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eIntroduction to Building Information Modeling (BIM) for Steel Reinforced Concrete

What is Building Information Modeling (BIM)?

Building Information Modeling  (BIM) is a 3D process used to generate and man-age digital models of buildings and infra-structure. This process is used by those who plan, design, construct and manage facilities. The process involves creating and maintaining intelligent models that repre-sent physical characteristics of a facility, as well as contain parametric data about the elements within the model. Numerous software packages exist that fall within the definition of BIM, each having distinct ad-vantages to different parts of the life cycle of a facility, from the design to construction through operation.

Although the focus of most BIM discus-sions centers on the 3D model itself, the information contained within is of equal im-portance. The National Building Information Model Standard1 (NBIMS) defines Building Information Modeling (BIM) as “the DIGITAL REPRESENTATION of physical and functional characteristics of a facility. As such it serves as a shared knowledge resource for information about a facility, forming a reliable basis for decisions during its life cycle from inception onwards.”

In general, BIM encompasses more than a 3D computer-rendered virtual mock-up of a structure, it includes a database of infor-mation. In addition to physical architectural attributes, the complete BIM contains all the building component information, from wall systems, structural systems, electri-cal systems, HVAC equipment, plumbing fixtures, door and window schedules and finishes. Often supplemental information is included such as the manufacturer, sup-plier, and square footage of every material specified on the project. In other words, BIM is an “Intelligent 3D Model”. BIM is intended to be used as a tool for facility owners and operators to better manage their facility throughout its entire existence.

BIM is applied to the details of concrete reinforcement in both the design and

construction phase of a facility. In the de-sign phase, BIM is often used by the design team to define the physical characteristics of the reinforced concrete elements by de-fining concrete shapes and edges in physi-cal space. The reinforcement information is input as either data within the concrete el-ements, or physical representations of the reinforcement. This definition of concrete and reinforcement information is often to a ‘design intent’ level of modeling. In the construction phase, the concrete geometry is often defined to a construction level of detail, and the reinforcement is defined to a level from which it can be fabricated and installed.

How is Building Information Modeling (BIM) Utilized on a Steel Reinforced Concrete Project?

BIM can be utilized on a project in differ-ent ways and is highly dependent on the makeup of the project team, BIM capacity (software, experience, etc.) and the desired outcomes and deliverables. In some cases, simple 3D models of specific areas are all that is desired. In others, the full BIM pro-cess is used.

At the start of a project, it is important that the expectations between the Contractor and the Fabricator related to BIM are dis-cussed in detail, so all parties involved un-derstand the project requirements. These discussions need to include:

• What is the contractual scope be-tween Fabricator and Contractor?

• Is the 3D modeling being used solely by the contractor for visualizing and troubleshooting areas of high con-gestion or other concerns?

• Will the model itself be a deliverable to the Engineer and/or Contractor?

• Will the Contractor be supplying the Fabricator with a model to work from?

• Additional information, as needed.

2 Introduction to Building Information Modeling (BIM) for Steel Reinforced Concrete [ETN D-9-21]

These discussions should ultimately lead to a project plan for the use of BIM. Commonly, these four applica-tions are encountered:

• Spot Modeling

• 3D Modeling

• BIM

• IPD (Integrated Project Delivery)

Level of Development (LOD) Specification

The Level of Development (LOD) Specification2, as prescribed by the American Institute of Architects (AIA) and the BIMForum, provides a means to communicate the degree of usability of data found within Building Information Models (BIM’s) as they progress through-out the design, construction, and operations stages of a structure.

Section 2.2 of the LOD Specification states “LOD is sometimes interpreted as Level of Detail rather than Level of Development. This Specification uses the con-cept of Level of Development. There are important dif-ferences. Level of Detail is essentially how much detail is included in the model element. Level of Development is the degree to which the element’s geometry and at-tached information has been thought through – the de-gree to which project team members may rely on the information when using the model.

In essence, Level of Detail can be thought of as input to the element, while Level of Development is reliable output.”

LOD definitions range from 100 to 500, starting with LOD 100 as a simple conceptual identification of an el-ement within a structure, through LOD 500 as a fully field-verified element complete with all element geome-try and non-graphic information. It is important to under-stand that these definitions are not meant to identify the exact state of an entire model, since various elements are certain to exist at different LOD’s within any given model at any given time during its lifecycle. Instead, the LOD definitions were created as a means to convey the reliability of information of specific element sets at spe-cific stages.

