abbaskhan2294

Try section modifier for torsion as 0.01 and then check. It may help

Hello everyone. I want to discuss this general issue of Etabs related to column reinforcement distribution along the stories. I usually observe that the reinforcement in the top story exceeds the bottom story whereas in convention if u go through the mechanics the load on the lowest stories is maximum as compared to the column at the top story at the same level. What can be the possible reason for this? Note that the columns size and material used are same throughout the stories. Also the reinforcement of columns in a high rise building at the topmost story is shown greater by etabs than the columns at the same position in the preceding story (normally a story or two below). I understand that is probably because of the reduction in the redundancy of the structural element?

Indeed it is a very tall retaining wall and constructing it in steps is a good option. I will suggest u to provide the stepped face on the opposite side of the backfill as it can cause stress concentration at the backfill end which can be a big problem.

Dear all, I'm designing a retaining wall with 22 ft height of stem and angle of internal friction as 30 deg. I thought of doing it in RCC but somebody told me that retaining walls have been casted in PCC with much more heights i-e above 50ft. Can anyone guide me on this as PCC is a much more cost effective approach as compared to RCC. Thanks.

In some cases "yes" and in some cases "no". Torsional irregularity is due to more stiffness at one corner as compared to the other corner. Illustration is given in the first figure where grid#9 had a full panel of shear wall where as in grid # 5 the length of the shear wall was restricted due to architectural issues so as grid#9 was more stiff as compared to grid#5 , the structure gave severe torsional irregularity. The solution I came upto was to either increase the stiffness of walls along grid#5 (which was possible to achieve by either increasing length of the panel or increasing its thickness or increasing the strength of concrete) or by decreasing stiffness of wall along grid #9 which was a more feasible option in my case. you can see the second figure i posted to control the torsional irregularity.

That must be a basement wall a type of retaining wall. The design of shear wall and retaining wall is no different, u just need to add in the load of the soil retained. the load can be added through the option given below.

6/5 rule is enough to satisfy strong column weak beam check. If u r interested in shear force at the joint, then the shear force at the support mid (maximum) incase of beams will be the one governing the design.

Yes u got that right. Or u can say that the ratio of the nominal capacity of the column to that of the beam should be greater or equal to 1.2 for strong and weak beam check. What do u want to check in beam-column joint? Shear particularly?

As per ACI code, for strong column and weak beam the nominal flexural capacity of the column must be greater than atleast 1.2 times of the beam flexural capacity. In Etabs the option displayed in the snap will do your job.

Yes that was a major issue and i did consider over-strength factors for the design of the structural members.

Thanks umer for your suggestion. But let me share what I did to overcome this problem. I figured that the topmost grid in x axis is too much stiff as compared to the bottom grid in x direction with shear walls. These shear walls were not in architectural planning but I had to add them for structure stability. Also I was not allowed to make the bottom grid concrete throughout again due to architectural issues. So I thought to decrease the stiffness of the topmost grid in x axis by reducing the length of the shear wall and luckily it worked to overcome the torsional instability in seismic zone 3. Below are the images of the remedial methods adopted.

The RCC structure below was checked in etabs for UBC-97 stability checks. It passed all the design and stability checks except torsional stability check i-e the ratio of the average displacements of the extreme corners were really high, the highest being 2.4. What can be the possible solution to overcome this issue. The structure consists of basement and G+3 stories.

I need design calculations or some example reference for the design of steel roof truss having UDL. As a result the members along with direct tensile and compression stresses are also subjected to secondary bending. I'm just confused about the strut chords in the truss and their design.

Rana what if i have 4 columns in a row at corner of mat footing then what should I do for option 2?

Once u have added bracing elements in between the frames now its upto you how u consider ur structure to behave either as Building frame system or dual system. My recommendation will be to use building frame system in Zone 1 ,2A and 2B and go for dual system in siesmic zone 3 and 4. Furthermore if u r going for building frame system modify the moment of inertia about x and y directions in the section modifiers of the columns as 0.1 for both x and y directions. If u r going for dual system let the section modifiers be as for moment resisting frame. Compute the total base shear and the base shear shared by the column. If the base shear shared by the columns is less that 25% of the total base shear you need to amplify the base shear. Again how you can amplify it? E.g : If base shear shared by the columns comes out to be 5% of the total base shear, go to load cases and for Earthquake loads in x and y direction change the factor to 5 as 5x5 = 25. and when u rerun the model design the columns for 25% of the base shear. Again another thing to note is that use the first model with no earthquake load amplification for design of bracing elements and the 2nd model with earthquake load amplification is to be used for columns design only. Hope you got it.

I have two questions related to mat footing design in SAFE v16. 1) How to calculate the width of the design strips of mat footing? 2) I imported the model base reactions to Safe but punching shear design is not checked. What can be the possible solutions of the problem?

Based on experience by professional engineers. You can search for literature related to serviceability of structures regarding this query.

For serviceability purpose we never allow drift or deflection greater than 1 in.