Masonry Magazine July 2005 Page. 32
WALL BRACING
to allow braces to be removed at those locations. Intermediate Period bracing must remain in place until final lateral stability from supporting structural elements is in place. During the Intermediate Period, the Restricted Zone must be evacuated at wind speeds of 35 mph or higher.
Bracing Basics
WHEN BRACING masonry walls, a minimum of two braces is required per wall panel (the distance between control joints). Using two braces per panel is important because with only one brace per panel, the wall can wobble in and out at the control joints and snake in the winds. The maximum permitted length of wall between control joints is 25' per national Building Codes. Any length over 25' is deemed illegal and should not be built as it is a violation of building codes. (A good rule of thumb is to encourage your architect to put control joints at 24'8" apart, if possible, since block can be laid out to that distance without cutting.)
Braces must be installed with 20% of the wall outside of each brace at the control joint. The easiest way to figure this is to take the panel length and multiply by .2. For example, a 25' long wall multiplied by .2 would leave each brace located at 5' from the control joints and 15' between the braces.
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Being proactive with your wall bracing will help you to not have to walk onto your job site looking like the one in the picture above.
Keep in mind that a masonry wall is considered to be reinforced 12 hours after the grout is placed.
Brace heights vary based on which period of construction the wall is in, the weight of the units you are installing, and your method of grouting.
Keep in mind that a masonry wall is considered to be reinforced 12 hours after the grout is placed. So if you are low-lift grouting as the masonry is being laid, your walls will be braced much more sufficiently internally. This is due to the grout having time to set while you are laying the next four to six feet of wall above it. Once the grout in the wall reaches that 12-hour mark, the masonry wall enters into the Intermediate Period, and lower braces can be moved up based on the Standard Practice.
In addition to the Standard Practice, another good source of information is the MCAA's Masonry Wallbracing Design Handbook, which has over 700 schematic examples of wall bracing.
Monitoring Wind Speed
LANG MASONRY CONTRACTORS have wind monitors on each job site to measure the wind speed. These wind instruments, called anonometers, cost between $80 and $200 and are well worth the investment. Some will even sound an alarm when the established wind speed is exceeded.
If you do not have these instruments onsite, you may use the visual method of measuring wind as long as you have trained your people how to measure visually based on the Beaufort Wind Scale (BWS). However, if you use this visual method to measure, evacuation times change due to the decrease in accuracy of the visual method.
Using the BWS method, evacuation in the Restricted Zone changes from 20 mph to 15 mph for the Initial Period. This is considered a moderate breeze, where thin branches on trees move or dust and paper rises. During the Intermediate Period, evacuation of the Restricted Zone changes from 35 mph to 30 mph using the BWS method. This is considered a strong breeze, where