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DESIGN BASES: PIPING DESIGN

Posted by Antony Thomas at Sunday, August 16, 2009

DESIGN BASES: PIPING DESIGN




Wind Load:


The majority of all piping system installations are indoors where the effects of wind
loading can be neglected. However, there are sufficient numbers of outdoor piping
installations where wind loading can be a significant design factor. Wind load, like
deadweight, is a uniformly distributed load that acts along the entire length, or that portion of the piping system that is exposed to the wind. The difference is that
while deadweight loads are oriented in the downward vertical direction, wind loads
are horizontally oriented and may act in any arbitrary direction. Since wind loads
are oriented in the horizontal direction, the regular deadweight support system of
hangers and anchors may have little or no ability to resist these loads. Consequently,when wind loading is a factor, a separate structural evaluation and wind load supportsystem design is required.

Determination of the magnitude of the wind loadings is based upon empirical
procedures developed for the design of buildings and other outdoor structures.
Analysis of piping system stresses and support system loads is accomplished by
using techniques that are similar to those applied for deadweight design.



Snow and Ice Loads:


Snow and ice loads, like wind loads, need to be considered in the design of piping
systems which are installed outdoors, particularly if the installation is made in the
northern latitudes. Since snow and ice loads act in the vertical direction, they are
treated the same as deadweight loads. In design, they are simply added as distributed
loads in the deadweight analysis.


Snow Loads.


ANSI/ASCE 7–95, Minimum Design Loads for Buildings and Other
Structures, provides recommendations and data for developing design loadings due
to snow. The methods used in this standard are generally applicable to sloping or
horizontal flat surfaces such as building roofs or grade slabs.

Ice Loads:


Ice storms are sporadic in the frequency of their occurrence and in
their intensity. Weather records dating back to the turn of the 20th century for a
typical midwestern state relate instances of ice storm deposits of 1/8 in (3.2 mm) to
4 in (102 mm) in thickness. The American Weather Book10 cites examples of ice
accumulations of up to 8 in (203 mm) in northern Idaho (1961) and 6 in (152 mm)
in northwest Texas (1940) and New York State (1942).


Seismic (Earthquake) Loads


Under certain circumstances it is necessary or desirable to design a piping system to
withstand the effects of an earthquake. Although the applications are not extensive,
piping system seismic design technology is well developed and readily accessible.
Many currently available piping stress analysis computer programs are capable of
performing a detailed seismic structural and stress analysis, in addition to the
traditional deadweight and thermal flexibility analyses. Most of these programs run
on desktop microcomputers.
Because of the higher construction costs and design complexities introduced by
the application of seismic design criteria, this type of work is normally done only
in response to specific regulatory, code, or contractual requirements.

EXTRACTED FROM PIPING HAND BOOK

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