In many circumstances, the structural design of high-rise and long span modern composite buildings demands a higher level of stiffness of concrete and steel materials. While it seems the current trend of material science only focus on high strength material instead, and no much was mentioned on high stiffness material. Is there such material available and applicable in structural engineering practice?
Virtually all steel materials have the same elastic modulus of 200 GPa, regardless of their yield or ultimate strengths. Elastic modulus of high strength concrete can be significantly more than that of normal strength concrete. For example elastic modulus of a high strength concrete can easily surpass 50 GPa while this value for conventional concrete is about 25 GPa.
Carbon fibers can provide elastic modulus of up to 350 GPa. However, these materials are very expensive, temperature dependent, brittle, and not suitable for conventional civil engineering projects.
In any case, stiffness is one of the parameters and it can be regulated through structural configuration rather than structural material. The most obvious example is a moment resisting frame and a concentrically braced frame. Both have the same material-level stiffness, while their system-level stiffness significantly differs.
Virtually all steel materials have the same elastic modulus of 200 GPa, regardless of their yield or ultimate strengths. Elastic modulus of high strength concrete can be significantly more than that of normal strength concrete. For example elastic modulus of a high strength concrete can easily surpass 50 GPa while this value for conventional concrete is about 25 GPa.
Carbon fibers can provide elastic modulus of up to 350 GPa. However, these materials are very expensive, temperature dependent, brittle, and not suitable for conventional civil engineering projects.
In any case, stiffness is one of the parameters and it can be regulated through structural configuration rather than structural material. The most obvious example is a moment resisting frame and a concentrically braced frame. Both have the same material-level stiffness, while their system-level stiffness significantly differs.
As Mr.Amin Mousavi already noted, stiffness for any complex structure has to be derived from structural geometry and true orientation of individual structural elements to maximize the value and we seldom consider material parameter in practice.
In general trend we are using high strengh material to counter the recent requirment of design demands. In steel structures elastic modulus is almost same for the 250 Mpa to 2000Mpa, however as the stength of concrete increases the elastic modulus increases. Hence, with high strength material we able to reduce the size and increase the spans of structural member of building, bridge etc. However there are several material available with the higher stiffness but these are not cost effective.
Thanks, Dr. Kumar. Can you give me some of the more specific examples of those higher stiffness material you mentioned in you reply above. Thanks again!
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