Movement Joints In Concrete Retaining Walls

1 3 movement and restraint in concrete structures restrained movement is a major cause of cracking in con crete structures.

Movement joints in concrete retaining walls.

6 to 9m factors influencing spacing of joints are. 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. Greater distances between movement joints 9 m and sometimes longer are possible in aggregate concrete blockwork walls depending on the location and block type. The hight shear force is applied at the horizontal construction joints located at the lower level.

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. For cantilevered and gravity walls vertical expansion joint spacing shall be a maximum of 60 feet on centers. They are essentially vertical planes of weakness built into the wall to reduce restraint and permit longitudinal movement due to anticipated shrinkage and are located where stress concentrations may occur. Typical movement joint spacing for unreinforced concrete masonry panels.

The friction of the concrete is the key factor that limits the movement. Internal or external restraint can develop tensile stresses in a concrete member and the tensile strength or strain capacity can be exceeded. As a rule of thumb it is normal to consider movement joints at approximately 6 m centres in straight lengths of autoclaved aerated concrete block walls. 8 to 12m external.

There is a special check to be done at the construction joints when larger retaining walls or structures having very high lateral loads are designed. 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. In reinforced walls and 6m in unreinforced walls. Tial basement walls and the national ready mixed concrete association ref.

Some designers recommend re ducing joint spacings by about 20 in walls with frequent openings such as doors and windows. The weaker the mix the increased ability to accommodate movement. In concrete walls the movement joints should normally be placed at a maximum spacing of 7 5m. Precast concrete cantilever wall expansion joints shall be in accordance with the standard specifications section 6 11 3 3.