1. Bridge Load Optimisation Analysis
21/04/2017
Bridge Load Optimisation Analysis
Thomas Li

2. Contents Introduction Build bridge model in GSA
21/04/2017
Introduction
Build bridge model in GSA
Axis, grid plane and their uses
Grid loads & their distributions
Data required for bridge analysis
Influence lines
Doing bridge analysis
Bridge analysis tools
Inspecting bridge results

3. Introduction
21/04/2017
Bridge analysis is not a normal sense analysis as it does not produce analysis results such as displacement, element forces & moments
Bridge analysis optimises the distribution of bridge loads according to the influence lines
Influence lines are drawn for each influence effects on every path and lane, the influence effects can be displacements, rotations, forces or moments
The main results from bridge analysis are new load cases that represent the most adverse distributions of the bridge loads

4. Introduction
21/04/2017
Fully automatic optimisation availabhle for the following bridge codes
Hong Kong – SDM
UK – BD37
EC1 – UK annex
UK - Assessment loading
Step-by-step optimisation for the following bridge codes
Hong Kong UK
EC1
Australian US …
Brief view of the bridge model with optimised load cases

5. Build bridge model in GSA
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Choose appropriate bridge code
Define appropriate axis
Define grid plane for the deck
Define alignment that is used as the guideline of carriageways and paths
Create the bridge model
Using the same method as building other GSA model, e.g. copy & paste etc
Using ‘Extrude Selection…’ method to make use of alignment so the bridge model is well aligned with the alignment ….
Define carriageways/paths
Define influence effects
Define path loading if step-by-step method is used …
GSA demonstration

6. Axis, grid plane & their uses
21/04/2017
Axis, grid plane & their uses
Axis
Types
Cartesian
Cylindrical
Spherical
The uses:
To define nodal coordinates
To define nodal constraint directions
To define load directions
To define element orientations
To define directions of results
To define Grid plane orientation

7. Axis, grid plane & their uses
21/04/2017
Axis, grid plane & their uses
Grid plane
A virtual plane parallel to the xy plane of the axis
It can be used for defining grid loads, current grid, bridge paths & polyline etc
To define the bridge deck
Current grid
To define the axis system used for the model
To define the current grid lines

8. Axis, grid plane & their uses
21/04/2017
Axis, grid plane & their uses
Creation of axis
Using axis tables if no elements and nodes have been created
Using sculpt tool
Highlight three non-coplanar nodes, then use sculpt tool (menu ‘Sculpt | Create User Axes...’) to open the dialog box to create axis
It is easy and quick especially for axes not parallel to global axis

9. Axis, grid plane & their uses
21/04/2017
Axis, grid plane & their uses
Creation of grid plane
Using grid plane tables
Axis – grid plane is parallel to the xy plane of the axis
Element list – the elements associated with this grid plane, e.g. applying grid loads or viewing on graphic
Tolerance – another way to control the elements associated to this grid plane
Span – how the grid loads on this grid plane to be distributed to 1D elements, one way, two way or multiple way
Using sculpt tool
Highlight one node that the grid plane will pass, then use sculpt tool (menu ‘Sculpt | Create Grid Plane...’) to open the dialog box to create the grid plane

10. Grid loads & their distributions Grid loads
Loads apply to the whole grid plane or part of a grid plane
It is a convenient way to apply floor loads, wind loads and patch loads etc.
Grid load can be point loads, line loads or area loads
The way to expand bridge is controlled by grid plane span type, one way, two way or multiple way.

11. Grid loads & their distributions
Grid load distribution
Grid loads are expanded to element loads implicitly before doing analysis, the failure of expanding grid loads will affect the analysis.
Grid loads can only be distributed to 1D elements (beam, bar, tie or strut) that are forming a closed panel
If the panel is not closed, dummy element can be used to close it up, but it is not allowed to connect one dummy element to another dummy element.
The way the grid loads are distributed depends on the grid plane span type - one way, two way or multiple way

12. Grid loads & their distributions
Grid load distribution
The valid panel should not have internal angle larger than 180 degrees
Valid
Invalid

13. Depends on straightness torlerance
Grid loads & their distributions
Grid load distribution
The internal angle is allowed to slightly larger than 180 degrees
Valid or invalid?
Depends on straightness torlerance

14. Grid loads & their distributions
Grid load distribution
Check ‘Draw current grid panels’ box on ‘Display method’ dialog box to view valid & invalid panels
Make sure the current grid uses the grid panel to be viewed
Expand grid load tool (menu ‘Tools | Expand grid loading…’) can also be used to check whether the grid loads can be expanded successfully

15. Data required for bridge analysis
Axis
Grid plane
Alignment
Path
Carriageway – fully automatic analysis
Lane & track etc – step-by-step analysis
Vehicle
Bridge variable UDL - VUDL
Influence effects
Path loading
Bridge loading

16. Data required for bridge analysis
Axis
It is used to define grid plane orientation
Grid plane
It is used as the reference of the bridge deck
Alignment
A straight or curved line that is used as the guideline of bridge paths or carriageways

17. Data required for bridge analysis
Path
Lane-by-lane analysis, use these
Lane
Track
Vehicle
Footway
Fully automatic analysis, use these
Carriageway 1
Carriageway 2
The only difference between Carriageway 1 & Carriageway 2 is that the number of lanes are doubled when calculating the lane factors if Carriageway 1 is used for HK or UK codes

