BPA Spacer Cart MECHANICAL/STRUCTURAL ISSUE ANALYSIS AND REDESIGN

ME 493 Final Report - Year 2016 June 3rd

Sponsor company: Bonneville Power Administration

Contact Engineer: Kevin Machtelinckx

Academic Advisor: Huafen Hu, Ph.D.

Group members:

- Joshua Ponder -Carlos Jiménez - Robert Lawrence - Austin Ferrante

-Mackenzie Larson-Weber -Sam Levin - Bao Phan - Stephen Randall

Executive Summary:

The maintenance of high voltage transmission lines is a critical operation that ensures that the power grid upon which our cities rely on is always working. In order to perform this maintenance, linemen must use Spacer Carts; hanging carts that provide a stable platform from which they can perform electrical line repairs. The condition of these carts is critical to the work of the linemen, as well as their safety. The current Spacer Cart utilized by BPA was designed in-house to address the unique challenges of performing repairs on transmission lines of the Pacific Northwest; however, the current design has defects in regards to structural integrity and ergonomics. BPA would like to have the design issues addressed through an in-depth engineering re-design. The work commissioned by BPA through PSU’s Mechanical Engineering Capstone includes a re-design of the cart focusing on three main areas: structural support for the frame, ergonomic re-design of the crossbar linking the arms, and ergonomic re-design of the pinch wheel mechanism that maintains the cart attached to the electrical lines.

Table of Contents:

1. Introduction …………………...…………………………………………….Page 12. Mission Statement …...…………………………………………………….Page 23. Project Timeline …………………………………………………………Page 24. Main Design Requirement ...……………………………………………….Page 45. Top Level Design Alternatives ...……………………………………….Page 76. Final Design ...……………………………………………………………….Page 107. Product Design Specification Evaluation ...……………………………….Page 148. Conclusion …………………...…………………………………………….Page 169. Appendix ...……………………………………………………………….Page 17

Introduction and Background Information:

The Bonneville power administration is a federal nonprofit agency located in the Pacific Northwest; responsible for maintaining 75 percent of the high voltage transmission lines in Oregon, Washington, western Montana, and part of eastern Montana. Given the importance and scale of such an operation, maintenance must regularly be performed on the transmission lines. Spacer carts provide an effective means for linemen to travel along the power lines while performing the necessary maintenance required to keep the lines in working order. While the current cart design is capable of performing its duties, several details regarding ease of use and safety were not addressed in its initial design. Under normal operating conditions, impacts to the support arms cause stresses in the frame. If left alone, these stress impacted locations eventually fail. Another separate issue with the current design is the lack of an efficient engagement method for the pinch-wheels. Due to the effort required to engage the current pinch-wheel assembly, linemen sometimes choose not to use them. This causes the cart to be more prone to slipping and derailment.

Figure 1 - Marty Lyons demonstrating the use of a Spacer Cart at 35 degrees @ BPA facility

Mission Statement:The purpose of the project is the re-design of the spacer cart currently in use by BPA.

Overall project scope is limited to addressing safety/functionality limitations with the current design. The goal of the new design is to reduce stresses in the frame caused by impacts sustained by the arms during normal operation, and to address access and ease of use issues experienced with the arms, cross-bars, and pinch wheel assemblies. These new designs must all pass design requirements/envelopes specified by BPA for line clearance. BPA would like a prototype available to them for testing by June 1, 2016.

Project Timeline:A project timeline was created and submitted to BPA in order to track the project

milestones, utilizing the seven steps outlined in the design process taught in the Capstone sequence. A Gantt chart showing the milestones and delivery dates is shown in the graph below.

Figure 2: Spacer Cart project timeline

The main goal of the project was to complete a prototype of the different cart modifications which were scheduled to be fabricated and tested by June first. Several iterations of design review were needed for the modified components. This caused the final design iterations to be by delayed until early May. One of the components to be manufactured required special tooling delaying its delivery for 6 weeks. As such, instead of providing a finished prototype for testing by June 1, we modified the final goal to provide a complete print packet to BPA, alongside FEA analysis, by June 2. BPA will be reviewing the prints and finite element analysis. They will also be fabricating and testing the modified designs during summer 2016.

Main Design Requirements:The design requirements include performance, safety, environment and ergonomics,

maintenance and parts, installation, and cost. The following tables present the Product Design Specifications (PDS) as discussed with BPA.

