Oregon State University

1. Oregon State University 2008 PEER Seismic Design Competition

2. 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

3. 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

4. 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.

5. 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

6. 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

7. 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

8. 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

9. 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

10. Summary Architecture • Mostly an afterthought through the design process • Turned out very pretty • 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

11. 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

12. 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