This Buildings Bulletin was released on May 24, 2017 and explains the requisites for bracing masonry walls and plans of action during construction to ensure protection of property and the public.
Background
In any construction, public safety and protection is of utmost importance so it is imperative that ample protection be provided for the public including properties during construction. BC 2104.6 requires the contractor to install bracing for masonry walls to ensure the stability of these walls when constructing. They are also required to keep the bracing plans onsite. These plans should contain pertinent details of the plan including drawings, directions and all necessary details to ensure the stability of masonry walls in order to protect public and property during the construction of said walls. Bracing plans for masonry walls constructed within a distance that is less than its height from an adjacent property and/or public right of way should be signed and sealed by a licensed and registered Professional Engineer.
Design Criteria
Compliance with BC 2104.6, TMS 402/ACI 530/ASCE 5, BC 1609, and ASCE 7-05 is a must when designing for the bracings of masonry walls and when the action plan complies with the requisites of BC 1618.3 and this buildings bulletin, then the bracing permitted can be designed with a reduced load pursuant to the provisions of BC 1618. Block density, width, volume is considered when designing the bracing support and preparing the bracing plan as well as the position of reinforcements for the wall, foundation anchor and mortar/grout to be used, curing and development strength, configuration of the walls as well as the wall’s aspect ration. You can make use of industry accepted standards as a general guideline for masonry wall bracing like the NCMA TEK 3-4b and the Standard Practice for Bracing Masonry Walls Under Construction but conditions specific to the actual construction site should be considered when designing and planning course of actions to ensure safety.
Action Plan
Contractors and/or permit holders should ensure that an action plan is in place when making use of reduced loads for designing the wall bracing. All wind conditions including those specified in BC 1609 should be addressed by the action plan and any plan should be implemented in 1 day or less and should contain the following:
1. Specifications on how workers should brace masonry walls at the end of day as well as when the walls reach a specific height. Recommendations for bracing based on wall height and thickness, wind speed, reinforcement and bonding can be found in Table 2 of NCMA TEK 3-4b.
2. How the monitoring of wind speed will be completed by the responsible party at the construction site at all times. Weather advisories/bulletins, meteorological station reports, calibrated instruments and visual methods like Beaufort Wind Scale are some suggested ways.
3. Establishment of a safety zone, when applicable as well as standoff distances/perimeter location on each side of the wall. This zone should not exceed beyond the property line. In cases where safety zones cannot be established or work cannot be avoided in an adjoining public right-of-way, and proper protection for the public is required, BC 3307 provides the guidelines.
4. Identification of responsible individuals/personnel for the monitoring of wind conditions and notification of appropriate personnel if wind speeds exceed or is expected to exceed the established safety thresholds and initiating action plans for the safety of everyone concerned.
5. Establishment of procedures for safe evacuation of the site and proper documentation of such as well as training of workers for such procedures to ensure compliance.
6. Specification of time frames as to the addition and removal of structural and non-structural elements, loads and sacrificial elements to ensure that the structure will resist unreduced forces as necessary for the permanent structure.
7. Specification on the location and proper procedure on tying down loose construction materials and debris should high winds be expected as well as proper clean up of such at the end of day.
8. Identification of responsible personnel to ensure the implementation of the action plan should it be necessary.
It should also be noted that worker safety requirement for masonry construction can be found in OSHA 1926.706 and it states that a restricted zone equal to the height of the unbraced walls measured at right angles on each side of the wall along its entire length and additional four feet should be established.