SE3492: Schematic Design in Autodesk Revit Structure: Leveraging the Value of BIM for Early Design Decisions

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1 SE3492: Schematic Design in Autodesk Revit Structure: Leveraging the Value of BIM for Early Design David J. Odeh, PE, SECB Odeh Engineers, Inc. This class will focus on how structural design professionals can leverage the features of Autodesk Revit Structure, Robot Structural Analysis Professional, and the Autodesk Extensions to make important decisions during the conceptual and schematic design phases of a project. We will first discuss a methodology for parameterizing key structural properties of a building, such as bay size and floor-to-floor height. Next, we will use the Revit Structure design options feature, combined with some of the Autodesk Extensions (including the Composite Designer and Load Takedown tools), to perform rapid analysis, visualization, and optimization of the structure and foundations based on these parameters. Discussion will also focus on interaction with other disciplines to coordinate design options using Revit Structure model-linking capabilities. Finally, we will review several examples of real projects where the method was successfully used by designers to make early design decisions that resulted in substantial savings to the owner. Learning Objectives At the end of this class, you will be able to: Deliver more value to your clients by using BIM in early project phases Use the design options feature of Revit more effectively to illustrate and analyze different structural system concepts Develop a workflow for conceptual and schematic design using Revit Structure Use Revit Extensions to rapidly explore different design concepts for steel framing systems About the Speaker David Odeh is vice president and principal at Odeh Engineers, Inc., a leading structural engineering firm that practices throughout the eastern United States and has used BIM for all of its work for the last six years. He also oversees the firm s software development group, which creates custom BIM applications for design and analysis of buildings. Since 2001, David has also been on the adjunct faculty of the Brown University School of Engineering, and regularly lectures at other universities and at professional conferences. David is an active participant in engineering professional societies, and serves as the cochair of the Joint National Committee on Building Information Modeling of the ASCE Structural Engineering Institute and Coalition of American Structural Engineers (CASE).

2 Elevating the Role of Schematic Design Since the advent of digital design technology for building construction, our industry has recognized the importance of building virtually prior to building physically. The cost and risk associated with design changes increases exponentially with time during a construction project. Early in the design process, key decisions can be made with great impact on the downstream constructability and economy of a project. However, as construction approaches and begins to get underway, design changes can result in disproportionately large costs and schedule impact. Unfortunately, the traditional design process weights far more effort to the construction documentation effort than these early stages of conceptual and schematic design where design decisions have much greater leverage. Thus, much opportunity for cost reduction and project efficiency is lost when key design decisions are poorly considered or rushed into place. Patrick Macleamy famously illustrated this concept in the Macleamy Curve, introduced in the Construction Users Roundtable s Collaboration, Integrated Information, and the Project Lifecycle in Building Design and Construction and Operation (WP-1202, August 2004). The Macleamy Curve, now featured in numerous publications, shows that the traditional design process weights design efforts towards a period of time when the ability to impact cost and functional capabilities in a building has been greatly reduced, and the cost of design changes is significantly higher than early stages of design. The Macleamy Curve has been used to illustrate the benefit of alternative project delivery methods, such as Integrated Project Delivery. (see AIA s Integrated Project Delivery: A Guide, Regardless of the project delivery method, BIM is a tool that can enable more informed design decisions at the early stages of the process. Much research and writing has focused on the ability to leverage BIM for improved coordination and systems integration during design, thus eliminating costly late design changes. No discipline is more important than structure in the early design process. This importance stems from the reliance of all other systems on the structural frame to be in place prior to the beginning of construction. For this reason, structural engineers must often produce an early release package of foundation and steel or concrete framing that precedes the rest of the construction documents. Lack of coordination of these early release designs with other disciplines creates the risk of costly downstream design changes. BIM coordination between disciplines can improve, but not necessarily eliminate this problem. However, a less well recognized problem with this approach is the fact that conceptual and schematic design of the structure is often reduced to quick on the fly decision making or limited consideration of design alternatives. Rather than leveraging the value of these important 2

