building construction& material: Building materials

Sunday, May 13, 2012

The materials which normally used for framed structures are steel , concrete ( reinforced or prestressed ) , timber & aluminium alloys .
Materials for framed structure , particularly when it is tall or wide in span , need to be stribg , stiff & light in weight .
The stronger a material , the smaller the amount which will be required to resist a given force .

Depth / Span Ratio

The stiffer the material , the less will the structure & its members deform under load .
Since the excessive deflection of beams & the buckling of columns must be avoided then in any given circumstances , the use of stiffer materials will result in smaller members .
The relationshipp of the depth of a structure necessary to keep its deflection within acceptable li mits to its spans is known as its depth / span ratio .

Dead / Live load Ratio :

A material which is light in weight as well as adequate in strength results in structures of low self-weight .
The self or dead weight of the structure contributes to the stresses set up within it .
low dead weight is an important economic factor especially in structures carrying light loads such as roofs .
if the dead weight is considrerably greater than the imposed load , the structure must be designed primarily to carry its own weight rather than the load imposed on it .
The smaller the self or dead weight of a structure relative to the load to be carried the more efficient & economic the structure .

Strength / Weight ratio

The relationship of the weight of a material to its strength provides an indication of its efficiency in terms of the weight rewuired to fulfill the structural funcion .
This is epressed as the strength / weight ratio , a high value indicating high strength with low self weight , resulting in a minimum weight of material to fullfill a partocuilar structural purpose .

Factors affecting the choice of materials :

building construction& material