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