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Civil Engineering/concept of stiffness


hello sir,

  i am student of civil engineering,pursuing bachelors.i want to know the basic concept of in-plane stiffness and out-of plane stiffness.

 Thank you,

Dear Saad

Usually in the case of shell element , we are faced with a phenomenon known as in plane and out of plane behaviour which in turn is related to stiffness and strength.

Suppose a sheet of paper . The in plane tensile stiffness can be feeled and tested manually when you pull out the paper. If you trace a line along the direction of pulling you can admit that the length of the line doesnt increase in a sensible way, when you pull the paper out. In plane tensile stiffness of the paper is significant

In turn, the out of plane pushing of the paper will result to a very large distorsion and crumpling. We can say that out of plane stiffness of the sheet of paper is very small.

You know that stiffness is defined as the force needed to make a unit deflection or displacement in the material. In the above case in plane tensile stiffness of of the sheet of paper is much more than the out of plane stiffness. You Can admit that the stiffness may be related to the mechanism of behaviour of the structure. For the case above the sheet of paper bahaves in moment and shear mode when loaded out of plane.


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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.

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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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