I am designing a Seismic Moment Frame system in RAM Structural System and I am utilizing the built in RAM Connection module to help design the baseplate connections to the foundation. Per ASCE and AISC, the column base connection should be designed including Omega for seismic overstrength. When the loads export from RamSS and the connection rebuilds the combinations, it is correctly creating amplified seismic combinations that include Omega. If I look at the drop down load tab in the connection editing page, it shows the correct loads values, but when I go into the design results, it is reporting all 0's for the forces in those same combinations and is not designing the connection with Omega. Am I missing something? Does Connection not design for the Amplified Seismic cases?
As noted, the amplified seismic combinations are not currently considered in strength checks. I logged an enhancement not long ago to add this, details below. Meanwhile you can only get these to be considered by editing the combinations to be design type (note, you would have to change the Ram Connection - Load Combinations - Additional Configuration to not use Ram Frame combinations, restart Ram Connection, and then redefine the original combinations as type "design" for this all to work).
Enhancement 1095609: Option to consider steel amplified seismic type combinations for strength checks in base plates (e.g. for SMF frames) AISC 341-10
Reviewing AISC 341-10, this was the code provision D2.6c
6c. Required Flexural Strength
Where column bases are designed as moment connections to the foundation, the required flexural strength of column bases that are designated as part of the SFRS, including their attachment to the foundation, shall be the summation of the required connection strengths of the steel elements that are connected to the column base as follows:
(a) For diagonal braces, the required flexural strength shall be at least equal to the required flexural strength of diagonal brace connections.
(b) For columns, the required flexural strength shall be at least equal to the lesser of the following:
(i) 1.1RyFyZ (LRFD) or (1.1/1.5)RyFyZ (ASD), as applicable, of the column, or
(ii) the moment calculated using the load combinations of the applicable building code, including the amplified seismic load.
Hello Seth,
How about the current STAAD version with its Ram Connection module. I composed amplified seismic combinations within STAAD analytical modeling module. I selected them for connection design, but when I specify those combinations as amplified seismic the utilization ratio of that connection calculation pad goes to infinity? any clarification on that?
Is the "LVL_Brace" template noted in the image above something you have customized? I ran your model and added some SCBF Connections CBB_DA connections and the ratio is not infinity.
I was able to reproduce the issue with a CBB_DA connection, I just had to re-optimize. It crashed on me after that however, so I have not yet been able to check into the report details.
Looks like something in the connection of the Gusset to the Column, in the check of the angles. Here's the section of the report leading to an infinite ratio:
Resulting tension capacity due prying action [kip] 0.00 4.65 LC-2201-71 ∞ p. 9-12, p. 9-10
fv = F/(Ab*Nbolts) = 87.897 [kip] /(0.442 [in2] *4) = 49715.46 [lb/in2] Sec. J3.7
F'nt = min(max(1.3*Fnt - Fnt*fv/((1/W)*Fnv), 0.0), Fnt) = min(max(1.3*90000 [lb/in2] - 90000 [lb/in2] *49715.46 [lb/in2] /(0.5*54000 [lb/in2] ), 0.0), 90000 [lb/in2] ) = 0 [lb/in2] Eq. J3-3
(1/W)Rn = (1/W)*F'nt*Ab = 0.5*0 [lb/in2] *0.442 [in2] = 0 [kip] Eq. J3-2
pinner = min(p, s, 3.5*b) = min(3 [in] , 3 [in] , 3.5*1.685 [in] ) = 3 [in] p. 9-12
pouter = min(p, s, 3.5*b) = min(3 [in] , 3 [in] , 3.5*1.685 [in] ) = 3 [in] p. 9-12
a' = Min(a + d/2, 1.25*b + d/2) = Min(9.625 [in] + 0.75 [in] /2, 1.25*1.685 [in] + 0.75 [in] /2) = 2.481 [in] p. 9-12
b' = b - d/2 = 1.685 [in] - 0.75 [in] /2 = 1.31 [in] p. 9-12
r = b'/a' = 1.31 [in] /2.481 [in] = 0.528 p. 9-12
d = 1 - d'/p = 1 - 0.813 [in] /3 [in] = 0.729 p. 9-11
tc = ((4*B*b')/((1/W)*p*Fu))0.5 = ((4*0 [kip] *1.31 [in] )/(0.599*3 [in] *58000 [lb/in2] ))0.5 = 0 [in] p. 9-13
a' = (1/(d*(1 + r)))*((tc/tp)2 - 1) = (1/(0.729*(1 + 0.528)))*((0 [in] /1.38 [in] )2 - 1) = -0.898 p. 9-13
Q = 1 p. 9-12
Tavail = 4 * (B*Q) = 4 * (0 [kip] *1) = 0 [kip] p. 9-10
If I use a single plate rather than an angle, or some angle with more rows of bolts or welds I eventually get real numbers. I think in the specific case I reviewed the angle of the brace was shallow (just over 30 degrees) which makes this connection tricky (small vertical length).
Thank you very much for taking the time to address this. On the connection pads you created, please try to change the load type from "Design" to "Amplified Seismic". I think the only time when it actually checks the analysis requirement of section F2.3, is when you make that change. otherwise, it only checks load cases provided and gives you a warning that Amplified Seismic need to be used.
Thanks, I will review your reply. hopefully, this will resolve it.