Hybrid Wood and Steel System: Overstrength and Ductility

M.A.Sc Student: Carla DickofSupervisor: Professor Stiemer, UBC;

Professor Tesfamariam, UBC OkanaganFP innovations: Erol Karacabeyli

Marjan Popovski

Goal: Analyse and provide guidelines for the design of the hybrid seismic force resisting system, steel moment frames with infill wood shear walls

Hybrid System of Interest:• Hybridize steel and wood into a vertical seismic force resisting system.• Focus on steel moment frames with a wood infill wall system• Address material incompatibilities with special attention to hydroscopic

properties in wood• Provide values for equivalent static seismic design of system

Project Description

Hybrid System: Base Building

Building Plan Frame Elevation

Hybrid System: Parameters

Parameter Options

Infill Wall Types CLT shear walls Midply shear walls

Ductility Limited Ductility Ductile

Storeys 9 6 3Braced Bays One Bay 2 Bays 3 bays

Bracket Properties Gap between infill and steel frame

Infill Case 1 Infill Case 2 Infill Case 3

Bare Frame Design

• Steel moment frame to be designed based with NBCC ductility requirements

• Infill walls to be added and compare the response of the frame and the response of plain wood wallsDuctility Type

Steel Moment

Wood

Rd Ro Rd Ro

D 5.0 1.5

2.0 1.7MD 3.5 1.5

LD 2.0 1.3

Infill Walls: Midply Shear WallsMidply walls have higher strength compared to standard plywood shear walls• Nails in double shear• Nail head does not

pull through sheathing

• Increased nail edge distance

Failure of walls occurs through buckling of studs

Infill Walls: CLT WallsParallel to grain

Perpendicular to grain

ELASTIC PROPERTIESElastic 7800 MPa 4600 MPaShear 250 MPaSTRENGTHTension 16.5 MPaCompression 24 MPaCrushing 30 MPaShear 5.2 MPa

• Approximated as elastic perfectly plastic with plasticity model

• Elastic properties determined using composite theory

• Strength limits determined from product data

• Plain CLT systems show all deformation in connectors

• Confinement from surround frame may cause deformation in the panel

Pure Rocking Shear and RockingPure Shear

Connection between Wall and Frame• Nailed bracket

connection developed for CLT walls

• Bracket behaviour is independent in different directions

• Confinement also provided along edges of panel to provide confinement using “gap” elements

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

-50

-40

-30

-20

-10

0

10

20

30

40

50

PerpPara

Displacement (mm)

Forc

e (K

N)

0 0.01 0.02 0.03 0.04 0.050

100

200

300

400

500

600

700

Bas

e S

hear

(KN

)

Drift (mm/mm)

bare framemidply infillCLT infill

Effect of Infill Panel Type: Single Storey Single Bay Frame

Pushover Results

Effect of Gap Size between Infill Panel and Frame: Single Bay Single Storey Frame

Pushover Results

0 0.01 0.02 0.03 0.04 0.050

200

400

600

800

1000

1200

Bas

e S

hear

(KN

)

Drift (mm/mm)

no gapgap=3mmgap=10mmgap=20mmgap=50mmunconfinedbare frame

Effect of Moment Frame Ductility: 3 Storey Steel for all Infill Configurations

Pushover Results

0 0.05 0.10

1000

2000

3000

4000

Base

She

ar (K

N)

Drift (mm/mm)

Type D Frame

0 0.05 0.10

1000

2000

3000

4000

Drift (mm/mm)

Type LD Frame

plain CLT1 CLT2 CLT3Frame YieldPanel Yield

Effect of Number of Storeys: Limited Ductility Steel Moment Frames for all Infill Configurations

Pushover Results

0 0.05 0.10

1000

2000

3000

4000

5000

Base

She

ar (K

N)

Drift (mm/mm)

3 Storey Frame

0 0.05 0.10

1000

2000

3000

4000

5000

Drift (mm/mm)

6 Storey Frame

0 0.05 0.10

1000

2000

3000

4000

5000

Drift (mm/mm)

9 Storey Frame

plain CLT1 CLT2 CLT3Frame YieldPanel Yield

Pushover Results3 Storey Frame 9 Storey Frame6 Storey Frame

DuctileLim

ited Ductility

Comparison of Frame and Panel Yield for all Frames and Infill Configurations

1 2 3800

1300

1800

2300

2800

3300

996.6Base

She

ar (K

N)

1 2 3800

1300

1800

2300

2800

3300

1223.8

1 2 3800

1300

1800

2300

2800

3300

1108.9

1 2 3800

13001800230028003300

1032.2

Infilled Bays

Base

She

ar (K

N)

1 2 3800

13001800230028003300

1132

Infilled Bays1 2 3

80013001800230028003300

977

Infilled Bays

1659.6

1958.52221.7

3041.1 2613.4 2736.1

977800

1800

2800

1 2 3Infilled Bays

frame yield panel yield bare frame yield

Overstrength (Ro or Ω) • Overstrength is the ratio of the

design load to the ultimate load of the system

• Looking at the innate overstrength in this type of system, the design load is taken as the load at first yield

Ductility (Rd or µT)• Ductility is the ratio of the

displacement at the ultimate load to the displacement at failure

• Failure is taken as an 80% reduction in strength after the ultimate load has been acheived according to FEMA P695

NBCC Seismic Factor Definition

Ductility Factor for all Frames

NBCC Seismic Factors

3 6 90.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.07.8

6.9

4.8

1.62.1

2.63.0

1.8 1.6

2.71.9 1.6

3.7

2.2 1.9

3.5

2.31.9

3.22.6

2.2

3.7

2.82.2

D bare frame LD bare frameD + 1 bay infill LD + 1 bay infillD + 2 bay infill LD + 2 bay infillD + 3 bay infill LD + 3 bay infill

Frame Storeys

Duc

tility

3 6 90.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

2.01.7 1.8

1.3

1.82.02.0 1.9 2.0

1.2

2.02.3

2.2

1.82.1

1.1

2.02.3

2.01.8

2.1

1.1

2.02.3

D bare frame LD bare frameD + 1 bay infill LD + 1 bay infillD + 2 bay infill LD + 2 bay infillD + 3 bay infill LD + 3 bay infill

Frame Storeys

Ove

rstr

engt

h

Overstrength Factors for all Frames

NBCC Seismic Factors

Future Work

• FEMA P695 guidelines for dynamic analysis• Partial Incremental dynamic analysis

– 22 ‘Far-Field’ ground motions

Our supporters at NewBuildS through NSERC and Canadian Steel Institute of Steel Construction

Thanks to everyone at FPInnovations, with special thanks to Dr. Popovski and Prof. Karacabeyli, industrial advisors to the project

Special thanks to the supervisors Dr. Stiemer and Dr.Tesfamariam from the University of British Columbia

Acknowledgements to UBC grad students: Yalda Khorasani, Mathieu Angers, Hassan Pirayesh, Carla Dickof, Caroline Villiard, Benedikt Zeisner.

Acknowledgements