Using non-linear analysis solver in GSA 1GSA

Bridge Load Optimisation Analysis

Thomas Li

Using non-linear analysis solver in GSA 2GSA

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

Contents

Using non-linear analysis solver in GSA 3GSA

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

Using non-linear analysis solver in GSA 4GSA

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 …

Introduction

Using non-linear analysis solver in GSA 5GSA

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 …

Build bridge model in GSA

Using non-linear analysis solver in GSA 6GSA

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

Using non-linear analysis solver in GSA 7GSA

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

Using non-linear analysis solver in GSA 8GSA

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

Using non-linear analysis solver in GSA 9GSA

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

Using non-linear analysis solver in GSA 10GSA

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

Using non-linear analysis solver in GSA 11GSA

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

Using non-linear analysis solver in GSA 12GSA

Grid load distribution The valid panel should not have internal angle

larger than 180 degrees

Grid loads & their distributions

Valid Invalid

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Grid load distribution The internal angle is allowed to slightly larger than

180 degrees

Grid loads & their distributions

Valid or invalid? Depends on straightness torlerance

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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

Grid loads & their distributions

Using non-linear analysis solver in GSA 15GSA

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

Using non-linear analysis solver in GSA 16GSA

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

Using non-linear analysis solver in GSA 17GSA

Path Lane-by-lane analysis, use these

Lane Track Vehicle Footway

Fully automatic analysis, use these Carriageway 1 Carriageway 2 Footway

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

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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

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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

Using non-linear analysis solver in GSA 20GSA

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

Using non-linear analysis solver in GSA 21GSA

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

Using non-linear analysis solver in GSA 22GSA

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

Using non-linear analysis solver in GSA 23GSA

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

Using non-linear analysis solver in GSA 24GSA

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’

Data required for bridge analysis

Using non-linear analysis solver in GSA 25GSA

Influence effect 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

Using non-linear analysis solver in GSA 26GSA

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

Influence lines

Using non-linear analysis solver in GSA 27GSA

Doing bridge analysis Load, analysis & combination cases

Load cases – no analysis results associated Analysis cases – with analysis results Combination cases

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

Using non-linear analysis solver in GSA 28GSA

Analysis wizard 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

Using non-linear analysis solver in GSA 29GSA

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

Using non-linear analysis solver in GSA 30GSA

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: Lane-by-lane analysis

Using non-linear analysis solver in GSA 31GSA

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

Using non-linear analysis solver in GSA 32GSA

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.

Doing bridge analysis: Fully automatic analysis

Using non-linear analysis solver in GSA 33GSA

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

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Expand bridge loading 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

Bridge analysis tools

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Inspecting bridge results 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”

Using non-linear analysis solver in GSA 36GSA

Inspecting bridge results 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”

Using non-linear analysis solver in GSA 37GSA

Inspecting bridge results 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”

Using non-linear analysis solver in GSA 38GSA

Inspecting bridge results 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

Using non-linear analysis solver in GSA 39GSA

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