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On the evaluation of the structural redistribution factor in FRC design: a yield line approach

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Abstract

Fibre-reinforced concrete (FRC) is a material that can be characterized by a high standard deviation in the post-peak tensile region. As consequence, structures made of FRC show a too safe prediction of the maximum bearing capacity when derived from characteristic values identified by means of small standard specimens. The Model Code 2010 has introduced a coefficient, named structural redistribution factor, that is able to take into account a reduced variability of the structural response when compared to that of material. A simplified procedure to provide an upper bound estimation of the structural redistribution factor based on the yield line method and able to take into account the material heterogeneity is presented. As case studies, a FRC full-scale elevated flat slab, a slab on ground and a full-scale beam are considered.

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Abbreviations

CMOD:

Crack mouth opening displacement

COD:

Crack opening displacement

COV:

Coefficient of variation

CTOD:

Crack tip opening displacement

FRC:

Fibre reinforced concrete

d f :

Fibre diameter

E :

Young’s modulus

f c :

Concrete compressive strength

f eq1 :

Average flexural nominal strength in the CTOD range between 0 and 0.6 mm

f eq2 :

Average flexural nominal strength in the CTOD range between 0.6 and 3 mm

f R1 :

Residual flexural nominal strength of FRC corresponding to CMOD = 0.5 mm

f R3 :

Residual flexural nominal strength of FRC corresponding to CMOD = 2.5 mm

f Fts :

FRC serviceability uniaxial tensile residual strength

f Ftu :

FRC ultimate uniaxial tensile residual strength

f If :

Flexural nominal stress corresponding to a CTOD equal to 25 μm

f L :

Limit of proportionality

k :

Subgrade modulus

K :

Fibre orientation factor

K Rd :

Redistribution factor

\(K_{{_{\text{Rd}} }}^{\text{MC}}\) :

Model Code definition of the redistribution factor

K Rdj :

Alternative definitions of the redistribution factor proposed by [1] j = 1, 2, 3, 4

l f :

Fibre length

m :

Moment per unit width

m u :

Ultimate moment per unit width

P :

Load

P cr :

Load at the elastic limit, first cracking load

P max :

Maximum load

P u :

Ultimate load

\(P_{\text{eq}}^{\text{u}}\) :

Ultimate equivalent load

q u :

Distributed load

V :

Fractured volume at failure involved in a structure

V 0 :

Fractured volume at failure involved in a classification test

w u :

Maximum crack opening accepted in structural design

W E :

External work

W I :

Internal work

α :

Percentile level

β:

Factor to account fibre distribution over slab thickness

δ :

Virtual displacement

θ i :

Angle of rotation

υ :

Poisson’s ratio

Hom:

Homogeneous

k :

Characteristic value, 0.05 percentile value

m :

Mean value, 0.5 percentile value

Rand:

Random; heterogeneous

cr:

Cracking

max:

Maximum

u:

Ultimate

α :

Percentile level

^:

Percentile estimate

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Colombo, M., Martinelli, P. & di Prisco, M. On the evaluation of the structural redistribution factor in FRC design: a yield line approach. Mater Struct 50, 100 (2017). https://doi.org/10.1617/s11527-016-0969-3

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