Table 1: PDS - Performance

Performance

Requirements Primary Customer

Metrics & Targets

Metric Target Target Basics

Verification

Angle of Incline BPA

Cart must climb/descend a line at an angle.

degrees 35Customer Defined

Site Testing

Weight Rating BPA Working Load Limit lbs 550

Customer Defined

Site Testing

Pinch Wheels BPA

Must traverse on wire and increase contact friction

inches ½Customer Defined

Site Testing

Table 2: PDS - Safety

Safety

Requirements Primary Customer

Metrics & Targets

Metric Target Target Basics

Verification

Structural Frame BPA

Frame to withstand vibrations and impact load under working weight limit(Impact Loads to be provided by BPA)

Physical Testing 550

Withstand / support all loads (Static / Dynamic) associated with normal cart operation and WLL

Lab Testing

Safety Factor BPA

Establish safety factor based on industry standards(applicability to be defined by BPA)

Specified applicable design criteria

N/A

Customer/ Project Team Decision

Customer Interview

Table 3: PDS - Environment and Ergonomics

Environment and Ergonomics

Requirements

Primary Customer

Metrics & Targets

Metric Target Target Basics

Verification

Crossbar Redesign BPA

Crossbars should be redesigned to be easier for technicians to remove

Operation Efficiency

BPA Foreman Approval

Ease of Use

Site Testing

Wind, Rain and Cold Environment

BPA

Cart must withstand use in wind, rain and cold environments

Duration -Years

5

Corrosion Resistance

Field Use

Operational Design Envelope

BPA

All physical modifications must fall within operational envelope restrictions

Design envelope standard as provided by BPA

All modifications fall within design envelope restriction

Specified Design Envelope

Physical Inspection

Table 4: PDS - Maintenance and Parts

Maintenance and Parts

Requirements

Primary Customer

Metrics & Targets

Metric Target Target Basics

Verification

Frame Reinforcement

BPA

Years in service without frame repair

Years 5 years Customer Defined

Site Testing, FEA analysis

Table 5: PDS - Installation

Installation

Requirements

Primary Customer

Metrics & Targets

Metric Target Target Basics

Verification

Pinch Wheel Assembly BPA

Pinch Wheel mechanism to be installed easily

Operation Efficiency

BPA Foreman Approval

Ease of Operation

Site Testing

Cross-Arm Bar Assembly

BPA

Cross-arm bar assembly to be easy to use while on the line

Operation Efficiency

BPA Foreman Approval

Ease of Operation

Site Testing

Table 6: PDS - Cost

Cost

Requirements Primary Customer

Metrics & Targets

Metric Target Target Basics

Verification

Cost must not exceed original spacer cart production cost by a significant amount

BPA N/A N/A A relative value

BPA will decide what cost(s) are acceptable.

Record keeping of budget expendi-tures and production costs

Top Level Design Alternatives:The redesign of the pinch wheels went through several iterations, each had its own

advantages and disadvantages.The first squeeze wheel design, design A, consisted of a small housing attached to the

frame which utilized an ACME screw and nut to vertically adjust the height of the wheel. A pin was to be inserted into one of two holes at different heights to secure the housing to the main frame. This provided a secondary means of vertical adjustment.

The primary advantages of this design were that it was light, and the assembly could be removed without much effort. The disadvantage of this design was that tools were required for adjustment.

The second squeeze wheel iteration (design B), consisted of two contact wheels as opposed to just one. The purpose of these wheels is to provide contact with the conductor when it was at a significant angle. The two wheeled design would have pivoted with the line, ensuring constant contact.

The height of the pinch wheels would have been adjusted by turning a handle, which in turn drives a power screw, raising or lowering the wheels. Once in the desired position, a serrated locking nut would have been lowered onto the adjustable nut controlled by the handle

to prevent any further rotation. The mounting assembly to the frame could also have been adjusted by a lever which would have locked the pins into holes set in the frame at different heights. The purpose of this was to provide further height adjustment.

The advantage of this design was that tools were not needed for adjustment. This design also allowed for the possibility of a braking mechanism to be implemented at a later date. The primary disadvantage of this design was that it would have added significant weight to the cart.

