turnbuckle assembly worksheet

Turnbuckle Assembly Worksheet

Note: See last section for actual worksheet and layout.

Instructions:

This worksheet refers to turnbuckle assemblies used in steel construction. All loads and

strengths should be designed by a licensed engineer. They will consider factors beyond tensile

strength and include considerations such as high wind pressure, additional load from

accumulated snow or ice, vibration due to seismic activity, the desired safety factor, etc.

Material:

Turnbuckle rods can be made of any type and grade of round bar. For architectural effect,

square bars are sometimes specified. Squares require turning down the ends until they are

round, otherwise all other considerations are as shown.

If the material is carbon steel, it’s typically round bar grade A-36, or less often grade 55, A-449

or A-105. Carbon steel bars are usually 20’ in length. The common grade A-36 diameters are

also available in 40’ lengths. Stainless steel is usually 303/304 and sometimes 316 or 316L.

Stainless is most readily available in 12’ lengths and less frequently in 20’ and 24’. See the

section below on rod length for options when a turnbuckle assembly needs to be longer than

the rods available will allow.

The turnbuckles and clevises can also be made of any material desired and can be heat treated

for strength. Most often for the purpose of steel construction carbon steel assemblies are made

with C1030 / C1035 hardware. Stainless steel hardware is in grade 316. This covers assemblies

that require 316 as well as superceding those calling for the lower grades.

Clevis pins are typically made from C1035 round bar, while stainless is usually made from the

same round bar material as the rod.

Finish:

Carbon steel assemblies can be manufactured in plain steel, primed or hot dip galvanized.

Electroplating is available but for the purposes of steel construction this would only be called

for on an exposed assembly for architectural effect.

Stainless steel is usually installed plain but should be polished if visible corrosion is a concern.

For more information on the conditions and reasons for polishing, visit our website here:

http://www.thesteelsupplyco.com/stainless-steel-clevis-and-turnbuckle-polishing/

Navigate : www.thesteelsupplyco.com > Products > Turnbuckle and Clevis Rod Assemblies >

Click link at mid-page, See note on Stainless Steel Surface Rust.

Round Bar Diameter

The main factor in detemining round bar diameter is tensile strength. The standard round bar

grades are shown below;

Grade

Tensile (psi)

Yield (psi, min)

Carbon 36

58 - 80,000

36,000

55

75-95,000

55,000 105

125-150,000

105,000

Stainless 303/304

75,000

30,000 316

75,000

30,000

Important Note: The engineer’s calculation for tensile strength is based on the smallest

diameter (nominal diameter) of the threaded area, not the full body diameter of the round bar.

Threading

Unless specified otherwise, threads are to UNC 2A/2B. The thread pitch is determined when the

round bar diameter is chosen, i.e. if the turnbuckle rod is 1” diameter, the turnbuckle and clevis

threading will be to 1 -8 thread pitch (one inch diameter round bar is 8 threads per inch. Actual

thread pitch diameter is .9188”. Minor diameter is .8466”).


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Overall Length

See Fig. 1. It is measured from the center of the clevis pin to the center of the opposite clevis

pin. On drawings it often appears as COP / COP. This measurement may vary from the original

plans due to field conditions.

Fig. 1

Rod Length

The length of each individual rod requires some decisions and calculating.

First, determine how this assembly will function. It can be designed so the OAL (Overall Length)

is the middle extension or maximum extension.

The drawing below (Fig. 2) shows the rods are set so they can be turned in or out. The erector

can make it longer or shorter. For example, assume the assembly in Fig. 2 is 10’ OAL. If the

turnbuckle has a take-up of 6” and the clevises each have 2” of useable take-up this assembly

has a total take-up of 10”. As shown below it can be a maximum of 10’ 5” or a minimum of 9’

7”.

Fig. 2 Middle Extension

In the next drawing below (Fig. 3), the rods are set so they can not be turned any further out.

All adjustments on this assembly will be inward. For example, assume the assembly in Fig. 3 is

10’ OAL. If the turnbucle has a take-up of 6” and the clevises each have 2” of useable take-up

this assembly can be a maximum of 10’ or a minimum of 9’ 2”.

Note: It is very important that all threaded locations be fully threaded. If any location is partially

threaded it compromses the strength of the turnbuckle assembly.

Fig. 3 Maximum Extension

1) Determine if the turnbuckle assemblies will be installed in a criss-cross pattern. (Fig. 4) If

so, centering the turnbuckles will make it very difficult for the erector to rotate the

turnbuckle. Fig. 5 and 6 show the correct turnbuckle position for this type installation.

This allows the erector free space with enough clearance to rotate the Turnbuckle.

Fig. 4 Incorrect

Fig. 5 Correct

Fig. 6 Correct

Next, calculate the total take up available in the turnbuckle and both clevises. The clevises will

have variable amounts of take-up based on the Grip Width and the location of the hole in the

clevis plate. (For clevis grip width vs. take-up, see the section below Thread Length at clevis.

