Behavior of Concrete-Filled U-Shaped Steel Beam to CFSST Column Connections
Abstract
:1. Introduction
2. Connection Details
3. Experimental Program
3.1. Design and Production of the Specimens
3.2. Test Setup and Loading Procedure
3.3. Experimental Results
4. Finite Element Model
4.1. Material Modeling
4.2. Finite Element Type and Mesh
4.3. Boundary and Loading Conditions
5. Numerical Results
5.1. Verification of FEA Model
5.1.1. Failure Mode
5.1.2. Load Versus Displacement Curves
5.2. Stress Analysis
5.2.1. Stress Analysis of the End of Bottom Plate for U-Shaped Steel Beam and the Internal Diaphragm
5.2.2. Stress Analysis of Steel Tube in the Connection Zone
- For each specimen, the stress in the compressive region of the steel tube flange of the connection zone is smaller than that in the tensile region, due to the fact that the concrete in the beam participates in transferring the compressive force and thus increases the loading area of the flange and reduces the stress level in the compressive region. In addition, the concrete in the steel tube is closely compacted under compression, preventing the deformation of the tube wall, which contributes to reduced stress in this region. For the tensile region, however, the tensile forces are mainly transferred to the flange of the steel tube through the steel plate or rebar in the composite beam, resulting in higher stress.
- For the RS connection, the stress in the left and right flanges of the tube adjacent to the concrete slab is smaller than that of the RT connection due to the fact that there are some holes on the surface of the tube to let the longitudinal rebars pass through, resulting in stress concentration in this region. Furthermore, the upper interior diaphragm of the RS connection can not only transfer the force in the longitudinal rebars but also provide extra support for the steel tube, which constrains the deformation of the column flange and hence reduces the stress in this region.
5.2.3. Stress Analysis of Concrete in Connection Zone
5.2.4. Stress Analysis of Rebars
5.2.5. Stress Development of Steel Components
6. Parametric Analysis
6.1. Effects of Thickness of U-Shaped Steel
6.2. Effects of Ratio of Longitudinal Rebar in Concrete Slab
6.3. Effects of Strength of Concrete in Beam
6.4. Effects of Strength of U-Shaped Steel
6.5. Effects of Thickness of Internal Diaphragm
7. Conclusions
- The numerical results are in agreement with the experimental results, which indicate that the developed finite element model could be used to analyze the behavior of the composite connection with proper precision.
- The stress analysis shows that the stress in the tensile bottom plate of the U-shaped steel beam near the connection zone has reached the ultimate strength of the steel, while the stress in the components that are far away from the panel zone is much smaller when the RS and RT connection fail. Furthermore, for the RS connection, the stress comparison shows that not only the stress distribution in the flanges and webs of the steel tube near the junction is more uniform, but also the inclined concrete compression struts in the panel zone exhibit better behavior due to the upper internal diaphragm.
- The parametric analysis indicates that the thickness of the U-shaped steel, the ratio of the longitudinal reinforcement in the concrete slab, and the strength of the U-shaped steel have a notable effect on the loading capacity of the connection, while the strength of concrete in the beam and the thickness of the internal diaphragm has a lighter effect on that.
- Based on the parameter analysis results of the connections and construction practicability, the bearing capacity of connections can be improved by increasing the ratio of the longitudinal reinforcement in the concrete slab and the thickness of the U-shaped steel in practical engineering when the structural requirements of reinforcement and the design conditions of strong column and weak beam are met.
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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Specimen | Column | Beam | Internal Diaphragm | Axial Load Ratio | ||||
---|---|---|---|---|---|---|---|---|
Steel Tube bc × bc × tc | U-Shaped Steel hw × b × b1 × tb | Negative Rebar | Width | Length | Thickness | The Vertical Load Values | ||
C-1 | 250 × 250 × 10 | 160 × 120 × 50 × 6 | 4D14 | 230 | 230 | 10 | 0.2 | 800 KN |
C-2 | 250 × 250 × 8 | 160 × 120 × 50 × 6 | 4D14 | 234 | 234 | 10 | 0.2 | 800 KN |
C-3 | 250 × 250 × 10 | 160 × 120 × 50 × 6 | 4D14 | 230 | 230 | 10 | 0.2 | 800 KN |
Type | Thickness (mm) | Yield Strength fy (MPa) | Ultimate Strength fu (MPa) | Elastic Modulus (105 MPa) | Elongation δ (%) |
---|---|---|---|---|---|
Steel tube | 8 | 312 | 455 | 1.99 | 35 |
10 | 330 | 435 | 2.03 | 34.5 | |
U-shaped steel beam | 6 | 285 | 423 | 1.97 | 31 |
Diaphragm | 10 | 370 | 445 | 2.09 | 31.5 |
Grade | Mix Proportion (kg/m3) | Cube Compressive Strength (MPa) | ||
---|---|---|---|---|
Cement | Sand | Gravel | ||
C20 | 336 | 640 | 1172 | 21.9 |
C30 | 360 | 609 | 1220 | 29.3 |
C40 | 420 | 523 | 1280 | 42.6 |
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Lin, Y.; Zhao, Z.; Gao, X.; Wang, Z.; Qu, S. Behavior of Concrete-Filled U-Shaped Steel Beam to CFSST Column Connections. Buildings 2023, 13, 517. https://doi.org/10.3390/buildings13020517
Lin Y, Zhao Z, Gao X, Wang Z, Qu S. Behavior of Concrete-Filled U-Shaped Steel Beam to CFSST Column Connections. Buildings. 2023; 13(2):517. https://doi.org/10.3390/buildings13020517
Chicago/Turabian StyleLin, Yan, Zhijie Zhao, Xuhui Gao, Zhen Wang, and Shuang Qu. 2023. "Behavior of Concrete-Filled U-Shaped Steel Beam to CFSST Column Connections" Buildings 13, no. 2: 517. https://doi.org/10.3390/buildings13020517