John Hochwalt, PE, SE Concrete Columns In High-Rise Buildings

John Hochwalt, PE, SEKPFF Consulting Engineers, Seattle, WAConcrete Columns in High-RiseBuildingsACI Spring 2012 ConventionMarch 18 – 21, Dallas, TXACIWEB SESSIONSACIWEB SESSIONSOVERVIEW Project Description Designer’s Perspective Deformation Compatibility – ACI 318-11ACIWEB SESSIONSDEFORMATION COMPATIBILITY OFCOLUMNS IN HIGH RISE BUILDINGS Conceptual ApproachA Designer’s Perspective QuestionsJohn M. Hochwalt, PE, SEKPFF Consulting Engineers, Seattle, Washington ExampleACIWEB SESSIONSPROJECT DESCRIPTIONPROJECT DESCRIPTION – LATERAL SYSTEM 40 Story Hotel and Condominium Special Reinforced Concrete Walls Seattle, Washington Exceeded the IBC Height Limit Concrete Strengths up to 9 ksi Non-Linear Response History Analysis Peer Reviewed Flexural Yielding of Wall and Coupling Beams Maximum Interstory Drift 1.8%ACIWEB SESSIONSACIWEB SESSIONS1

PROJECT DESCRIPTION – GRAVITY SYSTEMDESIGNER’S PERSPECTIVEPriorities Mildly Reinforced Concrete Flat Plate Life Safety (Code compliance or equivalent) 8” Thick, spanning 23 feet Owner’s Interests Deformation Compatibility of Joints Cost Schedule Performance My InterestsACIWEB SESSIONS Least effort to meet the above Engineering is driven by drawings Drawings are driven by constructionACIWEB SESSIONSDEFORMATION COMPATIBILITY – ACI 318-11DEFORMATION COMPATIBILITY – ACI 31-11CALCULATING FORCESACI 21.13 CommentaryModels used to determine design displacementof buildings should be chosen to produce resultsthat conservatively bound the values expected ofthe design earthquake and should include, asappropriate, effects of concrete cracking,foundation flexibility, and deformation of floor androof diaphragms.ACIWEB SESSIONSACIWEB SESSIONSDEFORMATION COMPATIBILITY – ACI 31-11DEFORMATION COMPATIBILITY – ACI 31-1121.13.3.3f’c 8,000 psiACIWEB SESSIONS 2.5%21.13.4.3ACIWEB SESSIONS2

CONCEPT FOR HIGH RISE BUILDINGSACIWEB SESSIONSCOLUMN CAPACITY - INTERACTION DIAGRAM – X AXISCONCEPT FOR HIGH RISE BUILDINGSACIWEB SESSIONSSLAB CAPACITY – FLOOR SYSTEMCONCEPT FOR HIGH RISE BUILDINGSACIWEB SESSIONSSLAB CAPACITY – PUNCHING MODELCONCEPT FOR HIGH RISE BUILDINGSACIWEB SESSIONSCOLUMN CAPACITY - INTERACTION DIAGRAM – Y AXISCONCEPT FOR HIGH RISE BUILDINGSACIWEB SESSIONSSLAB CAPACITY – FLEXURECONCEPT FOR HIGH RISE BUILDINGSACIWEB SESSIONSSLAB CAPACITY – FLEXURAL MODEL3

EXAMPLE – DESIGN STEPSEXAMPLE - DETERMINE Mpr FOR SLAB Determine Mpr for Floor Framing Determine Pn,min and Pn,max for Column Basedon Mpr/2 Compare Pu,min and Pu,max to Acceptable Rangefor Pn Determine Minimum Confinement Check Shear Capacity Based on MinimumConfinementACIWEB SESSIONSACIWEB SESSIONSEXAMPLE - DETERMINE Mpr FOR SLABWhere:ACIWEB SESSIONSDETERMINE MPREXAMPLE - DETERMINE Mpr FOR SLABWhere:POSTIVE MOMENT CAPACITYEXAMPLE - DETERMINE AXIAL COLUMN CAPACITYACIWEB SESSIONSNEGATIVE MOMENT CAPACITYEXAMPLE - DETERMINE AXIAL COLUMN CAPACITY Mpr/2 (184 238) /2 211 k-ftACIWEB SESSIONSMOMENT DEMANDACIWEB SESSIONSAXIAL CAPACITY – X AXIS4

EXAMPLE – COMPARE PU,MIN AND PU,MAXEXAMPLE – COMPARE PU,MIN AND PU,MAX Minimum Pu for 18x24 column, 8 ksi, 2.54% reinforcing is 1,114 kips incolumn L-12 at the sixth floor. Maximum Pu for 18x24 column, 8 ksi, 2.54% reinforcing is 1,608 kips incolumn L-12 at the seventh floor. These demands are well within range established based on Mpr.ACIWEB SESSIONSAXIAL CAPACITY – Y AXISEXAMPLE – MINIMUM CONFINEMENTACIWEB SESSIONSEXAMPLE – MINIMUM CONFINEMENT Since Pu 0.35P0, ACI 21.13.3.3 Controls. Maximum Tie Spacing Is The Larger Of: 6db of smallest longitudinal bar (#8) 6 inches 6 inches ACIWEB SESSIONSMAXIMUM TIE SPACINGEXAMPLE – MINIMUM CONFINEMENTACIWEB SESSIONSMAXIMUM TIE SPACINGEXAMPLE – MINIMUM CONFINEMENT Since Pu 0.35P0, ACI 21.13.3.3 Controls. Tie Area Is One-Half That Required by ACI 21.6.4.4:0.76 in2 / 4 legs 0.19 in2Provide #4 @ 5”.ACIWEB SESSIONSMINIMUM CONFINEMENT AREAACIWEB SESSIONSMINIMUM CONFINEMENT AREA5

EXAMPLE – MINIMUM CONFINEMENTEXAMPLE – SHEAR STRENGTHVu Mpr / 2hVu / 2(9.33)Vu kips#4 @ 5” Ties are okay byinspection.0.54 in2 / 3 legs 0.18 in2Provide #4 @ 5”.ACIWEB SESSIONSMINIMUM CONFINEMENT AREAACIWEB SESSIONSSHEAR DEMANDQUESTIONS?ACIWEB SESSIONS6

Engineering is driven by drawings Drawings are driven by construction ACI WEB SESSIONS DEFORMATION COMPATIBILITY – ACI 318-11 ACI WEB SESSIONS DEFORMATION COMPATIBILITY – ACI 31-11 CALCULATING FORCES ACI 21.13 Commentary Models used to determine design displacement of buildings should be chosen to produce results