algerian seismic code

BUILDING RESEARCH INSTITUTE INTERNATIONAL INSTITUTE OF SEISMOLOGY AND EARTHQUAKE ENGINEERING 2009/2010 Report Assignment on

Seismic Design Code II Part 1: History of Algerian Seismic Regulations Part 2: Comparison of Algerian Seismic Design Code with Japanese and European Seismic design codes Submited by Rafik TALEB Supervised by Prof. S. SUGANO On april 8th, 2010 1

INTRODUCTION .................................................................................................................................................... 2

2

HISTORY OF SEISMIC DESIGN REGULATION IN ALGERIA .................................................................... 2 3.1 3.2 3.3 3.4

3

AFTER THE 1716 ALGIERS EARTHQUAKE .......................................................................................................... 2 AFTER 1954 EL-ASNAM EARTHQUAKE.............................................................................................................. 3 AFTER 1980 EL-ASNAM EARTHQUAKE.............................................................................................................. 4 AFTER 2003 BOUMERDES EARTHQUAKE ........................................................................................................... 5

COMPARISON OF RPA99 REV. 2003 WITH BSL AND EUROCODE 8 ........................................................ 6 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12 3.13 3.14

SEISMIC ZONE FACTOR ...................................................................................................................................... 6 GROUND MOTION ............................................................................................................................................... 7 SOIL CLASSIFICATION ........................................................................................................................................ 8 DESIGN RESPONSE SPECTRUM ............................................................................................................................ 9 IMPORTANCE FACTOR ...................................................................................................................................... 12 RESPONSE MODIFICATION FACTOR (BEHAVIOR FACTOR) ................................................................................. 14 APPROXIMATE FUNDAMENTAL PERIOD ............................................................................................................ 16 DESIGN BASE SHEAR COEFFICIENT ................................................................................................................... 18 VERTICAL DISTRIBUTION OF SEISMIC FORCES .................................................................................................. 20 WEIGHT OF THE BUILDING ............................................................................................................................... 22 STORY DRIFT LIMIT .......................................................................................................................................... 23 LIMIT OF STRUCTURAL FACTORS IN RC BUILDINGS ......................................................................................... 23 IRREGULARITY FACTOR ................................................................................................................................... 25 TARGET PERFORMANCE ................................................................................................................................... 28

REFERENCES ................................................................................................................................................................. 29

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1 Introduction In this report, an overview of the development of seismic design regulations in Algeria is presented. In the second part, a comparison is made between Algerian seismic design code (RPA), Japan seismic design code (BSL) and European code (Eurocode 8). 2 History of seismic design regulation in Algeria The first reported earthquake in Algeria goes back to the 3rd March 1359. This earthquake was reposted as a very strong earthquake which destroys the city of Algiers. The other strong earthquake also recorded on 3rd January 1365. 3.1 After the 1716 Algiers Earthquake The most cited historical earthquake is the earthquake which stroke Algiers in 3rd February 1716 (intensity was estimated at IX (MMI), 20000 victims). It was reported that about 200 houses collapsed and many others were damaged; the large mosque was cracked, even the country houses suffered considerable damage and some of them were thrown to the ground; in a distance of about 3 km from the city, the ground had large openings. The number of the victims was reported to have reached 20 000, most of them buried under the debris. Several pathologies were recorded which were the main cause of the damage. The three main pathologies (vulnerabilities) are listed in what follows:  The absence of links between the walls which caused their collapse;  The bad construction of masonries which was a direct cause to its destruction and the collapse;  The absence of anchoring of the floors to the load-bearing walls and the absence of their linkage which contributed to the collapse of the higher floors. Following that earthquake disaster, it is deferred that the authority of that time, in fact the “Dey” (Governor of Algiers) imposed to the Algiers population a preventive construction measures. The “Casbah” of Algiers built in 1520 by the Ottomans. Some of these structural countermeasures are summarized as follows: 

Use alternate crossing of wood logs to consolidate the angles of main walls and well connect with partition walls. The links are realized every 50 cm in height with wood logs of about 2 m long (Figure 1).



Floor is built by superposition of two layers of wood logs inserted in all width of bearing walls (rigid diaphragm) (Figure 2).



Frontal balcony overhanging and supported by wood logs forming an angle with bearing-wall (Figure 3).

2

Figure 1 – Wood logs to consolidate structural walls corners

Figure 2 – Floor is built by superposition of two layers of wood logs

Figure 3 – Wood logs forming an angle with bearing-wall

3.2 After 1954 El-Asnam Earthquake Since the 1954 El-Asnam (Orléansville) earthquake (M6.7, 1243 deaths and about 20.000 houses destroyed) disaster, the French government edited the seismic recommendations for construction “AS55” which mainly contain the seismic zone map (Figure 4), the ground acceleration level and specifications design. The “AS55” became after revisions the French seismic code “PS69” and “PS69 Rev.73”.

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Figure 4 - Seismic zone map adopted for Algeria in the "AS55"

In 1976 a study was launched with the collaboration of Stanford University to investigate the seismic risk in Algeria, which was achieved two years later. The results of this investigation were used as a basis for the development of the first version of the actual code. In 1978, a macrozonation map and a preliminary version of the Algerian seismic regulations were established inspiring from the American code (UBC 73/76). The seismic forces are calculated based on equivalent static method. 3.3 After 1980 El-Asnam Earthquake After El-Asnam earthquake 10th October 1980 (M7.2, 2633 deaths, more than 20,000 houses destroyed, 48,000 honeless) “PS 69 Rev. 73” or “RPA81” then “RPA 81 Rev. 83”. Investigations of the damages induced indicated that the redesigned and constructed buildings was done without following the elementary rules of seismic resistant design and construction which had been know for many years and some of which were contained in the seismic code specifications “AS 55”. The mains causes of damages can be listed as follow:  Damages dues to short columns  Poor conceptual design  Poor structural material  Inadequate detailing for structural elements

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Figure 5 - Seismic zones in the RPA81, RPA81 Rev.83, RPA88 and RPA99

Edition of the first Algerian seismic regulations “RPA81”, which became “RPA81 Rev. 83”. The “RPA81 Rev. 83” has been revised in 1988 (“RPA88”) and in 1999 (“RPA99”). The mains revised features in the “RPA99” are:  Modification of the equivalent static method  Promotion of the dynamic spectral method  Complete and easy to read version 3.4 After 2003 Boumerdes Earthquake The last revision of the seismic code was made just after the May 21, 2003 Boumerdes earthquake which amended the following clauses:  Subdivision of moderate seismicity zone into two sub-zones IIa and IIb  The seismic zoning map is revised to include the recently affected area in zone III  The increase of values for the seismic zoning factor, A  Restriction on the number of stories for buildings with reinforced concrete frames and recommends the use of concrete shear walls  Restrictions on open space at the ground floor level to avoid the soft story problem  Strength of the cast-in-place concrete  The size of structural elements, especially the columns.

