Using the Revit Extensions for Steel Framed Floor Design and Analysis

Transcription

1 Using the Revit Extensions for Steel Framed Floor Design and Analysis David J. Odeh, PE, SECB Odeh Engineers, Inc., North Providence, RI Many structural engineering firms have adopted Autodesk Revit Structure 2011 software to help improve the productivity and efficiency of their practices. Using Autodesk Revit Structure 2011, engineers can create a single building information model (BIM) that can be used for many purposes, including construction documentation, detailing, and coordination with other disciplines. CONTENTS Overview of the Revit Structure Extensions..2 Workflow for Floor Design and Analysis...3 Example Projects...9 Summary...12 Autodesk Revit Structure 2011 also generates an analytical model that can be used to link with other external analysis tools, such as Autodesk Robot Structural Analysis Professional 2011 software, or to perform design and analysis functions directly inside of the model using the Autodesk Revit 2011 Structure Extensions. The Autodesk Revit Structure 2011 Extensions are particularly useful to structural engineers because they help to minimize the need to create and maintain multiple models for construction documentation and analysis. This white paper explores two new Autodesk Revit Structure 2011 Extensions for steel framed floor system design and analysis: the Composite Design Extension and the Vibrations Analysis Extension. These tools enable the engineer to analyze and optimize steel member sizes, evaluate floor vibrations, and directly populate the Revit Structure model with calculated design information. Specific applications of the extensions include: conceptual review of floor framing options, detailed design of new steel framed floors, and analysis of existing floor systems. The new extensions help engineers be more productive by performing typical daily design tasks directly within the Autodesk Revit Structure 2011 model, minimizing the need to run separate applications or perform tedious hand calculations. This white paper demonstrates a workflow and some design examples that illustrate the use of the extensions in a typical structural engineering design office. NOTE: All content herein is intended to illustrate the use of the design tools within Autodesk Revit Structure 2011 and does not represent formal design of any specific structure. All concepts and tools discussed in this whitepaper are intended to be used by a qualified structural engineer with proper license in the location of the project. All results and designs computed by the system must be reviewed by a qualified engineer, who shall be fully responsible for any final design or documentation prepared using these tools.

2 Overview of the Autodesk Revit Structure 2011 Extensions The Autodesk Revit Structure 2011 Extensions are available as a package of useful tools that work as add-ons to the Autodesk Revit Structure 2011 software. Autodesk Subscription customers can download the extensions or by visiting the Subscription center at subscription.autodesk.com The extensions are accessed via the Add-Ins tab in Autodesk Revit Structure 2011 in the Extensions Manager (see Figure 1 below), under the Autodesk Robot Structural Analysis Professional 2011 Extensions. In this white paper, the discussion focuses on the Composite Design Extension (CDE) and the Vibrations Analyzer Extension (VAE). FIGURE 1 Revit Extensions Manager and Add-Ins Palette 2

3 Workflow for Floor Design and Analysis The Composite Design Extension (CDE) and Vibration Analysis Extension (VAE) were designed to work together, helping the engineer to optimize and analyze floor framing that is selected from the Autodesk Revit Structure 2011 model. The typical workflow to use these tools consists of the following three steps: Step 1: Create the Model in Autodesk Revit Structure 2011 Create the Autodesk Revit Structure 2011 model, including specification of the floor slabs, initial beam sizes, column or wall supports. Material properties, such as steel strength, concrete density and strength are applied in the Autodesk Revit Structure 2011 model. Autodesk Revit Structure 2011 creates a parallel analytical model automatically. The engineer can manage the analytical model by creating Analytical views (in plan or 3D) and performing adjustments and consistency checks to help evaluate if the model is consistent and properly completed. Apply loads to the floor in Autodesk Revit Structure 2011 (through the Analyze ribbon in Autodesk Revit Structure 2011). The CDE recognizes dead loads and live loads placed on slabs or beams (point loads must be placed on top of a beam). FIGURE 2 Applying Loads to Analytical Model in Revit Structure 3

