Month: June 2017

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The introduction of high energy dissipation in base-isolated structures is often prescribed to minimize the device displacements as well as the effects of near-field earthquakes. The identification of effects on the superstructure due to the high energy dissipation is, therefore, an important aspect of the base-isolated structure design. In this study, the seismic response of base-isolated structures with Lead Rubber Bearing (LRB) devices is estimated aiming at the evaluation of the adverse effect of damping on the structural response parameters. Four base-isolated structures are considered taking into account a complete damping matrix. Their structural seismic response evaluation is first performed using nonlinear response history analysis (NRHA) by considering a bilinear device behaviour. The increase in the superstructure response parameters is detected. A structural analysis by considering an equivalent linear viscoelastic LRB behaviour was also performed. A frequency domain method through transmissibility was applied to explain the influence of isolation damping on the higher mode effects and inter-storey drift ratios. The comparison between the NRHA results and response spectrum analysis (RSA) results highlights meaningful differences between the values of some structural response parameters (displacements of the isolation system and inter-storey drift ratio). A seismic analysis of baseisolated structures with High Damping Rubber Bearing (HDRB) and supplemental linear viscous damping (VD) devices is also carried out. The results point out that the use of HDRB devices with linear viscous dampers, as compared to LRB devices, lead to a reduction of the devices displacements and to a beneficial or least detrimental effects on the superstructure response parameters in base-isolated structures.

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In this work, through analyzing the effects of large deformation, lining damage and collapses, which happen frequently in the soft rock tunnels in the Guang-Gan Expressway, the characteristics and causes of the geological disasters for the soft-rock tunnels are investigated. The results show that the large deformation and collapses occur near the vault and tunnel face. The poor mechanical properties and weak self-bearing capacity of the surrounding rock and the softening caused by the groundwater are important factors for the disasters. The lack of experience in design and construction in the meizoseismal area and the aftershocks are other important factors. The field test indicates that three benches and the reserved core soil construction method should be applied to control the stability of the broken phyllite tunnels, and the key technology should be strictly controlled during the construction. In particular, increasing the stiffness of the supporting structure and enclosingof theliningin timeare efficient methods to control the large deformation and collapses in crushing soft-rock tunnels in the meizoseismal areas.

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In order to meet the requirements of maintaining the original condition of rock faces, avoiding the heavy excavation to protect the ground environment, and reducing support cost of large-span shallow buried cavern, a new supporting method of shallow- buried caverns was proposed in this paper. Such a supporting method was successfully applied to the underground cavern project. For this project, some crisscross small tunnel sheds were embedded in the overburden layer. As a result, the interaction between the surrounding rock and supporting structure can play a significant role in the constructed supporting system, and the surrounding rock can display its self load-bearing capacity in the shallow buried cavern.

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In the last decades many strategies for seismic vulnerability mitigation of structures have been developed through analytical studies and experimental tests. Among these, energy dissipation by external devices assumes a great relevance for the relative design simplicity, even if applied to complex structures, and the effectiveness in reducing seismic demand. In particular, the use of fluid viscous dampers represents a very attractive solution because of their velocity-dependent behaviour and relatively low costs. The application on structures requires specific study under seismic excitation and a particular care of structural details. In this context the use of proper constitutive models for the dampers assumes a fundamental role. Seismic codes, as well as literature models generally provide a velocity-dependent relationship with two characteristic constants defining the shape of the force-displacement curve. In this paper an experimental campaign aimed at the determination of the damper constants in the range of low velocities is presented. A fluid viscous damper is tested with different ramp velocity functions. Results show that the assumption of velocity independence of the damper constants fails for the case of low velocity, giving rise to new issues about the limit of validity of the constitutive models generally adopted for viscous dampers.

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In the last twenty years, the field of earthquake engineering experienced a noticeable improvement. The results of experimental and theoretical researches have contributed to the development of modern technical codes, which provide innovative solutions for the structural assessment and new design approaches. Despite this large amount of improvements, several open questions are still open, and the need for large scale testing has been deeply proved and discussed. A new research facility, namely the Laboratory of Earthquake engineering and Dynamic Analysis (LEDA), has been recently completed at the University of Enna “Kore”. This research centre, funded with a grant from Italian Ministry of Education, University and Research, includes several laboratories operating in the fields of structural engineering and dynamics. The most attractive features of LEDA are the wide range of tests that can be performed and the simultaneous presence of a high capacity strong floor – reaction wall system and of two six-degrees-of-freedom shaking tables, so that the complementarity of both traditional techniques (pseudo-dynamic and dynamic tests) can be fully exploited and advanced hybrid testing method can be explored. In this paper the features of the main research facilities in LEDA are briefly presented. Furthermore, the design procedures of the reaction structure, built in order to perform large scale static and pseudo-dynamic testing, are described and discussed.

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The objective of this research is to investigate the seismic performance of typical confined masonry (CM) walls under acidic atmospheric environment and to then present a hysteretic model precise, which is capable of simulating seismic performance of CM walls under acid corrosion. Hence, quasi-static tests of six CM walls were performed, which were corroded by artificial climate accelerated corrosion testing techniques. By obtaining the damage process and characteristics, the influence of different corrosion cycles on displacement-load hysteretic curve, skeleton curve, stiffness degradation and energy dissipation capacity were extensively studied. Moreover, the degradation law of specimen mechanical properties were also obtained. The cycle degradation indices was proposed based on energy dissipation, which were used to characterize the degradation law of specimen mechanical properties. Subsequently, the hysteretic model of CM walls was established, where the specific hysteretic rule was also obtained. The results demonstrated that the ultimate bearing capacity, initial stiffness and energy dissipation capacity of the specimen could all gradually decrease with the increase in the number of corrosion cycles, where the decay rate of the stiffness would gradually increase. The proposed hysteretic model can desirably reflect the hysteretic characteristics of CM walls with reversed loading in an acidic atmospheric environment.

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This study concerns the mechanical response of an innovative energy dissipation device. Using this device, beam–column frames can be easily and safely strengthened at many predefined levels according to the seismic load demands of technical standards. The energy dissipation mechanism of the superimposed blades functions via both steel yielding and frictional forces between the blades. The streghtening level can easily be adjusted by the appropriate selection of the number and dimensions of the superimposed blades, their elastoplastic properties, as well as the friction coefficient at their interface. The device was fabricated and investigated both analytically and experimentally under cyclic loading conditions. The analytical model was based on an analytical hysteresis model. The obtained results describe the overall mechanical behavior of the device.

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