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3 Comparison of RPA99 Rev. 2003 with BSL and Eurocode 8 3.1 Seismic Zone Factor 3.1.1 Algerian Seismic Design Code (RPA99 Rev. 2003) In fact, the zone factor in the Algerian seismic design code (RPA99 Rev. 2003) is expressed as a fraction of the acceleration of gravity, and is defined as a function of both Seismic Zone and Building Category (Importance Category) According to Algerian Seismic Design Code (RPA99 Rev. 2003), the Algerian territory is subdivided into five (05) zones (Figure 6): Zone 0 Zone I Zone IIa and IIb Zone III

:Negligible seismicity : Low seismicity :Average seismicity :High seismicity CLASSIFICATION SISMIQUE DES WILAYAS D'ALGERIE

CGS: Centre National de Recherche Appliquée en Génie Parasismique ZONE III

ALGER

BOUMERDES

ZONE II b

ANNABA

TIZI-OUZOU TIPAZA

ZONE II a

SKIKDA

JIJEL

EL TARF

BEJAIA

BLIDA

CHLEF

AIN DEFLA

MILA BOUIRA

MOSTAGANEM

ZONE I

CONSTANTINE

GUELMA

SETIF

RELIZANE

ORAN

O.EL BOUAGUI TISSEMSSILT AIN TEMOUCHENT

MASCARA BATNA

SIDI BELABES

Maroc

Tunisie

ZONE 0

SOUK AHRAS

B.B. ARRERIDJ

MEDEA

M'SILA TIARET

KHENCHELLA

TLEMCEN

TEBESSA

DJELFA

SAIDA

BISKRA

NAAMA

LAGHOUAT

EL BAYADH

El OUED

Figure 6 - Seismic zones in the RPA99 Rev. 2003 Ghardaia

Ouargla

a) Building importance category Bechar

Adrar

According to the seismic zone and the Building Category, the Zone acceleration coefficients are given in Table 1 Table 1 - Zone Acceleration Coefficient A Category 1A 1B 2 3

Zone I 0.15 0.12 0.10 0.07

IIa 0.25 0.20 0.15 0.10

IIb 0.30 0.25 0.20 0.14

III 0.40 0.30 0.25 0.18

3.1.2 Japan Seismic Design Code (BSL) According to BSL, The earthquake zone coefficient (Z) is a numerical value representing the probability of seismic motion.

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Figure 7 - Seismic zone factor (BSL)

3.1.3 European Seismic Design Code (Eurocode 8) For the purpose of Eurocode 8, national territories shall be subdivided by the National Authorities into seismic zones, depending on the local hazard. The seismic hazard is described in terms of the value of the reference peak ground acceleration a gR . The reference peak ground acceleration, a gR , for use in a country or parts of the country, may be derived from seismic zone maps found in its National Annex.

Figure 8- The PGA distribution in Europe and Mediterranean area

3.2 Ground motion 3.2.1 Algerian Seismic Design Code (RPA99 Rev. 2003) For the RPA99 Rev. 2003, the earthquake ground motion is represented by an equivalent static lateral load or horizontal ground acceleration response spectrum. These two methods will be presented in details in followings paragraphs. Vertical component of the ground motion is not considered.

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Time history representation of the earthquake motion is allowed, but no details mentioned for the selection of time history record. Hence, this representation is not used in the practice. 3.2.2 Japan Seismic Design Code (BSL) The earthquake ground motion is represented by an equivalent static base shear forces for each story or horizontal ground acceleration response spectrum. It is notable that Japan has adopted a system of design peer-review. The review is mandated for special structures like highrise structures (defined as those not shorter than 60 m) and baseisolated structures. In the peer-review, seismic hazard at the site is considered; site specific ground motions are chosen; and nonlinear pushover and nonlinear time history analyses are carried out to check whether or not the adopted structure satisfies the design criteria. 3.2.3 European Seismic Design Code (Eurocode 8) Within the scope of Eurocode 8 the earthquake motion at a given point on the surface is represented by an elastic ground acceleration response spectrum, henceforth called an “elastic response spectrum”. The horizontal ground motion is described by two orthogonal components assumed as being independent and represented by the same response spectrum. For the three components of the seismic action, vertical component of response spectra may be adopted. Timehistory representations of the earthquake motion may be used. The ground motion can also represented by a “design ground displacement” corresponding to the design ground acceleration. As an alternative to represent the seismic action, Time-history can be used as well as Spatial model of the seismic action when necessary (multi-support excitation) 3.3 Soil classification 3.3.1 Algerian Seismic Design Code (RPA99 Rev. 2003) The sites are classified into four (04) categories according to the mechanical properties (basically Vs ) of the constituting soils. For each Site Category the associated characteristic periods are given (Table 2). Table 2 - Soil Classifications (RPA99 Rev. 2003) Site type

Characteristics

Characteristic periods T1 T2

S1 rocky soil

Rock or other geological formation characterized by an average shear wave velocity Vs  800m / s .

0.15

0.30

S2 (hard site)

Very dense gravel or sand and/or over consolidated clay deposits with a thickness of 10 to 20 meters and Vs  400m / s from a depth of 10 meters.

0.15

0.40

S3 (soft site)

Thick deposits of moderately dense gravel and sand or moderately stiff clay with Vs  200m / s from a depth of 10 meters.

