Design notes for seismic design of building accordance to Eurocode 8

AUTHOR: VALENTINOS NEOPHYTOU BEng (Hons), MSc
REVISION 1: June, 2013
Design notes for seismic
design of building accordance
to Eurocode 8

ABOUT THIS DOCUMENT
This publication provides a concise compilation of selected rules in the Eurocode 8, together with
relevant Cyprus National Annex, that relate to the design of common forms of concrete building
structure in the South Europe. Rules from EN 1998-1-1 for global analysis, regularity criteria, type
of analysis and verification checks are presented. Detail design rules for concrete beam, column
and shear wall, from EN 1998-1-1 and EN1992-1-1 are presented. This guide covers the design of
orthodox members in concrete frames. It does not cover design rules for steel frames. Certain
practical limitations are given to the scope.
Due to time constraints and knowledge, I may not be able to address the whole issues.
Please send me your suggestions for improvement. Anyone interested to share his/her knowledge
or willing to contribute either totally a new section about Eurocode 8 or within this section is
encouraged.
For further details:
My LinkedIn Profile:http://www.linkedin.com/profile/view?id=125833097&trk=hb_tab_pro_top
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Valentinos Neophytou BEng, MSc Page 3
Fundamental requirements
(ΕΝ1998-1-1,cl.2.1 and CYS NA EN1998-1-1,cl NA2.2)
1. “No collapse”(ULS):The structure should be design and constructed as follow:
 Withstand the seismic action without local or global collapse, thus retaining
its structural integrity and residual load bearing capacity after the seismic
event (Protection of human life).
 A design seismic action (for local collapse prevention) with 10% exceedance
probability in 50 years (mean return period: 475 years).
2. “Damage limitation”(SLS):The structure should be design and constructed as
follow:
 Withstand the seismic action having a larger probability of occurrence than
the design than the design seismic action, without the occurrence of damage
and the associated limitations of use, the cost which would be
disproportionately high in comparison with the cost of the structure itself
(damage limitation).
 Seismic actions are determined for mean return period of TDLR=95 year and
probability of exceedance is PDLR=41%. The corresponding design life of
the structure is a TL=50 years design life of structures.
Importance classes for buildings
(ΕΝ1998-1-1,table.4.3 and CYS NA EN1998-1-1,cl NA2.12)
Importance
class
Buildings Important
factor γI
I
Buildings of minor importance for public safety, e.g.
argricultural buildings, etc.
0.8
II Ordinary buildings, not belonging in the other categories. 1.0
III
Buildings whose seismic resistance is of importance in view
of the consequences associated with a collapse, e.g. schools,
assembly halls, cultural institutions etc.
1.2
IV
Buildings whose integrity during earthquakes is of vital
importance for civil protection, e.g. hospitals, fire stations,
power plants, etc.
1.4
The level of seismic action is depending on its important and
consequences of failure (Importance classes of building)

Seismic zones
(CYS NA ΕΝ1998-1-1,cl.NA 4)
 10% probability to be exceeded in 50 years

Ground condition
(ΕΝ1998-1-1,cl.3.2.2.1(6) and CYS NA EN1998-1-1,cl NA2.3)
Ground condition
(ΕΝ1998-1-1,cl.3.2.2.1(6) and CYS NA EN1998-1-1,cl NA2.3)
 Ground investigation may be omitted for building with importance class of I and II. They also
omitted for classes III and IV whenever there is adequate information.
 The construction site and the nature of the supporting ground should normally be free from risks of
ground rupture, slope instability and permanent settlements caused by liquefaction or densification in
the event of an earthquake.
Type of ground soil
(ΕΝ1998-1-1,cl.3.1.2)
Groun
d type
Description of straigraphic profile Parameters
vs,30 (m/s)
NSPT
(blows/30cm)
cu (kPa)
A Rock or other rock-like geological
formation, including at most 5 m of weaker
material at the surface.
>800 - -
B Deposits of very dense sand, gravel, or very
stiff clay, at least several tens of metres in
thickness, characterised by a gradual
increase of mechanical properties with
depth.
360-800 >50 >250
C Deep deposits of dense or medium dense
sand, gravel or stiff clay with thickness from
several tens to many hundreds of metres.
180-360 15-50 70-250
D Deposits of loose-to-medium cohesion less
soil (with or without some soft cohesive
layers), or of predominantly soft-to-firm
cohesive soil.
<180 <15 <70
E 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.
S1 Deposits consisting, or containing a layer at
least 10 m thick, of soft clays/silts with a
high plasticity index
<100
(indicative)
- 10-20
S2 Deposits of liquefiable soils, of sensitive
clays, or any other soil profile not included
in types A – E or S1

vs,30: average value of propagation velocity of S waves in the upper 30m of the soil profiles at shear strain
of 10-5
or less.
NSPT: Standard penetration test blow count
cu: Undrained shear strength of soil
Vertical elastic response spectrum
(ΕΝ1998-1-1,cl.3.2.2.3)
The vertical listed below:
 for horizontal structural member spanning 20m or more,
 for horizontal cantilever components longer than 5m,
 component of the seismic action should be taken into account if the avg>0.25g (2.5m/s2
) in the cases
for horizontal pre-stressed components,
 for beams supporting columns,
 in based-isolated structures.
Vertical elastic response spectrum
(ΕΝ1998-1-1,cl.3.2.2.3)
0 ≤ 𝑇 ≤ 𝑇𝐵: 𝑆 𝑣𝑒 𝑇 = 𝑎 𝑣𝑔 ∙ 1 +
𝑇
𝑇 𝐵
∙ 𝜂 ∙ 3,0 − 1 (ΕΝ1998-1-1,Eq. 3.8)
𝑇𝐵 ≤ 𝑇 ≤ 𝑇𝐶: 𝑆 𝑣𝑒 𝑇 = 𝑎 𝑣𝑔 ∙ 𝜂 ∙ 3.0 (ΕΝ1998-1-1,Eq. 3.9)
𝑇𝐶 ≤ 𝑇 ≤ 𝑇𝐷: 𝑆 𝑣𝑒 𝑇 = 𝑎 𝑣𝑔 ∙ 𝜂 ∙ 3.0
𝑇 𝐶
𝑇
(ΕΝ1998-1-1,Eq. 3.10)
𝑇𝐷 ≤ 𝑇 ≤ 4𝑠: 𝑆 𝑣𝑒 𝑇 = 𝑎 𝑣𝑔 ∙ 𝜂 ∙ 3.0
𝑇 𝐶 𝑇 𝐷
𝑇2
(ΕΝ1998-1-1,Eq. 3.11)
Damping correction factor η: 𝜂 = 10/ 5 + 𝜉 ≥ 0.55
Design ground acceleration on type A ground: ag=γIagR
Note: the value of S is not used in the above expression cause the vertical ground motion is not very much
affected by the underlying ground condition
Vertical elastic design spectrum (ΕΝ1998-1-1,cl.3.2.2.5(5))
. 0 ≤ 𝑇 ≤ 𝑇𝐵: 𝑆 𝑑 𝑇 = 𝑎 𝑣𝑔 ∙
2
3
+
𝑇
𝑇 𝐵
∙
2.5
𝑞
−
2
3
(ΕΝ1998-1-1,Eq. 3.13)
𝑇𝐵 ≤ 𝑇 ≤ 𝑇𝐶: 𝑆 𝑑 𝑇 = 𝑎 𝑣𝑔 ∙
2.5
𝑞
(ΕΝ1998-1-1,Eq. 3.14)

