foundation system of burj al arab

Loading Rate and Strength of Concrete

In general, strength of concrete means compressive strength and flexure strength. In both cases, load is applied on concrete specimen at certain rate and applied until failure occurs. The range of usual speeds that are applied has significant effect on apparent strength of specimen.

It is very interesting to see that the lower the rate of strength increase, the lower will be measured strength. A probable cause can be included here that slow increase produce creep in sample which allow strain increase with time (creep means increase in strain under sustain load) and when strain reached limiting value, failure of specimen occur.

Compressive strength:

At first we will discuss about compressive strength; applying compression loading over a (30 ~ 240) min period yield failure 84% to 88% of ultimate strength derived by applying loading rate 30 psi/s (0.2 MPa/s, approximately). Depending on variation in loading rate concrete may even withstand stress as low as 70% of strength derived by loading rate of 30 psi/s (0.2 MPa/s).

Following Figure shows variation of strength with rate of applying compressive strength over a wide range of 0.1 psi/s to 107 psi/s [plot is SI unit]. It is interesting to notice that with this range apparent strength becomes double.

Now we are discussing about loading rate; does concrete member may be subjected to such rate loading? Raphael’s (1984) study on concrete was applied in dam;