness requirements for seismic detailing.
• The wall thickness-to-diameter ratio must be controlled to prevent local buckling of the steel tube under cyclic loading.

Key Questions and Reflections

A significant question raised by this study is whether the 1:10 scale factor adequately captures the size effect on the concrete confinement behavior within the steel tube. At smaller scales, the concrete confinement effect may be overestimated due to the relative increase in steel tube wall thickness. Future studies should consider testing at larger scales or conducting parametric numerical investigations to validate the scaling assumptions.

Another important reflection is that the study only evaluated the frequent earthquake scenario. Engineers should seek additional data on the structure's performance under rare and fortification-level earthquakes, where inelastic deformation and potential local buckling of the steel tube become critical concerns. The connection design and steel tube material properties under large plastic strains warrant further investigation.

Study Insights and Implications

This shake table test provides valuable experimental validation for the seismic design of CFST frame structures. The measured dynamic characteristics and elastic seismic response are consistent with theoretical predictions, lending confidence to the use of CFST systems in seismic regions. For steel pipe manufacturers and structural engineers, the study underscores the importance of maintaining high fabrication quality and ensuring that the steel tube geometry, material properties, and welding details are all optimized for composite seismic performance. The results also suggest that CFST frames can achieve satisfactory seismic performance without requiring excessive structural redundancy, which has direct economic implications for project feasibility.