𝑇𝐶 ≤ 𝑇 ≤ 𝑇𝐷: 𝑆 𝑑 𝑇 = 𝑎 𝑣𝑔 ∙
2.5
𝑞
𝑇𝐶
𝑇
≥ 𝛽 ∙ 𝑎 𝑣𝑔 (ΕΝ1998-1-1,Eq. 3.15)
𝑇𝐷 ≤ 𝑇 ≤ 4𝑠: 𝑆 𝑑 𝑇 = 𝑎 𝑣𝑔 ∙
2.5
𝑞
𝑇 𝐶 𝑇 𝐷
𝑇2
≥ 𝛽 ∙ 𝑎 𝑣𝑔 (ΕΝ1998-1-1,Eq. 3.5)
For the vertical component of the seismic action the design spectrum is given by expressions (3.13) to
(3.16), with the design ground acceleration in the vertical direction, avg replacing ag, S taken as being equal
to 1,0 and the other parameters as defined in 3.2.2.3.
Parameters values of vertical elastic response spectra (CYS NA EN1998-1-1,cl NA2.8)
Spectrum avg/ag TB (s) TC (s) TD (s)
Type 1 0.90 0.05 0.15 1.0
Special provisions:
 For the vertical component of the seismic action a behaviour factor q up to to 1,5 should generally
be adopted for all materials and structural systems.
 The adoption of values for q greater than 1,5 in the vertical direction should be justified through an
appropriate analysis.

Horizontal elastic response spectrum
(ΕΝ1998-1-1,cl.3.2.2.2)
0 ≤ 𝑇 ≤ 𝑇𝐵: 𝑆𝑒 𝑇 = 𝑎 𝑔 ∙ 𝑆 ∙ 1 +
𝑇
𝑇 𝐵
∙ 𝜂 ∙ 2,5 − 1 (ΕΝ1998-1-1,Eq. 3.2)
𝑇𝐵 ≤ 𝑇 ≤ 𝑇𝐶: 𝑆𝑒 𝑇 = 𝑎 𝑔 ∙ 𝑆 ∙ 𝜂 ∙ 2.5(ΕΝ1998-1-1,Eq. 3.3)
𝑇𝐶 ≤ 𝑇 ≤ 𝑇𝐷: 𝑆𝑒 𝑇 = 𝑎 𝑔 ∙ 𝑆 ∙ 𝜂 ∙ 2.5
𝑇 𝐶
𝑇
(ΕΝ1998-1-1,Eq. 3.4)
𝑇𝐷 ≤ 𝑇 ≤ 4𝑠: 𝑆𝑒 𝑇 = 𝑎 𝑔 ∙ 𝑆 ∙ 𝜂 ∙ 2.5
𝑇 𝐶 𝑇 𝐷
𝑇2
(ΕΝ1998-1-1,Eq. 3.5)
Damping correction factor η: 𝜂 = 10/ 5 + 𝜉 ≥ 0.55
Design ground acceleration on type A ground: ag=γI*agR
The viscous damping ratio of the structure
TYPE OF STRUCTURE Damping ration ξ
%
Steel
Welded 2
Bolts 4
Concrete
Unreinforced 3
Reinforced 5
Wall Reinforced 6
Design spectrum of elastic analysis
(ΕΝ1998-1-1,cl.3.2.2.5)
0 ≤ 𝑇 ≤ 𝑇𝐵: 𝑆 𝑑 𝑇 = 𝑎 𝑔 ∙ 𝑆 ∙
2
3
+
𝑇
𝑇 𝐵
∙
2.5
𝑞
−
2
3
(ΕΝ1998-1-1,Eq. 3.13)
𝑇𝐵 ≤ 𝑇 ≤ 𝑇𝐶: 𝑆 𝑑 𝑇 = 𝑎 𝑔 ∙ 𝑆 ∙
2.5
𝑞
(ΕΝ1998-1-1,Eq. 3.14)
𝑇𝐶 ≤ 𝑇 ≤ 𝑇𝐷: 𝑆 𝑑 𝑇 = 𝑎 𝑔 ∙ 𝑆 ∙
2.5
𝑞
𝑇𝐶
𝑇
≥ 𝛽 ∙ 𝑎 𝑔 (ΕΝ1998-1-1,Eq. 3.15)
𝑇𝐷 ≤ 𝑇 ≤ 4𝑠: 𝑆 𝑑 𝑇 = 𝑎 𝑔 ∙ 𝑆 ∙
2.5
𝑞
𝑇 𝐶 𝑇 𝐷
𝑇2
≥ 𝛽 ∙ 𝑎 𝑔 (ΕΝ1998-1-1,Eq. 3.5)
Design ground acceleration on type A ground: ag=γI*agR
Lower bound factor for the horizontal spectrum: β=0.2
Note: the value of q are already incorporate with an appropriation value of
damping viscous, however the symbol ηis not present in the above expressions

