Masonry walls during and immediately following construction are inherently unstable. It doesn't take a lot of lateral force against the face of the wall to push it over.
Braces can be designed to hold up the wall in every conceivable situation-a 100-mph wind or a large earthquake-but they might cost more than the wall. Or you can prop a couple of 2x10 scaffold planks against the wall and hope the wind doesn't blow, but a fairly light wind could take the wall down. Or you can install bracing that will handle a moderate wind. More and more, masonry contractors are choosing the last option because it greatly reduces their risk at a reasonable cost.
OSHA requires "adequate" bracing for walls taller than 8 feet, and contract documents often require bracing. But deciding what is adequate is normally left up to the contractor's discretion. In truth, bracing is not a safety issue. The site could simply be evacuated whenever the wind blows.
Bracing systems are justified for taller walls, partly to protect workers in case of sudden wind gusts and partly to protect the investment of time and money. The contractor must then decide what kind of bracing is right for the project. Here are the options:
Wood: Bracing built onsite with lumber
- Steel cables installed on both sides of the wall and tied to a large concrete deadman
- Steel pipes
Many masonry contractors have adapted tilt-up braces to masonry walls. Dur-O-Wal (a subsidiary of Dayton Superior) and Meadow-Burke Products have taken this a step further by producing special connectors specifically for masonry walls. Dur-O-Wal does not currently sell their Brace-Rite wall braces but rather leases them to contractors and then only when an engineering analysis has been done. The wall tie used in the Brace-Rite system is installed when the masonry is laid; then the strongback and pipe brace are attached with wedges and pins, which makes for quick installation and removal of the braces.
Meadow-Burke's adaptation of their tilt-up braces is perhaps not as slick as Dur-O-Wal's but just as effective. This system uses a pair of 5-inch channels for the strongback, bolted through the wall to a wood 2x10 on the opposite side. A minimum of three horizontal reinforced bond beams is required where the anchors go through the wall. These braces are designed for a 48-mph wind with a 1.5 safety factor.
The Footlock Bracing System is another bracing system that is effective for lower masonry walls, especially foundation walls that are being backfilled before the grout gains full strength and the floor is placed. This device uses a 4x4 wood brace connected to steel brackets bearing on the ground and wall. These brackets are tied to a chain that is anchored to the wall's footing with a #4 rebar hook installed when the footer was placed. A lever mechanism tightens the chain, providing up to 8,000 pounds of support to the wall.
The idea of reinforcing a wall and relying on the early strength of the reinforcement to provide resistance to lateral loads has been investigated. Research done by Russell Brown at Clemson University, with funding from the Council for Masonry Research, showed very rapid strength development in a grouted wall, and this concept was incorporated into the design sections of the bracing standard. There is also some thought that post-tensioning might be able to help support a wall prior to its being attached to the lateral support system. These efforts are in the very early stages, and nothing definitive is known at this time.