To determine rod length:

For Middle Extension

OAL – ( 1/2 Turnbuckle Take-Up) – (1/2 Useable Take-Up for both Clevises) =

Total Length for Both Rods

For Maximum Extension Assembly

OAL – (Turnbuckle Take-Up) – (Useable Take-Up for Both Clevises ) =

Total Length for Both Rods

If the turnbuckle assembly will not cross another like in Fig. 4, divide the total length for both

rods in half to get the length for each rod.

If the assembly does cross another, offset the turnbuckle as shown is Fig. 5 and 6. Divide the

total length for both rods by 2, then add approximately 2’ to either rod and subtract the same

amount from the other.

Most round bar is readily available in 20’ lengths. 40’ lengths are rolled however they are

sometimes difficult to find in the required diameter and grade. Using 20’ lengths on both sides

of the turnbuckle allows for 40’, and adding the gaps for turnbuckle and clevis take-up, an

assembly can usually go to an OAL of 41’. For assemblies longer than 41’ (this number varies

based on clevis size and take-up) one of three solutions must be selected.

1. A coupling nut must be used on one or both sides to join additional rods in the

assembly.

2. A second turnbuckle can be included. This will allow for a third rod to be added

to the assembly and provide extra take-up as well. Fig. 7.

3. 40’ round bar lengths must be available in the desired diameter and grade.

Fig. 7

Turnbuckle

Unlike the clevis, the thread diameter will dictate the turnbuckle diameter. What does need to

be determined is the “take-up.” Fig. 8 - 6 shows a 1” diameter turnbuckle with 6” take-up, and

Fig. 8 – 12 is 1” x 12” take-up.

Fig. 8 – 6

Fig. 8 – 12

Take-up lengths of 6” and 12” are the standards, however some of the more popular diameters

have additional sizes. To view the full list visit our site at:

http://www.thesteelsupplyco.com/turnbuckle-turnbuckles/


Turnbuckles

Thread Length at Turnbuckle

Important: In a turnbuckle rod assembly, the only left hand threads should be on one side of

the turnbuckle. Sometimes drawings come through, showing left hand threads at the clevis

also. While it does not hurt the assembly, these are unnecessary and will confuse the erectors.

Thread length at the turnbuckle should be a minimum of 1/2 the take-up ( T) plus the thickness

of the bolt end. (B)(Fig. 9) Refer to the chart on our website at the link above for the B

dimension.

As an example, if the rod diameter was 1” and the take-up is 6” it would be part number TB110.

The nut end (B) is 1-3/8”.

6 ÷ 2 + 1-3/8” = 4-3/8” Threading

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Fig. 9.

Extra thread is sometimes advantageous. If a given location is smaller than was intended there

may not be enough take-up to compensate. With extra thread the erector can correct the

problem immediately by cutting the rod and re-threading. This should not be considered

automatic. Sometimes on assemblies that will be exposed the designer wants to limit the

exposed thread for esthetic reasons. In the is the case be careful about adding too much extra

thread.

Clevis Number

The engineer should specify the required clevis numerically by size. See the chart on our

website to undestand how the I.D. number relates to the size.

http://www.thesteelsupplyco.com/clevis-clevises/


Clevises

Thread Length at Clevis

Always be sure the threads are fully engaged at both the clevis and the turnbuckle.

The minimum thread should be the length of the nut end of the clevis. In Fig. 10 see dimension

N. If the threads are not fully engaged the assembly will not provide the indicated load capacity.

Clevis chart above shows “N” values.

Fig. 10

Providing extra threading at the clevis allows for

addition take-up beyond what is provided by

the turnbuckle. The width and hole location of

the clevis plate will effect how far beyond the

nut end the rod can protrude.



Thread Length at Clevis: Clevis Plate Hole Location

In Fig. 11 two clevis plates are shown. Assume they are both 6” wide x 8” tall, with a thickness

of 1-1/4”. The hole diameter is 2-1/8” to allow for a 2” pin. Looking at the clevis chart shows a

pin of 2” requires a clevis no smaller than CL35. The “A” dimension for #CL35 is 6”.

The pin in this case is 2”, so from the A dimension 1” is subtracted for half the pin width. This

leaves 5” open area between the forks from the inner edge of the nut end to the inner edge of

the pin.

The clevis plate on the left has the hole offset so it is 2” from both the side and top. The plate

on the right shows the hole is centered at 3” from the side and top. Note the plate on the right

requires 4-1/4” clearance to the corner. Clevis #CL35 has available space of 5”. If all

measurements are correct the #CL35 clevis would allow 3/4” clearance in each clevis and 1-

1/2” take-up per assembly, which is very little tolerance.

