Seismic Braced Frames

212 Pages·2005·13.46 MB·English

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