S E R I E S

SEISMIC ENGINEERING RESEARCH INFRASTRUCTURES

FOR EUROPEAN SYNERGIES

COMMISSION OF THE EUROPEAN COMMUNITIES

FP7- INFRASTRUCTURES-2008-1

SP4-Capacities

Assessment of the Seismic Response of

Concentrically-Braced Steel Frames TA Project Team

Brian Broderick, Alan Hunt (Trinity College Dublin)

Philippe Mongabure, Alain LeMaoult (CEA Saclay)

Jamie Goggins, Suhaib Salawdeh, Gerard O’Reilly (NUI Galway)

Darko Beg, Primoz Moze, Franc Sinur (University of Ljubljana)

Ahmed Elghazouli (Imperial College London), Andre Plumier (U Liege)

Concentrically Braced Frames

Brace Configurations

Cyclic Brace Response

Axial Force

D

Tens.

Comp.

Shortening Elongation

A Elastic loading

B Tension yielding

C Elastic buckling

D Straightening

A

B

C

Seismic Design

Tension only or

tension-compression

based design

Non-dimensional member

slenderness:

5,0/ cryA NAf

Hollow cross-section

bracing members: cross-

section slenderness:

b/t; d/t

SEISMIC ENGINEERING RESEARCH INFRASTRUCTURES FOR EUROPEAN SYNERGIES

Low cycle fatigue fracture of hollow

section brace members

Cyclic testing: brace

fracture following global

and local buckling

Higher slenderness Lower slenderness

Displacement ductility predictions:

(Nip et al)

(Tremblay)

(Goggins et al)

Gusset plate connection behaviour

Conventional Design

Leads to large, thick gusset plates:

Ryt,gusset >> Ryt,brace

Brace buckling

Gusset plate buckling

Elliptical Clearance Proposal (Roeder, Lehman)

Facilitates more compact and

thinner gusset plates such that

Ryt,gusset >≈ Ryt,brace

Balanced Design

Ryt,gusset = Ryt,brace

TA Project BRACED: Objectives

Investigate under realistic earthquake loading and response conditions some key characteristics of CBFs with hollow section brace members and gusset plate connections:

• Influence of low cycle fatigue on ductility capacity of brace members

▫ evaluation of prediction equations for mD

• Influence of gusset plate connections designs on ultimate response:

▫ conventional and balanced design approaches

▫ connection to beam and column or beam only

• Influence of brace size and connection design on

▫ stiffness and damping in elastic range

▫ evolution of stiffness and damping with response level

• Obtain experimental data for the validation of numerical models

▫ OpenSees and Abacus

SEISMIC ENGINEERING RESEARCH INFRASTRUCTURES FOR EUROPEAN SYNERGIES

Experimental Design

• Multiple experiments performed on one test frame.

• Brace-connection test specimens changed between experiments.

• Specimens with different brace cross section dimensions and connection details.

• Uniaxial earthquake excitation.

• Three levels of seismic loading:

▫ elastic (~50% / 50)

▫ post-yield/buckling (~10% / 50)

▫ ultimate (~2% / 50)

Test Frame

Model CBF

Test Specimens

(Brace Member

and Connections)

• Repeat low level white noise excitation to measure stiffness and damping at different damage levels

• Brace fracture at ultimate response level.

SEISMIC ENGINEERING RESEARCH INFRASTRUCTURES FOR EUROPEAN SYNERGIES

BRACED Test Frame

CB CA

SEISMIC ENGINEERING RESEARCH INFRASTRUCTURES FOR EUROPEAN SYNERGIES

Experimental Programme Test ID Brace

Size

d/t Connection

Type

Gusset

Plate Design

1.S1-CA-G1 80 x 80 x 3 1.04 23.7 Beam & Column Conventional 0.28

2.S3-CA-G1 80 x 40 x 3 2.03 23.7 Beam & Column Conventional 0.35

3.S4-CA-G1 60 x 60 x 3 1.35 17.0 Beam & Column Conventional 0.36

4.S2-CA-G1 100 x 50 x 3 1.49 30.3 Beam & Column Conventional 0.23

5.S1-CA-G2 80 x 80 x 3 1.03 23.7 Beam & Column Balanced 0.73

6.S2-CA-G2 100 x 50 x 3 1.55 30.3 Beam & Column Balanced 0.68

7.S3-CA-G2 80 x 40 x 3 2.05 23.7 Beam & Column Balanced 0.62

8.S1-CB-G1 80 x 80 x 3 0.98 23.7 Beam Only Conventional 0.27

9.S2-CB-G1 100 x 50 x 3 1.48 30.3 Beam Only Conventional 0.24

10.S4-CB-G2 60 x 60 x 3 1.36 17.0 Beam Only Balanced 0.64

11.S2-CB-G2 100 x 50 x 3 1.32 30.3 Beam Only Balanced 0.69

12.S3-CB-G2 80 x 40 x 3 1.47 23.7 Beam Only Balanced 0.62

SEISMIC ENGINEERING RESEARCH INFRASTRUCTURES FOR EUROPEAN SYNERGIES

Braced Test Frame

Earthquake Record & Scaling

Test ID Brace

Size

Area

(mm2)

Yield Strg

(N/mm2)

2%/50

pga (g)

10%/50

pga (g)

50%/50

pga (g)

