Beenay Beenay

I don't think helping out somebody in their individual blind spots is a drawback. These individual problems are the ones that bring out the generic issues that everyone can benefit from and create the talking points. It helps identify the problems and search for the solutions that anyone can face in their individual projects and endeavors. Generic issues and topics can also be addressed in colleges or universities or through books. These individual sharing and caring and learning from it is where these types of forums shine at and I think this is actually the beauty of these types of forums rather than a drawback. Helping out individuals in their specific issues is I think one of the most beautiful and useful advantage of this type of forum. I don't think anybody should be discouraging people from using these types of forums in such ways and benefiting from it.

ok! Thanks a lot for your helping hand.

@abbaskhan2294 I downloaded the file you have uploaded in your previous reply, but it still says, it has been created in later version of etabs than mine.

@mortezamobariz Thanks a lot for taking time to check my model. But I think here is one problem. I mistakenly uploaded the etabs file in which I have deleted all the cantilever beams and just slab has remained. I am uploading the file that has cantilever beams. house for thulo kancha uncle 2.EDB

I have used 12 inchx14inch beam too. The the problem is the same. I have uploaded the model at the begining of this topic,

I have checked the loads and even remodeled it few times in two version of etabs ie 2015 and 2016. I hope someone can find my blind spot in modelling or loading.

I have attached the plan and elevation of the model showing cantilever failure. I have also attached the shear design summary of one of the cantilever beams. Shear force in it is 830 KN which is greater than the reaction at the base of the column for normal residential building of 4 story and 12ftx12ft grid.

Thank you for your support. You guys in Sepakistan have been most supportive so far. I couldn't open the etabs file you uploaded because it might have been saved in the later version of etabs than mine. I did not modified any modifier from default value of 1 except for torsional constant in which I plugged in 0.001. I think its ok to leave all the modifiers at the default value of 1. Plugging in the value of 0.35 and 0.7 for beam and column respectively give less reinforcement. These modifiers are only supposed to be used in deflection check from what I have read in discussion forums. Only changing one modifier i.e. torsional constant to 0.001 to avoid torsion in beams, hence avoiding the beam failure in torsion(as beams can transfer torsion to columns and other beams as moment) should suffice for a good design) from what I have read in forums. I was just wondering how can "not changing" the modifiers to the above values can show the cantilever beams as failed. I know modifying the torsional constant to negligible value to avoid beam failure in recommended. But I think leaving other modifiers to value of 1 should not be a problem. I would appreciate if you can provide any explanation or clarification on this issue. Thanks a lot!

I did that. I provided torsional constant of 0.001.

Actually there is nothing much to elaborate. I have designed many buildings in etabs. I came across this problem in two buildings and I cant find the cause. Cantilever beams just fail in shear no matter how big of a section I assign or how little load I apply. Its just a regular building. Nothing exceptional about it. I have remodeled it few times in Etabs 2015 and 2016 to see if there is some issue with the version of etabs that I am using. But I came across the same problem in both versions. But cantilever beams don't fail when I remove earthquake load pattern. Design summary show very very high unrealistic shear force. I don't know the reason why. thanks for showing interest.

cantilever beam fails in etabs no matter how big section I assign. Please help! my etabs file in attached herewith. cantilever beam failure elevation view grid 2.bmp cantilever beam failure.Docx shear failure in cantilever beam.bmp house for thulo kancha uncle 2.EDB

triangular load can be provided by assigning non-uniform shell load via equation as described in etabs documentation. My issue is how do I find the reinforcement for the out of plane forces in retaining wall or basement wall. I think what etabs gives is the reinforcement for the in-plane forces assuming it a shear wall by default. But retaining wall or basement walls are different animals. they are simply a cantilever slab or a two way or a one-way slab just placed vertically. how do I design a vertical slab? or get etabs to treat wall as a slab rather than shear wall?

C/B ration should be greater than 1. It should be 1.4 according to IS cod 2016, 1.3 according to eurocode, 1.2 according to ACI code. It ensures that moment capacity of columns at a joint is greater than that of beams. B/C ratio is inverse of C/B ratio. I should be smaller than 1.

higher the story, lower will be the reinforcement in column due to less gravity load and seismic shear in it. But beam reinforcement remain same in all stories because the gravity and seismic load remain same in beams in all stories. As you go up, the cloumns become weaker and weaker bur strength of beam remains same so the C/B capacity ratio (opposite of B/C capacity ratio) become lower and lower. on top of that, at the top story joints there in only one column end at the bottom of the joint but two beam ends so two beam capacity is added for calculation for C/B capacity ratio but there in only one column capacity. So in the top joint C/B capacity is even drastically reduced. Wheres in all other stories except the top story each joint has at least to column ends and the joints in the middle have two beam ends. Here, moment capacity of two columns are added to calculate B/C capacity ratio. Also, moment capacity of two beams are added.

how would steel bars effect the modulus of elasticity of concrete section? I need the moment of inertia and modulus of elasticity of reinforced concrete section with effect of percentage of steel. actually I need it because I need stiffness of column to calculate the stiffness of whole story of the building. I modeled a RC building in etabs. etabs gives me stiffness of the story after I run the analysis. but i haven't even run design. How did it calculate the story stiffness even before the reinforcement percentage in column is determined. Is it calculating stiffness of columns with no reinforcement in it ? or is it calculating stiffness of column with minimum required percentage of steel? will it change the stiffness of columns and then the stiffness of whole story after I run design in accordance with the amount of steel it calculates for each column? is the stiffness of the whole story sum of stiffnesses of all the columns of that story?