Special shear reinforcement including ties and stirrups
is generally required to allow large post-elastic behavior.
The designer should carefully balance the selection of
small but heavily reinforced (i.e., congested) sections with
larger sections with lower levels of reinforcement.
Connections for steel construction should be ductile
and develop as much moment connection as practical.
Connections for cladding and exterior walls to steel
frames shall develop the capacity of the wall system
under blast loads.
In general, single point failures that can cascade, produc-
ing wide spread catastrophic collapse, are to be avoided.
A prime example is the use of transfer beams and girders
that, if lost, may cause progressive collapse and are
therefore highly discouraged.
Redundancy and alternative load paths are generally good
in mitigating blast loads. One method of accomplishing
this is to use two-way reinforcement schemes where
U.S. Census Bureau, Bowie, MD
possible.
In many cases, the ductile detailing requirements for
In general, column spacing should be minimized so that
seismic design and the alternate load paths provided by
reasonably sized members can be designed to resist the
progressive collapse design assist in the protection from
design loads and increase the redundancy of the system.
blast. The designer must bear in mind, however, that the
A practical upper level for column spacing is generally
design approaches are at times in conflict. These conflicts
30 ft. for the levels of blast loads described herein.
must be worked out on a case by case basis.
In general, floor to floor heights should be minimized.
Unless there is an overriding architectural requirement, a
The following additional references are recommended:
practical limit is generally less than or equal to 16 ft.
Biggs, John M. Introduction to Structural Dynamics.
It is recommended that the designer use fully grouted and
McGraw-Hill. (1964).
reinforced CMU construction in cases where CMU is
The Institute of Structural Engineers. The Structural
selected.
Engineer's Response to Explosive Damage. SETO, Ltd., 11
It is essential that the designer actively coordinate
Upper Belgrave Street, London SW1X8BH. (1995).
structural requirements for blast with other disciplines
Mays, G.S. and Smith, P.D. Blast Effects on Buildings:
including architectural and mechanical.
Design of Buildings to Optimize Resistance to Blast
The use of one-way wall elements spanning from floor-to-
Loading. Thomas Telford Publications, 1 Heron Quay,
floor is generally a preferred method to minimize blast
London E14 4JD. (1995).
loads imparted to columns.
National Research Council. Protecting Buildings from
Bomb Damage. National Academy Press. (1995).
253
SECURITY
DESIGN
8.7
Structural Engineering
Revised March 2005 PBS-P100
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