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Structural Analysis with Autodesk® Revit® Structure ModelsMike King – Odeh Engineers, Inc.

SE5263

More than six years ago, we started our first Revit Structure projects with the promise that we would be able to send our models to the analysis package of our choice, size all our members, bring it all back into Revit Structure, and save ourselves countless hours of work. Six years later, we are still working on it. The good news is that we are a lot closer. Revit Structure 2012 offers a totally redesigned analytical model which gets you where you need to be. We will discuss multiple analysis packages along with Autodesk Extensions for Revit Structure. We will look at how the Revit Structure analytical model relates to the physical, which settings affect design, and how things translate between packages. We will show you best practices for a couple tools as well as tips and tricks to streamline the workflow and truly capitalize on this promise of BIM.

Learning ObjectivesAt the end of this class, you will be able to:

Reduce duplication of effort and increase productivity when modeling

Visualize and manipulate the Revit Structure analytical model and explain how the physical and analytical models interact

Examine load paths and member reactions using Revit Extensions

Round trip models and member sizes to external analysis packages

About the SpeakerMike King is a software engineer proficient in Microsoft® .NET technology. He has a background in civil/structural engineering and in-depth experience in .NET development of all types. He has worked to customize AutoCAD® from Visual LISP® and VBA to ObjectARX® and Microsoft .NET, and has significant experience with the Revit® Structure API. At Odeh Engineers, Inc., he has developed both line-of-business applications, such as a corporate intranet that incorporates CMS, CRM, and PM functionality, and specific-needs applications such as custom tablet PC tools for documenting field [email protected]

* Updated versions will be posted leading up to AU 2011

Structural Analysis with Autodesk® Revit® Structure Models

Introduction

Target AudienceI just want to make it clear that this class is really for structural engineers. I firmly believe that maintaining and properly using the analytical model in Revit should be the responsibility of the project engineers, not the drafter. It should be considered on a par with any other design software package.

OutlineTopic Integration Level

1 Analytical Modeling in Revit Structure2 Analysis Extensions Fully Integrated3 Autodesk® Robot™ Structural & Autodesk Project Storm Well Integrated4 Bentley RAM Structural System & ETABS from CSI Berkeley Getting better!

We’re going to start out with a fairly comprehensive discussion of the Revit Analytical Model, which is fundamental to getting any analysis tool to work either within Revit or via a link. After that we’ll look at the structural analysis and design extensions available with your subscription, and then we’ll look at Autodesk® Robot™ Structural Analysis Professional and Autodesk Project Storm. Finally, we’ll take a quick look at links to RAM Structural System from Bentley and ETABS from CSI Berkeley.

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Structural Analytical Model

Historical ChallengesDifferent programs from different companies evolve over many years. They have separate assumptions, limitations and internal representations. They specialize in different types of design, support different codes and standards and often focus on specific markets. Analytical models are often stick frame style simplifications of real buildings. It isn’t necessary to include every single element. Different engineers design different things in different programs (gravity, lateral, connections, foundations, infrastructure, etc.). There is no well supported comprehensive industry standard. Despite all that, we’ve decided that all programs should be able to seamlessly transmit all of their modeled data from any one to any other even as new versions come out and products change. Honestly, why would that work? It’s a tremendous development challenge for companies that often have no strong incentive to let you bring your work to a competitor’s application.

What Changed?Autodesk acquires Robobat in 2006 showing a real commitment to the structural engineering discipline as a market focus. Suddenly the incentive and means exist for one company to really make this work. They have knowledge of both ends of the process and the resources to get it done. In the 2012 versions Robot Structural Analysis and Revit Structure share a common analytical model format. This means, at a fundamental level, they can express the same things in the same ways. Developers working on interoperability have access to the guts of each program in a way no 3rd party could. The advent of Project Storm (Autodesk’s Structural Analysis in the Cloud application) and a growing suite of structural analysis and design extensions that run directly in Revit show this focus is paying off.

Workflow

Expect to: Put a qualified skilled engineer in charge of the Revit analytical model Spend time maintaining the analytical model Keep a set of analytical views setup for review Model for your desired target link / application Invest time reading the manual, learning the quirks

This isn’t a free ride; no one can alleviate the design engineer from the responsibility of understanding and maintaining the analytical model that express their design intent. There is no

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one right way to interpret the physical model of a structure, you need to tweak and clarify. The time saved is in coordination and remodeling, and the accuracy and integration is worth it.