3 early design phases, the early release process constrains or even eliminates the opportunity to explore valuable alternatives that could greatly improve the efficiency and constructability of the building. Once construction documentation is underway, momentum or inertia can make it nearly impossible to go back and reconsider the major systems. In this presentation, we will explore a method for using Revit Structure 2012 and some of its extensions tools to create design options and consider multiple approaches to structural systems. We will look at practical case studies where design options were used to make key decisions, resulting in very significant cost and/or schedule savings to the downstream construction of the building. Workflows for Concept Design and Schematic Design The following is a suggested workflow for structural engineers in early design stages to assist clients with key decisions related to the structural systems: Step 1: Identify key cost drivers for the project in collaboration with the project team (example: steel vs. concrete frame, composite deck vs. steel joist floor system, steel piles vs. precast concrete piles). Step 2: Model key systems with sufficient Level of Detail for comparison, not necessarily the absolute value of quantities. For example, you might compare the incremental increase in steel quantity for a braced frame system as compared to a rigid frame/moment frame system. Include enough members and detail to capture the majority of the structural cost estimate additional costs (for example, connections) to include as contingencies. You can learn more about suggested Level of Detail in other AU Classes, and also from the CASE White Paper available online ( Step 3: Create design options in same model with Revit Structure for comparison. Model the main structure in common as the central model, with design options sub-systems like foundations, lateral force resisting system, and floor framing. Step 4: Extract design option quantitative data using schedules and takeoffs from Revit. For certain options, consider using the Revit Extensions that are available to perform quick analysis and design for comparison purposes. Step 5: Create presentation graphics and comparison matrix. Use qualitative and quantitative measures of design options to compare and contrast the options considered. Step 6: Select design options for further development. Ultimately, merge into the main model those options that are selected by the design team for construction. 3

4 Using Design Options in Revit Structure 2012 One of Revit s most useful features for conceptual and schematic design is the ability to specify design options. Frequently used by architects, this feature is relatively new to most structural engineers but can be leveraged to greatly enhance the benefits of BIM in schematic design. Key features of design options include: Engineers can create design option sets with alternatives for key pieces of the structure. For example, several different options for foundations could be modeled (such as spread footings, concrete piers, or steel piles) Design options can vary in complexity. At early stages of design, they can be very simple (such as simple blocks for footings or estimated pile counts), then developed further as the project progresses. Design options can be used at any point in design of the project, but are particularly useful in conceptual and schematic design to explore different alternates for structural features and systems. Once an option is selected, it can be incorporated into the main model and further developed for construction documentation. In general, the process of using design options is as follows: 1. Decide on the areas for which you want to develop design options. For example, you could choose to develop design options for foundations and for the lateral force resisting system of the building. 2. Create the building model, including all elements that will be common to all of the design options. (This is the main model.) For example, you could model all of the gravity columns and floor framing in the building, but exclude lateral columns and bracing. Note: If you add elements to a building and later decide that those elements should be part of a design option, you can move them to the design option. 3. Create a design option set for each area in which you would like to explore alternates. For example, foundations and lateral force resisting system. 4. For each design option set, edit the primary option. When you create a design option set, Revit also creates a primary option for the set. The primary option is typically the preferred design or the design that you think will be chosen. It will be displayed in project views by default. Other design options will appear in views only when you specify. 4

5 Edit the primary option to add elements to the design as desired. For example, the primary option for the lateral force resisting system might be shear walls. 5. Create secondary options for each design option set. You can create one or more secondary options for each set. For example, we can add an option of steel braced frames to our Lateral System design set. In general, any elements that will be modified or referenced in an option should belong to the design option instead of the main model. 6. Create views that display each design option. By default, all project views display the main model with primary design options only. To see secondary options, create project views that show them. (These are called dedicated views.) You can then place these views on sheets to present the designs to clients. 5

6 The figure below shows an example of two dedicated views for a lateral force resisting system design option set. The left view is a view of the shear wall (primary) option. The right view is the braced frame option. In these views, the design option elements are made active by selecting the appropriate design option from the status bar. To create the view, just go to Visibility/Graphics under the Design Options tab, and specify the option you wish to view. 6

7 7. Incorporate a design option into the main model. After the client has selected the desired option for each option set, you can incorporate the selected designs into the main model. Do this by selecting Accept Primary in the Design Options dialog. This process deletes the design option set, so the other options in the set are no longer available, and the selected option becomes part of the building model. Be sure to save older versions of the model in case the client changes his/her mind! Some considerations of using design options for structural alternatives include: 7

