Civil Engineering Reference
In-Depth Information
TABLE 3.4
Safety Factors Based on API RP2A
Loading
Axial
Tension
Hoop
Compression
Design Condition
Bending
Axial Compression
Where the basic
allowable stresses
would be used (e.g.,
pressures that will
definitely be encoun-
tered during the
installation or life of
the structure)
1.67
F
y
/
F
b
1.67 to 2.0
2.0
Where the one-third
increase in allowable
stresses is appropriate
(e.g., when consider-
ing interaction with
storm loads)
1.25
F
y
/1.33
F
b
1.25 to 1.5
1.5
3.7 TUBULAR JOINT DESIGN
In older versions of API RP2A, punching shear governed the design of the
tubular joints. The historical development of the API RP2A-WSD provisions
clarifies the background of the most recent major updates. According to
Marshall
and Toprac (1974)
, the third edition of API RP2A-WSD, issued in 1972, intro-
duced some simple recommendations based on punching shear principles. The
fourth edition introduced factors to allow for the presence of load in the chord
and the brace-to-chord diameter ratio (
). In the ninth edition, issued in 1977, dif-
ferentiation was introduced in the allowable stress formulations for the joint and
loading configuration, i.e., T/Y, X and K.
Between 1977 and 1983, much work was done, including large-scale load
tests to failure, to improve the understanding and prediction of joint behavior.
This work culminated in the 14th edition of API RP2A-WSD, in which the
punching shear stress formulations were considerably modified and included
a more realistic expression to account for the effect of chord loads, as well as
providing an interaction equation for the combined effect of brace axial and
bending stresses. The 14th edition also introduced the alternative nominal
load approach, which gives equivalent results to the punching shear method.
The guidance then essentially remained unchanged for all editions up to the
21st, although further recommendations were added on load transfer through
the chord in the 20th edition (1993).
β
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