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Tall Buildings Initiative Summary of Case Studies Farzin Zareian University of California, Irvine Quake Summit 2010 San Francisco, Oct 8, 2010

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Collaborators Jack Moehle, Yousef Bozorgnia. UCB John Wallace, Zeynep Tuna. UCLA Tony Yang. UBC Pierson Jones. UCI Nilesh Shome. RMS Paul Somerville. URS

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Sponsors California Seismic Safety Commission California Office of Emergency Services (CalEMA) FEMA City of Los Angeles

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Objective and Scope Development of earthquake ground motions for design studies. Development of building analytical models Conduct a large number of earthquake simulations of tall buildings to develop statistics of engineering demand parameters Perform loss estimation for designed buildings Few side studies: simulated vs recorded motions, effect of vertical component of ground motion, etc. Assess the performance of designed tall buildings using latest technology

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1.5Km, Puente Hills 7.3Km, Hollywood 8.8Km, Raymond 11.5Km, Santa Monica 24.5Km, Elsinore 40.0Km, Sierra Madre 56Km, San Andreas San Andreas Raymond Hollywood Santa Monica Newport-Inglewood-Rose Canyon Elsinore (Whittier) Elsinore (Chino) Sierra Madre (San Fernando) Sierra Madre (Cucamonga) Verdugo

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Significance of several modes of vibration in response of the building. Similar ground motions for all structures. Five hazard levels needs to be looked at: (SLE- 25, SLE-43, DBE, MCE, OVE) A large number of motions are required (we used 15) to have a reasonable estimate of the dispersion in EDP. Challenges in Ground Motion Selection

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Selection : Used a subset of NGA database (no aftershocks & etc.) Only two recordings from any single event was selected No restriction on Magnitude R min &R max at 0.0 and Km Min and Max shear wave velocity = and m/s Low pass filter cutoff frequency of the selected motions are less than 0.1 Record Selection and Scaling

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Scaling : Maximum acceptable scale factor = 5.0 The scale factor, by which the smallest weighted error between the target spectrum and the geometric mean spectrum of a single recording is acquired, is computed. Records are matched between T min &T max at 0.5 & 10.0 sec. o Largest T = 6.47 sec. (Bldg. IIIB) 6.47X1.5 = 9.7 sec. o Smallest T = 4.28 sec. (Bldg IIB) 4.28X0.2 = 0.86 sec. Record Selection and Scaling

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Error Weight Period 10% %60 30% 26% %42 32% Uniform Variable Scaling : Maximum acceptable scale factor = 5.0 The scale factor, by which the smallest weighted error between the target spectrum and the geometric mean spectrum of a single recording is acquired, is computed. Records are matched between T min &T max at 0.5 & 10.0 sec. Record Selection and Scaling

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Response Spectra SLE25 (25 year)

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Response Spectra SLE43 (43 year)

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Response Spectra DBE (475 year)

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Response Spectra MCE (2475 year)

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Response Spectra OVE (4975 year) 7 unscaled pairs are from simulated motions (URS/SCEC)

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Rec Sim Med Target Period Sa(T) Response Spectra OVE (4975 year)

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Building Design and Modeling 42-story reinforced concrete core wall 42-story reinforced concrete dual system 40-story steel special moment-frame Three Building Systems After: Zeynep Tuna

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Building Design and Modeling Building 1A (Code design) Building 1B (PBEE design) Building 1C (PBEE+ design) Designed using IBC Designed using 2008 LATBSDC procedure. Designed using PEER TBI guideline. All provisions were followed except the height limit. All provisions were followed. Except: 1) V min was waived. 2) SLE was checked using 25-yr EQ (w 2.5%) instead of 43-yr EQ (w 5%). No more than 20% of the elements are allowed to reach 150% of the code specified capacity. Similar to 1B design Except: 1) SLE was check 43-yr EQ (w 5%). 2) All ductile elements such as the coupling beams and flexural yielding of the concrete walls are allowed to reach 150% of the code specified capacity. Building 1A (Code design) Building 1B (PBEE design) Building 1C (PBEE+ design) Designed using IBC Designed using 2008 LATBSDC procedure. Designed using PEER TBI draft guideline. Performance-based design guideline for tall buildings After: Tony Yang

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42-Story Concrete Core Wall 3D nonlinear dynamic finite element model (Perform3D). Ignored the gravity system. Basement walls below grade were modeled using elastic shear wall elements (E eff = 0.8 E) Slabs below grade were modeled using elastic shear shell element (E eff = 0.25 E) General Modeling Assumptions

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42-Story Concrete Core Wall Shear wall flexural behavior: Nonlinear fiber wall element with expected material property. After: Tony Yang

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42-Story Concrete Core Wall 1A: Code 1B: PBEE 1C: PBEE+ Wall:StrongStrongerStrongest Coupling beam: Stronger Strong 1 st mode Period: T 1EW = 5.2 sec T 1NS = 4.0 sec T 1EW = 4.8 sec T 1NS = 3.6 sec T 1EW = 4.6 sec T 1NS = 3.5 sec 24” 28” 32” Building Design Comparison After: Tony Yang

