Seismic Action and Eurocode 8

Predicting Ground Motion

EN-1998 Two-Tier Design

• No-Collapse: Will withstand design seismic

event without collapse and maintaining a

residual capacity

• Damage Limitation: Will withstand a seismic

event with higher probability than design event

(lower magnitude) without excessive damage

and loss of operation capacity

Gutenberg-Richter Relation

0.0001

0.001

0.01

0.1

1

10

100

1000

10000

0 2 4 6 8 10

Moment Magnitude

λM

Annual Measured Events

G-R Equation

ln(λM)=8.06337-1.70832MM

λM=exp(8.06337-1.70832MM)

0.0518.883.0

8.90.1126.0

Return Period, yrsMean Annual Rate of ExceedanceMagnitude

Dissipative Strucutures

1

2

3

Load

Displacement

Load

Displacement

Area=Energy

Dissipated

Deposits of liquefiable soils, of sensitive clays, or any other

soil profile not included in types A – E or S1

S2

10 -

20

_ < 100 Deposits consisting, or containing a layer at least 10 m thick,

of soft clays/silts with a high plasticity index (PI > 40) and

high water content

S1

A soil profile consisting of a surface alluvium layer with vs

values of type C or D and thickness varying between about 5

m and 20 m, underlain by stiffer material with vs > 800 m/s.

E

< 70 < 15 < 180 Deposits of loose-to-medium cohesionless soil (with or

without some soft cohesive layers), or of predominantly soft-

to-firm cohesive soil.

D

70 -

250

15 -

50

180 –

360

Deep deposits of dense or medium-dense sand, gravel or stiff

clay with thickness from several tens to many hundreds of

metres.

C

>

250

> 50 360 –

800

Deposits of very dense sand, gravel, or very stiff clay, at least

several tens of meters in thickness, characterised by a gradual

increase of mechanical properties with depth.

B

_ _ > 800 Rock or other rock-like geological formation, including at

most 5 m of weaker material at the surface.

A

cuNSPT vs,30

ParametersDescription of stratigraphic profileType

Type 1 Elastic Response Spectra

Soil

Matters

Conceptual Design EC-8

• structural simplicity;

• uniformity, symmetry and redundancy;

• bi-directional resistance and stiffness;

• torsional resistance and stiffness;

• diaphragmatic behaviour at storey level;

• adequate foundation.

Allowed Simplifications

Decreased valueModalSpatialNoNo

Reference valueLateral ForceaSpatialbYesNo

Decreased valueModalPlanarNoYes

Reference valueLateral ForceaPlanarYesYes

(for linear analysis)Linear Elastic AnalysisModelElevationPlan

Behavior FactorAllowed SimplificationRegularity

Diaphragmatic Behavior of Floor

Direction of Shaking-Plan View

Stress Concentrations No Load Transfer

Levels of Reliability

External Loads on Foundation

Dynamic Analysis Results

Comparison Dynamic Pseudo-Static

Waves

Rayleigh, R

Surface

Shear,SSecondary

Compression, P Primary

Crosshole TestingOscilloscope

PVC-cased Borehole

PVC-cased

Borehole

Downhole

Hammer

(Source) Velocity

Transducer

(Geophone

Receiver)

∆∆∆∆t

∆∆∆∆x

Shear Wave Velocity:

Vs = ∆∆∆∆x/∆∆∆∆t

Test

Depth

ASTM D 4428

Pump

packer

Note: Verticality of casing

must be established by

slope inclinometers to correct

distances ∆∆∆∆x with depth.

Slope

InclinometerSlopeInclinometer

Liquefaction

• Determine Loading Function

– Empirical estimates based on amax

– 1-D Response analysis

• Determine Soil Resistance

– Based on SPT, CPT, or Vs profile

– Modified by correction factors

• Compare Loading and Resistance Profiles

Liquefaction Spread, Charleston SC, 1886

Probability of Liquefaction for Fines-Modified Field

Values and Cyclic Stress Ratios (Seed et al, 2003)

Liquefaction

• Blast Induced– Charleston Bridge Project

Liquefaction

• Blast Induced– Lateral Load Test After Liquefaction

Thank-you