Experimental Evaluation of Rigidity Center

Abstract

It is known that when a reinforced concrete building exposed to a horizontal load is subjected to torsional moments around its center of rigidity, additional shear stresses occur in the vertical load-carrying elements, such as the columns and shear walls. Therefore, in order to estimate the additional stresses caused by the torsion, the rigidity center should be calculated precisely. It is known that there are several analytical approaches to calculating the rigidity center location. These approaches do not calculate the rigidity centers close to each other in asymmetric buildings. As significant differences were observed in the calculation of the rigidity center using analytical methods, it was decided to seek verification by conducting an experimental study. In order to calculate and verify the location of the rigidity center, an extensive experimental study was planned. A total of 20 scaled and revised buildings were built, and they were tested in the specially designed test setup. The tested buildings had square, rectangular and irregular floor plans. In addition, vertical load-carrying members were either symmetrically placed on the floor plan or kept asymmetrical to see the effect of their location on the rigidity center. All the buildings were tested under their self-weight, and the corresponding displacements were recorded. Additionally, all the buildings were modeled using ETABS to verify the theoretical background of the rigidity center. From the test results, it was found that the resultant shear force can be calculated by multiplying the displacements of each member of a given story found from the tests on its bending stiffness, and this will give the location of the rigidity center. The rigidity center was found to be identical to the results obtained from the 3D model analysis using ETABS, although it uses a different procedure. As the results from the experiment and 3D model are close to each other, it can be said that the rigidity center of reinforced concrete buildings can be found from simple tests using any material that has almost uniform mechanical properties.