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Build materials. e$ W2 d- L& [& p
Materials for building must have certain physical properties to be structurally useful. primarily ,they must be able to carry a load , or weight , without changing shape permanently . when a load is applied to a structure member , it will deform ; that is , a wire will stretch or a beam will bend . however , when the load is removed ,the wire and the beam come back to the original position ,this material property is called elasticity ,if a material were not elastic and a deformation were present in structure after removal of the load , repeated loading and unloading eventually would increase the deformation to the point where the structure would become useless . all material used in architectural structure , such as stone and brick , wood , steel , aluminum , reinforced concrete ,and plastics , behave elastically within a certain defined range of loading . if the loading is increased above the range , two type of behavior can occur ; brittle and plastic . in the former , the , material will break suddenly . in the latter , the material begins to flow at a certain load (yield strength) , ultimately leading to fracture . as example , steel exhibits plastic behavior , and stone is brittle . the ultimate strength of a material is measured by the stress at which failure (fracture) occurs ./ L, h0 l: J, c/ W
建筑材料6 j- T p7 M2 C3 q$ a
建筑材料必须具有对结构有用的某些物理性质。 首先，建筑材料必须能够承受荷载或重量，而不会永久改变其原有的形状。当荷载施加到结构单元上时，材料将发生变形，也就是说，线材将伸长或梁将会弯曲。然后卸载后，线材和梁将恢复原状。材料的这种性质称为弹性。如果某种材料是非弹性的，在卸荷后结构将残留变形，重复加荷和卸荷，结构的变形将持续增加，直至最后结构失效。用于建筑结构的所有材料，诸如砖石、木材、钢材、铝材、钢筋混凝土的塑料等，在一定范围的荷载作用下均表现出弹性如果荷载增加超过这个范围，材料将表现出两种类型的性质：脆性和塑性。若为前者，材料将会突然断裂；若为后者，材料在达到某一荷载（屈服强度）开始塑性流动，最后破坏。例如，钢材表现出塑性，石材则是脆性的。材料的最终强度用材料破坏时的极限应力来表示。7 E ?! k/ Y5 z4 D* Y/ t
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