# How much do these bolts hold? Marked 10.9, with shank area of 153 sq mm

A certain truck has 5 (per side) *2 sides= 10 bolts holding the body to the frame. The bolts are marked 10.9 and the area of the shank is 153 sq mm. From my math I got 3e8 lbs for all 10 bolts together.

From a mechanical engineering point of view, how would you describe the mechanical characteristics of these bolts?

Edit:

Thank you for the discussion. I was dividing by the bolt section area; I should have been multiplying. Now the answers make much more sense.

Each bolt has a tensile strength of about 32,000 lbs * 10 bolts = 320k lbs.

Of course the more interesting tests in a vehicle application are the shear loads you would encounter in a collision, but that is also a MUCH more complicated question.

The nominal capacity of a high tensile bolt are defined by its designation eg 10.9 here the first figure (10) is the ultimate tensile stress in hundreds of MegaPascals and the second figure (after the point) is the yield stress as a fraction of the UTS ie 9 represents 9 tenths or 90%

Conveniently if you multiply the yield stress (MPa) by the bolt section (mm) you get an answer for the yield load in tension of the bolt in Newtons.

Having said that the static tensile strength of the bolt is only part of the capacity of a bolted joint and you need to consider any loads in other direction as well as the effect of dynamic loading.

Also the preload on a bolt will have a significant effect on how it behaves, not all joints are preloaded but when they are external shear loads are carried by friction between the mating surfaces. It is also possible for bolted joints to fail in ways other than the bolt breaking eg by pulling through the member they are attached to.

Equally the design load for a structure may incorporate a factor of safety which puts the rated safe working load at some fraction of the theoretical maximum and where you have multiple bolts you can't always assume that they are equally loaded.

This is further complicated in something like a vehicle chassis in that the members are also carrying other loads as well.

Finally I would add that if you are working from metric units your answer should be metric as well, convert your final answer as well if necessary but having the problem and the answer in mixed units makes errors more likely and more difficult to identify.

• I was dividing by the bolt section area; I should have been multiplying. Now the answers make much more sense. So each bolt has a tensile strength of about 32,000 lbs * 10 bolts = 320k lbs. Of course the more interesting tests in a vehicle application are the shear loads you would encounter in a collision, but that is also a MUCH more complicated question. – Cameron Sours Oct 26 '16 at 20:56