1Suspended high-rise Prof Schierle 1Suspended high-riseSuspended high-rise Prof Schierle 2Suspended high-riseChallenges• Load path detour: load travels up totop, then down to foundation• Combined hanger / column deflectionyields large differential deflectionArchitectural rational• Column-free ground floor• Planning flexibility at ground floor• Facilitates top down future expansionwith minimal operation interference • Small hangers replace large columnsStructural rational• Eliminates buckling in hangers,replacing compression by tension• High-strength hangers replace largecompression columns • Concentration of compression to a fewlarge columns minimizes bucklingOptions• Multiple towers to reduce lateral drift• Multiple stacks control deflection• Adjust hangers for DL and partial LLto reduce deflection • Prestress hangers to reduce deflection1 Gravity load path2 Differential deflection3 Prestress to reduce deflection4 Ground anchors for stability1 Single tower2 Multiple towers3 Multiple stacks4 Multiple stacks / towers5 Triple stacks6 Triple stacks / twin towers Suspended high-rise Prof Schierle 3BMW headquarters MunichArchitect: Karl SchwanzerStandard Bank Center, JohannesburgArchitect: Hentrich and Petschnigg2Suspended high-rise Prof Schierle 4Hypo Bank MunichArchitect: Bea and Walter BetzFour circular towers support a mid-level mechanical floor thatsupports the floors above while floors below are suspended from it.Suspended high-rise Prof Schierle 5UN Center Viennabuilt projectArchitect: J StaberDesign objectives:Independent expansionof conference center and offices was required Triangular grid allows horizontal expansion of conference center in threedirectionsSuspended high-rise allows independent top-down expansionUN Center Vienna competition entry -Architect: G G SchierleSuspended high-rise Prof Schierle 6Federal Reserve Bank, MinneapolisArchitect: Gunnar Birkerts• Parabolic suspenders are supported by 2 towers• Top trusses resist lateral suspender thrust• Floors below parabola are suspended• Floors above parabola are supported by columns• Support type is expressed on the facade3Suspended high-rise Prof Schierle 7Westcoast Transmission Tower, VancouverArchitect: Rhone & Iredale Engineer: Bogue BabickiConcrete core wall thickness t = 1’ Suspender cables 2 2 7/8”Guy cables 227/8” + 221/2”Average wind pressure (80mph, Exposure B) P = 30 psfLive load reductionsBeam: R = 50 %Suspender: R = 60 %Gravity loadsConcrete slab = 40 psfPartitions = 20 psfFraming = 15 psfFloor/ceiling = 5 psfDL = 80 psfBeam live load0.5 (50) LL = 25 psfSuspender live load0.4(50) LL = 20 psfTotal loads:Beam 105 psfSuspender 100 psf108’36’ 36’ 36’174’Suspended high-rise Prof Schierle 8Uniform beam loadw = 105 psf x12’/1000 w =1.26 klfBeam bending M = wL2/8 = 1.26x362/8 M = 204k’S = M/Fb= 204 x12/22 S = 111 in3Use W21x57 S = 111Suspender loadP = 13x100 psf x[182+18x(18+9)/2]/1000 P = 737 kSuspender cross section (twin 2 7/8”, 70% metallic)A = 2  0.7(2.875/2)2A = 9 in2Suspender stress f = P/A = 737/9 f = 82 ksiGuy force (from vector graph) P = 1042 k Guy cross section (2 suspenders + 2 - 2.5” strands)A = 9 in2+ 20.7(2.5/2)2A = 15.9 in2Guy stress f = P/A = 1042/15.9 f = 66 ksi737k737k108’36’ 36’ 36’Suspended high-rise Prof Schierle 9108’36’ 36’ 36’Outrigger beamBending moment (from last side) M = 204 k’Compression (from vector graph) P = 737 kTry W21x223 A = 65.4S = 510 in3I = 5950 in4Axial stress fa= P/A = 737/65.4 fa= 11.27 ksiBending stressfb=M/S = 204k’x12”/510 fb= 4.8 ksibeam radius of gyration r = (I/A)1/2=(5950 / 65.4)1/2r = 9.54”Slenderness ratio (y-direction braced by floor)KL/r = 36’x12”/9.54 kL/r = 45Allowable buckling stress Fa= 18.78 ksiCheck combined stress fb/Fb + fa/Fa <= 1fb/Fb + fa/Fa= 4.8/22 + 11.27/18,78 = 0.82 0.82 < 1737k737k4Fy = 36 ksi AISC table, copyright © American Institute of Steel Construction Inc. Reprinted with permission of AISC. All rights reservedSuspended high-rise Prof Schierle 11Overturn moment ( 30 psf wind pressure)M = 30[36(30+144+50)2/2+2x36x144(30+72] /1000 = 58,821 k’Core moment of Inertia I(Ioutside–Iinside– two 6’ doors)I = (B4-b4)/12 - Ay2 = 364-344) /12 - 2x6x182I = 24.719 ft4Bending stress fb = Mc/I = 58.821 k’ x18’/24,719 ft4= 42.83 ksffb = 42.83 ksf x1000/144 fb = 298 psiDead load (13 stories @ 80 psf)P = 13x80 psf x1082P =12,130,560 #fc= P/A = 12,130,560/[2(36+30)144] fc= 638 psi > 298fb < fc = no tensile stress 108’36’ 36’ 36’30’12x12=144’50’Suspended high-rise Prof Schierle 12Overbeek House Rotterdam ~ 90’x90’ - 11 stories Architect: Verbruggen & GoldsmidtEngineer: Aronsohn5Suspended high-rise Prof Schierle 13Hong Kong Shanghai BankArchitect: Norman FosterEngineer: Ove ArupSuspended high-rise Prof Schierle 14Assume35 storiesMax. 8 floors per stackTypical story height h = 12.8’Ground floor story height h = 24’Wind load P = 3.8 kPa P = 80 psfHK statutory wind load varies fromP = 1.2 kPa @ ground toP = 4.3 kPa @ 140 m)Gravity loadDL = 90 psfLL = 63 psf (3kN/m2) = 153 psfMasts: 17’x16’ (5.1x4.8m) 4 pipes, max. 55”x3.9” thick(1400x100mm)Hangers: max. 16”x2.4” thickpipes (400x60mm)Finite Element analysis of mast Scheme development  Computer analysis Suspended high-rise Prof Schierle 15Tributary tower area:105’x53’Tributary hanger area: 55’x27’Base shear (per mast pipe, 8 pipes/bay)V = 80psf x53’x590’/(8x1000) V = 313 kPipe bending momentM = V h/2 = 313x12”x24’/2 M=45072 k” Section modulus (S=(D4-d4)/32D)S = (554 - 47.24)/(32x55) S = 7474 in3Bending stressfb = M/S = 45072/7474 fb=6.0 ksiOverturn moment (per bay)M = 80psf x53’x5902/(2x1000) M=73,797