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Home › Publications › OHS Regulation › WCB Standards

WCB Standards

WCB Standard: G601 Log Loader and Log Yarder Backstops, March 1990

© Workers' Compensation Board of British Columbia. All rights reserved. No part of this document may be copied, reproduced, or distributed for profit or other commercial enterprise, nor may any part be incorporated into any other publication, without written permission of the Workers' Compensation Board of B.C.

1. General

1.1. Scope
This standard pertains to equipment such as log loaders and log yarders and other mobile or stationary equipment where the operator may be exposed to head-on collision or impact with large logs. Examples of mobile equipment where backstops are mandatory are: straight heel boom loaders, crane boom loaders, knuckle boom loaders, dipper stick boom loaders, goose neck boom loaders, Bohemian type boom loaders and grapple yarders. Refer to Standard G602 if the machine does not come within the above category.

1.2. Other References
This standard is supplemented by the following:

1.2.1 G602 WCB Standard for Log Loader and Log Yarder Raised Cabs

1.2.2 G603 WCB Standard for Log Loader and Log Yarder Operator's Cab Window Guards

1.3. Purpose
This standard is intended to describe the minimum requirements for the design and fabrication of grid elements, framework and supports for guards over exposed fronts and sides of operators' cabs.

1.4. Terminology and Illustration

1.4.1 For the purpose of this standard, the following definitions shall apply:

• "Backstop" means any protective structure designed to protect the operator from large intruding objects without causing excessive visual interference to the operator. A Backstop may be an integral part of the overall Equipment Protective Structure.
• "Equipment Protective Structure" means any protective structure designed to protect the machine from serious impact damage from extraneous objects. It is fabricated with such structural elements as angles, I-beams, Hollow Structural Sections, etc.
• "Framework" means the main structural members of a Backstop, consisting of horizontal edge beams, vertical edge beams, and overhead beams. See Appendix "A".
• "Main Frame" refers to the structural part of the undercarriage.
• "Major Grid Element" means the member along the longitudinal direction of a rectangular frame. Usually, it is the vertical member.
• "Overhead Beam" means the member along the lateral direction of a rectangular frame. Usually, it is the horizontal member.
• "Substructure" refers to the structural members of the Equipment Protective Structure. The framework may be connected to the Substructure providing that such is capable of transferring the applied load to the Main Frame.
• "Supports" refer to the structural members connecting the Backstop onto the Main Frame.

1.4.2 Illustrations attached are shown to clarify the terminology used and are not to be construed as model designs

2. Design Principles and Assumptions

The following points are outlined to clarify the underlying principles and assumptions of this Standard.

2.1.
A static force resistance design criteria is adopted for this Standard.

2.2.
The recommended design force will not necessarily duplicate the force imparted by an actual intruding log.

2.3.
It is assumed that if the Backstop can resist a certain static force, then it will have adequate resistance to a relative dynamic force.

2.4.
A recommended impact strength requirement is included to ensure that all component members of the Backstop will have adequate resistance to brittle fracture at low ambient temperature.

2.5.
A visibility requirement is stipulated to ensure that the operator's vision will not be unduly obstructed.

2.6.
Compliance with the design criteria may be achieved by adhering to the design requirements given in Clauses 3.1.1 and 3.1.2 or by adhering to the recommended minimum sizes in Clause 4.

3. Design Requirements

3.1. Static Strength Requirements
3.1.1 Grid Element
Grid element dimensions and fabrication shall be designed to withstand a minimum distributed area ultimate load of 120 kPa (2500 psf) applied over an area of 0.65 m² (7.0 ft²), equivalent to a 0.92 m (3 ft.) diameter circular area. For design purposes, the distributed load may be applied at each grid junction. (See Appendix "B".)

