AEC From the Ground Up--Digital Options for Structural Analysis1 Mar, 2006 By: AIA ,H. Edward Goldberg
Structural software can work with architectural software.
WHERE CAD AND BIM (building information modeling) software are productivity tools for the architect and designer, structural software is the productivity tool for the engineer. When these software types can work together, a project team's productivity can improve dramatically.
Architects and engineers work closely during a project. The architect usually determines the schema for a project and then asks the engineer to suggest solutions for the structure. Before the computer, the engineer would calculate loads and forces by hand, slide rule or calculator. Because this method was so time consuming, changes were costly. Unusual concrete structures were so difficult to analyze that actual models were subjected to loading to evaluate their soundness.
Today, practically every engineer depends on some type of software to help with engineering problems. In a typical structural engineering firm, the structural engineer passes design information to the structural designers, who use CAD drawing tools to document the design intent on construction drawings.
This process has its inefficiencies. If a beam size changes in the analysis model, the engineer has to communicate the change verbally or through a sketch to the designer. The duplication and lack of integration between the structural engineer's and designer's tools contributes to a lack of productivity. With the advent of structural BIM, companies can shift the focus of the deliverable from construction drawings to a 3D model.
Structural applications can be classified according to how they share geometry information with the architect:
Stand-alone software typically cannot import CAD data or export it back to the CAD program. Sometimes these applications are complex programs that address a very specific area of engineering.
Linked software uses a standard file format such as DWG, DXF, DGN or IFC to import and export information to and from 2D and, in some cases, 3D CAD. The vendor-neutral CIS/2 standard provides a framework for structural applications to share information with steel-detailing applications. Vendor-specific linkages also occur when vendors develop links to and from their specific applications.
You cannot export back to the CAD or BIM drawing to automatically make changes with these final engineering solutions. These linked solutions rely on each system holding its own discipline-specific model, with the other system working as a viewer or postprocessor of the linked information. The architect can see the engineer's model and vice versa, but managing changes can become quite challenging for both.
Bidirectional software is usually integrated through the architect's BIM design software. Engineering software can receive data from, solve and then update the architect's BIM model. This approach generally dictates that one system manage a master model that can export and import information to other applications, and edits occur in the main model.
Round-trip software allows any of the applications to perform work. Team members can exchange the model at any point in the design, and changes made in any application carry throughout all the others. This method allows each discipline to work in its preferred application and allows all involved to feel confident in the model's accuracy.
Here's an example of the round-trip workflow. An engineer receives an architectural design (in 2D or 3D) and develops a physical model, including structural members, load cases, boundary and releases conditions and material properties. This physical model, which drives the construction documents, simultaneously creates an editable analytical model, which is exported to the analysis software. On completion of structural analysis and design, the analysis software sends any changes back to the model, and the affected columns, beams, slabs and walls update with a push of a button. Changes are never a problem because these solutions manage the database and virtually eliminate coordination errors.
What follows is a quick survey of engineering applications and how they connect to architectural models.
Autodesk Revit Structure
Revit Structure is BIM software with an open API (application programming interface) that enables other software to integrate bidirectionally with the Revit Structure model. When any change is made to the model, the change is propagated to all related views. Import and export to popular industry formats such as DWG, DXF, DGN, SAT and IFC are supported. Moreover, Revit Structure is interoperable at the object level with Architectural Desktop and Autodesk Building Systems. Three structural analysis suppliers—CSI, RISA Technologies and Robobat—have delivered bidirectional and partial round-trip integrations with Revit Structure and one or more of their products. Several more integrations are under development.
Bentley: Bentley Structural, RAM Structural and STAAD
Bentley recently expanded its structural lineup with the acquisition of STAAD.Pro and RAM products. They join Bentley Structural, a MicroStation-based round-trip BIM solution that supports 2D/3D and analytical workflows. Bentley Structure integrates with Bentley Architecture, Building Mechanical Systems and Electrical Systems. Its integrated physical modeling and analytical modeling methodology allows the user to work in either view at any time, while all changes are synchronized between the two. Drawings are automatically generated using industry-standard representations of structural systems—all of which are fully customizable. Bentley Structural features round-trip integration with GT STRUDL, ROBOT, MIDAS/GENw, SFRAME and of course its own RAM and STAAD software.
Figure 1. Bentley's RAM Steel facilitates the analysis, design and drafting of load-resisting members in steel buildings.
RAM Structural System (www.bentley.com/ram) comprises RAM Steel, RAM Concrete, RAM Frame and RAM Foundation. It bidirectionally connects with with RAM CADstudio (a 3D AutoCAD-based drawing production system), Architectural Desktop, AutoCAD, MicroStation, aSa Rebar, SDS/2 and Tekla Structures. In addition, DXF import capabilities allow the creation of models directly from CAD files.
RAM Modeler is used to build a graphical model of the entire building structure, including geometry, structural properties and loading. Modeling is performed in plan and elevation. RAM Steel (figure 1) facilitates the analysis, design and drafting of the gravity load-resisting members in steel buildings.
RAM Concrete models both gravity and lateral systems and performs gravity and lateral load generation and distribution, including live load reduction and skip loading per ACI-318. It also determines design and detail reinforcing requirements for beams and columns and produces complete CAD files for floor framing plans, frame elevations and beam and column schedules.
RAM Frame is the FEA (finite-element analysis) component of the RAM Structural System. It performs static and dynamic lateral analysis of building systems, including frames and walls of any type and any building material.