0.15

0.50

S4: (very soft site)

Loose sands deposits with or without soft clay with Vs  200m / s within the 20 first

0.15

0.70

meters. Soft to moderate stiff clay with Vs  200m / s within the 20 first meters.

3.3.2 Japan Seismic Design Code (BSL) BSL classify soils into three (03) categories (Table 3). 8

Table 3 - Soil Classifications (BSL) Soil type Hard soil Medium soil Soft soil

Tc

Ground characteristics Ground consisting of rock, hard sandy gravel, etc. classified as Tertiary or older. Other than hard type or soft one. Alluvium consisting of soft delta deposits, topsoil, mud, or the like (including fills, if any), whose depth is 30m meters or more, land obtained by reclamation of a marsh, muddy sea bottom, etc., where the depth of the reclaimed ground is 3 meters or more and where 30 years have not yet elapsed since the time of reclamation.

(sec)

0.4 0.6 0.8

3.3.3 European Seismic Design Code (Eurocode 8) The site should be classified according to the value of the average shear wave velocity, Vs ,30 , if this is available. Otherwise the value of SPT test should be used. The average shear wave velocity Vs ,30 should be computed in accordance with the following expression: Vs ,30 

30 hi  i 1 Vi N

Table 4 - Ground types (EC8) Parameters Ground type A

Description of stratigraphic profile Rock or other rock-like geological formation, including at most 5 m of weaker material at the surface. 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. Deep deposits of dense or medium dense sand, gravel or stiff clay with thickness from several tens to many hundreds of metres. Deposits of loose-to-medium cohesionless soil (with or without some soft cohesive layers), or of predominantly soft-to-firm cohesive soil. 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. 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 Deposits of liquefiable soils, of sensitive clays, or any other soil profile not included in types A – E or S1

B C D E S1 S2

N SPT

Vs ,30

cu (kPa)

> 800

-

-

360 – 800

> 50

> 250

180 – 360

15 - 50

70 - 250

< 180

< 15

< 70

< 100 (indicative)

-

10 - 20

Table 5 - Response spectra parameters classified by soil type (EC8) Soil type S

A 1.00

B 1.20

C 1.15

D 1.35

E 1.40

TB TC

(sec)

0.15

0.15

0.20

0.20

0.15

(sec)

0.40

0.50

0.60

0.80

0.50

TD

(sec)

2.00

2.00

2.00

2.00

2.00

Generic spectrum

3.4 Design response spectrum 3.4.1 Algerian Seismic Design Code (RPA99 Rev. 2003) The RPA define directly the seismic action a “Design Response Spectrum” as following:

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  T Q  1.25A1   2.5  1   R   T1    Q 2.51.25A   S a  R  2/3 g   Q  T2  2.51.25A      R  T  2/3  5/3  2.51.25A  T2   3   Q    3  T R

0  T  T1 T1  T  T2 T2  T  3.0s T  3.0s

A : Seismic zone acceleration coefficient (Table 1).

 : Damping correction factor (equal to 1 for 5% viscous damping), T1 , T2 : Characteristic periods associated to the type of soil (Table 2). From which the elastic design spectra is derived as follow:   T  1.25 A1  2.5  1  T 1     2.5 1.25 A Se  2/3  T  g 2.5 1.25 A 2  T   2/3 5/3  2.5 1.25 A T2   3        3  T 

0  T  T1 T1  T  T2 T2  T  3.0s T  3.0s

3.4.2 Japan Seismic Design Code (BSL) BCJ stipulates the following expressions for elastic spectra Rt , with reference to a PGA equal to 0.40g (prescribed almost everywhere in Japan). The spectrum value Rt is given as a fraction of acceleration of gravity.

0  T  Tc Tc  T  2Tc T  2Tc

Rt  1 T  Rt  1  0.2  1  Tc  T Rt  1.6 c T

2

Where the period Tc is determined according to the soil type and is equal to 0.4, 0.6 and 0.8 sec for soil types 1, 2 and 3, respectively (Table 3). For moderate earthquakes, the ordinates of the elastic spectra Rt are multiplied by CO  0.2 . 3.4.3 European Seismic Design Code (Eurocode 8) EC8 defines reference elastic spectra Se (in terms of the pseudo-acceleration) as a function of the building natural period, T , by means of the following expressions:

10

Where,

a gR is the reference peak ground acceleration for ground type A (established in the national annexes on the basis of the seismic risk maps). With reference to ordinary buildings, a gR equal to 0.40g, and  equal to 5% viscous damping.

 I is the structure importance factor,  is the damping correction factor (equal to 1 for 5% viscous damping), S is the soil amplification factor,

TB , TC and TD are characteristic periods of the response spectrum depending on the soil type. Elastic spectra corresponding to moderate earthquakes are obtained by multiplying the ordinates of the reference spectra by a reduction factor  . The values  to be ascribed to for use in a country may be found in its National Annex. The recommended values of  are 0.4 for importance classes III and IV and  = 0.5 for importance classes I and II. Figure 9 and figure 10 shows a comparison of reference elastic response spectrum for level 1 and level 2 design. It should be noted that Algerian seismic design does not consider level 1 design. A big deference in acceleration level is observed for level 1 design between BSL and EC8 which can be explained by ductility permission for EC8 even for level 1 design.

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Reference elastic response spectrum EC8 (Soil A) 1.40

EC8 (Soil B) BSL (Hard soil) RPA (Soil S1)

1.20

RPA (Soil S2)

1.00

Se/g

0.80

0.60

0.40

0.20

0.00 0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

P e r i o d ( se c )

Figure 9 – Comparison of reference elastic spectra of the RPA, BSL and EC8 (Level 2) Hard soil - Level 10.7 EC8 (Soil A) EC8 (Soil B) BSL (Hard soil)

Co x Rt (Co=0.2) & uSe/g (u=0.5)

0.6

0.5

0.4

0.3

0.2

0.1

0.0 0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Period (sec)

Figure 10 – Comparison of reference elastic spectra of the BSL and EC8 (Level 1)

3.5 Importance factor 3.5.1 Algerian Seismic Design Code (RPA99 Rev. 2003) In the RPA99 Rev. 2003 the importance category of the structure is selected according to The importance category is used to determine the acceleration zone factor.

Table 6.