Suggested Roles: Drafter: Setup and maintain views, documentation, sheet setup, details, markups Junior Engineer: Physical modeling, connections, system design, analytical adjustments Senior Engineer: Analytical model review, design intent, structural analysis link Principal: Project review, initial planning, consistency checks, standards

Setup Analytical Views

For each plan, section, elevation and 3d view you have, you should have an analytical view.

Turn on linear analytical element end differentiation in the Structural Settings Analytical Model Settings dialog box

Setup analytical model end colors in Visibility and Graphics

Create a view template to maintain your preferred settings, feel free to experiment and modify as needed to see exactly what you need to.

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Use sectioned 3d views to inspect individual floors, frames or sub-structures in 3d to fully understand the framing conditions being modeled.

The goal of analytical views is to reduce clutter and cut to the heart of the structural model. Remove anything and everything you don’t need and simplify as much as possible. You should be able to see what you need to at a glance to make it more likely you’ll check often and notice issues.

Analytical Considerations

Analytical / physical relationship Materials Loads Boundary conditions

Revit attempts to infer the analytical model from the physical, it’s not always right! Check it and, when needed, fix it. Make sure all your structural elements have structural materials applied. Model whatever loads you want to design for then apply boundary conditions on your model

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Toggling Analytical ModelAll structural elements have an “Enable Analytical Model” setting in their structural properties. Turn this off to remove an element from analytical consideration entirely. Some elements also have a Structural setting; this older setting also turns off the analytical model. Turning off the structural setting also prevents you from adding reinforcement to concrete elements that support it.

Horizontal Stick Framing Properties

When the analytical model is activated, horizontal stick frame elements expose a variety of properties on their analytical model.

Analyze AsSpecify Gravity or Lateral, controls how this is used in design. Check specific links for support.

Start / End ReleasesFixed, Pinned and Bending Moment (fixed against torsion) are available by default. User defined gives complete (maybe excessive) control, not all analytical tools will use this (Robot / Project Storm do).

Note that there are also Start/End Connection properties on the physical model that can be set to None, Cantilever Moment or Moment Frame. These settings affect some tools (e.g. Composite Design extension, RAM Structural System) and are used for construction

documents.

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Rigid LinksFor beams, you can set this to Yes, No, or From Column. From Column means, essentially, respect the columns setting for this property. Rigid Links are infinitely stiff weightless connections that can be formed between a beam and a column representing an eccentric connection.

Analytical AlignmentThese settings allow you to override the default analytical model placement relative to the physical model. You can assign the analytical model to either follow the physical location line or snap to a grid line or other reference. Later on we’ll look at directly grip editing the analytical model.

Columns & BracesMost analytical properties are similar to beams. Rigid links setting is either on or off. Alignment options can be specified for both the XY (horizontal) plane and the Z axis (vertical). Again, those points can be grip edited.

FloorsEither one-way or two-way, alignment methods can be specified or perimeter edited manually.

Wall Elements Configure as gravity, lateral or both. Analytical projection relative to the physical model is editable as is the top and bottom projection.

FoundationsElements can be analyzed as either foundations or slabs on grade. A foundation element can accept load, slabs on grade only support themselves.

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Analytical Settings

Understanding the analytical settings tab is key to successfully auditing and maintaining your analytical model.

Automatic Checks Model validated as you work Best enabled when model is stable Manual checks not available when active Remaining settings on this tab relate to these two checks

Tolerances Relate to analytical / physical model relationships Left column: warnings occur during checks Right column: Placement of analytical model when set to auto-detect

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Circular Reference Check: Trigger warning for circular bearing chain

Analytical / Physical Model Consistency CheckControls specific consistency checks performed during analytical / physical check (either automatic or manual). Distances shown here are dependent on tolerances specified above.

Analytical Model Visibility: Leave this on, it’s useful.

