1. Seismic Performance of Outriggered Tall Buildings
Jeremy Atkinson
MASc Candidate
Advisor: Prof. Yang
University of British Columbia

2. What is an outrigger?
-deep girder or truss to couple the core wall and columns, which provides a counteracting moment in the core

3. Why are outriggers used?
Typical Reasons:
Architectural expression
Reduce lateral drift
Reduce overturning moment
Reduce foundation demand
Allows more slender core  more saleable area
New Reasons:
Better seismic performance
Supplemental energy dissipation / damping
Architecture, tall slender structures
Reduce lateral drift
Reduced overturning moment and foundation demand
New reasons
Seismic performance
Supplemental energy dissipation and damping

4. Research Objectives
Evaluate the performance of conventional and outrigger buildings
Adapt performance-based design approach for outrigger systems
Verify performance-based design approach
My research has three main objectives
Compare the performance of conventional and outrigger systems
-currently in progress
Adapt PBD approach for the system
Verify the PBD approach

5. Prototype Buildings Survey of Vancouver’s Tallest Buildings
Ductile Shear Wall (R=5.6) and Ductile Coupled Walls (R=6.8) in central core
Diagonally reinforced coupling beams
Single slab span to perimeter columns around core, many with PT slabs
Blade columns
1000 – 1500 m2 (9000 – ft2) floor plates
30-60 stories (height m)
Need a sense of what is a typical Canadian tall building
-A colleague and I did a survey of Vancouver’s tallest buildings
This defines the design space that our studies will encompass

6. Prototype Buildings Assume a simple but typical Vancouver layout
Coupled walls / Ductile walls
Two C-shaped piers with diagonally-reinforced CBs
Perimeter columns around core
Outrigger in ductile wall direction
Automatically generated, analyzed, and designed using MATLAB + OpenSees
Using the survey, we have come up with a design space for the prototype buildings
Similar traits to Vancouver’s buildings
Automatically designed using code I wrote

7. Capacity Design Ff Ff Fuse Link Brittle Link F F Fr Ensure Fprob
Choose a hierarchy of energy dissipating mechanisms (‘Fuses’)
Provide sufficient reserve strength to other components (‘Brittle Links’)
Ensure desired mechanism forms, even with uncertainty in demands, etc
Fuse Link
Brittle Link F F Fr
Ensure
Fr > 𝐹 𝑓 ( 𝐹 𝑝𝑟𝑜𝑏 𝐹 𝑓 )
Fprob
Ensure
Fr > Ff Fr Δ Δ
Current design methodology in Canada follows a Capacity design approach
-Choose a mechanism hierarchy
-design fuses for the system demands
-design brittle links for the demands corresponding to the probable fuse strength
Consider chain analogy
-The hierarchy must include well detailed, (and hence ductile), energy dissipating mechanisms
-Capacity design should ensure that, in spite of the uncertainties of GMs, strengths, etc, the favorable mechanism will form.
-Three requirements: Stiffness, Strength, Ductility
Brittle Links
Fuse Link
Brittle Links Ff Ff

8. Traditional Design Approach
Mech. 1
Elastic analysis for code-specified hazard level / demands
Choose a hierarchy
Design Mech. 1 for EQ forces
Calculate Mech. 1 Overstrength
Design ‘Brittle Links’
Design Mech. 2
Calculate Mech. 2 Overstrength …
Steel Fuse, BRB, etc.
Mech. 2
Plastic Hinge
So adopting the current approach for an outrigger system would involve: …
But is this good? Does it ensure good performance? Is this overly conservative?
-A performance-based approach is ideal
The system collapse mechanism is enforced
But how is the performance? Can PBD provide improvements?

9. Incremental Dynamic Analysis
Prototype:
40 story
commercial use
ductile wall / coupled wall
outrigger in ductile wall direction
1250m2 plate
designed using traditional approach
One of the ways for comparing the performance is thru IDA,
-the dynamic equivalent of a pushover analysis
-ground motions are incrementally scaled until the system collapses
Here is an IDA response plot of one of the conventionally-designed outrigger systems.
-System properties
-Collapse margin ratio was around 12
-Other prototypes are currently in progress -
CMR ~ 12

10. Ongoing… Next Steps… More prototype designs of various configurations
Comparison of outrigger and conventional buildings
More advanced analysis
Next Steps…
Adapt and implement performance-based design procedure
Comparison of performance-based and traditional designs
Ongoing:
-cover entire design space
-comparing outrigger and conventional buildings
-spot check using more advanced analysis
Next Steps:
-adapting and implementing pbd procedure for the system
-comparing the resulting design and performance

11. Thanks to Sponsors!
Finally I would like to thank the organizations and companies that sponsored the symposium – we wouldn’t be here today without them.

12. Questions and Discussion