Design guidance on Eurocode 8 for practicing engineers ... TECHNICAL RESEARCH CENTRE OF FINLAND...

Design guidance on Eurocode 8 forDesign guidance on Eurocode 8 for practicing engineers for timber structures

Tomi Toratti

VTT TECHNICAL RESEARCH CENTRE OF FINLAND

Earthquake hazard and risk

• Earthquake hazard: Any physical phenomenon, such as ground h ki d f il th t ishaking or ground failure, that is

associated with an earthquake and that may produce adverse effects on h man acti ities (Science andhuman activities. (Science and Technology Dictionary)

• Earthquake risk: The probability that i l i fsocial or economic consequences of

earthquakes will equal or exceed specified values at a site, at several sites or in an area during asites, or in an area, during a specified exposure time. (STD)

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http://www.seismo.ethz.ch/gshap/


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Surface faulting

Mole-track Izmit (source: Tom Fumal USGS)

Retaining wall (source: Tom Fumal, USGS)

Collapsed barn (source: Tom Fumal, USGS)

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Fumal, USGS) USGS)


Liquefactions

• Sand ejected through a crack forming a series of sand boils along the railroad tracks

• Tilting of apartment buildings at Kawagishi-Cho, Niigata, produced by liquefaction of the soil during the tracks y q g1964 Niigata Earthquake

Moss Landing State Beach (Source: Dan Orange, www es ucsc edu/)

Shinano river bank, Kawagishi-cho apartment buildings suffered bearing capacity failures (source:

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www.es.ucsc.edu/) suffered bearing capacity failures (source: www.ce.washington.edu/)


Tsunamis

• Tsunami is a sea wave that results from large-scale seafloor displacements.

After Tsunami in Banda Aceh, Sumatra 2005 (source: USGS)

Building damage, Banda Aceh, Sumatra 2005 (source: USGS)

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Landslides and floods

• 1995 landslide in La Conchita, California • Southeastern end of Izmit Bay showing

coastal subsidence Izmit Turkeycoastal subsidence, Izmit, Turkey Earthquake, August 17, 1999

7(source: USGS)

(source: http://www.ngdc.noaa.gov/)


Fire following earthquakes

• San Francisco Earthquake (1906) • Great Kanto Earthquake (1923)

(source: http://nisee.berkeley.edu/)

(http://www.rekihaku.ac.jp/)

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Ground shakingP ti l ll f f• Partial collapse of r.c. frame structure in Bucharest during Vrancea earthquake, Mar. 4, 1977

• Office building with partially destroyed first floor during Kobe earthquake, January 16, 1995

source: http://www.ngdc.noaa.gov/

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source: http://nisee.berkeley.edu/


August 17, 1999 earthquake of 7.4 M , - 15000 - 20000 casualties, - 35000 totally destroyed buildings

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Amplitude parameters - PGA and PGV

• Peak ground acceleration (PGA): related to the force induced in rigid structures

• Peak ground velocity (PGV): good correlation to damage in structures• Disadvantage

A i l k i f l ti• A single peak is a poor measure for a complex motion.• Structural properties are not accounted for.

V 30 08 1986 M l (B) EW

1

2

n, m

/s2

Vrancea, 30.08.1986, Magurele (B), EW

-1

0

-1.15

acce

lera

tion

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0 10 20 30 40 50-2

time, s


ag = 0.4 g

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Local site effects - Frequency content

• Stiff soil: amplificationS so a p ca oof spectral accelerations in the short-period rangeshort-period range

• Soft soil: amplificationof spectral

l ti i thaccelerations in the long-period range

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Factors affecting seismic motion4

1. Source factors2. Travel path 1

4

2

3

3. Local site effects4. Soil-structure interaction Parkfield 1966, Cholame #2, 065

Loma Prieta 1989, Corralitos, 090Northridge 1994, Sylmar, 360

El Centro 1940, Imperial Valley, S00E

Vrancea 1977, INCERC, NS

Western Washington 1949, Olympia, 086

Erzincan 1992, Meteorological Station, FN

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Elastic spectrum Se(T) in Eurocode 8 (Ec8)

