# Numerical Investigation of the Collapse of a Steel Truss Roof and a Probable Reason of Failure
## 5 Conclusions  
The space truss roof structure, the columns, and the spherical steel supports of the factory building were put through several numerical analyses, and their behaviour was evaluated using the commercial software Abaqus (Dassault Systemes, Velizy-Villacoublay, France). These static stress analyses were performed using the finite element method and considering geometric nonlinearities. Based on the results of these simulations, the following conclusions about the real failure of the structure were drawn:  
* According to the global analysis, the structure is quite strong and insensitive to the vertical dead loads (rain, snow, etc.) even at some higher values, which are judged to be extreme and unrealistic. The most dangerous region of the space frame system in terms of vertical loads is the corridor with the largest column span in the A, C, and E blocks. However, this region is still safe, and the damage occurred somewhere else.
* Using the results of the global analysis, the most critical support connection was individually investigated and found safe, although it is more sensitive to horizontal forces. However, in the analysis, all the effects that create lateral forces caused by the wind and similar homogeneous distributed loads could not make the structure exceed the safety limits and cause any damage in the locations where the real damage occurred.
* It is judged that the thermal expansion of structural members increases the horizontal forces at the supports and the stresses at the members. The temperature change was assumed to be caused by lightning strikes. To investigate the effects of the temperature change, a simplified analysis with a uniform temperature rise was conducted and produced results that point out critical regions that are the same as the real damaged zones.
* The significant change of temperature of the air surrounding the lightning channel and the electric current that passes through the structure may cause heating of the roof system rapidly and locally. The lightning at the scene may also cause a sudden pressure change that can be amplified by the presence of water on top of the structural surface. In addition to the thermal expansion, it is judged possible that the blast effect may have a significant role in the failure of the structure.
* Testing the idea of temperature change, the damage prediction was found to be consistent with the real failure mode. It was concluded that the bolts and the bolted members attached to the supports in the real damaged regions of the space truss roof system were overloaded and damaged, as it can be seen in Figure 15.  
**Author Contributions:** Conceptualization, E.T. and A.D.; methodology, E.T. and A.D.; software, M.T.; validation, E.T., A.D., and M.T.; formal analysis, M.T., E.T., and A.D.; investigation, M.T.; resources, A.D.; data curation, M.T.; writing--original draft preparation, M.T., E.T., and A.D.; writing--review and editing, M.T., E.T., and A.D.; visualization, M.T.; supervision, E.T. and A.D.; project administration, A.D.; All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research received no external funding.  
**Acknowledgments:** The authors would like to thank [PERSON] for her support in visualizing the results.  
**Conflicts of Interest:** The authors declare no conflict of interest.