Title: Shallow precast concrete floor
without beam ledges or column corbels
Date Published: July - August 2019
Volume: 64
Issue: 4
Page Numbers: 41 - 54
Authors: George Morcous, Eliya Henin, and Maher K. Tadros
https://doi.org/10.15554/pcij64.4-02
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Abstract
The use of shallow floor systems in office buildings is
desirable because it reduces the overall building height
and saves on the cost of architectural, mechanical, and
electrical building systems. Precast, prestressed concrete
floors consisting of hollow-core slabs on inverted-tee
beams are known for their superior quality and speed of
construction. However, when the depth of the hollow-core slab, inverted-tee beam ledge, and column corbel are added, the total floor depth becomes significantly
larger than that of cast-in-place, post-tensioned slabs.
This paper presents a system by which the hollow-core
slabs are framed next to the beam rather than on top of a
ledge, and the beams are framed into the column without
the aid of a permanent concrete corbel. For the development of the system, a 30 by 30 ft (9.1 by 9.1 m) bay size
is considered typical for office floors. Hollow-core slabs
that are 8 in. (203 mm) deep are supported on 10 in.
(254 mm) deep beams using a new beam–hollow-core
connection that is designed using shear-friction theory.
Methods of temporary support until the composite topping is cured are presented. Full-scale testing confirmed
satisfactory performance.
A beam–column connection is also developed using column recesses at the beam location and reinforcing bars
through a void in the column to allow the beam to be
continuous and its reaction to be resisted by the column
without the conventional corbel. A temporary steel angle
support is used until the connection grout is hardened.
Full-scale testing of the beam–column connection
showed excellent behavior. The main advantages of this
shallow floor system are its high span-to-depth ratio (up
to 30) and its efficient and economical production and
erection techniques. Some of the features of the developed system were implemented in a four-story office
building in Lincoln, Neb. Experience with this application is also discussed.