(ΕΝ1998-1-1,cl.3.2.2.2)
Design spectrum of elastic analysis
(ΕΝ1998-1-1,cl.3.2.2.5)
Design spectrum Vs Elastic spectrum Parameters of Type 1 elastic response spectrum (CYS NA EN1998-1-
1,table 3.2)
Ground
Type
S TB (s) TC (s) TD (s)
A 1.0 0.15 0.4 2.0
B 1.2 0.15 0.5 2.0
C 1.15 0.20 0.6 2.0
D 1.35 0.20 0.8 2.0
E 1.4 0.15 0.5 2.0
Note: For important structures (γI>1.0), topographic amplification effects
should be taken into account (Annex A EN1998-5:2004 provides
information for topographic amplification effects)

The inertial effects of the design seismic action shall be evaluated by taking into account the presence of the
masses associated with all gravity loads appearing in the following combination of actions:
𝑮 𝒌,𝒋 + 𝝍 𝑬𝒊 𝑸 𝒌,𝒊 (ΕΝ1998-1-1,Eq. 3.17)
Where:
Combination coefficient for variable action is: 𝜓 𝐸𝑖 = 𝜙 ∙ 𝜓2𝑖 (ΕΝ1998-1-1,Eq. 4.2)
Values of φ for calculating 𝝍 𝑬𝒊(CYS NA EN1998-1-1:2004)
Type of
Variable
action
Storey φ
Categories
A-C1
Roof
Storeys with correlated
occupancies
Independently occupied storeys
1,0
0,8
0,5
Categories
A-F1 1.0
1
those categories are describes in EN 1991-1-1:2002
Note: the value of φ is take into account only for calculating the seismic mass.
Calculation of seismic mass
(EN1998-1-1,cl.3.2.4)
Spectrum Type 1
0≤T≤TB
TB≤T≤TC
TC≤T≤TD
TD≤T≤4s
≤4s
YES
NO
Elastic
response spectrum
Elasticdisplacement
response spectrum
Elastic displacement response spectrum (EN1998-1-1,cl.3.2.2.2(6))

Second-order effects (P-Δ effects) need not be taken into account if the following condition is fulfilled in all
storeys:
𝜗 =
𝑃𝑡𝑜𝑡 ∙𝑑 𝑟
𝑉𝑡𝑜𝑡 ∙𝑕
≤ 0,10 (ΕΝ1998-1-1,Eq. 4.28)
Ptot: is the total gravity load at and above the storey considered in the seismic design situation dr: is the
design interstorey drift, evaluated as the difference of the average lateral displacements ds at the top and
bottom of the storey under consideration and calculated in accordance with 4.3.4.
Vtot: is the total seismic storey shear.
h: is the interstorey height.
Consequences of value of P-Δ coefficient θ on the analysis
θ≤0,1 No need to consider P-Δ effects
0,1≤θ≤0,2
P-Δ effects may be taken into account approximately by
amplifying the effects of the seismic actions by
1
1−𝜗
0,2≤θ≤0,3
P-Δ effects must be accounted for by an analysis
including second order effects explicity
θ≥0,3 Not permitted
Second order effects P-Δ(EN1998-1-1,cl.4.4.2.2)

1.
Approximately” symmetrical distribution of mass and stiffness in plan (in X-Y)
2.
A “compact” shape, i.e one in which the perimeter line is always convex, or at least encloses not more
than 5% of total area as show in figure below.
3.
The floor diaphragms shall be sufficiently stiff in-plane not to affect the distribution of lateral loads
between vertical elements. EC8 warn that this should be carefully examined in the branches of
branched systems, such as L, C, H, I and X plan shapes.
3. The ratio of longer side to shorter side in plan does not exceed 4 (λ=Lmax/Lmin<4).
4.
The geometrical stiffness – lateral torsional response and torsional flexibility should be satisfied by
the following expressions:
Lateral torsional response condition:𝑟𝑥 > 3.33𝑒 𝑜𝑥
𝑟𝑦 > 3.33𝑒 𝑜𝑦
Torsionally rigidity condition: 𝑟𝑥 > 𝐼𝑠
𝑟𝑦 > 𝐼𝑠
𝐼𝑠 = 𝑙2 + 𝑏2 /12
Where the torsional radius rx and ry are:
𝑥 𝑐𝑠 =
(𝑥𝐸𝐼𝑦 )
(𝐸𝐼𝑦 )
𝑦𝑐𝑠 =
(𝑦𝐸𝐼𝑥)
(𝐸𝐼𝑥)
CRITERIA FOR REGULARITY IN ELEVATION
(EN1998-1-1,cl. 4.2.3.2)
CRITERIA FOR REGULARITY IN PLAN (EN1998-1-1,cl. 4.2.3.2)

𝑟𝑥 ≈
𝑥 − 𝑥 𝑐𝑠
2 𝐸𝐼𝑦 + 𝑦 − 𝑦𝑐𝑒
2 𝐸𝐼𝑥)
𝐸𝐼𝑦
𝑟𝑦 ≈
𝑥 − 𝑥 𝑐𝑠
2 𝐸𝐼𝑦 + 𝑦 − 𝑦𝑐𝑒
2 𝐸𝐼𝑥)
𝐸𝐼𝑥
5.
In multi-storey buildings only approximate definitions of the centre of stiffness and of the torsional
radius are possible. A simplified definition, for the classification of structural regularity in plan and
for the approximate analysis of torsional effects, is possible if the following two conditions are
satisfied:
a) all primary members, run without interruption from the foundations to the top of the building.
b) The deflected shapes of the individual systems under horizontal loads are not very different.

