1. Hybrid Wood and Steel System: Overstrength and Ductility
M.A.Sc Student: Carla Dickof
Supervisor: Professor Stiemer, UBC;
Professor Tesfamariam, UBC Okanagan
FP innovations: Erol Karacabeyli
Marjan Popovski

2. Project Description 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
For this project I looked at the hybridization of wood and steel into one seismic system.
Specifically I was looking at the placement of wood panels within a steel moment frame
I was attempting to determine the effect to strenght and stiffness the panels would have
Additionally we hoped to provide some estimates at the seismic factors used for static design in most codes

3. Hybrid System: Base Building
Building Plan
Frame Elevation
We started by creating a test building to analyse.
4x3 bays
Analysed one frame with 2D analysis
3 bay frame with exterior bays of 9m and an interior bay of 6m
Ground floor height of 4.5m and all other stories 3.65m typical for an office building

4. Hybrid System: Parameters
Options
Infill Wall Types
CLT shear walls
Midply shear walls
Ductility
Limited Ductility
Ductile
Storeys 9 6 3
Braced Bays
One Bay
2 Bays
3 bays
Bracket Properties
Gap between infill and steel frame
We looked at several parameters
The type of infill wall
The ductility of the desing of the steel frame
3 different heights of building
The configuration of infill bays
As well as the gap spacing between the edge of the panel and the steel frame
Infill Case 1
Infill Case 2
Infill Case 3

5. 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 walls
Ductility Type
Steel Moment
Wood Rd Ro D
5.0
1.5
2.0
1.7 MD
3.5 LD
1.3
The steel frames were designed to meet the criteria in Canada’s steel design code
One set of frames was designed to meet the ductility requirements of a highly ductile frame and ther other for a limited ductility frame
To allow for a more direct comparison of strengths and stiffnesses both were design for an equivalent static load associated with the ductility of a wood building between bare frames and infilled frames

6. Infill Walls: Midply Shear Walls
Midply 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
For the infill walls, two types of walls were looked at. The first was midply plywood shear walls
These provide a central layer of plywood between 2 studs instead of on the outside of the wall
Allows for higher strength and stiffness compared to typical shear walls because the nails are in double shear
These were modeled taking in to account as non-linear systems taking in to account the strength and ductility after the peak strength is reached

7. Infill Walls: CLT Walls
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
Parallel to grain
Perpendicular to grain
ELASTIC PROPERTIES
Elastic
7800 MPa
4600 MPa
Shear
250 MPa
STRENGTH
Tension
16.5 MPa
Compression
24 MPa
Crushing
30 MPa
5.2 MPa
The other type of wall considered were CLT walls.
CLT walls include both rocking behaviour and shear deformation in the panel
The shear in the panel is often ignored as they are so much more stiff than the connectors
Within a steel frame bay, even after the connectors fail, the panel will continue to be loaded
Little information is available about the failure in in-plane shear of CLT panels
A simplified elastic perfectly plastic model was used here with the ultimate strenght of 5.2MPa
Further testing is required to determine the true behaviour of these panels
Shear and Rocking
Pure Rocking
Pure Shear

8. 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
The connections were modeled using the behaviour shown here as developed at FPInnovations
Different behaviours were noticed parallel and perpendicular to the grain grain
Also, links representing the confinement were modeled around the panels that act in compression only
The panels were modeled to sit directly on the steel beams below them
A gap of varying size was provided around the sides and the top of the panel

9. Pushover Results
Midply walls do not add significant stiffness or strength to the system;
CLT infill walls show significant gains over plain steel moment frame
Effect of Infill Panel Type: Single Storey Single Bay Frame

10. Pushover Results
Initial stiffness is due the combined stiffness of the moment frame, and the connections between the infill wall and the CLT frame
Second linear stiffness is present once gap is close and frame is directly loading the CLT walls,
As the connection yields the confinement continues to contribute significantly until the frame begins to fail
Effect of Gap Size between Infill Panel and Frame: Single Bay Single Storey Frame

11. Pushover Results
Ductile vs Limited Ductility
The shape of the pushover curve is similar for infilled ductile and limited ductility frames
Ductile frames do not maintain the flat, post yield behaviour
For systems with 2 or 3 infilled bays, the ductile frame shows the panel yielding around the same time as the frame
Comparatively the limited ductilit frame shows the panels yielding prior to the frames
This could allow for more redundancy in the system
Effect of Moment Frame Ductility: 3 Storey Steel for all Infill Configurations

12. Pushover Results
As the number of stories increasing, the post yield behaviour gets worse
The manor of yielding does not change between frame systems
Effect of Number of Storeys: Limited Ductility Steel Moment Frames for all Infill Configurations

13. Pushover Results 3 Storey Frame 6 Storey Frame 9 Storey Frame
Ductile
Limited Ductility
For ductile frames, the frame consistently yields before the panle begins the fail
For limited ductility frames, the panel begins to fail at or before the frame begins to yield in the 3 and 6 storey cases
All cases showed a significant increase in strength of the system with the addition of infill panels.
The yield strength of the frames increased with each panel that was added in a fairly linear manner
The yield strength of the panels was much more consistent regardless of the number of infill panels added.
Higher panel yield strengths for the systems with only one infilled bay could be attributed to more significant rocking in these shorter panels
In all cases the addition of
Because the frame is the gravity resisting system, it is preferable for the frame to remain undamaged and the panel to absorb energy through failure
Comparison of Frame and Panel Yield for all Frames and Infill Configurations

14. NBCC Seismic Factor Definition
Overstrength (Ro or Ω)
Ductility (Rd or µT)
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 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
In determining the overstrength and ductiliy, the FEMA P695 guidelines were use
The over strength is generally taken fromt eh maximum load achieved over the design load; instead we used the yield load
The ductility was taken as the poust ultimate deflection over the deflection at ultimate. This correspondes well with the canadian code standards

15. NBCC Seismic Factors Ductility Factor for all Frames
The ductility is significantly decreased for the ductile moment frames
The ductility is consistent, or even increased compared with a limited ductility bare moment frame
As you can see, the ductilities are all well below the design ductility allowed for ductile moment frames
Here, the ductility for a limited ductility moment frame, which coincides with the ductility factor subscribed for CLT walls by FP Innovations, is fairly consistent with the initial ductility factors found for the infilled system
Ductility Factor for all Frames

16. NBCC Seismic Factors Overstrength Factors for all Frames
The overstrengths does not show large variability compared to the bare frame.
Here you can see that the overstrength, especially for taller systems, also corresponds better with an overstrength of 1.7, associated witha limited ducitlity moment frame, compared to the 1.5 for a ductile moment frame,
Overstrength Factors for all Frames

17. Future Work FEMA P695 guidelines for dynamic analysis
Future work will consider a dynamic analysis of the system following the FEMA P695 guidelines
This will allow further refinement of the seisic design factors
A design guideline for the strength and stiffness impact of infill walls is also needed
Perhaps most importantly, testing of the infill system is required to confirm the model
FEMA P695 guidelines for dynamic analysis
Partial Incremental dynamic analysis
22 ‘Far-Field’ ground motions

18. Acknowledgements
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.
I would like the thank our supporters are NewBuildS through NSERC, as well as the Canadian Institue of Steel Construction.
Special thanks to everyone at FP Innovations who have been so helpful as well as my supervisors Dr. Stiemer, and Dr. Tesfamariam, and all the other students who have worked on the project.
Any questions