Theory and design of Structures

EBCS EN 1998:2015 divides ETHIOPIA INTO 5 SESMIC ZONES. ZONE 1 BEING ZONE WITH ZERO GROUND ACCLERATION, WHILE ZONE 5 BEING REGIONS WITH SESMIC GROUND ACCLERATION OF ABOUT 20 PERCENT OF GRAVITY. @theoryanddesignofstructures

The practice this days is to use DCM for REGIONS such as Addis Ababa and DCL for REGIONS such as hummera and others with a very low seismic event occurance probability. @theoryanddesignofstructures

DCH OR HIGH CLASS DUCTILITY STRUCTURES ARE FAVORED IF A STRUCTURE IS EXPECTED TO PERFORM IN AN EXCELLENT MANNER DURING A SESMIC EVENT. IT IS THE MOST COSTLY DUCTILITY CLASSES AND HAVE A MORE STRINGENT CONTROL OVER HOW A STRUCTURE SHOULD BE DETAILED TO PERFORM WELL. THIS CLASS HAS THE ADVANTAGE OF A VERY HIGH BEHAVIOR FACTOR WHICH IS FOLLOWED BY A VERY STRINGENT DETAILING REQUIREMENTS. @theoryanddesignofstructures

DCM , MEDIUM CLASS DUTILITY, WHICH MOST DESIGNERS FAVOR FOR ITS EASE ON DETAILING REQUIREMENTS THAN DCH, PROMOTES A HIGHER BEHAVIOR FACTOR WITH A MORE STRICT REQUIREMENTS ON DETAILING OF STRUCTURAL MEMBERS. WITH DCM A MORE RELIABLE STRUCTURE CAN BE DESIGNED AT THE COST OF MORE REINFORCEMENT ( with appropriate DETAILING) AND LARGER COLUMN CROSS SECTION. IF A DESIGNER CHOSES TO USE DCM , THEN A SERIES OF CHECKS NEED TO BE MADE ON THE STRUCTURE TO SEE IF IT FULLFILLES ALL THE REQUIREMENTS OF THE CODE. @theoryanddesignofstructures

EBCS EN 1998:2015 SPECIFIES THREE DUCTILITY CLASSES WITH DIFFERENT LEVEL OF EXPECTATION ON THE PERFORMANCE OF THE STRUCTURE. DCL, DCM AND DCH ARE THE DUCTILITY CLASSES THAT THE CODE SPECIFIES. DCL IS LOW CLASS DUCTILITY WHICH THE CODE RECOMMENDS FOR REGIONS WITH LOW OR NO SESMIC EVENT. THIS DUCTILITY CLASSES HAS LESS STRINGENT CONTROL ON DETAILING OF STRCTURAL MEMBERS AND COMPENSATES THIS WITH VERY LOW BEHAVIOR FACTOR,I.E, MORE SESMIC LOAD. @theoryanddesignofstructures

COLLAPSE prevention is achieved through CAPACITY OR OVERDESIGN of structural members. CAPACITY DESIGN IS PERFORMED ON STRUCTURAL ELEMENTS WITH THE SOLE GOAL OF PREVENTING BRITTLE FAILURE MODE OF STRUCTURES GLOBALLY OR LOCALLY. GLOBAL DUCTILITY IS ACHIVED BY MAKING FRAME SYSTEMS TO HAVE STRONG COLUMNS and WEAK BEAMS. LOCAL DUCTILITY IS ACHIEVED THROUGH PREVENTING SHEAR TYPE OF FAILURE MODE. TO DO SO MEMBERS ARE INTENTIONALLY DESIGNED TO FAIL IN FLEXURE DURING SESMIC EVENT. FROM THE WHOLE MEMBER A SPECIFIC REGION IS SELECTED TO ABSORB SESMIC ENERGY, DISSIPATE IT AND FAIL IN A DUTILE FAILURE MODE. THIS REGION IS CALLED CRITICAL REGION @theoryanddesignofstructures

DAMAGE LIMITATION is achieved through limiting the drift that the structure undergoes during a frequent seismic event. This LIMITATION is achieved through a stiffer structural system. @theoryanddesignofstructures

EBCS EN 1998:2015 THE NEW ETHIOPIAN CODE FOR SESMIC DESIGN OF STRUCTURES THE GOAL OF EBCS EN 1998:2015 IS DAMAGE LIMITATION DURING FREQUENT SESMIC EVENT AND COLLAPSE PREVANTION DURING A MAJOR OR DESIGN SESMIC EVENT @theoryanddesignofstructures

This values are based on ACI code. Although they are very conservative, it is better to use the recommendation from the new code. @theoryanddesignofstructures

This is how the stiffness modifiers would be given to ETABS as an input based on the above article( ES EN 1998:2015 ARTICLE 4.3.1[7]). @theoryanddesignofstructures

ES EN 1998:2015, ARTICLE 4.3.1, SUB ARTICLE 7 👉 unless a more accurate analysis of the cracked elements is performed, the ELASTIC FLEXURAL AND SHEAR STIFNESS properties of concrete and masonry elements may be taken to be equal to ONE-HALF of the corresponding stiffness of the uncracked elements. @theoryanddesignofstructures

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👆 The theoretical aspects of cover based on ES EN 1992:2015 are discussed here.