1.
All primary members, shall run without interruption from their foundations to the top of the building.
2.
Mass and stiffness must either remain constant with height or reduce only gradually, without abrupt
changes. In the absence of a quantitative definition in EC8, it is recommended that the decrease with
height may be considered gradual if both the mass and stiffness of every storey is between 70% and
100% of that of the storey below.
3.
In framed buildings the ratio of the actual storey resistance to the resistance required by the analysis
should not vary disproportionately between adjacent storeys
3.
Buildings with setbacks (i.e. where the plan area suddenly reduces between successive storeys) are
generally irregular, but may be classified as regular if less than limits shown in figure below. This
shows that the setback at any level on one side may not exceed 10% compared to the level below.
Where the setbacks are symmetrical on each side, there is no limit on overall reduction; however, for
asymmetrical setbacks, the overall reduction is limited to 30% of the base width. The exception is that
an overall reduction in width of up to half is permissible within the lowest 15% of the height of the
building. Note that „overhangs‟ (i.e. inverted pyramid shapes) as opposed to „setbacks‟ are always
classified as highly irregular.
CRITERIA FOR REGULARITY IN ELEVATION
(EN1998-1-1,cl. 4.2.3.2)

STRUCTURAL ANALYSIS
(EN1998-1-1,cl.4.3)
CONSEQUENCES OF STRUCTURAL REGULARITY ON SEISMIC ANALYSIS AND
DESIGN (ΕΝ1998-1-1,table 4.1)
The structural regularity if the building is play significant role to the following aspects of the seismic
design:
 Construction of structural model (planar or spartial model)
 Method of analysis (response spectrum analysis/lateral force procedure of a modal
 The value of behaviour factor q (low value of q is for building not regular in elevation)
Consequences of structural regularity on seismic analysis and design
Regularity Allowed Simplification Behaviour factor
Plan Elevation
Model Linear-elastic
Analysis (for linear analysis)
Yes Yes Planar Lateral force Reference value
Yes No Planar Modal Decreased value
No Yes Spatialb
Lateral forcea
Reference values
No No Spatial Modal Decreased value
Notes: a
There are also maximum limits on the period of vibration for the lateral force
method to be allowed (see equation above)
b
The reference behaviour factor is multiplied by 0.8 for buildings with irregular
elevations.
c
Torsionally flexible concrete buildings, defined, are assigned much lower reference q
values than equivalent concrete buildings which are regular. Certain other buildings
which are irregular in plan also attract a lowered q value
d
Separate planar model may be used. e It is observed that equivalent linear analysis may
not always be suitable for irregular buildings. Highly irregular buildings.

METHOD OF ANALYSIS
(ΕΝ1998-1-1,cl. 4.3.3)
Analysis type Criteria
Lateral force analysis
𝑇1 ≤ 4𝑇𝑐
𝑇1 ≤ 2,0𝑠
 Regular in plan and elevation
 Regular in elevation and irregular in plan
 Fundamental period:
 Height of building: H<10m
Response spectrum
modal
 Regular in plan and irregular in elevation
 Irregular in plan and elevation
 Fundamental period: Not special requirements
Non-linear  High irregular structures

LATERAL FORCE ANALYSIS
(ΕΝ1998-1-1,cl 4.3.3.2)
Fundamental period (EN1998-1-1,Eq.4.6)
T1=CtH3/4
(For heights up to 40m)
Value of Ct(EN1998-1-1,cl.4.3.3.2.2(3))
Ct = 0.085 (for moment resisting steel frames)
Ct= 0.075 (for moment resisting concrete frames)
Ct= 0.05 (for all other structures)
(EN 1998-1-1:2004, cl. 4.3.3.2.2(3))
Ct= 0.075/√ΣAc(for concrete/masonry shear wall
structures)
(EN 1998-1-1:2004, Eq. 4.7)
Ac= Σ[Ai·(0,2+(lwi/H2
))]
(EN 1998-1-1:2004, Eq. 4.8)
Fundamental period requirements
(EN1998-1-1,Eq.4.6)
T1≤4TCT1≤2sec
IF this
YES NO
LATERAL FORCE
ANALYSIS
RESPONSE SPECTRUM
ANALYSIS
Correction factor λ(EN1998-1-
1,cl.4.3.3.2.2(1Ρ))
λ=0.85 if T1≤2TC and more than 2 storey
λ=1.0 in all other case
Design spectrum
Sd(T)(EN1998-1-
1,cl.3.2.2.5)
0≤T≤TB
TB≤T≤TcTC≤T≤TDTD≤T
Seismic mass(EN1998-1-
1,cl.3.2.4)
ΣGk,j/g”+”ΣψE,i.Qk,i/g
(EN 1998-1-1:2004, Eq.3.17)
Base shear(EN1998-1-
1,cl.4.3.3.2.2)
Fb=Sd(T1).m.λ
(EN 1998-1-1:2004, Eq. 4.5)
Fi = Fb ∙
si ∙ mi
sj ∙ mj
Horizontal seismic forces
(according to displacement of
the masses)
(EN 1998-1-1:2004, Eq. 4.10)
Fi = Fb ∙
zi ∙ mi
zj ∙ mj
Horizontal seismic forces
(according to height of the
masses)
(EN 1998-1-1:2004, Eq. 4.11)
Displacement (EN1998-1-1,cl.4.3.4)
ds=qd.de
(EN 1998-1-1:2004, Eq. 4.23)

MODAL RESPONSE SPECTRUM ANALYSIS
(ΕΝ1998-1-1,CL 4.3.3.3)
MODAL
RESPONSE
SPECTRUM
ANALYSIS
Criterion
1
The sum of effective modal masses along each individual seismic action
componenet, X, Y or Z, considered in design, of at least 90% of the total
mass, addresses only the magnitude of the base shear captured by the
modes taken into account.
Criterion
2
All the modes whose effective modal mass is higher than 5% of the total
mass are taken into account (X,Y or even in Z direction).
Spatial analysis
Minimum number of modes is:
k≥3.√n
and
Period of vibration of mode:
Tk ≤0.20sec
k: is the number of modes taken into account
n: is the number of storey above foundation or the top of a rigid
basement.
Tk: is the period of vibration of mode k.
Combination of
modal responses
𝐸 𝐸 = Σ𝐸 𝐸𝑖
2
The response in two vibration modes:
Tj≤ 0.9 Ti
Seismic action effects:
EE: is the seismic action affect under consideration (force,
displacement, etc)
EEi: is the value of this seismic action affect due to the vibration
mode i.