It was determined by BPA that pinch wheel design option A would handle powerline angles of up to 35 degrees without the use of design B. In light of this, the implementation of design B would be unnecessary. Nonetheless, an issue that remained with design A was that tools would still be necessary for adjusting the height of the pinch wheel while the cart was in operation. To resolve this issue, a new iteration, (Design C) was created. The new design incorporated the same handle and screw mechanism for raising and lowering the pinch wheels as design B, but at a smaller scale. This solved the issue of having to use tools. It was also inverted with the adjustment onto the top as opposed to the bottom in order to simplify adjustment. A secondary height adjustment attached to the frame is also implemented. This would allow the height to be adjusted by inserting a pin into one of three holes. However, when design C was presented to BPA, it received negative reviews. The primary issue with design B was that it incorporated a double cantilever beam which connected the pinch wheel assembly to the frame. Due to the pinch wheel-conductor interactions, it was noted that the double cantilever beam would cause issues in the cart. Both design B and C were ultimately rejected.Design D, the new and finalized design for the pinch wheels meets the requirements and was approved by BPA. It is light, easily adjustable and removable without tools being required.

The initial redesign of the frame and cross arms presented by the PSU capstone team were satisfactory and no further iterations were necessary.

Design A: Same mounting arrangement - Removable - Lightweight - No significant structural change -

Design B: New mounting arrangement - New Operation - Assures traction at any line angle - Adds significant weight to cart - Requires conductor guides be easily removable

Design C: Same handle/screw adjustment as design B but smaller and lighter - No tools required for height adjustment

Final Design:

Support Arms:This is the most important component of the project. The frame arms are subjected to high stress levels while the cart is secured on the conductor and in motion, this is especially true when they travel over line components such as spacers, dampers and armor rods. After being subjected to many hours of operation, cracks resulting from fatigue and plastic deformation begin to form in the arms, frame, and pivot points.For the final design, it was decided that a truss would be added to the original arm design. This was approved by BPA as the addition of struts to the arms distributed the impact loads experienced by the frame more effectively than the original design. The trusses are pinned together near the center of the cart with a removable ball lock pin, simplifying the alignment of the cross-bars. The purpose of the support arm redesign is to absorb and distribute the stresses in the frame caused by the impact moments generated when the cart passes over obstacles during regular operation. The addition of the struts also helps to prevent bending and plastic deformation from occurring in the arms. The current support arm design is shown below.

Cross Bar:The main purpose of the cross-bar is to provide support to the two vertical “candy cane”

arms, keeping them parallel to one another. This is especially important when going over obstacles along the conductor. Without the cross-bars installed, the rear idler wheels tend to get stuck on obstacles causing the rear arms to experience impact loads. The impact loads transfer through the arms to the pin connections, and impart stresses on the frame.A cotter key and hole is used to secure the cross-bar to the support arms. When the holes don’t line up exactly, installation of the cross-bar becomes difficult and time consuming. Because of this, the cross-bars often go unused.

It was decided that the final design would consist of a bolt action method for removing and locking the cross arms into place. The design itself consists of a bolt action assembly in which a knob is protruding from the inner cross-bar shaft and can be locked in place by sliding the knob into a locking groove cut in the outer support sleeve affixed to the drive arm candy canes. When this action is complete, the cross bar will be aligned with the idler arm’s outer support sleeve retaining pin holes. Last the ball lock retaining pin would be inserted into the idler arm support sleeve. The cross bar can be easily removed by simply removing the ball lock pin and sliding the knob out of the groove. A spring is also utilized to provide the necessary tension on the knob against the groove to prevent the protruding knob from sliding out of the locking groove.

Pinch Wheels:The Pinch wheels secure the spacer cart to the conductor, which is important when the

conductor is at a steep angle. When the cart is operating on a steep incline the rear idler wheels often lift off of the conductor, requiring the linemen to realign the wheels so they can regain contact with the line. The pinch wheels were incorporated to keep all four cart wheels in contact with the line at all times during operation. They were designed to be moved out of the way when not needed. The main issue with the original design was that it was not user friendly and required tools to engage and disengage. For this reason the pinch wheels were rarely used.

The final design presented by the capstone team to BPA resolved many of the issues that the linemen were facing during operation. The design itself consists of an easy-to-use height adjustment method in which a nut is turned on a threaded screw by a ratchet. As the nut turns, the pinch wheel is raised or lowered to the desired height. The design also consists of a simple method of moving the pinch wheel out of the way of the conductor when not in use. A spring actuated pin lock handle located on the arm mounting assembly is retracted and the upper portion of the squeeze wheel can be pulled to disengage the pinch wheel from the frame. A cam lever can then be pulled to release tension and enabling the pinch wheel assembly to pivot 180 degrees out of the way of the conductor when it is not in use. For repairs or routine maintenance, the entire assembly can be removed entirely by pulling both the upper and lower portion of the pin lock handles.Design D (Final Design): Design is light - easily adjustable and removable without tools being required - minimal unwanted stresses during operation.

