Frederick Leuchte
Structural
Hello everyone,
I am designing a 25-story building with the ASCE 7-22, and have got some questions about the new seismic provisions of this standard.
[ol 1]
[li] When computing the design story drifts in accordance with Section 12.8.6, do we now have to consider the following load combination?
1.0*D + 0.5*L + 1.0*E[sub]h[/sub] = 1.0*D + 0.5*L + Q[sub]E[/sub],
where L is equal to 0.4*L[sub]0[/sub] if the live loads do not exceed 4.79 kN/m[sup]2[/sup], and 0.8*L[sub]0[/sub] otherwise, instead of:
1.2*D + E[sub]v[/sub] + E[sub]h[/sub] + L + 0.15*S = (1.2 + 0.2*S[sub]DS[/sub])*D + Q[sub]E[/sub] + L + 0.15*S
0.9*D - E[sub]v[/sub] + E[sub]h[/sub] = (0.9 - 0.2*S[sub]DS[/sub])*D + Q[sub]E[/sub].
Note: Here ρ = 1.0, because of Section 12.3.4.1 Item 2.
Furthermore, this Section also seems to require the use of other expected gravity loads, such as snow, rain and roof live loads, which would imply the use of the more refined set of load combinations:
1.0*D + 0.5*L + 1.0*E[sub]h[/sub] = 1.0*D + 0.5*L + Q[sub]E[/sub]
1.0*D + 0.5*L + 0.5*(0.5*L[sub]r[/sub] or 0.3*S or 0.5*R) + 1.0*E[sub]h[/sub] = 1.0*D + 0.5*L + 0.5*(0.5*L[sub]r[/sub] or 0.3*S or 0.5*R) + Q[sub]E[/sub]
(with L taken as mentioned above, and L[sub]r[/sub], S and R perhaps taken as 0.5 times their design load values --- the 0.5 factor in front of (0.5*L[sub]r[/sub] or 0.3*S or 0.5*R) is another assumption I am making after noticing that the ASCE 7-22 standard seems to be silent on what set of load factors should one consider for L[sub]r[/sub], S and R at expected service level). I am just wondering if I am interpreting this Section correctly.
[/li]
[li] When designing the collector elements in accordance with Section 12.10.2, do we have to consider the following set of load combinations?
[ul]
[li] Basic load combinations as per Section 2.3.1:
1.4*D
1.2*D + 1.6*L + (0.5*L[sub]r[/sub] or 0.3*S or 0.5*R)
1.2*D + (1.6*L[sub]r[/sub] or 1.0*S or 1.6*R) + (L or 0.5*W)
1.2*D + 1.0*(W or W[sub]T[/sub]) + L + (0.5*L[sub]r[/sub] or 0.3*S or 0.5*R)
0.9*D + 1.0*(W or W[sub]T[/sub]).
[/li]
[li] Basic load combinations with seismic load effects as per Sections 2.3.6 and 12.10.2.1(a):
1.2*D + E[sub]v[/sub] + E[sub]mh[/sub] + L + 0.15*S = (1.2 + 0.2*S[sub]DS[/sub])*D + Ω[sub]0[/sub]*Q[sub]E[/sub] + L + 0.15*S
0.9*D - E[sub]v[/sub] + E[sub]mh[/sub] = (0.9 - 0.2*S[sub]DS[/sub])*D + Ω[sub]0[/sub]*Q[sub]E[/sub] + L + 0.15*S
with Q[sub]E[/sub] determined by the equivalent lateral force procedure of Section 12.8 or the modal response spectrum analysis procedure of Section 12.9.1.
[/li]
[li] Basic load combinations with seismic load effects as per Sections 2.3.6 and 12.10.2.1(b):
1.2*D + E[sub]v[/sub] + E[sub]mh[/sub] + L + 0.15*S = (1.2 + 0.2*S[sub]DS[/sub])*D + Ω[sub]0[/sub]*Q[sub]E[/sub] + L + 0.15*S
0.9*D - E[sub]v[/sub] + E[sub]mh[/sub] = (0.9 - 0.2*S[sub]DS[/sub])*D + Ω[sub]0[/sub]*Q[sub]E[/sub] + L + 0.15*S
with Q[sub]E[/sub] determined by Equation 12.10-1, which must be used in conjunction with Equations 12.10-2 and 12.10-3.
[/li]
[li] Basic load combinations with seismic load effects as per Sections 2.3.6 and 12.10.2.1(c):
1.2*D + E[sub]v[/sub] + E[sub]mh[/sub] + L + 0.15*S = (1.2 + 0.2*S[sub]DS[/sub])*D + ρ*Q[sub]E[/sub] + L + 0.15*S
0.9*D - E[sub]v[/sub] + E[sub]mh[/sub] = (0.9 - 0.2*S[sub]DS[/sub])*D + ρ*Q[sub]E[/sub] + L + 0.15*S
with Q[sub]E[/sub] determined solely by Equation 12.10-2. Since this time the seismic load effects do not include overstrength, Section 12.3.4.1 Item 5 does not apply, and therefore, ρ is not necessarily equal to 1.0. But not sure if I am interpreting this provision correctly, anyways.
