cab products messenger wire evaluation - hooks, … · ... (i.e. the maximum vertical load that...

CAB Products Messenger Wire Evaluation

Structural Report

Revision: 2

March 10, 2016

HDR Project No: 164-274775



701 Xenia Avenue South Suite 600 Minneapolis, MN 55416

hdrinc.com

Page | 1

Contents

1. Introduction ................................................................................................................... 3

2. Design Assumptions ..................................................................................................... 4

3. Evaluation Results ........................................................................................................ 5




hdrinc.com

Page | 2

Revision Log

Engineer of Record (EOR) Attestation

The State of California Professional Engineering Certification that has been applied to this

document covers all sections of this report except as described below:

Analysis data developed by any firm other than HDR and that is referenced or attached to this report is not being certified by HDR. This data has only been included in this document since it was used to develop the opinions and conclusions presented in this report.

Rev Description of Change Effective Date

0 Issued for CAB Products review. 3/1/2016

1 CAB Products comments addressed; reissued to CAB Products. 3/4/2016

2 Adjusted Figure 1 and added Figure 2. 3/10/2016




hdrinc.com

Page | 3

1 Introduction

This report summarizes the assumptions, design parameters, conclusions, and recommendations

that came out of the evaluation of the messenger wire that is used in the CAB Products cable

management system. The intent of this evaluation was to investigate the behavior of the messenger

wire when it is exposed to a range of temperatures and to a range of wind and vertical loads.

The work that went into this evaluation was based on the use of the proprietary software Power Line

Systems – Computer Aided Design and Drafting (PLS-CADD) which treated the messenger wire

system as a distribution line. The wind loads were developed in accordance with ASCE 7-10 and

then input into the PLS-CADD models. Different temperature conditions and vertical loading

conditions were part of the evaluation. The transverse, longitudinal, and vertical reactions in the

messenger wire was then calculated at its anchor point on the dead end pier.

The intent of this evaluation was to develop the following items:

• Dead end pier loading table that provides the expected maximum end reactions in the

messenger wire at the dead end pier,

• Messenger wire sag chart that provides the sag of the messenger wire between support

piers that the messenger wire should be installed to before any cables are hung,

• Messenger wire tension chart that provides the tension that the messenger wire should be

installed to before any cables are hung.

The results of this evaluation does not provide site specific messenger wire tension values for every

type of environmental load (i.e. snow, ice, wind) that would be expected in the United States. Instead

these results provide the tension load in the messenger wire under a range of Allowable Strength

Design (ASD) vertical loads, wind pressures, and temperature ranges.

When evaluating a project specific messenger wire system, the project specific design vertical loads

shall be calculated per ASCE 7-10 by the contractor’s engineer of record registered in the state that

the system is being installed in. Once the contractor’s engineer has calculated the maximum ASD

vertical load of their system (i.e. the maximum vertical load that results from the ASCE 7-10 ASD

load combinations that include dead load, live load, snow load, and ice load) they can then use the

results presented in Table 4 to determine the maximum expected end reactions at the dead end pier.

The evaluation of the messenger wire system that was performed for this report was not dependent

on the direction of the run of the messenger wire (i.e. wire spans along the North-South or the East-

West direction). This is because the messenger wire system is not affected by the orientation of the

PV panels above but is only affected by the design level ASD loads that are expected to occur on

the wire proper at a project site.




hdrinc.com

Page | 4

To demonstrate that the orientation of the messenger wire does not affect the results presented in

this report, Figure 1 and Figure 2 have been set up to show two types of messenger wire

orientations that are possible for a tracker system with the wire running in the North-South and then

in the East-West direction. In each case the PV panel arrangement does not come in contact with

the messenger wire system and thus will not affect the reported results of this evaluation.

