Concrete tie beam 1

[hello12345hello]

A steel braced frame columns are supported on Spread Footing with tie beam between the columns. I have vertical and horizontal reaction from Frame. So designing tie beam i have to consider that has regular concrete beam with axial load (Horizontal reaction from column) ?

 

[7thSky]

hello12345hello

Normally if columns of the steel structure are braced i dont think you really need a Tie beam.Tie beam could be a compressive or tensile member it really depends.
if I were you and I would design a steel structure say 1 floor building and I wouldnt bother to provide tie beam however if my structure is multi story building i would provide Tie beam.

7thsky

 

[PUEngineer]

Based on the sketch that was sent. If the bracing is tension only, then I don't see the 'tie beam' in tension at any point. Even if it's not tension only bracing, I'm not sure it would ever be in tension.

Outside of a code requirement for the beam/strut, I would only provide the beam/strut if required to resist sliding.

 

[JLNJ]

The tie will serve to distribute the horizontal forces. Be conservative in your assumptions about which footing will resist how much sliding.

 

[ahmedhegazi]

Regardless of if this tie beam is subjected to tension force of no , i provide tie beams in most structure to avoid differential settlement which can be under vertical loads or due to any unexpected factor like leakage of water next to foundation,excavation next to next for any reason

 

[hello12345hello]

100 kip of horizontal load 10X10 Footing won't provide enough passive pressure resistance and Reaction from column is not much when its min. load combination. Can we consider that load transfer into tie beam and provide sliding resistance.?

 

[BAretired]

The tie/strut member will engage the other footing, but if the two footings combined lack the necessary passive and sliding resistance, additional foundations must be similarly connected until the required resistance is obtained.

BA

 

[msquared48]

Two additional thoughts:

1. The tie beam will limit lateral movement in the footings due to any seismic activity or subgrade movement.

2. If the beam is extended to other adjacent footings, it can become a grade beam where it can pick up additional dead load if needed, to resist overturning from the braced frame.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[hello12345hello]

BAretired,

if i will consider combine effects of both footings and Min. Load combination, say i have uplift on one footing and downward load on the other footing so Addtional load on other footing will help me to provide sliding resistance. (Sliding coefficient * Vertical Reaction). + (Passive Pressure reaction Times two from both footing). Correct?

 

[BAretired]

That is correct.

BA

 

[TLHS]

You might want to look into your code and make sure you don't need to use mechanical or welded splices for this member.

The Canadian code CAN/CSA A23.3 requires mechanical or welded splices for tension tie members, and does not allow lap splices. The definition in the appendix leaves some leeway for interpretation, but I think this is pretty clearly something that would fall under that clause. I wouldn't be surprised if there's a similar clause in the ACI code, given that they generally have the same history.

 

[JLNJ]

AISC has smilar provisions for a member in direct tension (i.e. "tension tie"), but there is some wiggle room provided in the commentary which talks about non-mechanical splices in less-critical tension members.

 

[hello12345hello]

I have compr. strut/tension tie beam between two footing. To check for overturning at footing base do i have to count overturning moment from Hori. Load.? I will count moment from overturning moment from uplift load.