OREGON STATE UNIVERSITY2008 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

Very rigid or very flexible buildings will have the smallest acceleration and drifts.

1 100

0.05

0.1

0.15

0.2

0.25

Spectral Acceleration

El Centro

Kobe

Northridge

Period (s)

Spec

tral

Acc

el. (

g's)

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 comparedto 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 Looked up material properties:

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

Specific Gravity

Static Bending Stress at Proportional Limit

Static Bending Modulus of Rupture

Static Bending Modulus of Elasticity

Compression Parallel to grain stress at Proportional Limit

Compression Parallel to grain Maximum Crushing

Compression Parallel to Grain Modulus of Elasticity

Compression Perpendicular to Grain Tangentially

Compression Perpendicular to Grain Loaded Radially

Shear Parallel to Grain Tangential

Shear Parallel to Grain Radial

Tension Perpendicular to Grain Tangential

Tension Perpendicular to Grain Radial

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

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

SUMMARY

Mostly an afterthought through the design process

Turned out very pretty

ARCHITECTURE

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

Best guess or worst case estimates: Annual Income: $1,468,000 Total Building Cost: $247,000 Annual Seismic Cost: $159,000 Annual Building Revenue: $1,062,000

0 1 2 3 4$0

$5

$10

$15

$20

Engineering Design Parameter 2

El CentroNorthridgeKobe

EDP2-Maximum Acceleration (g's)

ED

P2 C

ost

(X$106

0 0.02 0.04 0.06 0.08$0

$5

$10

$15

Engineering Design Parameter 1

El CentroNorthridgeKobe

EDP1-Peak Drift Ratio

ED

P1 C

ost

(X$106

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