土木工程专业英语 教学课件 陈瑛 1.1 Classification and Behavior of Structural Systems and Elements.ppt

Cable-stayed structures （斜拉结构） are used to support roof surfaces buildings, particularly in long-span situations. Membranes, Tents, and Nets 膜、 帐篷、网 A membrane is a thin, flexible sheet. Tent structure Cable membrane structure索膜结构 Pneumatic （[nju(:)5mAtik]装满空气的）membrane structure 充气膜结构 Stress-skin membrane structure 应力蒙皮膜结构 帐篷膜结构 Tent structure A common tent is made of membranes surfaces. Both simple and complex forms can be created using membranes. For surfaces of double curvature, such as a spherical surface, however, the actual surface would have to be made as an assembly of much smaller segments, since most membranes are typically available only in flat sheets. 斜拉式索膜cable-suspended membrane structure A further implication of using a flexible membrane to create the surface is that it either has to be suspended with the convex side pointing downward or, if used with the convex [5kCn5veks]side （凸侧）pointing upward, ( it has to be )supplemented([5sQplimEnt ])by some mechanism to its shape. Radial pleated （褶皱） suspended tensile structure convex side Cable-suspended membrane Pneumatic, or air-inflated, structures充气式膜结构 The shape of the membrane is maintained by the internal air pressure inside the structure. Stressed-skin structures 应力蒙皮结构 Another mechanism is to apply external jacking （抬升）forces that stretch the membrane into the desired shape. Various stressed-skin structures are of this general type. The need to pretension the skin, however, imposes various limitations on the shape that can be formed. Spherical surfaces, for example, are very difficult to pretension by external jacking forces, while others, such as the hyperbolic paraboloid, can be handled with comparative ease. Nets three-dimensional surfaces made up of a series of crossed cables. Nets are very analogous to membrane skins. By allowing the mesh opening to vary as needed, a wide variety of surface shapes can be formed. An advantage of using crossed cables is that the positioni