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 (1) Detailed discussions and recommendations on the design of
connections for precast concrete structures can be found in PCI
publications, Design Handbook Precast Prestressed Concrete, Manual for
Structural Design of Architectural Precast Concrete, and Manual on Design of
Connections for Precast Prestressed Concrete. However, connections may
require modification to account for the effects associated with the reversal
stresses caused by rebound. Most of the connectors found in blast resistant
design consist of seated connections and embedded steel plates which are
connected by field welding "loose" steel plates or structural shapes to the
embedded plates. Other standard PCI connections, such as bolt and insert
connections and drilled-in-dowel connections are not recommended due to a
lack of test data concerning their behavior under dynamic loading. These
type of connections tend to fail because of concrete pullout and therefore
lack the ductility required for blast design.
(2) In the design of connections the capacity reduction factor,
[phi], for shear and bearing stresses on concrete are as prescribed by ACI
code, 0.85 and 0.7 respectively. As recommended by NAVFAC P-397, no
capacity reduction factor is used for moment calculations and no dynamic
increase factors are used in determining the capacity of a connector.
Capacity of the connection should be at least 10 percent greater than the
reaction of the member being connected to account for the brittleness of the
connection. In addition, the failure mechanism should be controlled by
tension or bending stress of the steel, and therefore the pullout strength
of the concrete and the strength of the welds should be greater than the
steel strength.
(3) The following connections are standard for use in blast design
but they are not intended to exclude other connection details. Other
details are possible but they must be able to transmit gravity ad blast
loads, rebound loads, and lateral loads without inducing moments.
(a) Column-to-Foundation Connection. The standard PCI
column-to-foundation connection may be used for blast design without
modification. However, anchor bolts must be checked for tension due to
rebound in order to prevent concrete pullout.
(b) Roof Slab-to-Girder Connection. Figure 62 shows the
connection detail of a roof panel (tee section) framing into a ledger beam.
The bearing pads transmit gravity loads while preventing the formation of
moment couples. The bent plate, welded to the plate embedded in the flange
of the tee, transmits lateral loads but is soft enough to deform when the
roof panel tries to rotate. The angle welded to the embedded plate in the
web of the tee restricts the panel, through shear action, from lifting off
the girder during the rebound loading. The effects of dimensional changes
this type of connection.
(c) Wall Panel-to-Roof Slab Connection. The basic concepts
employed in the roof slab-to-girder connection apply to the wall
panel-to-roof slab connection shown in Figure 63. The roof panel instead of
bearing on the girder, bears on a corbel cast with the tee section. The
angle that transmits lateral loads has been moved from the underside of the
flange to the top of the flange to facilitate field welding.
2.08-226
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