An engineer should consider using structural steel tubes when the concrete masonry spans from column to column. Steel columns are often erected out-of-line, and sometimes not within allowable construction tolerances. Concrete masonry, which was detailed to fall within the flanges of the column, now abuts one of these flanges, making proper anchor installation nearly impossible.
Designing the steel frame with structural tubes eliminates this problem. Also, utilizing structural steel tubes in lieu of wide flange columns simplifies the installation of flashing. Structural steel tube columns eliminate flashing end dams and pockets which are required and difficult to install successfully when wide flange columns are used.
When concrete masonry spans between columns constructed of steel tubes, an adjustable anchor, which engages a slotted metal channel, should be specified. This connection braces the wall laterally to the column from wind loads.
The distribution of the wind load acting on the wall is resisted by both masonry wythes in proportion to their relative flexural stiffness. Joint reinforcement secures the brick wythe to the concrete masonry, 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 column. This connection laterally braces the masonry wall to the steel column. (See diagrams below)
Consider shear strengths and resistance to torsion when selecting anchor types. If required, a strip anchor may be specified in lieu of a triangular type.
The inner end of the base flashing is usually set in the bed joint of the inner wythe of concrete masonry. This joint terminates where columns exist. When columns are constructed of structural steel tubes, the flashing and sealing procedures are less complex. Flashing can be cut and set in a heavy bed of mastic directly against the outer surface of the steel tube column. Flashing dams and pockets are eliminated.
The space between the steel tube and masonry can be sealed by placing a compressible/expandable filler in the space, or by applying flashing tape over the space and sealing it to the surface of the column and concrete masonry.
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.