ces321585 bridge detailing 2.0: computational modelling

CES321585

Bridge Detailing 2.0:Computational modelling methods using Civil 3D,Revit & DynamoJim Crabtree BIM-CPJacobs

DescriptionFinding an automated workflow suitable for complex bridge design isn't easy. Bridge models areoften at the mercy of corridor changes; add to this the fact that bridge designers often usedifferent software to the alignment team and the result can be a disconnected, isolated process.Using Dynamo and the open-source CivilConnection node package, this class will show howRevit bridge geometry can be dynamically linked to alignment data, reducing abortive work andincreasing the efficiency of implementing design changes. This class will provide an introductionto formulating agile and powerful workflows allowing the best parts of Civil 3D and Revit to beleveraged together in the bridge detailing process. The result is an ability to bring computationaldesign, predominantly still seen as suitable only for preliminary production, firmly into thedetailed design arena.

Speaker(s)Jim Crabtree is a civil engineer working in the Bridge sector. He has experience from roles asstructural inspector, railway site safety controller, design engineer and CAD manager. His loveof digital design and construction includes over 18 years’ using Autodesk tools. In recent yearsas a BRE BIM Certified Practitioner, Jim has turned his focus to information management andproject automation on several major UK highways projects. Jim also takes a leading role in thedevelopment of design automation workflows and strategy in the Jacobs Bridges business unit.

[email protected]/in/je-crabtree

Learning Objectives· Use the Subassembly Composer to create custom parametric bridge components· Build a Civil 3D corridor describing complex bridge deck geometry· Create a Dynamo definition to produce Revit objects from Civil 3D corridors· Understand how custom Dynamo nodes are created for bridge modelling, which

bring agility and transferability to workflows

Contents

Introduction ............................................................................................................................................... 3A Real-World Case Study ........................................................................................................................ 4The Workflow ............................................................................................................................................ 7Subassembly Composer ....................................................................................................................... 10Civil 3D ..................................................................................................................................................... 18Dynamo – Linear Elements ................................................................................................................... 21Dynamo – Discrete Elements ............................................................................................................... 25Dynamo – Framing Elements ............................................................................................................... 27Dynamo – Custom Nodes ..................................................................................................................... 28Revit Model Setup .................................................................................................................................. 30Postface - Next Steps............................................................................................................................. 33

IntroductionDigital bridge engineers have much to contend with. As part of the comprehensive design of anybridge, aspects including earthworks design, alignment control, site constraints and structuraldesign requirements all need to be considered. Add to this the fact that whilst digital design &automation moves us towards a world of drawing-less delivery, many bridges still requirecomplex technical drawing and schedule production. Workflows that provide interoperability aretherefore key – using Civil 3D and Revit together in the design process is the most establishedmethod in the business, and when done well creates powerful results.

No two bridges are exactly alike. The intention of this class is to provide an efficient, versatileworkflow that works for a range of structural types, and whilst the case study we’ll be looking atis a specialist type structure, similar ‘Linear Structures’ principles can be applied to a range ofbridge types and other linear structures.

In this class we will examine the modelling methods used in order to achieve the Revit modeloutput for ‘Bridge K’; a cable-stayed bridge structure currently at the preliminary design stage.Each initial stage of the workflow is looked at in detail within this handout, the intention being toprovide an introduction to the main principles of using the open-source CivilConnection Dynamonode package to link Civil 3D and Revit model content.

The primary purpose of using CivilConnection within this context is to leverage the bestfunctionality of both Civil 3D and Revit for bridge designers within a single process:

· Civil 3D offers the most relevant tools for ‘linear’ element and earthworks design. Byusing shared project data shortcuts to alignment and surface content, the bridge modelgeometry is linked to the alignment design and other multi-disciplinary project content.

· Revit outputs provide parametric object modelling, as well as schedule and 2D drawingcontent creation.