Horizontal components of the seismic action
Horizontal seismic
action is to be
acting
simultaneously:
X – direction
(independent)
Y – direction
(independent)
Structural
response spectrum
shall be evaluated
separately:
X – direction
(independent)
Y – direction
(independent)
Maximum seismic
action calculation
Method 1: Square root of the sum of the squares (SRSS)
Method 2: Complete quadratic combination (CQC)
Combination of the horizontal
components are:
(EN1998-1-1,Eq. 4.18&4.19)
EEdx„‟±‟‟0,30EEdy
0.30EEdx „‟±‟‟EEdy
Behaviour factor q
If the structural system or the regularity classification of the building
in elevation is different in different horizontal directions, the value of
the behaviour factor q may also be different
Vertical component of the seismic action
Rules of vertical seismic
action
The effects of vertical action need to be taken into account ONLY for the
elements that are listed in the section of “Vertical component of the seismic
action” and their directly associated supporting elements or substructures.
Combination of the vertical
components are:
(EN1998-1-1,Eq.
4.20,4.21&4.22)
EEdx„‟±‟‟0.30 EEdy „‟±‟‟0,30EEdz
0.30EEdx „‟±‟‟ EEdy „‟±‟‟0,30EEdz
0.30EEdx „‟±‟‟0.30 EEdy „‟±‟‟EEdz
COMBINATION OF THE SEISMIC ACTIONS
(ΕΝ1998-1-1,cl 4.3.3.5)

DISPLACEMENT CALCULATION
(EN1998-1-1,cl.4.3.4)
Linear analysis case:
ds=qd.de ds<Displacement from the elastic spectrum analysis
ds:is the displacement of a point of the structural system induced by the
design
seismic action
qd: is the displacement behaviour factor, assumed equal to q unless
otherwise
specified
de:is the displacement of the same point of the structural system, as
determined by
a linear analysis based on the design response spectrum

Rule of masonry
infilled is APPLIED to
the following
structural system
ONLY
DCH
Frames
Frame equivalent dual
concrete systems
Steel or steel-concrete
composite moment resisting
frames
Rule of masonry
infilled is NOT
APPLIED to the
following structural
system ONLY
Wall
Wall-equivalent dual
concrete systems
Steel braced or steel-concrete
composite systems
For buildings not
regular in plan
(EN1998-1-
1,cl.4.3.6.3.1)
Strongly irregular, unsymmetrical or non-uniform arrangements of infills in plan
should be avoided
In the case of severe irregularities in plan due to the unsymmetrical arrangement
of the infills (e.g. existence of infills mainly along two consecutive faces of the
building), spatial models should be used for the analysis of the structure.
Infill panels with more than one significant opening or perforation (e.g. a door
and a window, etc.) should be disregarded in models for analyses
When the masonry infills are not regularly distributed, but not in such a way as to
constitute a severe irregularity in plan, these irregularities may be taken into
account by increasing by a factor of 2,0 the effects of the accidental eccentricity
For buildings not
regular in elevation
(EN1998-1-
1,cl.4.3.6.3.2)
If there are considerable irregularities in elevation (e.g. drastic reduction of infills
in one or more storeys compared to the others), the seismic action effects in the
vertical elements of the respective storeys shall be increased.
Magnification factor, η
𝜂 =
1 + Δ𝑉𝑅𝑤
𝑉𝐸𝑑
≤ 𝑞
Note: If η< 1.1, there is no need for modification of action effects
MASONRY INFILLED FRAMES
(ΕΝ1998-1-1,cl 4.3.6)

ΔVRw: is the total reduction of the resistance of masonry walls in the storey
concerned, compared to the more infilled storey above it.
ΣVEd: is the sum of the seismic shear forces acting on all vertical primary
seismic members of the storey concerned.
DCL, DCM, DCH
Additional rules should
be taken into account
(EN1998-1-1,cl.4.3.6.2)
The consequences of irregularity in plan produced by the infills shall be taken
into account.
The consequences of irregularity in elevation produced by the infills shall be
taken into account.
Mechanical properties, method of attachment and possibility of modification.
Shear failure of column under shear force induced by the diagonal strut action of
infills
Damage limitation of
infills(EN1998-1-1,cl.
4.3.6.4)
Slenderness ratio: min(Lwall,Hwall)/twall>15
To improve both in-plane and out-of-plane integrity and behaviour, include light
wire meshes well anchored on one face of the wall, wall ties fixed to the columns
If there are large openings or perforations in any of the infill panels, their edges
should be trimmed with belts and posts

Resistance condition
(EN1998-1-1,cl.4.4.2.2)
Ed ≤ Rd
Ed:is the design value of the action effect, due to the seismic design situation
Rd :is the corresponding design resistance of the element
Global and local
ductility condition
(EN1998-1-1,cl.4.4.2.3)
Soft plastic mechanism
ΣMRc≥ 1.3 ΣMRb
ΣMRc:is the sum of the design values of the moments of resistance of the columns
framing the
the joint. The minimum value of column moments of resistance within the range
of column
axial forces produced by the seismic design situation
ΣMRb:is the sum of the design values of the moments of resistance of the beams
framing the joint
When partial strength connections are used, the moments of resistance of these
connection
are taken into account in the calculation of ΣMRb
Note: 1. This expression is only applied to the building with two or more
storeys, and should be satisfied at all joints.
2. The above expression is waived at the top level of multi-storey
buildings.
Resistance of
foundation
(EN1998-1-1,cl.4.4.2.6)
Pad/strip/raft foundation
EFd=EF,G + γRdΩEF,E
γRd: is the overstrength factor, taken as being equal to 1,0 for q ≤3, or as being
equal to 1,2 otherwise
EF,G: is the action effect due to the non-seismic actions included in the
combination of actions for the seismic design situation
ULTIMATE LIMIT STATE
(ΕΝ1998-1-1,cl 4.4.2)

EF,E: is the action effect from the analysis of the design seismic action; and Ω is
the value of (Rdi/Edi) ≤ q of the dissipative zone or element iof the structure
which has the highest influence on the effect EF under consideration; where
Rdi: is the design resistance of the zone or element i
Edi: is the design value of the action effect on the zone or element iin the
seismic design situation.
Note: If Ω=1 =>γRd= 1.4
Damage limitation
(EN1998-1-1,cl.4.4.3)
For non-structural
elements of brittle
material attached to
the structure
For building having
ductile non structural
elements
For building having
non-structural
elements fixed in a way
so as not to interfere
with structural
deformation
drv≤0.005h drv≤0.0075h drv≤0.010h
dr: is the interstorey drift
h: is the storey height
v: is the reduction factor
Reduction factor of limitation to interstorey drift
(CYA NA EN1998-1-1,cl.NA.2.15)
Importance class Reduction factor v
I 0.5
II 0.5
III 0.4
IV 0.4