[/li]
[/ul]
[/li]
[li] When designing the diaphragms (including the chords) in accordance with Section 12.10.1, do we consider the following?
[ul]
[li] Basic load combinations as per Section 2.3.1:
1.4*D
1.2*D + 1.6*L + (0.5*L[sub]r[/sub] or 0.3*S or 0.5*R)
1.2*D + (1.6*L[sub]r[/sub] or 1.0*S or 1.6*R) + (L or 0.5*W)
1.2*D + 1.0*(W or W[sub]T[/sub]) + L + (0.5*L[sub]r[/sub] or 0.3*S or 0.5*R)
0.9*D + 1.0*(W or W[sub]T[/sub]).
[/li]
[li] Basic load combinations with seismic load effects as per Section 2.3.6:
1.2*D + E[sub]v[/sub] + E[sub]mh[/sub] + L + 0.15*S = (1.2 + 0.2*S[sub]DS[/sub])*D + ρ*Q[sub]E[/sub] + L + 0.15*S
0.9*D - E[sub]v[/sub] + E[sub]mh[/sub] = (0.9 - 0.2*S[sub]DS[/sub])*D + ρ*Q[sub]E[/sub] + L + 0.15*S
with Q[sub]E[/sub] determined by the equivalent lateral force procedure of Section 12.8 or the modal response spectrum analysis procedure of Section 12.9.1. This load combination was added because of this mention in 12.10.1.1: "floor and roof diaphragms shall be designed to resist in-plane seismic design forces from the structural analysis but shall not be less than that determined in accordance with Eq. 12.10-1." Since none of the conditions set forth in 12.3.4.1 apply, ρ should not necessarily be taken as 1.0. But this is my own guess.
[/li]
[li] Basic load combinations with seismic load effects as per Sections 2.3.6 and 12.10.1.1:
1.2*D + E[sub]v[/sub] + E[sub]mh[/sub] + L + 0.15*S = (1.2 + 0.2*S[sub]DS[/sub])*D + Q[sub]E[/sub] + L + 0.15*S
0.9*D - E[sub]v[/sub] + E[sub]mh[/sub] = (0.9 - 0.2*S[sub]DS[/sub])*D + Q[sub]E[/sub] + L + 0.15*S
with Q[sub]E[/sub] determined by Equation 12.10-1, which must be used in conjunction with Equations 12.10-2 and 12.10-3. Here ρ = 1.0, because of Section 12.3.4.1 Item 7.
[/li]
[/ul]
[/li]
[/ol]
Thank you,
Frederick
I am designing a 25-story building with the ASCE 7-22, and have got some questions about the new seismic provisions of this standard.
[ol 1]
[li] When computing the design story drifts in accordance with Section 12.8.6, do we now have to consider the following load combination?
1.0*D + 0.5*L + 1.0*E[sub]h[/sub] = 1.0*D + 0.5*L + Q[sub]E[/sub],
where L is equal to 0.4*L[sub]0[/sub] if the live loads do not exceed 4.79 kN/m[sup]2[/sup], and 0.8*L[sub]0[/sub] otherwise, instead of:
1.2*D + E[sub]v[/sub] + E[sub]h[/sub] + L + 0.15*S = (1.2 + 0.2*S[sub]DS[/sub])*D + Q[sub]E[/sub] + L + 0.15*S
0.9*D - E[sub]v[/sub] + E[sub]h[/sub] = (0.9 - 0.2*S[sub]DS[/sub])*D + Q[sub]E[/sub].
Note: Here ρ = 1.0, because of Section 12.3.4.1 Item 2.
Furthermore, this Section also seems to require the use of other expected gravity loads, such as snow, rain and roof live loads, which would imply the use of the more refined set of load combinations:
1.0*D + 0.5*L + 1.0*E[sub]h[/sub] = 1.0*D + 0.5*L + Q[sub]E[/sub]
1.0*D + 0.5*L + 0.5*(0.5*L[sub]r[/sub] or 0.3*S or 0.5*R) + 1.0*E[sub]h[/sub] = 1.0*D + 0.5*L + 0.5*(0.5*L[sub]r[/sub] or 0.3*S or 0.5*R) + Q[sub]E[/sub]
(with L taken as mentioned above, and L[sub]r[/sub], S and R perhaps taken as 0.5 times their design load values --- the 0.5 factor in front of (0.5*L[sub]r[/sub] or 0.3*S or 0.5*R) is another assumption I am making after noticing that the ASCE 7-22 standard seems to be silent on what set of load factors should one consider for L[sub]r[/sub], S and R at expected service level). I am just wondering if I am interpreting this Section correctly.
[/li]
[li] When designing the collector elements in accordance with Section 12.10.2, do we have to consider the following set of load combinations?
[ul]
[li] Basic load combinations as per Section 2.3.1:
1.4*D
1.2*D + 1.6*L + (0.5*L[sub]r[/sub] or 0.3*S or 0.5*R)
1.2*D + (1.6*L[sub]r[/sub] or 1.0*S or 1.6*R) + (L or 0.5*W)
1.2*D + 1.0*(W or W[sub]T[/sub]) + L + (0.5*L[sub]r[/sub] or 0.3*S or 0.5*R)
0.9*D + 1.0*(W or W[sub]T[/sub]).