Whilst workflows using a combination of these tools are not new, the toolset whichCivilConnection provides changes the game in terms of the required complexity. Within thisguide you won’t find any reference to utilising Python code or CSV point input; whilst these areno doubt powerful allies in the quest for automation, CivilConnection simplifies the process ofextracting Civil 3D corridor information. This guide will hopefully demonstrate that much can begleaned from the use of Dynamo alone to achieve the required computational model behavior,and this provides a sound foundation of knowledge for further forays into more complexmethods as required.

The content of this handout is therefore intended only to act as a guide to the first fundamentalsteps in this process. Once these are well understood, further development of model definitionis possible through use of further Dynamo computation, parametric family editing andCivilPython scripting.

A Real-World Case Study‘Bridge K’ is a 160m long cycleway bridge over the River Severn in the UK, comprising 7 spansof lightweight steel deck construction with reinforced concrete approach ramps at either end.The main cable-stayed river span is 70m long, supported by 26m high dual steel masts with5No. support cables on each side of the deck.

3 potential alignments are being considered during the preliminary design; one straightalignment and two with increasing horizontal curvature. The preferred alignment is straight, andit’s this option that we’ll be looking at in depth.

The bridge design is currently in the preliminary stages, with any modelling output intended tofollow on into the detailed design process.

BRIDGE K

THREE ALIGNMENT OPTIONS

The SiteThe chosen bridge site over the River Severn is well suited to a cycle bridge; topology isrelatively flat and ground levels on either side of the river are similar, leading to a bridgelong section with a very shallow longitudinal gradient and only one vertical change indirection. Whilst ground conditions are fair it is likely that piled foundations will berequired.

The intention of the bridge is to link public footpaths on each side of the river.Construction space on both sides is ample, however interfaces with telegraph cablesimmediately to the south of the bridge site, as well as proximity to private residencesmust be considered as design constraints.

ELEVATION

THE BRIDGE SITE

The Workflow

CivilConnectionCivilConnection is a Dynamo for Revit package that enables the exchange of informationbetween Civil 3D, Dynamo and Revit. The open source package is available todownload from https://github.com/Autodesk/civilconnection, along with referencedocumentation. A full feature list is available on this page, but in short, its featuresinclude:

· The ability to work directly with an open instance of Civil 3D, pulling data intoDynamo in a live fashion for immediate updates

· The ability to read corridor features includingo Alignmentso Auto-corridor feature lineso Assembly shapes

· Placement of Revit elements according to feature line information· Lofting of assembly shapes into smooth mass solids with no faceting/tessellation· Creation of AutoCAD entities· Sending commands to the Civil 3D command line and creation of command line

scripts

The ‘Linear Structures Workflow Guide’ (available via the above link) provides in-depthbackground, installation and usage information. It is highly recommended that referenceis made to this document before attempting to use CivilConnection.

Note –CivilConnection is available for all Civil 3D release numbers from 2017 onwards.Install for the version of Civil 3D you are using, not Revit!

You must be using Dynamo for Revit 1.3+

Element BreakdownSuccessful deployment of any automation methods requires a clear modelling strategyfrom the outset, and a clear understanding of how each structure element shall beproduced and controlled in terms of position or dimensions. This class defines bridgeelements in terms of three broad categories, and in our modelling method we’ll betackling these as follows:

1. Linear Elements (shown in the figure below in blue) include the deck, girders,parapet rails, ducting & drainage channels, etc…

These will be created as a Civil 3D corridor. A Dynamo definition will handlethe extraction of the corridor assembly shapes to create lofted mass solids inRevit, each within their own component family.

2. Discrete Elements (shown in the figure below in red) include cross girders,parapet posts, foundations, etc…

These will be created as parametric families, prepopulated in the Revit project.Their placement and orientation will be controlled via offset, angle & elevationfrom given feature line stations within the Dynamo definition.

3. Framing elements include elements requiring more than a single placementpoint such as diaphragms, deck bracing, and in the case of our bridge, the cable-stays.

These can be created via adaptive components or structural framing families,with the start/end points derived from the Dynamo definition.

ELEMENT BREAKDOWN OF BRIDGE K

Note that these categories make no reference to the standard engineering terminologyof longitudinal & transverse as these may not apply in all cases.

