Experimental Tests on Hollow Core Slabs Made with FRC - On Shear Behavior of Structural Elements Made of Steel Fiber Reinforced Concrete - page 135

according to RILEM [ 7 ] and MC2010 [ 6 ]. To obtain the elements shear theoretical

values, each HCS can be approximated to a single double T beam; when the web
width b o was the sum of all the webs widths which composed the HCS. For the
calculations, the fact that all the webs contributed in the same manner to resist shear
was taken into account. However, some authors, like Elliott et al. [ 8 ], suggested that
the shear capacity of HCS is not the same as the shear capacity of each component
section, unless web widths are exactly equal; since shear failure

'

nally occurs in the
critical web. Therefore, it seems reasonable to calculate shear by not taking into
account all the webs of the HCS. As HCS were treated as a sum of the double T
beams, the contribution of the

fl ange to the shear was considered in the calculations

for the HCS made from bers, by means of factor k f (Table III.2), proposed in the

RILEM guidelines. This value (k f ) was equal to 1.036 for all the cases. Neither EN
1168+A2 nor MC2010 considered

fl anges contribution to shear. For the HCS

without bers, MC2010 shear strength was calculated by applying the most

accurate form (Level III of Approximation), which permitted the calculation of ʵ x

(see Table III.1 in the introduction to Part III) and directly calculated the corre-
sponding inclination of the compression stresses ( ʸ ). Level III of Approximation

was based directly on the equations of the Modi ed Compression Field Theory

(MCFT) [ 9 ]. The resistance of HCS with bers were calculated by applying the

formula proposed in MC2010 (see Table 7.7 ), which included the effect of bers

inside the concrete matrix contribution. All the formulas used to calculate shear
strength are clearly summarized in Table 7.7.
Code formulae included limitations on several parameters, such as the ρ l rein-

forcement ratio for longitudinal reinforcement, the ʾ factor which considers size

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

due to prestressing actions, and the minimum concrete contribution due to shear
V cu , as presented in Table III.2 (see introduction to Part III). None of these limi-
tations affected the values calculated in the beams tested in these Series. The safety
margins (SM = V test /V theo ) were used as a reference parameter to compare the
results obtained from the different beams and Codes. Table 7.8 shows the shear
values (experimental and theoretical) and their SM; it also indicates the shear values
corresponding to the

fl exure failure mode and their corresponding SM. The ultimate

fl bers contribution,

according to MC2010 [ 6 ]. In the SM columns (Table 7.8 ), the values exceeding the
unit are shown in boldface.

exural moment was calculated by taking into account the

7.3.3.2 Series I: Shear Values According to Current Design Codes

By way of general conclusion, and as expected, all the slabs of Series I presented a
failure mode through shear-

exure, therefore theoretical shear values were calcu-
lated in regions cracked in bending.
Figure 7.16 plots the SM of all the HCS in Series I, except HCS (I-50-3.1),
which had a failure through bonding. We can observe that the shear SM and the
fl

fl

exure SM are higher than the unit. These results demonstrate that exceeding both