Joints in Concrete Construction

Description

Joints are necessary in concrete structures for a variety of reasons. Not all concrete in a given structure can be placed continuously, so there are construction joints that allow for work to be resumed after a period of time. Since concrete undergoes volume changes, principally related to shrinkage and temperature changes, it can be desirable to provide jointsand thus relieve tensile or compressive stresses that would be induced in the structure. Alternately, the effect of volume changes can be considered just as other load effects are considered in building design.

Various concrete structural elements are supported differently and independently, yet meet and match for functional and architectural reasons. Inthis case, compatibility of deformation is important, and joints may be required to isolate various members. Many engineers view joints as artificial cracks, or as means to either avoid or control cracking in concrete structures. It is possible to create weakened planes in a structure, so cracking occurs in a location where it may be of little impor-tance, or have little visual impact. For these reasons, ACI Committee 224—Cracking, has developed this report as an overview of the design, construction, and maintenance of joints in various types of concrete structures, expanding on the currently limited treatment in ACI 224R.

While other ACI Committees deal with specific types of structures, and joints in those structures, this is the first ACI report to synthesize information on joint practices into a single document. Committee224 hopes that this synthesis will promote continued re-eval-uation of recommendations for location and spacing of joints,and the development of further rational approaches. Diverse and sometimes conflicting guidelines are found for joint spacing. Table 1.1 reports various recommendations for contraction joints, and Table 1.2 provides a sampling of requirements for expansion joints. It is hoped that, bybringing the information together in this Committee Report, recommendations for joint spacing may become morerational, and possibly more uniform.