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Bridging Your Innovations to Realities

Date: February 23rd , 2012

Topic: Construction Stage Analysis

Presenter: HyeYeon Lee

midas Civil Advanced Webinar

2

Introduction

Modeling Features

Construction Stage Analysis Control

Results

Contents:

Bridging Your Innovations to Realities

1. Introduction

midas Civil Construction Stage Analysis

Need of Construction Stage Analysis:

Construction Sequence may lead to critical force effects which may lead to shear or flexural failure

Long Unsupported cantilever sections may induce forces which may be substantially different

from those in completed structure:

Time Dependent material properties also play a major role in segmental bridge construction

Negative Moments

Construction Stage

Final Bridge Profile – Continuous Structure – Lesser Negative Moments at Mid Supports

Bridging Your Innovations to Realities Construction Stage Analysis

Modeling of Structure

Defining Structure Groups

Defining Loads under Load Group

Defining Boundary under Boundary Groups

Generation of Construction Stages

Defining Construction Stage Data

Construction Stage Analysis Control

1. Introduction

midas Civil

Flow Chart of Construction Stage Analysis:

Bridging Your Innovations to Realities Construction Stage Analysis

1. Introduction – Construction Stage Definition

midas Civil

Bridging Your Innovations to Realities Construction Stage Analysis – Modeling Features midas Civil

1. Importance of Defining Groups

Groups

Structure Boundary Load

Groups are important because:

Only the structure groups, load groups or boundary groups can be activated or deactivated

in the construction stages, element number or load case name cannot be used to deactivate.

Tendon group is not used to activate or deactivate a tendon, it is just used to see the results

of a certain number of tendons together.

Bridging Your Innovations to Realities midas Civil Construction Stage Analysis – Results

MODEL

Spliced Girder Bridge

Bridging Your Innovations to Realities midas Civil Construction Stage Analysis – Model

Stage 1

Stage 1:

Construction of Concrete Box Girder

Temporary supports are provided as shown

Concrete Box Girder will be modeled as

a grillage model

Self Weight of the Girder and Piers will be

activated

Bridging Your Innovations to Realities midas Civil Construction Stage Analysis – Model

Stage 2

Stage 2:

Construction of Prestressed Beams

Prestressed Girders will be simply supported

via temporary supports

Beam End release will be used to simulate the

simply supported nature

Activation of end supports

Self weight and prestressing will be considered

Deck will be casted on day 10, so the weight of

scaffolding and wet concrete will be activated

on day 10


Stage 3

Stage 3:

Deck will be activated by activating part 2 of

the composite section.

Scaffolding weight and wet concrete weight will

be removed.

Temporary Supports will be removed

Post – Tensioning will be done


1. Element Activation/Deactivation

Activate those elements which will become structural components in a Construction Stage

The elements which still have scaffolding or wet concrete should be included as weight as

they would not contribute in the stiffness of the structure.

Precast girder lifting Cast in-situ balanced cantilever



Elements 17 and 25 have to be activated in CS3

Step 1: Elements Modeled

Step 2: Assign Structural Groups to Elements

Drag and Drop

Step 3: Structure Group Activated in CS3



Define age of

the element

at the time of

activation,

used in

determining the

time dependent

material

properties

Define the

percentage of

the forces

resisted by the

element to be

deactivated

that needs to be

distributed

to other elements

CS 2

Casting

of Deck

CS 3

Scaffolding

Removed

0 30 40

CS 1

60

Age = 21 days



How to Model an Element which has been casted but the scaffolding will be removed in the next stage

1. Elements Load must be activated in the construction stage in which it is casted by nodal loads or

moments if needed.

2. When the scaffolding is removed, nodal load defined in 1 must be deactivated and element must be

activated. The self weight function will now automatically consider the weight of the element.

3. Self Weight must be activated at day 1 of the 1st constructions stage

Scaffolding Scaffolding

CS 8 – Elements casted

on day 7

CS 9

Bridging Your Innovations to Realities midas Civil Construction Stage Analysis – Modeling Features


CS 8 : Activating the wet concrete and

scaffolding weight on day 7 CS 9 : Activating the Element



CS 9 : Deactivating the load

Bridging Your Innovations to Realities Construction Stage Analysis midas Civil

2. Composite Section Activation/Deactivation

How to define the composite section for construction stages?

