performance-based earthquake engineering for geotechnical and structural engineers

EERI TechnicalSeminar Series

Impact of Soil-Structure Interaction on Response of StructuresSeminar 1: Practical Applications to Shallow Foundations

Performance-Based Earthquake Engineering for Geotechnical and Structural Engineers

Mike Mahoney, FEMA



Introductory remarksImpact of Soil-Structure Interaction on Response of Structures

Seminar 1: Practical Applications to Shallow Foundations

Craig D. Comartin



EERI Technical Seminars

BackgroundGeo-Structural Series

• Current: SSI and shallow foundations• Future Subjects:

Deep foundationsLiquefactionBasement wallsGround motions



Related documentsATC-40 (1996): The Seismic Evaluation and Retrofit of Concrete Buildings

FEMA 273/274 (1997) and FEMA 356 (2000):Prestandard and Commentary for the Seismic Rehabilitation of Buildings

FEMA 440 (2005): Improvement of Nonlinear Static Seismic Analysis Procedures

ASCE 41: Seismic Rehabilitation of Existing Buildings



FEMA 356/ASCE 41

Inertial effectsFoundation stiffness and strengthRadiation damping

Kinematic effectsBase slab averaging (x,y)Embedment (z)

Soil–Structure Interaction



Structure

Concrete shear wall

Concrete frame

Spread footings



Analysis model

k v2k v3

K h3

K h2K h1

k v1



Geotechnical component behavior

Force, Q

Displacement, Δ

Qlower c

upper Q c

Khigh

Q

KlowActualBehavior

Envelope Stiffness, K=Q

Δ

Force, Q

Displacem

ent, Δ

Qlow

er c

upper Qc

Khigh

Q

Klow

Actual

Behavior

EnvelopeStiffness,K=

QΔ



Nonlinear static procedures(Push-over analysis)

Equivalent Linearization Displacement Modification

ATC- 40Capacity Spectrum Method

(CSM)

FEMA-356Displacement Coefficient

Method (DCM)



1. Neglecting ascending branch of design spectra 2. Incoherent input to relatively large plan

dimensions 3. Embedment (basements) 4. Radiation and material damping in supporting

soils5. Concentrating building masses at floor and

roof levels

Factors that affect response of short period buildings

SSI EFFECTSSSI EFFECTS



FEMA 440/ASCE 41

FEMA 440/ASCE 41

FEMA 440/ASCE 41

FEMA 356/ASCE 41

Inertial effectsFoundation stiffness and strengthRadiation damping

Kinematic effectsBase slab averaging (x,y)Embedment (z)

Soil–Structure Interaction



Effects of Foundations on Performance

Foundation stiffness and strength affectvarious structural components differently.

Δ, small

Stiff and Strong Foundation

Smalldisplacementsprotect framefrom damage

High forcescause shearwall damage Δ, large

Flexible and Weak Foundation

Largedisplacementscause frame

damageFoundationyielding androcking protectsshear wall

Stiff and strong is not always favorable;nor is flexible and weak always conservative.

Foundation stiffness and strength affectvarious structural components differently.Foundation stiffness and strength affectvarious structural components differently.

Δ, smallΔ, smallΔ, small

Stiff and Strong Foundation

Smalldisplacementsprotect framefrom damage

High forcescause shearwall damage

High forcescause shearwall damage Δ, largeΔ, largeΔ, large

Flexible and Weak Foundation


damage


damageFoundationyielding androcking protectsshear wall





Example building



Shear wall and frame

77 ft.

20.5 ft. typ.



Fixed base NSPInelastic mechanism controlled by shear in walls

Displacement demand



Flexible base NSPInelastic mechanism controlled by pile yielding

Displacement demand



Barrington Medical Office Building(January 17, 1994)

performance-based earthquake engineering for geotechnical and structural engineers

Documents