507-120804 Hi guys My question is

[SALTRAM4567777]

507-120804
Hi guys
My question is regarding Base Plates.Most of the design methadology suggests to use Rigid Bases than Flexilble Ones but AISC allows us to use Plastic Section Modulus to calculate the thickness of Base Plate instead of Elastic Section Modulus.
Please help

 

[dik]

Both work... with rigid base plates, any prying action is reduced. If I have a lot of the same kind and they are lightly loaded, I go to the lighter base plate.

Dik

 

[SALTRAM4567777]

Hey!
As per AISC Design Guide 1 it uses Plastic Section Modulus and thus the thickness of Base Plate wlrks out to be less instead of using Elastic Section Modulus and still it is not considering the effect of Prying forces, both for Base Plates with Moment and without moment.
My question is that if we are using Plastic Section Modulus and LRFD Design Methadology ,we want Plastic Hinges to form in our Base Plate which I think is not a great idea due to non uniform stress all over the base plate amd considerable deformation.Then why AISC is allowing us to use Plastic Section Modulus?

 

[dik]

I've always used the plastic section modulus for base plates... the rectangular steel section develops the full plastic capacity and there is an increase of 50% between Zx and Sx. For the base plate to yield, plastic secion is developed.

Dik

 

[SALTRAM4567777]

So when you are using Plastic Section Modulus you are allowing your base plate to undergo Plastic deformations. If you check British codes they always use elastic section modulus to compute Base Plate Thickness and the reason they give is that we want Base Plate to be Rigid.
By using Plastic Section modulus you may end up with a flexible plate and you need to check for prying force which clearly in AISC Dedign Guide you are told not to check.Am i missing something?