Figure 1: Typical North-South Messenger Wire System Layout

Figure 2: Typical East-West Messenger Wire System Layout

Dead End Pier CAB Hanger

Electrical Cables

Span

Run

Messenger Wire

Sag Dead End Pier

Mid-Support Pier

Vertical (ASD) Load

PV Array Panels

Dead End Pier CAB Hanger

Electrical Cables

Span

Run

Messenger Wire

Sag Dead End Pier

Mid-Support Pier

Vertical (ASD) Load

PV Array Panels




hdrinc.com

Page | 5

2 Design Assumptions

o Site Location: Anywhere with wind speed ≤ 170 mph per ASCE 7-10.

o Structural Standards/Codes: ASCE 7-10

o Messenger Wire:

� Type ¼” Diameter, 7 strand � Material ASTM A475, Class C Coating � Grade EHS (210 ksi Tensile) � Breaking Strength 6,650 lbs

o Maximum expected sag of messenger wire with 10 lb/ft loading @ 60F

� NOTE: Below listed sag values include initial sag when no load is hanging from messenger wire + the sag that will occur when 10lb/ft of vertical load is hung from the messenger wire. � 15 ft span = 4.0 inches

� 20 ft span = 6.0 inches



o Wind is the only horizontal load applied in this evaluation.

o Seismic is considered negligible on wire systems and therefore was not included.

o Reported longitudinal forces only occur at the dead end pier. Equal tension occurs in

the messenger wire on both sides of a mid-support pier which will result in no longitudinal force on the mid-support piers.

o Reported vertical and transverse forces only occur at the dead end pier. Vertical and

transverse loads on the mid-support piers are twice the reported forces in Table 4.

o Dead end and mid-support piers were not evaluated. Their design and evaluation shall be by the solar array foundation engineer of record.

o The dead end piers shall be designed at the point of the messenger wire connection to

not exceed ½ inch lateral displacement during the everyday (Dead Load only) load case per ASCE 7-10.

o The messenger wire attachment hardware to the mid-support piers and to the dead end

piers were not evaluated. Their design and evaluation shall be by the installation contractor’s engineer of record.

o Installation contractor shall hire a professional engineer licensed in the state that the

project is being installed who shall calculate site specific vertical and lateral ASD

loads on the messenger wire system in accordance with ASCE 7-10. This engineer

shall then use the results of this evaluation to determine what the expected maximum

vertical, longitudinal, and transverse force will be at the dead end pier and the mid-

support pier.




hdrinc.com

Page | 6

Evaluation Results




hdrinc.com

Page | 7

The following tables summarize the results of this messenger wire evaluation. Table 1 and Table 2

provide the tension and sag values at temperature that are required during installation. Either table

can be used by the installation contractor as they will result in the same condition of the messenger

wire. Note that the temperature is of the messenger wire proper and not the air temperature.

Note: Tension values in Table 1 are what the messenger wire shall be pulled to before any electrical cables or cable supports are

hung from the messenger wire (i.e. only the bare messenger wire).

Note: Mid-span sag of the messenger wire proper shall be per Table 2. This sag occurs before any electrical cables or cable

supports are hung from the messenger wire (i.e. only the bare messenger wire).

Table 1: Messenger Wire

Stringing Tension Chart

Span

Temperature (Degrees F)

-40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100 110 120

Longitudinal Tension

(lb)

0ft – 15ft 369 322 276 231 187 146 107 73 50 37 30 26 23 20 19 17 16

15ft – 20ft 284 239 196 154 117 84 62 48 39 34 30 27 25 23 22 21 20

20ft – 25ft 183 144 109 83 64 53 45 39 35 32 30 28 26 25 24 23 22

25ft – 30ft 92 74 62 53 47 42 39 36 34 32 30 29 27 26 25 24 23


Stringing Sag Chart

Span


-40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100 110 120

Sag (inches)

0ft – 15ft 0.12 0.12 0.12 0.12 0.24 0.24 0.36 0.60 0.84 1.08 1.32 1.56 1.80 2.04 2.16 2.40 2.52

15ft – 20ft 0.24 0.36 0.36 0.48 0.60 0.84 1.20 1.56 1.80 2.16 2.40 2.64 2.88 3.12 3.36 3.48 3.72

20ft – 25ft 0.60 0.84 1.08 1.32 1.80 2.16 2.52 2.88 3.24 3.48 3.72 4.08 4.32 4.56 4.80 5.04 5.16

25ft – 30ft 1.80 2.16 2.64 3.12 3.48 3.84 4.20 4.56 4.92 5.16 5.40 5.76 6.00 6.24 6.48 6.72 6.96




hdrinc.com

Page | 8

Table 3 provides the maximum sag that is expected in the messenger wire system after the hangers

and cables have been hung. Three temperature ranges have been provided since there is not a

large difference in sag when the temperature changes by 10 F. Note that this sag only occurs when

the maximum vertical load is as listed in the table and is not of just the messenger wire self weight.