For cast-in-place reinforced concrete structures, LOD definitions for elements such as foundations, beams, columns, etc. could be interpreted as follows:

LOD 100 – Concrete members may or may not be graph-ically shown in the model and any data or geometry should not be relied upon for any specific purpose. If shown, members are represented in approximate loca-tions and member thicknesses and cross sections are approximate.

LOD 100 presents no value for a reinforcing bar de-tailer, as rebar is typically not included.

CRSI Technical Note 3

LOD 200 – Concrete members exist graphically in the model; however, they should be considered generic and any data or geometry should not be relied upon for any specific purpose. Members are represented in approxi-mate locations and member thicknesses and cross sec-tions are approximate.

Typical reinforcement may be represented through notes attached to a member.

LOD 200 presents no value for a reinforcing bar de-tailer, but may be helpful to an estimator.

LOD 300 – Structurally significant concrete members are to be accurately positioned and dimensioned in the model with proper respect to the model origin. Non-graphic data (i.e. material strength) may also be repre-sented through notes attached to a member.

Primary reinforcement is represented either graphi-cally and/or as non-graphical information in notes associ-ated with or attached to the reinforced elements. Some reinforcement and reinforcement information may still be missing or approximate.

LOD 300 presents no value for a reinforcing bar de-tailer, other than to provide a visualization tool, but may be helpful to an estimator.

LOD 350 – Concrete members should be represented in actual locations with correct thicknesses and cross sections. Members should be complete and include penetrations, openings, joints, etc.

Primary reinforcement is represented either graphi-cally and/or as non-graphical information in notes associ-ated with or attached to the reinforced elements.

Rebar may be graphically shown at congested areas and for general representation. Graphic and non-graphic data as required to convey design intent should also be attached in its entirety.

Items like expansion/contraction joints, pour stops and closure strips are represented in correct locations. Design specific lap locations should be identified graphi-cally or through notes.

The model at LOD 350 should clearly communicate design intent, but may not take into account con-struction sequencing & scheduling, doweling, splices of reinforcing bars, etc. However, it should provide enough information for the reinforcing bar detailer to coordinate with industry standards, project typi-cal details, and construction sequencing/scheduling in order to create placing drawings.

Column with 8 #8 verticals & #4@10”ties

Footing with #6@12” EW

4 Introduction to Building Information Modeling (BIM) for Steel Reinforced Concrete [ETN D-9-21]

LOD 400 – Concrete members should be represented in actual locations with correct thicknesses and cross sections. Members are modeled completely and are “fabrication ready” to include specific quantities, siz-es, shapes and orientation of the element, as well as all required reinforcing data to be supplied by the rebar fabricator.

A model at LOD 400 will be the result of the rein-forcing bar detailer’s work and is the minimum LOD that a reinforcing bar detailer should provide to an-other party.

The model takes into account construction se-quencing & scheduling, doweling, splices of rein-forcing bars, etc. and all reinforcing is fully detailed (quantity, size, length, callouts, etc.) and ready to present on placing drawings and bar lists for fabrica-tion and installation.

LOD 500 – Element is a field verified representation of the completed element and all components installed pri-or to concrete pour. Per BIMForum interpretation, “Since LOD 500 relates to field verification and is not an indica-tion of progression to a higher level of model element geometry or non-graphic information, this Specification does not define or illustrate it.”

Note that the LOD Specification does not state who should be the author of model elements at any given LOD. Such assignments often vary from project to proj-ect and will likely be specified within each project’s BIM Execution Plan (BIMXP). In lieu of a project BIMXP, the above definitions could be interpreted as LOD 100-350 being the stages through which designers develop and formalize the information necessary to convey de-sign intent to the reinforcing steel supplier and other “downstream” disciplines. LOD 400 would be the stage through which the Detailer/Fabricator would convey their

interpretation of the design intent as a fabrication ready model to contractor, designer, placer and other involved parties.

