Concrete Material Dialog Box

The Concrete Material dialog box is used to define the material for either a column or a superstructure cross section.

To modify the concrete material for the cross section, click the Material button in the Multi-Cell CIP Box Section dialog box. To modify the concrete material for a pier definition, click the Material button for the column in the desired pier in the Pier and Column Definitions dialog box.

Defining Unit Weight (Cross Sections)

Enter the material's weight in the Unit Weight field. The unit weight is used in the calculation of self-weight dead load. This field defaults to 150 PCF.

Defining Modulus Elasticity (Cross Sections & Piers)

Define the 28-day modulus of elasticity by entering the value in the E-Modulus, E28 field. This value is independent of concrete strength (f*c), and is used to calculate member stiffness, which in turn affects deflections, prestress losses, and resulting forces and stresses.

Defining Poisson's Ratio (Cross Sections & Piers)

Enter the value of Poisson's Ratio in the Poisson's Ratio field. This field defaults to 0.20.

Defining Compressive Concrete Strength (f*c) (Cross Sections)

Enter the value of the 28-day compressive concrete strength in the f*c field. This field is used to calculate the allowable stresses for the Final condition.

Calculating the Ultimate Creep Coefficient (Cross Sections)

There are two options for calculating the ultimate creep coefficient. By selecting the Calculate option, the program automatically computes the time-dependent properties according to the loss type selected on the Project tab. To manually input the ultimate creep coefficient, select the User Input option and enter the desired value.

Note: The ultimate creep coefficient is typically between 2 and 3.

Defining Initial Concrete Strength (f*ci) (Cross Sections)

Define the concrete strength at the time of post-tensioning by entering the value in the f*ci field. This value is used in calculating the allowable stresses for the Initial condition. It is also used to determine the elastic modulus at the time of stressing when ACI, CEB, or LRFD Loss Types are used.

Defining Humidity (Cross Sections)

Enter the average humidity value in the Humidity field. Average humidity is used in the calculation of creep, shrinkage, and prestress losses.

Defining Thermal Expansion (Cross Sections)

Enter the thermal expansion value of the material in the Thermal Coeff field. This value affects temperature and temperature gradient load cases.

Applying Concrete Material Values to All Sections (Cross Sections)

To apply the values you entered to all sections of the structure, click the box next to the Apply to All Superstructure Sections option.

Applying Concrete Material Values to All Pier Columns (Piers)

To apply the values you entered to all of the columns in a pier, click the box next to the Apply to All Columns in the Pier option.

Calculating the Ultimate Shrinkage Strain (Cross Sections)

There are two options for calculating the ultimate shrinkage strain. By selecting the Calculate option,CIP RC/PT Girder automatically computes the time-dependent properties according to the loss type selected on the Project tab. To manually input the ultimate shrinkage strain, select the User Input option and enter the desired value.

Note: The ultimate shrinkage strain is typically between 0.5 and 0.6 microstrains.

Technical Discussion

For cross sections, the concrete material properties affect the loss of prestress through creep and shrinkage values, the allowable stress values based on code equations, and the shear and moment capacities based on code equations.

For piers, the concrete material properties for the substructure affect the response in the superstructure including the loss of prestress.