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 3.
Interior span of continuous beam with 3 or more spans:
EQUATION:
ru = 16Mp/L
(89)
EQUATION:
KE = 300EI/L4
(90)
(3) Design for Flexure. The design of a structure to resist the
blast of an accidental explosion consists essentially of the determination
of the structural resistance required to limit calculated deflections to
within the prescribed maximum values. In general, the resistance and
deflection may be computed on the basis of flexure provided that the shear
capacity of the web is not exceeded. Elastic shearing deformations of steel
members are negligible as long as the depth-to-span ratio is less than about
0.2 and, hence, a flexural analysis is normally sufficient for establishing
maximum deflections. For any system for which the total effective mass and
equivalent stiffness are known, the natural period of vibration can be
expressed as:
EQUATION:
TN = 2[pi](me/KE)1/2
(91)
where,
me
=
mKLM, the total effective mass per unit length and
KLM
=
mass factor from table 10
KE
=
ru/XE = equivalent spring constant
ru
=
ultimate resistance
XE
=
equivalent elastic deflection
In the low and intermediate pressure ranges, it is recommended that the
structure in the preliminary stage be designed to have an equivalent static
ultimate resistance equal to the peak blast force for a reusable structure
and 0.8 times the peak blast force for a non-reusable structure.
(4) Design for Shear. At points where large bending moments and
shear forces exist, the assumption of an ideal elasto-plastic stress-strain
relationship indicates that during the progressive formation of a plastic
hinge, there is a reduction of the web area available to shear. This
reduced area could result in an initiation of shear yielding and possibly
reduce the moment capacity. The yield capacity of steel beams in shear is
given by:
EQUATION:
Vp = FdvAw
(92)
where,
Vp = dynamic shear capacity
Fdv = dynamic shear yield strength of the steel
Aw = area of web
2.08-133
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