It’s worth noting that the concrete approach ramps in the above figure are categorised aslinear elements, and therefore initially produced as part of the Civil 3D corridor. This willbe useful if the alignment is to change to a curved configuration, as well as automaticallyproviding their tapered vertical profile. In other cases, it may be suitable to class theseas discrete objects and create parametric families for them, and indeed as the design ofBridge K develops, there is the potential to:

1. Develop these families for further detail (such as providing bearing shelves)2. Remove the respective Civil 3D corridor regions3. Update the Dynamo definition to control them instead as discrete elements (via feature

line station, offset, angle, elevation).

Note –Where a higher level of automation is required for pile configurations, they can becreated via structural column families and point input via Dynamo. In the case of ourbridge, all piles are produced as part of the parametric substructure families.

Modelling MethodThe overall workflow can be summarised as follows:

The following sections of this handout will cover each of these steps in further detail.

SubassemblyComposer• Custom

subassemblies arecreated for thelinear elements

• Point codes aredefined for thecreation of featurelines

• Shapes are defined

Civil 3D•Alignment, profile

and assemblyinformation is usedto create a corridordescribing thelinear elements ofthe bridge

Dynamo•Corridor shapes are

collected and loftedinto masses

•Feature lineinformation is usedto define thesetting out ofdiscrete elements

Revit•Project coordinates

are set•Project is populated

with families ofdiscrete elements

•Project is populatedwith families oflinear elements

•2D Documentationproduced

Subassembly Composer

InstallationThe composer comes included as an optional subcomponent of Civil 3D and is notavailable separately. If you don’t see it under the Civil 3D heading in your Start bar:

· Go to Apps & Features in the Windows settings/Control Panel· Find the relevant installation of Civil 3D· ‘Modify’ the installation, and add the Composer when prompted

Step 1 - Creating ParametersCreating your parameters first will allow you to then apply these within the pointsconfiguration in the next step. Think carefully about what parameters you require andhow you want your assembly to ‘flex’; careful consideration now may make for fastdesign changes later, as parameters can be changed in the Civil 3D environment onceloaded. Let’s look at the primary deck cross section for Bridge K:

We have 2 diamond shaped beams, and some deck surfacing. Note that the crossgirders aren’t included – they are discrete objects and come later. We want to maximisethe flexibility of this cross section, so 4 parameters have been created under the‘Input/Output Parameters’ tab, which will parameterise the deck width and beam size.

Step 2 – Adding Points and Links· Points define the basic structure, and when coded, produce auto-corridor feature

lines· Links connect points, and when coded, produce surfaces· Shapes are defined by a closed region of links, and may be extracted into solids

Always start by creating ‘sequences’ in the workflow area. These will allow you toorganise your points, links & shapes effectively, and can be useful when things start toget complex. Our subassembly is 3 shapes only - If you’re dealing with a complex deckconfiguration (say, a multi-girder composite type deck), consider creating these asseparate subassemblies.

USING SEQUENCE GROUPS

Create your points, adding dimensions (doubles), or expressions including yourparameter names where relevant:

ADDING PARAMETERS

Step 3 – Defining VariablesAdding variables to your subassembly flowchart is a way of parameterising expressions,allowing them to be recalled and used quickly throughout the flowchart.

One possible application of this is to affect the behaviour of one parameter by the resultsof another. Within the Bridge K deck subassembly, an IF statement has been added as avariable, which will affect the deck system thickness according to its span:

IF(Width_L + Width_R < 3, 0.05, 0.06)

“If the combined deck width is less than 3m, then the deck surfacing system shallbe 50mm thick. If not, it shall be 60mm thick”

The expression can then be named and called as a parameter as normal.

