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Distribution of horizontal shear stree by BS8110, cl.5.4.7.2.Helpful Member! 

Jasonlee (Civil/Environmental) (OP)
25 Jul 01 5:52
Distribution of horizontal shear stree by BS8110, cl.5.4.7.2.
Anyone can show me how?

The clause said that the average horizontal shear reinforcement should be distributed in proportion to the vertical design shear force diagram to give the horizontal shear stress at any point along the length of the member. But how?

Finding the average vertical shear force and then distributed it by ratio? or other method?

Please help
Helpful Member!  prex (Structural)
25 Jul 01 8:38
I suggest you to go back to your schoolbooks and to deepen your knowledge of beam stress theory.


prex
motori@xcalcsREMOVE.com
http://www.xcalcs.com
Online tools for structural design

ocean13 (Civil/Environmental)
26 Jul 01 0:54
what r u designing?

links provide shear resistance acting in tension to hold back the diagonal shear crack in a beam in flexure.

your horizontal shear can be taken care by shear studs if you say casting a composite steel-concrete deck. then u have to know the shear stress at the interface
JSA (Structural)
26 Jul 01 1:40
In this area we use The Uniform Building Code and ACI-318.  If you can get ahold of an ACI publication titled, "Notes on ACI-318", it has excellent step-by-step examples of how to design this reinforcing.  A local university engineering library may have a copy.
phuduhudu (Structural)
26 Jul 01 3:00
What it means is that the horizontal shear stress diagram is the same as the vertical one. I presume this is for design of shear studs. With a UDL for instance your shear stress varies linearly along the beam with zero shear at midpoint and max at supports. So if you calculate your total horizontal shear stress you know that it varies in the same way from zero at midspan to max at the support. So waht you can do is calculate how many shear studs you need for the total shear stress and then just arrange them with linearly increasing spacing towards the support. This is in theory the most economical arrangement. For practicality you will want to split your span into zones and use even spacing in each of the zones.

Carl Bauer
www.bauerconsultbotswana.com

Jasonlee (Civil/Environmental) (OP)
26 Jul 01 3:50
What I am designing is a composite slab, precast slab in the bottom and in-situ slab on the top.

I have checked BS5400, cl 7.4.2.3 and BS8110, 5.4.7. They are suggesting different methods for estimating the horizontal or interface shear stress.  BS5400 sugguest using v=VQ/IB ( which is the exact shear stress at the point being considered ), while BS8110 sugguest to find the average horizontal shear first ( C= M/Z , C/bd ,C-compression ) and then distribute it in proportional to the vertical shear diagram. I feel it is quite hard to understand on distributing the horizontal shear stress as the code seems unclear on this point.

Besides, is it OK for providing horizontal shear reinforcement in against the Utimate horontal force on the interface , regardness the horizontal shear stress distribution along the beam or slab?
Guest (Visitor)
26 Jul 01 8:30
Prex,

If you know the answer then you should provide it rather than making smug comments.
If you don't then maybe you should go back to your books too.

My understanding of the question is the same as carlbauers
270771 (Structural)
26 Jul 01 9:55
I agree with the Ginger Mincer.

These forums are not for smart arses like Prex. to bolster their egos by sounding off to try to prove their superiority to themselves.
It's no wonder that the profession is in the state that it is.
Thank God that not everyone views learning in this manner. Hope that Prex never has to ask for help from anyone else.

Oswald19
Hariharan (Marine/Ocean)
12 Aug 01 7:02
The basic question asked by Jasonlee seems to have been
missed out. I am also interested in this topic albeit for a
slightly different reason. What is the consideration required for
proper bond between old concrete (precast)  and new concrete
(in-situ)? We recently designed a jetty with grid beams of such
composite construction. The lower half was precast, and the
upper half was cast in place. We computed shear stress at the
interface as per ( VQ/IB ) and provided shear reinforcement
and additional dowels to carry the horizontal shear. In such
cases we normally roughen the interface precast concrete
surface as early as possible after concrete sets, so as to acieve
better bonding with new concrete. I felt that
the reinforcement could be reduced, but could not confidently  
justify it!

Incidentally, we saw the design of an adjacent jetty structure
designed by an australian firm. They had provided 225mm
thick precast concrete slab + 225 mm thick cast-in-situ
concreta slab. There were no dowels, stirrups etc. There were
no special notes. We were not confident about justifying the
composite action without being sure about the shear at the
interface. (We could not adopt that design concept anyway
because our loading cases were very different, and ours was
more severe).

Has anyone come across similar instances? This is a very
interesting and crucial situation. Significant reduction in
detailing and a greater confidence level in such construction
could be achieved.

Hariharan

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