Types of Joints in Construction Prepared By Alka

Types of Joints in Construction Prepared By: Alka Shah Civil Engineering

Joints in Constructions Any joint, is a physical break or gap between members, in a concrete structure or building Why joints are needed q Cracking due to tensile stress due to weight on floor q Member or structure cannot be constructed as a monolithic unit in one placement of concrete q Cracking in structure due to temperature changes i. e. cooling and heat q Maintenance and repair

Types of joints 1. Expansion Joint or Isolated Joint 2. Contraction or Control joint 3. Construction joint

1. Expansion Joint or Isolated Joint: Ø Structural separation between building elements that allow independent movement without damage to the assembly Ø Safely absorb thermal expansion and contraction of various construction materials Ø Absorb vibration Ø Provided in bridges, railway tracks, and other structures

1. Expansion Joint or Isolated Joint: Ø Allow movement in both vertical and horizontal directions Ø They separate or isolate concrete slabs from columns, walls, footings and other points of restraint such as machine foundations and stairwells Ø No connection should be made across an isolation joint either by reinforcement, keyways or bond.

1. Expansion Joint or Isolated Joint:

2. Contraction Joint or Control Joint: Ø Cuts or grooves made in concrete or asphalt at regular intervals Ø Made at locations where there are chances of cracks or where the concentration of stresses are expected, so that when a concrete does crack, the location will be known. In such a way a concrete will not crack randomly but in a straight line (i. e. control joint) Ø Pre-Planned Cracks may be due to temperature variations or drying shrinkage or other reasons Ø Joints depth should be 25% of the depth of the slab.

2. Contraction Joint or Control Joint: Ø Load is transferred across control joints by interlock of aggregates in crack faces formed at the joint or by contact of the tongue and groove in a keyed joint as shown in figure ØSawed control joints must be deep enough to create a plane of weakness so that cracks occur at the joint

2. Contraction Joint or Control Joint: Ø Dowel bars are also sometimes used to transfer loads in floors which carry heavy wheeled traffic ØWhen wire mesh is used in the slab it should not cross a contraction joint. If it does, the joint won’t open properly and cracking may occur at some other location.

2. Contraction Joint (Control Joint):

3. Construction Joint: Ø In projects there is a starting and stopping points, the entire concrete work may not be done at once, hence concrete pouring need to be stopped causing a joint in element which known as Construction Joint Ø It Placed at points of ending and beginning of construction for provision of a smooth transition between pours Ø It Formed between successive building element parts during construction work, in which one part is allowed to harden before the next is placed.

3. Construction Joint:

3. Construction Joint: • If construction joints are located where no movement is wanted, tie bars or welded wire fabric can be used to hold the adjacent slabs together.