GNGTS 2021 - Atti del 39° Convegno Nazionale

371 GNGTS 2021 S essione 2.2 ON THE SEISMIC RELIABILITY OF CODE-COMPLIANT REINFORCED CONCRETE BUILDINGS IN ITALY M.A. Zanini 1* , L. Hofer 1 , F. Faleschini, P. Gardoni 2 1 Dipartimento di Ingegneria Civile, Edile e Ambientale, Università degli Studi di Padova, Padova, Italia 2 Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, USA Introduction Current building codes require structural engineers to design new earthquake-resistant structures able to offer an adequate horizontal capacity with respect to a set of predefined performance levels. However, the sized code-compliant buildings, once assessed, may not show a controlled probability of failure, even if the design ground-shaking intensities are probabilistically defined, as inmany codes currently in force worldwide (Bradley 2011; Faleschini et al. 2019). In other terms, the use of semi-probabilistic approaches for the seismic design of new buildings is not able to explicitly control the resulting seismic reliability. Code compliance and seismic performance are in fact strictly coupled by a strong underlying relationship, and a modern code must be able to indicate simple and effective prescriptions that can implicitly be reflected in the fulfillment of target performance levels defined a priori. For these reasons, this paper focuses on a more in-depth seismic reliability assessment of code-compliant RC bare and masonry-infilled archetypes to analyze the underlying relationship between seismic design accelerations and resulting performance in terms of seismic failure rates, and to compute the Italian seismic reliability maps of such building types. Different configurations are considered in terms of the number of stories (i.e. 3-, 6- and 9- stories) as well as assumed design ductility classes (e.g. high (DCH) and medium (DCM) ductility class). Buildings are automatically designed and later assessed with the use of a prototype software described in detail in Zanini and Feltrin (2021). Prototype seismic design and assessment software This section presents a brief description of the prototype seismic design-assessment software used for sizing and subsequently assess the archetype structures. First, the user has to specify materials to be considered, main geometrical features of the archetype RC frame, class of use to derive design accidental loads, and desirable ductility class (i.e. select the behavior factor q). The software then designs the beams’ sections and reinforcements with an iterative loop, then sizes the columns to fulfill a correct capacity design (i.e. ensuring strong column-weak beam criterion). Once designed, the code-compliant frame is assessed with respect to relevant performance levels to quantify related fragility curves. To do this, the capacity curve is first derived by means of a pushover analysis on a non-linear model that uses a lumped plasticity modeling technique with plastic hinges calibrated via a fiber-cross section discretization modeling strategy with the joint adoption of suitable non-linear stress-strain material laws. Masonry infills are accounted only for the infilled configurations to capture the increment in the stiffness on the overall seismic response. Given the large computational burden, frames are idealized as Single Degree of Freedom Systems (SDOFs), with hysteretic behavior calibrated based on the idealized tri-linear capacity curve. NLTHAs are later performed to obtain samples of the non-linear seismic behavior to be post-processed with the Cloud Analysis method (Cornell et al. 2002) to obtain fragility curves. In detail, SDOF systems are subject to a limited set of n unscaled ground motion records and the fragility curve takes origin from the sample of n ground motion intensities and the