new Morocco SEISMIC DESIGN - Europaelsa.jrc.ec.europa.eu/eurocodes2006/pdf/pres240.pdf · EUROCODES Workshop - 27-29 November 2006, Varese, Italy Building the Future in the Euro-Mediterranean

EUROCODES

Workshop - 27-29 November 2006, Varese, Italy

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The seismic design code for buildings:A priority for seismic risk reduction in Morocco

Prof. Khalid EL HARROUNI

Ecole Nationale d’Architecture, BP 6372, Rabat Instituts, Morocco

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Vue aérienne du Ksar Ait Ben Haddou

Seismic zones: Acceleration coefficient A(g)0.01 for zone 10.08 for zone 2 0.16 for zone 3

Morocco is exposed to a number of natural hazards such as earthquakes, but the regulatory framework for risk management has not been yet fully established.

Recent even (the earthquake of February 2004, Al Hoceima in the northern region) demonstrated the lack of preparedness of the country to cope with natural disasters. This earthquake was however the occasion for strengthening the efforts to apply the national building code requirements for earthquakes (RPS2000), to create a new approach to civil protection and the recent creation of the National Committee of Earthquake Engineering.

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Agadir Earthquake, 1960

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Al Hoceima Earthquake, 2004

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Which are the different structures concerned by the Code?It concerns buildings with reinforced concrete or steel specific structures:

• rigid frame structure (beams – columns structure)• Wall bearing structure• Mixed structure

ANTISEISMIC BUILDING CODE IN MOROCCO (RPS2000)

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When the Code is used ?

• For New constructions• For great modifications of existing buildings • Not for bridges and dams• Not for industrial buildings such as nuclear and electric units and • Not for buildings realized by materials or systems not stipulated by

the standards

ANTISEISMIC BUILDING CODE IN MOROCCO (RPS2000)

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Building the Future Application of the RPS 2000:

Did RPS 2000 contribute to the development of construction in the sector of the Buildings and civil engineering in Morocco?

Is it applied by the whole of the building actors?

Which are the difficulties encountered at the time of its application?

What has been done to overcome the difficulties?

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After 5 years of existence, the RPS 2000 does not seem to achieve all the goals initially discounted at the time of its creation.

Actually, the engineers, architects and Engineering Offices which apply this code correctly are very few.

The Engineering Offices were not prepared with the application of this law and the computational tools were not standardized.

72% of the building owners decline the use of the code

55% of the technical studies and engineering offices apply it only occasionally or at all.

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50% of the Engineering Offices have never made antiseismic calculations, 98% cannot do it and only 2% are able to do it.

The problem of application of the RPS 2000 is a mentality problem, a professional engagement problem, but also the difficulties of application and comprehension.

77% of the Engineering Offices do not overcome the difficulties or are not satisfied for given solutions.

46 to 59% bind these difficulties to the incomprehension of the seismic parameters and the classification of the site and the buildings.

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The code RPS 2000 will be improved in 2007

Problem of training and formation:

The State plays the part of catalyst and architects, engineers, engineering offices and control should organize training courses, diffusion and dissemination.

We must answer the engineers and architects questions in order to eliminate all the difficulties which can block the application. It is also necessary to learn from the seism of Al Hoceima and other codes to improve the code RPS 2000.

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Some General Considerations Regarding the Anti-Seismic Design

ByProf. Driss BEN SARI

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Case of tall buildings

The technical provisions resulting in a safe economical anti-seismic structure aim at :

• Decreasing the seismic loach by given nominal acceleration. This require as light as possible structure in its upper parts.The structure should also be as « soft » as possible (seismic response is roughly proportional to its fundamental frequency).

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The center of gravity be as close as possible to the torsional center for minimizing the torsional effects.

• Increasing the strength of the structure in order to offer a better resistance to seismic forces.

• Ensuring that the structure does not collapse suddenly if the intensity of the earthquake exceed the design value.

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Favorable effects of ductile behavior are obtained by designing multiframed structures which dissipate a large quantity of energy through plastic flexural strain.Requirements for a structure to be more flexible and more ductile on one hand and more resistant on the other hand are to a large extent contradictor. The designer has to look for the most suitable compromise in terms of quality and economy.

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• For an apartment building (or hotels) heavy partition are required for soundproofing.

• The overall weight of the structure will increase if these partitions are required for soundproofing.

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Tentative design of a monolithic structure

The calculations made as indicated above a monolithic structure showed natural frequencies of 0.98Hz in the E-W direction and 0.54Hz in the N-S direction.Actually, such a monolithic structure presents several drawbacks since it is :

• Heavy• Stiff due to a slenderness ratio that is exceptionally low for

a high-rise building

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• Without any symmetry owing to the architectural choices made

• A structure with a poor elastic ratio due to the triangular cross section.Thus, seismic loads would govern the design of a monolithic structure and would raise construction costs considerably.

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Advantages of anti-seismic bearings

The advantages of such devices are :• A considerable reduction in the seismic loads due to lower

natural frequencies.• An equivalent reduction of shear forces and corresponding

bending moments in transverse lintels allowing lower reinforcement ratios.

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• A reduction of maximum bearing pressure of the raft on the foundation soil and elimination of uplift.

• The improvement of ultimate ductility since the neoprene distortion rate remains much lower than the allowable maximum.

• The possibility to keep the sidewalls unchanged.

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These advantages greatly surpass by far the drawbacks which are :

• The cost of the bearing themselves• The need for a large expansion joint all around the first floor

of the tower• The increase in the horizontal displacement of the tower

under wind loads.

Source : A. Coin in Recent advances in Earthquake engineering and structural dynamics

Documents

new Morocco SEISMIC DESIGN - Europaelsa.jrc.ec.europa.eu/eurocodes2006/pdf/pres240.pdf · EUROCODES Workshop - 27-29 November 2006, Varese, Italy Building the Future in the Euro-Mediterranean