Masonry Magazine February 1999 Page. 53
Safe Zone
If wind speeds exceed those allowed in the Initial and Intermediate Periods there is a chance that the masonry wall under construction could fail. In this case it is essential that the area defined as the Safe Zone is unoccupied in order to insure life safety.
Other Terms
Wind speeds as defined in this Standard are measured five-second wind speed gusts at the job site. Both instrumental and visual methods are allowed. When visual methods are used, the measured speed needs to be increased by five miles per hour. For instrumental measurements, the device must have an accuracy of +2 miles per hour. In practice, this will mean that the observed five-second gust speed cannot exceed the values in chart below.
| Period | Maximum Allowable Observed 5 Second Gest Speed (mph) |
| :----------- | :------------------------------------------------------- |
| | Instrumental |
| Initial | 18 |
| Intermediate | 33 |
| | Visual |
| :----- | :----- |
| | 15 |
| | 30 |
It will take a great deal of experience to become proficient in using one of several visual methods for determining wind speed. Because of this, it is anticipated that the use of wind speed indicators will be the method of choice for most contractors.
Because of the need for management and maintenance of the Safe Zone, the Standard identifies individuals who are responsible for monitoring wind speed and maintaining bracing during the time when the mason contractor is actively engaged in erecting masonry walls on the job site and when the mason contractor leaves the job site before the Intermediate Period is over. The "Responsible Person" is designated by the mason contractor to monitor wind speed and maintain bracing while the mason is on-site. The "Authorized Project Agent" is a person, active in the management of the project with knowledge of Safe Zone requirements and the authority to evacuate all work forces from the Safe Zone when necessary. It is anticipated that the Authorized Project Agent will be an employee of the General Contractor and will be on the job site even when the Mason Contractor's personnel are not.
Bracing masonry walls during construction is often neglected by masonry contractors with catastrophic results. Even in those cases where some nominal bracing is provided, it is generally observed that they are inadequate and could overstress or fail under lateral loads. One of the reasons is the fact that some masonry contractors lack the in-house engineering expertise to properly evaluate the conditions necessary to design the masonry bracings. Proper bracing design entails a number of factors, e.g., strength and age of masonry, mortar and grout, location and magnitude of reinforcing bars, maximum wind speed beyond which masonry work is not permitted, support conditions, opening sizes, etc. Before the Mason Contractors Association of America (MCAA) began its effort in 1997, there were no uniform structural design guidelines for the contractors and engineers to follow while designing the braces. The formation of the Council for Masonry Bracing by MCAA is a step undertaken to fill this gap which is expected to provide specification and design parameters for structural bracing design. The Council, among others, includes technical representatives of major organizations dealing with masonry. In addition, it is expected to provide bracing examples for some typical conditions which the contractors could simply adopt and use, in the event the contractors do not wish to undertake the design effort.
Mohammad Ayub, PE
Director, Office of Engineering
Directorate of Construction, OSHA
Washington, DC
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