⎧ ⎤⎡ T3

Type 1TB TC

Analytical formulation:

( )

⎪⎪⎪⎪⎧

≤≤⋅⋅⋅

≤≤⎥⎦

⎤⎢⎣

⎡−⋅+⋅⋅

TTTSa

TTTTSa

CBg

BB

g

5.2

015.21

η

η2

SA

Type 1,Soil A,PGA=1

TB TC

⎪⎪⎪

⎪⎨

⎤⎡

≤≤⎥⎦⎤

⎢⎣⎡⋅⋅⋅⋅

==

TT

TTTTTSa

TSDC

Cg

e5.2

S)( Aη 1

S

TD

⎪⎪

⎩≤⎥⎦

⎤⎢⎣⎡ ⋅⋅⋅⋅⋅ TT

TTTSa D

DCg ,5.2 2η 0

0 1 2 3 4T(s)

PGASWhere:5%for ,1 ==

=⋅

ξη

PGASagWhere:

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Design spectra for different soil types

4Type 1, Soil A, PGA=1

3

Type 1, Soil A, PGA 1Type 1, Soil B, PGA=1Type 1, Soil C, PGA=1Type 1, Soil D, PGA=1Type 1, Soil E, PGA=1

Soil type

S TB(s) TC(s) TD(s)

A 1 0 15 0 4 2

1

2SA

Type 1, Soil E, PGA 1A 1 0.15 0.4 2

B 1.2 0.15 0.5 2

C 1 15 0 2 0 6 2

0

1

0 1 2 3 4

C 1.15 0.2 0.6 2

D 1.35 0.2 0.8 2

E 1.4 0.15 0.5 2 0 1 2 3 4

T(s)

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Elastic design using Ec8 spectra

Required:

Location → Spectral parameters TB, TC, TD, S and ag }Damping ratio (ξ)

Period of vibration (T)

}3

2SA(T)

(T)SmF AH ⋅=

F1

SA

A( )HF

F F0

0 1 2 3 4

T(s)T

YF FY>FH

Don’t change rigidity!

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Particularities of the elastic approach

• Advantages: • Takes into account the dynamic properties of the ”building” by the

fundamental period (T) and damping (ξ).• Shortcomings:

• The simplification of a structure into an SDOF may not be acceptable.The simplification of a structure into an SDOF may not be acceptable.• The supposition that the oscillator is elastic is also restrictive. Usually,

it is not feasible to build buildings which withstand earthquakes in the elastic rangeelastic range.

• Solutions:• Use of multi-mass oscillator (MDOF).

C bi lti l ib ti d Ad t ith “ ti ” ffi i t• Combine multiple vibration modes. Adapt with “correction” coefficients and procedures the SDOF response to an MDOF response.

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Definition of design goals in ”modern” codes

• At ultimate limit state (ULS) Ec8 aims at “no-collapse requirement”. • This means that the structure shall withstand the design seismic g

actions (DSA) without local or global collapse and must retain structural integrity and a residual load bearing capacity. The primary aim is to save the lives of the occupantsprimary aim is to save the lives of the occupants.

• DSA defined by a reference seismic action with probability of exceedence of 10 % in 50 years, or the reference return period of 475475 years.

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IntroductionIntroduction• Main sources Eurocode 5 and 8, Step lectures B13 and C17• Timber structures have a good reputation with regard to seismic• Timber structures have a good reputation with regard to seismic

loadings

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Factors effecting the seismic performance

V l bl t i ti b t t th j i t h• Vulnerable parts in timber structures are the joints, anchorages, floor diaphragms and soft stories

• Advantages of timber structures:- Low self-weight- Ductility and energy dissipation of mechanical connections (and- Ductility and energy dissipation of mechanical connections (and shear walls)

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Soft storey failure in the foundation

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Eurocode 8

• Eurocode 8 part 1-1, General rules - Seismic actions and general requirements for structures. In this part, the general requirements

d d fi iti f i i i t t b ildi t t d Al thand definitions of seismic-resistant buildings are stated. Also, the calculation method of seismic loads and relevant load combinations are givenE d 8 t 1 2 G l l f b ildi Thi t tli• Eurocode 8 part 1-2, General rules for buildings. This part outlines the general rules regarding seismic resistance.

