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Need of Detailing Awareness For Safe Structures
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es_jayakumar
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PostPosted: Sun Oct 19, 2014 4:12 pm    Post subject: Reply with quote

Dear Sir,

I fully agree with your views. I have another doubt now. In the detailing diagram of slabs as adopted from Menon & Pillai book (Fig11.9, page 2 of this discussion topic ) or SP 34 (Fig.9.5), for the slab supported on the spandrel beam (at the edge), the curtailment length shown is 0.1 Iy beyond the inner face of the beam. Is this length sufficient to cater for the negative moment developed due to the possible partial restraint ? In most of the cases, this length will be less than the development length too.

E S Jayakumar
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thirumalaichettiar
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PostPosted: Sun Oct 19, 2014 4:36 pm    Post subject: Reply with quote

Dear Er.J.K,

I am happy that each time you raise an interesting and important point on detailing. I expect  more sefians (out of 18660 members as only few posted) to post more queries or post some information on detailing.

I am also not happy with the 0.1 length of span since if the span is 3' can we cut a length of o.3' and place? If we issue a sketch of this the bar bender or mastry will modify it and he will not follow the sketch.

As it has been drawn as per IS code provisions (theoretical)  it is  the structural engineer has to provide at least the anchorage/overlap  length of 50dia. If the bar is 12mm the length is 2' or 12 db which is 144mm(6") but if I were to detail I will add at least 18" which can be cut and tied. From this it is clear that structural engineer has to use his judgement from his knowledge and experience. Also note that there will be always some restrains if the slab is even built over brickwall because of the coefficient of friction between concrete and brick unless a graphic or nylon sheet with grease  is put under the slab. Not to take risk add some extra length.

Hope this is my opinion and others can comment.

T.RangaRajan.
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thirumalaichettiar
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PostPosted: Tue Oct 21, 2014 2:21 pm    Post subject: Reply with quote

Can anybody of the 18000 sefians post some detailed drawings on some specific structures like arches, culverts, variable sections etc so that it can be good for learing to all?

T.RangaRajan.
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thirumalaichettiar
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PostPosted: Thu Oct 23, 2014 9:02 am    Post subject: Reply with quote

No response so far?

T.RangaRajan
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Sudhakaran
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PostPosted: Thu Oct 23, 2014 11:02 am    Post subject: Reply with quote

Failure mode of concrete cover due to insufficient development Length.


Regards,


Sudhakaran.



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B.V.Harsoda
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PostPosted: Thu Oct 23, 2014 2:04 pm    Post subject: Reply with quote

Respected Dr. NS Sir, Er. T. RangaRajan Sir,  Er. S. P. Shrinivasan, Er. Sudhakaran, Er. Jaykumar, Er. Sayed, &  Er. Rao,


Thank you very much for your valuable response regarding this topic. Due to my very busy work schedule I am late, sorry for that. Hope more response from All.

Regards,
Er. B. V. Harsoda


Last edited by B.V.Harsoda on Thu Oct 23, 2014 2:08 pm; edited 1 time in total
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thirumalaichettiar
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PostPosted: Thu Oct 23, 2014 2:04 pm    Post subject: Reply with quote

Dear Er.Sudhakaran,

Thanks for posting in response to my post.

The figure you posted remind the structural and site engineers of the facts:

1. It is absolute necessity to provide the required cover the main as well as for stirrups and ties. Let us have a discussion over this  even though there was a discussion already in this forum. This is the requirement for Durability (less cover leads to corrosion etc) , Strength (more cover causes less effective depth reducing the BM etc).

2. Necessary that  sufficient spacing is required to avoid cracks and bonding.

3. Good development as well as anchorage length are the fundamental requirement not only for elastic range but are very important for inelastic range(Lateral load).

Hope this is a good to discuss all of the above with reference to the structural elements-SLAB, BEAM & COLUMNS etc.

T.RangaRajan.
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thirumalaichettiar
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PostPosted: Thu Oct 23, 2014 2:43 pm    Post subject: Reply with quote

Dear Er.sudhakaran,

Pl.read the article on cover which may be useful. The article is attached.

Also study the PPT notes on cover as per ACI .

