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What Is Precast Concrete Frame?

- Apr 20, 2018 -

What Is Precast Concrete Frame?

Types of precast concrete frames are buildings and structures

Precast concrete frames were built before the actual construction started and were shipped to the site for installation. There are various types of precast concrete frames, such as skeletons, H-frames and portal frames.

This article discusses the details of the precast concrete frame, its design, and its use.

Consider the following field frame and its bending moment diagram.


As can be seen from the above figure, the joint in the prefabricated frame is located in the position of the minimum bending moment.


The correct position of the skeletal skeleton joint is shown below.



However, in order to facilitate the prefabrication, skeleton frame joints are formed near the beam-column connections as shown below.



The bending moment diagram of the precast concrete skeleton will be different from the bending moment diagram of the field frame, because the joint is usually regarded as pinned, although the torque joint is possible. Under vertical loading, greater sagging moments are produced in the beam. Column times are much smaller and are usually generated in columns.



Under lateral loads, the column moments increase so that they can no longer be distributed into the beam.

The skeleton is most widely used in the UK. Usually used in high-rise commercial buildings, offices and schools.

Whether the framework can be built as a series of individual components, it provides a degree of design flexibility, ease of manufacture and ease of transport.

However, since the skeletal framework is usually not designed in a fixed manner, the frame moment cannot be generated, and therefore it needs to be supported. Therefore, the skeleton does not have the same degree of design flexibility as a structure with a fixed joint.



H frame:

The bending moment of the H-frame is similar to the bending moment of the field frame, but it is necessary to provide substantially pinned joints at the intersections of the frame elements. H-frames tend to be used on external frames rather than on internal frames to provide peripheral support.

One advantage of an H-frame is that it allows the components to be designed to work together, resulting in a shallower structural depth. Lateral forces can be carried on the frame, allowing wind loads to be transmitted to the frame and joints.

The disadvantages of the H-frame are mainly related to the dimensions of the frame elements, which can lead to difficulties in transportation and manufacture. The tolerances may also have to be smaller to allow very precise assembly of the joints.



Portal framework:

The gantry is similar to the H-frame and the bending moment is close to the rigid field frame.

There are basically two types of portal frameworks - less common flat portals and high-end portals. Both are mainly used in industrial warehouses and are relatively inexpensive and easy to design and build.

Torque joints and some other features at the beam-column connections may require special attention. The portal framework is mainly limited to high-level single-tier work.