Numerical Analysis of Seismic Performances of Post-Fire Scoria Aggregate Concrete Beam-Column Joints
Abstract
:1. Introduction
2. Analysis Procedure
- (1)
- Heat transfer analysis: the heat transfer analysis was performed first in ABAQUS to determine the temperature distributions of the joints. This type of analysis is used when the stress or deformation field in a structure depends on the temperature field in that structure, but the temperature field can be found without knowledge of the stress/deformation response. Additionally, this type of analysis is usually performed by first conducting an uncoupled heat transfer analysis and then a stress/deformation analysis.
- (2)
- Seismic analysis: after the thermal damage of both rebars and SAC was both transmitted to the mechanical model, the seismic analysis considering thermal degradation of the material was implemented. However, the mechanical properties of SAC after fire needed to be measured experimentally. For this reason, before simulating the seismic performance of SAC beam-column joints, an experiment to get the mechanical properties of SAC after fire was designed and conducted in this paper.
- (3)
- Validation: to validate the FEM, the results of seismic performance of post-fire NAC joints simulated by the same FEM were compared with the test data of the reference [26] and analyzed. On the basis of this, effects of various parameters on the seismic performance of SAC beam-column joints after fire were investigated in depth reasonably. The workflow is shown in Figure 1.
3. Heat Transfer Analysis of SAC Joints
3.1. Thermal Material Modelling for SAC
3.2. Heat Transferring Analysis in ABAQUS
4. Post-Fire Seismic Analysis of SAC
4.1. Thermomechanical Damage Modeling for SAC
4.1.1. Test Program
4.1.2. Material Simulation through Experimental Tests Results Regression
- (1)
- Compressive and splitting tensile strengths
- (2)
- Peak Strain
- (3)
- Ultimate strain
- (4)
- Elastic modulus
- (5)
- Stress-strain curve
- (6)
- Constitutive equation
4.1.3. Thermal Damage Coefficient of SAC
4.1.4. Thermomechanical Damage Model for Rebars
4.2. Bond–Slip Model Considering Material Degradation of Rebars and SAC
4.2.1. Bond–Slip Model
4.2.2. Implementation in ABAQUS Using Spring Element
4.3. Element Selection
4.4. Geometrical Modeling
4.5. Analysis Results
5. Analysis Procedure Validation
5.1. Heat Transfer Analysis of NAC Joints
5.1.1. Thermal Material Modelling for NAC
5.1.2. Heat Transferring Analysis in ABAQUS
5.2. Post-Fire Seismic Analysis of NAC
5.2.1. Thermomechanical Damage Model of NAC and Rebars
5.2.2. Bond–Slip Model Considering Material Degradation of Rebars and NAC
5.3. Test from the Reference
5.4. Validation Results
6. Analysis of the Effect of Different Parameters on Seismic Performance of Post-Fire SAC Beam-Column Joints
6.1. Analysis of the Effects of Fire Time
6.2. Analysis of the Effects of Reinforcement Ratio
6.3. Analysis of the Effects of Axial Compression Ratio
7. Conclusions
- (1)
- The simulated hysteretic curves and skeleton curves are in good agreement with the test data, indicating the proposed FEM is accurate and can be used to predict the seismic behaviors of post-fire SAC beam-column joints.
- (2)
- Nonlinear spring elements were used between the reinforcement and concrete with both scoria and natural aggregate to simulate the bond–slip behavior. The spring elements can simulate the pinching hysteretic curves well and avoid the overestimation of seismic performance of post-fire RC beam-column joints.
- (3)
- Analysis of the simulation results shows that the increase of fire time causes a significant decrease in the load bearing capacity, stiffness, and energy dissipation capacity of the SAC joints. The application of spring elements can simulate the pinching effect of the hysteresis curves well, but the simulations of the falling section of the curves are not very obvious, which may be caused by the insufficient consideration of the spalling of concrete after high temperature by the FEM delaying the strength degradation of the concrete.
- (4)
- Although the increase in the reinforcement ratio of tensile rebars can slightly increase the strength and stiffness of the SAC joints, an excessively high reinforcement ratio will weaken the energy dissipation capacity and ductility of the SAC joints. Therefore, when the reinforcement ratio exceeds 1.5%, it will be detrimental to the seismic performance of post-fire SAC structures.
