R coefficient for knee braced elevated deck

[bdruehl]

do i need to use a 1 1/2 for R for a free standing raised retail storage deck (mezzanine)... seismic design class E and and a required 25% of live load included for siesmic (right?) makes 31.25 + 10 dl = 41.25 # /sf!!! with R=1.5, im getting a .7E of .36!! so 15#/sf of storage! thats a lota lateral!

 

[bdruehl]

If i use 1.5 for Cs as allowed by asce 12.8.1.3 then i can get it down to .231 W lateral... not bad i guess... anybody regularly employ this max 1.5 for Cs for less than 5 stories and < .5 second period structures?

 

[bdruehl]

so, i do calculations and im almost done and seem to find out that timber frames that already have to use a horrible 1.5 for R coefficient(unless you can tell me that a wood post beam with kicker is some other kind of siesmic resisting constructon table 12-2.1 asce7-5) arent even allowed in seismic zone E!!! oops... is that right ??? i cant build a knee braced mezzanine? doesnt seem right!

 

[JAE]

Shouldn't you be using Chapter 15 of ASCE 7-05?

Bottom of Table 15.4-2, "All other self-supporting structures..."

 

[bdruehl]

The storage is open to retail (the public), so i thought that 15 would direct me right back to 12 requirements... which i think it does for seismic loading, but you are right, at least there is an argument that this falls into "all other self supporting" and therefore, a "carport" storage mezzanine is allowed. The r -value is worse though! My knee connections are already a bit max'd out as it is ....20% additional from 1.5 to 1.25 R.... doesnt help!

im going to suggest that we do shear wall corners for the mezzanine, as opposed to strictly posts.

any other thoughts? also, of great importance to me... anybody else regularly employ the 1.5 Ss Max (12.8.1.3) It matters a great deal in zone D-F. When I do, i dont apply the .7E, but certain building officials apparantly are used to seeing unreduced Ss being used in load comb 8.