Thickness Calculation of Annular Base plate

The maximum unit moment (m) in a cantilevered plate subjected to a

concentrated load (P) is given as

𝑚 =𝑃 ∗ 𝑝. 𝑐.𝑑

𝜋 ∗ 𝑝. 𝑐. 𝑑=

𝑃

𝜋

The load (P) on any anchor in a bolt group subjected to an applied moment

based on an elastic distribution of loads to the bolts is given by

𝑃 =𝑀 ∗ 𝑦

𝐼𝑏𝑜𝑙𝑡 𝑔𝑟𝑜𝑢𝑝

Where,

P = the force in an anchor bolt due to the applied moment

M = the applied moment

y = distance from center of the bolt group to the bolt considered, for

maximum P it would be p.c.d

𝐼𝑏𝑜𝑙𝑡 𝑔𝑟𝑜𝑢𝑝 = 𝑛

2 𝑝. 𝑐. 𝑑/2 2, moment of inertia of bolt group, n being number of

bolts in annular base plate.

So, for maximum P, the expression would be

𝑃 =4 ∗ 𝑀

𝑛 ∗ 𝑝. 𝑐.𝑑

Also, there is an external vertical load from the weight of shaft and head

frame of structure. The vertical load would be shared by n bolts and hence

vertical load shared by each bolt would be

𝑃′ = 𝐹𝑣𝑛

So applied unit moment would become

𝑚 =4 ∗ 𝑀

𝜋 ∗ 𝑛 ∗ 𝑝. 𝑐.𝑑+

𝐹𝑣𝑛 ∗ 𝜋

Also, unit moment capacity for annular base plate would be governed by

thickness and yield strength of the base plate

So,

𝑚 =𝑌 ∗ 𝑡2

4

So design thickness should be higher than t when unit moment capacity is

compared with applied unit moment

This equation could be basis of calculating desired thickness

Or,

𝑡 = 4

𝑛 ∗ 𝜋 ∗ 𝑌

4 ∗ 𝑀

𝑝. 𝑐.𝑑+ 𝐹𝑣