Aluminium

• Aluminium varies in strength according to the particular alloy from about three-quarters of mild steel to strengths somewhat greater than steel . 
• Although stiffer than either concrete or timber , aluminium alloys are only about one-third its weight . 
• These characteristics make them suitable for roof structures ( which carry only light imposed loads ) , particularly thoise with long spans , & less for normal building frames . 
• The high cost of aluminium usually precludes its structural use other than very wide span roof structures. 

properties of aluminium 

• strength varies according to type of alloy 
• higher stiffness as compared to concrete & timber but lower than steel 
• high strength to weight ratio 
• used for : 
• - long span roof structures 
• expensive