The degree of safety for each type of structure, required by the code, varies according to the type of building occupancy. Three return periods, 500, 100 and 50 years are assigned to structures in the following categories.

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Table 6 - Building Category in the RPA99 Rev. 2003 Group

Constructions

Vital Construction Vital constructions should stay operational after major earthquake for the needs of the region, the public safety and the national defense, that is; - buildings housing strategic decision making centers - building housing staff and equipment for rescue and/ or national defense having an operational role such as civil defense centers, police or military barracks, parking lots for emergency and rescue equipment and vehicles - public health department buildings such as hospitals and centers equipped with emergency and surgical services - public communication department buildings such as centers for telecommunication, broadcasting and reception of information (radio and television), radio relays, airport and air traffic control - drinking water production and storage facilities of vital importance - historical and cultural public buildings of national importance - energy production and distribution facilities of national importance - administrative or any other buildings that should stay operational in case of an earthquake occurrence

1A

Construction of high importance Constructions housing frequently large groups of persons - public building occupied by more than 300 people at the same time such as large mosques, office buildings, commercial and industrial buildings, schools, universities, sport and cultural buildings, jails and, great hotels - buildings for collecting housings or office services with height exceeding 48m

1B

Public buildings of national importance or having a great social, cultural and economical importance - library or depository buildings of regional importance, museum, etc. - health department buildings other than those in group 1A - energy production or distribution facilities other than those in group 1A - water towers and water tanks with high to moderate importance

Current constructions or those of moderate importance Constructions non classified in the other groups 1A, 1B or 3, such as;

2

- buildings for collective housing or office services with height not exceeding 48m - other buildings occupied by less than 300 persons at the same time such as office buildings, industrial buildings, etc. - public parking lots

Constructions of low importance 3

- industrial or agricultural buildings sheltering low value goods - buildings with limited risk for people - temporary constructions

3.5.2 Japan Seismic Design Code (BSL) BCJ does not stipulate an importance factor. 3.5.3 European Seismic Design Code (Eurocode 8) Buildings are classified in 4 importance classes, depending on the consequences of collapse for human life, on their importance for public safety and civil protection in the immediate postearthquake period, and on the social and economic consequences of collapse. The importance classes are characterized by different importance factors

 I as described in Table 7.

Table 7 - Importance factor (EC8) Importance class I II III IV

Buildings Buildings of minor importance for public safety, e.g. agricultural buildings, etc. Ordinary buildings, not belonging in the other categories. Buildings whose seismic resistance is of importance in view of the consequences associated with a collapse, e.g. schools, assembly halls, cultural institutions etc. Buildings whose integrity during earthquakes is of vital importance for civil protection, e.g. hospitals, fire stations, power plants, etc.

I 0.8 1.0 1.2 1.4

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3.6 Response modification factor (behavior factor) 3.6.1 Algerian Seismic Design Code (RPA99 Rev. 2003) The behavior factor R depends on the type of lateral-resistant system used in the structure (Table 8). Table 8 - Global Behavior Coefficient R (RPA99 Rev. 2003) Category

A 1a 1b 2 3 4a 4b 5 6 B 7 8 9a 9b 10a 10b 11 C 12 D 13 14 15 16 17

Value of R

Description of Lat. Force Res. Systems

Reinforced Concrete Moment resistant frames without stiff masonry infill Moment resistant frames with stiff masonry infill Bearing shear walls Central core Mixed moment resistant frames/ shear walls with interaction Frames braced by shear walls Vertical cantilever with distributed masses Inverted pendulum

5 3.5 3.5 3.5 5 4 2 2

Steel Ductile moment resistant flames Ordinary moment resistant flames Structure braced by X triangulated elements Structure braced by V triangulated elements Mixed moment resisting frames/ X triangulated frames Mixed moment resisting frames/ V triangulated frames Vertical cantilever frames

6 4 4 3 4 5 2

Masonry Bearing tied Masonry

2.5

Other Systems Steel structure braced by diaphragm Steel structure braced by reinforced concrete core Steel structure braced by reinforced concrete shear walls Steel structure with mixed bracing including a reinforced concrete core and steel braces or frames in façade Systems including transparencies (soft stories)

2 3 3.5 4 2

3.6.2 Japan Seismic Design Code (BSL) The Structural Characteristics Factor Ds takes into account inelastic deformation and energy dissipation, and then to reduce the elastic response story shear according to the available ductility. Table 9 - Structural characteristics factor (BSL) Frame format Frame properties (1)

(2)

(3)

(4)

Frames in which an especially high degree of plastic deformation is especially high (e.g. where failure resulting from a sudden decline in strength against such as shear failure in response to forces stress acting on frame members is very unlikely) Frames other than those referred in (1) in which inelastic deformation is high (e.g. where failure resulting from a sudden decline in strength against such as shear failure in response to forces stress acting on frame members is unlikely) Frames other than those referred in (1) and (2) that will not suffer a sudden decline in strength (e.g. where shear failure will not occur in members as a result of forces stress that causes inelastic deformation in the members concerned) Frames other than those referred in (1), (2) and (3)

(a) Rigid frames or similar format frames

(b) Frames other than those referred to in Columns (a) and (c)

(c) Frame formats in which lateral forces that occurs in individual stories are mainly borne by bearing walls or braces in the said story

0.3

0.35

0.4

0.35

0.40

0.45

0.40

0.45

0.50

0.45

0.50

0.55 14

3.6.3 European Seismic Design Code (Eurocode 8) In EC8, earthquake-resistant structures are classified in three structural ductility classes with reference to the available ductility of their members: low (DCL), medium (DCM) and high (DCH). In addition, two different approaches may be used in design. According to the first approach, the expected structural behavior is low in energy dissipation. The design internal forces are evaluated by means of elastic analysis, the structure may belong to the low ductility class (DCL), and a qvalue greater than 1.5 is not allowed. A q-value equal to 1.5 takes into account the overstrength of the structure and, therefore, the expected behavior is elastic. The second approach takes into account the capability of the structure to resist the earthquake through the inelastic behavior of its members. In this case the structure has to belong to the DCM or DCH ductility classes and qvalues greater than 1.5 are allowed. Earthquake resistant buildings shall be designed in accordance with one of the following concepts (Table 10):  Concept a) Low-dissipative structural behavior;  Concept b) Dissipative structural behavior. Table 10 - Reference behavior factor according to class of ductility (EC8) Design concept Concept a) Low dissipative structural behavior Concept b) Dissipative structural behavior

