The Implications of adopting Eurocodes for designing disaster resilient buildings in Sri Lanka

Abstract

Sri Lanka has prioritized designing disaster-resilient buildings and evaluating the degree of disaster-resilience of the existing buildings due to the challenges posed by natural and man-made hazards. This approach challenges the common practice of the Sri Lankan construction industry to use British Standards as its industrial standards. Since the British Standards had been replaced by Eurocodes, Sri Lanka has started using Eurocodes but without critically evaluating the effectiveness of Eurocodes and national annexes in designing buildings with disaster resilience features. Therefore, it is crucial to evaluate the structural vulnerability of buildings to gravity, wind, and seismic loads. To fulfill these timely needs, this study envisages to examine the effectiveness of Eurocodes and national annexes to design disaster-resilient buildings in Sri Lanka, assessing the degree of disaster resilience of the existing buildings, and examining cost implications. To this end, this study put forwards a novel framework to evaluate the structural resilience of code-compliant and non-code-compliant reinforced concrete buildings under extreme wind and seismic loads. The framework constitutes non-linear static pushover analysis for wind assessments, non-linear dynamic time-history analysis, incremental dynamic analysis, and fragility assessments for seismic evaluations. The framework was first applied to a typical office building before assessing a three-story school building, an eight-story university building, and a six-story hospital building, designed according to Eurocodes (EN1990. (2005), EN 1991-1-1. (2002), EN 1991-1-4. (2010), EN 1992-1-1. (2004), EN 1998- 1. (2013)) and Sri Lankan national annexes, as well as a seven-story mixed-use defective building and its retrofitted version. The results showed that the Eurocode- based building designs have a significantly larger base shear capacity than the base shear force triggered by a wind with a 1700-year return period, the highest return period considered for the wind performance evaluation. Although these buildings have reasonable structural resilience against extreme seismic loading, they do not meet the more stringent performance requirements, such as Fully Operational and Operational, in the seismic performance objectives. Therefore, Eurocode-based designs can sometimes fail to meet the performance objectives for structural resilience, even though these objectives are assumed to be implicitly satisfied by the design codes and standards. The analysis of the defective building confirmed the building’s inadequate capacity to carry gravity, wind, and seismic loads. The retrofitted building with structural jacketing had enhanced load carrying capacities, indicating the effectiveness of structural jacketing as a retrofitting measure for defective buildings in Sri Lanka. The comparison of material properties, partial safety factors, load combinations, and design methodologies of Eurocodes and British Standards for designing beams and columns revealed that British Standards generally require more reinforcement for a given section size, mainly due to more conservative partial safety factors in load combinations. However, the differences in section sizes and reinforcement requirements strongly depend on the building type and loading conditions, such as gravity loading alone or a combination of gravity and lateral loading.