Product Design Specification Evaluation:Each item listed in the PDS has been evaluated, and the results compiled in the tables below.

Table 7: Product Design Evaluations

Performance

Requirements Metrics & Targets Target Result

Angle of Incline

Cart must climb/descend a line at an angle.

35 degrees

Site testing will be conducted with the modifications once BPA completes fabrication. The design modifications will allow the cart to function as well as the original design in regards to its climb and descent, therefore this target should be easily met.

Weight Rating Working Load Limit 550 lbs

The modifications to the cart have increased the cart weight by 23 lbs. Current cart weight is app. 350 lbs, therefore expected weight is < 400 lbs.

Pinch Wheels Must traverse on wire and increase contact

½ inches The final design has a height adjustment of 7/16”

friction. Adjustment of wheel height when in contact with wire to be at least ½ inch.

Safety

Structural Frame

Frame to withstand vibrations and impact load under working weight limit

550 lbs

FEA analysis was performed using 2500 lbs as detailed in Appendix A1. The modifications on the cart arm frame shows that it is able to withstand the static force without yielding.Lab testing of the new design will be performed by BPA in summer of 2016.

Safety FactorEstablish safety factor based on industry standards

Lower than 8:1

After performing research, the team recommends the use of a 5:1 safety factor based on 29 CFR 1926, Subpart L. See Appendix A2.

Table 8: Product Design Evaluation (continued)

Environment and Ergonomics

Requirements Metrics & Targets Target Result

Crossbar Redesign

Crossbars should be redesigned to be easier for technicians to remove

BPA Foreman Approval

Crossbar has been redesigned to use a bolt-action lock with a ball-lock pin instead of a cotter pin.

Wind, Rain and Cold Environment

Cart must withstand use in wind, rain and cold environments

5 years Metric will be determined based on field use.

Operational Design Envelope

All physical modifications must fall within operational envelope restrictions listed in Appendix A4.

Modifications meet design envelope

All design modifications performed by the Capstone team meet the design envelope established by BPA.

Maintenance and Parts

Frame Reinforcement

Years in service without frame repair

5 years

Metric will be determined based on field use. FEA analysis of dynamic loads has not yielded conclusive data. FEA analysis of static loads meets current requirements.

Installation

Pinch Wheel Assembly

Pinch Wheel mechanism to be installed easily

BPA Foreman Approval

Improved design uses a spring-actuated pin lock handle that allows the entire pinch wheel assembly to mount/unmount from the cart arms. It eliminates the need for tools for installation.

Cross-Arm Bar Assembly

Cross-arm bar assembly to be easy to use while on the line

BPA Foreman Approval

Bolt-action lock and ball-lock pin provided easier interface than current cotter-pin design.

Cost

Cost must not exceed original spacer cart production cost by a significant amount

N/A A relative value

All of the modifications to the cart can be done in a per-piece basis, therefore the only costs incurred will be in fabrication of new components and labor cost for assembly. The modified parts can then be installed on the existing carts.

Conclusions:The PSU capstone team has succeeded in meeting essentially all possible PDS specifications pertaining to overall design, however true evaluation of the design’s overall performance, safety, ergonomics, maintenance, installation and cost remain to be seen after prototyping and destructive testing. FEA analysis of dynamic loads has not yielded conclusive data pertaining to whether or not fatigue will affect the cart in 5 years’ time. Furthermore, it is still unknown as to whether or not the modified components will withstand long term environmental exposure. Regardless, both BPA and the PSU capstone team are very satisfied with the outcome of the project and the team has full confidence that the redesigned spacer cart will prove to be reliable, structurally sound, and ergonomically pleasing.

Appendix:

A1 - Finite Element Analysis Studies:

Support Arms Study

The purpose of the study is to see of how much of an improvement the new cart arm design is over the original. Because static load testing has been done on the original design that will be the focus of the report. In the original test, one of the idler arms failed at a load of 9310 lb. This will be the approximate load applied to both the original and new cart arm designs.

