BS2573

[Badri07]

HI All,
I am trying to verify a runway beam,against the code BS273:1957,the bolted connection on the beam seems to be a problem.The factor of saftey seems too large and the bolts are failing against the code.

I would appreciate if you could let me know if there is a work around to solve this problem.

Thanks

 

[Badri07]

Hi All,
Sorry for putting the wrong code in the heading,its infact it has to be read as BS2853.

Thanks
Badri.

 

[Ussuri]

The allowable stresses given in the codes you mention are from the 1950's and are imperial.

BS916 states the bolts minimum tensile strength is 26ton/sq.m (=395MPa depending on what tonne you use, i used 1000kg but it might be long or short)

The allowable stress in tension is 3 or 4 ton/sq.m (=45MPa). Giving a FOS of 8.7.

If you are having a problem with the strength of the bolts why do you not use modern bolts? The QA associated with manufacture was not as it is today. They had greater variability in the finished product so included higher factors of safety to account for it.

Referring to a more modern code BS 449 from 1969. For a grade 4.6 metric bolt. The Tensile strength is 400 MPa with a yield of 240MPa. However, the allowable in the code is 120MPa in tension. Giving a factor of 3.3 against ultimate.

 

[Badri07]

Hi Ussuri,
Thank you for the post,i am just wondering is it ok to jump codes as you say from BS2853 to BS449:1969 just for the bolts.

you are correct,BS2853 has got FOS of 8 on bolts,thats the reason its not passing the code.

Thanks

 

[Ussuri]

Well, I suppose it depends if you can actually get bolts as per the 1950's specification. I checked with the British Standard Institute and BS2853 is still current. BS 916 is current/obsolescent. It does say in the Amendment 4, 1966:

"...this recommendation means that B.A, B.S.F and B.S.W should become obsolescent and should not be used for new designs..."

Personally, I have never used any of the codes you are looking at. I guess it is possible they have reduced the allowable stresses in the bolts for some other reason. You need to understand why the FOS of 8 is included, whether it is due to material variability or something else. Once you know that you can make a decision on whether it is still applicable. An allowable of 45MPa is very small.

I would suggest speaking to someone who has experience in this area.