This Safety and Health Information Bulletin is not a

standard or regulation, and it creates no new legal

obligations. The Bulletin is advisory in nature, informational in content, and is intended to assist employers in providing a safe and healthful workplace. The

Occupational Safety and Health Act requires employers to comply with hazard-specific safety and health

standards. In addition, pursuant to Section 5(a)(1),

the General Duty Clause of the Act, employers must

provide their employees with a workplace free from

recognized hazards likely to cause death or serious

physical harm. Employers can be cited for violating

the General Duty Clause if there is a recognized

hazard and they do not take reasonable steps to

prevent or abate the hazard. However, failure to

implement any recommendations in this Safety and

Health Information Bulletin is not, in itself, a violation

of the General Duty Clause. Citations can only be

based on standards, regulations, and the General Duty

Clause.

U. S. Department of Labor

Occupational Safety and Health Administration

Directorate of Science, Technology & Medicine

Office of Science and Technology Assessment

SHIB 06-02-2004

Hazards Associated with Strand Restraint Devices in Manufacturing

Prestressed Concrete Beams

Safety and Health Information Bulletin

Purpose

The purpose of this Safety and Health Information

Bulletin is to

1. Alert manufacturers of prestressed concrete

beams to hazards associated with strand

restraint devices;

2. Emphasize that manufacturers should follow

safety related recommendations detailed in the

Precast/Prestressed Concrete Institute’s

Manual for Quality Control for Plants and

Production of Structural Precast Concrete

Products; and

3. Provide additional safety recommendations for

employers who use strand restraint devices in

the manufacturing of prestressed concrete

beams.

Background

The Bismarck, North Dakota Area Office investigated

a fatal accident that involved the failure of a drape

strand restraint device during the manufacture of

prestressed concrete bridge beams. The process

required the tensioning of six extremely high strength

0.60-inch-diameter wire ropes to a tensile load of

approximately 47,000 (166,000 psi) pounds each.

For load bearing purposes, the wire ropes are then

embedded in concrete to create a slight arch along the

longitudinal axis of the beam.The tensioning deck is

comprised of two sections to simultaneously form two

identical beams.

Incident Description

An employer was engaged in manufacturing

prestressed concrete beams. To obtain the proper

tension and arch, the wire ropes were strung through

steel strand restraint devices near the base of the

concrete beam. These wire ropes are identified as the

“drape strands,” which, when tensioned, impose a

total upward force of approximately 13,400 pounds

on each of the two outside restraint devices for each

section. Within each section, the two outside restraint

devices were supporting four wire ropes, while the

two inside restraint devices were supporting only two
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wire ropes. The bottoms of the devices were

positioned approximately 1.5 inches above the bed of

the pouring deck using wood shims under each

device. After the proper tension was placed on the

cables, the shims were removed to allow the entire

device and wire ropes to be embedded in concrete.

The removal of the wood shims was accomplished by

using a sharpened piece of rebar, which was

approximately 19 inches long by 3/8-inches in

diameter. An employee struck the rebar with a

hammer, splitting each shim, and then drove the

broken shims out from beneath the device with the

rebar. Employees were instructed not to lean over the

pouring bed while removing the shims.

An employee was in the process of removing the

shims when the two outside strand restraint devices

(holding four cables) in one section failed. This, in

turn, caused the two inside restraint devices (holding

two cables) in the same section also to fail, but in a

different manner. The two outside restraint devices

failed at their base due to tensile and bending stresses.

On the two inside devices the bolts holding the cables

failed, possibly due to bending stresses. When the

drape strand cables released, a cable struck an

employee in the head, resulting in a fatality. Because

of cold weather conditions at the time of the accident,

cold brittle metal fracture also contributed to the

restraint device (clevis) failure.

The non-pivoting design of the restraint devices also

imposed bending (flexural) stresses in the base of the

devices, which further contributed to the failure of the

devices.

Recommendations

The following procedures are recommended to

eliminate the potential hazard of restraint device failure

and the unintended release of the drape strands or

other wire cables under tension on the pouring bed:

1. Ensure that strand restraint devices are

engineered and designed to withstand the

forces and moments imposed by the drape

strands and to prevent cold brittle fracture

during cold weather. Several manufacturers

make strand restraint devices that have been

so engineered and designed. Pivoting or

swiveling-type restraint devices can be used to

prevent the bending (flexural) stresses in the

base of the restraint device.

2. Redesign the prestressed concrete pouring

process so there is no need to install a wood

shim under the restraint devices holding the

drape strands. The elimination of the wood

shim would prevent impact loading on the

devices as a result of removing shims and

reduce or eliminate employee exposure to the

danger zone. Properly engineered strand

restraint devices should eliminate the need to

use wood shims.

Completely failed clevis due to cold

brittle fracture

Figure #1

 Failed clevises (restraint devices)
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Figure 2: Shows the entire length of the pouring bed with the restraint devices installed near the clevis

locations prior to tensioning

Figures 2 and 3 show changes made to the process.

3. Implement and follow all the safety-related

practices presented in the Precast/Prestressed

Concrete Institute’s Manual for Quality

Control for Plants and Production of

Structural Precast Concrete Products. For

example, the manual specifies that protection

shall be provided for personnel engaged in the

tensioning operation by means of effective

shields adequate to stop a flying strand resulting

from strand breakage. All personnel not

required to perform the tensioning shall leave

the area adjacent to the bed.
Figure 3. Close-up View of Restraint Device.

Figure 3: Shows a restraint device installed to prevent cables from releasing in the event of clevis failure during

tensioning.

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