landrover77
Mechanical
- Jan 16, 2004
- 40
Hi, I’m trying to assess the anchor bolt loads for a jib crane that we’re proposing to relocate. Structural calcs are not my field.
I can easily replicate the bolting currently in place to ensure safety, however for my own satisfaction I wanted to calculate the bolt loadings for the anchor bolts to check the epoxy resin we’re proposing to use is adequate. The concrete floor 600m thick with 25mm reinforcing.
However in doing so, I must be missing the approach taken in determining the division of loads on the bolts.
If we assume a floor mounted 1ton jib crane or boom length of 5m with 360º rotation.
This give a moment around the column of 1000*9.81*5 / 1000 = 49.05KNm (unfactored loads). Also for simplicity of the example ignoring rigging and boom weights.
Thus my assumption has been that if the base has 8 bolts, in the worse case rotation position, then 3 bolts are in tension preventing the tipping motion, 2 being on the centre line of rotation and 3 being on the side where the base plate of the column is in compression into the floor. The bolts are at an average distance (S) 0.4m from the columns centre of rotation.
Therefore assuming equilibrium where Ra is tensile force on bolts
Ra x 0.4 - 49.05KNm = 0. Thus Ra = 49.05/0.4 = 122.6KN.
Divide between 3 bolts this gives 41Kn / bolt.
We’re using M20 high tensile bolts, so I’ve no concerns over these, however the epoxy resin design loads are only 56KN. Which by the time apply a SF of 2.0 are nowhere near adequate.
However I know the crane install is fine and so what additions do I need to make to my simplistic analysis? Is there some derating assuming that the area of the base plate in compression takes some of the loading, and does this depend upon the flatness of the floor surface and grouting around the base?
Many Thanks for your help in advance.
I can easily replicate the bolting currently in place to ensure safety, however for my own satisfaction I wanted to calculate the bolt loadings for the anchor bolts to check the epoxy resin we’re proposing to use is adequate. The concrete floor 600m thick with 25mm reinforcing.
However in doing so, I must be missing the approach taken in determining the division of loads on the bolts.
If we assume a floor mounted 1ton jib crane or boom length of 5m with 360º rotation.
This give a moment around the column of 1000*9.81*5 / 1000 = 49.05KNm (unfactored loads). Also for simplicity of the example ignoring rigging and boom weights.
Thus my assumption has been that if the base has 8 bolts, in the worse case rotation position, then 3 bolts are in tension preventing the tipping motion, 2 being on the centre line of rotation and 3 being on the side where the base plate of the column is in compression into the floor. The bolts are at an average distance (S) 0.4m from the columns centre of rotation.
Therefore assuming equilibrium where Ra is tensile force on bolts
Ra x 0.4 - 49.05KNm = 0. Thus Ra = 49.05/0.4 = 122.6KN.
Divide between 3 bolts this gives 41Kn / bolt.
We’re using M20 high tensile bolts, so I’ve no concerns over these, however the epoxy resin design loads are only 56KN. Which by the time apply a SF of 2.0 are nowhere near adequate.
However I know the crane install is fine and so what additions do I need to make to my simplistic analysis? Is there some derating assuming that the area of the base plate in compression takes some of the loading, and does this depend upon the flatness of the floor surface and grouting around the base?
Many Thanks for your help in advance.