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42-Story Concrete Core Wall

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Structural design: Wall thickness: Wall vertical reinforcement: Coupling beam reinforcement: Structural period: Structural response: Wall stress safety index: Coupling beam demand: Inter-story drift and wall edge strain: 1A < 1B < 1C 1C < 1A ~ 1B 1C < 1B < 1A 1B < 1A < 1C 1A < 1B < 1C 1C < 1B < 1A After: Tony Yang

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Building Design and Modeling 42-story reinforced concrete core wall 42-story reinforced concrete dual system 40-story steel special moment-frame Three Building Systems After: Zeynep Tuna

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42-Story Concrete Dual System 3D nonlinear dynamic finite element model (Perform3D). Ignored the gravity system. Basement walls below grade were modeled using elastic shear wall elements (E eff = 0.8 E) Slabs below grade were modeled using elastic shear shell element (E eff = 0.25 E) General Modeling Assumptions

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EI eff =0.7*EI g M θ Column Effective Stiffness M P Axial Force Moment Strength Beam Rigid end zone Nonlinear Rotation Hinges 42-Story Concrete Dual System General Modeling Assumptions

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42-Story Concrete Dual System 2A: Code 2B: PBEE 1C: PBEE+ Building Design Comparison Wall:StrongestStrong Coupling beam: Strong 1 st mode Period: T 1EW = 4.5 sec T 1NS = 4.0 sec T 1EW = 4.3 sec T 1NS = 3.9sec 24” 18” 24” 18” 16” 36 X X X 46 Columns: 36 X X X 46 Columns:

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42-Story Concrete Dual System Building 2A – Inter-story drifts in H1 direction

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42-Story Concrete Dual System Building 2B – Inter-story drifts in H1 direction

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Inter-story drifts in H1 direction 42-Story Concrete Dual System

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Building 2A –Peak Floor Acc. in H1 direction Building 2A – Peak Floor Accelerations in H1 42-Story Concrete Dual System

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Building 2B – Peak Floor Accelerations in H1 Structural and Earthquake Engineering 42-Story Concrete Dual System Building 2B – Peak Floor Acc. in H1 direction

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Overall behaviors of the two building designs are quite similar. Median inter-story drift ratios (max ≈ 2%), median core wall strains (max ≈ tension; compression), median coupling beam rotations (max ≈ 0.02 rad) are all well below established limits. Wall shear stresses and strains are slightly higher in the code-based design. Column axial forces in the code-based design are twice as high as those in the PBD. Wall design for shear appears conservative. (Requires further study) 42-Story Concrete Dual System Summary of findings

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Overall behaviors of the two building designs are quite similar. Median inter-story drift ratios (max ≈ 2%) are all well below established limits. Wall shear stresses and strains are slightly higher in the code-based design. Column axial forces in the code-based design are twice as high as those in the PBD. 42-Story Concrete Dual System Summary of findings

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Building Design and Modeling 42-story reinforced concrete core wall 42-story reinforced concrete dual system 40-story steel special moment-frame Three Building Systems After: Zeynep Tuna

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Bldg. 3A Bldg. 3BBldg. 3C 40-Story Buckling Restrained B.F. General View

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PERFORM3D (version 4.03) structural analysis software by Computers and Structures Inc. was used for the nonlinear time history analysis. The only nonlinear element employed in the model is the Buckling Restrained Brace element. (R y = 1.1, ω = 1.25, and β = 1.1.) The brace components in the model have a maximum deformation capacity of (20ε y ) Gusset plate will have full ductility capacity. No cyclic deterioration was modeled 40-Story Buckling Restrained B.F. General Modeling Assumptions

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Elastic Column element, equivalent steel cross section used (axial, torsional, and bending stiffness modified to account for concrete) BRBF “brace” element, nonlinear. Connections modeled as pins. BRBF “stiff endzone” 30% length linear elastic bar Elastic Beam Element with pinned connections to columns Rigid panel zone 40-Story Buckling Restrained B.F. General Modeling Assumptions

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Bldg. 3A Bldg. 3B Bldg. 3C 300K-500K 501K-800K 801K-1200K KEY: BRB strength [Kips] NOTE: GRID LINE 2&7 N-S DIRECTION 40-Story Buckling Restrained B.F. T 1NS = 5.3sec T 1EW = 3.8 sec T 1NS = 6.5 sec T 1EW = 4.5 sec T 1NS = 5.7 sec T 1EW = 4.2 sec Building Design Comparison

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MAXIMUM IDR N-SE-W N-S median %16 th and %84 th Individual earthquake Building 3A 4975 (years) Return Period OVE MCE DBE SLE43 SLE25 GM set 2475 (years) 475 (years) 43 (years) 25 (years)