3.1.2 Framework
The framework shall consist of sections with the following sections modulus:

S > 186 x	L f	metric
S > 4200 x	L f	imperial
S = Section modulus cm3, (in3)
L = Unsupported length of beam cm, (in)
f = Allowable working stress MPa, (lb/in2)

The section modulus (S) shall in no case be less than 50 cm³ (3 in³).

3.1.3 Supports
The framework shall be secured to the Main Frame or other substructure. Such substructure shall be adequately designed and constructed to resist all loads imposed on them by the Backstop.

3.1.4 Fastenings
If nuts and bolts are used in the fabrication of the Backstop, they shall conform to or exceed the ASTM Designation A325 requirements.

3.1.5 Weldment
Weldments shall conform to applicable sections of General Specification for welding of Steel Structures CSA W59.1-1970 (or latest version thereof) and should be performed by certified welders only.

3.2. Impact Strength Requirement
All members of the guard shall be fabricated of material with good impact absorbing properties. The following guideline may be used:

• Low Carbon content (less than 0.28 %).
• High Manganese - carbon ratio.
• Low phosphorous content.
• Fine grain size.
• Heat Treated.
• High ultimate energy resistance.

Examples of steel meeting or exceeding the above requirements:

• ASTM A36, CSA G40.21 33G, 44W - for plates, bars and angles.
• CSA G40.21 50W - for HSS

3.3. Visibility Requirements
Minimum interference with operator's visibility shall be one of the governing criteria in the design and positioning of the vertical members of the guard. If flat bars are used as grid elements, they should be in a radiating pattern in line with the operator's line of sight. Each grid opening shall not be greater than 400 cm² (64 in²).

3.4. Location
Backstops shall be installed in front of all sides exposed to collisions with run away or sliding logs. All Backstops shall be positioned at least 10 cm (4 in) (20 cm (8 in) for wire rope Backstops) away from the glazed windows and exterior faces of the cab.

4. Structural Details Guidelines
The following recommendation may be used in lieu of Clause 3.1.1 and Clause 3.1.2.

4.1.
Minimum Minor Grid Element size shall be 1 inch diameter mild steel rods or equivalent.

4.2.
Minimum Major Grid Element size shall be 1/2 x 4 inch bars or equivalent.

4.3.
Minimum edge beam size shall be:

4.3.1	4 x 3 x .2500 HSS for edge beam less than 3'.
4.3.2	6 x 4 x .2500 HSS for edge beam less than 6'.
4.3.3	7 x 5 x .2500 HSS for edge beam less than 9'.

4.4.
Gusset plates shall be incorporated where the length of the edge beam exceeds three feet.

5. Design Aid

5.1. Equivalent Strength Table

	Grid Element
1" diameter mild steel rod	5/8" 6 x 19 IWRC Wire Rope*
1/2 x 4 steel flat bar	3/4" 6 x 19 IWRC Wire Rope*

5.2. Typical Design

Overall Dimension 50" x 98" (See Appendix "B")

X-Section Size

Grid Element
Short direction	1" diameter ASTM A36 rod	5/8" 6 x 19 IWRC Wire Rope*
Long direction	1/2 x 4 ASTM A36 flat bar	3/4" 6 x 19 IWRC Wire Rope*
Edge Beam
Short direction	7 x 5 x .2500 HSS	7 x 5 x .2500 HSS
Long direction	CSA G40.21 (40.16 and 40.17)	CSA G40.21 (40.16 and 40.17)

* Wire Rope may be considered as equivalent provided they are adequately anchored and tensioned. (See illustration attached.)

Materials with equal or superior properties may be use in place of those stipulated in this standard.

 

 

G 601 APPENDIX C.

WCB Recommended Practice for Boom Mounted Backstops

1. Introduction

1.1. Background
OPS Mounting problems have been frequently encountered in retrofitting older log loaders. The lack of sound substructure makes it very difficult to anchor or fasten the OPS adequately. Quite often, the main frame consists only of the turntable bearing mounts. The existing cab substructure is usually too light to permit any significant load transfer to the main frame. The recommended practice which follows summarizes methods to comply with G601 when conventional mounting methods are not feasible.