18. Data required for bridge analysis
Vehicles (standard or user defined)
Standard UK
Hong Kong
AASHTO
Australian
Eurocode
User defined
Any number of axels and wheel loads

19. Data required for bridge analysis
Bridge variable UDL – VUDL
UDL loads but the density varies
Standard
HA (UK)
HA (HK)
Foot (UK)
Foot (HK)
Sidewalk (US)
User defined
Any types

20. Data required for bridge analysis
Influence effects (the objectives of the bridge load optimisation analysis, i.e. maximum & minimum values to be produced)
Nodal forces
Nodal displacements
Beam forces
Beam displacements

21. Data required for bridge analysis
Path loading – Required only by lane-by-lane analysis
Standard
UK/HK highway
UIC or UK railway
US highway
Australian highway
Eurocode highway
User defined
User vehicle or standard vehicle
User VUDL or standard VUDL …

22. Data required for bridge analysis
Bridge loading
Static bridge loads
It is normally generated by bridge optimisation analysis
It can also be edited directly on the table
It has to be expanded as grid loads to be used in the analysis

23. Data required for bridge analysis
Bridge loading
Moving bridge loads
It is a manual way to put moving loads on the bridge, but the loads do not move until they are expanded to grid loads to simulate the moving loads
When it is expanded, it will produce a number of loads (each with a different load case) representing each of the locations of the moving bridge loads
The same as Static bridge load, It has to be expanded as grid loads to be used in the analysis

24. Data required for bridge analysis
Bridge loading
Bridge loads do not associate with any load cases and they will not be considered in GSA analysis.
Before using these loads in analysis, they must be expanded to grid loads using tool command ‘Tools | Bridge Analysis | Expand Bridge Loading’

25. Influence lines Influence effect Influence line
Displacement, force or moment etc at the particular point to be studied by the influence line
Be selective using engineering judgement and do not select unnecessary influence ettects
Influence line
Gives effect of moving load at the influence effect point
Influence effect & influence line
One influence line is related to one influence effect only
One influence effect can have many influence lines depends on the number of paths on the bridge

26. Influence lines Example influence line
The influence effect – bending moment at the second support from left
The value at any point along the influence line represent the moment at the influence effect point (2nd support) when the load is acting on the same point

27. Doing bridge analysis Load, analysis & combination cases
Load cases – no analysis results associated
Analysis cases – with analysis results
Combination cases
Envelope cases
Open ‘Combination Case and Envelope Details’ output view for details
Analysis tasks
An unique analysis unit for the solver
Contain one or more common analysis cases, e.g. mode 1 to mode 12 of a dynamic analysis
Manipulation of analysis tasks – new, copy, paste and delete etc on analysis task view

28. Doing bridge analysis Analysis wizard Bridge analysis task
Create new analysis task
Modify analysis task
Bridge analysis task
One allowed
Delete it will also delete all data/results generated by this task, e.g. static bridge loads, grid loads etc.

29. Doing bridge analysis: Lane-by-lane analysis
1. Enable bridge analysis
2. Set bridge design code to ‘undefined’
3. Define a user axis
4. Design a grid plane
5. Define an alignment
6. Define a series of paths (not carriageway)
7. Define node and/or beam influence effects
8. Define a series of path loads

30. Doing bridge analysis: Lane-by-lane analysis
9. Do influence analysis only and do the followings, or check all check boxes on the analysis wizard to do the analysis as a batch run
10. Optimise the path loads (by tools) which generate Static bridge loads
11. Expand static bridge loads to have the equivalent grid loads
12. Carry out static analysis using the equivalent grid loads
13. Setup combination cases

31. Doing bridge analysis: Fully automatic analysis
1. Enable bridge analysis
2. Select a bridge design code
3. Define a user axis
4. Design a grid plane
5. Define an alignment
6. Define a carriageway, footway

32. Doing bridge analysis: Fully automatic analysis
7. Define node and/or beam influence effects
8. Carry out Bridge Analysis which will produce optimised bridge loads (two load cases for each influence effect) and the combination cases, the load case will be analysed.

33. Generate static vehicle load
Bridge analysis tools
Generate static vehicle load
Manually create some vehicle loads
Optimise path loading
Active after influence analysis has been done
To produce static bridge loads from ‘Path loadings’

34. Bridge analysis tools Expand bridge loading Delete grid loads
Expand static or moving bridge loads as grid loads that can be used by analysis
Delete grid loads
Delete automatically generated grid loads from bridge analysis

35. Inspecting bridge results
21/04/2017
Output tables
Tabular numerical outputs of analysis results as well as input data
Open from menu ‘View | New Output View’
Default settings – to set default output view settings, open the view and set preferences, then click menu item “View | Save default view settings”

36. Inspecting bridge results
21/04/2017
Diagram
Diagram views of analysis results on graphic view such as moment & shear diagram etc
Define by clicking ‘Diagram settings’ button
Default settings - to set default settings, get the preferred diagram view opened and then click menu item “View | Save default view settings”

37. Inspecting bridge results
21/04/2017
Contour
Contour views of analysis results and data on graphic view such as stress & strain etc
Define by clicking ‘Contour settings’ button
Default settings - to set default settings, get the preferred contour view opened and then click menu item “View | Save default view settings”

38. Inspecting bridge results
21/04/2017
Chart view
Line or histogram plot views of one variable versus another one or more results such as time versus acceleration, displacement versus load factor etc
Chart view settings – the setting is different for different result types, there is no common settings like output and diagram view etc.
Access from menu ‘View | new Chart View | ...’
e.g. cut section forces