Structural Concrete - Hassoun

2.4 Tensile Strength of Concrete 19
Figure 2.2
Typical stress–strain curves of concrete.
Figure 2.2 shows typical stress–strain curves for concretes of different strengths. All curves
consist of an initial relatively straight elastic portion, reaching maximum stress at a strain of about
0.002; then rupture occurs at a strain of about 0.003. Concrete having a compressive strength
between 3000 and 6000 psi (21 and 42 N/mm 2 ) may be adopted. High-strength concrete with a
compressive strength greater than 6000 psi (6000 to 15,000 psi) is becoming an important building
material for the design of concrete structures.
2.4 TENSILE STRENGTH OF CONCRETE
Concrete is a brittle material, and it cannot resist the high tensile stresses that are important when
considering cracking, shear, and torsional problems. The low tensile capacity can be attributed to
the high stress concentrations in concrete under load, so that a very high stress is reached in some
portions of the specimen, causing microscopic cracks, while the other parts of the specimen are
subjected to low stress.
Direct tension tests are not reliable for predicting the tensile strength of concrete, due to
minor misalignment and stress concentrations in the gripping devices. An indirect tension test in