Experimental Tests on Parameters Influencing on Shear - On Shear Behavior of Structural Elements Made of Steel Fiber Reinforced Concrete - page 67

was determined by equaling the ultimate capacity for yielding stirrups with the
ultimate capacity for crushing of concrete struts (see Commentary to Eurocode
[ 13 ]). For all beams,

ʸ ≈ 13 ° was obtained, so ʸ values were lower than the

minimum bound value 21.8 ° , corresponding to cotg ʸ = 2.5; ʸ = 21.8 ° was

therefore used for the calculations.

To obtain predictable concrete resistance, partial safety factors for material
properties were considered in the calculation as ʳ s = 1 and average values

were utilized when a characteristic value appeared in a formula.
Code formulas include limitations on several parameters such as the

ʳ c = 1 and

ˁ l rein-

forcement ratio for longitudinal reinforcement, the ʾ factor which takes into account

the size effect, the ˃ ck average stress acting on the concrete cross-section for an

axial force due to prestressing actions and minimum concrete contribution to shear
Vcu, as presented in the Introduction to Part III. None of these limitations affected
the values calculated in the beams tested in this study.
Table 4.5 presents the theoretical shear strength values calculated with the
current Codes for each beam. Figures 4.11 and 4.12 represent contributions to shear
by means of concrete, stirrups and bers for the Spanish Code EHE08, the EC2 and

the MC2010, for all of the beams tested. In Fig. 4.11 , the results were evaluated by
considering average values without applying safety factors. Figure 4.12 reproduces
the values evaluated by considering design values (obtained by dividing the char-
acteristic value by its corresponding material safety factor).
As all the formulas (except MC2010 for concrete without bers) include an

identical and explicit term after considering the favorable effect of prestressing
reinforcement on the concrete contribution, a line showing the level of this effect
has been drawn in Figs. 4.11 and 4.12 .
Figure 4.12 shows how the

ber effect is underestimated by the Codes, in
particular by MC2010. Finally, Table 4.6 reports the shear contributions as a per-
centage attributable to stirrups, concrete and

bers.

Table 4.5 Shear strength (kN) calculated from the current design codes without safety factors
Specimen ID V test V EHE08 V EC2+RILEM V MC2010

HF600TR/1 571.61 491.21 423.76 474.40

HF600TR/2 592.70 491.21 423.76 474.40

H600TR/3 491.34 384.99 331.55 404.34

HF600/4 392.40 281.62 290.97 249.58

HF600/5 347.20 281.62 290.97 249.58

HF400h/6 420.00 298.81 308.86 261.58

HF400/7 390.00 292.91 302.40 259.42

HF400/8 428.30 292.91 302.40 259.42

HF260/9 325.60 292.19 300.72 269.24