PEER/CSSC Tall Building Design Case Study Building #1 J. Andrew Fry John Hooper Ron Klemencic Magnusson Klemencic Associates
Building Information Located in Los Angeles 42-Story 410 ft Tall 108 ft X 107 ft Plan Dimensions Core Wall System Approximate Period: 5 Sec
Tower Plan
Tower and Core Wall Isometric
Two Designs Performed Design #1A Prescriptive provisions of the 2006 IBC All prescriptive provisions observed except height limit Capacity design principles were not employed
Two Designs Performed Design #1B Performance-Based Seismic Design conforming to the 2008 LATBSDC Seismic Design Criteria, with the following two exceptions: 25-year EQ used in Serviceability Analysis 2.5 % viscous damping Only a limited number of elements allowed to reach 120 % of their capacity The minimum base shear waived Minimum strength provided by 25-year EQ and Wind
Design #1A Wind Design Criteria Basic Wind Speed: 85 mph Exposure: B Occupancy Category II: I W = 1.0 Topographic Factor (K ZT ): 1.0
Design #1A Seismic Design Criteria Occupancy Category II: I e = 1.0 Mapped Spectral Accelerations: S s = 2.147; S 1 = 0.720 Site Class C F a = 1.0; F v = 1.3 Spectral Response Coefficients: S DS = 1.145; S D1 = 0.521 Seismic Design Category: D
Design #1A Seismic Design Criteria Lateral System: Building Frame, Special Reinforced Concrete Shear Walls, R = 6 T code = 2.55 sec (based on H = 410 ) C s = 0.060 (Eq. 12.8 6 governs) V = 0.85C s W (w/ RSA scaling) V = 4,565 kips
Design #1A Results Core Wall Thickness Grade Level 25 = 24 inches Level 25 Roof = 21 inches Building Modes: Mode 1 T X = 6.7 Sec Mode 2 T Y = 4.8 Sec Mode 3 T Z = 2.6 Sec
Design #1A Results Shears at Grade: Seismic V X = 4,581k V Y = 4,581k Wind V X = 2,080k V Y = 2,080k Overturning Moment at Grade Seismic M Y = 587,000 k-ft M X = 697,000 k-ft Wind Maximum Story Drifts: Δ X = 1.1% Δ Y = 0.8% M Y = 540,000 k-ft M X = 513,000 k-ft
Design #1B Performance Objectives 25-yr EQ: Serviceability: Structure to remain essentially elastic with only minor damage MCE: Collapse Prevention: Extensive structural damage; repairs are required and may not be economically feasible
Design #1B Serviceability Model 3-D Model using ETABS Elastic RSA Model Included Slab Outriggers
Design #1B Serviceability Acceptance Criteria Story Drift Limitation: 0.5 percent Coupling Beams Shear: Remain Essentially Elastic Core Wall Flexure: Remain elastic Core Wall Shear: Remain elastic Slab Outriggers: Columns: Remain essentially Elastic Remain elastic
Design #1B MCE Model 3-D model using CSI Perform-3D Modeled as inelastic: Coupling beams Core wall flexural behavior Slab beams Modeled as elastic: Core wall shear behavior Diaphragm slabs Columns Basement walls Model extended to mat
Design #1B MCE Acceptance Criteria Story Drift: 3 % Coupling Beam Rotation: 0.06 radian limit Core Wall Reinforcement Axial Strain: Tensile strain = 0.05 Compression strain = 0.02 Core Wall Concrete Axial Strain: Fully Confined Concrete Compression Strain = 0.015 Core Wall Shear: Post-Analysis Verification Performed
Design #1B Seismic Hazard Spectra
Design #1B Results Core Wall Thickness Grade Level 13 = 28 & 32 inches Level 13 Level 31 = 24 inches Level 31 Roof = 21 inches Building Modes: Mode 1--T X = 4.2 Sec Mode 2--T Y = 3.1 Sec Mode 3--T Z = 1.6 Sec
Design #1B Serviceability Results
Design #1B Serviceability Results
MCE Results: Building Story Drift
MCE Results: Core Wall Shear
MCE Results: Core Overturning Moment
MCE Results: Coupling Beam Rotations
MCE Results: Core Wall Tensile Strains
Case Study #1 Observations Core wall shear is the governing design parameter & governs wall thickness Walls thicker for Design #1B versus #1A T #1B = 28-32 at base & 21 at roof T #1A = 24 at base & 21 at roof Serviceability Design governed over Wind Design V Servicability = 5,013 and 6,018 kips = 1,816 and 1,918 kips V Wind Design
Case Study #1 Observations Serviceability Design of #1B larger than Design of #1A V #1B = 5,013 and 6,018 kips V #1A = 4,581 and 4,581 kips MCE Shear Design of #1B larger than Design of #1A V #1B = 12,556 and 13,409 kips V #1A = 4,581 and 4,581 kips Tensile Strains are low, but yielding occurs over height of core wall Spectral Matching reduced dispersion in the results