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MAXIMUM IDR median Individual earthquake 4975 (years) Return Period OVE MCE DBE SLE43 SLE25 GM set 2475 (years) 475 (years) 43 (years) 25 (years) %16 th and %84 th N-SE-W N-S Building 3B

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MAXIMUM IDR median Individual earthquake 4975 (years) Return Period OVE MCE DBE SLE43 SLE25 GM set 2475 (years) 475 (years) 43 (years) 25 (years) %16 th and %84 th N-SE-W N-S Building 3C

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median Individual earthquake MAXIMUM ACCELERATION [g] 4975 (years) Return Period OVE MCE DBE SLE43 SLE25 GM set 2475 (years) 475 (years) 43 (years) 25 (years) %16 th and %84 th N-SE-W N-S Building III–A

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median Individual earthquake MAXIMUM ACCELERATION [g] 4975 (years) Return Period OVE MCE DBE SLE43 SLE25 GM set 2475 (years) 475 (years) 43 (years) 25 (years) %16 th and %84 th N-SE-W N-S Building III–B

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median Individual earthquake MAXIMUM ACCELERATION [g] 4975 (years) Return Period OVE MCE DBE SLE43 SLE25 GM set 2475 (years) 475 (years) 43 (years) 25 (years) %16 th and %84 th N-SE-W N-S Building III–C

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%Exceedance Of 3% Drift Ratio Safe maximum IDR considered to be IDR=.03 There were no component failures for the BRBF lateral load system 25% 20% 15% 10% 5% 0% OVE MCE DBE SLE43 SLE25 Building 3C did not exceed the safe IDR in any of the ground motions, was considered to perform the best. Building 3A generally performed better than the performance based design (Building 3B) $256/SF $249/SF $245/SF 40-Story Buckling Restrained B.F.

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Behavior of Building 3C is different from Buildings 3A and 3B (different structural system) Stiffer building (3A) observes larger acceleration and smaller deformation compared to other two buildings. No collapse was indicated Building 3B appeared to be the one with higher probability of exceeding the drift limit of 3% in MCE and OVE hazard levels. Building 3A exceeded the limit only at the OVE level. Summary of findings 40-Story Buckling Restrained B.F.

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direction h1 target response spectrum (4975 yr) recorded ground motion - median recorded ground motion - individual simulated ground motion - median simulated ground motion - individual T 1 * T 2 * T 3 * T 4 * direction h2 Key *The periods and mode shapes correspond to deformation parallel to the direction of analysis. h2 h1 Comparison of Results for Simulated and Recorded Motions in OVE set for BRBF40-CBD

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A.) B.) Comparison of IDR time histories simulated vs recorded: How was the IDR envelope developed?

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h1 simulated match, h1 recorded match, h2 simulated match, h2 recorded match, direction h1 target response spectrum (4975 yr) recorded ground motion - median recorded ground motion - individual simulated ground motion - median simulated ground motion - individual T 1 * T 2 * T 3 * T 4 * direction h2 Key *The periods and mode shapes correspond to deformation parallel to the direction of analysis. h2 h1 Key Combination of drift demand due to the two highest modes of vibration: IDR=[ Mode1 + mode2 ] Mode1 = IDR from 1 st mode shape Mode2 = IDR from 2 nd mode shape assumptions: For simplicity the mode combinations do not consider modes of vibration higher than the second mode, although they certainly contribute to the analysis IDR response is treated as completely elastic, which is certainly not the case. First mode IDR, mode1, is not factored so the value of IDR on the x-axis does not correspond to IDR values in the results. Mode combinations at peak IDR demand for T 1 and T 2

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[ Mode1 + mode2 ] h1 simulated match, [ Mode1 + mode2 ] h1 recorded match, [ Mode1 + mode2 ] h2 simulated match, [ Mode1 + mode2 ] h2 recorded match, recorded ground motion - median recorded ground motion - individual simulated ground motion - median simulated ground motion – individual Key For h2, when response is out of phase, a bulge occurs in stories 1-20 For h2, when response is in phase, a bulge occurs in stories Mode combinations at peak IDR demand for T 1 and T 2

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Basic Assumptions for Loss Calculations Based on inter-story drift and floor acceleration results only. Similar components in all buildings. The EDPs from nonlinear time-history analysis are used directly for loss calculations without any fitting as done commonly for loss estimations.

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Limitations for Loss Calculations Residual drift ratio was not used in the loss estimation process. Variability of EDPs given the ground motion intensity is not accurately modeled. However, for the purpose of loss estimation this shortcoming has been adjusted. Ground motion selection and scaling is mostly focused on matching spectral acceleration at long periods. This can underrepresent accelerations at short periods

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After: Nilesh Shome

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General Summary 1.Performance of 9 tall buildings at five hazard levels were evaluated: Three lateral load resisting systems X Three design guidelines. 2.The progress in reduction in estimated loss from CBD to PBD+ designs shows the a general success in proposed design guidelines for tall buildings. 3.On going efforts: Loss estimation methodology

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Thank You

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