The stage in which the section becomes composite can be defined in:

Load -> Construction Stage Analysis Data -> Composite Section for Construction Stage


3. Boundary Activation/Deactivation

Activate the support/boundary which becomes active in a certain construction stage

Deactivate the temporary support



Step 1: Define Boundary Groups

Step 2: Assign boundary groups to supports

Step 3: Activate Supports



Original: Apply the

boundary condition to the

un-deformed position. This

is equivalent to imposing

forced displacements to the

original position prior to

providing the supports.

Deformed: Apply the

boundary condition to the

deformed position



Original and Deformed option

Original option Deformed Option

This is equivalent to imposing forced

displacements to the original position prior

to providing the supports.



Original and Deformed option

Original option is used when the structure will be lifted to a desired support location



Beam End Release: Useful to simulate the Non Continuous nature of girder before the deck is casted.

Simple Girder

2 span continuous girder


4. Load Activation/Deactivation

Step 1: Define Load Groups

Step 2: Assign Load Groups to load cases

Step 3: Activate Loads


5. Tendon Activation/Deactivation

Tendon Activation

Tendons are activated as loads

1. Define the tendon prestress load under a load group.

2. Activate the load group when the tendon is installed or prestressed


6. Construction Stage Load Type

Construction Stage type load case is only applied to the constructions stages.

Static load cases are applied to constructions stages as well as Post CS mode.

If self weight is defined as Construction Stage load type, the force effect will be

accumulated through all the stages

If the self weight is defined as Dead Load, the self weight is applied to the final structure for

obtaining force effects in Post CS.


7. Creep And Shrinkage

Procedure:

1. Define Creep and Shrinkage Properties – Model -> Properties -> Time Dependent

Material(Creep/Shrinkage)

2. Link the property so defined with material using Model -> Properties -> Time

Dependent Material Link

Model -> Properties -> Time

Dependent Material(Creep/Shrinkage)

Model -> Properties -> Time Dependent Material Link



Creep and Shrinkage Function can be defined by the user.

Model -> Properties -> Time Dependent Material ( Creep & Shrinkage )



Creep Coefficient can also be defined in

Construction Stage Loads -> Creep Coefficient for construction stage

A Creep coefficient is directly entered in a form of load, which is necessary to provide freedom to user-specify

the desired creep coefficients for specific members.

The entered creep coefficient by this feature overrides the creep coefficient defined by the creep function.



Application of Creep and Shrinkage:

Creep and Shrinkage coefficients for the elements are taken as per the age of the activation

of the element in the construction stage definition.

Creep coefficients and shrinkage values can be seen either in :

1. Results -> Results Table -> Construction Stage -> Element Properties at each stage

2. Out File Generated : Results -> Text Output



Notational Size of the Member:

Notational Size = 2*Ac/u ( Ac = Sectional Area , u = perimeter in contact with atmosphere.

1. Beam Elements: Notational Size can be defined while defining the time dependent

material property for creep and shrinkage or by Changing the Time Dependent material

parameters.

Time dependent material property for creep and shrinkage

Changing the Time Dependent material parameters



1. Beam Elements ( Composite Sections ): Individual notational size can be defined for

girder and deck in Composite Section for Construction stage dialogue box



1. Plate/Solid Elements: Notational Size can be entered either while defining time

dependent material property for creep/shrinkage or by Change Element Dependent

Material Property.

Automatic Function cannot be used in Change Element Dependent Material Property

for plate and solid Elements.

Definition of Ac and u for Plate and Solid Elements :

Ac : Area of Cross section

u : Perimeter in contact with atmosphere:



Important Consideration for Plate and Solid Elements:

1. Local Direction of the Elements must be aligned.

2. Local x axis of the elements must coincide with the bridge direction

Incorrect

Correct



Construction Stage Loads can be used to define the time lag in the construction of segments.

Segment A constructed 100 days before Segment B

Construction Stages for Segment A and Segment B are same. Hence construction stages can be modeled such

that the elements for segment A and B appear simultaneously.

