I think that your critique might br omitting the constructability angle. Consider this; The bottom bars might have been designed like that for uniformity and ease of construction. 5 feet of a single #16 bar might not be worth differentiating the top and bottom teinforcement of the beam, especially if its a part of a continous bea. 3#16 bars on the top could be sufficient to carry the negative moment. The bars on the bottom, however, might just be a continuation of the reinforcement of the neighbouring span left like that on purpose.
Another method in the cantilever beam is to provide hanger rebar along the junction. The spacing of the stirrups along the junction should be nearer with 50mm space, then 100mm, then at the end with 150 to 200mm.
So in case of cantilever the hogging occurs which means the tension in the upper zone and compression in the lower zone of beam that's why we always provide rebars especially in tension zone as steel can carry very powerful tensile loads without failure. We also provide steel in compression zone also but we use it very less as concrete is sufficient to carry the highly compressive loads and stresses. Just try to avoid or make less rebars in compression zone! What about torsional stresses? Where we will give torsional rebars if there is a chance of torsion???
I am a structural engineer. I think your structural engineering knowledge is based on the office designs. The construction site people may be not qualified as you. They provide same steel at top and bottom in a cantilever because to avoid mistakes of placing smaller diameter bars at top. Also it will cost minimum compared to the failure of the cantilever. Stirups no need to be closer at the support. Provide what is required. People do mistakes at site. Think practical than the book work.
Rebar in middle height of section could be torsion reinforcement. Cantilevers should be designed to withstand tension on both top and bottom in case of moment reversal and vertical seismic forces. Continuous rebar over columns should be sufficient for development length if amount of steel rebar is correct. Hooks on hoop reinforcement should be 135 degrees and spacing should be checked for VP.
Hello, im just a student so im sorry if my comment dosnt make sence. I remember, that we were told, that if the beam is to high we should add a rebar in the middle it relates to capacity of main diagonal (sorry not sure whats the right transcription)
that is correct. in EC2 if the beam height is above 700mm you provide additional "side" reinforcement. this is both for constructive purposes and to take torsion
@@emanuellallawmkima3750 it depends on the beam height. If it is above 700mm, but less than 1000mm you just need 2 constructive bars (1 on each lateral face) tied by a tie or stirrup. If it's above and there is no significant torsion, you place these constructive bars 400mm apart. So more than 1 per face can occur. (have not seen more than 2 in my practice)
Because concrete is weak in tension and in cantilver beam at the top of the neutal axis is in tension and below that is compression.... to make it safe from failure more r/f is provided on the top side.
I'm quite scared about the structural capacity of buildings in your country/area after seeing this amateuristic way of correctly determining the needed amount of reinforcement...
You can see that the stirrups are closely spaced near the fixed end.the fixed end is the region where the shear force will be max in a cantilever beam. We provide stirrups to resist shear force and so the region near the fixed supports have closely spaced stirrups. But on the other hand the free end of the cantilever has relatively low or even negligible shear stree. So it is unnecessary and uneconomical to provide more stirrups at the free end. I hope you get it. Thanks
Bars taken from continuous beam connected to the cantilever portion should be fine, so regular rebars of 3 on top and bottom shouldn't be a problem, two extra bars at the middle might be torsion bars but for that depth might not have required so yes could have been used at the top. Stirrups of 4" spacing should also be fine but considering the 5' of cantilever, shorter spacing would be better, but I've never seen use of just 2" stirrups spacing even for any cantilevers.
Wont the top flange of the beam provide lateral stability? so the beam wont really experience a moment about the weak axis, so the steel in the midsection will be redundent.
@@louiszadupreezwell designer probably used staad where slabs aren't modelled as part of the analytical model so cantilever ends up with side face reinforcements for torsion which is conservative designwise
Wastage of steel rods. Wait man. It would be answered by person who designed this structure. You are just a site engineer and your work is to make sure to implement the structural drawing
Exactly. Dude is going on passing comments like he has designed the structure. He doesn't even look at the drawings, what the structural engineer has provided. Because of guys like him, many of the beginners think whatever he is saying is right.
@@mukundkrishna5161 exactly. I've come across so many videos where these people are sounding like they are some sort of authorities. You would find site engineers without any clue about how to do structural design manually or by using software. These guys just follow right hand rules( past practices).
