Bridging Your Innovations to Realities midas Civil Cable Stayed Bridge
2
Introduction
Problem Statement
Preliminary Design
Determination of Cable Force
Optimization of Deck
Construction Stage Modeling
Cable Tension Forces in Construction Stages
Time Dependent Material Effect
Non Linear Effect
Dynamic Analysis
Post Processsing
Wind Load Analysis
Contents:
Bridging Your Innovations to Realities
1. Introduction
midas Civil Cable Stayed Bridge
Cable Stayed Bridge
Wheel Load
Cable Supports
Tension In cables
Flexure In Deck
Axial Load in Pylon
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Stiffness of the cable is dependent on : 1. Load Applied
2. Tension Applied
P1 P1 P2 P2
Cable Stayed Bridge
midas Civil
Bridging Your Innovations to Realities Project Applications
Cable Stiffness can be determined as per the following two techniques: 1. Equivalent Truss Method 2. . Elastic Catenary Cable
Cable Stayed Bridge
midas Civil
Bridging Your Innovations to Realities Project Applications
Cable Bridges are highly indeterminate structures:
Cable Stayed Bridge
midas Civil
Bridging Your Innovations to Realities Project Applications
Change of Cable Stiffness with Pretension High Indeterminacy
Difficult Analysis
Cable Stayed Bridge
midas Civil
Bridging Your Innovations to Realities Project Applications
Cable Shape and pretension are in turn dependent on the load applied on the cable.:
Geometric Non Linear Analysis
Cable Stayed Bridge
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2. Problem Statement
midas Civil Cable Stayed Bridge
Problem Statement:
100 m 200 m 100 m
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2. Design Process
midas Civil Cable Stayed Bridge
Steps of Design : Determination of Cable Forces for Fully
Constructed Model
Check for Resisting Moments of Deck and Pylon Section
Change the Deck and Pylon Sections
Construction Stage Analysis
Non Linear Analysis
Dynamic Analysis
Preliminary Design
Check for Final Design
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Preliminary Design 1. Deck, Pylon Cross section. 2. Diameter of Cables. 3. Height of Pylons
3. Preliminary Design
midas Civil Cable Stayed Bridge
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Determination of Cable Forces 1. Use the unknown Load factor.
4. Determination of Cable Tension
midas Civil Cable Stayed Bridge
What is Unknown Load Factor ? Ans: It is a feature with which you can calculate the cable pretension force that would satisfy certain constraints in terms of displacements, bending moments etc.
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4. Determination of Cable Tension
midas Civil Cable Stayed Bridge
Bridging Your Innovations to Realities
5. Optimization
midas Civil Cable Stayed Bridge
Check the Design forces for the deck, pylon and cables and modify.
Bridging Your Innovations to Realities Cable Stayed Bridge
6. Forward 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
midas Civil
Bridging Your Innovations to Realities Cable Stayed Bridge
6. Forward Construction Stage Analysis
Implication with Forward Construction Stage Analysis
New Tendons
S Stage 10
Stage 11
More Pretension is required
midas Civil
Bridging Your Innovations to Realities Cable Stayed Bridge
6. Forward Construction Stage Analysis
Lack of Fit Force: It calculates the additional pretension required for cable installation
midas Civil
Bridging Your Innovations to Realities Cable Stayed Bridge
7. Unknown Load Factor With Time Dependent Materials
The material Properties changes with time and the cable pretension force depends on the creep. The unknown load factor can take that into consider and the program can perform iterations to find the pretension in the cable which will include the time dependent effect.
Construction Stage
Construction Stage
Unknown Load Factor
Check
End
Unit Pretension loading
Set constraints and calculate unknown load factor by step
Using influence coefficient to reanalyze construction stage
[Iterative analysis procedure
to calculate unknown load factor]
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8. Eigen Value Analysis
midas Civil Cable Stayed Bridge
Analysis -> Eigen Value Analysis Control
Ritz Vectors Unlike the natural eigenvalue modes, load dependent Ritz vectors produce more reliable results in dynamic analyses with relatively fewer modes. The Ritz Vectors are generated reflecting the spatial distribution or the characteristics of the dynamic loading.
