Steel joist connection to masonry walls

Masonry Construction, July-August, 2004 by Walter A. Laska

All walls must be braced laterally to resist wind loads. They are commonly braced by floor or roof systems constructed with steel joists. The steel joists (and metal decking) act as a diaphragm to brace the wall against wind loads. Columns, piers, pilasters, or crosswalls are not required for lateral bracing if the wall is built within the height limitation allowed by code.

Normally, masonry walls are braced by the steel joist at the bearing connection. Steel joists are fabricated with an extended top chord to enable the joist to bear on the concrete masonry wythe. The required bearing for an open web steel joist is determined by its span and depth. The three most commonly specified joists--as designated by the Steel Joist Institute--are the K-Series, LH-Series, and DLH-Series.

K-Series joists have depths ranging from 8 inches to 30 inches, with a maximum span of 60 feet. The minimum bearing requirement on masonry is 4 inches. LH-Series joists have depths ranging from 18 inches to 48 inches, with a maximum span of 96 feet. DLH-Series joists have depths ranging from 52 inches to 72 inches, with a maximum span of 144 feet. The minimum bearing requirement for the LH-Series and DLH-Series is 6 inches.

The allowable height of a masonry wall can be raised without increasing the thickness or the addition of vertical reinforcement by bracing it to the bottom chord of the joist. This connection can be achieved by extending the bottom chord of the steel joist and welding it to a clip angle, which has been bolted into the concrete masonry wall. The joist should not be welded to the clip angle until all the roof or floor dead load is in place. Bracing the wall to the bottom chord can increase the overall wall height by the dimension of the joist depth (approximately).

A continuous bond beam should be installed in the concrete masonry at the steel joist bearing point. A continuous bulb tee can be solidly grouted into the bond beam to serve as a bearing plate. The bond beam functions as a structural element distributing loads imposed by the joists to the bearing wall below. Performing as part of the diaphragm, the bond beam also acts as a horizontal stiffness.

Additional information on this general subject is available in the "Masonry and Steel Detailing Handbook" authored by Walter A. Laska. The price for the 218-page book is $51, and it can be ordered at www.wocbookstore.com.