As BIM continues to evolve and become more com-monplace as a method of communication, collaboration, and information exchange, it is becoming ever more criti-cal to have a clear method of defining the reliability of each piece of information found in a model at any given moment in the lifecycle of a project. The intent of the LOD Specification is to provide such a reference to the AEC community.

Benefits of BIM for a Steel Reinforced Con-crete Project

The benefits of using BIM are numerous and vary from project to project and depending on where in the de-sign/construction process it is utilized. Potential benefits include:

Design and Detailing

• Better visualization, especially when dealing with complex structures.

• Improved coordination between trades through the sharing of information, which is one of the tenets of BIM.

• Ability to easily provide multiple ‘what-if’ scenarios.

• Improved communications and efficiency and re-duced errors through:

» Addressing items earlier in the process, thereby reducing the number of RFI’s and issues in the field.

» Clearer communication of structural geometry and design intent from the Engineer to the re-inforcement Detailer than that which is possible using traditional 2D documents.

» Reinforcing bar details presented in 3D at a con-struction level of development.

» Better communication of reinforcement fabrica-tion and placement information to downstream entities.

Construction

• Enhanced project visualization made possible by having full building models and related information at your fingertips.

• More accurate material take-offs, leading to less waste and reduced overall project costs.

• Improved jobsite safety through earlier collabora-tion, visualization and planning.

• Improved project coordination, clash detection and resolution achieved by combining 3D models from various Sub-Contractors into a single consolidated model.

CRSI Technical Note 5

• 4D Schedule simulation animations produced by combining the 3D model with a construction sched-ule.

Operation

• Better ‘as-built’ documentation than conventional 2D drawings, leading to easier remodels, rebuilds and additions.

• Improved management of a building’s lifecycle achieved by using the 3D model as a central data-base of all of the building’s systems and compo-nents.

• Enhanced tracking of building maintenance needs.

What are the challenges with BIM?

As BIM usage increases and additional benefits contin-ue to be realized, the adoption of BIM certainly presents the industry with a new set of challenges. To start, BIM requires different visualization skills over that of tradi-tional 2D tools. While many who are new to the industry have probably grown up with 3D games and other such visual applications, those unfamiliar with these environ-ments may struggle to adjust. This should be considered when selecting who will be given these advanced tools. Once users have been selected, proper training is es-sential, as is affording the user time to become com-fortable and ultimately efficient. In addition to the costs of software and likely hardware upgrades, such training and the initial decrease in productivity levels should also be anticipated and budgeted for.

Beyond the initial costs and resource demands, several other factors should be considered. Because specifica-tions and expectations vary from project to project, it is critical to understand one’s responsibilities and what de-liverables will be required. Current trends often see BIM on larger, more complex projects with multiple suppli-ers and trades utilizing a multitude of BIM applications. To facilitate model exchange and to bring different team members models into a single tool for review and col-laboration, a common, non-proprietary file format is nec-essary. While the use of IFC files (discussed below) is quickly becoming the standard, and organizations such as the American Concrete Institute (ACI) (with help from CRSI and its members) are working to assure that nec-essary information is properly defined, inconsistencies between products and models occasionally arise. Such file exchanges and team collaboration will require BIM users to understand these processes, and the success of each project will depend upon someone taking a lead role to consolidate models from each supplier to review all as one. Which team member will accept these roles should be agreed upon at the onset of the project, as should any additional costs that will result from the use of BIM and the shift away from traditional responsibili-ties to this more collaborative workflow.

Working Together—IFC Files and BIM File Transfers

Numerous BIM software packages are capable of defining concrete geometry and data, detailing rein-forcement, or both. Most of these applications are now compatible with an open file format specification know as Industry Foundation Classes, or IFC’s. This is an ob-ject-based file format that allows for the ease of interop-erability between software platforms. IFC files are able to be exported from and imported into most BIM soft-ware platforms and collaborative viewing applications, allowing model content created in different software to be viewed and used in other software and by a variety of users and teams.