T.RangaRajan



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B.V.Harsoda
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PostPosted: Thu Oct 23, 2014 3:01 pm    Post subject: Re: Need of Detailing Awareness For Safe Structures Reply with quote



Dear Er. Shrinivasan'

Thanks for posting in response to my topic. I also appreciate your sharp vision toward Detailing.
Your answer for fig. 1 is correct but reason is not clear. In design we consider dx for lower layer & dy for upper layer so long bars are to be kept in lower layer.  For more clear concept please refer Pillai & menon  2nd Edition Ex. 14.3 or any standard book. Your habit  of adding  Clear Remarks in drawing  is very good. Without this most of Rebar benders makes Mistake. It is a psychological mistake, because they are kipping in mind the system of two way roof slab. You have share your experience very  frankly. Your experience gives massage of importance of Detailing awareness.


Regards,
Er. B. V. Harsoda








spsvasan wrote:
Dear Er.Harsoda

Figure 1 is correct since the bending moment in the longer direction is higher and the long bars are to be kept in the lower layer. In my early days, once or twice, I had noted errors as in Fig 2 in my sites. Since then I have added a "remarks" column in my footing schedule stating "long bars are in lower layer" or "NS bars are in lower layer" etc.

Once I came across a raft beam drawing detailed similar to the floor beams - with midspan reinforcement at the bottom and support reinforcement at top. The drawing was revised before execution.
Again, in my early days, there were a few instances of failure of relatively large sunshades. Each investigation revealed that the bars of the sunshades were kept at the bottom. Each of the site was supervised by a technically qualified engineer. But the bar benders had convinced the relatively inexperienced site engineers that the bars should be at bottom so as to "hold" the concrete in place. Since then I am showing a blown up section of the sunshades with the bars clearly shown at top. I also indicate in bold letters that "bars are to be provided at top" wherever necessary.

In one case a long sunshade collapsed. The building was of load-bearing masonry and the sunshade had been de-shuttered without construction of brick wall above.

In my early days, I once designed a 1.5m sunshade present on all four sides of a courtyard. The sunshade developed diagonal cracks at the bottom at each of the four corners. At the corners, the sunshade slab had spanned between the adjacent walls. There was no bottom reinforcement and slab had cracked. Fortunately since equilibrium conditions were satisfied, the sunshade did not collapse. I created a joint at the four corners and the sunshades are behaving well. A few years later I came across the German code on RCC and this code deals specifically with this case and indicates calculation for the bottom reinforcement in such cases.

I do hope, other SEFIans will come out with their experience and observations to make this topic useful to all.

Regards
S.P.Srinivasan





B.V.Harsoda wrote:
Dear All,

I want to raise the Topic "Need of Detailing Awareness For Safe Structures", as I feel,  it is very very  important. Computer software is commonly used to provide design information, but without proper detailing & site awareness regarding detailing, design Strength can not be achieved.

Below given case  I have read  from Book:-


Failures in Concrete structures
By
Robin Whittle

Case of Failure of two way slab due to lake of awareness of Site Engineer toward Detailing:-
"A two-way spanning slab was designed in accordance with the design rules.One side was significantly longer than the other and this meant that the reinforcement provided for the short span was considerably greater than that for the long span.When the drawing arrived on site, the site engineer decided that the drawing contained a mistake and that the reinforcement in the long span should be the greater. He instructed the reinforcement layout to be swapped around and the slab was built that way. Later, when the full load was applied, the slab collapsed."



All of us has Design Footings, but how many has deeply observed reinforcement placing at site  is the question ?

Please Refer below two Figures & say which method of reinforcement  arrangement  is correct and why ?


Warm Regards,
B. V. Harsoda


Last edited by B.V.Harsoda on Fri Oct 24, 2014 1:17 am; edited 1 time in total
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mtamil
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PostPosted: Thu Oct 23, 2014 5:49 pm    Post subject: Reply with quote

Hi all,

I am in full agreement with all sefians in this discussion, that detailing is a very very important subject. But it is very unfortunate that it wasn't taught in colleges. I am saying so, based on my interaction with young engineers. It is not their fault entirely. I think, the recruiters ( private, public, Govt.) are to be blamed. For example, I was not able to recall, any question on detailing in GATE / IES / NTPC /  any other Competitive exam or in any screening test by private employers / interviews. I hadn't seen SP34 till my graduation. (PDFs were not in existence(?) by then.)

Thanks for everyone for a good discussion on reinforcement detailing. Very infromative.

I have a small observation on the original question by Er. B. V. Harsoda & SPSs trailing discussions, that, it is also important to know the column size and orientation before deciding which reinforecement where.

Regards
Tamilarasan
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