R Value of a Moment Frame with a Fixed Base
R Value of a Moment Frame with a Fixed Base
(OP)
If I have a steel moment frame, does the base fixity have an affect on the R value used for seismic design? The R value for a cantilever column system is 1.5, and I wasn't sure if fixing the base of the moment frame would somehow create a combined system of moment frame and cantilever column requiring the use of the lowest R value.






RE: R Value of a Moment Frame with a Fixed Base
DaveAtkins
RE: R Value of a Moment Frame with a Fixed Base
The validity of a "fixed-base" is also somewhat debated. It will be pretty hard to get something to behave truly as "fixed". So make sure you pay particular attention to not just strength but also stiffness of the base connection and supporting foundation.
RE: R Value of a Moment Frame with a Fixed Base
I was a bit unsure, I guess, of what a cantilever column system consisted of. I was thinking that it may be any column with a fixed base, but I now am understanding it as columns with fixed bases that are not part of moment frames. Would this be a correct understanding, or too simplistic?
RE: R Value of a Moment Frame with a Fixed Base
See ASCE 7 section 11.2 for the definition of cantilevered column system. It states that such a system is defined as a system where "lateral forces are resisted entirely by columns acting as cantilevers from the base."
Maine EIT, Civil/Structural.
RE: R Value of a Moment Frame with a Fixed Base
RE: R Value of a Moment Frame with a Fixed Base
RE: R Value of a Moment Frame with a Fixed Base
RE: R Value of a Moment Frame with a Fixed Base
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RE: R Value of a Moment Frame with a Fixed Base
A cantilevered column system has single curvature.
Mike McCann, PE, SE (WA)
RE: R Value of a Moment Frame with a Fixed Base
Maine EIT, Civil/Structural.