State of the Technology

BIM has been around for nearly 20 years as of this publication, but one thing that makes it different from past technologies is that it is ever changing and evolv-ing. The current state of BIM is very dependent on the region and market sector, but its adoption and use are ever expanding. The introduction of tablet computers, la-ser scanning, drones, 3D printers and more have all had a role in shaping where BIM is today and where it is go-ing. A primary focus behind the evolution of BIM is the ability to utilize this vast array of content by different us-ers using different tools. This focus is not only intended for designer to designer, but to provide for a means of collaborative information sharing throughout the project workflow and lifecycle. There has also been much effort in developing ways to transfer the data for downstream uses allowing structural steel, pipe and duct, and even reinforcing bar fabricators the ability to seamlessly utilize the information from the BIM for use in fabrication of these elements.

References

1. National Institute of Building Sciences build-ingSMART alliance® (2015), “National BIM Standard – United States® Version 3”

2. BIMForum (December, 2020), “Level of Development (LOD) Specification Part I & Commentary For Building Information Models and Data”, 272 pp.

Contributors: The authors of this publication are Mark Agee (Whitacre Engineering, Inc.), Dennis Fontenot (Commercial Metals Company), Robbie Hall (Headed Reinforcement Corp.), David Grundler (aSa - Applied Systems Associates, Inc.), Greg Rohm (Harris Rebar), and Peter Zdgiebloski (Commer-cial Metals Company).

Keywords: buildings, building information modeling, BIM, computer aided design, design, detailing, reinforced concrete, reinforced concrete buildings, reinforcement, reinforcing steel.

Reference: Concrete Reinforcing Steel Institute - CRSI (2021), “Introduction to Building Information Modeling (BIM) for Steel Reinforced Concrete, CRSI Technical Note ETN-D-9-21 Schaumburg, IL, 6pp.

Historical: None. New Technical Note.

Note: This publication is intended for the use of professionals competent to evaluate the significance and limitations of its contents and who will accept responsibility for the application of the material it contains. The Concrete Reinforcing Steel Institute reports the foregoing material as a matter of information and, therefore, disclaims any and all responsibility for ap-plication of the stated principles or for the accuracy of the sources other than material developed by the Institute.

933 North Plum Grove Rd.Schaumburg, IL 60173-4758

p. 847-517-1200 • f. 847-517-1206www.crsi.org

Regional Offices NationwideA Service of the Concrete Reinforcing Steel Institute©2021 This publication, or any part thereof, may not be reproduced without the expressed written consent of CRSI.

Resources for More Information

http://bimforum.org/

https://www.nationalbimstandard.org/

http://www.buildingsmart-tech.org/

http://dcom.arch.gatech.edu/aci/

https://network.aia.org/technologyinarchitecturalpractice/home/bimstandards

Introduction to Industry Foundation Classes (IFC) and the Role of IDM and MVD

https://www.youtube.com/watch?v=wAeKNuJM_wk

Commonly Used AcronymsAEC ArchitectureEngineeringandConstructionBIM BuildingInformationModelingBOQs BillofQuantitiesCAD Computer Aided DesignCAE Computer Aided EngineeringCAM ComputerAidedManufacturingCIS/2 CIMSteelIntegrationStandardsCGI Computer Generated ImageryDBMS DatabaseManagementSystemEDI Electronic Data InterchangeFCI FacilityConditionIndexFM FacilitiesManagementgbXML GreenBuildingXMLGIS GeographicalInformationSystemIAI InternationalAllianceforInteroperabilityIDM InformationDeliveryManualIFC IndustryFoundationClassIPD IntegratedProjectDeliveryIPE IntegratedProjectEnvironmentsISO InternationalOrganizationforStandardizationLPM/5 LogicalProductModel,Release5LOD LevelofDevelopmentMEP MechanicalElectricalPlumbingMVD ModelViewDefinitionsNBIMS NationalBuildingInformationModeling StandardCommitteeNIBS NationalInstituteofBuildingSciencesNIST TheNationalInstituteofStandardsandTechnologyPMR ProductModelRepositoryQTO QuantityTakeOffROI ReturnonInvestmentSTEP StandardfortheExchangeofProductModelDataVBE VirtualBuildingEnvironmentVDC VirtualDesign&ConstructionVDCM VirtualDesign&ConstructionManagerVRML VirtualRealityModelingLanguageWD WorkingDraft2D Two-dimensionaldrawing3D Three-dimensionalmodel4D Linkingof3DCADcomponentsor assemblieswithtime/schedule5D Linkingof3DCADcomponentsor assemblieswithschedule&cost