The corrections in this case are:

1) Most commonly, the fabricator will round the corner of the clevis plate. Since it

is 3” from the center of the hole to the top and side, that should be the

minimum radius for rounding.

2) Move the hole closer to the plate edge. This requires engineering approval as it

lowers the strength of the connection.

3) Increase the size of the clevis to #CL50 which has an A dimension of 7”. As a

point of reference this the cost of a #5 clevis is approximately double the cost of

a #3.5 clevis.

Fig. 11

Thread Length at Clevis: Clevis Grip Width

Fig. 12

This is determined by the clevis plate

thickness. The grip (G) should be 1/16”

to 1/8” wider than the plate.

Fig. 13

Figure 12 has a grip width greater than

the diameter of the threads so the take-

up extends to the clevis plate. In this

case, the clevis take-up is;

Dimension A less the distance from the

center of the clevis pin hole to the farthest edge of the clevis plate that will interact with the

clevis.

(Refer back to Fig. 11). Leave some room for clearance and field conditions.

Figure 13 shows a more common situation where the grip is less than the rod diameter. As the

forks come closer together (G) they block the rod. Clevis take-up is is variable in these

situations.

Clevis Hole Diameter

For pin diameters up to 2-3/4”, the clevis hole is typically 1/16” larger than the diameter of the

Pin. 3” diamters and larger allow for a hole 1/8” larger than the pin diameter.

Clevis Pin Diameter

Again this should be called out by the engineer. As a rule, the clevis pin diameter should never

be smaller than round bar used for the turnbuckle rod. The standard clevis dimensions, known

as Grinnel Standards, show the pin as follows:

Turnbuckle Rod Diameter up to 1-3/4”, the pin is 1/8” larger diameter.

Turnbuckle Rod Diameter from 2” and above, the pin is 1/4” larger diameter.

To view the list of Grinnel Standard Clevises:

http://www.thesteelsupplyco.com/clevis-clevises-grinnel-standards/


Grinnel Standard Clevises

http://www.thesteelsupplyco.com/clevis-clevises-grinnel-standards/


Clevis Pin Type

For the purposes of steel construction, there are two clevis pin types, straight and headed. (Fig.

14) While they function the same, the headed pin adds cost and is usually only used where the

artistic design calls for it.

Fig. 14

Clevis Pin Length

The clevis pin will have two lengths. The useable length (L) and the overall length (O).

Useable length is the distance between the cotter pins. This is the more important of the two.

Useable length is determined by the grip width and clevis number. The chart showing clevises

has a column that indicates the fork thickness.



Clevises

On the chart, see column T. The useable length of the clevis pin needs to be at least the width

of the grip (and any clearance) plus the width of both forks. It is best to add a small amount of

extra length for workability.

Caution: Some assemblies call for flat washers underneath the cotter pins. Remember to add 2

times the thickness of the washer if required.



Fig. 15

Worksheet

Centered Turnbuckle

Specifications

Middle Extension or Fully Extended (circle one)

Overall Length COP/COP __________________________

Steel Type Carbon A-36 GR-55 A-105

Stainless 303 / 304

Other ____________________

Finish Carbon Plain Hot Dip Galvanized Electrp-Plating

Stainless Plain Stainless Polished

Rod Diameter __________________________

Hardware

Turnbuckle Take-Up __________________________

Clevis Number _____________________

Clevis Grip Width _____________________

Clevis Pin Hole Diameter _____________________

Clevis Pin Type: Straight w/2 Cotter Pins Headed w/ 1 Cotter Pin

Diameter __________ Useable Length __________ Overall Length __________

Rod Length Left Rod _______________ Right Rod _______________ (Both Equal)

Threading

Thread Length at Clevis _____________________ (Both right Hand Threads)

Thread Length at Turnbuckle _______________________ (One rod right hand, one left hand)

Worksheet

Offset Turnbuckle

Specifications

Middle Extension or Fully Extended (circle one)

Overall Length COP/COP __________________________

Steel Type Carbon A-36 GR-55 A-105

Stainless 303 / 304

Other ____________________

Finish Carbon Plain Hot Dip Galvanized Electrp-Plating

Stainless Plain Polished

Rod Diameter __________________________

Hardware

Turnbuckle Take-Up __________________________

Clevis Number _____________________

Clevis Grip Width _____________________

Clevis Pin Hole Diameter _____________________

Clevis Pin Type: Straight w/2 Cotter Pins Headed w/ 1 Cotter Pin

Diameter __________ Useable Length __________ Overall Length __________

Rod Length Left Rod _______________ Right Rod _______________ (Unequal for offset)

Threading

Thread Length at Clevis _____________________ (Both right Hand Threads)

Thread Length at Turnbuckle _______________________ (One rod right hand, one left hand)

turnbuckle assembly worksheet

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