Frame system
Structural system in which both
the vertical and lateral loads are
mainly resisted by spatial frames
whose shear resistance at the
building base exceeds 65% of
the total shear resistance of the
whole structural system
Dual system
(frame or wall
equivalent)
Dual system in which the shear
resistance of the frame system at
the building base is greater than
50% of the total shear resistance
of the whole structural system
Dual system in which the shear
resistance of the walls at the
building base is higher than 50%
of the total seismic resistance of
the whole structural system
Ductile wall
system (couple or
uncoupled)
Structural system in which both
vertical and lateral loads are
mainly resisted by vertical
structural walls, either coupled
or uncoupled, whose shear
resistance at the building base
exceeds 65% of the total shear
resistance of the whole structural
system
Structural system
(EN1998-1-1,cl.5.1.2)
SPECIFIC RULES FOR CONCRETE BUILDINGS
(EN1998-1-1,cl.5)

System of large
lightly reinforced
walls
Wall with large cross-sectional
dimensions, that is, a horizontal
dimension lw at least equal to 4,0
m or two-thirds of the height hw
of the wall
Inverted
pendulum system
System in which 50% or more of
the mass is in the upper third of
the height of the structure
Torsionally
flexible
Dual or wall system not having a
minimum torsional rigidity

Multiplication factor (EN1998-1-
1,cl.5.2.2.2(5a))Frames or frame-
equivalent dual systems.
Structural system au/a1
One-storey building 1.1
Multistorey, one-bay frames 1.2
Multistorey, multi-bay
frames or frame-equivalent
dual structures
1.3
1,cl.5.2.2.2(5b))Wall- or wall-equivalent
dual systems
Wall system with only two uncoupled
walls per horizontal direction 1.0
Other uncoupled wall system 1.1
Wall-equivalent dual, or coupled wall
systems
1.2
1,cl.5.2.2.2(6)Building not regular in
plan
One-storey building 1.05
Multistorey, one-bay frames 1.1
Multistorey, multi-bay
frames or frame-equivalent
dual structures
1.15
Multiplication factor
αu/a1
Behaviour factor qo
(EN1998-1-1,cl.5.2.2.2(2))
Approximate values of
αu/a1
Explicit calculations (Push
over analysis)
LIMIT
αu/a1≤1.5

Behaviour factor qo for DCM structural system
(Extract from IStructE Manual to EC8)
STRUCTURAL TYPE
Regular
in plan
Not regular structures
In plan
In
elevation
In plan
and
elevation
Frame system, dual system, coupled wall system
One storey (au/a1) 3.3 3.15 2.64 2.52
Multi-storey,one bay
(au/a1)
3.6 3.3 2.88 2.64
Multi-storey,multi-bay
(au/a1)
3.9 3.45 3.12 2.76
System of coupled walls or wall equivalent dual system 3.6 3.3 2.88 2.64
Uncoupled wall system,
Large lightly reinforced walls
3,0 3.0 2.4 2.4
Tosrionally flexible system 2,0 1.6 1.6 1.6
Inverted pendulum system 1,5 1.2 1.2 1.2
Note: For buildings which are not regular in elevation, the value of qo should be reduced by 20%

Behaviour factors for horizontal seismic actions, q
(EN1998-1-1,cl.5.2.2.2)
q = qo . kw ≥ 1.5
(EN1998-1-1,Eq.5.1)
The factor kw
(EN1998-1-1,Eq.5.2)
Frame and frame –
equivalent dual system
kw = 1.0
Wall, wall – equivalent and
torsionally flexible
ao = Σhwi / Σlwi
kw = (1+ao) / 3
0.5≤ kw ≤ 1.0
μφ = 2qo – 1 if (T1≥TC)
μφ = 1+2(qo – 1)·TC/T! if (T1≤TC)
Curvature ductility factor, μφ
(EN1998-1-1,cl.5.2.3.4)
REINFORCEMENT
CLASS
B
REINFORCEMENT
CLASS
C
1.5 μφ μφ

Importance class/Ductility class
I II III IV
DCL DCM
DCH
DCM
DCH
DCH
Ignore “topographic
amplification effects”
Consider “topographic
amplification effects”
IF
Slopes <15o
Cliffs height
<30m
Slopes <15o
Cliffs height
<30m
Ignore Consider
Regular in plan: YES
Regular in elevation YES
Regular in plan: NO
Regular in elevation YES
Regular in plan: YES
Regular in elevation NO
Regular in plan: NO
Regular in elevation NO
Type of soil:
A , B ,C ,D, E, S1, S2
Type 1 elastic response
spectrum
0≤T≤TB
TB≤T≤TC
TC≤T≤TD
TD≤T≤4s
LATERAL
FORCE
MODAL
ANALYSIS
Displacement
ds=qd·de
P-Δ effects
θ≤0.1 – Ignore
0.1≤θ≤0.2 Consider
0.2≤θ≤0.3 Consider
θ≥0.3 Not Permited
Interstoreydrift
drv≤0.005h - Brittle
drv≤0.0075h - Ductile
drv≤0.010h - Other
Frame joint
ΣMRC≥1.3ΣMRB
Storey ≥ 2

Allowable material for primary seismic element(EN1998-1-1,cl.
5.4.1.1)
Type of material Requirements
Concrete
(EN1998-1-1,cl.5.4.1.1(1)P)
C16/20 and higher
Reinforcement steel
(EN1992-1-1,Table C.1) Class B or C (ribbed bars)
Allowable material for primary seismic element
(EN1992-1-1,cl. 2.4.2.4)
Type of material Partial factor
Concrete
(CYS NA EN1992-1-1,Table 2.1
γc=1.5
Reinforcement steel
(CYS NA EN1992-1-1, Table 2.1
γs=1.5
Design and detail concrete frame with DCM (EN1998-1-1,cl.5.4)

