Response of TBI case study buildings ANALYSIS OF STEEL BUILDING Pierson Jones & Farzin Zareian May 7 th, 2010
Introduction Three 40-story Building BRBF Systems building Structural and Earthquake Engineering
Building Information 40-story Buckling Restrained Braced Frame (Bldg. III) Three designs by Simpson Gumpertz&Heger, Inc. Building III-A Code-based Design (IBC 2006 and not considering the maximum height limit, ) Building III-B Performance-based Design (LATBSDC) Building III-C Performance-based Plus Design Perform 3D models provided by designer for Building III-B and III-C.
Code Based Design 2007 California Building Code ASCE 7.05 Standard for Minimum Design Loads for Buildings and Other Structures. (S DS = 1.145, SD 1 = 0.52, R = 7) AISC 360.05 Spec. for Steel Buildings AISC 341.05 Seismic Spec. ACI 318-08 Building Code Requirements for Reinforced Concrete
Performance Based Design Layout is identical to Code Based Design except that 2 bays of bracing have been removed (in the lower stories of the perimeter braced frames in the ) BRB member sizes have been reduced. Designed to meet the LATBSDC seismic design guidelines
Performance Based Design Plus Layout is identical to Performance Based Design except that outriggers are added to mitigate serviceability level design requirements. Designed to meet the Guidelines for PEER Seismic Design of Tall Buildings
General Comparison Bldg. III-A Bldg. III-B Bldg. III-C
TYPICAL COLUMNS, BRACES, AND CONNECTIONS BOLTED CONNECTION (301-500K BRACES) CONCRETE FILLED BOX COLUMN BOLTED CONNECTION (501-800K BRACES) FROM 18 SQUARE TO 60 SQUARE fc =10,000 psi PINNED CONNECTION (801-1200K BRACES) elevation
Comparison of BRB strength along similar grid lines KEY: BRB strength [Kips] 300K-500K 501K-800K 801K-1200K NOTE: GRID LINE 2&7 DIRECTION Bldg. III-A Bldg. III-C Bldg. III-B
General Modeling PERFORM3D (version 4.03) structural analysis software by Computers and Structures Inc. was used for the nonlinear time history analysis. 3-D models of the building are subjected to 2-component ground motions. The only nonlinear element employed in the model is the Buckling Restrained Brace element.
General Modeling Columns and Beams were modeled with elastic elements. Elastic behavior was verified in these elements by monitoring their demand-capacity ratios and ensuring that they remained in the elastic range. Models that included the gravity frame were developed but did not significantly change the seismic demands. The perimeter shear walls were modeled with elastic wall elements with 50% of the gross stiffness and 40% of elastic shear modulus to account for cracked section properties. Diaphragm assumed rigid
BRBF Typical Bay-connection details Assumption gusset plate will have full ductility capacity. i.e. the connections are well engineered and will behave as pins even under severe ground motions.
BRBF Typical Bay modeling details Rigid panel zone BRBF brace element, nonlinear. Connections modeled as pins. BRBF stiff endzone 30% length linear elastic bar Elastic Column element, equivalent steel cross section used (axial, torsional, and bending stiffness modified to account for concrete) Elastic Beam Element with pinned connections to columns
BRBF Modeling Buckling-restrained braces were modeled using a built-in model in Perform 3D software with R y = 1.1, ω = 1.25, and β = 1.1. 30% of the length of buckling-restrained braces are considered as End Zone The brace components in the model have a maximum deformation capacity of (20ε y ) as determined by SGH. If this capacity is exceeded during the time-history analysis, the analysis stops No strength or stiffness degradation Backbone curve for BRBF. Image source: Simpson Gumpertz and Heger
Modal Properties: Building III-A Story Number Dominance of flexural mode of vibration in and E- W. Building III-A Modal Properties () 40 35 30 25 20 15 10 5 0-1 -0.5 0 0.5 1 Mode Shape Value Mode 1 Mode 2 Mode 3 Story Number Building III-A Modal Properties () 40 35 30 25 20 15 10 5 0-1 -0.5 0 0.5 1 Mode Shape Value Mode 1 Mode 2 Mode 3 Mode Number 1 2 3 4 Period 3.80 1.27 0.69 0.48 Mass Part. 0.72 0.17 0.05 0.02 Mode Number 1 2 3 4 Period 5.25 1.48 0.77 0.51 Mass Part. 0.57 0.24 0.09 0.04
