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US-11 The use of stand-off brackets for C-shaped cornice hooks for scaffolding support

Report ID: 909

Published: CROSS-US Newsletter 1 - March 2020

Report Overview

A correspondent reports that using stand-off brackets with C-shaped cornice hooks for supporting suspended scaffolding have been contributing factors in safety incidents in certain circumstances.

Report Content

A reporter notes that using stand-off brackets with C-shaped cornice hooks (Figure US-11) for supporting suspended scaffolding have been contributing factors in safety incidents in certain circumstances, such as failure and falling of parapet coping stones. This has led to them being banned in 2019 as an interim measure in a major US city. A stand-off bracket is a rigid member that extends an assembly as shown in Figure US-11, and the problem can occur when there is an installation or use of a stand-off bracket attached to a cornice hook (C-hook) to provide a suspended scaffold additional outreach from the face of a parapet or wall.

The ban will remain until such time as the city is able to further study the use of such brackets and promulgate regulations to ensure their safe installation and use.

Comments

C-shaped cornice hooks are commonly used to anchor suspended scaffold support lines to building cornices and parapets. Clearly the adequacy of the anchorage depends on the structural capacity of cornice or parapet to which the hook is attached. While such devices may be used in new construction of buildings or in the repair and maintenance of existing buildings, the concern is more acute with existing buildings as (1) the original construction may not be as robust in older construction as in new, (2) deterioration particularly of masonry parapets is common, and (3) it is generally more difficult to ascertain the as-built condition of old construction than new.

These devices will induce compressive, flexural-tensile, and lateral shear loads to various components of the cornice or parapet. In particular, older masonry construction may have little to no flexural-tensile or bond-shear capacity. The special concern with standoff brackets is that they exacerbate the loads imposed on the supported element, especially at the connection of the coping stone to the masonry, by increasing the eccentricity of the downward suspension cable load. The reporter cites concerns and accidents, including failure and/or falling of coping stones. While use of C-shaped cornice hooks without standoff brackets could potentially be a concern in certain situations, the reporter noted personal knowledge of failures only when standoff brackets were used.

In the United States the applicable regulation of such anchorages is commonly governed by OSHA 29 CFR 19261, Safety and Health Regulations for Construction, Subpart L or variations on this adopted by state or municipal authorities. These requirements include the design loads and factors of safety required, employee training, and pre-use evaluations by a competent person. 1926.451(d)(5) contains special requirements for suspension scaffold support devices such as cornice hooks, roof hooks, roof irons, parapet clamps, or similar devices.

Key to a safe and compliant installation is an evaluation by a competent person(1926.451(d)(3)(i)). During façade work, suspended scaffolds are frequently moved, so the evaluation must include all locations where the cornice hook may be moved. Where a competent person recognizes a hazard, he/she may need to seek support from a qualified person (1926.32 (f) & (l)). Clearly such evaluations cannot and need not always require destructive evaluation, load testing, or calculations, but such evaluations must have an appreciation for the load-resisting mechanics and construction conditions involved in the ability to safely resist loads. We hope this report will serve to increase awareness of the important considerations involved with C-shaped cornice hooks for scaffolding support that employ standoff brackets.

 

1 US Department of Labor, Occupational Safety and Health Administration, 29 CFR Part 1926, Health and Safety Regulations for Construction.

Images

Figure US-11: C-shaped Cornice Hook with Stand-off Bracket



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