High Tensile Bolt Specifications

[101RRS]

I am after the SWL of various size high tensile bolts - after pull (tension) strength and shear (if used as a pin) strength.

I did a google search but didn't come up with anything.

Does anyone have a link to a site that provides shear and pull strength of these bolts.

Thanks

Garry

[Andrewpv01]

This may help.

Bolt Depot - Bolt Grade Markings and Strength Chart (http://www.boltdepot.com/fastener-information/Materials-and-Grades/Bolt-Grade-Chart.aspx)

Andrew

[Slunnie]

When you calculate off that, don't forget that you'll be using the minor thread diameter and not the metric sizing.

[101RRS]

I am not quite sure how that chart works - eg a 1.2" (approx cross section of 1 square inch) grade 9 bolt has a tensile strength of 150,000psi - so what does that mean in terms of actual strength - does this mean it could safetly hold something that weighs 150,000ibs or about 70 tons. So a bolt with a cross section of .5 square inch can only hold 35 tons. From this chart how do I work out shear strength?

Thanks for the link

Garry

[Aaron IIA]

Most of the bolts that you buy now come from China, and even though they are marked grade 5, are not actually high tensile. I have had a few failures when putting in new bolts. The only place to reliably buy bolts from is Caterpillar. Their bolts all meet the specification that they are meant to. Buying good materials and tools is becoming increasingly hard. Even Sidchrome is now made in China.
Aaron.

[JDNSW]

I am not quite sure how that chart works - eg a 1.2" (approx cross section of 1 square inch) grade 9 bolt has a tensile strength of 150,000psi - so what does that mean in terms of actual strength - does this mean it could safetly hold something that weighs 150,000ibs or about 70 tons. So a bolt with a cross section of .5 square inch can only hold 35 tons. From this chart how do I work out shear strength?

Thanks for the link

Garry

Tensile strength is NOT safe working load! Tensile strength is the load at which the bolt will break. Safe working load is much less, how much less depends on a lot of factors such as the environment and the levels of acceleration and vibration expected. (typically perhaps 20% of tensile strength).

John

[isuzurover]

Tensile strength is NOT safe working load! Tensile strength is the load at which the bolt will break. Safe working load is much less, how much less depends on a lot of factors such as the environment and the levels of acceleration and vibration expected. (typically perhaps 20% of tensile strength).

John

Not quite - it is (AFAIK) the point at which the bolt will begin to plastically (permanently) deform. So in laymans terms, when the bolt will begin to stretch, but failure will occur shortly after.

For (single) shear, tensile strength x 2/3 (0.66) will give you an approximate value.

John (Bush65) is the expert on bolts and bolted joints though. Dig up some of his posts or send a PM if you want the best answer.

[Dougal]

Are you using metric or imperial bolts? The grades and markings are quite different.

Typical metric markings
grade 8.8 means 800MPa ultimate tensile strength (breaking load) and 80% of that (640MPa) yeild (when it starts to bend or stretch).
Likewise grade 4.6 means 400MPa tensile strength and 240MPa yield. These are basically mild steel and as soft as they get.

The highest tensile metric bolts you'll find are cap screws (allen key head), these are readily available in up to 14.9 and 12.9 depending on the size.

Safe working limits depend entirely on the geometry of the joint you're using them in.

[Aaron]

mpa ?

[Dougal]

mpa ?
That's the unit used for stress. It's short for MegaPascal.
A pascal is 1 N force per square meter. A MegaPascal is 1000,000 Newtons per square metre which works out at 1 Newton per square millimetre.

1 kilogram weighs 9.81 Newtons (on earth).

[JDNSW]

Not quite - it is (AFAIK) the point at which the bolt will begin to plastically (permanently) deform. .........


Depends on your definition....

"There are three typical definitions of tensile strength:

Yield strength
The stress at which material strain changes from elastic deformation to plastic deformation, causing it to deform permanently.
Ultimate strength
The maximum stress a material can withstand.
Breaking strength
The stress coordinate on the stress-strain curve at the point of rupture."

Courtesy Wikipedia, which has quite a good discussion of the subject.

In practice of course, you should never use a fastener anywhere near any of these definitions.

John

John

[Bush65]

Bolts don't have a SWL as such.

A good reason for this is that some bolts may be simultaneously subjected to tensile and shear loads - see below.

The main codifications for bolt design are included in the steel structures code and the pressure vessel and piping codes.

It is many years since I have had to design bolts to the crane code, and I can't remember what is required for bolts in mechanisms. IIRC bolted connections in crane structures are designed in accordance with the steel structures code.

Guessing what you are after, the steel structures code is more relevant.

About 20 years ago, the steel structures code changed from using working stress methods (allowable stress / factor of safety), to limit states methods. This is in line with the rest of the world.

