**Acknowledgements**

The Series B of the beams is transversely reinforced by stirrups, the ultimate shear force of this series represents the contribution of concrete (*Vc*) and the contribution of stirrups (*Vs*) to the shear strength of HSC beams. The ultimate shear strength of this series is also shown in **Figure 17**. The concrete contribution *Vc* represents 70% of the total shear force and the steel contribution *Vs* represents 30%. Therefore, the presence of the transverse reinforcement has improved the ultimate

On adding up the contribution of concrete and the contribution of the stirrups to the shear strength of HSC beams, Eurocode 2 seems to give the best predictions for

The five universal design codes require more refinement to reflect the real contributions of both materials; the HSC and the steel reinforcement, to the shear

A Series of high strength reinforced concrete beams under shear was investigated. The effects of the concrete and the transverse reinforcement on the shear behaviour of the beams were verified. The experimental and the theoretical results

• The HSC is sudden, expressing the brittleness and the low ductility of this

• The Series A of beams, without stirrups exhibit a relatively fragile behaviour.

• The addition of the stirrups in the Series B of the HSC beams, improves the ductility of this series. The improvement of the ductility is particularly needed

• The diagonal cracking is efficiently restrained by the stirrups, because their occurrence is delayed and their opening is very fine and did not exceeds the

• The digital image correlation technique gives best and very precise results.

• The ultimate shear resistance of HSC beams is increased with the presences of

in the regions of higher seismicity to avoid the catastrophic failure of

serviceability limit of crack width (*Wk* = 0.3 mm).

the stirrups. An increase of around 50% was recorded.

the ultimate shear strength compared to other code models.

resistance of high strength reinforced concrete beams.

shear strength of HSC beams by around 30%. The five design codes greatly overestimate the contribution of the stirrups to the shear strength of HSC beams. An average overestimation is around 45% was recorded. This is due to the fact that the contribution of the stirrups to the shear strength developed in the five code models is based on the yielding of this reinforcement; this is the Ritter [23] and Mörsch [24] truss analogy. The analogy proposes that a reinforced concrete beam failing after yielding of the transverse reinforcement, and before the crushing of concrete. In all tested beams, the failure mode is characterized by crushing of concrete after the complete penetration of the diagonal cracking in the compression zone of the beam as shown in **Figure 10(b)**, and in the same time the transverse reinforcements have not yielding. The contradiction between the analogy of Ritter and Mörsch and the experimental observations led to a greatly overestimation of the transverse reinforcement contribution to the shear strength of reinforced concrete

beams.

*Digital Imaging*

**4. Conclusion**

material.

structures.

**58**

led to the following conclusion:

The experimental investigation presented in this chapter was sponsored by the Ministry of Higher Education and Scientific Research of Algeria. The tests were carried out at Laboratory of Engineering of the Materials of Bretagne (LIMATB) at the University of Bretagne Sud, Lorient, France. Also, Dr. Thibaut Lecompte is gratefully thanked for their willing discussion and active participation in the project.
