Time Dependent Material (Creep/Shrinkage/Relaxation) Function

The user directly defines the time dependent material properties (creep, shrinkage, and relaxation) of concrete. The properties are applied to Construction stage analysis and Heat of hydration analysis.

Select User Defined as the Code in the Add/Modify Time Dependent Material (Creep/Shrinkage) dialog box and select the Creep Function and Shrinkage Strain Function defined here.

Select User Defined as the Relaxation Coefficient in the Tendon Property dialog box and select the Relaxation Function defined here.

From the Main Menu select Properties > Time Dependent Material > Function.

Click under the tab being considered for data entry.

Click to check or change or click to delete the entered data. Click

to copy previously entered data.

Creep tab

Define the time dependent creep property of concrete material.

Function Name: Enter the name of Creep Function, which is referred to in the Add/Modify Time Dependent Material (Creep/ Shrinkage) dialog box if User Defined is selected in the Code field.

Creep Function Data Type
Select one of the Creep Function Data Types.

Specific Creep: Strain per unit stress excluding immediate deformation

Creep Function: Strain per unit stress including immediate deformation

Creep Coefficient: Ratio of creep strain to elastic strain ( )

Elasticity
Enter the modulus of elasticity of concrete.

midas uses Specific Creep for creep analysis. For more details, refer to Time Dependent Analysis Features > Time Dependent Material Properties in the "Analysis Manual"

A frequently used Creep Function may be saved in and recalled from a file. The data file, fn.TDM retains the following form:

Scale Factor: Multiplier for values

Graph Options: Check on for Log Scale graph

Description: Descriptive text for the Function

Shrinkage Strain tab

Define the shrinkage strain, which is a function of time.

Function Name: Enter the name of the function defining the change of creep strains, which is referred to in Shrinkage Strain Function of Add/Modify Time Dependent Material (Creep/ Shrinkage) dialog box when the Code is User Defined.

A frequently used Shrinkage Strain Function may be saved in and recalled from a file, whose type is fn.TDM as for the Creep tab.

Scale Factor: Multiplier for values

Graph Options: Check on for Log Scale graph

Description: Descriptive text for the Function

Note. Recommended number of creep/shrinkage functions for accurate results

In order to obtain accurate creep results, at least 5 creep/shrinkage functions need to be defined with different loading age. Using the defined functions, midas Gen performs linear interpolation during the construction stages. If there was only one creep function defined in the model file, the program could not get the exact results from the linear interpolation.

In case of creep/shrinkage database such as CEB-FIP, midas Gen internally generates 48 functions with different loading age.

Relaxation tab

Define the time dependent relaxation rate of prestressing tendon. The relaxation rate is based on the initial jacking force defined in Tendon Prestress Load. For the long-term relaxation loss, the program assumes the relaxation is constant after the final relaxation rate defined by the user.

Function Name: Enter the name of Relaxation Function, which is referred to in the Tendon Property dialog box if User Defined is selected in the Relaxation Coefficient field.

Option for Relaxation Time
Select one of the unit of horizontal axis of Relaxation Function Data.

Hour

Day

A frequently used Relaxation Function may be saved in and recalled from a file. The data file, fn.TDM retains the following form:

Scale Factor: Multiplier for values

Graph Options: Check on for Log Scale graph

Description: Descriptive text for the Function