Are the design limitations in this article still valid for ACI318-14 for Sway Frame Columns in RAM Concrete? Have there been any progress on the open defect and enhancement numbers referenced? communities.bentley.com/.../ram-concrete-column---aci-slenderness-design
Frame Column, Sway These columns are designed using lateral forces from the RAM Frame Analysis and gravity forces from either RAM Concrete or RAM Frame (see option in RAM Concrete Column – Criteria – Column Design – Design Checks/Forces tab). The design procedure follows the moment magnification procedure for sway frames in ACI 318-05 10.13. The equation for the magnified end moments is M = Mns + Delta_Sway*Ms, where M = total magnified end moment Mns = non-sway moment Delta_Sway = sway moment magnifier Ms = sway moment In previous versions, ACI 318 permitted magnified sway moments (Delta_Sway*Ms) to be determined from an elastic, second order analysis (see ACI 318-05 10.13.4.1). This is the assumption that is used in RAM Concrete, and a sway moment magnifier of 1 is assumed. Due to this assumption, P-Delta should always be included in the RAM Frame Analysis. The non-sway moments are the gravity moments, which are taken from RAM Frame or RAM Concrete. In the ACI equation above, the non-sway moments are not magnified. If the option to use gravity forces from RAM Frame is used, the analyzed gravity load cases would include second-order effects from the P-Delta analysis. In most cases, the story displacements associated with the gravity load forces are small, so the increase in forces due to P-Delta effects should also be small. If there is a concern about using an amplified non-sway moment due to P-Delta effects, then gravity forces from the RAM Concrete analysis should be used to design the columns. For slender columns with high axial loads, the maximum moment may be between the ends of the column and P-delta effects can be important. For this reason, the ACI 318-05 and earlier separated columns for which the slenderness (lu/r) was greater than 35/sqrt(Pu/f’c/Ag). When this threshold was exceeded, the program calculated from the following equation (see ACI 318-05 10.13.5) M = Delta_NonSway*(Mns + Delta_sway*Ms) This provision was removed in ACI 318-08. In ACI 318-08 and later, the sway moments are required to be determined from one of the three slenderness methods (nonlinear second-order, elastic second-order, or moment magnification) for any slenderness ratio. As noted previously, the program is not equipped to run a nonlinear second-order analysis, the elastic second-order analysis does not include P-delta effects, and the sway moment magnification procedure is not implemented. The best the program can do is to combine the elastic second-order analysis with the moment magnification procedure using the same design procedure that is used when the ACI 318-05 is selected. ACI 318-08 and 318-11 10.10.2.2 requires second-order effects along the length of the member to be considered when the member is slender. Since P-delta effects are not included in RAM Frame, the program should apply 10.10.6 to slender, sway columns. This is not currently done by the program. This is logged as Defect #215527 in our database. Other Notes ACI 318-05 limited kl/r to 100 unless a non-linear, second-order analysis was used. This provision was removed in ACI 318-08 but was still enforced in RAM Concrete when ACI 318-08 or ACI 318-11 is used. Defect #215695 was filed for this issue, and it was corrected in v15.09.00. RAM Concrete does not check ACI 318-11 10.10.2.1: total moment including second-order effects shall not exceed 1.4 times the moment due to first-order effects. Defect #215527 has been filed with the development team. RAM Concrete does not calculate Q ACI 318-11 10.10.5.2 (Eq 10-10). Enhancement #275537 has been filed .with the development team. RAM Concrete does not include an option for using the moment magnification procedure for sway columns. Enhancement #215521 has been filed with the development team. ACI 318-05 10.12.3.1 included a lower bound of 0.4 for the parameter Cm. This lower bound was removed in ACI 318-08 but was still enforced in RAM Concrete when ACI 318-08 or 318-11 was used. Deflect #214767 filed for this issue, and it was corrected in v15.09.00. Slenderness effects are not included in RAM Concrete Shear Wall.
