(1) Design requirements
The roof design of large-span buildings, like other roofs, requires waterproof, thermal insulation, and heat insulation, but most large-span buildings are large public buildings with a long service life. The roofs should have better waterproof, thermal insulation performance, and they are crowded. In places with a large number of gatherings, fire safety requirements are higher, and the roof should have sufficient fire resistance limit to ensure safe evacuation in case of fire. At the same time, special attention should be paid to reducing the self-weight of the roof and choosing light-weight, high-strength and durable materials and construction methods. In this type of public buildings, the roof shape requirements are higher, and careful consideration should be given to the roof form, color, texture and detail treatment. In addition, the large-span building has a large scale and a long construction period. The roof design should create conditions for accelerating the construction speed and implement the design principles of standardization and finalization. In short, the roof design of large-span buildings should comprehensively consider the influence of factors such as building waterproofing, building thermal engineering, material selection, construction practices, building construction, building fire protection, and architectural art, and make it as applicable, safe, economical and beautiful as possible.
(2) Roof structure composition
The roof of a large-span building is composed of load-bearing structure, roof base layer, thermal insulation layer, roofing layer, etc. The type of load-bearing structure has been discussed in the first section of this chapter. The roof base layer is divided into a purlin scheme and a purlinless scheme. The former is to place the purlin on the roof load-bearing structure first, and then joists and roof panels are placed on the purlin. The roof thermal insulation layer is processed according to the specific engineering design, and can be set on the roof panel, or hung under the joist, or placed on the suspended ceiling. The roof surface layer includes coil surface layer, paint surface layer, metal tile surface layer, and color profiled steel surface layer.
When a thin shell structure or a folded plate structure is used as the roof load-bearing structure, no roof panel is required. When the inflatable membrane structure and the tent membrane structure are used as the roof, there is no need to set up the roof base layer and waterproof surface layer, because this kind of structure has multiple functions such as load-bearing, enclosure, and waterproof.
