To John Daley;
I have had similar conditions in a 1906 six story building in Pasadena.
Some of the hollow clay tile formwork has been removed over time for
various tenant improvements. The five-inch thick reinforced concrete
topping slab is adequate by itself to span between the steel beams. In the
past I have tended to ignore isolated zones of lost tile. Lately, however,
I have been re-thinking this.
A quick working stress computation using the topping slab as the
compression block with the buried steel tie rods between the tile units as
the tension side give a moment capacity for the composite floor system.
Anticipated moment demands on a per foot basis when multiplied by the tie
rod spacing seem to justify the original layout of the rods. When you
expose the original rods between the tiles, the rods are no longer taut. Is
the removal of the compressed tile forms related to the loss of the
pre-stress of the rods?
I have considered using a fiber-reinforced epoxy composite applied to the
bottom of the tiles in localized zones of the building. Doing this
throughout the whole building, however, may not be economically viable.
This system would potentially retain the existing tiles, support
replacement of missing tiles and increase the floor capacity. Computation
techniques for these types of composites have appeared recently in the ACI
Journals. A company in San Diego also markets this type of system. For my
project, the historic appearance of the ceilings are not critical as they
are concealed by modern T-bar systems (bracing of the T-bar is a separate
can of worms).
The clay tile around the steel beams is the original fire-protection for
the steel and it has to be renewed in some fashion if this tile is lost.
The topping slab has adequate fire-protection without the tile.
In California, many engineers are concerned about the cohesion of the
arched clay tile formwork systems during earthquakes. I haven't personally
observed global distress to these archaic floor systems after past
earthquakes even with some tiles missing prior to the shaking. More
discussion would be useful.
Michael Krakower SE
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