Result Summary

Although the model of the original support arm did not yield the same results as the physical test, the similarity in application of loads and boundary conditions between the modified and original FEA models still give a reasonable approximation of how much better the new design performs. Based off of these results, it is reasonable to say that the new design will meet the newly specified safety factor requirements for the spacer cart.

Detailed Analysis:

Model

The study was conducted with ABAQUS FEA software. The parts were modeled under static loading conditions using shell and beam elements. A unit system of inch-pound-seconds was used. The locations of the boundary and loading conditions for both models can be seen below.

Original Support Arm Modified Support Arm

The axles in both assemblies were assigned pinned boundary conditions (U1=U2=U3=0), while the bottom of the vertical bars were restrained in the X and Z directions (U1=U3=0). Each assembly was assigned a total load of 2500 lb in the negative Y direction (U2). The shells were joined to the beams with tie constraints.

Material Properties

The Parts in the assembly are made up of 4130 chromoly and ASTM A36 Steel. The properties assigned to them are as follows:

Elastic Modulus (Psi) Yield Stress (Psi)

ASTM A36 Steel 21,072,000 53,700

4130 Chromoly 28,300,000 63,100

Results

The results for both models indicate that neither model yields at the failure load acquired through physical testing. The locations and magnitudes of the largest stresses experienced in both models can be seen below.

The modified support arm experiences approximately half the maximum stress of the original.

Conclusion

While the model of the original cart does not fail at the same loading as the physical test, useable information can still be gathered from this study. Because both models share the same boundary and loading condition schemes, it can be assumed that the differences in maximum stress values are similar to the difference that would be seen had the original model behaved identically to the physically tested support arm. Additionally, it should be noted that the maximum stress located in the original support arm model occurred in the same location as the fracture in the physical test run by BPA.

Crossbar Study:

The original crossbar for the BPA spacer cart primarily serves as an anchor point for the cart to be carried to the destination by helicopter. However, the redesign for the cross-bar includes modifying the existing tube collar with a slot for the bolt handle; this slot weakens the structural integrity of the collar. The purpose of this analysis is to determine whether or not the slot will cause yielding failure of the collar.

Result SummaryThe analysis indicated that the slotted collar does not yield from the loading that would

be experienced while being transported by helicopter, with the collar experiencing a maximum stress value of 76% yield stress (48,000 psi stress versus the 63,100 psi yield strength). This means that the cross-bar redesign offers a factor of safety of approximately 1.3. While not ideal, it indicates that the redesign shouldn’t fail under normal conditions, and manufacturing and testing can proceed.

Detailed Analysis:

Model

The analysis was performed with Abaqus FEA software. The model was defined using the inch-pound-second system of units and tested under static conditions. The model used was composed of full 3D models of the cross-bar and the bolt collar, arranged together as shown.

The collar and bar were partitioned as necessary in order to allow the majority of each part to be meshed with hex elements. The collar is held fixed by two 0.25 in2 face partitions positioned at either end of the collar. The bar is pinned at the far end, to simulate the support of the second collar tube. Force is applied as a vertical traction load along a 4.25 in long area of the lower surface of the cross-bar with a total magnitude of 400 lbs to simulate the cart being carried by helicopter. Contact conditions are described between the bolt and the bolt slot edges, and the inner surface of the bolt collar and the outer surface of the bolt end of the cross bar.

Material Properties

Contact Properties

Results

The results of the static analysis indicate that the entire crossbar assembly yields in two regions, as shown.

Yield strength for 1080 carbon steel is approximately 53,700 psi. This stress is exceeded in the regions that are colored orange red; this means that the crossbar has supposedly yielded at the pinned end, and in the center where the load is applied. However, the focus of the study is the slotted collar, and so the indicated yielding of the crossbar will be ignored.

An enhanced view of the slotted collar is shown on the next page. There are two notable regions of high stress, which are labeled with the highest stress value in those regions. However, neither of these regions exceeds the 63,100 psi yield strength of 4130 Chromoly, meaning that the slotted collar does not yield. The highest stress experienced is roughly 48,000 psi, or 76% of the yield strength, offering a factor of safety against yielding of 1.31. It is notable, however, that the highest stress is in a location that indicates the tab is more likely to deform lengthwise instead of bending upwards and uncurling.

Should testing indicate that the slotted collar requires reinforcement, the two locations of stress concentration should be the first points to be reinforced.