Step 4 – Applying TargetsUsing offset targets allows the horizontal geometry of your section (width) to becontrolled via polylines or feature lines within Civil 3D. This has 2 significantapplications in bridge deck design:

· Decks of varying width can be rendered by applying targets on one or both sidesof the bridge structure at a tapered angle to the alignment:

· Where dealing with curved horizontal road alignments, straight polylines on eitherside of the deck targeted to the deck edges can be applied to render a straightdeck over the curve (a common detailing method for shorter span bridges):

Using elevation targets allows the vertical geometry (depth) to be controlled via verticalprofiles. This again, has significant applications:

· Dealing with differences in construction depth between the deck and roadsurface, particularly for producing flat/linearly sloped decks over alignments withvertical curvature:

· Decks or deck elements of varying depth, such as steel beams or concrete boxgirders with an arched profile:

Create your entries in the ‘Target Parameters’ tab and apply these to the required pointsin a similar fashion to the input parameters. Note that any targets will override the Inputparameters previously created when they are applied.

Note – Even when use of targets is anticipated, always provide Delta X/Y formulaas a default value

Step 5 – Creating Links & ShapesA suite of nodes exists within CivilConnection to read subassembly shapes, allowingthem to be lofted into editable Revit masses and placed within generic families. Thismethod has the following advantages over other methods of producing deck solids (suchas extracting in Civil 3D and linking to Revit via IFC):

· Geospatial coordination is automatically handled by CivilConnection. Assumingthe Revit project coordinates are set, no further translation is required.

· Smooth solids are produced with no visible facets, providing a significantadvantage at the drawing production stage, particularly for curved elements.

· These solids are produced along NURBS type curves intersecting allsubassembly points, negating the need to consider tight assembly frequencies ormid-ordinate distances within the Civil 3D corridor and allowing for a simpler,leaner corridor model.

· Discontinuations (or ‘creases’) in lofted solids can be defined at station locationsif required. This is useful for abrupt changes in direction or segmented deckprofiles.

Shapes should therefore be defined within your subassembly by forming closed loops oflinks and then defining a shape within them, noting that each shape will produce aseparately lofted solid.

Step 6 – Adding Point CodesWhen coded, points produce auto-corridor feature lines. These are a crucial part of theworkflow, allowing discrete elements to be placed along and controlled spatially via theDynamo definition.

As a minimum, a centreline point code should always be provided as part of the deckassembly. As part of decks of constant cross section, this may be enough to place allrequired discrete elements, when we consider that the offset and elevation of elementsfrom the feature line can be defined as a node input. For more complex geometry,consider a range of codes which may include stringcourse edges, girder centrelines andeven ducting positions.

A suitable name should be added in double quotation marks in order to correctly identifythe feature lines required within list outputs in the Dynamo definition.

ADDING POINT CODES

Tip –Parameterising your point code names will allow them to be changed in the Civil3D Subassembly Properties once loaded. Add a string type input parameter andenter the parameter name as the Point Code value.

Creating further subassembliesAs our corridor will comprise several regions, the cross sections of all need to beconsidered.

The approach ramps can also be defined using the Composer. This one has parametersfor the slab thickness and overall width. There are also defined targets; an elevationtarget on the base slab will allow us to control the trough depth via vertical profile, andoffset targets for controlling the width via horizontal polyline if required:

Further examples – other bridge typesMuch can be achieved through the use of good subassembly planning. The exampleimage below comes from an assembly for a composite type bridge deck, comprisingseparately created subassemblies for the steel girders and concrete deck. Flexibleparameters include:

· Girder overall depth· Girder plate thicknesses and widths· Deck slab thickness· Deck slab width· Deck slab crossfall grade· Stringcourse depth and width

Tip -Always consider your total construction depth. The baseline indicator of theassembly above represents the carriageway surface centreline, and therefore sitsabove the slab top face for coordination purposes.

Civil 3D

Data ShortcutsUsing data shortcuts has distinct advantages when working on multidisciplinary projects.By using the same centralised alignment and surface data as included in the highwaysdesign (or any other transportation corridor, for that matter), as a bridge designer youcan ensure synchronicity between the primary corridor model content and the bridgemodel.

For highways bridges or other structures reliant on geometry produced by other teams,using data shortcuts is therefore highly recommended.

