Architecture2

（2）Furthermore ,a structure must be well built,it could have such permanence as the purpose for which it is intended demands and as the materials chosen may allow. The raw materials of architecture-stone,brick,wood,steel,or glass-in part govern the forms of the building and are expressed by them.Stone can resist compression almost indefinitely.While it is possible to crush stone in a laboratory,for practical purposes its compressive strength is unlimited.On the other hand,stone is weak in withstanding tension.Any beam spanning a void tends to bend downward between the supports,putting the lower half of the beam under tension.It follows from the tensile weakness of stone that beams of this material must be comparatively short and supported at frequent intervals.Moreover,stone columns must be sturdy ,rarely more than 10 times as high as they are wide. In stone buildings,,windows,doors,and the spaces between columns are almost compelled to be taller than they are wide-the vertical rectangle of the stone aesthetic.

(3) Wood,a fibrous material,withstands tension as readily as it does

compression.Wooden beams may be relatively longer than stone beams,and wooden posts slender and widely spaced.A horizontal rectangle,wider than it is high,results from the natural properties of wood,as may be seen in Japanese architecture,Steel also has tensile strength that is equal to or greater than its compressive strength.Anymore who has observed a steel building under constrction must have noticed the gridiron of horizontal rectangle produced by the slender,widely spaced columns and the long beams of each floor.The nature of wood and of steel suggests frame consteuction -a skeleton to support floors and roof-with whatever surfacing material may be necessary.Wood and steel also permit cantilever construction in which beams project beyond the last point of support.