Function
- Define an analytical model for each construction stage by assigning activated or inactivated sections corresponding to each construction stage of a composite bridge.
Checking member forces & stresses for each part of a composite section
1. Strain due to a moment applied to a composite section
2. Stress calculation for each part
3. Member force calculation for each part
The member forces (axial & moment) for each Part are calculated by integrating the stresses shown in the above diagram. Shear forces are not calculated for each part, as the shear flow pattern widely varies depending on the section profile.
The member forces of each Part are calculated on the basis of compatibility of the concrete and steel girder. If the concrete deck and the steel girder are modeled as beam elements, which are rigidly linked, the member forces will not be identical to the above composite concept, unless the spacing of the rigid links approaches 0.
Call
From the main menu, select [Load] tab > [Type : Construction Stage] > [Construction Stage Data] group > [Composite Section For C.S]
Input
Add
Add a new composite section to be used for Construction Stage analysis to the section list. The new composite section is added to the end of the list.
Modify
Modify or check the data for the composite section selected in the list.
Delete
Delete the composite section selected in the list.
Update all H
Delete the composite section selected in the list. This is used when loading a model that was created in a previous version and does not have the "h" value entered. If the Section Type is "Composite" or "PSC", the "h" value can be automatically calculated using the cross-sectional information.
Add/Modify Composite Section for Construction Stage dialog box
Active Stage
Specify the construction stage at which the composite section defined becomes activated. Generally, this is the step activating each section before the composite action occurs.
Section
Specify the Section from the list.
Composite Type
Specify a Composite Section Type.
Normal : This option is selected when using composite or PSC (prestressed concrete) sections with specific types such as PSC-1CELL, 2CELL, PSC-3CELL, PSC-nCELL, PSC-NCELL2, PSC-HALF, or PSC-CMPWEB. The selected section type is used for analysis based on its characteristics.
User : This option is selected when not using the cross-sectional information from the section or when using arbitrary sections. If an arbitrary section is used, please refer to the "Composite Construction Stage Analysis Modeling Procedure Using User Type" in the hidden features section of the website for detailed instructions.
Section Type
Check the Section Type specified.
Section Shape
Check the Section Shape specified.
Element List
Check the Element Numbers for which the composite section is specified.
The centroid of the section is adopted in different manner for General/Normal and User type.
1. User type: The centroid of the section before and after composite will be different and Midas Civil positions the members such that in the non composite section, the centroid of section ( the one you have assigned to the element ) would coincide with the Line Beam. ( In other words , the line beam passes through the centroid of section. The centroid assumes the same position even after the composite section.
2. Normal/General Type: The centroid is always the centroid of the composite section and the Line beam has the properties of the part ( that has been activated) lumped to that line.
Construction Sequence
Part : Location of each portion of a composite section.
Mat. Type
Element : Select by element. In this case, the material properties that are already defined for the element are used.
Material : Select by material. In this case, the material properties selected are used for the analysis, whereas the material properties already defined are not used.
SRC material can be used for Composite Section. When a Composite Section with SRC material applied is selected and Element is selected as the Material Type, Steel properties of SRC material will be used.
Material : Select Material. If 'Material' is selected from 'Mat. Type'. the user can define the material property in this section.
Compo. Stage : Select the Construction Stage in which the composite section becomes activated. Since part no.1 is a part before the composite action for the section occurs, Part No.1 needs to be selected as the Active Stage.
Age : Specify the age when the composite section becomes activated. The age inputted during the general construction stage will be ignored, whereas the age inputted here will be activated and used during analysis.
h : Enter the Notional Size of Member for each Part. h=2*Ac/u (Ac : Section Area, u : Perimeter in contact with atmosphere)
Limitation for the value of 'h'
The value of h must be greater than zero. If h is zero, analysis will be not proceed except for the following conditions:
1. When elements to which selected sections are assigned in Section does not exist at Active Stage
2. When section types are Steel-I or Steel-Box, specified as Part 1.
3. When Material Type is specified as Material, and Material is specified as Steel.
4. When Material Type is specified as Element, and all the elements defined in the Element List are steel.
Data processing when opening a model file generated in an older version
When Material Type is specified as Element, enter zero for 'h' except for the following conditions.
1. When the values of h in the Change Element Dependent Material Property dialog have been entered identically for all the elements specified in the Element List.
2. When identical Time Dependent Material properties have been assigned to all the elements specified in the Element List.
When Material Type is specified as Material,
1. Materials properties selected in Material and the h values of the linked time dependent properties are used.
2. When using the Volume Surface Ratio in the time-dependent properties associated with the selected material, it is treated as "0".
1. In case of Composite & PSC section types, "h" is automatically calculated and the user may revise the values.
2. When calculating total perimeter "u", the influence coefficient for the enclosed part is not considered.
3. In the case of Section Type "Composite," the calculation of "h" uses the total slab width instead of individual girder areas and perimeter.
Scale : This defines the scale. Input the scale for section properties of each part.
Stiff. : Specify the section Stiffness of each part.
Section properties entered in Section are not applied to Composite Section for Construction Stage, but are used to only show the shape. Rather section properties input in Composite Section for Construction Stage will be used. This is because time-variant modulus of elasticity must be reflected in Composite Section for Construction Stage.
Stiff. Scale : Specify Scale Factor for section properties.
Torsional stiffness and effective shear areas are calculated by summing the values of each part, which are different from the actual section properties of the post-composite section. Stiffness Scale Factor allows us to adjust the section properties for the post-composite section.
Compo. Stiff. : Display the composite section properties of the composite section including the parts, which became composite thus far.
By checking the section properties of each part of a composite section, can we then detect any modeling error for a composite section.
When construction stage analysis is carried out using Composite Section for Construction Stage, member forces and stresses can be checked from Results>Results Tables>Composite Section for C.S.