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

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

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

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

Build bridge model in GSA 21/04/2017 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

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

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

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

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

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.

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

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

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

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

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

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

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

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

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

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

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 …

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

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

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’

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

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

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

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.

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

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

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

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.

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’

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

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”

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”

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”

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

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