Some features of CSI ETABS program that needs revision regarding capacity design to Eurocode 8:
BEAM:
1. while determining moment capacity of ductile beams, the program uses the moment calculated from analysis. this could be okay for beams with small difference between the amount of area of steel calculated and provided also if the contribution of the slab reinforcement to the flexural capacity of the beam(CEN 5.2.3.3(3)) is neglected. If the moment capacity of ductile beams is to be considered as per Eurocde the program should include:
2.since the moment capacity determined from the program is underestimated as mentioned above, the shear demand calculated for the non critical region is also underestimated. and also the sum of the moment capacity of the beam on both ends( i and j which is the shear demand from flexure capacity of the beam ) is divided by the whole span of the beam. this should be avoided by the program since the code states the sum of the moment capacity at both ends should be divided by the span of the beam less the critical region length at both ends of the beam. in order to do so the program should include a way to calculate the critical length of the beam or have a way for the user to input the data. to this end the shear demand calculated at the non critical region by ETABS is not conservative and code compliant.
COLUMNS
1. CSI has now included a feature to calculate the moment demand of columns based on weak beam strong column analogy. yet it still compares the moment demand from analysis of the column to beam. this should be corrected by making it based on moment capacity of the section and beam capacity should be based on the comments under beam section.
DUCTILE WALLS
1. The boundary element calculated by the program is vague on the procedure. since the boundary length depends on the amount of confinement required and the way the confinement is detailed, the program should include a way to account for this by interacting with the user.
2. Design Moment is directly taken from analysis. this is not conservative and code compliant when it comes to Eurocde. as per figure 5.3 of Eurocde 8 the moment envelope diagram for the given pier label shall be prepared by the program. otherwise the reinforcement resulting from the program isn't code compliant.
3. Shear is magnified as per the magnification factor provide by the user yet shear envelop diagram isn't prepared by the program. this should be modified, otherwise the shear demand calculated in the non-critical height of the wall by the program isn't conservative and code compliant.
GENERALLY
If the program includes automatic way of displaying the amount of lateral load taken by wall and frame it would make it easy to identify the structural system. although we now user several method to extract this output, automation would help.
P.s the above comments goes for almost all programs that claim they do capacity design as per Eurocode.
P.s Eurocode needs a whole lot of simplification and as I agree with Mr. ashraf codes are complicated.
BEAM:
1. while determining moment capacity of ductile beams, the program uses the moment calculated from analysis. this could be okay for beams with small difference between the amount of area of steel calculated and provided also if the contribution of the slab reinforcement to the flexural capacity of the beam(CEN 5.2.3.3(3)) is neglected. If the moment capacity of ductile beams is to be considered as per Eurocde the program should include:
a. A factor that account for the difference between area of steel calculated and provided
b. A way to include the amount of slab reinforcement contributing to the beam flexural capacity( either user provided or program calculated. (this feature has been Incorporated in CYPECAD)2.since the moment capacity determined from the program is underestimated as mentioned above, the shear demand calculated for the non critical region is also underestimated. and also the sum of the moment capacity of the beam on both ends( i and j which is the shear demand from flexure capacity of the beam ) is divided by the whole span of the beam. this should be avoided by the program since the code states the sum of the moment capacity at both ends should be divided by the span of the beam less the critical region length at both ends of the beam. in order to do so the program should include a way to calculate the critical length of the beam or have a way for the user to input the data. to this end the shear demand calculated at the non critical region by ETABS is not conservative and code compliant.
COLUMNS
1. CSI has now included a feature to calculate the moment demand of columns based on weak beam strong column analogy. yet it still compares the moment demand from analysis of the column to beam. this should be corrected by making it based on moment capacity of the section and beam capacity should be based on the comments under beam section.
DUCTILE WALLS
1. The boundary element calculated by the program is vague on the procedure. since the boundary length depends on the amount of confinement required and the way the confinement is detailed, the program should include a way to account for this by interacting with the user.
2. Design Moment is directly taken from analysis. this is not conservative and code compliant when it comes to Eurocde. as per figure 5.3 of Eurocde 8 the moment envelope diagram for the given pier label shall be prepared by the program. otherwise the reinforcement resulting from the program isn't code compliant.
3. Shear is magnified as per the magnification factor provide by the user yet shear envelop diagram isn't prepared by the program. this should be modified, otherwise the shear demand calculated in the non-critical height of the wall by the program isn't conservative and code compliant.
GENERALLY
If the program includes automatic way of displaying the amount of lateral load taken by wall and frame it would make it easy to identify the structural system. although we now user several method to extract this output, automation would help.
P.s the above comments goes for almost all programs that claim they do capacity design as per Eurocode.
P.s Eurocode needs a whole lot of simplification and as I agree with Mr. ashraf codes are complicated.