Modal Properties: Building III-B Dominance of flexural mode of vibration in and a balance between the flexural and shear mode in the E- W. Building III-B Modal Properties () 40 Building III-B Modal Properties () 40 35 35 30 30 Story Number 25 20 15 10 Story Number 25 20 15 10 5 5 0-1 -0.5 0 0.5 1 Mode Shape Value 0-1 -0.5 0 0.5 1 Mode Shape Value Mode 1 Mode 2 Mode 3 Mode 1 Mode 2 Mode 3 Mode Number 1 2 3 4 Period 4.49 1.50 0.81 0.56 Mass Part. 0.74 0.16 0.04 0.02 Mode Number 1 2 3 4 Period 6.47 1.77 0.88 0.58 Mass Part. 0.64 0.22 0.07 0.03
Modal Properties: Building III-C Story Number Dominance of flexural mode of vibration in and a balance between the flexural and shear mode in the E- W. Building III-C Modal Properties () 40 35 30 25 20 15 10 5 0-1 -0.5 0 0.5 1 Mode Shape Value Story Number Building III-C Modal Properties () 40 35 30 25 20 15 10 5 0-1 -0.5 0 0.5 1 Mode Shape Value Mode 1 Mode 2 Mode 3 Mode 1 Mode 2 Mode 3 Mode Number 1 2 3 4 Period 4.17 1.39 0.74 0.51 Mass Part. 0.73 0.17 0.05 0.02 Mode Number 1 2 3 4 Period 5.74 1.64 0.80 0.54 Mass Part. 0.67 0.20 0.06 0.03
Representative Results
Representative Results
Return Period GM set Building III A 4975 (years) OVE 2475 (years) MCE 475 (years) DBE 43 (years) SLE43 median %16 th and %84 th 25 (years) SLE25 Individual earthquake MAXIMUM IDR
Return Period GM set Building III B 4975 (years) OVE 2475 (years) MCE 475 (years) DBE 43 (years) SLE43 median %16 th and %84 th 25 (years) SLE25 Individual earthquake MAXIMUM IDR
Return Period GM set Building III C 4975 (years) OVE 2475 (years) MCE 475 (years) DBE 43 (years) SLE43 median %16 th and %84 th 25 (years) SLE25 Individual earthquake MAXIMUM IDR
Return Period GM set Building III A 4975 (years) OVE 2475 (years) MCE 475 (years) DBE 43 (years) SLE43 median %16 th and %84 th 25 (years) SLE25 Individual earthquake MAXIMUM ACCELERATION [g]
Return Period GM set Building III B 4975 (years) OVE 2475 (years) MCE 475 (years) DBE 43 (years) SLE43 median %16 th and %84 th 25 (years) SLE25 Individual earthquake MAXIMUM ACCELERATION [g]
Return Period GM set Building III C 4975 (years) OVE 2475 (years) MCE 475 (years) DBE 43 (years) SLE43 median %16 th and %84 th 25 (years) SLE25 Individual earthquake MAXIMUM ACCELERATION [g]
GM set: OVE Simulated vs. recorded ground motions T1 = 3.8 T2 = 1.3 Matched Spectra for TBI (OVE, 3 & 0.1, 7 & 0.6) 1.5 (Sa(T)/g [5% critical damping] Target Spectrum Median Spectrum Indv. Spectrum Rec./Scaled 1 Indv. Spectrum Simulated mean 0.5 T1 = 5.3 T2 = 1.5 0 0 1 2 3 4 5 6 Period (T) 7 8 9 10 MAXIMUM IDR %16th and %84th simulated ground motions recorded & scaled ground motions
GM set: OVE Simulated vs. recorded ground motions T1 = 4.9 T2 = 1.5 Matched Spectra for TBI (OVE, 3 & 0.1, 7 & 0.6) 1.5 (Sa(T)/g [5% critical damping] Target Spectrum Median Spectrum Indv. Spectrum Rec./Scaled 1 Indv. Spectrum Simulated mean 0.5 T1 = 6.5 T2 = 1.8 0 0 1 2 3 4 5 6 Period (T) 7 8 9 10 MAXIMUM IDR %16th and %84th simulated ground motions recorded & scaled ground motions
GM set: OVE Simulated vs. recorded ground motions T1 = 4.2 T2 = 1.4 Matched Spectra for TBI (OVE, 3 & 0.1, 7 & 0.6) 1.5 (Sa(T)/g [5% critical damping] Target Spectrum Median Spectrum Indv. Spectrum Rec./Scaled 1 Indv. Spectrum Simulated mean 0.5 T1 = 5.7 T2 = 1.6 0 0 1 2 3 4 5 6 Period (T) 7 8 9 10 MAXIMUM IDR %16th and %84th simulated ground motions recorded & scaled ground motions
%Exceedance Of 3% Drift Ratio 25% 20% 15% 10% 5% 0% $249/SF $256/SF $245/SF OVE MCE DBE SLE43 SLE25 Safe maximum IDR considered to be IDR=.03 All of the analysis completed -- there were no component failures for the BRBF lateral load system Building III-C did not exceed the safe IDR in any of the ground motions, was considered to perform the best. Building III-A generally performed better than the performance based design (Building III-B)
Summary Behavior of Building III-C is different from Buildings III-A and III-B (different structural system) Stiffer building (III-A) observes larger acceleration and smaller deformation compared to other two buildings. No collapse was indicated Building III-B appeared to be the one with higher probability of exceeding the drift limit of 3% in MCE and OVE hazard levels. Building III-A exceeded the limit only at the OVE level.