What is Semi-Rigid Diaphragm?

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Ismail Hakki Besler

Administrator
If the buildings with large gaps in the plan and also the buildings with A2 and A3 irregularities are solved with the classical rigid diaphragm assumption, erroneous results can be obtained that are far from the real behavior of the structure. For this reason, the Earthquake Code requires that these types of structures be taken into account. We divide diaphragms into three main groups: 1) Rigid diaphragm Axial force cannot be calculated in beams when a rigid diaphragm is accepted. Deformations in the floor plane are neglected. 2) Semi-rigid diaphragm (Elastic diaphragm) The finite element model, which is created by dividing the floors into shell elements, is the static and dynamic analysis of the structure by including beams, columns, ribs, shears, foundation beams and raft foundations into the global stiffness matrix. In the model, floor masses are considered as distributed masses along the floor. 3)Flexible diaphragm Structures that do not have slabs or the slab stiffness is too small and will not form a diaphragm. ideCAD Static 7.00 is a program that can perform static and dynamic analysis according to these three conditions. You can download the latest version containing the Semi-Rigid Diaphragm solution from the link below:
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There are many studies in the literature on the subject semi-rigid diaphragm you will find many documents:
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Let me add a few things, because I believe that this issue is not fully understood by the questions of the municipalities and most of the engineers around me. The flooring system is also very important in the acceptance of diaphragm rigidity, such as A2 and A3 irregularity, and a semi-rigid diaphragm (elastic diaphragm) solution can be foreseen in hollow hollow blocks and cork floors. Another important point is the comparison of the displacement capabilities of the YYTS (horizontal load bearing system) and the flooring system is also important in the selection of the diaphragm, that is, the YYTS is ductile, but if the flooring is excessively rigid, the rigid diaphragm is accepted. If it is much more ductile, flexible diaphragm acceptance is appropriate, if we reinforce it with an example, while semi-rigid diaphragm acceptance is more appropriate in a building with a 3m storey height, rigid diaphragm acceptance may be appropriate in the same flooring system with a floor height of 7-8m. Good work to everyone.
 
Dear Siromar, Semi-rigid diaphragm (elastic diaphragm) gives more accurate and sensitive results than analyzes made with a rigid diaphragm in all conditions. Because in the acceptance of Rigid diaphragm, you distribute the load coming from the floor level to the columns in a way that is proportional to their stiffness. In the past, when computer facilities were limited and we could not use 64-bit technology, the adoption of rigid diaphragms made things very quick and accelerated for the analysis of structures. However, it is now possible to solve the structures together with their tiling by using the processors in the computer in parallel (simultaneously) and thanks to the 64-bit programming technology. Therefore, solving all structures together with their flooring will give more accurate, realistic and precise results. However, it is essential to calculate the types of structures we have mentioned here, together with the floors. These systems can be listed as: 1) Structures with A2 and A3 irregularities 2) Cork plates without beams 3) Tunnel formwork systems 4) Ribbed systems 5) Cassette systems Best regards
 
Hello Mr. Ismail, I totally agree with what you said and I must say that I was very pleased when I heard about idecad's semi-rigid solution, and even after this analysis came with idecad, we included stairs-vaults etc. into the analysis as shell members and seriously got solutions close to building performance. I think we did. The acceptance of diaphragm rigidity according to the relativity of the diaphragm with YYTS at the end of what I wrote is an acceptance in the literature "yyts displacement on the floor >> if diaphragm displacement - rigid diaphragm " if yyts displacement on the floor - if diaphragm displacement close values - semi-rigid diaphragm if flexible diaphragm displacement 2* diaphragm displacement approximate diaphragm displacement In the literature, of course, the acceptance of a rigid diaphragm against 8-10 meters of floor height is an extreme example and it is not a very common situation. I added an SS regarding the issue. Solving the systems mentioned in the 5 items you gave with a semi-rigid diaphragm is both healthier and more beneficial. It is a fact that it will give more economic results. It is a great treat for the idecad team to offer this innovation to its users for free. As an adult and as someone who graduated from the school I graduated from before I was born, I would appreciate it if you correct me if there is something I misunderstood, with my best regards.
 
In the picture you sent, there is a pre-installation floor plan shown in gray and a deformed post-installation floor plan shown in red. If the geometry formed after loading is placed on the plan before loading, if there is an identical geometry, the floors are not rigid enough, if there is deformation in the flooring, it is understood that it is not rigid enough. Actually, the concept of semi-rigid here is perhaps confusing. In fact, it is more correct to say: The more rigid the floor slabs, the more rigid the diaphragm. In addition, the thickness and material of the plate also affect the rigidity. If the floor is covered only by thin sheets, this roof diaphragm is never rigid. However, floors in reinforced concrete systems can show quite rigid behavior. One thing needs to be opened up a little more. In fact, there is no physical part such as a rigid diaphragm in structures. Structures consist of columns, beams, curtains and floors. While creating the calculation model of the building, columns and beams form a space frame as bars. However, since this system is free of floors, the node points on the floor planes are not connected to each other. If we solve the system in this way, we will not include the rigidity of the floors. Years ago, in the computer technology of the 1980s, we could not include the flooring in the calculation, so we assumed a rigid diaphragm at floor levels. In other words, we made the assumption that the movements of the columns at floor level are in a plane, together and dependent on each other, consisting of two hotelings and a freezing. Thus, we have created a model that can show a behavior close to the real behavior of the structure under horizontal loads. Today, we no longer have to make assumptions with such an approach. The system can be modeled as columns and beams as bars, walls and floors as shell elements. This is how we model it. I think it was self explanatory. best regards
 
It was very explanatory and believe me, it is very clear. The important thing is not the simple assumptions in the literature. The deformation of the floor in the plane and the axial load calculation of the beams can be calculated with semi-rigid diaphragm analysis, that is, by including the floors in the system as shell members, and it will always give more realistic and accurate results. Thank you good. studies
 
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