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  • REINFORCED CONCRETE FRAMED STRUCTURES: NUMERICAL VALIDATION OF TWO PHYSICAL MODELS CAPABLE TO CONSIDER THE STIFFNESS CONTRIBUTION OF INFILL PANELS ON FRAMED STRUCTURES IN OPERATIVE CONDITIONS

    The present work proposes two different models to estimate, with adequate approximation, the stiffening contribution of an infill panel for low stress levels (elastic phase). The need for such models arose from a comparison previously carried out by some authors between the fundamental period values calculated with the formulation of the NTC 2008 and those obtained experimentally through a dynamic identification campaign on ambient noise conducted with reinforced concrete framed structures. After defining the problem, the study proceeds with the description of the various phases of the infill panel behaviour for various levels of action in the plane and then discusses the major numerical modelling techniques of the infill panel currently available. Based on considerations deduced from the analysis of various bibliographic contributions, the proposed calculation models are tested against experimental results obtained from various studies.

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  • NUMERICAL STUDY OF CFT COLUMNS UNDER AXIAL, ECCENTRIC AND LATERAL CYCLIC LOADING

    This paper presents a numerical study of the various steel tube sections of Concrete Filled steel Tube (CFT) columns under axial, eccentric and lateral cyclic loading based on the Ansys standard solver. The feasibility and accuracy of the numerical method was verified by comparing the numerical results with the experimental observations. Because of inconvenient performance of traditional CFT columns, new steel wall sections proposed in the current study to improve the strength and hysteresis behavior of these columns. For this purpose, eight CFT samples, including two polygons soffit sections, two polygons extrados sections, square section, circular section, circular section with reinforced bars, and octagon section with stiffeners proposed for the analyses. The results of analyses indicate the increase in strength and ductility of the suggested sections in comparison with traditional ones and they can be used in the seismic region and practical engineering applications.

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  • DIRECTIONALITY MODELS FROM GROUND MOTIONS OF ITALY

    Directionality effects on the expected strong ground motion in Italy are investigated. After a brief description of the directionality effect and the intensity measures involved, a wide Italian database of strong ground motion records is used, with a total of 949 horizontal accelerograms (two components). The analysis is performed for 5% damped response spectra in the 0.01–4 s period range. Rotation-independent intensity measures, resulting from combining maximum values of the as-recorded accelerograms, are investigated. The study has also been performed using maximum values of the time histories resulting from the previous combination of as-recorded time histories. Ratios between these rotation-independent intensity measures and those formerly used in ground motion predictive equations have been computed and modelled by means of a simple theoretical model. Thus, the results are useful for updating former strong ground motion predictive equations in a simple and straightforward way.

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  • SEISMIC ASSESSMENT OF IRREGULAR EXISTING BUILDING: APPRAISAL OF THE INFLUENCE OF COMPRESSIVE STRENGTH VARIATION BY MEANS OF NONLINEAR CONVENTIONAL AND MULTIMODAL STATIC ANALYSIS

    The paper presents a research study concerning some critical issues related to the seismic modelling and analysis of typical existing RC buildings in Southern Italy. When speaking of existing buildings, first important issue is represented by the reliable appraisal of the parameters involved in the structural modelling, such as the concrete mechanical strength. It is evident that a correct assessment is crucial for obtaining an effective structural model in the elastic and inelastic field. Another key point is the choice of the proper method of analysis, since in some cases the standard methods proposed by European Codes are not effective in order to evaluate the structural behaviour of existing buildings. In order to investigate the effects of these aspects on the structural response, extensive comparisons have been performed on different structural models, obtained by properly varying the concrete strength value and by considering also a possible inhomogeneous distribution of the concrete class at different floors. Considering the specific framework of irregular buildings, analyses and consequent discussions have been performed by comparing conventional and multimodal pushover analyses and nonlinear incremental dynamic analyses.

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  • FRACTURES DETECTION IN MASONRY CONSTRUCTIONS UNDER HORIZONTAL SEISMIC FORCES

    The investigation of masonry structures behaviour, considered as Normal Rigid No-Tension material (NRNT) and subjected to loads and settlements, is the principal purpose of the present work. The equilibrated solution is a minimum of the energy and, adopting piecewise-rigid (PR) displacement, a minimization strategy procedure is proposed. Some cases will be analysed to illustrate the numerical performances of the PR approach, pointing out the subdivision into macro-blocks arises naturally in solving these minimization problems, and that the subdivisions into macro-blocks predicted by the proposed approximation procedure, are in good agreement with the ones expected and seen in real masonry structures. In particular two applications on masonry panels with irregular openings are exposed simulating the effect of an earthquake, so that variable horizontal forces are applied to the floor levels. The examples shown that the PR strategy appears efficient in reproducing both the location of cracks and the horizontal collapse load multipliers as well as the related collapse mechanisms.

