Transcript Slide 1
OREGON STATE UNIVERSITY
2008 PEER Seismic Design Competition
DESIGN PROCESS: CRITERIA
To begin the design, look at how the project will
be scored:
Points can be won based on:
Seismic Performance
Rental Income
Presentation/Poster
Architecture/Workmanship
For the design of the structure, 3 categories
count:
Income
Building Cost
Performance
Architecture
RENTAL INCOME
The first design criteria we addressed was to
maximize the rental income
To do this
Maximize floor space
Maximize number of floors
Maximize floor space on upper floors
The first thing we designed was a 5’ tall tower
with 29 floors
BUILDING COST
Don’t bother minimizing this value
Larger footprints provide structural advantages
More weight means more members and more strength
The cheapest structure will not be the best
MAXIMIZING SEISMIC PERFORMANCE
Points are earned by having the lowest possible
roof acceleration and drift
Spectral Acceleration
3
Spectral Accel. (g's)
2.5
El Centro
2
Kobe
1.5
Northridge
1
0.5
0
0.01
0.1
1
Period (s)
Very rigid or very flexible buildings will have the
smallest acceleration and drifts.
STIFF BUILDING
We decided that it would be best to go with a very
rigid building
There is a trade off in using more materials:
Higher rigidity
Higher weight
Weight of balsa wood will be small compared
to the applied loads
Better to go with more wood
Adding more members also adds connections and:
Stiffness
Load paths
Redundancy
ADDITIONAL DESIGN METHODOLOGY
From past years, and common sense, simple,
uniform designs will win:
No re-entrant corners
No twisting
No tapering at top
Also allows max rental income
Irregularities cause torsion and stress concentrations
Rectangles fail easily compared to triangles
Using Diagonal members allowed us to:
Maximize the number of connections
Increase number of load paths
Distribute the load
ADDITIONAL DESIGN METHODOLOGY
Maximize dimensions of footprint
Larger shear walls
Larger lever arm – Increases cross section moment of
inertia – Section can carry larger loads
Minimize columns
Simply not necessary-saves on weight
Additional support for loads
Points of loading require additional reinforcement
Determine which floors will hold the loads (1/8*h)
Brace these laterally on the interior
Increased cross bracing through walls at these points
ANALYSIS
Tension Perpendicular to Grain
Radial
Tension Perpendicular to Grain
Tangential
Shear Parallel to Grain Radial
Shear Parallel to Grain
Tangential
Compression Perpendicular to
Grain Loaded Radially
Compression Perpendicular to
Grain Tangentially
Compression Parallel to Grain
Modulus of Elasticity
Compression Parallel to grain
Maximum Crushing
Compression Parallel to grain
stress at Proportional Limit
Static Bending Modulus of
Elasticity
Static Bending Modulus of
Rupture
Static Bending Stress at
Proportional Limit
Looked up material properties:
Specific Gravity
0.08
750
1250
260,000
370
700
210,000
75
42.5
170
147
103
68
0.10
900
1500
300,000
525
900
300,000
96
54
204
178
120
77
0.12
1050
1800
327,000
750
1150
420,000
103
78
238
227
136
104
0.16
1500
2740
580,000
1330
1850
660,000
147
92
350
288
167
120
0.18
1980
3310
650,000
1540
1995
810,000
160
110
414
320
174
124
0.20
------
3560
705,000
1,725
2435
865,000
187
140
448
388
231
147
Must appreciate the variability of wood
Ran SAP2000 using Time History and Response
Spectrum analysis on several variations
Analyzed rigid and flexible connections, used 80/20
weighted average
Doesn’t make a big difference
Averaged the two analyses
Picked the best overall design
CHANGES IN DESIGN
Our design looks like last year’s winner (OSU)
Same methodology (Stiffness, simplicity are good)
Good ideas last year, could use some improvement
More members near corners, and at load points
Fewer members elsewhere:
Not necessary
Saves self weight
This saves on weight
Decrease the angle of incline on the cross
members in all four walls
Lateral support system changed to increase
redundancy and the number of load paths
ARCHITECTURE
Mostly an afterthought through the design process
Turned out very pretty
SUMMARY
Our design will:
Maximize floor space and number of floors
Be very rigid, and structurally redundant
Be as simple and uniform as possible
Have wide walls
Have increased support at load points
PERFORMANCE PREDICTION
$15
$10
El Centro
Northridge
$5
Kobe
$0
0
0.05
EDP1-Peak Drift Ratio
Engineering Design
Parameter 2
EDP2 Cost (X$106
EDP1 Cost (X$106
Engineering Design
Parameter 1
$20
$15
El Centro
$10
Northridge
$5
Kobe
$0
0
2
EDP2-Maximum Acceleration (g's)
Best guess or worst case estimates:
Annual Income:
Total Building Cost:
Annual Seismic Cost:
Annual Building Revenue:
4
$1,468,000
$247,000
$159,000
$1,062,000
THANK YOU AND REFERENCES
Dr. Scott Ashford, CCE, OSU
Dr. Tom Miller, CCE, OSU
Transportation Professors, CCE, OSU
Pacific Earthquake Engineering Research Center
Laura Elbert, Student, CCE, OSU
Material properties from:
Dreisbach, John F. (1952) Balsa and Its Properties.
Columbia, Connecticut: Columbia Graphs