• Eurocode 8 part 1-3, Specific rules for various materials and structures. This part handles the different building materials (concrete, steel, timber and masonry) and gives detailed structural requirements as well as detailing the specifications for buildings

d f th t i l Th t d ibi ti b t t i imade of these materials. The part describing timber structures is in Chapter 8, on pages 158-164.

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Table 2.1 The significance of the building regularity (EC8)

Building regularity Simplification allowed Behaviour factor, q

Plan Elevation Model Analysis

yes yes planar lateral force * reference

yes no planar multi-modal decreased

no yes spatial lateral force * reference

no no spatial multi-modal decreased

* The fundamental period T0 should be less than 4×Tc and less than 2 seconds.

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Base shear force

The base shear force acts in both principal directions of the building.

Fb = Sd (T0) W λWhere T is the fundamental period of the buildingWhere T0 is the fundamental period of the buildingSd is the ordinate of the design spectrumW is the total weight of the building (see Chapter 6)λ is a correction factor, having a value of 0,85 if T0<TC or 1,0 otherwise.

To estimate the fundamental period, T0, of the building, EC8 has a simple procedure:

T0 = 0.05 H0.750

Where the building height is in metres and the time in seconds.

FFb

∑=

jii

iibi Wz

WzFF

2/3 x H

28Fb


52T ⎤⎡ ⎞⎛

).5(5.2

).5(15.21

0

0

bTTTjosSS

aTTjosqT

TSS

cbd

bb

d

<<=

<⎥⎦

⎤⎢⎣

⎡⎟⎟⎠

⎞⎜⎜⎝

⎛−+=

α

α

0.4

0.6

).5(5.20

0

cTTTjosTT

qSS

q

dcc

d <<≥⎟⎟⎠

⎞⎜⎜⎝

⎛= αβα 0.2

S E T

).5(5.202

0

dTTjosT

TTq

SS ddc

d <≥⎟⎟⎠

⎞⎜⎜⎝

⎛= αβα 0 1 2 3 4

0

T

Table 2.2 Parameters for the spectrum equations for the different subsoil classes (EC8). The national authorities will decide which type response spectrum will be used.

S b iS Tb

[ ]Tc[ ]

Td[ ]

S Tb[ ]

Tc[ ]

Td[ ]Subsoi

l class[s] [s] [s] [s] [s] [s]

Type 1 recommended for large earthquakes

Type 2

A 1.0 0.15 0.40 2.00 1.0 0.05 0.25 1.2

B 1.2 0.15 0.50 2.00 1.35 0.05 0.25 1.2

C 1.15 0.20 0.60 2.00 1.5 0.10 0.25 1.2

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D 1.35 0.20 0.80 2.00 1.8 0.10 0.30 1.2

E 1.4 0.15 0.50 2.00 1.6 0.05 0.25 1.2


The mass in seismic design

∑ ∑+= kiiEkj QGW ,ψGkj is the characteristic dead load and

iiE 2, ϕψψ =

jψE,iQki is the probable variable load during an earthquake.

ψ2i is the long-term value for variable loads0.3 for live loads,and 0.2 for snow loads in Nordic countries and for altitudes above 1000 m and 0 for other countriesabove 1000 m and 0 for other countries0 for wind loads (EC1 and EC5),

ϕ is 0.5 for all storeys except the top storey for which it is 1.0 (no correlation between storey loads, if correlation exists then ϕ = 0.8).

ϕ is 1 0 for storage loads (EC8)

∑ ∑++= kiiEbkjd QFGE ,ψγ

ϕ is 1.0 for storage loads (EC8)

Combining loads in seismic design

Where, γ is the importance factor (γI = 1.4 hospitals, fire stations, power stations; γII = 1.2 schools, cultural buildings; γIII = 1.0 residential and commercial buildings; γIV = 0.8 agricultural buildings), Gkj and Qki are the characteristic values of the dead and variable loads,

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kj Qki ,ψE,i is the seismic combination coefficient of the quasi-permanent value of the live load.