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  • INFLUENCE OF EC8 RULES ON P-DELTA EFFECTS ON THE DESIGN AND RESPONSE OF STEEL MRF

    The seismic design of steel moment resisting frames (MRFs) according to EC8 is largely influenced by the lateral stability checks. North American codes (e.g. ASCE7) impose different rules to verify the sensitivity of the structures to P-Delta effects. In this manuscript, both current EC8 and ASCE7 rules are compared against a possible alternative. The relevant implications on the design and performance of frames are also investigated by means of static and dynamic nonlinear analyses. The obtained results show that the rules given by EN1998-1-1 lead to overdesigned MRFs as respect to the structures designed according to ASCE7. The structures designed according to the recent modified version of the EN1998-1-1 gives solutions closer to North American codes

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  • MATERIAL DAMPING EVALUATION IN A TYPICAL CONCRETE GRAVITY DAM

    In the present paper, a new numerical approach here named as Developed Energy Dissipation Algorithm (DEDA), which is based upon finite element analysis is utilized for evaluating the material damping ratio and Rayleigh damping coefficients in the dynamic time history analysis of an existing concrete gravity dam. In this approach, damping ratio takes a function of unit dissipation energy, which is also a function of stress amplitude. An iterative process is used to update the damping ratio in every time step of analysis. For the numerical example, the Pine Flat concrete gravity dam under Taft ground motion is selected. The dam crest displacement of the DEDA approach is compared with the so-called computer program EAGD-84 and the results show good agreements. Comparing the results of the DEDA approach with the Traditional Rayleigh Damping Method (TRDM) gives the reasonable value, which agrees with the field tests.

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  • STUDY ON SEISMIC BEHAVIOR OF ANGLE STEEL CONNECTION JOINTS FOR CONCRETE-FILLED SQUARE STEEL TUBULAR COLUMN

    This paper presents a study on a new solution of steel-beam to CFST-column joint. The proposed solution could save space, avoid being cut off columns and have little influence on core concrete casting. Three specimens were tested. The hysteretic behavior of the joints was studied by tests and numerical analysis. The ductility and classification of the proposed joint were assessed. The analysis results showed that the failure mode of three specimens was the stiffener buckling and the tear of welding seams. Increasing angle thickness would increase the bearing capacity and initial stiffness of the joints, but decrease the rotation capacity of the joints. Increasing the angle length ratio could improve the seismic behavior of the joints. The rotation capacity of the joints could meet the requirements of seismic design and ductility design. According to two different classification systems, the proposed joint belongs to semi-rigid joint and exhibits good ductility.

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  • Special Issues
  • Number 2 – 2018 Complete

    DESIGN AND ASSESSMENT OF STEEL STRUCTURES
    IN SEISMIC AREAS: OUTCOMES OF THE LAST ITALIAN
    CONFERENCE OF STEEL STRUCTURES

    Elide Nastri

    Department of Civil Engineering, University of Salerno, Fisciano (SA), Italy

    Editorial

    The use of steel for seismic resistant structures is a hot-topic of seismic engineering. During the last Italian Conference of Steel Structures – CTA 2017, held in Venice, the largest part of  the conference proceedings was focused on seismic issues regarding the design and evaluation of seismic performances in new buildings and the use of steel for the retrofit of existing buildings. The use of steel in seismic areas is not new as testified by many patents starting from the first decades of the Italian Kingdom [Cocco, 2018]. In fact, as it is known, steel construction in seismic areas provides many advantages as the weight reduction with a consequent reduction in seismic actions demand. In addition, steel members are usually able to develop wide and stable hysteresis loops under seismic loadings, thus affecting the global ductility of buildings [Mitsui et al., 2018]. For this reason, the need to accurately model the actual cyclic behaviour of steel member by means of simplified model becomes an urgent need. In particular, recent research efforts have been devoted to the modelling of degradation phenomena and pinching effects affecting the ultimate behaviour of dissipative zones and the overall seismic response of the structure [Giordano et al., 2017; Chisari et al., 2017]. In particular, moment resisting frames behavior under seismic loadings can be strongly affected by the degradation phenomena occurring in dissipative zones [Bernuzzi et al., 2018; Montuori et al., 2016a; Dell’Aglio et al., 2017; Ferraioli et al., 2016; Ferraioli et al. 2018a; Ferraioli et al., 2018b]. Moment Resisting Frames are usually cheaper than other steel typologies and assures an adequate seismic dissipation, provided that, connections are appropriately detailed and able to support the required strength and behaving as rigid connections [Tartaglia et al., 2018; D’Aniello et al., 2017; Tenchini et al., 2018; Pecce, 2016]. However, Moment Resisting Frames could not be used for high-rise buildings because of their high deformability for which braced frames or dual systems are preferred [Bosco et al., 2016; Faggiano et al., 2016; Costanzo et al., 2016; Montuori et al. 2016b; Montuori et al. 2016c; Montuori et al. 2017b; Costanzo et al. 2017; Costanzo et al., 2018; Mastrandrea et al., 2013]. In the last years, also cold formed profiles are getting head in the seismic field, used not only as a system for the strengthening and retrofitting of existing buildings [De Matteis et al., 2016; Castaldo et al., 2016; Totter et al., 2018; Formisano et al.; 2016] or for pallet racks [Gabbianelli et al., 2016] but also as the main structural system of new buildings, showing very small interstorey drift [Campiche et al. 2018] or as an innovative bracing system [De Matteis et al., 2018]. Other research fields regard the use of dissipative devices in place of traditional dissipative zones such as beam ends for moment resting frames or link for eccentrically braced frames [Lemos et al. 2018; Latour et al. 2018; Titirla et al., 2017; Fabbrocino et al., 2016]. The use of these devices, properly located in points where the high displacement demand is expected allow the structure to remain in service also after the seismic event and an adequate reparability, benefit the maintenance costs. From the other side, the use of base seismic isolation remains a useful strategy to limit the plastic excursion and, as a consequence, the structural damage [Avossa et al., 2017; Castaldo et al., 2016b]. The finish line is now the design and construction of buildings able not only to assure an adequate level of dissipation and reparability but also the chance to control the residual drift after both the single seismic event and seismic sequences.

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