HELP!! 10 tonne plate and bolt in concrete

I have a 100mm diameter bolt which is going to be embeded in a 300mm thick concrete slab. The embedment depth of the bolt is 110mm. The end of the bolt in concrete is welded to a 290mm square and 20mm thick steel plate. The bolt protrudes 40mm above the top of slab. The bolt has been designed to resist 10 tonne load (100kN) in all directions.

My question is:
1/How do I check for bearing stress in concrete when considering the load in horizontal direction ? ie Horizontal shear force of 100kN at 40mm above concrete
2/If bearing stress is critical, what would be my options? ie provide additional reinforcement

Anyone's suggestions would be mostly appreciated.

 

[AJUK]

Are you sure you mean a 100mm dia bolt? Thats a big bolt!

100kN is not that great a load and should be able to be handled by a much smaller bolt. If you need a 100mm diameter bolt then the 300mm thick concrete section is way undersized.

 

Sorry,the bolt is actually M42 bolt , I meant to write the ferrule is 100mm in diameter and the bolt is screwed into it. The ferrule is actually embedded 110mm in the slab.

 

[idly123]

well to my knowledge u can always weld ur plate to the reinforcment sof the slab.
Just design a nominal weld to ensure that it takes that 100kn horizonal load
Then the reinforecemnt mat should take care.

There might be a more of shear coming at the replacement of concrete with steel plate and bolt extra reinforcement may be provided at that opening to account for shear
in a diaginal fashion around the bolt holelocation..again a regular design should help.

regards
raj

 

[Ginger]

I have modelled such a problem like this:-

1. Check bolt bending capacity assuming that the bolt is "fixed" in the concrete. M=100 x 0.04 = 4 kNm. Check bending stress in M42 bolt. If OK then go on to check the bearing.

2. For bearing stress on the concrete I model this based on there being zero bearing stress at the bottom of the bolt (where the plate washer is) and increase the stress linearly to a maximum at the concrete surface. This is an approximation of what really happens.

Then, for equilibrium, 100kN = area of bearing stress diagram x bolt diameter.

You can solve this to get the area of the triangle of the bearing stress diagram and knowing the length of the bolt embedment you get the maximum bearing stress. Compare this with the allowable stress for bearing on concrete.

If stress is too high you can:
1. Increase bolt diameter
2. Increase embedment length
3. Increase concrete grade
4. Analyse problem in terms of 3D bursting stresses (see work by Yves Guyon).

The model I have hypothesised is simple and conservative I believe.

Regards Andy Machon

 

[chichuck]

I think DrRag's answer is partially incorrect. You should never weld to reinforcing steel, as that material is not a weldable grade. The heat from the welding operations will cause reinforcing steel to become brittle.

The 2000 revision of the ACI 318 code in the US has a newly revised secition on anchorage, and should provide the necessary guidance.

 

[LittleWheels]

Hello chichuck,

Not all countries use unweldable reinforcing steel, just a thought.

 

[AJUK]

Welding of reinforcement is very common prctice in the UK and not a problem at all.