Frame structures

Single-storey buildings

Normally, the skeleton of a single-storey industrial building is composed of a series of basic portal frames. Each frame comprises two columns with moment-fixed connections at the foundations and a pin-joined roof beam. The latter can be with either a sloped pane or a straight profile. The building is normally stabilized by the cantilever action of the columns. The horizontal load action on the gable walls can be distributed to all columns by the diaphragm action of the roof. The distance between the portal frames is governed by the span of the roof and the facade construction.

Fig. 1 Industrial hall during construction

 

Skeletal structural systems are very suitable for buildings which need a high degree of flexibility, because of the possibility of using large spans and to achieve open spaces without internal walls. This is very important in industrial buildings, shopping halls, parking structures and sporting facilities, and also in large office buildings.

The roof can be made with prestressed hollow core elements or with light TT-units or steel sheet deck. The distance between the portal frames is governed by the span of the roof and facade construction - normally between 6 and 9 m for hollow core roof slabs and from 9 to 12 m for light TT-roof units. When steel sheet deck is used, the distance between the portal frames can be larger - up to 12 m and even 16 m- because of the lighter weight of the roof. Secondary beams are generally needed to support the steel sheet deck.

Another solution for large halls is to use large span roof units supported on rows of columns and straight beams. The roof units are saddle TT-slabs or light TT-roof units. The span of the roof units can be up to 32 m. For straight TT-units, the roof slope is obtained by alternating the height of the supporting beam rows. At the facades, the roof slabs can be supported on beams, or on load bearing
walls.

Fig. 2 Building structure with sloped I-profile beams and TT-roof slabs

Fig. 3 Saddle TT-roof slabs on load-bearing sandwich walls 

Fig. 4 Straight light TT roof slabs on longitudinal portal frames

Low-rise buildings with intermediate floors

In buildings basically constructed as single-storey structures, it may be necessary to insert intermediate floors in some parts or in the whole building. This is commonly achieved by adding a partly separate beam/column assembly to carry the intermediate floor slabs. The loads on the floors are generally much larger than on the roof. Consequently, the spans will normally be shorter. Span A - as indicated on the Figure - will normally be between 6 m and 18 m, depending upon the live loads and the type of floor slab selected. A good module for span B is 7.20 m to 9.60 m.

Multi-storey buildings

Multi-storey precast concrete frames are constructed with columns and beams of different shapes and sizes, stair and elevator shafts and floor slabs. The joints between the floor elements are executed in such a way that concentrated loads are distributed over the whole floor. This system is widely used for multi-storey buildings.

The structural frame is commonly composed of rectangular columns of one or more storeys height (up to four storeys). The beams are normally rectangular, L-shaped or inverted T-beams. They are single span or cantilever beams, simply supported and pin-connected to the columns. Hollow core floor slabs are by far the most common type of floor slabs in this type of structure.