Movement Joints In Concrete Walls

A single row of short thick dowels provides reasonable shear transfer but suffer from deformation.

Movement joints in concrete walls.

Expansion joints should normally be provided at a spacing of not more than 30m between successive expansion joints or between the end of the structure and the next expansion joint. These are vertical joints or grooves formed or cut into the wall that allows the concrete to shrink without noticeable harm. Staggers and movement joints in masonry walls other than clay brickwork should be engineer designed. In road construction movement joints can be provided in the transverse direction to allow the expansion and contraction of a concrete slab due to temperature and subgrade moisture variation.

Some designers recommend re ducing joint spacings by about 20 in walls with frequent openings such as doors and windows. Movement joints should not coincide with door or window openings due to the di culty in continuing. Movement joint then a movement joint should be introduced into one of the two lengths or at the stagger as shown in diagram 4. Movement joints are most commonly found between sections of building facades concrete slabs bridges pavements railway tracks pipelines and so on.

For tips on this check out bob harris s video or get a copy of his guide to stamped concrete joints are covered in chapter 23. They are usually either cast or drilled into the concrete. 4 recommends a contraction joint spacing of 30 times the wall thickness or 20 feet for an 8 inch thick wall 30 8 240 inches 20 feet. In reinforced walls and 6m in unreinforced walls.

Contraction joints are usually about 0 25 inches wide and about 1 2 to 3 4 inch deep and are provided at intervals of not exceeding 30 feet. Early entry saws make a nice clean cut for decorative concrete joints. This can lead to stress concentrations resulting in subsequent spalling of the concrete. Change in wall height or thickness see figure 1 figure 2 change of loading see figure 3 abutments of walls and columns see figure 4 junctions of dissimiliar materials see figure 5.

In concrete walls the movement joints should normally be placed at a maximum spacing of 7 5m. Movement control aggregate concrete blocks position of movement joints consideration for the location of movement joints should be given at. Expansion joints allow independent movement between adjoining structural members minimizing cracking when such movements are restrained. Saw cut contraction joints are ideal for decorative concrete because the joint is narrower and cleaner than a tooled joint.

Why do we need them. Dowels are used to transfer shear across construction and movement joints in concrete. It allows for thermal expansion and contraction without inducing stress into the system.