4 Step 2: Analyze/Design the Floor Framing for Strength and Deflections using the Composite Design Extension Select the area of the floor to be designed or analyzed. For the CDE, the engineer can select individual members, groups of members, or the entire floor (as long as the floor slab is continuous). Typically the CDE will be used first to evaluate the member strengths and static deflections, followed by a check of vibrations using the VAE. Initiate the extensions using the Autodesk Revit Structure 2011 Extensions Manager Autodesk Robot Structural Analysis Professional 2011 Composite Design. The extension opens a new dialog box with the selected members highlighted. FIGURE 3 Launching the Composite Design Extension from Autodesk Revit Structure 2011 Launching the Composite Design Extension from Autodesk Revit Structure

5 Using the CDE, members can be optimized or checked for both composite and noncomposite action. For composite members, the CDE will check the pre-composite loads and post composite loads for strength and deflection criteria against the American Institute of Steel Construction standards and user settings. Numerous design settings are available to the engineer to fine-tune the design. FIGURE 4 Member selection and detailed design information from Composite Design Extension (clockwise from top right: stud layout, moment diagram, detailed results report) 5

6 When satisfied with the design, clicking OK on the CDE dialog will update all of the members in the Autodesk Revit Structure 2011 model with the new member size, camber, and stud count (for composite members). FIGURE 5 Updating the Revit Structure Model after design in Composite Design Extension Member sizes, Studs, Camber 6

7 Step 3: Check the Design for Vibration Serviceability using the Vibration Analysis Extension Last, the design is checked for vibration serviceability using the VAE. The VAE analyzes bays in the floor framing, either from the user selected members or by inferring them from the slab that is selected by the user. FIGURE 6 Launching the Vibrations Analysis Extension from the Revit Structure Model after Designed Member sizes, slabs, bay layout 7

8 The VAE analyzes the floor based on user settings, and it can consider walking excitation, rhythmic excitation, and sensitive equipment vibrations as recommended in the American Institute of Steel Construction Design Guide #11 Floor Vibrations due to Human Activity. Bays that do not pass the vibration criteria can be adjusted in Autodesk Revit Structure 2011 and re-analyzed as required. FIGURE 7 Vibrations Analysis Options (top) and Detailed Results (bottom) from the Vibrations Analysis Extension 8

9 Example Projects The following examples illustrate real projects for which the Composite Design and Vibrations Analysis extensions were used. The extensions are very useful for both new design and evaluation of existing designs. Conceptual Design of New Floor Hospital Outpatient Clinic Building For a new three-story medical outpatient clinic building, several different design options needed to be considered for the floor framing. The design criteria were established in conjunction with the owner and architect as follows: 6" floor slabs using 3" composite slab-on-deck construction Maximum beam/girder depth of 18" Live load of 100 psf for entire floor Walking vibration criteria per AISC Design Guide #11 The design engineer created three different bay framing options in a Autodesk Revit Structure 2011 model (utilizing a linked Revit Architecture model for the column grids already established by the architect), including beam layouts, slabs on deck, and preliminary loads. Next, the Composite Design Extension was used to optimize the beam sizes within the established depth restriction from the architect of 18". The member sizes and stud counts were then saved directly back into the Autodesk Revit Structure 2011 model. Each design was also checked for vibration serviceability using the Vibrations Analysis Extension. FIGURE 8 Takeoff analysis of three options for hospital building layout, based on Revit Structure schedule/ quantity table 9

