Types of Precast Concrete Frames for Buildings and StructuresPrecast concrete frames are constructed before actual construction starts and is transported to site for erection. There are various types of precast concrete frames such as skeletal frame, H frame and portal frame. Details, methods of design and uses of precast concrete frames are discussed in this article. Consider the following in-situ frame and its bending moment diagrams.
Skeletal Frame:The correct position for the skeletal frame joint is shown below.
H Frame:The bending moments of the H frame are similar to those of the in-situ frame but require the provision of essentially pinned joints at the intersection of the frame unit. H frames tend to be used on the external frame rather than the internal frame, to provide perimeter bracing. An advantage of the H frame is that it enables components to be designed to act together, resulting in shallower structural depth. Lateral forces can be carried on the frame itself allowing wind loads to be transmitted into the frame and joints. Drawbacks of the H frame mainly concern the size of the frame elements, which can lead to difficulties with transportation and manufacture. Tolerance may also have to be smaller to permit joints to be assembled very accurately.
Portal Frame:The portal frame is similar to the H frame in that the bending moments approximate to those of the rigid, in-situ frame. There are essentially two types of portal frame- the flat portal which is less common, and the pitched portal. Both are mainly used for the industrial warehouses, being relatively cheap and easy to design and build. Moment joints at the beam-column connection and certain other features may require special attention. The portal frame is limited predominantly to tall single-storey work.
|Skeletal frame||Beam column connection||Commercial buildings||Relatively flexible, easy to manufacture and transport||Lacks the flexibility of a fixed structure.|
|H Frame||Minimum column moment||Perimeter bracing||Shallow structural depth||Size can cause problems with manufacture and transportation|
|Portal Frame||Column connection||Industrial warehouses||Large storage area||Limited to single storey work|