Tension Stiffening Case Study

2.1.8.5. Tension stiffening:

The term "tension stiffening" is defined as the effect of concrete acting in tension between cracks on the stress of steel reinforcement. At a crack, all the internal tensile forces are carried by the reinforcement, whereas between cracks some amounts of the tensile forces are transferred through bond to the surrounding concrete. This results in a reduction in the reinforcement stresses and strains. The reduction causes the reinforcement strain at uncracked zone to be less than the reinforcement strain at the cracked sections, as shown in figure (2.28). (Allam, Shoukry, Rashad and Hassan, 2013) Figure (2.28): Mean and steel bar stress–strain relationship (Allam, Shoukry, Rashad and Hassan, 2013)

At the end of the nineteenth century, in testing small concrete prisms reinforced with steel

At a section near to the end of the bar or a cracked location, stress in the concrete is higher and closer to the reinforcement bar and lower further away. The distribution gradually becomes uniform at sections away from the crack location. (Yun, 2010) Figure (2.29): Stress distribution of concrete and steel along the prism (Yun, 2010)

2.1.8.5.1. Tension stiffening terms in some codes ' equations:

2.1.8.5.1.1. Tension stiffening of normal weight concrete in Eurocode 2 (2004):

(Eurocode2-2004) gives the following equation for the mean tensile strain (ԑsm-ԑcm) and for calculating the crack width of a flexural member, as in Eq. (2.32).

ρeff = Aceff (effective tension area), is the area of concrete surrounding the reinforcement.

The term represents the tension stiffening part.

2.1.8.5.1.2. Tension stiffening of normal weight concrete in (ECP 203-2007):

The Egyptian Code (ECP 203-2007) gives the mean strain ԑsm as Eq. (2.33):

The term represents the tension stiffening