tilt wall base fixity

[broncosfan]

I am using ENERCALC to design some tilt walls. ENERCALC lets the engineer select the ACI 318-02 procedure. Under this analysis procedure, you can select a base fixity for the tilt panel. How do you determine the amount of fixity at the base of the panel? The program let's you select a fixity from 0 to 100%. Also, what types of details are usually provided to give fixity at the base of the panel. Thanks.

 

[UcfSE]

I think you would be better off designing them with zero fixity. When you start getting fancy or designing outside the norm, you're asking for problems.

 

[hokie66]

Broncosfan,

If the panel is simply doweled to footing or slab, it is pinned. If you have to achieve fixity, the way I have seen it done is to provide a deep slot in the footing, which is in turn grouted when the panel is in place. Of course, the footing has to be designed accordingly for the overturning, etc.

 

[apsix]

In some cases the panels are dowelled to a footing and also fixed to a slab at say 600mm higher.
I wouldn't call that 100% fixity, perhaps 50 - 75%?

 

[youngstructural]

You also need to be aware of stress/strain relief because of rotation in the support (ie: Think P-Delta effects). I have relied on fixity at the base of a tilt-wall, but have only ever used a maximum of 20%, same as I would with a steel portal frame's base fixity. Perhaps personal paranoia, but it's what I have done, and will continue to do.

Good luck,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[youngstructural]

Just a further thought: I would buy 100% fixity if you ran bars perpendicular through the wall and then poured the floor slab composite around them. In effect you would have a beam-column joint in concrete at the base of your wall.

Regards,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[broncosfan]

Thanks for the info. Youngstructural: What type of detail at the base will typically give a 20% fixity.

 

[waytsh]

If you are in an area with a deep frost depth and your panel is sitting directly on your footing you can get some fixity from the 3+ feet of backfill. During the design of metal buildings we often had to be aware of the base condition of the panel. If the panel was going to be buried and backfilled the building had to be held to a much higher deflection limit since the panels would tend to crack at the grade if they had not been design for fixity and/or the building was too flexible. Particularly if a concrete slab or pavement was then installed over the grade and against the panel.

 

[youngstructural]

Broncosfan: As long as I can transfer the moment induced, I will allow up to 20% without any particular detailing. So long as you comply with good detailing practices (retraining bars, stirrups, etc)and have the capacity through the connection, 20% is reasonable. Unfortunately I have never seen a research paper to this effect, but I have been taugh the principle by two eminent (and long in the tooth) engineers. It has yet to fail them in 80+ years of professional engineering practice, and I would be shocked were it ever to fail me.

My personal opinion and interpretation of this guidance is that going above this level would require specific detailing.

Cheers,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[youngstructural]

Oh, and with a nod to waytsh: Make damn sure you have the full load path considered. As waytsh points out; you need something to ultimately hold this load.

Cheers,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...