Structural ductility class DCL (Low) DCM (Medium) DCH (High)

Range of the reference values of the behaviour factor q ≤ 1,5 - 2 ≤4 also limited by the values of Table 6.2 only limited by the values of Table 6.2

The upper limit of reference values of b behavior factors for systems regular in elevation are given in Table 11 . Table 11 - Upper limit of reference values of behavior factors for systems regular in elevation (EC8) STRUCTURAL TYPE

Ductility Class DCM 4

DCH 5  u / 1

b) Frame with concentric bracings Diagonal bracings V-bracings c) Frame with eccentric bracings

4 2 4

4 2.5 5  u / 1

d) Inverted pendulum

2

2  u / 1

e) Structures with concrete cores or concrete walls f) Moment resisting frame with concentric bracing

4

a) Moment resisting frames

g) Moment resisting frames with infill Unconnected concrete or masonry infills, in contact with the frame Connected reinforced concrete infills Infills isolated from moment frame (see moment frames)

See section 5 5  u / 1 2 2 See section 7 5  u / 1

4

If the building is non-regular in elevation, the upper limit values of q listed in

Table 11

should be

reduced by 20 %. 15

1 is the value by which the horizontal seismic design action is multiplied in order to first reach the plastic resistance in any member in the structure, while all other design actions remain constant;

 u is the value by which the horizontal seismic design action is multiplied, in order to form plastic hinges in a number of sections sufficient for the development of overall structural instability, while all other design actions remain constant. The factor  u may be obtained from a nonlinear static (pushover) global analysis. 3.7 Approximate fundamental period 3.7.1 Algerian Seismic Design Code (RPA99 Rev. 2003) The value of the fundamental period ( T ) of the structure can be estimated from empirical formulae or can be calculated by numerical of analytical method (such as Rayleigh method or Eigen-values method). The empirical formula recommended is the following: 3

T  CT hN 4 Where,

hN : height measured in meters from the basis of the structure to the top of last level.

CT coefficient, function of the lateral force resisting system and of the type of infill (Table 12) Table 12 - Values of the coefficient CT (RPA 99 Rev. 2003) Case 1 2 3 4

Resisting System Steel Moment Resisting frames without infill masonry Reinforced Concrete Moment Resisting frames without infill masonry Steel or Reinforced Concrete Moment Resisting frames with infill masonry Partially or totally RC Shear walls, Braced Frames and Masonry Walls

CT

0.085 0.075 0.050 0.050

For cases 3 and 4, the following formula can be used also: T

0.09hN D

Where,

D is the dimension of the building measured at its basis in the direction of calculation. In this case the smaller value between the values given by the two formulas is considered. The values of T , calculated using numerical or analytical methods must not exceed those estimated by appropriate empirical formula of more than 30%. 3.7.2 Japan Seismic Design Code (BSL) For the determination of the fundamental period of vibration period T of the building,

T  0.02  0.01 H

 ratio of total height of stories to the total building (for steel building only).

16

3.7.3 European Seismic Design Code (Eurocode 8) For the determination of the fundamental period of vibration period T1 of the building, expressions based on methods of structural dynamics (for example the Rayleigh method) may be used. For buildings with heights of up to 40 m the value of T1 (in sec) may be approximated by the following expression:

T1  Ct H

3

4

Where,

H is the height of the building, in m, from the foundation or from the top of a rigid basement.

CT coefficient, function of the lateral force resisting system and of the type of infill (Table 13) Table 13 - Values of the coefficient CT (EC8) Case 1 2 3

Resisting System Steel Moment Resisting space frames Reinforced Concrete Moment Resisting spaces frames and eccentrically braced steel frames All other structures

CT

0.085 0.075 0.050

Alternatively, for structures with concrete or masonry shear walls the value CT in expression may be calculated as follow:

Ct  0.075

AC



AC   Ai .0.2  lwi H 

2



Ac is the total effective area of the shear walls in the first storey of the building, in m2; Ai is the effective cross-sectional area of the shear wall i in the first storey of the building, in m2; lwi is the length of the shear wall i in the first storey in the direction parallel to the applied forces, in m, with the restriction that lwi / H should not exceed 0,9. 4.0 BSL EC8-RPA (Ct=0.085)

3.5

EC8-RPA (Ct=0.075) EC8-RPA (Ct=0.050)

3.0

Period (sec)

2.5

2.0

1.5

1.0

0.5

0.0 0

20

40

60

80

100

120

140

Height (m)

Figure 11 – Comparison of period estimation in the RPA, BSL and EC8

17

3.8 Design base shear coefficient 3.8.1 Algerian Seismic Design Code (RPA99 Rev. 2003) The total seismic load V, applied to the base of the structure, must be calculated successively in two orthogonal and horizontal directions, according to the following formula:

V

ADQ W R

Hence, the base shear coefficient is:

C

ADQ R

Where,

A Seismic Zone Acceleration Coefficient (Table 1) R Behavior factor (Table 8)

Q Quality Factor (as defined below) D Average Dynamic Amplification Factor (as defined below) Average Dynamic Amplification Factor D depend on the site category, damping correction factor  and fundamental period of the structure T . The factor D is given by:

2.5  2 D  2.5 T2 T 3  2 5 2.5 T2 3.03 3.0 T 3

0  T  T2 T2  T  3.0s T  3.0s

T2 : Characteristic period associated to the category of the site (Table 2).