1.2. Scope and Limits
This recommended practice is directed mainly at track or rubber wheel mounted long crane boom log decking grapple loader engaged in operations such as dewatering where there is a limited hazard from intrusion of debris, logs or other foreign objects into the raised cab from the sides and rear.

Side and rear guards are mandatory whenever the loader or yarder is operating at dry land sorting areas, landings or in proximity to other yarders, standing trees, rock bluffs, etc.

The recommendations herein are not applicable to loaders or yarders equipped with a short boom, i.e. where normal operating radius would be less than 12 M (40 feet) or where the boom angle has to be changed constantly.

1.3. Purpose
This recommended practice is intended to describe the minimum requirements for the design and fabrication of grid elements, framework and supports for guards over exposed fronts of operators cab when all of the above-mentioned conditions have been considered.

1.4. General
The following recommended methods and materials are inferior to those of G601 Appendix A and B. Every effort should be made to comply with G601 Appendix A and B. Appendix C should be used only as a last resort. The backstop may be welded to the crane boom, however such weldment shall be performed by certified welders only and the crane boom shall be recertified by a registered professional engineer whether any actual modifications have been made to the crane boom or not.

2. Design Requirement

2.1. Static Strength Requirements
2.1.1 Grid Element
Grid element dimensions and fabrication shall be designed to withstand a minimum distributed area ultimate load of 1.2 MPa (2500 psf) applied over an area of 0.65 sq.m. (7.0 sq.ft.), equivalent to a 0.92 m. (3 ft.) diameter circular area. For design purposes, the distributed load may be applied at each grid junction.

2.1.2 Framework
The framework shall consist of sections with the following section modulus:

S > 130 x	L f	metric units
S > 3000 x	L f	imperial units
S = Section modulus (cm3), (in3)
L = Unsupported length of beam (cm), (in)
f = Allowable working stress (MPa), (lb/in2)

2.1.3 Supports
The framework may be welded or connected by lug and pin to the crane boom. Such crane boom shall be checked and recertified by a registered professional engineer or other person acceptable to the Board.

2.1.4 Fastening
As per 3.1.4 of G601

2.1.5 Weldment
As per 3.1.5 of G601

2.1.6 Braces
Strut braces should be installed at the top and bottom as well as at the middle of the frame.

2.2. Impact strength requirement
As per 3.2 of G601

2.3. Visibility requirement
As per 3.3 of G601

2.4. Location
Refer to 3.4 of G601. In dewatering operations, frontal backstop shall be mandatory. Side guards are optional.

2.5. Dimensions
At normal operating boom angle, the backstop shall extend at least six inches beyond the projected perimeter of the cab. The normal operating boom angle herein is defined as 50° to the horizontal.

3. Structural Detail Guidelines

Materials of better or equivalent properties and strength may be used in lieu of the following:

3.1.
Minimum Minor Grid Element Size shall be 1 inch diameter mild steel rods or 5/8"-6 x 19 IWRC Wire Rope adequately anchored and tensioned.

3.2.
Minimum Major Grid Element Size shall be 1/2 x 4 inch bars or 3/4" - 6 x 19 IWRC Wire Rope adequately anchored and tensioned.

3.3.
Minimum horizontal edge beam size shall be:

3.3.1	4 x 2 x 0.3125 HSS for width up to 3'.
3.3.2	5 x 2 x 0.3125 HSS for width up to 4'.
3.3.3	5 x 3 x 0.3125 HSS for width up to 6'.

3.4.
Minimum vertical edge beam size shall be equal to or greater than the horizontal edge beam size.

3.5.
Gusset Plates shall be incorporated at corners when the length of the edge beam exceeds three feet.

3.6.
Minimum horizontal strut brace size should be 13 x 3 x 1/4.

 

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