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Civil Engineering/Modelling of Lateral force resisting systems and RCC Design of Beam and Columns in Etabs

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Question
1.As per the definition of Building Frame System,the whole Lateral load to be resisted by the lateral load resisting system only of a building model. While modelling in Etabs, all the frame elements vertical (columns and shear walls) and horizontal (beams and slabs) will share the total lateral loads in proportion their stiffness. This will be ok for deformation compatibility of the system not resisting the lateral loads. At the same time, Lateral load resisting system shall be capable of taking the whole of the lateral load.

1.How can we model and allocate the whole lateral loads to only lateral load resisting shear walls using the 3D-Modelling in Etabs?

Similarly in case of Dual System also, the frame members shall be capable of resisting minimum 25% of the Lateral loads.

2.How can we allocate this 25% lateral load to the frame members in 3D-Modelling of Etabs.

3.In the case of RCC columns design the total reinforcement requirement is reported in Etabs the axis wise reinforcement requirement is not reported. How to distribute it?

4.The connectivity of slab elements to the columns is not considered while calculating the unsupported length, if there are no line elements, in Etabs design of columns. As slab connectivity will reduce the unsupported length of the column but it not considered in Etabs design. How can we overcome this problem? Same is the case when the line elements are not connected to centre of the column line elements although in physical condition there will be beam connectivity at one or other end of the columns?

5.Where is the check for long term deflection of beam in Etabs design of RCC beams and how can we modify or reduce the deflections by increasing the tension/compression reinforcements.

Regards'
Syed

Answer
Dear Syed

1,2 -  You should analyze the structure in several runs to tune the loading so that the main structure carry 100% of the code loading and the secondary one 25 % of it. For sure you may need to subject the structure to more than 100% of the code loading. You will need to neglect the secondary frame for one run and apply all the load to the main seismic resisting structure. You will find in this way the maximum drift of the main structure. When you tune the loading for dual system you should be certain of the total drift of the main structure to reach the maximum you analyzed the main structure. Hope being clear.

3- You define your own sections in etabs, you should have some try and error process to reach to a favorite result.

4- you can define dummy linear elements in floor levels.

5- The reinforcements are not good mean to restrict the deflections. Work on element size.

Regards
Beh

Civil Engineering

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Babak Esmailzadeh Hakimi

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