1.S1-CA-G1 80 x 80 x 3 850 372 0.60 0.35 0.15

2.S3-CA-G1 80 x 40 x 3 630 347 0.44 0.25 0.11

3.S4-CA-G1 60 x 60 x 3 650 348 0.41 0.23 0.10

4.S2-CA-G1 100 x 50 x 3 825 341 0.57 0.33 0.14

5.S1-CA-G2 80 x 80 x 3 917 338 0.60 0.35 0.15

6.S2-CA-G2 100 x 50 x 3 847 342 0.57 0.33 0.14

7.S3-CA-G2 80 x 40 x 3 661 371 0.44 0.25 0.11

8.S1-CB-G1 80 x 80 x 3 893 337 0.60 0.35 0.15

9.S2-CB-G1 100 x 50 x 3 840 340 0.45 0.33 0.14

10.S4-CB-G2 60 x 60 x 3 662 348 0.41 0.23 0.10

11.S2-CB-G2 100 x 50 x 3 854 342 0.57 0.33 0.14

12.S3-CB-G2 80 x 40 x 3 660 371 0.44 0.25 0.11

0 10 20 30 40 50

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

Table accX vs Time (Run037)

Acce

lera

tio

n [g

]

Time [s]

AxTab

0 10 20 30 40 50

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

Table accX vs Time (Run041)

Acce

lera

tio

n [g

]

Time [s]

AxTab

Elastic 50%/50 Ultimate 2%/50

S1-CA-G1

10% / 50

(pga = 0.35g)

Front view Side view

S2-CA-G1

2% / 50

(pga = 0.57g)

Front view

S3-CA-G1

2% / 50

(pga = 0.50g)

Front view Side view

Videos

0 10 20 30 40 50

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

0.2

Roof Drift vs Time (Run065)D

XB

Dri

ft [m

m]

Time [s]

DXB Drift

0 5 10 15 20 25 30

-1

-0.5

0

0.5

1

1.5

Roof Drift vs Time (Run069)

DX

B D

rift [m

m]

Time [s]

DXB Drift

0 10 20 30 40 50

-50

0

50

100

Brace Axial Force vs Time (Run065)

Bra

ce

Axia

l F

orc

e [kN

]

Time [s]

FbracedL

FbracedR

0 5 10 15 20 25 30-200

-100

0

100

200

300

Brace Axial Force vs Time (Run069)

Bra

ce

Axia

l F

orc

e [kN

]

Time [s]

FbracedL

FbracedR

-4 -2 0 2 4 6

-100

-50

0

50

100

Base Shear (Brace) vs. Relative Disp (Run065)

Ba

se

Sh

ea

r [k

N]

Relative DXB Displacement [mm]

VbBr

-30 -20 -10 0 10 20 30 40

-200

-100

0

100

200

Base Shear (Brace) vs. Relative Disp (Run069)

Ba

se

Sh

ea

r [k

N]

Relative DXB Displacement [mm]

VbBr

pga = 0.21g pga = 0.64g

drift v time

brace forces v

time

base shear v

drift

S2-C

A-G

1

S2-C

A-G

1

0 5 10 15 20 25 30-1.5

-1

-0.5

0

0.5

1

1.5

Roof Drift vs Time (Run082)

DX

B D

rift [m

m]

Time [s]

DXB Drift

pga = 0.77g S

1-C

A-G

2

0 5 10 15 20 25 30

-1

-0.5

0

0.5

1

1.5

Roof Drift vs Time (Run069)

DX

B D

rift [m

m]

Time [s]

DXB Drift

0 5 10 15 20 25 30-200

-100

0

100

200

300

Brace Axial Force vs Time (Run069)

Bra

ce

Axia

l F

orc

e [kN

]

Time [s]

FbracedL

FbracedR

-30 -20 -10 0 10 20 30 40

-200

-100

0

100

200

Base Shear (Brace) vs. Relative Disp (Run069)

Ba

se

Sh

ea

r [k

N]

Relative DXB Displacement [mm]

VbBr

pga = 0.64g

drift v time

brace forces v

time

base shear v

drift

S2-C

A-G

1

0 5 10 15 20 25 30-300

-200

-100

0

100

200

300

Brace Axial Force vs Time (Run082)

Bra

ce

Axia

l F

orc

e [kN

]

Time [s]

FbracedL

FbracedR

-40 -30 -20 -10 0 10 20 30 40

-300

-200

-100

0

100

200

Base Shear (Brace) vs. Relative Disp (Run082)

Ba

se

Sh

ea

r [k

N]

Relative DXB Displacement [mm]

VbBr

Brace and Connection Deformations

Initial natural frequency and damping

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

S1 S2 S3 S4

Da

mp

ing

(%

)

CA-G1

CA-G2

CB-G1

CB-G2

1

2

3

4

5

0 0.5 1 1.5 2 2.5 3

na

t fr

eq

ue

nc

y (

Hz

)

max drift (%) in prior test

2.S3-CA-G1

7.S3-CA-G2

3.S4-CA-G1

1

2

3

4

5

0 0.5 1 1.5 2 2.5 3

na

t fr

eq

ue

nc

y (

Hz

)

max drift (%) in prior test

1.S1-CA-G1

5.S1-CA-G2

8.S1-CB-G1

Change in natural frequency with response amplitude

Comparison of maximum response

0

0.5

1

1.5

2

2.5

3

0 0.2 0.4 0.6 0.8

Ma

x D

rif

t (%

)

pga (g)

80x80

80x40

60x60

100x50

Conventional Gusset Design

80 x 80 x 3 braces

SEISMIC ENGINEERING RESEARCH INFRASTRUCTURES FOR EUROPEAN SYNERGIES

Transnational Access

The BRACED Project Team