Joints | Provision & Necessity of joints a large Building

Joints

Provision/necessity of joints in a large building

• All building materials expand about contract due to change in temperature including variation in moisture content.
• That magnitude of such expansion about contraction depends upon the type of material used in construction and the range of variation in some temperature 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 permit 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

1. For load-bearing walls with cross-walls at intervals. A traditional type of one-brick thick or more. =30m
2. 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 at protected by layers of mud changes in direction as in phuska 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 at 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 construction joints into different structural components is as supporting.

For slabs

• 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 the either span

For Beams

• 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

• In 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 up after a break of at least 4 hours

For walls

• 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.