Structural Materials Must be assigned to all structural elements Structural materials have properties on Structure tab in Material viewer Structural properties usually come from Structure Property Set (can be material specific) Structure Property Sets are pre-populated, can be edited Only Steel, Concrete, Aluminum and Wood can be structural materials

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Assigning Structural Materials Can be Instance or Type parameter Materials and Finishes (instance parameter) Assigned / layer on layered elements (e.g. walls)

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LoadsModeling loads in Revit ensures all analysis products are using common criteria.

Load Cases

Load case has a name, which can be anything desired. Natures can be created and called anything desired as well and associated with cases. Categories are fixed in product and must be assigned to each case. Unfortunately the default set of cases seems very redundant. Case SNOW1 is of Nature Snow and Category Snow Loads… why? Well you can have many different “dead loads” that you might want to schedule, filter or tag according to different criteria. You might want to create load combinations that only include some. Each load defined in your Revit model is of exactly one load case.

Load combinations allow the definition of any number of different (generally code required) factored or unfactored load case combinations.

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Modeling Loads Hosted (by analytical element) or unhosted (independent) Point, line or area Reaction: means they are the result of another element, considered “internal loads” Load case assigned from above Oriented to desired work plane Point and Line can represent any combination of force vectors on three axis and

moment vectors on three axis Area loads can only represent force, still three axis Line loads may be uniform or linearly sloped Area loads may be constant or sloped in one or two directions with control points Not all tools support all load

Hosted loads automatically cover the analytical element they are assigned to. Points are assigned to one end of a linear element (a node). Lines are assigned to the full length of any analytical element. Areas are assigned to any surface element and follow it.

Recommendations Use hosted area loads when possible (very helpful) Other types of hosted loads, less often useful Use unhosted area loads for things like snow drift, storage rooms, etc. Keep loads as simple as possible, Revit can model far more than most analysis tools

can understand

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Boundary Conditions

Boundary conditions are used to represent things like foundations, adjacent buildings or other constraints that represent the edge of your analysis area. They are designed essentially absorb force or moment applied to them.

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Structural Analysis Extensions

Revit Structure extensions are available with your Revit subscription through your subscription management portal. They are easy to use, focused and work completely within your Revit model so there’s no link troubles to worry about. For that reason, they are the most tightly integrated of any of the analysis / design tools available. Unfortunately they are also very limited in scope so they are no replacement for a full feature analysis and design application.

Available at no additional cost with subscription Work within Revit Seamless integration Focused, easy to use Limited functionality Recommended for:

o Quick checkso Schematic design phaseo Response to changes after main design

Composite DesignThis tool is suitable for composite or non-composite design of wide flange steel beams under composite concrete on metal deck. This type of design is very common in US markets and makes effective use of concrete in compression and steel in tension (for positive moment regions). November 2011 update adds support for cantilevered and multispan beam design as well as dramatically improving performance and fixing a number of bugs. Quick checks of single beams to full floor design, settings driven, uses Revit loads, assigns studs, camber, beam size and reactions back to Revit model. Incorporates many of the features of the Static Analysis of Beams module for a larger selection and includes its own load takedown algorithm.

Conceptual Form SimulationThis tool allows analysis of arbitrarily loaded complex conceptual forms. It is suitable for finite element analysis of stresses, deformations and reactions of arbitrary 3d shapes.

Floor Vibrations AnalyzerSuitable for use after composite designer has been used to select steel sizes. Using AISC Design Guide 11 this tool can check a variety of acceleration drivers and sensitivity factors

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for an entire floor using automatically detected bays with assigned occupancy types. No design is possible, strictly a serviceability or human-comfort check.

Gravity Column Designer Design any selected wide flange or HSS column for loads with optional eccentricity Point loads from Revit or can be assigned within the tool Bracing and fixity at each level can also be assigned.

Load Takedown Distributes loads across floor systems to beams, columns and eventually foundations or

boundary conditions throughout your structure Useful for determining reactions and applied loads for a variety of design purposes Requires careful validation by engineer

Static Analysis of Beams, Frames, Slabs and TrussesPurely analysis tools useful for feeding reactions, stresses and internal forces to other design programs (including spreadsheet based calculators).

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learning objectivesaucache.autodesk.com/.../class_handouts/v2_se5263_king.docx · web viewhe has...

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