Tip –By avoiding using the ‘Rebuild – Automatic’ option on your corridor, you’ll benotified of an out of date corridor, allowing you to stay in control of designchange:

Corridor PropertiesWhere applicable, use regions to define any changes of cross section type. In the caseof our bridge, we have 3 regions (one for the deck, and two ramp approaches at eitherend). These regions can be organised and dealt with as separate entities in the Dynamodefinition.

THE BRIDGE K CORRIDOR COMPRISING THREE REGIONS

CORRIDOR PROPERTIES

1. Specify the alignment required as a horizontal baseline, and the correspondingdeck profile.

2. Specify the assembly required for each region.3. Always ensure that your regions & baselines are appropriately named. This will

make them easy to identify in the Dynamo definition.4. Station frequency plays a large part in CivilConnection calculation time. As a

general rule of thumb, use the lowest possible frequency to return acceptableresults on the geometry of the corridor. Generally speaking, a frequency of 20malong tangents, and 5m along curves with a mid-ordinate distance of 0.1 produceadequately precise geometry, and manageable list lengths in Dynamo. Higherfrequencies run the risk of long run times, and in the worst case the failure of theDynamo definition and are therefore not recommended.

5. Set the offset and elevation targets defined in your subassemblies usingpolylines, feature lines and additional profiles. In the case of our bridge, elevationtargets defining the approach ramp foundation slabs have been defined asadditional vertical profiles.

Tip -The same alignment can contain multiple baselines. Best practice for complexmulti-structure projects is to include the bridge lengths as separate baselineswithin the primary highway corridor. This will allow for easy identification of thebridge regions.

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SETTING TARGETS

ADDITIONAL PROFILES USED AS TARGETS

Using Multiple Corridors

One powerful feature of corridor modelling is the ability to target the auto-corridor featurelines in one corridor to affect the behaviour of another. For instance:

· Could you automatically control your deck width via feature lines at the edges ofthe highway design?

· Could you model a walkway slab to span between two independently controlleddeck corridors?

The following sections outline each of the major steps within the Bridge K Dynamo definition.

Dynamo – Linear Elements

Start Civil 3D Integration

1. Initialises the integration with an open instance of Civil 3D.2. When this node is included, the Periodic run option becomes available in

Dynamo. Note that it is generally recommended that you use only the ‘Manual’option when using CivilConnection.

3. Allows an open document to be specified by filename rather than an indexnumber (which drifts according to the number of open documents in Civil 3D).

Get Corridor Regions

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Get Subassembly Shapes

1. Draws the shapes in the Dynamo geometry preview and translates to the coordinatedgeospatial position

2. Organises shapes by name, in order that they are input into the lofting operation inrational order

Get Subassembly Stations

1. Creates a list of shape stations including the start and end stations, and any stationswhere a discontinuation (crease) is required (in our case, just one at the vertical kink inthe deck).

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Loft Deck Solids

1. The previously created shapes list organised by name2. A family template that supports freeform mass (an adaptive family).

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SHAPES IN THE DYNAMO GEOMETRY PREVIEW

COMPLETED REVIT FAMILIES

Dynamo – Discrete Elements

Identify Feature lines

Use a code block for quick extraction and identification of the feature line codes.

Create Family Instances

1. Takes sample line groups from the Civil 3D model and organises them into nested listsby Group,Station.

2. Creates multiple instances of a similar family type, with specified offsets, elevations androtations from the nearest point of the feature line.

Note –The angleZ only controls relative rotation to the nearest feature line segment –individual family instances are automatically rotated around curves when usingthis node. Refer to the Linear Structures Workflow Guide document for moreinformation.

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Dynamo – Framing Elements

Placing the cable stays

Whilst the full definition for placing the adaptive component cable stays is rather too complex todescribe in full detail here, it can be summarised as follows:

1. Points connecting to the deck are placed along feature lines at specified stations,using the Point.ByStationOffsetElevation node

2. Points connecting to the mast top are placed along a model line on top of thefamily instance using the ‘Select Model Elements’ node.

3. The corresponding points are connected with curves.4. Adaptive Component instances are created using the

AdaptiveComponent.ByPoints node.

