Seismic Braced Frames PDF
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Seismic Braced Frames Design Concepts and Connections Developed by: Rafael Sabelli, S.E. DASSE Design Inc. July 27, 2006 Chicago, IL The information presented herein is based on recognized engineering principles and is for general information only. While it is believed to be accurate, this information should not be applied to any specific application without competent professional examination and verification by a licensed professional engineer. Anyone making use of this information assumes all liability arising from such use. Copyright © 2006 By The American Institute of Steel Construction, Inc. All rights reserved. This document or any part thereof must not be reproduced in any form without the written permission of the publisher. Seismic Braced Frames Design Concepts and Connections Developed by: Rafael Sabelli, S.E. DASSE Design Inc. Seismic Braced Frames: Design Concepts and Connections Performance, Code Requirements, and Detailing Concepts But No Hysteresis Diagrams! Outline I. Seismic Design II. Behavior of Concentrically Braced Frames III. Special Concentrically Braced Frames (SCBF) A. Expected Performance B. Requirements C. Design Example D. Gusset Plate Design Tools Seismic Braced Frames: Design Concepts and Connections Outline IV. Ordinary Concentrically Braced Frames (OCBF) A. System B. Requirements C. Design Example V. Buckling-Restrained Braced Frames (BRBF) A. System B. Requirements C. Design Example Seismic Braced Frames: Design Concepts and Connections Ground Rules 1. 2002 & 2005 editions of AISC Seismic and the AISC Specification are used, with differences pointed out.New to 2005 2. LRFD is used. 3rd Edition LRFD Manual tools are used. 3. 2005 edition of ASCE 7 is used. Seismic Braced Frames: Design Concepts and Connections Part I: Seismic Design Seismic Braced Frames: Design Concepts and Connections When are the Seismic Provisions Required? Depends on Seismic Design Category Depends on Seismic Use Group Seismic Use Group Depends on Occupancy Depends on Soil Type Depends on Spectrum Proximity to Faults Capacity of Fault Soil Types A-E Spectrum Determined from USGS Maps Site-Specific Spectrum Soil Type F Site-Specific Spectrum Seismic Braced Frames: Design Concepts and Connections Seismic Design (Seismic Use Groups I&II) Seismic Braced Frames: Design Concepts and Connections Seismic Design (Seismic Use Group III) Seismic Braced Frames: Design Concepts and Connections Seismic Design Response Spectrum Based on Maximum Credible Earthquake Design Base Shear Depends on Building Period Reduced by Factor “R” RDepends on System Reflects System Ductility Includes System Overstrength Seismic Braced Frames: Design Concepts and Connections System Ductility What is “System Ductility”? Ability of System to Maintain Stability After Yielding/Overload of Some Elements Ability of Yielding/Overloaded Elements to Deform If yielding elements fracture, system may lose stability Ability of NonyieldingElements to Withstand Forces Redistributed by Yielding When an element yields, other elements may receive more load Ability of NonyieldingElements to Withstand Deformations Caused by Yielding System displacements increase after yielding, and deformation modes change So-called “nonyielding”members may have some inelastic deformation Seismic Braced Frames: Design Concepts and Connections System Ductility How is System Ductility Achieved? Designate certain elements to be fuses Ensure those elements are ductile Ensure other elements do not yield Determine maximum forces that yielding elements can impose Maximum forces can be much greater than design forces Resistance factor Conservative design equations Conservative design assumptions Higher-than-specified material strength Over-designed elements (e.g., Drift-controlled) Check strength or ductility at expected drifts Seismic Braced Frames: Design Concepts and Connections System Ductility How is System Ductility Achieved? Seismic Braced Frames: Design Concepts and Connections
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