Seismic Evaluation and Retrofit of Existing Steel...

Seismic Evaluation and Retrofit

of Existing Steel Structures

Canadian Seismic Research Network

Robert Tremblay

École Polytechnique, Montréal, Canada

August 2013

Plan

• Development of Guidelines based on

ASCE 41-13

• Braces & Connections in CBFs

• Connections in MRFs

• Use of Ductile Brace Fuses for CBFs

• Use of Supplemental Dampers

R. Tremblay, Ecole Polytechnique of Montreal 3

Guidelines Based on ASCE 41-13

Section Title

Ch 1 General Requirements

Ch 2 Seismic Performance Objectives

and Ground Motions

Ch 3 Evaluation and Rehabilitation Requirements

Ch 4 Tier 1 Evaluation

Ch 5 Tier 2 Deficiency-based Evaluation and Rehabilitation

Ch 6 Tier 3 Systematic Evaluation and Rehabilitation

Ch 7 Analysis Procedures and Acceptance Criteria

Ch 8 Foundations and Geologic Site Hazards

Ch 9 Steel

Ch 10 Concrete

Ch 11 Masonry

Ch 12 Wood And Light Metal Framing

Ch 13 Architectural, Mechanical, And Electrical Components

Ch 14 Seismic Isolation And Energy Dissipation

Ch 15 System Specific Performance Procedures

App 1 Tier 1 Checklists

Assessment of 10-Storey CBF in 1980


Y. Balazadeh-Minouei, S. Koboevic & R. Tremblay

Ecole Polytechnique

5 @ 9144 = 45 720

X-Bracing

X-Bracing

N-S

Chevron Bracing

Chevron Bracing

E-W

45

72

5 @

91

44

= 4

5 7

20

9 @

39

62

= 3

5 6

58

N

Gravity loads: Roof: Dead = 3.0 kPa Snow = var. Floor: Dead = 3.0 kPa Partitions = 1.0 kPa Live = 2.4 kPa Exterior walls = 1.0 kPa

Assessment based on NBCC 2010

& CSA S16-09 (Rd = 1.5)


X-Bracing

N-S

Braces


& CSA S16-09 (Rd = 1.5)


X-Bracing

N-S

Brace Connections


& CSA S16-09 (Rd = 1.5)


X-Bracing

N-S

Columns


Assessment based on ASCE 41-06 (LDP)

m = Ductility factor

QCE = Expected Strength

QUD = Seismic Demand

Braces = Deformation-Controlled



X-Bracing

N-S

NBCC 2010


Assessment based on ASCE 41-06 (NDP)



NBCC 2010

X-Bracing

N-S

ASCE 41 LDP



QCL = Lower-Bound Strength

QUF = Seismic Demand

Columns = Force-Controlled

Columns subjected to P & M:



X-Bracing

N-S

NBCC 2010



X-Bracing

N-S



NBCC 2010

X-Bracing

N-S

ASCE 41 LDP



Braces

Columns

+



X-Bracing

N-S

ASCE 41 NDP

with linear columns

Assessment & Retrofit

4-Storey CBF (Braces & Connections)


Y. Jiang, R. Tremblay & L. Tirca

Ecole Polytechnique, Concordia University

4 @ 6 m = 24 m

6 @ 63

.5

= 381

558

44.5

290

44.544.5

50.8

[mm]

A325 3/4”Bolts

4 @

4 m

=

16

mW2

00

x3

6

W2

00

x3

6

W2

00

x5

2

W2

00

x5

2

734 kN

4 @

6 m

= 2

4 m

A

15

E

Structure Plan View

Frame Elevation

Brace Connection at Level 1

N

Gravity loads: Roof: Dead = 3.0 kPa Snow = 1.52 kPa Floor: Dead = 3.0 kPa Partitions = 1.0 kPa Live = 2.4 kPa Exterior walls = 1.0 kPa

2L102

x89x

9.5

2L102

x89x

7.9

2L76x

51x6

.4

785

kN

594

kN

306

kN

882 kN

2L127x76x9.5

W2

00

x5

2W

250

x8

0


In Braced Frame

In 12 MN Load Frame

Test Program on 2L Braces and Connections



Brace with End Gusset Plate ConnectionsFiber Cross-Section

End Connection ModelStitch

ConnectorEnd Connection

Detailed 2L Brace O/S Model




Retrofitted connection with

slotted holes

• 15% less capacity

• Similar ductility

Original Connection Retrofitted Connection

Retrofit Strategy


Hybrid Simulations (Collapse Predictions)



Collapse Prediction

(FEMA P695)

Brace Connections


P. Castonguay & R. Tremblay

Ecole Polytechnique

J. Hartley, A. Caruso & C. Rogers

McGill University

Samples made from new material Samples taken from existing

structures


0 40 80 120

inel (mm)