Ultimate limit state

Resistance

The following condition should apply for all structures and connections

{ } }{,,M

kdkiEibkjd

fRRQFGfEγ

ψγ =≤= ∑ ∑

The design resistance of the structures is determined so that the material strength corresponds to the instantaneous load duration class. The material safety factor is γM = 1.3 for non-dissipative structures (Type A) and γM = 1.0 when the structure dissipates energy (Types B and C). γM p gy ( yp )

Ductility

Equilibrium

- anchorage for overturning: upward tension at ends of shear walls,- anchorage for sliding, base shear at the bottom of shear wallsg g

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Special rules for timber structures

Type A, q = 1.5: Structures having low capacity to dissipate energy such as: cantilevers, beams, two or three pinned joint arches, trusses joint with connectors.

Type B, Structures having medium capacity to dissipate energy such as: q = 2 0 :Glued wall panels with glued diaphragms connected with nails and boltsq 2,0 :Glued wall panels with glued diaphragms, connected with nails and bolts, trusses with doweled and bolted joints, mixed structures with timber frame and non-load-bearing infill.q = 2.5: Hyperstatic portal frames with doweled and bolted jointsq 5 ype stat c po ta a es t do e ed a d bo ted jo ts

Type C, Structures having high capacity to dissipate energy such as: yp g g p y p gyq = 3.0: Nailed wall panels with glued diaphragms, connected with nails and bolts, trusses with nailed jointsq = 4.0 : Hyperstatic portal frames with doweled and bolted joints q = 5.0 : Nailed wall panels with nailed diaphragms, connected with nails and bolts.

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Shear capacity of different sheathing panels in seismic design

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12 Fasteners screw 3.5 (3.9x29 Gyprocille) K100 mm

21 mm Kerto-Q LVL27 mm Kerto-Q LVL

15 mm spruce plywood

8

10 9 mm spruce plywood

12 mm spruce plywood

4

6

Gypsum board

2

4 yp(Gyproc GN13)

0 1 2 3 4 5 6

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Example 2, A four-storey timber house case, calculation of the seismic load and design of some details

Input values:Ground acceleration = 0.35 g, Subsoil class BSubsoil class BFloor dead load 1 KN/m2 (the weight of the walls is assumed to be included in this figure)Roof dead load 0.75 KN/m2

Live load qh = 2.0 KN/m2qh

Importance factor γIII = 1.0 (residence)

The seismic load is determined considering the vertical loads present in the different storeys of the building. This load i l l t d i 6is calculated using eq. 6:

∑ ∑+ kiiEkj QG ,ψ

Gkj is the characteristic dead load and ψEIQki is the probable live load during a seismic event.

Combination coefficient:

ψ2i is 0.3 (the quasi-permanent value of the live load (EC1 and EC5) ,ϕ is 0.5 except for the top storey for which it is 1.0 (EC8)

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Table L2.1 combining the loads in the different storeys.g yStorey Gkj Qki ψ2i ϕ ψE,i Gkj + ψEIQki

Roof 0.75 0.75Storey 4 1.0 2.0 0.3 1 0.30 1.60yStoreys 2,3 1.0 2.0 0.3 0.5 0.15 1.30Storey 1 Loads transferred directly to the foundations

Following the table above, the total vertical load is:

= 0.75 + 1.60 + 1.30 + 1.30 = 4.95 KN/m2∑ ∑+ kiiEkj QG ,ψ

•Ground acceleration is ag = 0.35 g

•Subsoil class B

∑ ∑j

•Building braced with shear walls of plywood sheathing and mechanical fasteners,

5 0q = 5.0 .

•Building area: 288 m2

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Traditional timber-masonry building from Turkeybuilding from Turkey.

(Izmit Turkey Earthquake August 17 199917, 1999. http://www.eerc.berkeley.edu/turkey/index.html).y )

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Design guidance on Eurocode 8 for practicing engineers ... TECHNICAL RESEARCH CENTRE OF FINLAND...

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