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Diaphragm is the mathematical operator which transfers the lateral forces to the vertical elements.

 Diaphragms are of two types.

1. Rigid Diaphragm and
2. Semi-Rigid Diaphragm

 

Rigid Diaphragm 

• When we opt to go with the Rigid Diaphragm the software will consider the infinite stiffness in its very own plane.
• Horizontal forces in the elements such as beams and the slabs shall be equal to zero where the rigid diaphragm is defined.
• The Centre of mass and the center of rigidity shall be computed and reported by the software.

 

 Uses:

• To identify the location of the center of mass and the center of stiffness for a given structure one would opt to go with the rigid diaphragm.
• For podium or large span slabs with a limited amount of opening or ducts, one can opt to use rigid diaphragm.
• To account the accidental torsion effect in the mathematical model for a given building or structure while performing seismic analysis one would opt to go with the rigid diaphragm.

 

Semi-Rigid Diaphragm 

• Horizontal the stiffness would be calculated by the program and accordingly, the lateral forces will be distributed to the vertical elements such as columns, Shear-walls & Etc.
• The Centre of mass and center of stiffness cannot be established by the software.
• Axial forces in the slab, the beam can be calculated and established by the software.

 

Uses:

• At the last phase of the design, a Semi-rigid diaphragm should be used.
• Accidental torsion effect would be considered by the program by performing Seismic analysis.

 

No Diaphragm Conditions: 

• The software will not establish the eccentricity in a given building.
• The software will not establish the drift and displacement of any given structure.
• The design lateral load will not be established by the software.

 

Recommendations:

For initial analysis phases of a given structure, it is recommended to opt to go for the rigid diaphragm and after solving centre of mass and centre of stiffness issue, then one can opt for the semi-rigid diaphragm to distribute the lateral loads to the vertical elements in a realistic manner.