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Desi n of Concentricall

Braced Frames

Anindya Dutta, Ph.D., S.E.

Example Configurations

X-Braced Inverted V (Chevron) 2 Story X-Braced

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Example Configurations

V (Inverted Chevron) Zipper

Special Concentrically Braced Frames

Primary location of energy dissipation are the

Braces dissipate energy by tension yielding

and compression buckling

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Special Concentrically Braced Frames

Special Concentrically Braced Frames

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Special Concentrically Braced Frames

Column Axial Load Distribution

Special Concentrically Braced FramesColumn Axial Load Distribution

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Special Concentrically Braced Frames

Beam Design Axial Load

Special Concentrically Braced FramesBeam Design: Flexure

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Special Concentrically Braced Frames

Basic Design Procedure

Calculate the demand based on ASCE 7

Analyze the structure; find brace forces

Size the fuses i.e. braces

Capacity design other non yielding members

Special Concentrically Braced FramesBasic Design Procedure

Use expected brace capacity

Eliminate conservative design assumptions

Do not use factors for expected strength

. y

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Requirements for Member Design

Brace Effective Length

Requirements for Member DesignBrace Effective Length

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Requirements for Member Design

Brace Effective Length: End Fixity

Requirements for Member DesignBrace Effective Length

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Requirements for Member Design

Required Strength

If UAntRyFyAg

Max load indicated by analysis that can be

transferred to the brace by the system

Requirements for Member DesignLateral Force Distribution

All compression or tension

system (generally not allowed)Sum of horz. Comp. on either

compression or tension 0.7V NG

70% of the force is to be resisted by brace in tension

Exception allowed when compression braces are designed

for Amplified () load combinations of ASCE 7

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Requirements for Member Design

Lateral Force Distribution

0.3V Tension 0.7V 0.3V Tension 0.7V

0.3V Compression 0.7V

OK

0.3V Compression 0.7V

OK

Members to be seismically compact. Follow

Requirements for Member DesignWidth-Thickness Limitations

- -

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Requirements for Member Design

Local Buckling

Design of SCBF Connections

Connections to be designed for expected

This force need not exceed the max load

indicated by analysis that can be transferred

to the brace by the system

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Design of SCBF Connections

Design of SCBF Connections

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Design of SCBF Connections

Pin ended

Fixed ended

Design of SCBF Connections

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Design of SCBF Connections

Design flexural strength of the connection

xe

Design compressive strength of the

pyn MRR 1.1

detailingnyn PRR 1.1

Design of SCBF Connections2t Offset

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Design of SCBF Connections

2t Offset @ Concrete Filled Deck

Design of SCBF ConnectionsTearing of Gusset: No Hinge Zone

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Design of SCBF Connections

Gusset Compression

Design of SCBF ConnectionsGusset Compression

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Design of SCBF Connections

Gusset Compression

Design of SCBF ConnectionsGusset Compression

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Design of SCBF Connections

Design of gussets

Design of SCBF ConnectionsDesign of gussets: Uniform Force Method

Ruc

u

Pusin-Aub

eb

wp

Aub

ec

Ruc+Rub-Pucos

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2

Design of SCBF Connections

Design of gussets: Uniform Force MethodPuVuc u

cucuuc P

eHPV ==

Hub

Vub

Huc

Vub

ub

ubuub Pr

eVP

rH

rr

==

where

Rub

Pusin -AubRub -Vub

Pusin -Aub -Hub( ) ( )22

bc eer +++=

Design of SCBF: Specials for Chevron

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Design of SCBF: Specials for Chevron

Design of SCBF: Specials for Chevron