# why we commonly use only two saddles in horizontal pessure vessel

#### dhaya

as using more than two saddles make pressure statically indeterminate both internally and externally
what is the mean of statically indeterminate ??
when number of unknowns exceeds the number of equations to find horizontal and vertical forces this type of condition is called statically indeterminate
what is the degree of indeterminacy ??
the number of unknowns that are more than the number of equations are called degree of indeterminacy.

degree of indeterminacy = number of unknowns - number of equations
http://125share.com/search-bk.phpReference for for detail

#### ChipB

PHF Helper
dhaya - is there a question here? If you're looking for comments on your answers, I would offer these:

First I assume here that your term "saddle" as applied to a pressure vessel has to do with how the vessel is supported. "Statically indeterminate" means that you can't determine forces and/or moments using principles of statics alone. You are correct that one example of a statically indeterminate problem is when there are more than two supports for a rigid body, as simply setting sum of forces = 0, sum of y forces = 0 and sum of moments = 0 results in too few equations to resolve the unknowns. However this should not limit the use of supports in actual structures. Obviously three or more supports may be advantageous to help spread loads across a foundation, or for redundancy. To determine the forces at each support in a statically indeterminate system requires techniques other than statics, which you will learn when you get to beam equations and start to apply techniques involving differential equations rather than simple statics.

BTW - the link you providesd is flagged as "unsafe" by my browser, so I did not open it.