# Experimental Evaluation of Rigidity Center
## 4 Conclusions  
The location of the rigidity center in a reinforced concrete building should be calculated realistically as it directly affects the additional shear forces that will affect the vertical structural elements, such as columns and shears. In this study, a total of 20 scaled and revised buildings in 4 groups were constructed using balsa wood and tested under _self-weight_, and the rigidity center of each building was found from the displacement values recorded during the tests. The following conclusions can be drawn from the results of this study:  
* The rigidity centers of reinforced concrete buildings can be found from simple tests using any material that has almost uniform mechanical properties;
* The only problem in the test was seen in the different mechanical properties of the vertical load-carrying members. As the stiffness of an individual member influences the rigidity center of a building, any change in the stiffness (in the case of this study, it was the _modulus of elasticity_ of balsa wood) will affect the rigidity center location;
* Balsa sticks and balsa plates, being light in _weight_, were found to be convenient materials for such a test as they allow large displacements due to their low _modulus of elasticity_. Large displacements were found to be beneficial during the tests to interpret the results clearly;
* The rigidity center of a floor plan can be found from the displacements of the vertical load-carrying members caused from the related _self-weight_ or any additional loading. These displacements should be multiplied by the stiffness of the member to add information on the _modulus of elasticity_ and moment of inertia of the member;
* The test results were compared with the results found from the 3D modeling performed in ETABS, which calculates the rigidity center considering the displacement demands related to the unit loading in the plan directions and the unit rotation in the z axis. Identical rigidity center locations were calculated, indicating that reliable results can be taken from the tests of frame buildings and frame-shear wall buildings;
* Symmetrically planned buildings were observed to have some rotations upon loading, which may be attributed to the change in mechanical properties;
* It has been observed that structural analysis programs calculate the rigidity center separately for the x and y directions of the building and can calculate the rigidity center in the middle of the floor plan in the case of a symmetrical layout on both axes. However, tests revealed that rigidity centers were close to the regions where there were more shear walls.  
As the correct calculation of the rigidity center location is directly related to seismic performance, it has been determined that reinforced concrete building models should be created in a way that is close to reality, important assumptions should be avoided, the element nodal points should be located close to their real positions, and loadings must be applied to the elements correctly.  
Conceptualization: F.K. and B.E.; methodology, F.K. and B.E.; software, E.A.; validation, E.A., F.K. and B.E.; formal analysis, E.A.; investigation, E.A., F.K. and B.E.; resources, F.K., B.E. and E.A.; data curation, E.A., F.K. and B.E.; writing--original draft preparation, F.K. and B.E.; writing--review and editing, F.K. and B.E.; visualization, E.A. and B.E.; supervision, F.K.; project administration, F.K.; funding acquisition, F.K. All authors have read and agreed to the published version of the manuscript.  
This research was funded by Van Yuzuncu Yil University Scientific Research Projects Department under Grant No. FYL-2022-9987.  
Not applicable.  
The authors declare no conflict of interest.