Conclusion

This analysis found that the slotted collar does not yield from the loading that would be experienced while being transported by helicopter, with the collar experiencing a stress value equal to 76% of the yield stress. However, this analysis does indicate that the cross bar itself yields under this load; actual usage of the current crossbars shows that this is not the case. This discrepancy indicates it is likely that either the loading used in this model is larger than the actual loading, or the cross bar has different material properties than those used in this study. Either way, the results of this study are promising, and indicate that manufacturing and testing can proceed.

A2 - Factor of Safety Research Documentation:

ANSI B77.1 Research:Excerpts from ANSI B77.1 w possible relevancy:Chapter 1: General Requirements

Chapter 2: Aerial Tramways

\

Chapter 3: Detachable Grip Aerial Lifts

Brake references:

Chapter 3: F.O.S. Reference for cable interface

- Testing of cable interface systems:

- Testing of the carriers:

Chapter 4: Fixed Grip Aerial Lifts

Stopping distances:

- Brake References:

- Factor of Safety References:

ANSI B77.1 Research Conclusion:After reviewing chapters 1-3 of the ANSI Aerial Tramway safety standard, it was determined that little or none of the document pertains directly to the spacer cart. The way in which factors of safety are defined is based on the aerial tramway type which none of the described types match BPA’s application directly.

The above notwithstanding, there are several references to factors of safety, friction coefficients, and braking speeds which may be of use when deriving a safety standard for the Aerial Line Carts. It was also noted that brakes are required on all types of these systems.

29 CFR Subpart L Part 1926 Research1926.450 Covers scope, application, and definitions.

Scaffold means any temporary elevated platform (supported or suspended) and its supporting structure (including points of anchorage), used for supporting employees or materials or both.

Mobile scaffold means a powered or unpowered, portable, caster or wheel-mounted supported scaffold.

Catenary scaffold means a suspension scaffold consisting of a platform supported by two essentially horizontal and parallel ropes attached to structural members of a building or other structure. Additional support may be provided by vertical pickups.

Suspension scaffold means one or more platforms suspended by ropes or other non-rigid means from an overhead structure(s).

Competent person means one who is capable of identifying existing and predictable hazards in the surroundings or working conditions which are unsanitary, hazardous, or dangerous to employees, and who has authorization to take prompt corrective measures to eliminate them.

Maximum intended load means the total load of all persons, equipment, tools, materials, transmitted loads, and other loads reasonably anticipated to be applied to a scaffold or scaffold component at any one time.

1926.451 (a)(1) Except as provided in paragraphs (a)(2), (a)(3), (a)(4), (a)(5) and (g) of this section, each scaffold and scaffold component shall be capable of supporting, without failure, its own weight and at least 4 times the maximum intended load applied or transmitted to it.

(3) Each suspension rope, including connecting hardware, used on non-adjustable suspension scaffolds shall be capable of supporting, without failure, at least 6 times the maximum intended load applied or transmitted to that rope.

(6) Scaffolds shall be designed by a qualified person and shall be constructed and loaded in accordance with that design. Non-mandatory Appendix A to this subpart contains examples of criteria that will enable an employer to comply with paragraph (a) of this section.

1926.451(b)(2) Except as provided in paragraphs (b)(2)(i) and (b)(2)(ii) of this section, each scaffold platform and walkway shall be at least 18 inches (46 cm) wide.(3) Except as provided in paragraphs (b)(3)(i) and (ii) of this section, the front edge of all platforms shall not be more than 14 inches (36 cm) from the face of the work, unless guardrail systems are erected along the front edge and/or personal fall arrest systems are used in accordance with paragraph (g) of this section to protect employees from falling.(10) Scaffold components manufactured by different manufacturers shall not be intermixed unless the components fit together without force and the scaffold's structural integrity is maintained by the user. Scaffold components manufactured by different manufacturers shall not be modified in order to intermix them unless a competent person determines the resulting scaffold is structurally sound.1926.451(d)(14)Gasoline-powered equipment and hoists shall not be used on suspension scaffolds.1926.451(f)(6)Exception to paragraph (f)(6): Scaffolds and materials may be closer to power lines than specified above where such clearance is necessary for performance of work, and only after the utility company, or electrical system operator, has been notified of the need to work closer and the utility company, or electrical system operator, has de-energized the lines, relocated the lines, or installed protective coverings to prevent accidental contact with the lines.The clearance between scaffolds and power lines shall be as follows: Scaffolds shall not be erected, used, dismantled, altered, or moved such that they or any conductive material handled on them might come closer to exposed and energized power lines than as follows: *Insulated Lines