NOTE: Reported sag values include initial sag when no load is hanging from messenger wire + the sag that will occur when the reported Maximum Vertical ASD Load is hung from the messenger wire.

Table 4 provides the Allowable Strength Design (ASD) level design loads that are expected to occur

in each principle direction at the dead end pier. Note that these values can also be used to

determine the expected loads on the mid-support piers. However, to do this the reported loads shall

be multiplied by two in the transverse and vertical direction. Longitudinal loads at the mid-support

piers are considered negligible.


Sag with Maximum Vertical ASD Load


Span

Maximum Vertical ASD Load (lb/ft)

2 5 10 15 20 25 30

Sag (inches)

0

0ft – 15ft 1.8 2.6 3.5 4.1 4.6 4.9 5.2

15ft – 20ft 3.0 4.2 5.4 6.2 6.8 7.3 7.8

20ft – 25ft 4.6 6.1 7.4 8.5 9.4 10.1 10.7

25ft – 30ft 6.2 8.2 9.8 11.2 12.2 13.1 13.9

60

0ft – 15ft 2.5 3.2 4.0 4.4 4.9 5.2 5.5

15ft – 20ft 3.8 4.9 6.0 6.6 7.2 7.7 8.2

20ft – 25ft 5.5 6.8 8.0 9.0 9.8 10.6 11.2

25ft – 30ft 7.3 8.9 10.5 11.8 12.7 13.6 14.3

120

0ft – 15ft 3.1 3.7 4.3 4.8 5.2 5.5 5.8

15ft – 20ft 4.7 5.5 6.4 7.1 7.7 8.0 8.5

20ft – 25ft 6.4 7.6 8.6 9.5 10.3 10.9 11.5

25ft – 30ft 8.4 9.7 11.2 12.2 13.2 14.0 14.8




hdrinc.com

Page | 9

Table 4: Dead End Pier Reactions

(Pounds, lb)

Maximum Vertical

ASD Load

(lb/ft)

Extreme Wind

Profile Used in

Reported Loads

(inches)

Span

ASCE 7-10 Unfactored Wind Speed

105 mph 110 mph 115 mph 120 mph 130 mph 140 mph 150 mph 170 mph

Tran Long Vert Tran Long Vert Tran Long Vert Tran Long Vert Tran Long Vert Tran Long Vert Tran Long Vert Tran Long Vert

2 3

0ft – 15ft 50 400 15 50 400 15 50 425 15 50 450 15 50 500 15 75 525 15 75 575 15 100 675 15

15ft – 20ft 50 450 20 50 475 20 50 500 20 75 525 20 75 575 20 75 625 20 100 675 20 100 800 20

20ft – 25ft 50 500 25 75 525 25 75 550 25 75 575 25 75 650 25 75 700 25 100 775 25 125 900 25

25ft – 30ft 75 550 30 75 575 30 75 600 30 75 625 30 75 700 30 100 775 30 100 825 30 125 1000 30

5 3

0ft – 15ft 50 575 50 50 575 50 50 600 50 75 625 50 75 625 50 75 650 50 75 700 50 100 775 50

15ft – 20ft 50 675 50 75 700 50 75 700 50 75 725 50 75 750 50 75 775 50 100 825 50 100 900 50

20ft – 25ft 50 750 75 75 775 75 75 775 75 75 800 75 75 825 75 100 875 75 100 925 75 125 1025 75

25ft – 30ft 75 825 75 75 850 75 75 875 75 75 875 75 100 925 75 100 975 75 100 1025 75 125 1125 75

10 5

0ft – 15ft 75 925 75 75 925 75 100 950 75 100 950 75 100 975 75 125 1025 75 125 1050 75 150 1150 75

