Masonry walls must be designed and constructed to resist wind loads. For multi-story buildings, the walls are typically supported at each floor line and at the roof line. If the walls are independent of the steel structure, and are designed to span vertically, the masonry must be anchored to the spandrel beam.
Wind load acting on the masonry wall is resisted by the brick and concrete masonry wythe in proportions to their relative flexural stiffeners. Joint reinforcement bonds the brick wythe to the concrete masonry wythe, which creates a positive bond.
Wind loads are transferred from the brick wythe to the concrete masonry wythe and through the anchor to the steel beam. This connection laterally braces the masonry wall to the spandrel beam. Anchorage to the steel columns is not required for this type of design.
Anchorage adjustability is critical when masonry walls are designed to completely bypass the structural steel frame. Exact alignment to the bed joint of the concrete masonry wythe rarely occurs because of construction tolerances.
An anchor with horizontal and vertical adjustability should be specified. The mason must be allowed some installation flexibility if proper anchorage of the masonry wall to the steel beam is to occur.
When anchor attachment to the beam web is required, a rectangular or triangular wire loop anchor that engages a receptor angle should be implemented. The loop anchors should be solidly embedded in the concrete masonry wythe, which can be accomplished by setting the anchor in a cell of the CMU solidly filled with mortar.
The leg of the angle receptor provides the additional rigidity required to prevent the anchor from buckling. The receptor angle can be welded or mechanically fastened to the web of the beam.
Horizontal spacing of the anchors should be determined by a structural engineer. The anchor should not span a distance in excess of 4 in. (span is the distance measured between the points at which the anchor engages the masonry and the receptor angle). If this distance is exceeded, a detailed anchor analysis must be performed by a structural engineer.
When the structural frame is loaded, the steel beam deflects while the masonry remains stationary. An adjustable anchor possesses the flexibility to accommodate the differential movement between the two systems.
Consider pull out strengths and resistance to buckling under loading when selecting anchor type and connection. This connection should not resist in-plane sheer forces.
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 atwww.wocbookstore.com.