10 Finally, a member piece count and steel weight were calculated using the Autodesk Revit Structure 2011 Scheduling/Quantities feature. A graphical summary of the results was prepared for consideration by the owner and construction manager, upon which the most economical scheme was selected. This scheme was immediately converted into a production Autodesk Revit Structure 2011 model to begin detailed design. Analysis of Existing Floor System Office Building High Density Storage Installation In this example, a tenant of an existing office building wished to install a high density file storage system, weighing approximately 250 psf, on an upper floor of the building. The original structural drawings indicated that the floors, constructed using a composite slab on deck system, were designed for typical office live loads of 50 psf + 20 psf partition loads. While the high density file storage system would result in higher loading than these design values, the higher loads would be localized to a limited area of the floor. A structural analysis was performed to assist the client in locating the storage system so that floor reinforcement could be minimized or avoided altogether. FIGURE 9 Revit Structure model showing loads traced over architectural layout of office space To perform the analysis, the engineer first created a Revit Structure model, utilizing Auto- CAD background drawings provided by the owner. Member sizes and stud counts were directly input into the Revit Structure model from information provided on the original design drawings. The AutoCAD background drawings also indicated the floor plans with partitions and proposed locations for new storage spaces. Using the AutoCAD drawing as an overlay in Revit Structure, the engineer sketched the loads in different areas to help simulate the effects of the high density file storage system (superimposed onthe other live loads present in the office and the actual partition loads as measured in the building). Each loading case was analyzed using the Composite Design Extension to help determine if the members met both strength and deflection criteria. Detailed results were printed indicating member pass/fail status. Ultimately, working with the client, a location was selected that required minimal structural reinforcement to the steel framing. 10

11 New Fitness Center and Natatorium In this example, a large steel framed fitness center and natatorium structure was designed using several third-party software applications. This structure consisted of composite slab-on-deck floors (for the fitness center), and a long-span steel truss roof system over the natatorium space. The lateral force resisting system was designed using reinforced masonry shear walls. Due to the hybrid nature of the construction, several applications were required to help perform the analysis and design of the structural elements. Member sizes and other information were input manually by the engineers into a Revit Structure model in order to coordinate design with the architect and prepare the final construction documents. For this project, clearly the extensions would be insufficient to complete the entire design of the structural framing. However, the Composite Design Extension was used by the project manager to help perform a quality assurance check on the output of the third party software application, as well as the accuracy of the input to the model. The CDE was run for the entire floor, and helped identify any failed members for strength or deflection. In most cases, such members were determined to be input incorrectly or had changed in span or tributary area at some point after the design was completed in the third party application. Rather than re-run the entire model through the third party software, these individual members could be more quickly resized using the CDE and checked for adequacy. Additionally, the VAE was used to check rhythmic vibrations on the floor framing for the fitness center. It was discovered that the bay sizes resulted in failure of the vibration criteria as initially designed in the third-party application, and member sizes were subsequently increased and stiffened to help meet the requirements for vibrations. FIGURE 10 Revit Structure model of new Fitness Center (front part of building, with elevated composite floors) and Natatorium (rendering produced in Autodesk 3D Studio Max Design software) The integrated extensions proved to be invaluable tools during detailed design for this project, since they could be rapidly deployed to check, fine-tune, and resize elements without resorting to a complete re-analysis using other software. 11

12 Summary The Revit Structure Extensions for steel framed floor design apply to both composite and non-composite floors, and can be used to more quickly analyze member strength and serviceability, more rapidly explore different design concepts for floor framing, and help create optimum framing designs by weight, cost, or depth. The new Vibrations Analysis Extension also helps users to evaluate all three vibration serviceability criteria included in the AISC Design Guide #11 Vibrations due to Human Activity. The Extensions work directly inside of Revit Structure by reading information from the analytical model, and saving results directly back into the model file. By using a single model, engineers can often eliminate the need to create and maintain separate models in third party applications, thus improving their efficiency in performing daily design tasks. Furthermore, even in complex models where third party design tools are required, the extensions are a very useful tool for helping with quick design revisions, quality assurance checking, and the review of third-party analysis results for accuracy. Autodesk, AutoCAD, Revit, and Robot are registered trademarks or trademarks of Autodesk, Inc., and/or its subsidiaries and/or affiliates in the USA and/or other countries. All other brand names, product names, or trademarks belong to their respective holders. Autodesk reserves the right to alter product and services offerings, and specifications and pricing at any time without notice, and is not responsible for typographical or graphical errors that may appear in this document Autodesk, Inc. All rights reserved.