_____________________________________________________________________ | | Voltage | Minimum distance | Alternatives____________________|________________________|_______________________ | |Less than 300 volts.| 3 feet (0.9 m) |300 volts to 50 kv.| 10 feet (3.1 m) |More than 50 kv.....| 10 feet (3.1 m) plus | 2 times the length | 0.4 inches (1.0 cm) | of the line | For each 1 kV over | insulator, but never | 50 kV. | Less than 10 | | feet (3.1 m).____________________|________________________|_______________________

*Uninsulated lines_____________________________________________________________________ | | Voltage | Minimum distance | Alternatives____________________|________________________|_______________________ | |Less than 50 kV.....| 10 feet (3.1 m). |More than 50 kV.....| 10 feet (3.1 m) plus | 2 times the length of | 0.4 inches (1.0 cm) | the line insulator, | For each 1 kV over | but never less than | 50 kV. | 10 feet (3.1 m).____________________|________________________|_______________________

1926.451(f) (12)Work on or from scaffolds is prohibited during storms or high winds unless a competent person has determined that it is safe for employees to be on the scaffold and those employees are protected by a personal fall arrest system or wind screens. Wind screens shall not be used unless the scaffold is secured against the anticipated wind forces imposed.

1926.451(g) Fall Protection(1)(i) Each employee on a boatswains' chair, catenary scaffold, float scaffold, needle beam scaffold, or ladder jack scaffold shall be protected by a personal fall arrest system(3) In addition to meeting the requirements of 1926.502(d), personal fall arrest systems used on scaffolds shall be attached by lanyard to a vertical lifeline, horizontal lifeline, or scaffold structural member. Vertical lifelines shall not be used when overhead components, such as overhead protection or additional platform levels, are part of a single-point or two-point adjustable suspension scaffold.(3)(i) When vertical lifelines are used, they shall be fastened to a fixed safe point of anchorage, shall be independent of the scaffold, and shall be protected from sharp edges and abrasion.

Safe points of anchorage include structural members of buildings, but do not include standpipes, vents, other piping systems, electrical conduit, outrigger beams, or counterweights.(3)(ii) When horizontal lifelines are used, they shall be secured to two or more structural members of the scaffold, or they may be looped around both suspension and independent suspension lines (on scaffolds so equipped) above the hoist and brake attached to the end of the scaffold. Horizontal lifelines shall not be attached only to the suspension ropes.(3)(iv) Vertical lifelines, independent support lines, and suspension ropes shall not be attached to each other, nor shall they be attached to or use the same point of anchorage, nor shall they be attached to the same point on the scaffold or personal fall arrest system.(4) Guardrail systems installed to meet the requirements of this section shall comply with the following provisions (guardrail systems built in accordance with Appendix A to this subpart will be deemed to meet the requirements of paragraphs (g) (4) (vii), (viii), and (ix) of this section):(4)(i) Guardrail systems shall be installed along all open sides and ends of platforms. Guardrail systems shall be installed before the scaffold is released for use by employees other than erection/dismantling crews.(4)(ii) The top edge height of top rails or equivalent member on supported scaffolds manufactured or placed in service after January 1, 2000 shall be installed between 38 inches (0.97 m) and 45 inches (1.2 m) above the platform surface. The top edge height on supported scaffolds manufactured and placed in service before January 1, 2000, and on all suspended scaffolds where both a guardrail and a personal fall arrest system are required shall be between 36 inches (0.9 m) and 45 inches (1.2 m). When conditions warrant, the height of the top edge may exceed the 45-inch height, provided the guardrail system meets all other criteria of paragraph (g) (4).(4)(iii) When midrails, screens, mesh, intermediate vertical members, solid panels, or equivalent structural members are used, they shall be installed between the top edge of the guardrail system and the scaffold platform.(4)(iv) When midrails are used, they shall be installed at a height approximately midway between the top edge of the guardrail system and the platform surface.(4)(vii) Each top rail or equivalent member of a guardrail system shall be capable of withstanding, without failure, a force applied in any downward or horizontal direction at any point along its top edge of at least 100 pounds (445 n) for guardrail systems installed on single-point adjustable suspension scaffolds or two-point adjustable suspension scaffolds, and at least 200 pounds (890 n) for guardrail systems installed on all other scaffolds.(4)(ix) Midrails, screens, mesh, intermediate vertical members, solid panels, and equivalent structural members of a guardrail system shall be capable of withstanding, without failure, a force applied in any downward or horizontal direction at any point along the midrail or other member of at least 75 pounds (333 n) for guardrail systems with a minimum 100 pound top rail capacity, and at least 150 pounds (666 n) for guardrail systems with a minimum 200 pound top rail capacity.(4)(xi) Guardrails shall be surfaced to prevent injury to an employee from punctures or lacerations, and to prevent snagging of clothing.