Dynamo – Custom Nodes

Dynamo definitions can quickly become unwieldly. One way of tackling this issue is to createyour own custom nodes by grouping various operations within. Advantages of using this methodinclude:

· Making your graphs clearer and easier to understand· Custom node packages can be easily shared between projects and within your

organisation

This custom node is used in the Bridge K definition to help rationalise the spacing of discreteelements:

Let’s take a look inside:

1. Input nodes are created for the inputs required, giving an Input name, and optionally anexpected data type, data structure and default value:

endstation: The input namevar Expected data type is a Variable (could also be int, double,

string, var, bool)[]..[] Defines an arbitrary list structure. More information exists

on the Dynamo website https://dynamobim.org/what-does-var-mean/

= 30 A default value

2. A code block which creates a distributed array of stations based on the input rules. Thiscould of course be achieved through standard Dynamo nodes – using DesignScript inthis way offers another way of optimizing your graph structure!

3. Output nodes are created and provide output names.

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Revit Model Setup

Working with Civil 3D coordinatesCoordination between the Civil 3D World Coordinate System (WCS) and Revit ProjectBase Point is a crucial aspect of using connected workflows. When usingCivilConnection the following steps should be taken to ensure synchronicity between thecoordinate systems of your Civil 3D and Revit models.

In a general sense this is achieved by linking a coordinated .dwg to your Revit modeland acquiring the coordinates from it. However, Revit experiences problems when tryingto link in AutoCAD information which is more than 20 miles in extents (that is, 20 milesaway from the origin), explained in this article:http://revitoped.blogspot.co.uk/2012/04/extents-greater-than-20-miles.html. This causesproblems when attempting to link AutoCAD files which use large regional coordinatesystems.

The following steps provide a workaround to this issue.

1. Link your CAD overlays using the Center to Center option. Assuming the object limitswithin the file are less than 20 miles high or wide, this will bring down the overall extentsto within 20 miles of the project base point and will allow you to insert it. It’s important tocheck that the dwg doesn’t contain any objects at the origin, as this will expand theextents of the file. In this case objects should either be removed, or a copy of the file canbe made that only contains the extents that you require (this should be a last resort, asvisibility of any changes made by other disciplines will be lost).

2. Now our CAD overlay is inserted but isn’t at grid position. Switch on visibility of theProject Base Point, in Viewà Visibility/Graphics

3. Unclip the Project base point using the paperclip (this allows it to be moved relatively toobjects within the model), and move it to a convenient point which can be identified inCivil 3D (using project monumentation such as a rectangle around the site is an easyway to achieve this).

4. Reclip the Project Base Point5. Identify the coordinates of that point in Civil 3D and enter them into the fields (checking

that units are correct)

6. The linked .dwg is now positioned to grid. An orthographic view can be set for thestructure, by rotating all objects about the Project Base Point within the Project Northorientation.

7. Acquire the coordinates from the CAD link via the Manage Tab, Coordinates:

Postface - Next Steps

How is your organisation enabling digital transformation?

Within Jacobs, we are looking to build on previous successes using CivilConnection. As thenumber of proficient Dynamo users & programmers within the organisation grows, we’reemploying a number of strategies to facilitate digital transformation, with several aims:

· Integrate and centralise the best work across the organisation into a single solution forbridge design

· Bring consistency to the way in which computational methods are implemented in bridgemodelling

· Improve the user experience and accessibility of these methods to the larger workforce

· Improve the transferability of workflows and resources across different project andstructural types

· Provide a framework for further development in the field

Spreadsheet InputUsing spreadsheets to tabulate input data and importing this into the Dynamo definition can:

· Improve the clarity of Dynamo graphs· Open up the possibility of design edits by non-Dynamo users· Improve design version control

Custom Node packagesCustom nodes improve the clarity of Dynamo graphs and facilitate sharing of Dynamo workflowsbetween projects & teams.

Python Scripting to the next levelNew automation opportunities await those using Python code to access both the Civil 3D andRevit APIs, including the possibility of automating Civil 3D object creation.

ces321585 bridge detailing 2.0: computational modelling

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