These columns are designed using lateral forces from the RAM Frame Analysis and gravity forces from either RAM Concrete or RAM Frame (see option in RAM Concrete Column – Criteria – Column Design – Design Checks/Forces tab).
The design procedure follows the moment magnification procedure for sway frames in ACI 318-05 10.13. The equation for the magnified end moments is M = Mns + Delta_Sway*Ms, where
M = total magnified end moment
Mns = non-sway moment
Delta_Sway = sway moment magnifier
Ms = sway moment
In previous versions, ACI 318 permitted magnified sway moments (Delta_Sway*Ms) to be determined from an elastic, second order analysis (see ACI 318-05 10.13.4.1). This is the assumption that is used in RAM Concrete, and a sway moment magnifier of 1 is assumed. Due to this assumption, P-Delta should always be included in the RAM Frame Analysis.
The non-sway moments are the gravity moments, which are taken from RAM Frame or RAM Concrete. In the ACI equation above, the non-sway moments are not magnified. If the option to use gravity forces from RAM Frame is used, the analyzed gravity load cases would include second-order effects from the P-Delta analysis. In most cases, the story displacements associated with the gravity load forces are small, so the increase in forces due to P-Delta effects should also be small. If there is a concern about using an amplified non-sway moment due to P-Delta effects, then gravity forces from the RAM Concrete analysis should be used to design the columns.
For slender columns with high axial loads, the maximum moment may be between the ends of the column and P-delta effects can be important. For this reason, the ACI 318-05 and earlier separated columns for which the slenderness (lu/r) was greater than 35/sqrt(Pu/f’c/Ag). When this threshold was exceeded, the program calculated from the following equation (see ACI 318-05 10.13.5)
M = Delta_NonSway*(Mns + Delta_sway*Ms)
This provision was removed in ACI 318-08.
In ACI 318-08 and later, the sway moments are required to be determined from one of the three slenderness methods (nonlinear second-order, elastic second-order, or moment magnification) for any slenderness ratio. As noted previously, the program is not equipped to run a nonlinear second-order analysis, the elastic second-order analysis does not include P-delta effects, and the sway moment magnification procedure is not implemented. The best the program can do is to combine the elastic second-order analysis with the moment magnification procedure using the same design procedure that is used when the ACI 318-05 is selected.
ACI 318-08 and 318-11 10.10.2.2 requires second-order effects along the length of the member to be considered when the member is slender. Since P-delta effects are not included in RAM Frame, the program should apply 10.10.6 to slender, sway columns. This is not currently done by the program. This is logged as Defect #215527 in our database.
ACI 318-05 limited kl/r to 100 unless a non-linear, second-order analysis was used. This provision was removed in ACI 318-08 but was still enforced in RAM Concrete when ACI 318-08 or ACI 318-11 is used. Defect #215695 was filed for this issue, and it was corrected in v15.09.00.
RAM Concrete does not check ACI 318-11 10.10.2.1: total moment including second-order effects shall not exceed 1.4 times the moment due to first-order effects. Defect #215527 has been filed with the development team.
RAM Concrete does not calculate Q ACI 318-11 10.10.5.2 (Eq 10-10). Enhancement #275537 has been filed .with the development team.
RAM Concrete does not include an option for using the moment magnification procedure for sway columns. Enhancement #215521 has been filed with the development team.
ACI 318-05 10.12.3.1 included a lower bound of 0.4 for the parameter Cm. This lower bound was removed in ACI 318-08 but was still enforced in RAM Concrete when ACI 318-08 or 318-11 was used. Deflect #214767 filed for this issue, and it was corrected in v15.09.00.
Slenderness effects are not included in RAM Concrete Shear Wall.
Most of those issues were fixed with 15.09. At lease one remains open. I updated the wiki with the latest info.
Thanks - I think #215527 is the big one that's open, because it's a hybrid approach to the problem, and really uses the techniques outlined in 318-05 but that are no longer in the code? Does this happen automatically or should we be running the design twice under the 05 and 14 codes?
Also a bigger a challenge now that everything has moved around in 318-14 is following the section references.