; Punching Shear Strength of Reinforced Concrete Slabs without Transverse Reinforcement. Paper by Aurelio Muttoni
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Punching Shear Strength of Reinforced Concrete Slabs without Transverse Reinforcement. Paper by Aurelio Muttoni

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The author is correct: the punching strength is a function of the opening of a critical shear crack in the slab. Nevertheless, the position of this crack can not be predicted through the slab rotation, hence can not be considered as an independent variable of the phenomenon.

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									                            REFERENCES                                      Brown, M. D.; Bayrak, O.; and Jirsa, J. O., 2006, “Design for Shear
                                                                          Based on Loading Conditions,” ACI Structural Journal, V. 103, No. 4,
  Brown, M. D., and Bayrak, O., 2007, “Investigation of Deep Beams with   July-Aug., pp. 541-550.
Various Load Configurations,” ACI Structural Journal, V. 104, No. 5,        Cross, H., 1952, Engineers and Ivory Towers, McGraw-Hill, New York,
Sept.-Oct., pp. 611-620.                                                  142 pp.



Disc. 105-S42/From the July-August 2008 ACI Structural Journal, p. 440

Punching Shear Strength of Reinforced Concrete Slabs without Transverse Reinforcement. Paper by
Aurelio Muttoni

Discussion by Andor Windisch
ACI member, PhD, Karlsfeld, Germany


   The author is to be complimented for his new failure criterion         The contributions of shear friction and dowel action can be
for punching shear based on the critical shear crack theory.              neglected, too. (The size effect originates from the limited
The failure procedure is explained12 as follows: “the shear               extent of the process zone in fracture mechanics and must be
strength is reduced by the presence of a critical shear crack             taken into account.)
that propagates through the slab into the inclined compression               The shear strength formulas in the different codes, that is,
strut carrying the shear force to the column.”                            Eq. (1), (2), and (4), referring to the slab depth d and the
   Regarding Fig. 2, this explanation shall be complemented               arbitrary control perimeter, smear the different contributions.
as follows: at the critical shear crack shown in Fig. 2(a), the           The smeared, mechanically inconsistent material characteristic
continuous thick line consists of (at least) two different                is than approximated with fc′1/2 or fc′1/3, which have no real
sections—the upper part is a typical flexural-shear crack and             physical meaning; they are relatively close to the calculated
the lower part is a sliding surface across the compression                figures only.
zone of the slab around the column, that is, this part cannot                The author’s interesting new failure criterion based on the
be considered an “ordinary” crack. The theoretical strut                  rotation of the slab must be opposed due to the two load-rotation
depicted in Fig. 2(b) cannot exist as described. It does not              curves shown in Fig. 3(a). The detrimental effect of the
develop around the critical shear crack, nor develops the critical        supplementary reinforcing ring db12 (one No. 4) cannot be
crack across the strut. The source of the inclined compressive            predicted by the rotation. Menétrey29 found similar
force in this strut, as shown in Fig. 2(b), is not clear either.          jeopardizing influence of reinforcing rings in his tests.
How does it develop on the top of the slab? The discusser
                                                                             The author is correct: th
								
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