15ft – 20ft 100 1100 100 100 1100 100 100 1125 100 100 1125 100 125 1175 100 125 1200 100 150 1250 100 175 1375 100

20ft – 25ft 100 1250 125 100 1250 125 100 1275 125 125 1300 125 125 1325 125 150 1375 125 150 1425 125 200 1575 125

25ft – 30ft 100 1375 150 125 1400 150 125 1425 150 125 1425 150 150 1475 150 150 1525 150 175 1600 150 225 1750 150

15 5

0ft – 15ft 100 1225 125 100 1225 125 100 1250 125 100 1250 125 100 1275 125 125 1300 125 125 1325 125 150 1375 125

15ft – 20ft 100 1450 150 100 1475 150 100 1475 150 100 1475 150 125 1500 150 125 1525 150 150 1575 150 175 1650 150

20ft – 25ft 100 1675 200 100 1675 200 125 1675 200 125 1700 200 125 1725 200 150 1750 200 175 1800 200 200 1875 200

25ft – 30ft 100 1850 225 125 1850 225 125 1875 225 125 1875 225 150 1900 225 175 1950 225 175 1975 225 225 2100 225

20 5

0ft – 15ft 100 1475 150 100 1475 150 100 1475 150 100 1475 150 125 1500 150 125 1500 150 150 1525 150 150 1575 150

15ft – 20ft 100 1750 200 100 1750 200 125 1750 200 125 1775 200 125 1775 200 150 1800 200 150 1825 200 175 1900 200

20ft – 25ft 125 2000 250 125 2000 250 125 2025 250 125 2025 250 150 2050 250 150 2075 250 175 2100 250 200 2175 250

25ft – 30ft 125 2225 300 125 2225 300 125 2225 300 150 2250 300 150 2275 300 175 2300 300 200 2325 300 225 2400 300




hdrinc.com

Page | 10

Note:

1. Dead end piers shall be designed to accommodate the above listed Transverse, Longitudinal, and Vertical loads.

2. Mid-support piers shall be designed to accommodate twice as much Transverse and Vertical load as reported in this table and have zero Longitudinal loads.

3. Reported loads are for one messenger wire. If a dead end or mid-support pier is supporting two parallel messenger wire systems then the reactions need to

be doubled on the dead end pier and multiplied by 4 on the mid-support piers. See Note 1 and Note 2 above for reference.

4. All reported loads are Allowable Strength Design (ASD) level loads and are intended to be used with project specific loads that are calculated in accordance

with ASCE 7-10 and its ASD load combinations.

5. Wind loads used in Table 4 were factored per ASCE 7-10 ASD load combinations.

6. The Extreme Wind Profile heights are based on the assumption that the cables can not be stacked higher than 3 inches when the total vertical dead load is

less than 5 lb/ft and that the maximum height of the stacked cables hung from the messenger wire is 5 inches for all vertical loads greater than 5 lb/ft. One

example would be (16) 500 kcmil + (16) #10 cables which will result in a wind profile of 5 inches and have a vertical load of 12 lb/ft / messenger wire.

Table 4: Dead End Pier Reactions (continued)

(Pounds, lb)

Maximum Vertical

ASD Load

(lb/ft)

Extreme Wind

Profile Used in

Reported Loads

(inches)

Span

ASCE 7-10 Unfactored Wind Speed

105 mph 110 mph 115 mph 120 mph 130 mph 140 mph 150 mph 170 mph

Tran Long Vert Tran Long Vert Tran Long Vert Tran Long Vert Tran Long Vert Tran Long Vert Tran Long Vert Tran Long Vert

25 5

0ft – 15ft 100 1700 200 125 1700 200 125 1700 200 125 1725 200 125 1725 200 150 1725 200 150 1750 200 175 1700 200

15ft – 20ft 125 2025 250 125 2025 250 125 2025 250 125 2050 250 150 2050 250 150 2075 250 150 2075 250 175 2125 250

20ft – 25ft 125 2300 325 125 2325 325 125 2325 325 150 2325 325 150 2325 325 175 2350 325 175 2375 325 200 2425 325

25ft – 30ft 125 2575 375 125 2575 375 150 2575 375 150 2600 375 175 2600 375 175 2625 375 200 2650 375 225 2725 375

