Base plate thickness equivalent 1

[Jandra11]

I'm designing a steel post and as the result of the calculation the required thickness of the base plate is 20mm. And the architect ask me if we can use 2- 10mm thick in order to obtain the 20mm thick(no other connection between the 2- 10mm plates except for the anchorage). Considering its a moment resisting support. Is this possible? or is there any loss in strength considering the baseplate is not monolithic. Any input will be much appreciated. thanks in advance.

 

[dik]

It helps, but, not enough... the 20mm thickness is based on the plate acting as a unit, not 'slipping' at mid depth. Best you stick with your 20mm plate. If you can weld the 10mm together so that there is no 'slippage' in the middle, then that should work, too.

 

[Jandra11]

Thank you dik.Is there any manual computation on this considering the plates are not welded?

 

[slickdeals]

What difference does it make to the architect if the 20 mm thick plate is a single piece or (2)-10mm thick plates? I would politely tell him to do his job and let you do your job.

For what it's worth, a single plate 20 mm thick has a section modulus (bt^/4) of two times the value of two individual 10 mm plates (not welded together).

 

[MonsieurR]

Why would the architect need that?
If the plates are not welded, then simply add up the inertias of 10 mm plates, which will be less than the inertia of one 20 mm thick plate.
If the plates are welded on the edges it will depend on the dimensions and demands but a safe estimate is still adding up the inertias.

 

[robyengIT]

same as in Italy : architects are frequently stupid

 

[KootK]

Welding two 10's will cost more than ordering one 20. And that's even considering your time to have no value.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Tomfh]

2x 10mm plate has 1/2 the strength and 1/4 the stiffness as a 20mm plate.

 

[dik]

slickdeals summed it up with the plastic section modulus and Tomfh summed up the strength issues... to reiterate... best to stick with the 20mm choice.

Dik

 

[TLHS]

You also don't have continuity for tension resistance. So for any situation where the bolts go into tension (moment or uplift), you only have one plate working.

 

[Jandra11]

Thanks for all the input. the reason is the availability of the material. he already had 10mm thick plates and he want to utilize it. But as what you guys said i already insisted to use 20mm thick plate. by the way is there any possibility that the plates can act as monolithic assuming only compression force is present?

 

[hokie66]

No, you have already been given the appropriate advice. Two 10 plates are not equivalent in bending to one 20 plate.

 

[Tomfh]

The clamping action will resist slipping of the plies to some degree, and thus result in partially composite action, but it’s not something you can easily quantify or rely upon. It won’t be anywhere near as good as monolithic.

 

[TLHS]

From a theoretical standpoint, you could work out the friction force and see if it's enough to allow for shear flow. If it was, it would effectively act as a single unit as long as that friction is there. From a practical standpoint, it's not a design practice that would be defensible if something goes wrong, so I'd never do it.

 

[dik]

If the plates have a slight oil, or have been sandblasted... you have no idea of what the friction value is...

Dik

 

[Jandra11]

Thank you for all you're answers.

 

[BJI]

The time it has taken you to discuss this is already more expensive than to buy the 20mm plate. Send the architect your quote to perform the calculations and he will quickly opt to buy the 20mm plate.

 

[bigengineer]

What TLHS said, I wouldn't count on the second plate doing anything, no more than I would consider leveling grout adding to the base plate section modulus, stiffness, etc.