w  (5.231) n  l w where n  integer, 1 for the fundamental mode of vibration, 2 for the second mode, . . . l  span of cable, ft w  load on cable, kips per ft g  acceleration due to gravity  32.2 ft / s2 T  cable tension, kips The spreaders of a cable truss impose the condition that under a given load the change in sag of the cables must be equal. But the changes in tension of the two cables may not be equal. If the ratio of sag to span / l is small (less than about 0.1). Eq. (5.222) indicates that, for a parabolic cable, the change in tension is given approximately by H  (5.232) 3 l 2 where  change in sag A  cross-sectional area of cable E  modulus of elasticity of cable steel Double cables interconnected with struts may be analyzed as discrete or continuous systems. For a discrete system, the spreaders are treated as individual members. For a continuous system, the spreaders are replaced by a continuous diaphragm that ensures that the changes in sag and rise of cables remain equal under changes in load. Similarly, for analysis of a cable network, the cables, when treated as a continuous system, may be replaced by a continuous membrane. (C. H. Mollman, Analysis of Plane Prestressed Cable Structures, Journal of the Structural Division, ASCE, Vol. 96, No. ST10, Proceedings Paper 7598, October 1970, pp. 20592082; D. P. Greenberg, Inelastic Analysis of Suspension Roof Structures, Journal of the Structural Division, ASCE, Vol. 96, No. ST5, Proceedings Paper 7284, May 1970, pp. 905930; H. Tottenham and P. G. Williams, Cable Net: Continuous System Analysis, Journal of the Engineering Mechanics Division, ASCE, Vol. 96, No. EM3, Proceedings Paper 7347, June 1970, pp. 277293; A. Siev, A General Analysis of Prestressed Nets, Publications, International Association for Bridge and Structural Engineering, Vol. 23, pp. 283 292, Zurich, Switzerland, 1963; A. Siev, Stress Analysis of Prestressed Suspended Roofs, Journal of the Structural Division, ASCE, Vol. 90, No. ST4, Proceedings Paper 4008. August 1964, pp. 103121; C. H. Thornton and C. Birnstiel, Threedimensional Suspension Structures, Journal of the Structural Division, ASCE, Vol. 93, No. ST2, Proceedings Paper 5196, April 1967, pp. 247270.) A true membrane is able to withstand tension but is completely unable to resist bending. Although it is highly efficient structurally, like a shell, a membrane must be much thinner than a shell and therefore can be made of a very lightweight material, such as fabric, with considerable reduction in dead load compared with other types of construction. Such a thin material, however, would buckle if subjected to compression. Consequently, a true membrane, when loaded, deflects and assumes a shape that enables it to develop tensile stresses that resist the loads. Membranes may be used for the roof of a building or as a complete exterior enclosure. One way to utilize a membrane for these purposes is to hang it with initial tension between appropriate supports. For example, a tent may be formed by supporting fabric atop one or more tall posts and anchoring the outer edges of the stretched fabric to the ground. As another example, a dish-shaped roof may be constructed by stretching a membrane and anchoring it to the inner surface of a ring girder. In both examples, loads induce only tensile stresses in the membrane. The stresses may be computed from the laws of equilibrium, because a membrane is statically determinate. Another way to utilize a membrane as an enclosure or roof is to pretension the membrane to enable it to carry compressive loads. For the purpose, forces may be applied, and retained as long as needed, around the edges or over the surface of the membrane to induce tensile stresses that are larger than the larger compressive stresses that loads will impose. As a result, compression due to loads will only reduce the prestress and the membrane will always be subjected only to tensile

Adhesive Spreader. A notched trowel or special tool that aids in application of laminating adhesives. Adhesive Wall Clips. Special clips or nails with large, perforated bases for mastic application to a firm surface. Adhesives: Contact. An adhesive that forms a strong, instantaneous bond between two plies of gypsumboard when the two surfaces are brought together. Laminating. An adhesive that forms a slowly developing bond between two plies of gypsumboard or between masonry or concrete and gypsumboard. Stud. An adhesive suitable for attaching gypsumboard to framing. Admixture. Any substance added to a plaster component or plaster mortar to alter its properties. (See also Dope.) Arris. A sharp edge forming an external corner at the junction of two surfaces. Back Blocking. Support provided for gypsumboard butt joints that fall between framing members. Back Clip. A clip attached to the back of gypsumboard and designed to fit into slots in framing to hold the board in place. Used for demountable partitions. Back Plastering. Application of plaster to one face of a lath system after application and hardening of plaster applied to the opposite face (used for solid plaster partitions and curtain walls). Backing (Backer) Board. A type of gypsumboard intended to serve as a base layer in a multilayer gypsumboard system or for application with adhesive of acoustical tile or panels. Band. A flat molding. Banjo Taper. A mechanical device that dispenses tape and taping compound simultaneously. Base (Baseboard). A plastic, wood, or metal trim or molding applied to a wall at the floor line to protect the wall from damage. Base Coat. The plaster coat or combination of coats applied before the finish

M
log A  1.73 log (3.3) D where M
earthquake magnitude 100 km from epicenter A
maximum amplitude of ground motion, micrometers D
distance, km, from epicenter to point where A is measured The larger the ground displacement at a given location, the higher the value of the number assigned on the Richter scale. A Richter magnitude of 8 corresponds approximately to a Modified Mercalli intensity of XI, and for smaller intensities, Richter scale digits are about one unit less than corresponding Mercalli Roman numerals. TABLE 3.1 Modified Mercalli Intensity Scale (Abridged) Intensity Definition I Detected only by sensitive instruments. II Felt by a few persons at rest, especially on upper floors. Delicate suspended objects may swing. III Felt noticeably indoors; not always recognized as an earthquake. Standing automobiles rock slightly. Vibration similar to that caused by a passing truck. IV Felt indoors by many, outdoors by few; at night some awaken. Windows, dishes, doors rattle. Standing automobiles rock noticeably. V Felt by nearly everyone. Some breakage of plaster, windows, and dishes. Tall objects disturbed. VI Felt by all; many frightened and run outdoors. Falling plaster and damaged