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Wall Bracing
Photo courtesy of MCAA
By Rashod Johnson
Director of Engineering, MCAA
| "Bracing
masonry walls during construction is often neglected
by mason contractors, sometimes with catastrophic
results. Even in those cases where some nominal bracing
is provided, it is often the case that they are inadequate
and can overstress and fail under lateral loads. One
of the reasons for this is that mason contractors
often lack the in-house engineering expertise to properly
evaluate the conditions necessary to design masonry
bracings. Proper bracing design entails a number of
factors, e.g. strength and age of masonry, mortar
and grout, location and magnitude of reinforcement,
openings, etc. Before the MCAA began its effort in
1997, there were no uniform structural design guidelines
for contractors and engineers to follow while designing
the bracing. The formation of the Council for Masonry
Wall Bracing was a step undertaken to fill this gap,
by providing specification and design parameters for
structural bracing. The Standard Practice for Bracing
Masonry Walls and the Masonry Wall Bracing Handbook
are excellent tools that provide guidance to the contractor
to adequately brace masonry walls." Mohammad
Ayub, PE
Director, Office of Engineering
Directorate of Construction, OSHA
Washington, D.C. |
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It's 6:00 a.m. on Monday. As you drive up to the
job site, the general contractor's superintendent meets you at the
gate. You look toward the site and, before even exiting the car,
you see a major problem. Your 30-foot tall concrete block walls
have blown down over the weekend. Thousands of dollars of scaffolding
is damaged, a forklift that was parked near the wall is totaled,
pallets of material are obliterated and unusable. You glance in
your rearview mirror and see an Occupational Safety and Health Administration
(OSHA) compliance officer pull up behind you. Happy Monday!
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Photo courtesy
of EZ Grout
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Realizing it was your responsibility to properly brace the block wall
on Friday, you know your supervisor will not be happy. Immediately,
you contact your supervisor to tell him what happened. Next, you sit
down in the trailer with the OSHA representative and general contractor
to discuss the previous weekend's events. Afterward, the three of
you take a walk through the site and assess the damage. Although there
is quite a bit of damage to the site, because the wall blew down over
the weekend, there were no workers on the job site. After the walkthrough
and a post walkthrough meeting, the OSHA representative leaves and
you and your crew are left to clean up the mess and rebuild the walls.
Chances are your company will have higher insurance premiums, be back-charged
by the general contractor, and likely receive an OSHA citation stating
that the bracing on the masonry walls was not adequate. But was it?
The Purpose of Wall Bracing
OSHA's mission is to assure the safety and health of America's workers
by setting and enforcing standards; providing training, outreach and
education; establishing partnerships; and encouraging continual improvement
in workplace safety and health. This means that OSHA's primary goal
is the safety of life. Given this focus, 29 Code of Federal Regulations
(CFR) Part 1926 Subpart Q Section 706 establishes the requirements
for masonry construction as it pertains to life safety.
Part A establishes a limited access zone. The
limited access zone shall:
- be established prior to the start of the construction of the
wall;
- be equal to the height of the wall plus four feet and run the
length of the wall;
- be established on the unscaffolded side of the wall;
- be restricted to entry by only the mason contractor; and
- remain in place until the wall is adequately supported.
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Photo courtesy
of Jakerstin Bracing, Inc.
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Part B simply states that "all masonry walls over eight feet in height
shall be adequately braced to prevent overturning and to prevent collapse,
unless the wall is adequately supported so that it will not overturn
or collapse. The bracing shall remain in place until permanent supporting
elements of the structure are in place." This
leads to an obvious question: What is adequate?
Some OSHA compliance officers feel as though if
the wall falls down, no matter how much bracing was installed, it
was inadequate. Conversely, if the wall stands, no matter how little
bracing was installed, it was adequate. This regulation is considered
a "performance standard," which requires both the controlling employer
(general contractor/construction manager) and the creating employer
(mason contractor) to develop a plan to support the masonry wall.
This places all of the liability upon the shoulders of the contractors,
with minimal direction from OSHA.
Industry Standardization
In Spring 1997, the Mason Contractors Association of America (MCAA)
decided to "standardize" the means and methods of bracing masonry
walls. In order to achieve this goal, the MCAA sought the help of
masonry industry experts by forming the Council for Masonry Wall Bracing.
The Council consisted of contractors, masonry design professionals
and a representative from OSHA.
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Photo courtesy
of Jakerstin Bracing, Inc.
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From the data, the Council conducted research and developed a standard
set of guidelines to show the contractor where typical masonry walls
needed to be braced. As a result, in July 1999 the Standard Practice
for Bracing Masonry Walls under Construction was published. This
new Standard Practice was the first industry-supported document giving
specific procedures for bracing masonry walls during construction.
The primary goal of this guide is to provide life safety for masons
and other workers on a construction site during the time when a masonry
wall is being constructed.
Research and Updates
Masonry construction is drastically different from other forms of
construction. For example, when precast and tilt-up walls are erected,
they have the majority of their final design strength and can resist
most wind loads. However, masonry walls are subjected to wind loads
before the final design strength is achieved. This means that masonry
walls can fall down under less severe wind conditions. This being
the case, the Council needed to determine what was the wind speed
at which the mason's safety was being compromised.
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Photo courtesy
of Jakerstin Bracing, Inc.
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After testing was completed, data indicated that masonry walls started
to severely alter their shapes when wind speeds reached 60 miles per
hour (mph). Testing also showed that wind speeds that high did not
allow the mason to accurately place the masonry unit, especially when
on scaffolding. Therefore, it was agreed upon by the Council that
the wall bracing in the Standard Practice be designed to resist
a wind speed of 40 mph and evacuated at 35 mph. Once evacuated, the
limited access zone then becomes a restricted zone where no workers
are allowed until the winds slow down. This keeps the Standard
Practice in line with both OSHA and MCAA's goal of protecting
the mason and other workers.
Figure A
In 2001, the Standard Practice
for Bracing Masonry Walls was updated. In the update, all of
the tables were adjusted to modular values, and design tables, which
change the heights of unbraced masonry above bracing as the wind
speed changes, were added to the Appendix.
In 2003, the MCAA published the Masonry Wallbracing
Handbook. This handbook contains over 700 different configurations
of masonry walls, including openings. While it is based off of the
Standard Practice, it is a step-by-step pictorial of where
wall bracing should be placed (see Figure B). The MCAA is currently
working to develop wall bracing software, which is scheduled for
completion by early 2005.
Figure B
Conclusion
The Council for Masonry Wall bracing recognizes that it is impossible
to prevent the collapse of a masonry wall during construction and
that life safety is the primary concern. The Standard Practice
and the Masonry Wallbracing Handbook have developed a procedure
whereby the wall and area around the wall is evacuated at a prescribed
wind speed. While the insurance companies may not agree with this
approach, it reaches the goal of preserving the safety of all workers
around a masonry job site. This means that, if a wall falls inside
of the limited access zone after it was evacuated, the wall bracing
was adequate... Adequate enough to make sure that no workers were
injured or close to being injured.
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