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9. Eigen Value Analysis
midas Civil Cable Stayed Bridge
To convert the final stage Cable forces to be used for determining cable stiffness for the Eigen Value Analysis
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9. Eigen Value Analysis
midas Civil Cable Stayed Bridge
Step 2: Eigen Value Analysis Results A) Natural modes (or mode shapes) B) Natural periods (or frequencies) C) Modal participation factors. D) Effective modal mass.
Eigenvalue analyses must precede dynamic analyses such as Modal Time History analysis or Response spectrum analysis.
The response spectrum analysis uses the natural periods from the eigenvalue analysis.
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Linear Case
Non Linear Case
R(x,xa) : Viscous Damping Fs(x): Variable Stiffness
10. Time History Analysis
midas Civil Cable Stayed Bridge
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Input Non Linear Links
Define Time History Load Case
Perform Non Linear Time History Analysis
Check the Results
Define Properties of Non linear Links
10. Time History Analysis
midas Civil Cable Stayed Bridge
Procedure of Eigenvalue Analysis:
Time Forcing Function
Ground Acceleration
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10. Time History Analysis
midas Civil Cable Stayed Bridge
Step 1: Defining Properties of Non Linear Links Model -> Boundaries -> General Link Properties
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Base Isolators: Lead Rubber Bearing Isolator Friction Pendulum System Isolator
Base Isolators Provided in midas Civil
Viscoelastic Damper Gap Hook Hysteresis System Base Rubber isolator Friction Pendulum System isolator
10. Time History Analysis
midas Civil Cable Stayed Bridge
Bridging Your Innovations to Realities
10. Time History Analysis
midas Civil Cable Stayed Bridge
Step 2: Define Time History Load Case Load -> Time History Analysis Data -> Time History Load Case
Transient: Time history analysis is carried out on the basis of loading a time load function only once. This is a common type for time history analysis of earthquake loads. Periodic: Time history analysis on the basis of repeatedly loading a time load function, which has a period identical to End Time. This type is applicable for machine vibration loads.
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10. Time History Analysis
midas Civil Cable Stayed Bridge
Step 2: Define Time History Load Case Load -> Time History Analysis Data -> Time History Load Case
Order in Sequential Loading: Select a time history analysis condition previously defined, which precedes the time history analysis condition currently being defined. The Analysis Type and Analysis Method for the current time history analysis condition must be consistent with those for the preceding load condition
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10. Time History Analysis
midas Civil Cable Stayed Bridge
Damping Method: the damping method can be one of : 1. Modal 2. Element Mass & Stiffness Proportional 3. Strain Energy Proportional
For Element Mass & Stiffness Proportional the relevant has to be provided in : Model -> Properties -> Group Damping: Element Mass and Stiffness Proportional
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The user can select the time history function from the list of various database earthquake or can generate its own:
Load -> Time History Analysis Data -> Time Forcing Function
10. Time History Analysis
midas Civil Cable Stayed Bridge
Bridging Your Innovations to Realities
Rotational angle about GCS Z-axis signifying the direction of the horizontal component of the ground acceleration. Sign convention is (+) in the counter-clockwise direction and (-) in the clockwise direction, with reference to the X-axis.
Select the Earthquake for X,Y and Z direction
Load -> Time History Analysis Data -> Ground Acceleration
10. Time History Analysis
midas Civil Cable Stayed Bridge
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The user can do the time history analysis with Moving loads using this feature. The user needs to define the moving loads as Dynamic Nodal Loads.
Load -> Time History Analysis Data -> Dynamic Nodal Loads
10. Time History Analysis
midas Civil Cable Stayed Bridge
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Load -> Time History Analysis Data -> Multiple Support Excitation
In a structure with multiple supports, different time history forcing functions in terms of ground acceleration can be applied to different supports at varying times.
10. Time History Analysis
midas Civil Cable Stayed Bridge