When I perform concrete design on an element, the output contains expressions such as "LONG. REINF.", "TRANS. REINF.", "TOP", "BOTT.", etc. Can you explain what these terms mean?
The design of an element involves determination of the reinforcement for moments Mx and My at the centroid of the element. The reinforcement calculated to resist Mx is called longitudinal reinforcement, and is denoted in the output by the expression "LONG. REINF.".
The reinforcement calculated to resist My is called transverse reinforcement, and is denoted in the output by the expression "TRANS. REINF.".
The sign of Mx and My will determine which face of the element the steel has to be provided on. Every element has a "top" face, and a "bottom" face, as defined by the direction of the local Z axis of the elements. Mx will cause tension on one of those faces, and compression on the other. A similar effect will be caused by My. The output report of reinforcement provided on those faces contains the terms "TOP" for top face, and "BOTT" for the bottom face.
The procedure used by the program to arrive at these quantities is as follows :
For each element, the program first scans through all the active load cases, to find the following maxima :
Maximum positive MxMaximum negative MxMaximum positive MyMaximum negative My
The element is then designed for all those four quantities. If any of these moments happen to be zero, or if the reinforcement required to resist that moment is less than the capacity of the element with minimum reinforcement, only minimum reinforcement is provided. For the ACI code, the rules governing provision of reinforcement for shrinkage and temperature are used in calculating minimum reinforcement.
The rules applicable for design of a beam for flexure are used in calculating the steel areas. The width used in this calculation is a unit width of the element. For determination of the effective depth, the steel for longitudinal moment is assumed to be the outer layer, and the steel for transverse moment is the inner layer.
The output will consist of the steel area required for all of four maximas. As described earlier, they will be reported using the terms LONG, TRANSVERSE, TOP and BOTT.