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 #1AWind Design Criteria

Basic Wind Speed: 85 mph Exposure: B Occupancy Category II: IW = 1.0 Topographic Factor (KZT): 1.0

Design #1ASeismic Design Criteria

Occupancy Category II: Ie = 1.0 Mapped Spectral Accelerations:

Ss = 2.147; S1 = 0.720 Site Class C

Fa = 1.0; Fv = 1.3 Spectral Response Coefficients:

SDS = 1.145; SD1 = 0.521 Seismic Design Category: D

Design #1ASeismic Design Criteria

Lateral System: Building Frame, Special Reinforced

Concrete Shear Walls, R = 6 Tcode = 2.55 sec (based on H=410) Cs = 0.060 (Eq. 12.86 governs) V = 0.85CsW (w/ RSA scaling) V = 4,565 kips

Design #1AResults

Core Wall Thickness Grade Level 25 = 24 inches Level 25 Roof = 21 inches

Building Modes: Mode 1TX = 6.7 Sec Mode 2TY = 4.8 Sec Mode 3TZ = 2.6 Sec

Design #1AResults

Shears at Grade: Seismic VX = 4,581k VY = 4,581k Wind VX = 2,080k VY = 2,080k

Overturning Moment at Grade Seismic MY = 587,000 k-ft MX = 697,000 k-ft Wind MY = 540,000 k-ft MX = 513,000 k-ft

Maximum Story Drifts: X = 1.1% Y = 0.8%

Design #1BPerformance 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 #1BServiceability Model

3-D Model using ETABS

Elastic RSA Model Included Slab

Outriggers

Design #1BServiceability 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: Remain essentially

Elastic Columns: Remain elastic

Design #1BMCE Model

3-D model using CSI Perform-3D Modeled as inelastic:

Coupling beams Core wall flexural behavior Slabbeams

Modeled as elastic: Core wall shear behavior Diaphragm slabs Columns Basement walls

Model extended to mat

Design #1BMCE Acceptance Criteria

Story Drift: 3 % Coupling Beam Rotation: 0.06 radian limit Core Wall Reinforcement AxialStrain:

Tensile strain = 0.05 Compression strain = 0.02

Core Wall Concrete AxialStrain: Fully Confined Concrete Compression Strain=0.015

Core Wall Shear: Post-Analysis Verification Performed

Design #1BSeismic Hazard Spectra

Design #1BResults

Core Wall Thickness Grade Level 13 = 28 & 32 inches Level 13 Level 31 = 24 inches Level 31 Roof = 21 inches

Building Modes: Mode 1--TX = 4.2 Sec Mode 2--TY = 3.1 Sec Mode 3--TZ = 1.6 Sec

Design #1BServiceability Results

Design #1BServiceability 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 VServicability = 5,013 and 6,018 kips VWind Design = 1,816 and 1,918 kips

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