Month: September 2018

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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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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 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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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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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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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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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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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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