**1. Introduction**

The shear behaviour of high strength concrete (HSC) beams is an interest research despite the abundance of literature on the subject. However, the principal of this solicitation remains insufficiently explained because up to now, there are no analytical methods which give in detail the different factors influencing shear capacity of HSC beams. For this reason, a number of empirical models, based on testing reinforced concrete beams, are used by the different design codes throughout the world to determine the shear strength of reinforced concrete beams, particularly in the seismic zone. Moreover, the HSC is considered as a new building

(mm) is used for the present work. This gravel has a water demand of the order of

*Experimental and Theoretical Investigation on the Shear Behaviour of High Strength Reinforced…*

**Fine mineral additions**: fine mineral additions consisting of blast furnace slag and limestone fillers. The slag additives were finely ground to give a specific surface

**Superplasticizer**: a high range water reducing admixture (HRWRA) in a liquid

of addition was provided by Ecocem in France. The fine limestone fillers is Betocarb®HP-EB, manufactured by the Omya-Meac Group in France, and were used in proportion of 23% by weight of cement. The mineral additives were used to fill in the finer gaps between the aggregates and hence to improve the density and

form, based on polycarboxylates (CHRYSO Fluid Optima 206), was used in a proportion of 2.5% by weight of cement. It is interesting to add the superplasticizer in 1/3 of the quantity with the mixing water to ensure the dispersion of the cement

The mix designs used in making the HSC beams are presented in **Table 1**.

reinforcement and with transverse reinforcement were measured through the crushing tests of cylindrical concrete specimens of 80 mm diameter by 160 mm in height, using a press with capacity of 500 kN. Measurements of the longitudinal compressive strains were carried out with the help of an extensometer (**Figure 2**) and enabled the modulus of elasticity of the HSC. The results were recorded in a data acquisition system (**Figure 3**) for the complete stress-strain curve of HSC

The compressive strengths of HSC used in making the beams without transverse

The tensile strength was also evaluated for the HSC by splitting tests of concrete

The results of the compressive strength *fc*, the tensile strength *ft* and the modulus

The longitudinal reinforcement composed of two high yield bars of 10 mm diameters in the top zone of the beam (compression), two high yield bars of 8 mm diameters in the bottom zone of the beam (tension) and 6 mm for the transverse reinforcement in the form of stirrups, as shown in **Figures 6(a)** and **7**. The steel was

382.5 38.25 88.0 1029 700 148.8 9.56 0.38 15

**Gravel Sand Water Admixture**

**(2.5%)\***

**W/C Slump test (cm)**

**Figure 4** shows that the pre-peak behaviour is quasi-linear with greater rigidity, and the average ultimate deformation (*εcu* = 2%) decreases with the increase in the compressive strength, which is below the ultimate deformation required by the different universal design codes (*εcu* = 3.5%) which reflects a decrease in ductility. It should be noted that the HSC specimens exhibit brittle and explosive fracture resulting from a

lack of ductility, major disadvantage of this material, as shown in **Figure 2**.

/g and were used in proportion of 10% by weight of cement. This type

2–3% of its mass.

the compactness of the concrete material.

*DOI: http://dx.doi.org/10.5772/intechopen.86499*

**Water**: potable tap water is used.

**2.2 Mechanical properties of concrete**

grains, and 2/3 remaining at the end of mixing [10].

cylinders, 80 mm in diameter and 160 mm in height.

of elasticity *Ec* of HSC are shown in **Table 2**.

**Limestone filler (23%)\***

*).*

**2.3 Steel reinforcement**

**Cement Slag**

*By weight of cement.*

*\**

**47**

**Table 1.**

**(10%)\***

*Mixing ingredients of HSC (kg/m<sup>3</sup>*

of 7000 cm2

(**Figure 4**).

**Figure 1.** *Diagonal cracking crossing the aggregates in HSC.*

material, and there is a lack of base data for shear strength of HSC beams, so all the models proposed by the design codes and developed essentially for normal strength concrete (NSC) were extrapolated to HSC, to validate the applicability of these empirical methods to this material. More investigation work is then required to cover this aspect and provide further information.

The present chapter aims to improve the structural behaviour of HSC beams particularly the shear, and thus ameliorate the performance of the built environment to ensure an adequate durability of constructions.

The HSC presents a low resistance under shear [1–3] because the crack surfaces are smooth and cross the aggregates particles as shown in **Figure 1**, which shows a low contribution of the aggregates in the shear strength. However, the HSC is characterised by high compressive strength and by better adhesion with steel reinforcement, which gives a best contributions of the compression zone and the dowel action effect to the shear strength of HSC beams.
