temporary masonry bracing – what designers …...requirement in your design. 2) require foundation...

Temporary Masonry Bracing – What Designers Need to KnowPresented by Todd Dailey, P.E.

Codes and Standards

OSHA Temporary Bracing Criteria – Summary: Overdue for Updating

Short Comings:1)Unrealistic

2)Too vague

3)No recognition of masonry wall behavior, including research of early-age strength development.

ELECTRONIC CODE OF FEDERAL REGULATIONS

e•CFR data is current as of July 7, 2016

Title 29 → Subtitle B → Chapter XVII → Part 1926 → Subpart Q → §1926.706

Title 29: Labor PART 1926—SAFETY AND HEALTH REGULATIONS FOR CONSTRUCTION Subpart Q—Concrete and Masonry Construction

§1926.706 Requirements for masonry construction.

(a) A limited access zone shall be established whenever a masonry wall is being constructed. The limited access zone shall conform to the following.

(1) The limited access zone shall be established prior to the start of construction of the wall.

(2) The limited access zone shall be equal to the height of the wall to be constructed plus four feet, and shall run the

entire length of the wall.

(3) The limited access zone shall be established on the side of the wall which will be unscaffolded.

(4) The limited access zone shall be restricted to entry by employees actively engaged in constructing the wall. No other employees shall be permitted to enter the zone.

(5) The limited access zone shall remain in place until the wall is adequately supported to prevent overturning and to

prevent collapse unless the height of wall is over eight feet, in which case, the limited access zone shall remain in place until the requirements of paragraph (b) of this section have been met.

(b) 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.

TMS 402/602 Temporary Bracing Criteria

Bracing System Design Options

Early-Age Grout/Rebar Strength

Compressive Strength of Masonry (f’i) per Standard Practice (“Early-age” Strengths)

Compressive Strength of Masonry (f’m) per TMS 602 (Masonry Specs/Code) (“Final” Strengths)

Early-age grout/rebar strengths are ½ of final strengths

(Vertical Cantilevered Wall)

INTERNALLY BRACED REINFORCED MASONRY WALL & “FIXED BASE”

Internal BracingQuite often it is temporary bracing

“for free”

Wall Stress Comparisons – Permanent vs Temporary Bracing


Structural Engineering Terms:“Moment”“Bending Stress”“Flexural Stress”

Internal Bracing Advantages

Basically improved safety at a lower wall cost:1. Don’t have to purchase, rent, store, install, de-install, and

otherwise touch braces and associated components (deadman, anchors, mounting plates, etc.).

2. Reduced conflicts with other trades and construction activities.

3. Any concerns about pipe brace capacities and inadequate deadmen are eliminated.

4. The bracing system is “non-removable”.5. Temporary bracing system gains reserve strength with

passage of time.

$$

Safety

Lake HS Temporary Bracing Statistics & Economics:

8640 - Total lineal feet of masonry walls

8380 - Lineal ft of “As-Is” internally braced walls (97%)

170 - Lineal ft of “modified” internally braced walls (2%)

90 - Lineal ft of externally braced walls (1%)- 8 Pipe Braces (reduced to 6 since corners were built

concurrently)- 2 Cable Braces for proscenium

Approximately 150 braces eliminated @ $500/brace, $75,000

Schedule and site access benefits

Temporary Masonry Bracing Issues

1. Standard Practice is underutilizeda) Does not have “Name Recognition” and usage throughout

the country.b) Mandatory in Michigan (MIOSHA).c) Part of EM385 (ACOE).d) Deemed “OSHA compliant”.

2. Lap splice “disconnects”a) Foundation dowels.

- Standard Practice requires “48 dь” minimum lap splices for reinforced internal bracing, however- The TMS 402/602 (permanent design code”)requires none.

Foundation Dowels – Wall Strength Comparison #1

Reinforced Fixed BaseMoment capacity = 733 ft. #

Unreinforced Fixed BaseMoment capacity = 302 ft. #




243% Stronger!!




323% Stronger!!

Temporary Masonry Bracing Issues

1. Standard Practice is underutilized

2. Lap splice “disconnects”a) Foundation dowels.

- Standard Practice requires “48 dь” minimum lap splices for reinforced internal bracing, however- The TMS 402/602 (permanent design code”)requires none.

b) Remainder of wall lap splices:- Standard Practice requires “48 dь” minimum lap splice- The TMS 402/602 (“permanent design code”) varies. Significantly!

Temporary Masonry Bracing Issues –Solutions & Recommendations

For Designers: 1) Incorporate the Standard Practice as a contractual

requirement in your design.2) Require foundation dowels to have a minimum projection

adequate for a full lap splice as defined in the Standard Practice (48 bar diameters).

3) Require all lap splices to be a minimum of 48 bar diameters.4) If unwilling to do items 2&3, at least allow the mason

contractor to do so voluntarily.

Temporary Masonry Bracing Issues –Current Update

1) IMI has formed a “Temporary Masonry Bracing Task Group”.2) Desire to upgrade the Standard Practice to a “consensus

document”.3) Investigating possible additional lap splice testing and

early-age strength development to see if lap splice requirements in the TMS 402/602 and the Standard Practice can be brought into closer alignment.

temporary masonry bracing – what designers …...requirement in your design. 2) require foundation...

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