[/li]
[li] Basic load combinations with seismic load effects as per Sections 2.3.6 and 12.10.2.1(a):
1.2*D + E[sub]v[/sub] + E[sub]mh[/sub] + L + 0.15*S = (1.2 + 0.2*S[sub]DS[/sub])*D + Ω[sub]0[/sub]*Q[sub]E[/sub] + L + 0.15*S
0.9*D - E[sub]v[/sub] + E[sub]mh[/sub] = (0.9 - 0.2*S[sub]DS[/sub])*D + Ω[sub]0[/sub]*Q[sub]E[/sub] + L + 0.15*S
with Q[sub]E[/sub] determined by the equivalent lateral force procedure of Section 12.8 or the modal response spectrum analysis procedure of Section 12.9.1.
[/li]
[li] Basic load combinations with seismic load effects as per Sections 2.3.6 and 12.10.2.1(b):
1.2*D + E[sub]v[/sub] + E[sub]mh[/sub] + L + 0.15*S = (1.2 + 0.2*S[sub]DS[/sub])*D + Ω[sub]0[/sub]*Q[sub]E[/sub] + L + 0.15*S
0.9*D - E[sub]v[/sub] + E[sub]mh[/sub] = (0.9 - 0.2*S[sub]DS[/sub])*D + Ω[sub]0[/sub]*Q[sub]E[/sub] + L + 0.15*S
with Q[sub]E[/sub] determined by Equation 12.10-1, which must be used in conjunction with Equations 12.10-2 and 12.10-3.
[/li]
[li] Basic load combinations with seismic load effects as per Sections 2.3.6 and 12.10.2.1(c):
1.2*D + E[sub]v[/sub] + E[sub]mh[/sub] + L + 0.15*S = (1.2 + 0.2*S[sub]DS[/sub])*D + ρ*Q[sub]E[/sub] + L + 0.15*S
0.9*D - E[sub]v[/sub] + E[sub]mh[/sub] = (0.9 - 0.2*S[sub]DS[/sub])*D + ρ*Q[sub]E[/sub] + L + 0.15*S
with Q[sub]E[/sub] determined solely by Equation 12.10-2. Since this time the seismic load effects do not include overstrength, Section 12.3.4.1 Item 5 does not apply, and therefore, ρ is not necessarily equal to 1.0. But not sure if I am interpreting this provision correctly, anyways.
[/li]
[/ul]
[/li]
[li] When designing the diaphragms (including the chords) in accordance with Section 12.10.1, do we consider the following?
[ul]
[li] Basic load combinations as per Section 2.3.1:
1.4*D
1.2*D + 1.6*L + (0.5*L[sub]r[/sub] or 0.3*S or 0.5*R)
1.2*D + (1.6*L[sub]r[/sub] or 1.0*S or 1.6*R) + (L or 0.5*W)
1.2*D + 1.0*(W or W[sub]T[/sub]) + L + (0.5*L[sub]r[/sub] or 0.3*S or 0.5*R)
0.9*D + 1.0*(W or W[sub]T[/sub]).
[/li]
[li] Basic load combinations with seismic load effects as per Section 2.3.6:
1.2*D + E[sub]v[/sub] + E[sub]mh[/sub] + L + 0.15*S = (1.2 + 0.2*S[sub]DS[/sub])*D + ρ*Q[sub]E[/sub] + L + 0.15*S
0.9*D - E[sub]v[/sub] + E[sub]mh[/sub] = (0.9 - 0.2*S[sub]DS[/sub])*D + ρ*Q[sub]E[/sub] + L + 0.15*S
with Q[sub]E[/sub] determined by the equivalent lateral force procedure of Section 12.8 or the modal response spectrum analysis procedure of Section 12.9.1. This load combination was added because of this mention in 12.10.1.1: "floor and roof diaphragms shall be designed to resist in-plane seismic design forces from the structural analysis but shall not be less than that determined in accordance with Eq. 12.10-1." Since none of the conditions set forth in 12.3.4.1 apply, ρ should not necessarily be taken as 1.0. But this is my own guess.
[/li]
[li] Basic load combinations with seismic load effects as per Sections 2.3.6 and 12.10.1.1:
1.2*D + E[sub]v[/sub] + E[sub]mh[/sub] + L + 0.15*S = (1.2 + 0.2*S[sub]DS[/sub])*D + Q[sub]E[/sub] + L + 0.15*S
0.9*D - E[sub]v[/sub] + E[sub]mh[/sub] = (0.9 - 0.2*S[sub]DS[/sub])*D + Q[sub]E[/sub] + L + 0.15*S
with Q[sub]E[/sub] determined by Equation 12.10-1, which must be used in conjunction with Equations 12.10-2 and 12.10-3. Here ρ = 1.0, because of Section 12.3.4.1 Item 7.
[/li]
[/ul]
[/li]
[/ol]
Thank you,
Frederick
