Laterl Analysis Question
Laterl Analysis Question
(OP)
I have a project that involves and existing building with a two-way slab floor system with concrete shear walls. I want to add steel braced frames as some of the shear walls are failing due to the additional mass of an additional floor we are adding. When using a mixed system for lateral such as this, do you use the lesser of the two R values?






RE: Laterl Analysis Question
RE: Laterl Analysis Question
RE: Laterl Analysis Question
RE: Laterl Analysis Question
Ordinary concentrically braced frame R=3.25
Therefore the R used should be 3.25, correct DST148?
This is true steellion.
I'm having to keep adding braces as the concrete shear walls want to pick up more of the load just as you said steellion. Another problem is that the building was originally designed in 1978 therefore the design needs to be brought to current code which is more then likely generating more seismic loading on the shear walls then it was originally designed....not to mention the additional loading coming for the new floor level we are adding.
RE: Laterl Analysis Question
As an aside - I live on the east coast with low seismic risk level.
To avoid using AISC 341-05 : Seismic Provisions for Structural Steel Buildings, we use R = 3 for structural steel systems not specifically detailed for seismic resistance. See ASCE 7-05, section 14.1.2 for guidance.
RE: Laterl Analysis Question
I'm experiencing its better to have a highr R value as it produces a lower Cs used in the Base shear formula. The R=5 presents a Cs=.069 (7% of the building weight) where as the R=3.25 presents a Cs=1.07 (107% of the building weight).
RE: Laterl Analysis Question
We better close this thread.
RE: Laterl Analysis Question