In building analysis, floors can be modeled in two different ways. The first of these is the Fully Rigid Diaphragm Adoption , where in-plane motion is neglected, assuming that the in-plane stiffness of the slabs is very high . The second is the Semi-Rigid Diaphragm Adoption , in which slab in-plane stresses and movement can occur, taking into account the stiffness of the slabs in the analysis model . It can be selected with the image shown below in the analysis settings.
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1- Fully Rigid diaphragm:
The rigidity of the slab; The system is accepted as a rigid diaphragm if the vertical bearing system elements designed to meet the effects of earthquakes are considerably larger than the stiffness. The difference between the center of mass and the center of rigidity causes twisting in the plan. According to Article 3.6.2.2 of TBDY , rigid diaphragm acceptance cannot be applied in buildings with A2and A3 type irregularities.
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Floor stiffness; It is an analytical model representing situations where the system is close to or equal to rigidity. Stiffness calculation is calculated depending on slab thickness, dimensions and material parameters. The semi-rigid diaphragm acceptance is the acceptance that reflects the most realistic behavior of the laying behavior in the structural analysis model. In the semi-rigid diaphragm model, floors are modeled with two dimensional finite elements (shells). Two dimensional finite elements create stresses on the shell element by their in-plane out-of-plane movement. According to this stress distribution, /wiki/spaces/2IMEI/pages/1123123680 reinforced concrete slab design can be made.
Analysis with semi-rigid diaphragm is based on the assumption that in-plane and out-of-plane deformation under the effect of earthquakes and the stresses resulting from these deformations are distributed over two-dimensional finite elements. Since the slabs are included in the analysis model, the stresses and strains can be seen in the analysis model. The analysis model of a building with the acceptance of Semi-Rigid Diaphragm is as shown below.
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In accordance with TBDY 2018 Articles 3.6.2.2 - 4.5.6.2 - 4.5.7.1 - /wiki/spaces/2IMEI/pages/11241720947.11.3, the in-plane and out-plane displacements of reinforced concrete slabs should be modeled with two-dimensional (shell, shell) finite elements to include degrees of freedom.
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