20120419 civil advanced webinar cablestayed
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midas Civil Cable Stayed Bridge
Bridging Your Innovations to Realities
Contents: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
2
midas Civil
Cable Stayed Bridge
Bridging Your Innovations to Realities
1. IntroductionCable Stayed Bridge
Wheel Load Flexure In Deck
Cable Supports Tension In cables Axial Load in Pylon
Project Applications
Cable Stayed Bridge
Bridging Your Innovations to Realities
Stiffness of the cable is dependent on :
1. Load Applied
2. Tension Applied
P1
P1 P2
P2
midas
Civil
Project Applications
Cable Stayed Bridge
Bridging Your Innovations to Realities
Cable Stiffness can be determined as per the following two techniques:
1. Equivalent Truss Method
2. . Elastic Catenary Cable
midas
Civil
Project Applications
Cable Stayed Bridge
Bridging Your Innovations to Realities
Cable Bridges are highly indeterminate structures:
midas
Civil
Project Applications
Cable Stayed Bridge
Bridging Your Innovations to Realities
Change of Cable Stiffness with Pretension
High Indeterminacy
Difficult Analysis
midas
Civil
Project Applications
Cable Stayed Bridge
Bridging Your Innovations to Realities
Cable Shape and pretension are in turn dependent on the load applied on the cable.:
Geometric Non Linear Analysis
midas
Civil
midas Civil
Cable Stayed Bridge
Bridging Your Innovations to Realities
2. Problem StatementProblem Statement:
100 m
200 m
100 m
midas Civil
Cable Stayed Bridge
Bridging Your Innovations to Realities
2. Design ProcessSteps of Design :Preliminary 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
Check for Final Design
midas Civil
Cable Stayed Bridge
Bridging Your Innovations to Realities
3. Preliminary DesignPreliminary Design 1. Deck, Pylon Cross section. 2. Diameter of Cables. 3. Height of Pylons
midas Civil
Cable Stayed Bridge
Bridging Your Innovations to Realities
4. Determination of Cable TensionDetermination of Cable Forces 1. Use the unknown Load factor.
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.
midas Civil
Cable Stayed Bridge
Bridging Your Innovations to Realities
4. Determination of Cable Tension
midas Civil
Cable Stayed Bridge
Bridging Your Innovations to Realities
5. OptimizationCheck the Design forces for the deck, pylon and cables and modify.
midas Civil
Cable Stayed Bridge
Bridging Your Innovations to Realities
6. Forward Construction Stage AnalysisModeling 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
Cable Stayed Bridge
Bridging Your Innovations to Realities
6. Forward Construction Stage AnalysisImplication with Forward Construction Stage Analysis
Stage 10
S
New Tendons Stage 11
More Pretension is required
midas Civil
Cable Stayed Bridge
Bridging Your Innovations to Realities
6. Forward Construction Stage AnalysisLack of Fit Force: It calculates the additional pretension required for cable installation
midas Civil
Cable Stayed Bridge
Bridging Your Innovations to Realities
7. Unknown Load Factor With Time Dependent MaterialsConstruction Stage
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.
Unit Pretension loading
Unknown Load FactorSet constraints and calculate unknown load factor by step
Construction StageUsing influence coefficient to reanalyze construction stage
Check
End[Iterative analysis procedure to calculate unknown load factor]
midas Civil
Cable Stayed Bridge
Bridging Your Innovations to Realities
8. Eigen Value AnalysisAnalysis -> Eigen Value Analysis Control
Ritz VectorsUnlike 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.
midas Civil
Cable Stayed Bridge
Bridging Your Innovations to Realities
9. Eigen Value AnalysisTo convert the final stage Cable forces to be used for determining cable stiffness for the Eigen Value Analysis
midas Civil
Cable Stayed Bridge
Bridging Your Innovations to Realities
9. Eigen Value AnalysisStep 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.
midas Civil
Cable Stayed Bridge
Bridging Your Innovations to Realities
10. Time History Analysis
midas Civil
Cable Stayed Bridge
Bridging Your Innovations to Realities
10. Time History Analysis
Linear Case
Non Linear Case
R(x,xa) : Viscous Damping Fs(x): Variable Stiffness
midas Civil
Cable Stayed Bridge
Bridging Your Innovations to Realities
10. Time History AnalysisProcedure of Eigenvalue Analysis: Define Properties of Non linear Links Input Non Linear Links Define Time History Load Case Time Forcing Function Ground Acceleration Perform Non Linear Time History Analysis Check the Results
midas Civil
Cable Stayed Bridge
Bridging Your Innovations to Realities
10. Time History AnalysisStep 1: Defining Properties of Non Linear Links Model -> Boundaries -> General Link Properties
midas Civil
Cable Stayed Bridge
Bridging Your Innovations to Realities
10. Time History AnalysisBase Isolators Provided in midas CivilBase Isolators: Lead Rubber Bearing Isolator Friction Pendulum System Isolator
Viscoelastic Damper Gap Hook Hysteresis System Base Rubber isolator Friction Pendulum System isolator
midas Civil
Cable Stayed Bridge
Bridging Your Innovations to Realities
10. Time History AnalysisStep 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.
midas Civil
Cable Stayed Bridge
Bridging Your Innovations to Realities
10. Time History AnalysisStep 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
midas Civil
Cable Stayed Bridge
Bridging Your Innovations to Realities
10. Time History AnalysisDamping 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
midas Civil
Cable Stayed Bridge
Bridging Your Innovations to Realities
10. Time History AnalysisLoad -> Time History Analysis Data -> Time Forcing FunctionThe user can select the time history function from the list of various database earthquake or can generate its own:
midas Civil
Cable Stayed Bridge
Bridging Your Innovations to Realities
10. Time History AnalysisLoad -> Time History Analysis Data -> Ground AccelerationSelect the Earthquake for X,Y and Z direction
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.
midas Civil
Cable Stayed Bridge
Bridging Your Innovations to Realities
10. Time History AnalysisLoad -> Time History Analysis Data -> Dynamic Nodal Loads
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.
midas Civil
Cable Stayed Bridge
Bridging Your Innovations to Realities
10. Time History AnalysisLoad -> Time History Analysis Data -> Multiple Support ExcitationIn a structure with multiple supports, different time history forcing functions in terms of ground acceleration can be applied to different supports at varying times.
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