Development Length of Steel in Shear
Development Length of Steel in Shear
(OP)
I have read an earlier thread on the topic, but the matter remains unclear.
Codes specify that the main tension rebar crossing a shear plane considered must be fully anchored (developed) either side of this plane. My understanding is that this is to keep the concrete together so that it can resist shear by means of friction. But if one provides shear links (stirrups) to increase shear capacity, why must the main bars be fully developed? If the concrete cannot resist the shear stress by friction the shear is resisted directly by the shear links which must shear off for the beam to fail.
The very reason one places shear links into the beam is because the shear stress exceeds capacity of the concrete section in friction. So for these shear links to "start working" the shear stress in the concrete resisted by friction must have been exceeded, so there is no need any longer to rely on the shear resistance is provided by the shear links.
Codes specify that the main tension rebar crossing a shear plane considered must be fully anchored (developed) either side of this plane. My understanding is that this is to keep the concrete together so that it can resist shear by means of friction. But if one provides shear links (stirrups) to increase shear capacity, why must the main bars be fully developed? If the concrete cannot resist the shear stress by friction the shear is resisted directly by the shear links which must shear off for the beam to fail.
The very reason one places shear links into the beam is because the shear stress exceeds capacity of the concrete section in friction. So for these shear links to "start working" the shear stress in the concrete resisted by friction must have been exceeded, so there is no need any longer to rely on the shear resistance is provided by the shear links.






RE: Development Length of Steel in Shear
No, it is to satisfy the logic of the Truss Analogy. Think of it as a normal truss with tension and compression cords and diagonal compression struts. The tension cord must develop its tension force at the point where it meets the diagonal strut.
RE: Development Length of Steel in Shear
RE: Development Length of Steel in Shear
RE: Development Length of Steel in Shear
To hopefully add to what you posted, it might help to consider that in an ideal world the stirrups would be placed at a 45 degree angle to be best positioned to take said diagonal shear. Since that is impractacle they are placed vertically at close enough intervals to accomodate the shear/diagonal tension.
RE: Development Length of Steel in Shear
RE: Development Length of Steel in Shear
RE: Development Length of Steel in Shear
My question would now be where does the code, in my case BS get the anchorage at support requirements from? BS needs 12x bar diameter past centre of support, but the support width of a precast beam for example needs only be enough to carry direct bearing stresses. Also the 12x bar diameter is hard to understand. If you use say ten 10mm bars with 12x bar diameter anchorage you are fine, but now if you use ten 12mm bars (almost double area) with 6 x bar diameter anchorage (so you can resist same tensile force) you are not satisfying code requirement. Doesnt seem right
RE: Development Length of Steel in Shear
RE: Development Length of Steel in Shear
RE: Development Length of Steel in Shear
Codes provide simplified solutions that they think are logical but do not tell the full story (and often have limitations. For example, the BS8110 rule on this is far too simplified and assumes for small loads you will use small bars for a start as well as not necessarily providing the termination development really required. If you want to understand this better, read Eurocode (which has supposedly replaced BS8110 by now anyway)on it. Especially 9.2.1.3 and associated clauses.
RE: Development Length of Steel in Shear