【文章內(nèi)容簡(jiǎn)介】 ucture, and therefore it wo uld be improper to roof a bowling alley with a dome. Similarly, a theater must have large, unobstru ucted spans but a fine restaurant probably should not. Stated simply, the structure must be appropri ate to the function it is to shelter. Second, the structure must be fireresistant. It is obvious that the structural system must be a ble to maintain its integrity at least until the occupants are safely out. Building codes specify the nu mber of hours for which certain parts of a building must resist the heat without collapse. The struct ural materials used for those elements must be inherently fireresistant or be adequately protected by fireproofing materials. The degree of fire resistance to be provided will depend upon a number of items, including the use and occupancy load of the space, its dimensions, and the location of the building. Third, the structure should integrate well with the buildingˊ s circulation systems. It should not be in conflict with the piping systems for water and waste, the ducting systems for air, or (most important) the movement of people. It is obvious that the various building systems must be coordin ated as the design progresses. One can design in a sequential stepbystep manner within any one system, but the design of all of them should move in a parallel manner toward pletion. Spatially, all the various parts of a building are interdependent. Fourth, the structure must be psychologically safe as well as physically safe. A highrise fra me that sways considerably in the wind might not actually be dangerous but may make the building uninhabitable just the same. Lightweight floor systems that are toobouncy can make the users very unfortable. Large glass windows, uninterrupted by dividing mullions, can be quite safe but 7 will appear very insecure to the occupant standing next to one 40 floors above the street. Sometimes the architect must make deliberate attempts to increase the apparent strength or solidness of the structure. This apparent safety may be more important than honestly expressing the buildingˊ s structure, because the untrained viewer cannot distinguish between real and perceived safety. 二． Modeling of Structures and Relation of Analysis and Design Structural analysis is the process of determining the forces and deformations in structures due to specified loads so that the structure can be designed rationally, and so that the state of safety of exi sting structures can be checked. In the design of structures,it is necessary to start with a concept leading to a configuration which can then be analyzed. This is done so members can be sized and the needed reinforcing determined, in order to. a)carry the design loads without distress or excessive deformations (serviceability or w orking condition)。 and b) to prevent collapse before a specified overload has been placed on the str ucture (safety or ultimate condition). Since normally elastic conditions will prevail under working loads, a structural theory based on the assumptions of elastic behavior is appropriate for determining serviceability conditions. Collap se of a structure will usually occur only long after the elastic range of the materials has been excee ded at critical points, so that an ultimate strength theory based on the inelastic behavior of the mate rials is necessary for a rational determination of the safety of a structure against collapse. Neverthel ess, an elastic theory can be used to determine a safe approximation to the strength of ductile struct ures(the lower bound approach of plasticity),and this approach is customarily followed in reinforced concrete practice. For this reason only the elastic theory of structures is pursued in this chapter. Looked at critically,all st