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Re: Foundations for a 3-pinned arch stadium

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Paul, the arch is a continuous curve, so it is perfectly flat at the apex.  I would like to understand your concern.  I can't see a mechanism forming until the top pin deflects to the level of the supports.  The geometry is a 200 ft span, with the central pin some 50 ft higher.

On 10/9/07, Paul Ransom <ad026(--nospam--at)> wrote:
> From: "Kevin Below" <kbofoz(--nospam--at)>

> I will ask potential
> arch suppliers what they expect for the allowable movement.  They may reply
> that it doesn't affect their structure, because of the central pin.  It may
> become an architectural constraint.

Is the arch configured to be nearly flat at the apex (central pin)? If so,
you have potential catastrophic problems with base movement. Recall those
structures classes where stability and mechanisms were discussed. Run a
quick model and look at the first order deflected shape.

> Any comments on the seismic aspect ?  The horizontal thrust could cause an
> appreciable movement during the vibrations of an earthquake if there were no
> tie-rods.
> The thing about passive resistance, as you all noted, is that there is no
> recovery after an extreme load.  Could there may actually be an accumulation
> of movements.  Any geotechs or seismic experts out there ?

There can be accumulation of movements, depending on specific conditions,
and seismic will lube the bearings, so to speak. What would be stopping the


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