Design and detailing requirements of EC8 – Primary Beams
Detailing rule name Equation Comments
Critical region length
(EN1998-1-1,cl.5.4.3.1.2(2))
2hw
Longitudinal bars
ρmin, tension side
(EN1998-1-1,Eq.5.12)
ρmin = 0.5fctm/fyk
The minimum amount of steel reinforcement is
provide in order to withstand to the applied
moment .
ρmax, critical regions
(EN1998-1-1,Eq.5.11)
ρmax= ρ‟+0.0018fcd/(μφεsy,dfyd)
The maximum amount of steel reinforcement is
provide in order to ensure that yielding of the
flexural reinforcement occurs prior to crushing of
the compression block.
As,min, critical regions bottom
As,min = 0.5 As,top
The minimum area of bottom steel, As,min, is in
addition to any compression steel that may be
needed for the verification of the end section for
the ULS inbending under the (absolutely)
maximum negative (hogging) moment from the
analysis for the design seismic action plus
concurrent gravity, MEd.
As,min, support bottom As,min = As,bottom-span/4
dbL/hc–bar crossing interior joint
(EN1998-1-1,Eq.5.50a)
𝑑 𝑏𝐿
𝑕 𝑐
≤
7.5 𝑓𝑐𝑡𝑚
𝛾 𝑅𝑑 𝑓𝑦𝑑
∙
1 + 0.8𝑣 𝑑
1 + 0.75𝑘 𝐷 𝜌′/𝜌 𝑚𝑎𝑥 Those equationsdeveloped in order to ensure that

dbL/hc–bar crossing exterior joint
(EN1998-1-1,Eq.5.50b)
𝑑 𝑏𝐿
𝑕 𝑐
≤
7.5 𝑓𝑐𝑡𝑚
𝛾 𝑅𝑑 𝑓𝑦𝑑
∙ 1 + 0.8𝑣 𝑑
the area is sufficient joint region through the
beam column joint where are existing high rate of
change of reinforcement stress.
Transverse bars
Outside critical regions:
Outside critical region
Spacing, sw
(CYS EN 1992-1-1,Eq.9.8)
0.75d
ρw≥0.08√fck/fyk
Critical region
Critical region
Spacing, s
(EN1998-1-1,Eq.5.13)
≤min{hw/4, 24dbw, 225mm, 8dbL}
Diamter, dbw
(EN1998-1-1,cl.5.4.3.1.2(6)P)
≥6mm
Shear design
VEd seismic
(EN1998-1-1,Fig.5.1)
𝑀 𝑅𝑏
𝑙 𝑐𝑙
𝑔 𝑘 + 𝜓2 𝑞 𝑘
VRd,max,seismic
(EN1992-1-1,cl.6.2.3)
VRd,max=0.3(1-fck/250)·bw·z·fcd·sin2θ
1≤cotθ≤2.5
Outside critical region, VRd,s,
(EN1992-1-1,cl.6.2.3)
VRd,s=bw·z·ρw·fywd·cotθ
1≤cotθ≤2.5
Critical region, VRd,s,
(EN1992-1-1,cl.6.2.3)
VRd,s=bw·z·ρw·fywd·cotθ
1≤cotθ≤2.5

Design and detailing requirements of EC8 – Primary Columns
Cross section sides, hc, bc -
Critical region length
(EN1998-1-1,Eq.5.14)
lcr=max{hc,bc,0.45m, lc/6}
Longitudinal bars
ρmin
(EN1998-1-1,cl.5.4.3.2.2(1)P)
ρmin=0.01
1. Symmetrical cross-section must be
symmetrically reinforced.
2. At least one intermediate bar should be
providealong in each corner in order to
ensure the integrity of column beam joint.
The column end is consider as critical
region .
ρmax
(EN1998-1-1,cl. 5.4.3.2.2(1)P)
ρmax=0.04
dbL ≥{8mm}
Bar per each side
(EN1998-1-1,cl.5.4.3.2.2(2)P)
≥{ 3}
Maximum spacing between restrained bars
(EN1998-1-1,5.4.3.2.2(11b))
≤{200mm}
Distance of unrestrained bar from nearest restrained
bar
(EN1998-1-1,cl.5.4.3.3(2))
≤{150mm}
Transverse bars
Outside critical regions:

dbw
(EN 1998-1-1,cl.5.4.3.2.2(10)P) ≥{6mm ,dbL/4}
Spacing, s
(EN1992-1-1,cl.9.5.3(3))
≤{20dbL,hc,bc,400mm}
At lap splices, if dbL>14mm: sw≤
(EN1992-1-1,cl.9.5.3(4))
≤{12dbL,0.6hc,0.6bc,240mm}
Within critical region:
dbw,
(EN 1998-1-1,cl.5.4.3.2.2(10)P)
≥ {6mm, dbL/4}
Spacing, s
(EN1998-1-1,Eq.5.18)
≤{bo/2, 175mm, 8dbL)
In critical region at column base:
ωwd,
(EN19981-1,cl.5.4.3.2.2(9)
≥0.08
In critical region at column base:
aωwd
(EN1998-1-1,Eq.5.15)
(EN1998-1-1,Eq. 5.16a & 5.17a)
(For cross section)
≥30μφvdεsy,dbc/bo-0.035
an= 1-Σbi
2
/6boho
as= (1-s/2bo)(1-s/2ho)
1. The amount of hoops at the critical
regions should be satisfy be this equation.
2. The mechanical volumetric ratio of
confining hoops within the critical
regions:
3. The confinement effectiveness factor,
equal to α=αn.αs
The mechanical volumetric ratio of confining
hoops within the critical regions:
a) For cross section:

(EN1998-1-1,Eq.5.16b& 5.17b)
(For circular cross section) an=1
as=(1-s/2Do)2
𝜔 𝑤𝑑 =
2 𝑕 𝑜 + 𝑏 𝑜 + 𝑕 𝑜
2 + 𝑏 𝑜
2
𝑕 𝑜 𝑏 𝑜 𝑠
∙ 𝐴 𝑠 ∙
𝑓𝑦𝑑
𝑓𝑐𝑑
≥ 0.08
b) For circular cross section with circular
hoops:
𝜔 𝑤𝑑 =
3 𝑕 𝑜 + 𝑏 𝑜
𝑕 𝑜 𝑏 𝑜 𝑠
∙ 𝐴 𝑠 ∙
𝑓𝑦𝑑
𝑓𝑐𝑑
≥ 0.08
Capacity design – beam column joint
Capacity design checks at beam-column joints
(EN1998-1-1,Eq.4.29)
Σ𝛭 𝑅𝑐 ≥ 1,3Σ𝑀 𝑅𝑏 This rule is not apply at:
-to a top level of multi-storey building
-in single storey building
Axial load ratio
Axial load ratio
(EN1998-1-1,cl.5.4.3.2.1(3)P)
𝑣 𝑑 = 𝑁𝐸𝑑 /𝐴 𝑐 𝑓𝑐𝑑 ≤ 0.65
Shear design
Shear design
(EN1998-1-1,Fig.5.2)
𝛾 𝑅𝑑 ∙
Σ𝑀 𝑅𝑐,𝑒𝑛𝑑𝑠
𝑙 𝑐𝑙
VRd,max,seismic
(EN1992-1-1,Eq.6.9)
VRd,max=0.3(1-fck/250)·bw·z·fcd·sin2θ
1≤cotθ≤2.5
VRd,s, seismic
(EN1992-1-1,cl.6.2.3)
VRd,s=bw·z·ρw·fywd·cotθ+NEd(h-x)/lcl
1≤cotθ≤2.5