0

200

400

600

800

1000

P (

kN

)

D01X - Yielding on Brace Gross Section

D02X - Failure of Parallel Welds

D03X - Bearing and Tearing

D04X - Failure on Net Section

D05X - Bolt Shear Failure

D06X - Block-Shear Failure

0 10 20 30 40

inel (mm)

0

200

400

600

800

1000

P (

kN

)

a)

b)Strengthened:

Existing:


Assessment / Buildings per 1965 Codes

Connections in MRFs


N. Kyriakopoulos & C. Christopoulos

University of Toronto


Weld Zipping

Backing Bar

CJP

Weld

Failure


0 100 200 300 4000

100

200

300

400

500

600

Total Drift (mm)

Bas

e S

hea

r F

orc

e (kN

)

Frame Fm Pushover

2nd Floor

3rd Floor

4th Floor

Penthouse

Penthouse No P−D

N.A.Vb

Mb

Vb

P

Mc

P=Vb/ 2

Vc

Mc =M

b*(H/ 2-a)/ H

a

a

NOTE: Height of column = H

T = Cst + C

bearing

No force transfer in top plate

Cbearing

Cst

T

Cbearing

Vb

Cst

Vc

Use of Ductile Fuses


• Control Forces in CBFs

• Achieve Higher Displacement Capacities

• Develop Enhanced Hysteretic Response

to Control Drifts

-8 -4 0 4 8

/ y

-1.2

-0.8

-0.4

0.0

0.4

0.8

1.2

P / Py

HSS 102x76x6.4 - KL/r = 112

Tu

Cu


E. Desjardins, A. Desrochers & F. Légeron

Université de Sherbrooke


E. St-Onge & R. Tremblay

Ecole Polytechnique


O. Egloff & R. Tremblay

Ecole Polytechnique

R. Vincent & S. Moreau

Goupe Canam

-5.0 -4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0 5.0

/ hs

-1.2

-0.8

-0.4

0.0

0.4

0.8

1.2

P /

AF

y

Design

Design

Cu

Tu

Test 1 - LF/LH = 0.11


T. Morrison & C. Rogers

McGill University

0

20

40

60

80

100

120

140

0 10 20 30 40 50 60

Axi

al L

oad

(kN

)

System Deformation (mm)

Original vs. Retrofited Tests

Original Sample Retrofitted Sample

-800

-600

-400

-200

0

200

400

600

800

-200 -150 -100 -50 0 50 100 150 200

TestData1

TestData2

R6D09b1

R6D09b2


C. Caprarelli, N. Danila & L. Tirca

Concordia University

-80 -40 0 40 80Displace m ent [m m ]

-800

-400

0

400

800

Force [k N]

Ex pe rimenta l res ult

Pinchin g

Sk elet on curve


M. Gray, C. Christopoulos & J. Packer


Use of Supplemental Dampers

Existing Guideline (ASCE-7 ch18, ASCE-41 ch14)

• Trial-and-error approach based on experience

• Hard to evaluate design alternatives from performance

target

• Hard to assess response under multiple hazards

• Does not provide insight on selection of damping system

Proposed CSRN Performance Spectra-based Guideline

• Ties performance targets directly to design properties

• Direct design, minimize iteration

• Assess alternative options at the beginning of design stage

• Assess multiple hazards at the beginning of design stage

J. Guo & C. Christopoulos



P-Spectra Procedure Overview

• Using basic building properties, evaluate damping

variables that gives desired performance from

performance spectra

• Transform performance spectra solution to MDOF

• Verify design using NLTHA (expected to be close to

target)


Performance Spectra


Features of P-Spectra

• Shows system sensitivity to damping properties

• Shows system sensitivity to ground motions

– East vs. West

– Viscous vs. hysteretic damping

• Shows system performance at other hazard levels

Vf scales with

hazard


0 0.2 0.4 0.6 0.8 10

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

Normalized Displacement, Rd

No

rmal

ized

Bas

e S

hea

r, R

v

Generic Hysteretic Damping Performance Spectrum

Specific Tf

Specific Vf

No

rmalized

Resid

ual D

rift, Rs

Increasing values ofdamper ductility, m

d

Increasing values ofratio of unbraced tobraced stiffness, a

Values of normalizedresidual drift ratios for different valuesof a


Conclusions


• Several Challenges in the Development

of Guidelines

• Braces, Brace Connections & Columns

may be Critical in CBFs

• Connections Critical in PR MRFs

• Ductiles Fuses Proposed to Enhance

the Performance of CBFs

• Effective Design Method Proposed for

Supplemental Damping

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