At the time of Joining of Segment A and Segment B, the time lag can be introduced by applying Time Load for

Construction stage


8. Development of Concrete Strength

Define Compressive Strength of concrete or the change of modulus of elasticity to reflect

the variation of modulus of elasticity with time.

Procedure:

1. Define the variation of Compressive strength in Model -> Properties -> Time

Dependent Material Property for Comp Strength

2. Link the variation to the material

Model -> Properties -> Time Dependent Material

Property for Comp Strength Model -> Properties -> Time Dependent Material

Link


8. Section Stiffness Scale Factor

Section Stiffness can be changed with construction stages by defining the section stiffness scale

factor in Section Manager.

Section Stiffness factor can be assigned to a section and defined under a boundary group.

Boundary Group can be activated in the construction stage.

For normalizing the section stiffness, another scale factor which normalizes the stiffness must

be activated along with the deactivation of pervious scale factor


9. Effective Width Scale Factor

Effective width scale factor can be defined to take into account the effective flange width for the

calculation of sectional stresses.

Effective width scale factor is considered only in determining stresses as against stiffness scale

factor which is used for generating stiffness matrix.

Effective width can be defined in two ways:

1. Automatically – By using the PSC Bridge Wizard

2. Manually – By Model -> Boundaries -> Effective Width Scale Factor

Effective Width scale factors can be assigned to a boundary group and activated at will.

PSC Bridge Wizard Effective Width Scale Factor


10. Dummy Stage For Obtaining Results

A Dummy stage having no elements or boundaries activated can be used to get the effect due to a

specific load.

Suppose, at the end of a 150 days of construction having each construction stage of 30 days,

temperature stresses are desired.

We will define a dummy construction stage rite after CS5 (30*5 = 150 days ) and activate the

temperature load in that stage. Thus the under the CS: Dead Load – the effect of temperature load

can be seen.


1. Final Stage

Final Stage for the analysis can be selected. If the final stage is defined as: CS2, then the analysis

stop at CS2. Stages beyond CS2 are not analyzed.

Bridging Your Innovations to Realities midas Civil Construction Stage Analysis Control

2. Restart Construction Stage Analysis

Restart the construction stage analysis from the specified stage.

Restarting the analysis from the modified stage saves time.


3. Time Dependent Effect

Select which time dependent

effect needs to be analyzed out

of Creep and Shrinkage



Select Convergence Criteria

for creep analysis



Perform the construction stage

analysis only using the creep

coefficients defined in creep

coefficient for Construction stage



Specify a number, which is used to

divide a construction stage to create

internal steps for considering creep.

The steps will only be used for

analysis, results cannot be seen

for those steps



Check on to reflect the effect of

prestressing tension loss of tendons

due to creep and shrinkage.



Check on to reflect the effect

of rebar confinement for creep

and shrinkage.



Whether or not the time

dependent effect is to be

applied to the POST CS



Check on to reflect the prestressing

tension loss of tendons due to the

elastic deformations of concrete due

to loads other than prestress load


4. P Delta Analysis Control


5. Erection Load

Select the load case which needs to be distinguished from the CS: Dead Load in the Construction Stage Analysis Results

Select the Load Type for the Erection Loads


6. Initial Force Control

The member (axial) forces of the last step of the last construction stage in a construction stage analysis are converted into

Initial Force for Geometric Stiffness to reflect the forces into the geometric stiffness of the structure at the post construction

(Post CS) stage.

Useful for Eigen Value Analysis considering geometric stiffness of cables.

When P – Delta Analysis is done this effect is already considered


6. Initial Force Control

If both Initial Element Forces table and Initial Element Forces(CS) table are entered, Initial Element Forces

table directly entered by the user will be applied first in priority.

However, if “Apply Initial Member Force to C.S.” is

checked on, (Initial Element Forces(CS)) at the last step of the last construction stage will be applied to the Post CS stage.


7. Initial Tangent Displacement to Erected Structues

This function calculates real displacements of the elements, which will be created in the next stage, considering

the rotational angles of nodes resulting from each current construction stage.