8 Elements in the main model or primary design option cannot reference or join to elements in secondary design options. For example, gravity beams in the main model of our sample cannot join to steel columns that are part of our braced frame alternative because it is a secondary option. If we want to do this, we need to either promote it to the primary option or move the affected connecting beams to the design option instead of the main model. Notice in the shear wall and braced frame option views of the example shown above, some of the floor framing beams that attach to the lateral force resisting system columns need to be included in both options. Levels, views, and annotations cannot be added to a design options. Add levels to the main model, and they will then be available within the design option sets. You cannot add views to a design option, but you can dedicate a view to a design option by using the Visibility Graphics settings/design Options Tab. Annotations only show up on the views they are created with, so you can annotate a design option by creating a dedicated view. Higher complexity design options may require separate models. As a rule of thumb, if more than 50% of the elements in the model are affected by one design option, it might make more sense to create a separate model. This will cut down on model overhead and improve performance. In class we will review a few examples of these features using a steel framed structure. Types of Design Option Sets for Structural Engineers You can develop design options for whatever specific issues are present in your project. Some key areas that deserve consideration as design option sets for typical structural projects include: Option Set Foundations Shallow and Intermediate Foundations Deep Basement Walls Superstructure Floor Framing Examples of typical options that can be modeled (primary and secondary) Footings, mat/raft, concrete piers Precast concrete piles, steel piles, concrete caissons/drilled shafts, auger cast piles Sheet piles with concrete, slurry wall, soil mix wall, secant pile wall Steel composite slab on deck, steel framing with noncomposite form deck 8

9 Superstructure Lateral Force Resisting System Superstructure Roof Framing Special Conditions Steel braced frames, steel moment frames, masonry shear walls, concrete shear walls, concrete moment frames Steel beams, open web steel joists, wood trusses, wood rafters, long span deck vs. short span deck Transfer girder options (e.g. plate girder vs. truss) Long span roof options (e.g. gable shaped truss vs. arched truss) Each project will have different unique conditions. A design office should consider preparing typical libraries of families for typical design options they will consider for projects in each of the categories described above. For example, develop a library of different pile caps and piles that can be easily inserted into a design option set for consideration in the model. This way, schematic design model option sets can be easily developed to a sufficient level of detail to provide qualitative and quantitative comparisons of typical systems. Also, it can be impressive to a client to see the different design options in one model they can get a true sense of the value that the engineer brings to the table in this critical decision making stage of the project! Creating Parametric Models for Design Consideration Schematic design is both objective and subjective in nature. Consider the key parameters that will drive the design decision. Often, this will require input from the owner, architect, MEP engineers, and construction manager. Parameterize your design options to compare both quantitative and qualitative characteristics of the project. You can set up shared parameters in your families to do takeoffs of each design option for comparison. Set up views in the model to help make the key qualitative comparisons that will drive the decision. In class we will look at some examples of spreadsheets you might use to develop a design decision for some key elements of the structure. The following table shows some typical items you might consider for comparison: 9

10 Option Set General considerations Foundations Shallow and Intermediate Foundations Deep Basement Walls Superstructure Floor Framing Quantitative Parameters Material quantity and counts Labor costs Volume of concrete Weight of rebar Number of footings/foundations Quantity of Soil Removal Pile count Pile cap/grade beam volume of concrete and rebar Volume of Concrete Weight of rebar Weight of steel framing Piece count of steel members Volume of slab concrete Area/weight of steel deck Depth of structural framing members Qualitative Parameters Constructability Aesthetics Ease of coordination Potential risks during construction Speed of construction Lead time of materials Time of year for concrete curing (winter vs. summer) Lead time for pile types Potential ground obstructions and broken piles Speed of construction Support of excavation requirements Ease of coordination with MEP systems Serviceability and durability Constructability Fire rating Soundproofing/acoustics Vibration characteristics Superstructure Lateral Volume of concrete/rebar in Ease of coordination with 10

11 Force Resisting System shear walls Weight of steel braced frames Piece count in steel braced frames Number of welded/special connections other systems Coordination of construction with temporary and permanent bracing Some parameters may be interdependent. For example, the shear wall and braced frame options for our earlier example will require different numbers of tension piles for uplift the shear walls are heavier and therefore require less uplift resistance at foundations. However, the extra weight may add more to the pile count. This suggests that we need to include the piles in the design options together with each lateral force resisting system to ensure an apples to apples comparison. To compare options, create a matrix of qualitative and quantitative data for comparison purposes. Include additional potential costs for each option that are not explicitly modeled, to be sure that these items are taken into consideration. Creating Parametric Models for Steel Design Another way of exploring alternatives in schematic design is to simply create multiple models of building parts for comparison. A good example of this is using bay studies to compare systems for a steel framed floor structure. Structural engineers must often perform these bay studies of typical bays to identify the most cost effective approach beam spacing and bay dimensions for a given building. Revit now has some excellent analytical tools to evaluate quick schematic designs for floors created in the model. You can use these tools to create some designs, then compare some key quantitative parameters to help make a decision on which option to choose for construction. NOTE: at this time, the Revit Extensions do not support Design Options. Consider an example of a steel composite slab on deck floor system with unshored construction. For this problem, let s assume that we have already agreed to a column grid with the architect. We now need to select an economical beam spacing and slab thickness for the given loading (let s assume it is 100 psf live load). We will create two different floor framing options in the same model to check different beam spacing and slab thicknesses: 11

