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Fwd: Concentrated Load on Concrete Joist

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Treat the deck as a beam, running at right angles to the T-beams. Let =
this beam be supported by springs at the location of each T-beam. Apply =
your load at the actual location and get spring reactions under the =
various T-beams. These reactions would show you the share of each =

The stiffness of the springs can be computed by placing any load =
(preferably use a large value so that you do not loose significant =
digits in deflection results, perhaps 100 Kips would be OK) on an =
isolated individual T-beam, at such a distance from the support, where =
the heavy actual load is placed on one of such beams. Solve the beam and =
get its deflection, at the point of application of the applied load. Now =
your deflection divided by the applied (100 Kips, if you use this value) =
is the stiffness (force required to cause unit deflection).=20

The important question that I have still not answered is: what width to =
assign to the part of the deck slab being modeled as a =
beam-on-elastic-foundation. I am not very sure as to what width would be =
realistic. But all I can say is that larger the width you use, stiffer =
would be the beam-on-elastic foundation and, in comparison, more =
flexible would be the elastic supports and greater would seem to be the =
distribution of the real load to T-beams other than the one on which the =
applied load directly rests. If you use the actual contact width of the =
load as the width of the beam, perhaps you would tend to get a lower =
bound on the actual distribution. Actual distribution would be at least =
the computed value but possibly more.

I am sure someone can point out a better estimate of the width.

Rizwan Mirza, P.E.
Lahore, Pakistan

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Subject: Concentrated Load on Concrete Joist
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Richard Lewis, P.E.
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