Statistical analysis of the compressive strength of concrete in structures

The relationship between the in-place compressive strength of concrete in structures and specified strength f(c)' is investigated through the use of factors F-1 and F-2. Factor F-1, the ratio of the average strength of standard 28-day-old cylinder specimens to the specified strength, is evaluated using data from 3756 cylinder tests representing 108 concrete mires produced in Alberta, Canada, between 1988 and 1993. Factor F-2, the ratio of average in-place strength to average cylinder strength, is evaluated using core and cylinder data representing 108 concrete mires with strengths less than 55 MPa that were investigated by others. A statistical description of the compressive strength of concrete in structures is derived that accounts for the inherent randomness of Factors F-1 and F-2 and also the typical strength variation within a specific structure. The probability of the in-place compressive strength of concrete in a 28-day-old column being less than f(c)' is approximately 13 percent. It is likely that a recalibration of the load and resistance factors for the design of new structures in Canada based on these findings would yield greater factored concrete strengths than are currently in use.