This functionality is used for fabrication cambers for structural steel and precast concrete members.

In Large Displacement analysis this function is by default considered


7. Initial Tangent Displacement to Erected Structures

New Segment

Deflection due to rotation of

node at which it has to be joined to


8. Stress Decrease at Lead Length Zone

Select a method of computing stresses over a transfer length in a post-tension model.

This feature is applicable only when a Transfer Length is entered in the Tendon Profile dialog.

If Composite section for Construction Stages is used this function cannot be applied.


9. Change of Beam Section Properties with Tendons

Select whether to consider the presence of tendons for calculating section properties.


10. Save Output for Current Stage/Step

Save Results for Current Stage

Results for Current Step can be seen by selecting Current Step Force


11. Options for Saving Results


1. Construction Stages Results


2. Deformation – Accumulated Deformation

The default results obtained for Construction Stage analysis are

accumulated results i.e. if we check the deformation due to dead load

for CS 2, if would be the deformation for CS1 + the deformation

obtained due to dead load in CS2.

Current Step deformations are obtained by applying the current step force

to the structure.


2. Deformation – Current Stage Displacement

Current Stage Displacement gives the deformations obtained by

applying the current step force ( activated in that step) to the structure.

Accumulated Deformation at CS10 = Accumulated Deformation at CS9

+ Current Stage Deformation CS10


2. Deformation – Stage/Step Real Deformation


3. Beam Diagrams – Accumulated

The default results obtained for Construction Stage analysis are

accumulated results i.e. if we check the bending moment due to

dead load for CS 2, if would be the bending moment for CS1 + the

bending moment obtained due to dead load in CS2.


3. Beam Diagrams – Current Step

Current Stage Beam Diagram gives the Diagram obtained by

applying the current step force ( activated in that step) to the structure.

Accumulated Bending Moment at CS10 = Accumulated Bending Moment at CS9

+ Current Stage Bending Moment at CS10


4. Stresses

Stresses can be checked for individual steps of Construction stages.


4. Stresses – Part 1 and Part 2

Individual stresses can be obtained for different parts of Composite

section.

The option becomes activated when the Composite section for

Construction stages is activated.


5. Tendon Time Dependent Loss Graph


5. Tendon Time Dependent Loss Graph

Loss Pre- Tensioned Post - Tensioned

Friction Loss

Anchorage Slip Loss

Elastic Shortening Loss

Creep/Shrinkage Loss

Relaxation Loss


6. Tendon Time Dependent Loss Table


6. Tendon Loss Table

Stress in the tendon after instantaneous loss.

Post – Tensioned Beams:

Instantaneous loss includes :

Friction Loss

Anchorage Loss

** Elastic Shortening loss is considered to have taken place

already during prestressing

Pre – Tensioned Beams :

Elastic Shortening Loss only due to prestressing ( not due to

self weight)



Anchorage Loss

Where: p is the frictional resistance per unit length determined the friction loss between the

anchorage and quarter length of the beam and dividing it by L/4

Friction Loss:



Other types of elastic shortening losses, which are caused by subsequent loadings

(self weight, live loads, creep, shrinkage, etc.) after the prestressing force is applied, are

included.

Elastic Shortening due to prestressing of other tendons is included:



Tendon Loss due to creep and Shrinkage



Tendon Loss due to Relaxation of Tendon


7. Stage/Step History Graph

Plot history graphs by steps and stages or load cases/combinations using the analysis

results of a structural model, which is analyzed for construction stages and steps that

typically form the basis for a geometric nonlinear analysis or construction stage

analysis.


8. Element Properties at Each Stage

Check the element properties at each construction stage (start age, end age, modulus

of elasticity at the start, modulus of elasticity at the end, cumulative shrinkage and

cumulated creep coefficient) in a spreadsheet format table.


9. Activation/Deactivation Status Table


10. Base Stages, Min/Max, Post CS

Base Stage: All the modeling is done in the base stage.

Min/Max: The minimum ( most negative ) and the maximum ( most positive) force effects

from the constructions stages.

Post CS: The structure obtained at the last stage at which the moving load analysis, dynamic

analysis is performed.


11. Load Combinations

Thanks

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