SEISMIC PERFORMANCE ASSESSMENT OF RC BUILDINGS ACCOUNTING FOR STRUCTURAL AND NON-STRUCTURAL ELEMENTS
Creators: name: De Risi, Maria Teresa
Publisher: name: Università degli Studi di Napoli Federico II
Year: 2015

description: Among the natural hazards, earthquakes are paramount due to their impact on civil structures worldwide. The considerable direct economic losses (property losses) due to earthquakes in conjunction with social impact and indirect economic losses have prompted a great interest in performance assessment of the civil structures to future seismic events. Therefore, performance evaluations beyond the traditional goal of life safety, are required to rightly estimate expected losses. A key ingredient of this evaluation process is the fragility, that describes the probability of failure to meet a performance objective depending on demand on the system, providing the link between seismic hazard and building losses estimation.
A correct fragility evaluation necessitates the development of reliable nonlinear analysis models that are able to simulate the behavior of structures from the onset of damage through collapse. Therefore, proper prediction of the nonlinear behavior and formulation of analytical models are essential prerequisites for a reliable evaluation of structural fragility and, then, of seismic performance and risk assessment of Reinforced Concrete (RC) structures. Moreover, within the performance-based approach, it is also essential to understand which mechanisms/elements have the higher influence on seismic performance depending on the analyzed performance level.
A lot of work should still be done towards this direction, especially for existing under-designed or non-ductile structures. With under-designed or non-ductile terms it will be referred to structures designed for gravity loads only or according to obsolete seismic and technical codes.
A contribution towards this direction is carried out in this work. 
Starting from the analysis of typical deficiencies of non-ductile RC frames and the definition of performance levels of interest, this work aimed to contribute to PBEE framework with (i) a critical overview on analysis methodologies and modeling approaches of the salient components of RC frames, namely flexural or shear-dominated beams and columns, and more in detail, beam-column joints and masonry infills, the core of this work, and (ii) with new proposals in terms of nonlinear modeling and analysis procedures to provide a more reliable evaluation of seismic performance and risk assessment of infilled RC structures, accounting for structural and non-structural (in particular masonry infills) elements at different performance levels.
For these purposes, existing analytical modeling techniques for RC frames' critical components were first reviewed and discussed. Then, a deep investigation on the influence of infills on seismic performance at different limit states, also for new constructions, has been carried out, in order to highlight the critical points that can interest also this kind of structures regarding infill presence.
The effect of infills on the global seismic behavior of RC frames was investigated, by analyzing their influence on global stiffness and strength, on the kind of collapse mechanism, on the displacement capacity and, consequently, on seismic capacity and seismic fragility at different performance levels, depending on the main characteristics of the RC frame, such as the design typology and the number of stories.
Recognized the importance of infills especially at lower seismic intensity and the widespread of linear analysis methodology among practitioner, new procedures are proposed as tools to better taking into account damage to infills also in linear analyses with or without the explicit modeling of infills in the numerical model. The attention has been focused both on the design of new constructions and the assessment of existing structures, providing a contribution towards desirable more comprehensive future code prescriptions at lower seismic intensity - that depend on mechanical properties of infills and proper displacement capacity thresholds - within the context of linear analyses.
From the point of view of the bare structure (without infills in the structural model) and in particular referring to higher intensity levels, proceeding from Damage Limitation (DL) LS towards Near Collapse (NC) LS, the analysis of RC frames different for design typology has highlighted the vulnerability points of such frames, already pointed out by experimental tests and past seismic events. In particular the influence of beam-column unreinforced joints is deeper investigated.
In literature there is not yet a commonly accepted approach for the determination of the shear strength and for nonlinear modeling of RC beam-column joints in moment resisting RC frames. In many studies, beam-column connections are modeled as rigid. However, many nonlinear joint models are available, but most of them may be unsuitable for modeling all sources of nonlinearity for the assessment of older concrete buildings. Some of them were developed and calibrated for confined beam-column joints or they are too complicated to implement.
On the basis of an extensive and critical review of previous experimental tests and existing joint modeling approaches, a new cyclic shear constitutive relationship is proposed for exterior unreinforced joints, different for failure typology, in order to describe nonlinear behavior of joint panels, to be used in conjunction with an explicit bond-slip spring, thus taking into account all sources of nonlinearity and different possible kinds of deficiencies.
Then, the influence of joint behavior on seismic performance at different performance levels, both in terms of strength and deformability contribution, also taking into account the record-to-record variability, was investigated in nonlinear dynamic analyses of under-designed frames.
Finally, after the investigation about the sensitivity of joint response to the main mechanical and geometrical properties of beam-column sub-assemblages, the results of two experimental tests are presented and discussed. The specimens have deformed bars and show different failure typology. These tests conducted under cyclic loading aim to improve the understanding of exterior joints seismic performance without transverse reinforcement in existing RC buildings. Experimental results are analyzed herein and compared with numerical results carried out through the adoption of the proposed numerical model.