topic Re: moment maps&provided reinforcement in Robot Structural Analysis Forum

moment maps&provided reinforcement

saclovitzky — Fri, 15 Dec 2017 11:35:50 GMT

Hello,

I have the following observations regarding moments maps and provided reinforcement,ie in a simply supported slab(one-way).

1. when the crack width is in default(0.30mm), the reinforcement in the "provided reinf" is almost identical when you based the reinforcement as per moment maps(ie, take the max moment in "moment maps" and simply do your manual calc for reinf design).

2. when the crack width is less that 0.30mm, definitely the reinfocrcement will increase in the "provided reinf",therefore, you cannot rely on the moment maps alone.

The reason for decreasing the "crack width" in the SLS parameters is for the increased reinforcement that will reduced deflection.

Anybody who had the same observation?

Any ideas will be greatly appreciated.

Re: moment maps&provided reinforcement

mustafahesenow — Tue, 19 Dec 2017 08:31:54 GMT

Hi @saclovitzky

Its exactly as per what you mentioned in your post.

The increasing of Reinforcement is to control cracking and deflection by adding more reinforcement to increase the effective moment of inertia which is depended on cracking moment.

Re: moment maps&provided reinforcement

Artur.Kosakowski — Tue, 19 Dec 2017 08:34:55 GMT

Hi @saclovitzky

What @mustafahesenow explained was demonstrated during the 5th Robot webinar as an alternative approach for reducing RC slab deflection with the aim of more uniform reinforcement distribution.

Re: moment maps&provided reinforcement

saclovitzky — Tue, 19 Dec 2017 10:23:18 GMT

@Anonymous and @Artur.Kosakowski, the reason for this post is I am bit alarmed due to the following;

1. if you do not have access to a finite element software and you rely only on spreadsheet and 3rd party element design module,
the basis of your result will be relying on maximum moment/shears and compared it to allowable L/d against actual L/d.

2. For example, if you have a simply supported slab with moderate loadings, it will pass on the criteria of allowable L/d
but most of the time it will fail on deflection based on finite element analysis(.ie, considering deflection = L/250).

2.1 one technique in ARSAP is to reduced crack width(ie, from 0.30 to .2, .15,.12 etc.) resulting in increased reinforcement but reduced deflection.
With corrrected deflection, I will yield a reinforcement,ie, of H16@100 using FEM while if I used a spreadsheet/TEDDS and passed the allowable L/d, it will only yield H16@175!

2.2 Having said that, ie, in simply supported slab, if the "provided reinforcement" suggested a bottom reinf(main bars) of H16@100 and H12@150
top bars, I have no problem with that but when it suggests that the secondary(perpendicular) bars shld be H12@150/H12@175, etc.,that's where my problem start. How come that secondary rebar exceeds what you set for in "Plate/Shell Reinf/Reinf/Bar dimension/d2,d2', both for 10mm dia?

For a simply supported slab, it makes sense for me, that the main reinforcement(and its top bars) are critical in controlling deflection but not secondary(perpendicular) bars.

Does ARSAP consider this?if it does, it doesnt make sense for me?It is very hard to justify this sort of secondary rebars for simply supported slab(one- way), at the end of the day you will be a laughing stock if you do.

2.3 FEM(ARSAP) is really good in analyzing an irregular/complicated two way slab system with multiple point/line loads. Aside from that, you do not have any option to check it,since it is quite complicated, you put your trust on FEM whatever the result it will give you. But how can you build up that trust when in a simple model(ie, simply supported slab) doesnt yield the result close to what you wanted?

Dont get me wrong, I love this software(we all do!), but to the development team,please have patience to have foolproof test to check ARSAP will not only yield theoretically correct but also "practical" result as well.

Re: moment maps&provided reinforcement

mustafahesenow — Tue, 19 Dec 2017 13:34:19 GMT

Hi @saclovitzky

I had before the same issue and I did very detailed calculation as per ACI code and unfortantely the design in RSA based on this code is not correct and have huge error variation.

So possibly its also not working for BS or Euro code .

Needs to check

Check the post here .

https://forums.autodesk.com/t5/robot-structural-analysis-forum/immediate-and-long-term-deflection-as-per-aci-code-on-robot/m-p/7167225/highlight/false#M54645

Re: moment maps&provided reinforcement

saclovitzky — Tue, 19 Dec 2017 16:18:23 GMT

Thanks Mustafa, I am just wondering how the development team works. Is there any particular dev't team assigned to,ie, Eurocode, ACI, BS etc.

The ideal set-up , I would say, is one group is assigned to eurocode/ACI(AMerican)/BS codes. These are the 3 major codes being used around the globe.

I think if this the case, basic code requirement(s) will not overlooked or in case error(s) appears can be easily corrected immediately.

Issues reported by the user(s) which are not acted upon for a "long time" are not acceptable.

Re: moment maps&provided reinforcement

Artur.Kosakowski — Tue, 19 Dec 2017 16:25:07 GMT

Hi @saclovitzky

Could you attach the TEDDS detailed calculation note so that I could compare with the RSA model?

Re: moment maps&provided reinforcement

saclovitzky — Tue, 19 Dec 2017 16:46:03 GMT

Hello Artur,

Pls. find attached as requested.

Re: moment maps&provided reinforcement

Artur.Kosakowski — Tue, 19 Dec 2017 16:59:37 GMT

Hi @saclovitzky

I'm not sure if I'm reading the note correctly. Could you indicate what is the actual value of the deflection?

Re: moment maps&provided reinforcement

saclovitzky — Tue, 19 Dec 2017 17:13:18 GMT

Hi Artur, if you are referring to TEDDS output, deflection checks are done using L/d limits(span to effective depth ratio) not the actual deflection,ie, 25mm

Re: moment maps&provided reinforcement

Artur.Kosakowski — Tue, 19 Dec 2017 17:15:48 GMT

Hi @saclovitzky

So how you actually compare this to the total deflection so that you could run Robot example against it?

Re: moment maps&provided reinforcement

saclovitzky — Tue, 19 Dec 2017 17:38:43 GMT

My main point is that, if you do not have access to FEM software you will rely on spreadsheet/TEDDS to check/satisfy deflection criteria based on L/d ratio(this is really conservative taking into account long term deflection). Again, pls. refer to my previous post.

Re: moment maps&provided reinforcement

Artur.Kosakowski — Wed, 20 Dec 2017 10:24:23 GMT

Hi @saclovitzky

I'm sorry but I don't understand what is your point. I think it is fine to use either of them to design a slab.