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In accordance with ASCE 7-16 Codes, the modeling of slabs as fully rigid or semi-rigid is determined by user selection. |
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Control of type 2 and 3 irregularities are made by the user. |
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In buildings with type 2 and 3 different types irregularities, story slabs have to be modeled with two-dimensional plate (membrane) or shell finite elements to show that they can safely transfer earthquake forces between vertical structural system elements in their own planes. |
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If type 2 and type 3 different types irregularities have been confirmed, selection of semi-rigid diaphragm should be made by user. |
If there is no type 2 and 3 irregularity, the floors can be modeled as a fully rigid diaphragm. In analysis settings Flexible and Rigid Diaphragm Types selection can be made upon request. |
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The analysis model of the slabs modeled by selecting the fully rigid diaphragm is created automatically. |
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The analysis model of the slabs modeled by selecting the semi-rigid diaphragm is created automatically. |
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İnternational Design Codes
ASCE 7-16 : Modeling Story Slabs per ASCE 7-16 with ideCAD
TSC 2018 : Slab Modelling
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Story floors;
(a) transfer the inertia forces created by the masses on the floors due to the earthquake accelerations, together with the beams, if any, to the vertical structural system elements thanks to their high in-plane stiffness,
(b) at the same time, and generally more importantly, are horizontal bearing system elements that enable the earthquake loads acting on the building to be distributed among vertical bearing system elements according to their rigidity. It is essential that floors, which may include gaps of various sizes, be modeled appropriately in order to accurately determine the load transfer in their own planes.
According to ASCE 7-16 12.3.2.1 Codes in buildings where there are Type 2 and Type 3 different types irregularities and / or floors are not intended to operate as a rigid diaphragm, and in flat slab systems, floors will be modeled with two-dimensional finite elements as a semi-rigid diaphragm.
If there is no type 2 and 3 irregularity, the floors can be modeled as a fully rigid diaphragm. In analysis settings Flexible and Rigid Diaphragm Types selection can be made upon request.
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It is essential to provide sufficient in-plane rigidity and strength in the floors of the transition floors, which are involved in the transition from normal floors to rigid basement floors and have to suddenly transfer all or most of the inertia forces that occur in the upper floors to the perimeter shearwalls in the basement floors. This condition is also valid for other transition floors where sudden stiffness changes are made for other reasons.
Referance: Seismic design of reinforced concrete Buildings, Jack Moehle, 2015 by McGraw-Hill Education.
Regardless of any irregularity control, floors in normal story and rigid basement story transitions are modeled with two dimensional shell finite elements (shell).
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It should be shown by calculations that the in-plane effects are safe to transfer to vertical bearing elements in floors analyzed with the acceptance of semi-rigid diaphragm.
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