I am working on the design of an eight-story medical center that has 14-foot floor-to-floor heights. The wall construction is brick veneer with steel stud backup. The windows are either individual punched openings or larger groups that span a width of 30-feet horizontally. The heads of the windows are located 8-feet above the floor line. There are continuous shelf angles at the floor lines throughout the building. To support the masonry of the windows, we used loose-laid lintels at the individual openings and suspended lintels at the wider openings.
Are vertical expansion joints needed at both sides of the masonry at the areas where the lintels are hung since the masonry above the windows is supported by the floor above, whereas the masonry on either side is supported on the floor below?
Whenever there are different supporting conditions in adjacent areas of masonry veneer, these locations need to be isolated with vertical joints so that they are free to move independently. In the case of loose-laid lintels, all the masonry is supported on the floor below and there is no problem. However, when the masonry over the windows is attached to the structure above, vertical expansion joints must be provided to isolate the masonry above the windows from the masonry on either side, In this case, the lintel angles should not extend into the masonry at the jamb of the windows.
An alternate approach is to move all the shelf angles down to the level of the head of the windows. This approach could be done both at the punched and wider windows. In this way, the masonry is all supported at the same level by angles suspended from the structure above.
Angle brackets could be constructed and positioned 2-feet on-center to support these shelf angles, which would eliminate the need for two levels of flashing and greatly simplify the flashing installation. Obviously, there are additional considerations that must be made, such as the cost of hanging the shelf angles throughout and designing the shelf angles to be sufficiently stiff to handle the bending moment and torsion.
Consideration also should be given toward either making angles adjustable in some way so that their height can be changed when the masonry is installed, or special provisions must be made to carefully locate the position of the shelf angles. One of these two approaches is necessary to prevent problems that otherwise might occur because the standard construction tolerance for steel is not as tight as it is for masonry construction.