Dual frame system in etabs according to asce-7-05 3

[ayelamayem77]

A dual system, is a structural system with the following essential features:

1. An essentially complete space frame provides support for gravity loads.
2. Resistance to lateral forces is provided by moment-resisting frames capable of
resisting at least 25 percent of the design base shear and by shear walls
(ASCE 12.2.5.1).
3. The two subsystems (moment-resisting frames and shear walls) are designed to
resist the design base shear in proportion to their relative rigidities
(ASCE 12.2.5.1).
to active the previous rules in etabs we have to make two models
the first model including all elements(slabs+beams+shear walls , etc) and apply all loads including all vertical loads + seismic loads + wind loads + etc...
[highlight #FCE94F]the second model the shear walls should be removed and 25% of seismic loads obtained from the first model should be applied in the second model my question what is the type of vertical loads should be applied to the second model if any?????
and what is meant by the first rule in dual-frame system ( An essentially complete space frame provides support for gravity loads.)????[/highlight]
best regards.

 

[salah0]

you have not to use two models for this.
You define one section cut for base shear wall, and anothere one for base columns. After calculation you can estimate if the ratio for the base shear is in the proportion of 25% or above for the columns using the value obtained for section cut..If not you modify the section of columns and shear wall to aim this values.

 

[salah0]

For the other part of the question all structure must provide support for gravity loads.

 

[ayelamayem77]

I made a model for reinforced concrete structure using Etabs
consists of columns shear walls and flat slabs i want the columns to take all the shear force under seismic load case
(my specific question haw can i prevent the shear walls from carrying any amount of the shear forces?????

 

[MrHershey]

You can modify in-plane stiffness for the walls to very low by assigning stiffness modifiers. If this is really what you want to do, you also need to be very careful in your detailing so that the walls cannot take the load in the actual structure. Just because the walls don't have any stiffness in the model doesn't mean they won't take any load in real life.

 

[johnbridge231]

MarkHirschi, in this way you are preventing the shear walls to carry gravity loads as well...

Analysis and Design of arbitrary cross sections
Reinforcement design to all major codes
Moment Curvature analysis

http://www.engissol.com/cross-section-analysis-design.html

 

[MrHershey]

Depends on which stiffness you modify. You could only modify horizontal stiffness and leave vertical alone if you wanted to.