Concrete Behavior

You define the concrete elastic modulus in the materials window. You can choose to use code equation 8.5.1 with the inclusion of w_c or a specified value.

When you directly specify values, there must be two elastic modulus values:

E_ci = value for initial service (transfer) cross section analyses
E_c = value for all other conditions

When the code equation is selected the following values are used:

E_{c i} = w_{c}^{1.5} 33 \sqrt{f_{c i}}

E_{c} = w_{c}^{1.5} 33 \sqrt{f_{c}}

where

f_ci	=	cylinder strength at stressing
f_c	=	28 day cylinder strength

For calculations based on the gross section, concrete is assumed to be a perfectly linear-elastic material with no stress or strain limits.

See Concrete Stress-Strain Curves for a description of the stress-strain curves used in a detailed cross section analysis.

The strength stress-strain curves are truncated at a strain of 0.003. The other stress-strain curves have no limit strain.

Where applicable, the lightweight concrete modification factor is calculated using the values in 8.6.1 as follows:

Lightweight concrete (assumed density of 105 pcf): 0.75
Sand lightweight concrete( assumed density of 115 pcf): 0.85
Normalweight concrete (assumed density of 145 pcf): 1.0

Linear interpolation is used between these values, which is also explicitly permitted by 8.6.1. The maximum density for the cross section is used in the calculation.