Etabs Beam Design: High Flexural Reinforcement At Midspan

[abdulqadeer29]

i am getting more reinforcement in bottom even though i am getting more moment values at support in few particular areas ..i am not sure why etab is showing more reinforcemet at bottom in these particular grids? any one having any idea?

 

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[WR1]

hmm! well u have secondary beams supported at mid of the main girders....you will defo have positive moment at the point...PL/4 formula !... and also do check shear here...and torsion too if u havent released it!

i didnt check ur model but just saw the snapshot...and yeah! check wich load combo is giving u this result..see whats in that particular combo..what loads?

otherwise do a simple thing....solve a single beam..with point load at the mid..and other udl from slab! and check whats the positive moment on (1.4D+1.7L) use for example wl²/10 or 11...just a rough value to compare the moments

or do it more precisely!

and you have put those slabs as shell? and the meshing every 96 inches..that too much...may be its ur initial model...best if u put it as membrane...as its not a flat slab..and if you are using shell make sure u manually mesh around the columns which are coming inside the slab...otherwise that column not gonna pick up the load...you can mix the system i mean put shell and mesh manually around these columns and put membrane and dont mesh it at other areas...always manually check the load transferred to these special columns on gravity..atleast...

Also, yar you have these load transfer errors

Warning: Area load transfer, Check ROOF, A1. Total loss = 33.523867 Kip. For load case LIVE.

Warning: Area load transfer, Check ROOF, A1. Total loss = 33.523867 Kip. For load case SDEAD.

Warning: Area load transfer, Check 5TH FLOOR, A1. Total loss = 67.047743 Kip. For load case LIVE.

Warning: Area load transfer, Check 4TH FLOOR, A1. Total loss = 67.047743 Kip. For load case LIVE.

Warning: Area load transfer, Check GROUND, A1. Total loss = 67.047743 Kip. For load case LIVE.

Warning: Area load transfer, Check LOWER GROUND, A1. Total loss = 67.047743 Kip. For load case LIVE.

Warning: Area load transfer, Check BASEMENT 2, A1. Total loss = 67.047743 Kip. For load case LIVE.

listen....if you get warning message when u click on run button...if u get this message never ignore..it..cz there is some area load transfer error...so stop running the model and fix it...how you gonna throw this load? in the sky?

and you can solve this error by deleting that area and draw it again....otherwise edit that area and check ur points are properly connected...i am sure they are not....

[abdulqadeer29]

got ur point ...

etab iz not mentioning those areas where load transfer error occurs, ....so how to check those areas where this load transfer error occur....???

[abdulqadeer29]

Rana Waseem @ one more point , i have checked my load combo's , but still getting same problem, etab is displaying end and midspan  moments correctly as i manually checked as well , but reinforcement issue is still there which i mentioned earlier....

[WR1]

if the moments are okay then reinforcement should be okay too.....if its a high seismic zone ETABS automatically checks for detailing and reinforcing limits...check for this ..may be thats the issue...it is in the concrete design overwrites..choose the appropriate seismic design category!

 

what do u mean etabs not mentioning where there is load transfer error....before running model goto anylysis menu and check model..tick on each option and it will report you the errors...just note down the area label names and then manually check on the particular floor where is that area with the same label name...if its difficult for example in a large plan then export points to excel and search for the label and see what are the connected points and then export the point coordinates and search in excel what is the x and y of that point....hope u got it!

[abdulqadeer29]

got ur point...

i have removed those errors which i were getting earlier...reduce mesh size as well..but still getting same results problem in case of beams../

[WR1]

tell me one thing! if the moments are okay then what is the problem in the reinforcement?