O REGON S TATE U NIVERSITY 2008 PEER Seismic Design Competition

D ESIGN P ROCESS : C RITERIA 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

R ENTAL I NCOME 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 B UILDING C OST 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

M AXIMIZING S EISMIC P ERFORMANCE 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.

S TIFF B UILDING 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

A DDITIONAL D ESIGN M ETHODOLOGY 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

A DDITIONAL D ESIGN M ETHODOLOGY 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

A NALYSIS 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 , , , , , , , , , , ,0001, ,

C HANGES I N D ESIGN 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

S UMMARY Mostly an afterthought through the design process Turned out very pretty A RCHITECTURE 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

P ERFORMANCE P REDICTION 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

T HANK Y OU AND R EFERENCES 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