30 5

0ft – 15ft 125 1900 225 125 1900 225 125 1925 225 125 1925 225 150 1925 225 150 1950 225 150 1950 225 175 1975 225

15ft – 20ft 125 2275 300 125 2275 300 125 2275 300 125 2275 300 150 2300 300 150 2300 300 175 2325 300 200 2350 300

20ft – 25ft 125 2600 375 125 2625 375 150 2625 375 150 2625 375 150 2625 375 175 2650 375 175 2675 375 225 2700 375

25ft – 30ft 125 2900 450 130 2900 450 150 2925 450 150 2925 450 175 2925 450 200 2950 450 200 2975 450 250 3025 450




hdrinc.com

Page | 11

2.1 Table 4 Definitions

� Long = Longitudinal Load – the tension force along the length of the messenger wire.

� Tran = Transverse Load – the horizontal force perpendicular to the messenger wire at the support pier.

� Vert = Vertical Load – the vertical (downward) force at the support pier.

� Dead End Pier = The last pier in a run that has a Long, Tran, and a Vert load as reported in Table 4. There are typically two

dead end piers per messenger wire run (one at each end). Note how the Long load is applied to either the strong or weak axis

of a dead end pier depending on which direction the messenger wire is being strung (see below).

Example: messenger wire strung along the East-West direction. Example: messenger wire strung along the North-South direction.

� Mid-Support Pier = a support pier located in-between the two dead end piers. These piers have zero Long loads and twice as

much Tran and Vert load as reported in Table 4 per messenger wire system (see Table 4, note 3).

Example: messenger wire strung along the East-West direction.

Example: messenger wire strung along the North-South direction.

� Run = the length of a messenger wire configuration that will consist of two dead end piers (1 at each end of the run) and

typically has multiple mid-support piers in-between the two dead end piers.

Long

Vert

Tran

Long = 0

2 x Tran

2 x Vert

2 x Tran

Long = 0

2 x Vert

Tran

Vert

Long




hdrinc.com

Page | 12

One way to estimate in the field if the messenger wire has been installed to the proper tension is to

perform a test called the Return Wave Test. Table 5 lists the approximate time (in seconds) that it

will take 10 waves to travel between two adjacent supports when the messenger wire is installed per

Table 1 or Table 2.

The Return Wave test is performed by initiating a wave in the unloaded (i.e. no hangers or cables

are installed yet) messenger wire close to one support. This can be done by striking the wire with a

hard object or by hanging a light, dry, nonmetallic rope or cord over the wire and pulling the wire

down strongly and then quickly releasing the wire. Once a wave is started measure the time it takes

for 10 waves to pass by and compare this value with the values listed in Table 5. The return wave

may be felt by placing a finger on the wire if the wire was struck, or if a cord was used to pull the wire

down the return wave may be felt in the cord by maintaining a light tension on the wire.

Note: Above listed approximate times will only occur when the messenger wire does not have any load on it (i.e. there are no cables or hangers hung below; just the self weight of the messenger wire). Reported times are for the maximum span of the four reported span lengths (15ft, 20ft, 25ft, and 30ft) while all other span lengths will result in a slightly different time.

Table 5: Return Wave Test

Time for 10 Waves to Pass by

Span


-40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100 110 120

Time (Seconds)

0ft – 15ft 0.96 1.02 1.11 1.21 1.34 1.52 1.78 2.15 2.60 3.02 3.35 3.63 3.87 4.07 4.25 4.41 4.55

15ft – 20ft 1.46 1.58 1.75 1.98 2.27 2.67 3.12 3.55 3.91 4.21 4.48 4.71 4.91 5.09 5.25 5.41 5.55

20ft – 25ft 2.27 2.55 2.93 3.36 3.82 4.23 4.58 4.88 5.14 5.38 5.59 5.78 5.96 6.12 6.28 6.42 6.55

25ft – 30ft 3.82 4.27 4.69 5.06 5.38 5.66 5.91 6.14 6.35 6.53 6.72 6.88 7.04 7.17 7.31 7.44 7.56

cab products messenger wire evaluation - hooks, … · ... (i.e. the maximum vertical load that...

Documents