The three usual limit states that are evaluated for load cases combining dead, live, wind and earthquake loads are; stability limit state (so it won't collapse), strength limit state (so it won't break) and serviceability limit state (so it won't deflect or vibrate such that it's function is adversely affected).

For strength limit state there are 3 steps:
1 - determine the "design action effects" (limit states talk for design loads)
2 - determine the "design capacity" (strength) of the member
3 - then compare these to ensure the design action effect is less than the design capacity.

The design action effects are determined by taking the "nominal actions" (loads) and multiply by "load factors" - typically dead loads times 1.25, plus live loads times 1.5. Then a structural analysis, using the factored loads, is carried out to determine the design action effects.

The design capacity is determined by multiplying the "nominal capacity"
by a "capacity factor".

The nominal shear capacity for a bolt is:
0.62 x fuf x kr x (nn x Ac + nx x Ao)

Where:
fuf is minimum tensile strength given in the Aus Standard for the bolt
kr is a reduction factor to account for the length of a bolted lap connection
nn is the number of shear planes with threads intercepting the shear plane
Ac is the minor diameter area of the bolt as specified in AS 1275 (screw threads)
nx is the number of shear planes without threads intercepting the shear plane
Ao is the nominal plain shank area of the bolt

The nominal tension capacity for a bolt is:
As x fuf

Where:
As is the tensile stress area of the bolt as specified in AS 1275 (screw threads)
fuf is minimum tensile strength given in the Aus Standard for the bolt

For bolts the capacity factor is 0.8

The design capacities for tension and single shear of common structural bolts have been calculated in accordance with the steel structures code and published by the Australian Institute of Steel Construction (AISC) - see below.

They also publish a chart showing diagrams for the design capacity when the bolts has combined tension and shear - see below

The tables refer to bolts with property class 8.8
Category 8.8/S, means class 8.8 bolt, snug tightened
8.8/TB, means class 8.8 bolt, fully tensioned, bearing
8.8/TF, means class 8.8 bolt, fully tensioned, friction

Snug tight is defined as tightened by the full effort of a man on a standard podger spanner.

Fully tensioned, means fully tensioned in a controlled manner to the requirements of the steel structures code. Note: tension wrenches are not permitted, because their accuracy is poor at the required tension, due to friction between the bolt, nut and joint. The acceptable methods can cause the bolt to exceed the yield stress for the bolt.

Edit: Only bolts in accordance with AS1252 (High Strength Structural Bolts) are designed for fully tensioning - they have larger hexagon and thickness heads and nuts to withstand the tensile load. An 8.8 bolt to AS1252 has a higher proof load than a normal class 10.9 bolt (or class 10 nut).

Bearing, means shear load is carried by the bolt bearing against the side of the hole in the joint.

Friction, means the shear load is carried by friction between the joint surfaces.

[Tombie]

Most of the bolts that you buy now come from China, and even though they are marked grade 5, are not actually high tensile. I have had a few failures when putting in new bolts. The only place to reliably buy bolts from is Caterpillar. Their bolts all meet the specification that they are meant to. Buying good materials and tools is becoming increasingly hard. Even Sidchrome is now made in China.
Aaron.

From Australian Steel...... :D

[101RRS]

Most of this stuff is all engineer stuff - isn't there something simple that says something like a x grade bolt of y size will hold z tons - surely the type of thread also has an impact.

Garry

[Aaron IIA]

For the same diameter shaft, a fine thread will be stronger than a coarse thread. When bolting into soft castings though, it will be wise to use the coarse thread.
Aaron.

[Dougal]

Most of this stuff is all engineer stuff - isn't there something simple that says something like a x grade bolt of y size will hold z tons - surely the type of thread also has an impact.

Garry

It depends entirely on the geometry of the joint. Draw a sketch of what you've got and we could give some recommendations.

[101RRS]

It depends entirely on the geometry of the joint. Draw a sketch of what you've got and we could give some recommendations.

I don't have anything particular in mind at the moment - other than replacing rusted out bolts in the rear x member of my truck and replacing some chinese high tensile bolts in a tow bar - eg I will need 4 bolts that will have a safe tension of 6 tonne between to four and about 1 tonne in tension. What size bolts/thread are needed if they are 6" long. This is just an example.

The chart that was posted earlier requires me to calculate the cross section of the bolt to determine its capability as the chart is in Psi and its metric equivalent.

If I go into a nut and bolt shop and ask for a nut and bolt to hold 10 tons the guy serving me does not get out the calculator and work out psis etc - he goes to chart and comes back and says I need this size bolt in this grade, or I need a much larger size bolt and nut in a lower grade.

This is the type of chart I am after.

Garry

[Rosco]

Perhaps this may help ...

[img=http://img208.imageshack.us/img208/7435/boltspage1rx8.th.jpg] (http://img208.imageshack.us/my.php?image=boltspage1rx8.jpg)


Edit. These are old safe working load tables (permissible stress) and as such
can be used by Joe Average in typical day to day operations.

Cheers