Concrete technology and durability design - Cowi

4Durability andservice life designVillamar at the Harbour Development Project, BahrainCOWI’s durability design services• Assistance in defining the owner’sservice life requirement, e.g. endof design life, level of reliability andfrequency of maintenance• Elaboration and evaluation ofdifferent durability design optionsincluding appropriate structuraldetailing• Assessment of macro and microexposure conditions• Modelling of deteriorationmechanisms for materials andenvironmental actions• Service life modelling and designusing the DuraCrete approach• Development of appropriatespecifications for materials throughdurability modelling• Conversion of specificationsto concrete mix designs andcompliance testing• Back analysis of service life uponcompletion of construction• Quality assurance programmes• Life cycle costing• The Birth CertificateProbabilistic service life designNowadays, civil engineering structures,such as bridges, tunnels, marinestructures and other infrastructureprojects, are designed for aservice life of 100, 120 or even 200years. This surpasses the assumeddesign service life of most codes andstandards substantially.The operational approach to designfor durability is to define durabilityas a service life requirement.In this way, the non-factual andrather subjective concept of ‘durability’is transformed into a factualrequirement of a number of yearsduring which the structure performssatisfactorily without unforeseenhigh costs for maintenance. In thisway, the time factor is introduced asa design parameter. Service life designbased on these functional requirementsis carried out in a similarway to the load and resistance factordesign concept used for structuraldesign.COWI’s leading position within durabilitydesign is based on morethan 40 years of worldwide experiencein design, operation and maintenanceof reinforced concrete structures.COWI, spearheading the internationaldevelopment of rational servicelife designs, provides a modernfully probabilistic design methodologyfor durable concrete structures,i.e. the DuraCrete approach. COWIimplements this state-of-the-art approachin new designs and in the reevaluationof existing structures. Ithas been adopted by national authoritiesand individual clients allover the world as well as by internationalassociations, e.g. fib.The DuraCrete approach can effectivelycombat chloride and carbonationinduced reinforcementcorrosion. All uncertainties regardingenvironmental exposure, materialproperties and deterioration aretaken into account.AssumptionsTerms of definitionsOther administrative provisionsPrinciples of service lifeDesign criteriaFull probabilisticapproachProbabilistic models:- Resistances- Load/exposure- GeometryPartial factor designDesign values:- Characteristic values- Partial safety factors- Combination factorsLimit states Design equations Design provisions Design provisionsDesign/verificationsProject specification for material selection and executionMaintenance planInspection/monitoring planQuality plan for execution(optional)Deemed to satisfy designExposure classesAvoidance ofdeteriorationExposure classesIn case of non-confirmity with the performance criteria, thestructure becomes either obsolete or subject to a redesignService life design flow chartafter fib: “Model Code forService Life Design”MaintenanceInspection of executionCondition control during service life