Design and detailing requirements of EC8 – Ductile wall
Web thickness, bwo
(EN1998-1-1,Eq.5.7)
≥ max{150mm, hstorey/20}
Critical region length, hcr
(EN1998-1-1,Eq. 519a & 5.19b)
hcr= max{lw, hw/6}
≤2lw
≤hsfor n ≤ 6 storey
≤2hs for n ≤ 6 storey
Boundary elements
Critical region
Length of the confined boundary element, lc
(EN1998-1-1,cl.5.4.3.4.2(6))
lc = max{0.15lw,1.5bw} length over which
εcu>0.0035
Thickness bw over lc
(EN1998-1-1,cl. 5.4.3.4.2(10))
bw≥ 0.20m and bw≥ hs/10
lc≥ max(2bw,0.2lw)
and
bw≥ 0.20m and bw≥ hs/15
lc≤ max(2bw,0.2lw)
Vertical reinforcement:
ρmin over Ac=lcbw
(EN1998-1-1,cl.5.4.3.4.2(8))
ρmin= 0.005
ρmaxover Ac
(EN1998-1-1,cl. 5.4.3.2.2(1)P)
ρmax= 0.04
Confining hoops

dbw
(EN 1998-1-1,cl.5.4.3.2.2(10)P)
Spacing oh hoops (at edges of the wall), sw
(EN1992-1-1,cl.9.5.3(4))
Spacing oh hoops (at the distance beyond to the edge
of wall), sw
(EN1992-1-1,cl. 9.5.3(4))
In the part of the section where : 0.02Ac
1. Distance of unrestrained bar in
compression zone from nearest restrained
bar ≤150mm
2. Hoops with dbw≥max{6mm, dbL/4}
3. Spacing of hoops, sw≤ min{12dbL, 0.6bwo,
240mm) up to a distance of 4bw above or
below floor beams or slabs or,
4. Spacing of hoops,
sw≤min{20dbL,bwo,400mm} beyond that
distance mansion at (3).
The transverse reinforcement of the boundary
elements may be determined in accordance with
EN1992-1-1 alone, if one of the following
conditions is fulfilled:
a. vd≤ 0.15
b. vd≤ 0.20 and the q-factor used in the
analysis is reduced by 15%.
(EN1998-1-1,cl.5.4.3.4.2(12a&b)).
ωwd,
(EN19981-1,cl.5.4.3.2.2(9)
0.08
aωwd
(EN1998-1-1,Eq.5.20)
xu,
(EN1998-1-1,Eq. 5.21)
εcu2,c,
(EN1998-1-1,cl. 5.4.3.4.2(6)
ωv,
(EN1998-1-1,cl. 5.4.3.4.1(5a))
αωwd≥ 30μφ (vd + ωv)εsy,dbc/bo – 0.035
xu = (vd+ωv)·lwbc/bo
εcu2,c = 0.0035 + 0.1aωwd
ωv = (Asv/hcbc)fyd/fcd
For walls of rectangular cross-section.
Web

Vertical reinforcement
ρv.min
(EN1998-1-1,cl. 5.4.3.4.2(11))
εc> 0.002: ρv.min≥0.005
In the height of the wall above the critical region
only the relevant rules of EN1992-1-1:2004
regarding vertical, horizontal and transverse
reinforcement apply.
ρv.max ρv.max = 0.04
Spacing of vertical bars, sv
(EN1992-1-1,cl.9.6.2(3))
≤ min{3bwo,400mm}
Horizontal reinforcement
ρh.min
(CYS NA EN1992-1-1,cl. 9.6.3(1))
ρh.min = max{0.001Ac , 0.25ρv)
Spacing of reinforcement, sh
(EN1992-1-1,cl. 9.6.3(2))
≤ 400mm
Axial load ratio
Normalised axial load, vd
(EN1998-1-1,cl. 5.4.3.4.1(2))
≤ 0.4
Design moments
Design moment, MEd
(EN1998-1-1,cl.5.4.2.4(4)P)
If the hw/lw ≥ 2.0, the moment distribution along
the height of slender primary seismic wall shall be
covered
The design bending moment diagram along the
height of the wall should be given by anenvelope
of the bending moment diagram from the
analysis, vertically displaced(tension shift). The
envelope may be assumed linear, if the structure
does not exhibitsignificant discontinuities of
mass, stiffness or resistance over its height.

Shear resistance
Design shear force, VEd
(EN1998-1-1,cl.5.4.2.4(7))
VEd = 1.5·VEd,seismic
Outside critical region
VRd,max,seismic
(EN1992-1-1,Eq.6.9)
VRd,max=0.3(1-fck/250)·bwo·0.8lw·fcd·sin2θ
1≤cotθ≤2.5
VRd,s
(EN1992-1-1,cl.6.2.3)
VRd,s = bwo (0.8lw)ρh·fywd·cotθ
1≤cotθ≤2.5
Critical region in web
VRd,max,seismic
(EN1992-1-1,Eq.6.9)
VRd,max=0.3(1-fck/250)·bwo·0.8lw·fcd·sin2θ
1≤cotθ≤2.5
VRd,s if as = MEd/VEdlw≥2
(EN1992-1-1,cl.6.2.3)
1≤cotθ≤2.5
VRd,s if as = MEd/VEdlw≤2
(EN1992-1-1,cl.6.2.3)
1≤cotθ≤2.5

Design notes for seismic design of building accordance to Eurocode 8

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Design notes for seismic design of building accordance to Eurocode 8