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2.
RECOMMENDED DESIGN STRESSES.
a. Structural Steel. The yield point of steel under uniaxial tensile
stress is generally used as a base to determine the yield stresses under
other loading conditions. The compressive yield stress of steel, for
example, is equal to Fy, the yield point in tension. The shear yield
stress is taken as O.55Fy. To determine the plastic strength of a section
under dynamic loading, the appropriate dynamic yield stress, Fdy, must be
used. This is to be equal to the dynamic increase factor times the
specified minimum yield stress of the steel. The dynamic yielding stress in
shear, Fdv, is taken equal to O.55Fdy.
TABLE 11
Dynamic Increase Factor, c
Pressure Range
ASTM A36  Steel
High Strength, Low Alloy Steels
Low to Intermediate
1.1
1.1
High
1.1 or a higher
1.1
value determined from
the actual strain rate
EQUATION:
Fdy = cFy
(80)
where,
c = dynamic increase factor
Fdy = dynamic yield stress in flexure
EQUATION:
Fdv = O.55Fdy
(81)
where,
Fdv = dynamic yield stress in shear.
b. ColdFormed Steel. The material properties of the steel used in the
production of lightgaged steel members conform to ASTM Specification A446
(Grades a, b, and c steel). In calculating the dynamic yield stress of
coldformed steel members in flexure, it is recommended that a dynamic
increase factor of 1.1 be applied irrespective of actual strain rate. The
value to be used in design should be:
2.08131


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