STAAD.Pro (www.bentley.com/staad) is used to design and evaluate low- and high-rise buildings, culverts, petrochemical plants, tunnels, bridges and piles. It supports steel, concrete, timber, aluminum and cold-formed steel construction methods. The program has a round-trip connection with Bentley Structural and Tekla Structures and links with ADAPT, Descon and Structural Desktop.
STAAD.Pro combined with Bentley Structural or Tekla Structures is a BIM system for structural engineers. Engineers can physically model all types of structures made of steel, concrete or any other material without having to use analytical concepts like nodes and breaking members. Users can share a model throughout the analysis, design, detailing, fabrication and erection phases, creating a smooth flow of information.
Computers and Structures Inc
Etabs connects bidirectionally with Revit Structure, Bentley Structural and Graphisoft ArchiCAD (figure 2). The program designs moment-resisting frames, braced frames, staggered truss systems, frames with reduced beam sections or side plates, rigid and flexible floors, sloped roofs, ramps and parking structures, mezzanine floors, multiple-tower buildings and stepped diaphragm systems with complex concrete, composite or steel-joist floor framing systems.
Figure 2. Etabs software from Computers and Structures works bidirectionally with the BIM Big Three: Revit Structure, Bentley Architecture and Graphisoft ArchiCAD.
Safe is a linked solution that automates the analysis and design of concrete flat plates and foundation systems using object-based modeling. The program can analyze and design slabs and mats of arbitrary shapes and varying thickness, drop panels, openings, edge beams and discontinuities.
Section Builder is stand-alone software for creating structural cross sections of steel, reinforced concrete or composite materials.
Dr. Frame3D is a stand-alone application for the development of frame structures (figure 3). Users can define and modify applied loads and supports interactively and see the resulting structural behavior immediately via a variety of feedback mechanisms such as displacement, shear and moment diagrams. This real-time feedback is useful for behavior exploration in certain settings—especially parameter analysis/configuration studies such as member sizing studies, load location and magnitude studies, dimensional variations and topological variations such as bracing.
Figure 3. Dr. Frame3D lets users apply loads interactively as they develop frame structures.
RISA-3D performs analysis and design of general frame, truss and plate/shell structures. It supports concrete, hot-rolled steel, cold-formed steel and wood structures, and comes with an assortment of steel, light-gage and wood shapes.
Like RISA-3D, RISAFloor is bidirectional with Revit Structure and linked with Bentley Structural. RISAFloor designs floor systems (figure 4). It manages loads, design beams and columns, and constantly serves RISA-3D information it needs for the design of lateral systems.
Figure 4. RISAFloor from RISA Technologies manages loads, design beams and columns for floor systems design.
RISA-2D is a subset of RISA-3D intended for small offices that don't need complex analysis. RISAFoot is used for spread footing analysis and optimization. The developer claims that it's the only exact solution for spread footings in biaxial loading with uplift.
RISASection is a linked solution that builds and calculates properties for complex cross-sections. The user can define any type of complex cross-section either by combining standard shapes or by defining new shapes. Multiple materials are permitted in the same section. Sections created in RISASection can be used in RISA-3D, RISA-2D and RISAFloor.
ROBOT Millennium targets the structural engineer who incorporates frames, finite elements and design in mixed materials (figure 5). The program is bidirectional with Revit Structure and ArchiCAD, and round-trip with Bentley Structural. It offers other analytical capabilities, including cables, geometrical and material nonlinearity. RCAD, for the modeling and drafting of steel and concrete structures, integrates with Autodesk products such as AutoCAD and Architectural Desktop.
Figure 5. RoboBAT Millennium is designed for frames, finite elements and design in mixed materials.
RCAD Reinforcement allows the fast definition of reinforced concrete structures inside AutoCAD. It comes with templates that comply with the detailing practices of different countries to ensure the use of local detailing methods and appropriate bar schedules.
ESOP is software developed for component design and analysis in Microsoft Excel.
CBS Pro is a software tool for modeling multistory structures in concrete and other materials. Using an object-oriented approach, CBS Pro allows users to build a structural model using components such as beams, columns, walls, floors and openings.
Tekla Structures is a structural BIM system that covers the structural design process for steel, concrete and timber buildings from conceptual design to detailing, fabrication and construction. Users can bidirectionally link via IFC or directly integrate with Revit Building and Structure, Bentley Structural and ArchiCAD. Tekla Structures can also link to architectural BIM solutions via the less data-rich DWG and DGN 3D object formats. Multiple users can work simultaneously on the same model. Interoperable tools and open interfaces ensure a smooth transfer of information from design system to MIS or ERP software.
When a structural model changes in Tekla Structures, the reference model in the architect's view changes upon synchronization. Also, the layering standards built into IFC allow the architect to reference in only the elements they wish to view in their own model. Reference object dimensioning and clash prevention procedures are available to architects to compare their model with the structural model. Tekla Structures also has several analysis and design links with products such as STAAD, SAP2000 and ETABS.
H. Edward Goldberg, AIA, NCARB, is a practicing licensed architect and AEC industry analyst. Ed's full-length book, Autodesk Architectural Desktop 2006: A Comprehensive Tutorial (Prentice Hall; www.prenhall.com) is now available. Contact Ed for online Architectural Desktop training delivered directly to the desktop. Visit www.hegra.org for more information, or e-mail firstname.lastname@example.org.
About the Author: H. Edward Goldberg
Autodesk Technical Evangelist Lynn Allen guides you through a different AutoCAD feature in every edition of her popular "Circles and Lines" tutorial series. For even more AutoCAD how-to, check out Lynn's quick tips in the Cadalyst Video Gallery. Subscribe to Cadalyst's free Tips & Tools Weekly e-newsletter and we'll notify you every time a new video tip is published. All exclusively from Cadalyst!