Joints | Joints a large Building
Provision/necessity of joints in a large building
- All building materials expand about contract due to changes in temperature including variations in moisture content.
- The magnitude of such expansion about contraction depends upon the type of material used in construction and the range of variation in some temperatures including moisture content.
- Components of a structure are not allowed free movements, therefore, internal stresses will be set up which may result in the formation of cracks.
- To control either isolate thermal including other movements to avoid danger over a structure.
- To break the continuity of a structure.
- Joints sub-divide each building toward smaller units including also permitting free movement of an individual unit.
The recommended spacing of expansion joints for different types of works as per I.S.3414-1168
- Walls:- c/c spacing of joints
- For load-bearing walls with cross-walls at intervals. A traditional type of one-brick thick or more. =30m
- Walls of warehouse-type construction (without cross walls.) =30 m
- Chajja’s, balconies and parapets. = 6 to 12 m
- Ordinary roof slabs of R.C.C. 20 to 30 m intervals and protected by layers of mud changes in direction as in paska or other insulating media in L, T, H &U shaped struct. un-framed construction.
- The unprotected slabs. =15 m
- Frames:- At 30 m intervals and corners of L, T, H, and U-shaped structures.
- Copings:- Corresponding to joints in the roof slabs.
Location of Construction Joints for Different Members
Some recommended position during the construction of joints into different structural components is as supporting.
For slabs Joints
- In the case of slabs supported on two sides, the construction joints should be vertical at support.
- It can also, be provided at the middle of the span at right angles to the main reinforcement
- Inside the case of two-way slabs, the joint tin be provided near the centre of either span.
For Beams Joints
- During the case of beams, the construction joint should be located in the centre about within the middle third of the span including it should be vertical
For columns Joints
- In the case of columns, the construction joint should be formed horizontally by stopping the concrete in a column about 75 mm below its junction with the lowest soffit of the beam
- The operation of concreting over the construction joint should be exerted after a break of at least 4 hours
For walls Joints
- The horizontal construction joint in walls should be located at the top of the plinth, top or bottom of the window opening or at any other convenient height.