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: IW = 1.0   Topographic Factor (KZT): 1.0

Design #1A—Seismic 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 #1A—Seismic 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. 12.8‑6 governs)   V = 0.85CsW (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—TX = 6.7 Sec   Mode 2—TY = 4.8 Sec   Mode 3—TZ = 2.6 Sec

Design #1A—Results

  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:   ΔX = 1.1%   ΔY = 0.8%

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: Remain essentially

Elastic   Columns: 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--TX = 4.2 Sec   Mode 2--TY = 3.1 Sec   Mode 3--TZ = 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   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