- (5)
- The increase of the axial compression ratio can increase the strength and initial stiffness of the SAC joints, reduce the degrees of pinching effects of the hysteretic curves, increase the energy dissipation capacity of the SAC joints, and delay the stiffness degradation of the SAC joints.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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T (°C) | Cubic Compressive Strength (MPa) | Splitting Tensile Strength (MPa) | ||
---|---|---|---|---|
SAC | NAC | SAC | NAC | |
20 | 41.66 | 39.95 | 2.69 | 2.02 |
200 | 37.33 | 34.25 | 2.26 | 1.44 |
400 | 34.83 | 32.67 | 1.96 | 1.37 |
600 | 20.74 | 17.66 | 1 | 0.65 |
800 | 11.1 | 8.09 | 0.6 | 0.22 |
Mechanical Properties | Equations |
---|---|
Cubic compressive strength | |
Splitting tensile strength | |
Peak strain | |
Ultimate strain | |
Elastic modulus |
T (°C) | Peak Strain | |
---|---|---|
SAC | NAC | |
20 | 0.00187 | 0.001887 |
200 | 0.001646 | 0.001551 |
400 | 0.002683 | 0.003564 |
600 | 0.003549 | 0.010222 |
800 | 0.005809 | 0.011266 |
T(°C) | Ultimate Strain | |
---|---|---|
SAC | NAC | |
20 | 0.00209 | 0.005243 |
200 | 0.00184 | 0.003438 |
400 | 0.003959 | 0.008294 |
600 | 0.008862 | 0.013817 |
800 | 0.015472 | 0.018866 |
T(°C) | Residual Elastic Modulus | |
---|---|---|
SAC | NAC | |
20 | 57,851 | 33,898 |
200 | 40,441 | 23,691 |
400 | 17,456 | 7100 |
600 | 7861 | 499 |
800 | 2039 | 229 |
T(°C) | n | |
---|---|---|
20 | 1.898 | 49.31 |
200 | 2.17 | 72.44 |
400 | 1.827 | 9.993 |
600 | 2.201 | 1.079 |
800 | 1.991 | 0.676 |
Diameter/mm | Elastic Modulus/MPa | Yield Strength/MPa |
---|---|---|
20 | 1.993 × 105 | 484 |
16 | 2.053 × 105 | 452.5 |
Parameters | Time for Exposure to Fire (min) | Ratio of Reinforcement | Axial Compression Ratio | |
---|---|---|---|---|
Numbers | ||||
SAC0-0.012-0.3 | 0 | 0.012 | 0.3 | |
SAC60-0.012-0.3 | 60 | 0.012 | 0.3 | |
SAC90-0.012-0.3 | 90 | 0.012 | 0.3 | |
SAC60-0.009-0.3 | 60 | 0.009 | 0.3 | |
SAC60-0.015-0.3 | 60 | 0.015 | 0.3 | |
SAC60-0.012-0.5 | 60 | 0.012 | 0.5 | |
SAC60-0.012-0.7 | 60 | 0.012 | 0.7 |
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Cai, B.; Hu, W.-L.; Fu, F. Numerical Analysis of Seismic Performances of Post-Fire Scoria Aggregate Concrete Beam-Column Joints. Fire 2021, 4, 70. https://doi.org/10.3390/fire4040070
Cai B, Hu W-L, Fu F. Numerical Analysis of Seismic Performances of Post-Fire Scoria Aggregate Concrete Beam-Column Joints. Fire. 2021; 4(4):70. https://doi.org/10.3390/fire4040070
Chicago/Turabian StyleCai, Bin, Wen-Li Hu, and Feng Fu. 2021. "Numerical Analysis of Seismic Performances of Post-Fire Scoria Aggregate Concrete Beam-Column Joints" Fire 4, no. 4: 70. https://doi.org/10.3390/fire4040070
APA StyleCai, B., Hu, W.-L., & Fu, F. (2021). Numerical Analysis of Seismic Performances of Post-Fire Scoria Aggregate Concrete Beam-Column Joints. Fire, 4(4), 70. https://doi.org/10.3390/fire4040070