Base Plate Design Guide 1 2

[SALTRAM4567777]

Hi!
I want to know that we follow Yield Line theory for End Plates(DG 16) but when we deal with Base Plates we take cantilever bending.Why?

 

[Agent666]

Well in that case it obviously isn't. When they are equal and the actual true capacity has been determined there is another theorem limit it is called, but the name of it eludes me currently.. ..

I've started approaching the thickness/prying question by ensuring the thickness meets the requirements in Eurocode for ensuring that prying is unlikely. Sometimes it results in thicker plates, but not stupidly so. But it makes me feel better that I'm not going to get the additional bolt forces that occur under prying if I have significant tension or tension due to moment. Either way typically some larger bolts could be provided for the prying case if it were to occur. But for cases governed by concrete breakout with no anchor reinforcement to take over the breakout duties I'd be weary. But for serious loads you're typically going to be providing anchor reinforcement right? So a bit more reinforcement and you've dealt with the prying increasing bolt forces.

 

[Settingsun]

Here are the conditions in which a lower bound analysis gives a safe design.

 

[dik]

They are part of the same puppy... just different aspects. My comments for general plastic design are applicable to plate design... also works with concrete with limitations.

Dik

 

[r13]

This is my understanding on stress under base plate with various stiffness. In most occasions, the plate behavior falls in between "flexible" and "semi-rigid". The design philosophy to keep in mind should be that - bolt mustn't fail prior to plate yield.

 

[SALTRAM4567777]

@retired13 Since we are uding lower bound theorem to calculate Base Plate Thickness we will end up with a Rigid Base Plate. That is the reason why most codes dont check for prying action of Base Plate

 

[r13]

Think logically and judge the failure mode to determine the need or not. Where did code says not to consider prying action for baseplate design? Design guide examples do not represent all cases, or inexplicitly advocate mood point/intention of the code. As long as the plate is capable of deform, prying force is there, the question is only on the magnitude, that may, or may not be negligible. Thinking practically, a flexible plate with strong anchors will produce ample noticeable warning before failure, on the other hand, breaking the bolts with plate remains intact is more likely a sudden event. Last, think critically that the consequence of a single column failure can bring, and are you ready to defend your design by refer to as "code said so", where?

 

[dik]

I have a little SMath program that calculates prying action... use if for BP, and end plate moment connections...

Dik

 

[r13]

dik,

If you can share that will be a great service to many, as most of us don't want to go through that tedious analysis, thus many are trying to find any justification to ignore it. It has been fine in the past, as the rigid framing, that resulting from elastic analysis/design, had prevented large displacement/deflection at the column base in most cases, but as structure getting slender, IMO, the importance of base support is elevated much more than before. If there is reliable tool, it helps, no matter the prying force is large or small.