 : Damping correction factor. The quality factor of the structure given by the following formula: 5

Q  1   Pq 1

Pq Penalty to be applied depending on whether the criteria of quality are satisfied or not (Table 14) Table 14 - Values of Penalties Pq Criteria Q 1. Minimal conditions on bracing lines 2. Redundancy in plan 3. Regularity in plan 4. Regularity in elevation 5. Control of material quality 6. Control of construction quality

Pq Observed 0 0 0 0 0 0

not observed 0.05 0.05 0.05 0.05 0.05 0.10

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3.8.2 Japan Seismic Design Code (BSL) Level 2 seismic forces are stipulated by a distribution of the minimum required story shear strength as follows:

Vun  DS ,i .Fes ,i .2Vi N

2Vi  2 Ci .W j j 1

2

Ci  Z .Rt . Ai .2 C0

Vun,i is the required strength, Ds ,i is the structural characteristic factor (conceptually, the inverse of the behavior factor q ) Fes ,i is the shape factor set according to the distribution of the story stiffness and eccentricity of the plan. A specified subscript “i” indicates that the quantity is referred to the i -th story. 2

Ci is the Level 2 story shear coefficient at the ith story,

w j is the weight evaluated for the seismic design situation at the jth floor, Z is the seismic zone factor Rt is the ordinate of the response spectrum corresponding to the fundamental period of the building Ai is the height distribution factor 2

CO is the standard shear coefficient for the Level 2 seismic force equal to 1.0.

The distribution factor Ai , which takes into account the higher mode effects, is given as a function of fundamental period of the structure, such that:

 1  2T1 Ai  1    i     1  3T1  i  N w i   j j i W Where,

W is the total weight of the building The Level 1 seismic force is stipulated by means of the following formulas: N

V 1 Ci . w j

1 i

1

j 1

Ci  Z .Rt . Ai .1 C0

where

V is the Level 1 story shear at the ith story

1 i

19

1

Ci is the Level 1 story shear coefficient at the ith story

1

CO is the shear coefficient for the Level 1 seismic force equal to 0.2, taken as one-fifth the Level 2

shear coefficient 2 CO . 3.8.3 European Seismic Design Code (Eurocode 8) According to EC8, the ultimate lateral strength of the structure has to be large enough to sustain the reference seismic forces representative of strong ground motions. If the structure meets the criteria for regularity in elevation and has a fundamental period not larger than 4TC and 2.0s , the seismic response of the building may be evaluated by applying a set of horizontal forces to the story masses statically. Otherwise, the modal response spectrum analysis should be performed. The seismic design base shear V1 due to the reference seismic forces is given by,

V1  Sd m Where,

m is the total mass of the building estimated by taking into account the presence of the dead gravity load and a fraction of the live gravity load

S d is the ordinate of the design spectrum corresponding to the fundamental period of the building

 is a reduction factor of the seismic forces. The reduction factor  takes into account the fact that in multi-story buildings the effective modal mass of the fundamental mode of vibration is smaller than the total mass. In particular, λ = 0.85 if the building has more than two stories and T1  2TC , and

  1.0 otherwise.

The design spectrum S d is obtained by reducing the ordinates of the reference elastic spectrum by means of the behavior factor q , which allows for the ductility expected for the structural system. 3.9 Vertical distribution of seismic forces 3.9.1 Algerian Seismic Design Code (RPA99 Rev. 2003) The global seismic force V at the base of the building should be distributed following height of the structure according to the following formula: n

V  Ft   Fi i 1

Where,

Ft force at the top of the building allows taking into account the influence of the high vibration modes of the structure.

0.07TV  0.25V T  0.7 sec Ft   T  0.7 sec 0 20

The differential part of V , i.e. (V  Ft ) should be distributed following the height of the structure following the formula:

Fi 

V  Ft Whi n

W h j

j 1

j

For a ten-story building with uniform mass distribution, the distributions along the height of the shear strength required by EC8 and BCJ have been evaluated. Comparison is presented in Fig. 4 for two values of the fundamental period (T1 = 0.5 and 2.0 s). The abscissa is the required story strength normalized with respect to the base shear 3.9.2 Japan Seismic Design Code (BSL) For BSL, the base shear coefficients (and forces) are directly calculated for each story. 3.9.3 European Seismic Design Code (Eurocode 8) The seismic forces Fi , which are distributed along the height according to an inverted triangular distribution, are evaluated as follows,

Fi  V1

zi mi N

z m j 1

j

j

Where,

N is the number of stories

mi floor mass of the ith story zi height measured from the foundation level. Requirement story strength (T=2.0sec)

Requirement story strength (T=0.5sec)

10

10

EC8/RPA

EC8/RPA

BCJ 9

8

8

7

7

6

6

story

story

BCJ 9

5

5

4

4

3

3

2

2

1

1

0

0 0.0

0.2

0.4

0.6 Vi/Vbase

0.8

1.0

1.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Vi/Vbase

Figure 12 – Comparison of vertical distribution in the RPA, BSL and EC8

21

For a ten-story building with uniform mass distribution, the distributions along the height of the shear strength required by RPA, BSL and EC8 have been evaluated. Comparison is presented in Figure 12 for two values of the fundamental period (T = 0.5s and 2.0 s). The abscissa is the required story strength normalized with respect to the base shear. A very close distribution is observed. 3.10 Weight of the building 3.10.1 Algerian Seismic Design Code (RPA99 Rev. 2003) The seismic weight W of the structure includes the dead weight of the building and the permanent equipment, and a fraction of the live load. The seismic weight W is given by:

W   WGi   .WQi  n

i 1

WGi : Weight of dead loads and eventual fixed equipment WQi : Live loads

 : Weighting coefficient depending on the nature and the duration of the live load (Table 15) Table 15 - Weighting Coefficient β depending on Nature and Duration of Live Load Case 1

2

3 4 5



Building Type Residential use building, offices and assimilated Buildings receiving the public temporality: - rooms of exhibition, of sport, places of cult, meeting rooms with stand up places - classrooms, restaurants, dormitories, meeting rooms with sitting seats Warehouses, hangars Archives, libraries, tanks and assimilated buildings Other buildings no aimed above

0.20 0.30 0.40 0.50 1.00 0.60

3.10.2 Japan Seismic Design Code (BSL) The weight Wi of ith story includes dead load plus reduced live load and, if located in the designated snowy zone, reduced snow load 3.10.3 European Seismic Design Code (Eurocode 8) 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

""  E ,i .Qk ,i

Where,

 E,i is the combination coefficient for variable action Qk ,i . The combination coefficients  E,i take into account the likelihood of the Qk , i loads not being present over the entire structure during the earthquake. These coefficients may also account for a reduced participation of masses in the motion

