Nijad Rudy Boukhalilstructural optionspring05
Presentation outlineProject backgroundExisting conditions Problem statementProposed solutionFloor systemLateral systemvibrationConstruction managementRecommendationsAcknowledgementsquestions
Project backgroundLocationon the corner of Bellevue Way 5 stories 3 above ground2 level parking39,000 square foot Rectangular shape 131x147Many openingsProject cost = $14 million
Project background
The museum has:
four classrooms for its Museum Schoolthree interactive Explore Galleriesa 90-seat auditoriuma multimedia librarya Museum storea small sidewalk caf2 story atriumOutdoor terraces
Project backgroundProject team
general contractor: Sellen construction Co. mechanical design/build contractor: Mckinstry Co.design architect: Steven Holl architects Associate Architect: Sclater Partners Architectsstructural engineer: Skiling Ward Magnusson barkshire, inc
Project backgroundArchitectural layout3 galleries 3 light qualities3 actions - see/explore/make (art, science, technology)3 main levels3 circulation directions
Existing conditionsFloor system
Composite steel deck3.5 concrete normal weight concretecompression strength fc = 4000 psi3 metal deckshear studs
AdvantagesGood with Long spanefficient and economicGood strength to weight ratioSmaller foundation needed
DisadvantagesCrane demandingDifficult coordinationvibration
Existing conditionsLateral system
Shear walls10 Cast-in-place#5 reinforcing barsbearing walls along perimeter and core around openings and the atrium. Advantages:The cast in place system: structure that is free of joints.achieve a continuous appearance of the applied finishes. provide the architect with the desired architectural finishShear walls
Existing conditionsSeismic Load Calculations (ASCE 7-02)AssumptionsOccupancy Category:IIISeismic Use Group:IISite Class:D
Seismic response coefficient: R=6
Problem statementSeismic hazard effect:Half of the states109 million people 4.3 million businesses
More frequent vibration key issue for a museum
Original systemFloor system: Composite floorLightweight system more subjected to vibration
Lateral system: Shear wallsGood choice against earthquakesEarthquake Cost damage:Direct cost: $1 billion/year indirect business losses: $2 billion/year
Proposed solutionsfloor system:
How vibrations dies outStiff diaphragm share the earthquake forces
Joist system spacing 2ft o.c (for vibration)
Advantages of joistLighter Weight reduce sizes of beams, columnsVarious sizes ~ Good for long spansLowers the overall cost of the project
Construction SpeededEach joist is a complete and independent unit.Allows field work to progress efficiently.
Proposed solutions
Lateral system
types of Lateral SystemsBracingMoment Frame
Why choose brace framesHave same advantagesused where shear walls are impractical.
Advantages of Braced Frames:High Strength and StiffnessMinimizes DeflectionsUses less MaterialCost Effective ~ Efficient and EconomicalStrong visual elementspeedy erection for faster return. More flexible to future changes than shear walls
Proposed solutionDifferent types of bracingsSingle Diagonals has to resist tension and compression caused by sideways forces in both directions on a frame.
Cross Bracing only need to resist tensionone brace is in tension for the sideways force in one direction on the frame, the other brace is in tension when the force is reversed. This is the most widely used type of bracing system.
Proposed solutionAdvantagesAllows for windows in walls, and other open spacesDisadvantagesLarge deflections
Larger Members
Cost increase
Why moment frames ok
Obstructions rejectedeliminates space limitations of solid shear walls braced frames. Moment frame:
floor systemJoist system using Vulcraft:Spacing = 2 o.c.Supports unchanged slab:3,5 concrete3 deck
Typical bay:
floor systemStress analysis The areas to be concerned about were around the elevator core and the openings
floor systemMoment diagram analysis
floor systemEncountered problem
A suspended stairway transports the visitor to the third floor along the north wall over head
floor systemSize up the beamThe right side beam of the staircase is required to be a W 40 X 183. The columns at the left support of the beam are a W 14X145, and the column at the right support is a W10X45 as shown in the figure below.Analysis in Etabs of the W 40 X 183:Deflection governedThe beam is spanning 60 feet, and with the shear walls gone, a W beam less than a W 40 X 183 will deflect more that L/480 = 1.5
Lateral systemChanges:
Core around elevatorShear walls braced framesAdd columns to replace shear wallsNeed moment frames around openings
Lateral systemCore:Braces: W12x96
Lateral systemNew columns in floor plan:
Lateral systemBracingWest facade
Lateral systemBracingSouth facade
Lateral systemBracingEast facade
Lateral systemType of moment connection:SidePlate Ideally suited against seismic
Up to 25% Reduction in Lateral Frame Tonnage
Up to 50%-65% Reduction in Field Welding Man-Hours
Lateral systemMoment connection distribution
Lateral systemETABS was used to design the lateral force resisting system of the buildingIBC 2000 earthquake pressureASCE 7-98 wind pressure.Check:DeflectionDrift controls
Lateral system Lateral drift
VibrationFloor vibrationHuman activities: walking Room: north gallery on 3rd floorVibration expectation: small to nonexistentUse design guide 11 from AISC
Goal: to understand which system is more adequate for vibration compare existing/new system
VibrationExisting systemComposite steel deck
VibrationModified systemJoist floor system
Both systems have the approximately the same percentage of the acceleration of gravity and are satisfactory to damp vibration while walking in the North gallery of the BAM.
Cost comparison
Cost comparisonRedesigned floor system
Cost comparisonExisting lateral system
Cost comparison
RecommendationsDisadvantages of Braced Frames: Obstructive interfere with architectural requirementsLow Ductility Disadvantages of Moment Frames: Expensive Lots of material plus labor-intensive connections.Low Stiffness
Floor system = joistLess expensiveVibration checked
decision
lateral system = shear wallsLess expensiveDrift checked
acknowledgmentsThank youMy AE classmatesMy friendsmy familyfriends & familyfacultyProf. Parfitt Dr. Boothby Dr. Hanagan Dr. MemariMr. Tim Bade Mr Ziad Jamaleddine Steven holl architects
Questions?