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jtlpad
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Joined: 12 Jun 2013
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 Posted: Fri Jun 21, 2013 1:58 pm Post subject: hanger stirrups in beam girder connections |
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Please see attached illustration of the hanger. The hanger stirrups serve as tension ties to transmit the reaction of the beam to the compression zone of the girder, where it can be equilibriated by diagonal compression struts in the girder. But I noticed many structural engineers didn't follow the details in the beam-girder connections. How about you. Do you do it? Who missed it and what did you do after construction where there is no hanger but only normal shear stirrups and at least 3 bottoms bars of 20mm size?
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thirumalaichettiar
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| Posted: Fri Jun 21, 2013 3:02 pm Post subject: |
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Dear Er.jtlpad,
What do you mean by many engineers ? Do you know more detailing of RCC structures? In your sketch there are many missing items? FInd out?
Pl. download the detailing of reinforcement avaialbe in the forum where you can have more details and also visit the experts forum.
T.Rangarajan.
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jtlpad
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| Posted: Fri Jun 21, 2013 10:16 pm Post subject: |
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| thirumalaichettiar wrote: | Dear Er.jtlpad,
What do you mean by many engineers ? Do you know more detailing of RCC structures? In your sketch there are many missing items? FInd out?
Pl. download the detailing of reinforcement avaialbe in the forum where you can have more details and also visit the experts forum.
T.Rangarajan. |
The sketch is done by another person who just wants to illustrate it. Of course, there are bars not indicated. Anyway. Please see attached picture of the actual girder beam joint before pouring. I'm just reviewing it. Note there are no hangars. But there are 3 pcs of 20mm bars at bottom bars. Would it be stable? The secondary is 6 meters. Demolishing the whole building would cost millions. Has none design girder beam joint like it?
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sknsrinivasan
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| Posted: Sat Jun 22, 2013 4:35 am Post subject: |
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Dear jtlpad
I think this picture Which you have produced second one shows Beam Intersection. In the primary Beam shear design If the shear force will be high we can not Design leg of STPS ,dia, and spacing, at that time only some Engineer's will provide crank bar under Primary Beam and Secondary Beam junction at 45 degree or 60 degree since it will take some amound of shear, Now Some Engineer providing Plate . Here what kind of Hanger bar you have Mentioned I do not Know
Thanks
N.Srinivasan
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jtlpad
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| Posted: Sat Jun 22, 2013 11:47 pm Post subject: |
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| Many structural engineers told me the bar hooks above and below is sufficient to prevent the joint from breaking up. Anyone familiar with compression struts working diagonally in the joint from the beam framing into it? Would the hook bars above help?
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thirumalaichettiar
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| Posted: Sun Jun 23, 2013 2:34 am Post subject: |
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Mr.jtlpad,
Can you please attach some sample calculations to support your statements for the provisions of extra stirrups at the beam junctions?
with technical reasons,references and code provisions?
T.RangaRajan.
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jtlpad
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| Posted: Sun Jun 23, 2013 3:06 am Post subject: |
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| thirumalaichettiar wrote: | Mr.jtlpad,
Can you please attach some sample calculations to support your statements for the provisions of extra stirrups at the beam junctions?
with technical reasons,references and code provisions?
T.RangaRajan. |
That's what I'm also looking for because many actual constructions I saw don't have these two extra stirrups inside the beam-girder junction. According to the book "Design of Concrete Structures" by Charles Dolan:
"Commonly in concrete construction, secondary floor beams are supported by primary girders, as shown in Fig. 11.13a and b. It is often assumed that the reaction from the floor beam is more or less uniformly distributed through the depth of the interface between beam and girder. This incorrect assumption is perhaps encouraged by the ACI code "Vc+Vs) approach to shear design, which makes use of a nominal average shear stress in the concrete, vc=Vc/Bw d, suggesting a uniform distribution of shear stress through the beam web.
The actual behavior of a diagonally cracked beam, as indicated by tests, is quite different, and the flow of forces can be represented in somewhat simplified form by the truss model of the beam shown in Fig. 11.13c (Ref. 11.7). The main reaction is delivered from beam to girder by a diagonal compression strut mn, which applies its thrust near the bottom of the carrying girder. Failure to provide for this thrust may result in splitting off the concrete at the bottom of the girder followed by collapse of the beam.
Proper detailing of steel in the region of such a joint requires the use of well-anchored "hanger" stirrups in the girder, as shown in Fig 11.13 a and b, to provide for the downward thrust of the compression strut at the end of the beam (Refs. 11.8 and 11.9). These stirrups serve as tension ties to transmit the reaction of the beam to the compression zone of the girder, where it can be equilibrated by diagonal compression struts in the girder. The hanger stirrups, which are required in addition to the normal girder stirrups required for shear, can be designed based on equilibrating part or all of the reaction from the beam, with the hanger stirrups assumed to be stressed to their yield stress fy at the factored load stage".
Well. To those who have ever designed concrete beam-girder joints. What is your comment? Have you ever seen a beam collapsed from a beam-girder joint?
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thirumalaichettiar
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| Posted: Sun Jun 23, 2013 5:28 am Post subject: |
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The book "DESIGN OF CONCRETE sTRUCTURE" IS BY Arthur.H.Nilson, David Darwin and Charles W.Dolan.
Did you ever design using the aboce statement. Attach rhe same with the drwing supplied to the client so that many of us learn from u?
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jtlpad
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| Posted: Sun Jun 23, 2013 9:20 am Post subject: |
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| thirumalaichettiar wrote: | The book "DESIGN OF CONCRETE sTRUCTURE" IS BY Arthur.H.Nilson, David Darwin and Charles W.Dolan.
Did you ever design using the aboce statement. Attach rhe same with the drwing supplied to the client so that many of us learn from u? |
No, my colleagues said the 4 bars above the beam framing into the girder with hook just like in the drawing shared earlier can work without causing any cracks below. He said most in the industry do it. But the book portion bothers me. Maybe it's describing beam without any hooks?
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thirumalaichettiar
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| Posted: Sun Jun 23, 2013 10:08 am Post subject: |
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From your postings it is clear that just by reading the book it is striking your mind that the statement by your friend are not correct. I appreciate your interest to know and you are correct that the hooks in the stirrups do have the function of not allowing the stirrups to burst when the loads exceed and keep them in tact till a maximum limit is reached and have no resisting any forces. The hooks shall be bent to 135 degree with a min. dimension of 10 times the dia of stiruup or 3".
The secondary beam reaction will be cusing a crack on main bar if the main bar can not resist it and if it has not been provided with extra stirrups on either side at a distance "d" and in addition as one of the sefians posted crank or bent up bar is provided.
Vide SP 34 and also the Detailing of reinforcement -PPT available in the forum.
You can calculate the Vu from secondary beam and design stirrups against it. 'You can refer some good RCC boos (not all books) for the design and detailing.
Best wishes.
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