Derivation of fragility curves at design stage through linear time-history analysis

•Simplified procedure for fragility curves through Linear Time-History Analysis.•Verification of LTHA-based fragilities through Nonlinear Time-History Analysis.•EC8-compliant 12-storey reinforced-concrete moment-resisting-frame case study.•Proposal of index allowing identification of unacceptable cases for LTHA design.•Sensitivity to ground motion suite size through bootstrap and robust fragility. The aim of this work is to open up new opportunities for designers towards a performance-based approach to derive fragilities at design stage. Nonlinear Time-History Analysis (NTHA) represents the current practice for the estimation of damage within the Performance-Based Earthquake Engineering (PBEE) framework. Among the NTHA approaches for fragility assessment, Cloud Analysis (CA) represents a convenient tool which allows evaluating the parameters of the conditional demand distribution based on simple regression of cloud-dispersed data points obtained from recorded ground motions. Notwithstanding the growth in computer processing power and software development, NTHA is generally time-consuming and it requires advanced expertise in nonlinear modelling, preventing its use in the professional field at design stage. Herein, a novel procedure for deriving fragility curves built up through Linear Time-History Analysis (LTHA) and CA is presented. It can be employed within a simplified PBEE approach at design stage for performance comparison of design solutions. Differences between LTHA results and those obtained through NTHA are compared for the assessment of a 12-storey Reinforced-Concrete Moment-Resisting-Frame building designed according to Eurocode 8. Assessment is performed for two limit states: Life Safety- and Damage Limitation- Limit State. Critical aspects for LTHA-based fragility assessment such as (i) influence of ground motion suite size and (ii) identification of “unacceptable cases” are investigated. The final level of approximation of these “design-fragilities” is very satisfactory making the full approach pursuable and useful for professional applications.