12 1. 5-1/2 thick slab with 2 deck, beams spaced at 7-6 o.c. in the long direction of the bay /2 thick slab with 3 deck, beams spaced at 10-0 o.c. in the long direction of the bay. We could also create other framing options for consideration say vary the beam span direction, or choose a different spacing and slab thickness. We can now use Revit s Composite Designer Extension to generate some sizes in each option for comparison. We run the Composite Designer for each option in this case we will just choose to design all members in the floor for the same constraints. (If you are interested in learning more about the composite designer and other steel design tools see class SE6588-L Effective Design of Structural Steel Using Autodesk Revit Structure 2012 ) Using some pre-defined schedules, we can now extract the weight of steel and piece count for each option to compare. Bringing it all together: Presenting to the Client One of the most compelling uses of design options in Revit Structure is to be able to create realistic views of the schematic design for client presentations, and to share with the design and construction team. These graphics tell the story of your design idea and help communicate the issues to other team members. Ultimately, the reaction to these graphics may push the team towards a particular option based on aesthetics, constructability, coordination, or other non-quantifiable qualities. Another useful method of working with design options in presentations is to be able to mix and match options together in real time for consideration by the team. We will review some examples of this in the next part of the presentation. Examples of Real Projects: Case Studies 1. New High-Rise Residence Hall This project, which we viewed briefly in the beginning of the presentation, is a 21-story steel framed residence hall structure built on an urban site in downtown Boston, MA. Key design options considered were for the lateral force resisting system (comparing shear walls to braced frames) and for the foundations (comparing high-capacity steel H-piles to lower capacity precast concrete piles). We used two design option sets one for each of these key subsystems. For the lateral force resisting system options, we also included the piles associated with the shear walls or braced frames in those options (outside of the model). This allowed us to account for the impact on the pile counts from the two different systems. 12

13 We used the Ram-Revit link to quickly evaluate the steel bracing system and shear wall system. This allowed us to use realistic sizes in the model. We did not include connections or other detailed elements in schematic design. Ultimately, we determined that the steel H-piles were more cost effective (a $500k +/- decision). Also, we selected the steel braced frames based on cost (approximately $250k savings in material costs) and schedule considerations identified by the contractor. 2. New Natatorium/Swim Center for University This project was a new pool and long-span roof structure for a natatorium. The key design decision was whether to use a mansard-shaped steel truss with flat top and bottom chords, or an arched shape truss system. For both options, we also considered using long-span metal deck vs. intermediate purlins with shallower deck. Thus, four design options were considered within one set (each type of truss with each type of decking system). We analyzed the structural frame for each option using the ETABS-Revit link to facilitate a quick design for schematic purposes. While the architect and owner reacted very positively to the arch shape truss, and also thought it would initially be more economical, we ultimately selected the flat top and bottom chord trusses with purlins and shorter span deck due to cost and schedule constraints. The savings associated with this decision was estimated to be $750k by the construction manager. 3. New Academic and Administrative Building This project is a new three-story steel frame structure to be built on a college campus for classrooms and offices. While steel was selected for the main superstructure, the design/build team for the project wished to study three different options for the floor framing, and two different options for the roof. We created two design option sets: one for the floor framing, and one for the roof framing. For the floor framing, we considered three design options open web steel joists with form deck and slab, composite slab on deck with 6-1/2 slabs on 3 deck, and composite slab on deck with 4-1/2 slabs on 2 deck with closer beam spacing. For the roof framing, we considered two options: composite slab on deck with 4-1/2 slabs on 2 deck, and open web steel joists with roof deck only. 4. Large Addition to Existing Hospital This last example is the most complex, and perhaps best illustrates the value of BIM visualization in schematic design for structures. The project involves a new 6-story addition that is to be constructed between two existing hospital buildings in Philadelphia, PA. The addition must be built over an active loading dock, and above the entry to an active underground parking structure. Thus, large transfer girders are 13

14 required above the ground level. The new addition must also be designed for a future 10-story vertical expansion. 14