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QUESTION: sir, can you explain about differences between plastic and elastic analysis? Which method is widely used and what are the advantages and disadvantagea of each.
thanks in advance

ANSWER: Dear Hani

When you design elastically you accept that under normal loading noone of members passes through the plastic berhavior. In plastic design you assume that a variety of hinge develop in structure to make it unstable. The loadings in this situation are assumed factored to the ultimate level. The development of each hinge allow the internal stresses to be distributed to the other location or other members. Plastic design is not very used because of difficulties but you can use it in difficult situation where you need extra capacities in your structure.


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QUESTION: i got to know that a diaphragm is a floor or roof slab taking part in lateral load transfer.But what is a flexible and rigid diaphragm?what is meant by inplane shear transfer?

Dear Hani

When you have a lateral system consisting of a number of resisting frames then a load transfer occurs between them. If you have a system like a RC roof the stifness of it is considered to be enough to be called as rigid . Sometimes specially in industrial buildings there are metal roof which mey be with lower stiffness. After all a transfer between lateral systems happens even with flexible diaphragms unless you can assume the stiffness of the diaphragm being zero .

This issue need more discussion to get clear . Please dont hesitate to ask further.


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Babak Esmailzadeh Hakimi


I can answer questions in Structural Engineering, Earthquake Engineering, Project Management and Project Control topics!


I am experienced in the area of earthquake engineering in electrical power industry, i.e. Lifeline Earthquake Engineering. My focus has been on structural seismic design of power installations. Recently I have got involved in project management in the category of constructional engineering.

Sinam Consulting Engineers Co.

Bs degree in Civil Engineering from Ferdowsi University ,1988, Mashhad Iran, Ms degree in Earthquake Engineering, Sharif University of Technology, 1993, Tehran, Iran

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