1926.452(r) Catenary Scaffolds

(1) No more than one platform shall be placed between consecutive vertical pickups, and no more than two platforms shall be used on a catenary scaffold.(2) Platforms supported by wire ropes shall have hook-shaped stops on each end of the platforms to prevent them from slipping off the wire ropes. These hooks shall be so placed that they will prevent the platform from falling if one of the horizontal wire ropes breaks.

1926.452(w) Mobile Scaffolds(1) Scaffolds shall be braced by cross, horizontal, or diagonal braces, or combination thereof, to prevent racking or collapse of the scaffold and to secure vertical members together laterally so as to automatically square and align the vertical members. Scaffolds shall be plumb, level, and squared. All brace connections shall be secured.(1)(i) Scaffolds constructed of tube and coupler components shall also comply with the requirements of paragraph (b) of this section;(2) Scaffold casters and wheels shall be locked with positive wheel and/or wheel and swivel locks, or equivalent means, to prevent movement of the scaffold while the scaffold is used in a stationary manner.(4) Power systems used to propel mobile scaffolds shall be designed for such use. Forklifts, trucks, similar motor vehicles or add-on motors shall not be used to propel scaffolds unless the scaffold is designed for such propulsion systems.(5) Scaffolds shall be stabilized to prevent tipping during movement.(6) Employees shall not be allowed to ride on scaffolds unless the following conditions exist:(6)(i) The surface on which the scaffold is being moved is within 3 degrees of level, and free of pits, holes, and obstructions;(6)(ii) The height to base width ratio of the scaffold during movement is two to one or less, unless the scaffold is designed and constructed to meet or exceed nationally recognized stability test requirements such as those listed in paragraph (x) of Appendix A to this subpart (ANSI/SIA A92.5 and A92.6);(6)(iii) Outrigger frames, when used, are installed on both sides of the scaffold;(6)(iv) When power systems are used, the propelling force is applied directly to the wheels, and does not produce a speed in excess of 1 foot per second (.3 mps); and(6)(v) No employee is on any part of the scaffold which extends outward beyond the wheels, casters, or other supports.(8) Where leveling of the scaffold is necessary, screw jacks or equivalent means shall be used.(9) Caster stems and wheel stems shall be pinned or otherwise secured in scaffold legs or adjustment screws.(10) Before a scaffold is moved, each employee on the scaffold shall be made aware of the move.

1926 Subpart L Appendix A (Non-mandatory guidelines)(r) "Catenary scaffolds." (1) Maximum intended load -- 500 lbs.(2) Not more than two employees shall be permitted on the scaffold at one time.(3) Maximum capacity of come-along shall be 2,000 lbs.(4) Vertical pickups shall be spaced not more than 50 feet apart.

(5) Ropes shall be equivalent in strength to at least 1/2 inch (1.3 cm) diameter improved plow steel wire rope.

Conclusion:From the definitions outlined in 29 CFR 1926.450 we believe the spacer cart qualifies as a mobile, catenary-type, suspended scaffold. Specifically, it is a temporary, elevated platform, used to support materials and employees. The spacer cart is also powered, portable, wheel-mounted, and supported by horizontal and parallel ‘ropes’. Some of the requirements, such as the distance from power lines and the tie off locations for personal arrest systems, are not feasible given the location of work to be accomplished, and will likely require consultation with an engineer accredited by the Scaffold & Access Industry Association (SAIA)

A3 - Drawings

Do to drawing native sheet size (ISO A2) - all drawings will be provided via separate correspondence.

A4 - Design Envelope Restrictions

Figure 3: Design change limit envelope - Axial view

Figure 4: Design change limit envelope - Transverse view