22

of the structure due to the non-rigid connection between them.  E,i for use in a country may be found in its National Annex. 3.11 Story drift limit 3.11.1 Algerian Seismic Design Code (RPA99 Rev. 2003) The relative displacement between two adjacent levels (inter-story drift)  l must be less or equal 1.0% of the height of the storey unless it is demonstrated that a bigger displacement could be admitted. 3.11.2 Japan Seismic Design Code (BSL) BCJ provides limits that have to be fulfilled by the inter-story drifts due to the Level 1 seismic forces. In particular, two limit values of  l are given in BCJ (Table 16). The former and stricter limit is more commonly applied. The latter applies when non-structural elements can tolerate relatively large deformations of the structure without damage. 3.11.3 European Seismic Design Code (Eurocode 8) According to EC8, the inter-story drift due to the moderate earthquakes can not be larger than the limit values, given as percentages of the story height,  l (Table 16). Such limits depend on the type of non-structural elements for their ability to accommodate the inter-story drifts without damage. Table 16 - Limits on inter-story drift in RPA, BSL and EC8 RPA Max

 l allowed (%)

1.0 (Ultimate limit state)

BSL Non-structural element Max

 l allowed (%)

Commonly used Drift tolerant

0.50 0.83

EC8 Non-structural element Max Brittle Ductile No interfering

 l allowed (%) 0.50 0.75 1.00

3.12 Limit of structural factors in RC buildings 3.12.1 Algerian Seismic Design Code (RPA99 Rev. 2003) - Limitation for RC structural systems

Moment resisting space frames without rigid masonry infill walls: The building must not exceed five (05) stories or 17m height in Zone I, four (04) stories or 14m height in Zone IIa, and three (03) stories or 11m in height Zone IIb and III.

Moment resisting space frames with rigid masonry infill walls: The building must not exceed five (05) stories or 17m height in Zone I, four (04) stories or 14m height in Zone IIa, three (03) stories or 11m height in Zone IIb and two (02) stories or 8m height in Zone III.

Dual-system (Frames-shear walls interaction): The bearing of Strutural RC walls shall not exceed 20% of vertical loads. Frames shall resist at least 25% of the story shear forces.

Frames braced by RC walls: The bearing of Structural RC walls shall not exceed 20% of vertical loads, and shall resist the total horizontal loads. Frames resist only vertical loads. In seismic zone III, Frames shall resist at least 25% of the story shear forces. 23

With this system of bracing the buildings are limited to 10 levels or 33 meters in height

Limitation for RC members  For the main elements, the concrete must have the strength f c 28 not less than 20 Mpa and less than 45 Mpa.  The normalized axial compression force in columns is limited as follow:



Nd  0.30 Bc . f c 28

Where,

f c 28 characteristic compression strength of concrete N d axial compression force due to seismic load combinations Bc gross cross-sectional area of column  Conventional shear stress  bu is limited to

 bu  d f c 28 Where, d  0.04 for short columns and d  0.075 otherwise  The Formwork for columns is limited according to seismic zone as follow: Min(b,h) ≥ 25 cm in Zone I an IIa, Min(b,h) ≥ 30 cm in Zone IIb an III and Min(b,h) ≥ he/20 (1/4 < b/h < 4) For the circular column, the diameter D must satisfy those conditions: D ≥ 25 cm en Zone I, D ≥ 30 cm en Zone Iia and D ≥ 35 cm en Zone IIb and III (D ≥ he/15).  The section of the columns in the side or the corner of the building shall be comparable than the central column.  Minimum ratio for longitudinal bars in columns is: 0.9% in Zone IIb and III, 0.8% in Zone Iia and 0.7% en zone I  Minimum diameter for longitudinal bars for columns is 12mm  Beams shall respect the following minimum dimensions:

b  20cm, h  30cm and h/b  4.0 3.12.2 Japan Seismic Design Code (BSL) Limit of structural factors in RC buildings are directly related to Ds factor

24

Table 17 - limitation of structural factors (BSL) Kind H0/D (Lower Limit) 0/Fc (Upper Limit) t(Upper Limit) u/Fc(Upper Limit)

FA ( 6) 2.50 0.35 0.80 0.10

FB( 4) 2.00 0.45 1.0 0.125

FC( 2) 0.55 0.15

FD -

3.12.3 European Seismic Design Code (Eurocode 8) Eurocode 8 limit the normalized axial compression force in columns as follow:

d 

N Ed  0.65 Ac . f cd

In addition, EC8 limit the class of concrete to be used according to the class of ductility 3.13 Irregularity factor 3.13.1 Algerian Seismic Design Code (RPA99 Rev. 2003) Each building should be classified according to its configuration in plan and in elevation as a regular building or not, in regard to the criteria hereafter mentioned: A. Regularity in plan: At each level and for each design direction, the distance between center of mass and center of rigidity should not be more than 15% of the building dimension perpendicular to the considered direction of the seismic action. The shape of the building should be compact with a length to width ration less than or equal to four (04). The sum of the dimensions of the re-entrant parts and setbacks in a given direction should not exceed 25% of the global dimension of the building in that direction. The total area of the floor openings should be less than 15% of the total area of the floor. B. Regularity in elevation: The bracing system should not present vertical discontinuous bearing element the load of which is not transmitted directly to the foundation. Mass ratio and stiffness ratio of two successive levels should be less or equal to 25% in the considered direction of the seismic action. In the case of setbacks in elevation, the variation of the horizontal dimensions of the building between two successive levels should not be more than 20% in the two design directions, decreasing along the height. The largest horizontal dimension of the building should not exceed 1.5 times its smallest dimension.

25

Figure 13 - Criteria for geometric regularity in elevation (RPA99 Rev.2003)

Figure 14 - Criteria for geometric regularity in elevation (RPA99 Rev.2003)

3.13.2 Japan Seismic Design Code (BSL) Building irregularity aspect is considered by BSL through the Fes factor. The Fes factor for each story is calculated by multiplying the value of Fs and Fe . Fs correspond to the stiffness ratio defined by:

Fs  1.0 Fs  2.0 

if Rs  0.6 Rs 0.6

if Rs  0.6

Where,

Rsi  rsi rsa

rsi  1 Ri n

rsa   rsi n i 1

and Fe correspond to the eccentricity ratio defined by:

Fe  1.0

if Re  0.15

Fs  1.5

if Re  0.3

If 0.15  Re  0.3 a value obtained through linear interpolation.

