## 6 Conclusions  
The seismic damage and behavior of L-shaped CFST column frames that were subjected to combined constant axial compressive load and cyclic lateral loading were investigated through a numerical model. A FEA model was established by using commercial finite element software ABAQUS. The accuracy of this proposed numerical model was validated by the experimental test results. The effects of the axial compressive load ratio and lateral loading direction were studied. Four L-shaped CFST column frame specimens were fabricated and tested. The main findings and conclusions from those investigations are summarized, as follows:  
1. the experimental results showed that the steel beam connected to L-shaped concrete-filled steel tubular column spatial frames had high earthquake resistance capacity. The failure modes of this composite frame followed the principle of the strong-column-weak-beam and strong-joints;
2. the FEA model developed in this paper was able to simulate the behavior of L-shaped concrete-filled steel tubular column spatial frames that were subjected to combined constant axial load and cyclic lateral loading accurately;
3. an effective stress-strain constitutive model was proposed in this paper, which described the behavior of confined concrete in L-shaped steel tube accurately. The interface and contact model introduced in the model improved the performance of the model in simulating the real behavior of the specimen; and,  
Figure 19: Stress distribution of steel tubular at the top of the second-story columns (CF4). (Unit: MPa)  
Figure 17: Stress distribution of steel tubular at the top of the first-story columns (CF4). (Unit: MPa).  
Figure 18: Stress distribution of steel tubular at the bottom of the second-story columns (CF4). (Unit: MPa)4. [4]cased on the results of the nonlinear analysis, the stress developing progress of L-shaped CFST columns was investigated. The load transferring mechanism and failure mechanism can be determined effectively. It should be noted that the effect of the bond-slip between steel tube and concrete and the restoring force model of the composite frame both had strong effect on the behavior of the composite structures. The influence of those structural variables should be further studied in future research works. At the same time, only envelope curves were employed in the FEA simulation. The cyclic loading effect, which is an important issue, will be studied while using the developed model in the future.  
[PERSON] and [PERSON] conceived and designed the experiments; [PERSON] performed the experiments; [PERSON] analyzed the data; [PERSON] and [PERSON] wrote the paper. [PERSON] proofread and revised the paper.  
This research received no external funding.  
This research work was supported by the National Natural Science Foundation of China (No. 51778065) and the National Natural Science Foundation of China (innovation group) (No. 51378077) and Science and Technology Research Project of Education Department of Hubei Province, China (No. D20151304). The tests were conducted in College of Civil Engineering at Tongji University, Shanghai 200092, PR China. These supports are highly appreciated.  
The authors declare no conflict of interest.