Movement Joints In Concrete Retaining Walls

The hight shear force is applied at the horizontal construction joints located at the lower level.

Movement joints in concrete retaining walls.

Internal or external restraint can develop tensile stresses in a concrete member and the tensile strength or strain capacity can be exceeded. Movement joints such as control joints are one method used to relieve horizontal tensile stresses due to shrinkage of the concrete masonry units mortar and when used grout. The friction of the concrete is the key factor that limits the movement. The weaker the mix the increased ability to accommodate movement.

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. 6 to 9m factors influencing spacing of joints are. Use of bedjoint reinforcement and moisture content of blocks when laid. Greater distances between movement joints 9 m and sometimes longer are possible in aggregate concrete blockwork walls depending on the location and block type.

These are vertical joints or grooves formed or cut into the wall that allows the concrete to shrink without noticeable harm. Some designers recommend re ducing joint spacings by about 20 in walls with frequent openings such as doors and windows. Typical movement joint spacing for unreinforced concrete masonry panels. Tial basement walls and the national ready mixed concrete association ref.

1 3 movement and restraint in concrete structures restrained movement is a major cause of cracking in con crete structures. 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. In reinforced walls and 6m in unreinforced walls. 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.

Precast concrete cantilever wall expansion joints shall be in accordance with the standard specifications section 6 11 3 3. 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. 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. 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.