Rex  ex rex , Rey  ey rey 26

e eccentricity distance between centers of gravity and translational stiffness along principal axis of the building.

re elastic radius defined as square root of torsional stiffness divided by the translational stiffness in the considered direction.

rex 

K Ri , rey  K Xi

K Ri KYi

3.13.3 European Seismic Design Code (Eurocode 8) For the purpose of seismic design, building structures are categorized into being regular or nonregular. With regard to the implications of structural regularity on analysis and design, separate consideration is given to the regularity characteristics of the building in plan and in elevation (Table 18). Table 18 - Consequences of structural regularity on seismic analysis and design Regularity

Allowed Simplification

Behavior factor

Plan

Elevation

Model

Linear-elastic Analysis

(For linear analysis)

Yes

Yes

Planar

Lateral force

Reference value

Yes

No

Planar

Modal

Decreased value by 0.8

No

Yes

Spacial

Lateral force

Reference value

No

No

Spacial

Modal

Decreased value by 0.8

A. Criteria for regularity in plan With respect to the lateral stiffness and mass distribution, the building structure shall be approximately symmetrical in plan with respect to two orthogonal axes. For each in-plan set-back, the area between the outline of the floor and a convex polygonal line enveloping the floor does not exceed 5% of the floor area. The aspect ration Lmax / Lmin of the building in plan shall be not higher than 4. At each level and for each direction of analysis x and y, the structural eccentricity e0 and the torsional radius r shall be in accordance with the two conditions below, which are expressed for the direction of analysis y:

e0 X  0.30.rX

rX  lS Where,

e0 X is the distance between the centre of stiffness and the centre of mass, measured along the x direction, which is normal to the direction of analysis considered 27

rX is the square root of the ratio of the torsional stiffness to the lateral stiffness in the y direction (“torsional radius”)

ls is the radius of gyration of the floor mass in plan (square root of the ratio of the polar moment of inertia of the floor mass in plan with respect to the centre of mass of the floor to the floor mass). B. Criteria for regularity in elevation All lateral load resisting systems, such as cores, structural walls, or frames, shall run without interruption from their foundations to the top of the building or, if setbacks at different heights are present, to the top of the relevant zone of the building. For gradual setbacks in elevation preserving axial symmetry, the setback at any floor shall be not greater than 20 % of the previous plan dimension in the direction of the setback. For a single setback within the lower 15 % of the total height of the main structural system, the setback shall be not greater than 50 % of the previous plan dimension If the setbacks do not preserve symmetry, in each face the sum of the setbacks at all stories shall be not greater than 30 % of the plan dimension at the ground floor above the foundation or above the top of a rigid basement, and the individual setbacks shall be not greater than 10 % of the previous plan dimension

Figure 15 - Criteria for geometric regularity in elevation (EC8)

3.14 Target performance 3.14.1 Algerian Seismic Design Code (RPA99 Rev. 2003) The present regulations aim at giving an acceptable protection for human lives and constructions against the adverse effects of the seismic actions through an appropriate design and detailing. For the current constructions, the aimed objectives are to provide the structure with: 28

 A sufficient strength and stiffness in order to limit the non-structural damages and to avoid the structural ones through an essentially elastic behavior of the structure while facing a relatively frequent moderate seismic event.  An adequate ductility and capacity of energy dissipation to allow the structure to undergo inelastic displacements with limited damages and no collapse nor loss of stability while facing a rare major seismic event. 3.14.2 Japan Seismic Design Code (BSL) According to BCJ, the ultimate lateral strength of each story of the structure has to be larger than the design story shear corresponding to strong ground motions (Level 2 design). In addition, the stresses due to moderate earthquakes (Level 1 design) should not exceed the allowable stresses. 3.14.3 European Seismic Design Code (Eurocode 8)

Damage limitation requirement (level 1): The structure shall be designed and constructed to withstand a seismic action having a larger probability of occurrence than the design seismic action, without the occurrence of damage and the associated limitations of use, the costs of which would be disproportionately high in comparison with the costs of the structure itself.

The seismic action to be taken has a probability of exceedance, 10%, in 10 years and a return period of 95 years

No-collapse requirement (level 2): The structure shall be designed and constructed to withstand the design seismic action without local or global collapse, thus retaining its structural integrity and a residual load bearing capacity after the seismic events. The seismic action to be taken has a probability of exceedance, 10%, in 50 years and a return period of 475 years References [1]. D. Benouar and A.A. Foufa, INVESTIGATION OF THE 1716 ALGIERS (ALGERIA) EARTHQUAKE AND THE TRADITIONAL SEISMIC PREVENTIVE MEASURES FROM HISTORICAL DOCUMENTS SOURCES, The 14 th World Conference on Earthquake Engineering, October 12-17, 2008, Beijing, China. [2]. Earthquake Engineering Research Institute, El-Asnam, Algeria Earthquake of October 10, 1980: A Reconnaissance and Engineering Report, Report No. CETS CND-022, January 1983. [3]. Sugano, S., Seismic Design codes II, International Institute of Seismology and Earthquake Engineering (IISEE), Building Research Institute (BRI), IISEE Lecture Note 2009-2010, March 2010. [4]. RPA99 Rev. 2003 Algerian seismic Regulation, Ministry of Housing and Urban-Planing, January 2004. [5]. RPA99 Algerian seismic Regulation, Ministry of Housing and Urban-Planing, January 2000. [6]. RPA88 Algerian seismic Regulation, Ministry of Housing and Urban-Planing, January 1989. [7]. RPA81 Rev. 83 Algerian seismic Regulation, Ministry of Housing and Urban-Planing, January 1984. [8]. European Committee for Standardization. prEN 1998-1-1:2003. Eurocode 8, Design of Concrete Structures, Part 1: General Rules and Rules for Buildings. Revised final draft, Brussels, Belgium, December 2003.

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