Leaderboard

Dear in normally earthquake resistant structure, it is not common to have large axia forces in the beams. So you do not need to check all members. Just for your own satisfaction you can check few beams. But if there are Transfer Girders or Beams connecting to tapered columns, beams supporting columns, then you need to check the axial force. In this case, in ETABS, you can just design that beam as column by providing in the section properties P-M2-M3 design Thanks Muneeb

Great answer thanks Muneeb.

Dear Abdul Qadeer, There are two points 1- You can add the stair in the structure and ramps in the model just to have a bracing in the members like column and retaining walls. This will provide you stiffness as well as the effective length of the other members reduced which is the actual and practical situation. As far as the addition of stairs and ramps for diaphragm concerned, you can not add these in the diaphragm. Basically as we all know diaphragm transfers the lateral forces to vertical members. The diaphragm design is basically the design of SLAB for inplane forces. If you have not design the slab for these inplane forces then you can not assume semi rigid or rigid diaphragm (In case of minor earthquake areas, normally the existing slab thickness will be enough and also not required by code to design diaphragm for minor earthquake areas). So diaphragm assumption will be valid if you provide a path to transfer the forces from Retaining wall to shearwall through slab at basement levels and from shear wall to slab at top levels. If there is an opening or there is a stair or ramp then you do not have any path to transfer the forces to the shearwall and you can not provide the reinforcement for inplane forces. In this case it is not good enough to model these ramps and consider them these are transferring the forces. Thanks Muneeb

According to ACI 318-08 Section 21.3.2, a structural member is to be treated as a 'beam', if the factored axial force DOES NOT EXCEED 'Ag f'c/10'. Otherwise, it will be treated as a 'column'. Regards.

IMO, the displacement should be applied to the nodes, located at the neutral axis level. If you are studying the effect of displacement normal to the horizontal plane, considering the beam as a linear member only, the displacement should be applied to all the nodes at NA level. Otherwise, displacement may be applied to one node at a time only. Displacement value should, of course, be 2 mm for each node. Regards.

One thing that I learned while dealing with above mentioned building is that area of the floor has significant effect on structural system to resist seismic loads. The building, under discussion, has an area of about 45000 sqft/floor. The building is 4 stories, the bay length is 26ft, the column size is 30 inches, and beams are 15x30 inches. Even then, one requires shear walls of about 130 ft length in both direction to satisfy strength and serviceability requirement of code. The shear in one wall exceeds the maximum limit set by the code if one uses lesser shear walls. The problem is base story shear, which is about 5000 kipps at second level.

Dear How r u designing the shearwall in shear? If shearwall is failing in shear then you can do following things as told by Mr. Umar 1- Try to increase the length of shearwall. The thickness increase will not matter too much. But if you can increase length that will be helpful to design shearwall in shear. 2- Try to increase the shear reinforcement in shearwall. 3- Try to increase fc' 4- Try to add some more shearwalls to reduce the total shear demand by structure. I think by these points of these four points you will be able to solve the issue because everything depends upon the shear force in shear wall. You also need to provide confinement in the confined zones as well for flexural reinforcement. Thanks Muneeb