Tie Beams Purpose 1

[drasticxxxx]

Tie Beams are two types
1.With foundation level
2.above foundation level

What is the difference between of them?

Actually If I said Tie beam ,I will say the following reasons for using it:

1. Hold Footings together under seismic load
2.Prevent differential settlement
3.Carry the block above them(walls)


However in terms of modeling in finite element, for the footings part we can model it, if it connected to footing at foundation level,and I never seen anybody model it when it is above the footings

So is this true or I have to model it in either way for (footings model)??

So from where i Will get the moment and shear to design this beams,,As I am thinking now,it suppose to be extracted form footings model by applying the vertical load form the walls above and applying the earthquake reactions from the building to the footings,in which the beams will hold the footings together,but again these beams will transfer internal forces ,and will do nothing with external stability


I would like to open a discussion to explain the different uses of this tie beams and how this will be implemented in finite element software(Mainly I would like to know what people are doing in practice).


Thank you all

 

[drasticxxxx]

upppppppp

 

[RPMG]

Personally, I don't model foundations and grade beams are considered a practical consideration for insulation and settlement.

 

[KootK]

What is the difference between of them?

Mostly just designer preference and construction economics I think. I don't know of any hard and fast rules regarding when one system ought to be selected over the other.

So is this true or I have to model it in either way for (footings model)??

Like RPMG, I rarely include foundation or grade beams in my models. There have been a few exceptions:

1) When I am using grade beams to smooth out serious differential deflection issues and I want to quantify that improvement.

2) When I am using grade beams as an integral part of a moment frame above and I want to quantify stiffness.

So from where i Will get the moment and shear to design this beams

When used as seismic ties, your code probably specifies the required axial capacity as a portion of the restrained column axial load. Something to the tune of 0.25 x Pu x Peak ground acceleration.

When used to support wall loads, or expansive soil displacement, moment and shear demands are calculated as for any other beam.

When used to mitigate differential deflection, I've done the following:

a) Made the beams strong and stiff enough to limit differential deflection as required.

b) An old rule of thumb is to design the grade beam for Vu=Pu/80 and Mu=Pu*L/160. L = span; Pu = highest axial load either end of beam.

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.

 

[drasticxxxx]

Thanks Kootk

Any reference for the following in ACI

1)When used as seismic ties, your code probably specifies the required axial capacity as a portion of the restrained column axial load. Something to the tune of 0.25 x Pu x Peak ground acceleration.
and
2)b) An old rule of thumb is to design the grade beam for Vu=Pu/80 and Mu=Pu*L/160. L = span; Pu = highest axial load either end of beam.

 

[wannabeSE]

1) The seismic tie requirements are in the International Building Code. Your code may differ. See 2015 IBC section 1809.13 and 1810.3.13

http://codes.iccsafe.org/app/book/content/2015-I-Codes/2015 IBC HTML/Chapter 18.html

2) I can't help with KootK's rule of thumb.

 

[KootK]

1) Thanks WSE.

2) Makes an appearance in ACI 314.

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.

 

[drasticxxxx]

Ktook Could you refer to section in ACI318 2014 please?

Thank you all
the discussion was really useful

 

[KootK]

Ktook Could you refer to section in ACI318 2014 please?

Nope. If I knew it by heart, I would have provided it initially.

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.