Month: June 2019

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Traditional shear walls are not suitable for current high-rise buildings. In this study, the performance of shear wall based on double-layer steel plate material was researched. Five sets of double-layer steel plate specimens were designed and tested with vertical seam, horizontal seam and shear span ratio as variables. Experimental phenomena and data were recorded for analysing the skeleton curve, strength, and stiffness degradation to understand the earthquake resistance. According to the experimental results, it could be found that the test pieces of the vertical and horizontal seams had higher strength and rigidity than other test pieces, and had better earthquake resistance. This study proves the seismic resistance of the double-layer steel shear wall through experiments and provides some theoretical support for its application in high-rise buildings.

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This  study  presents the  application of  different analytical and finite  element (FE)  models  aimed at  predicting  the  shear  resistance of reinforced concrete (RC) and reinforced concrete-encased steel joist (HRCESJ) beams with inclined transversal reinforcement in moment resisting frames (MRFs). In particular,  four  analytical  models  are  taken into account, two of  them  specifically  conceived  for  HRCESJ beams in seismic area. The analytical models considered are Eurocode-2 model for the shear strength of RC beams; a variable-inclination stress-field approach; a strut-and-tie additive model and, finally,  an  analytical  formulation  in  which  the  shear capacity depends on the number of pairs of inclined stirrups able to yield before concrete crushing. The models are validated against a large  experimental  and FE dataset covering a wide range of characteristic parameters of the beam typology. The results obtained are discussed  in  order  to stress the influence of different key assumptions adopted in both FE and analytical approaches.

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To investigate the progressive collapse behavior of steel moment frame with damper, a new-type mild damper consisting of cruciform steel plates is designed. The mechanical properties of the damper are validated through the theoretical calculation, previous tests and numerical analysis,  respectively  while  the  accuracy  of  model  structure  is  validated  with  different  FEM  software. Therewith,  the  studies  on the progressive collapse and seismic design of an in-plane model structure with new-type dampers are conducted. It is found that the progressive collapse resisting capacity of the structure is improved resorting to the damper. Better catenary action exists in the in-plane model structure with damper while the anti-seismic ability of structure becomes poor. Considering the spatial effect of structure, the optimization of damper arrangement is conducted for the seismic design. The results demonstrate that the dual action of damper, namely for the progressive collapse and seismic designs, could be guaranteed simultaneously in three-dimensional (3-D) structure. The  analysis  results in this  paper  provide a reference for the unified design of resisting the earthquake and vertical progressive collapse.

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In the moment in which Italy is crossed by several earthquakes  the  evaluation of seismic vulnerability  for existing buildings assumes a paramount  importance.  The  assessment  of  an  existing  building  must  be  preceded  by  an  investigative  phase  in  which  geometry, characteristics of structural elements, structural details, reinforcement ratio non-structural element must be known. An important role is also demanded to the modelling of the structures in plastic range, therefore, to perform  a  realistic  seismic  analysis  of  non-seismically detailed RC structures, it is important to have models to capture the hysteretic behaviour  of  beams, columns  and  joints.  The  problems being addressed in this paper regard the development of models for realistic assessment of seismic behaviour of non-seismically detailed R.C. frame structures with reference to beams, columns and joints. To this scope a R.C.  frame non-seismically detailed adopted as study case has been properly modelled and analysed by both non-linear static and dynamic analyses. A  critical  discussion  about  the optimal modelling of R.C. structures is also reported.

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The attention of the authors is focused on the study of low shape factor rubber blocks, having a low vertical stiffness. Firstly, the behaviour of natural rubber blocks is analysed when they are subjected only to an axial load, and then subjected to axial and shear combined action: in the first case, a model which takes into account the geometric non-linearity is considered, that  is  a  model  that  considers  the  shape  factor as a function of the current compressive strain; in the second case, the main issue is the influence of the axial load on the horizontal stiffness and on damping. For both cases, the analytical results are compared to the experimental ones.

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This paper deals with seismic reliability of nonlinear structural systems having an intermediate isolation degree  and  equipped with friction pendulum system (FPS) isolators, by adopting an equivalent inelastic two-degree-of-freedom model and considering  the friction coefficient as a random variable. Employing a set of natural  seismic records  and  L’Aquila (Italy) as reference site, the  inelastic  characteristics  of  the superstructures are designed according to NTC08 for increasing strength reduction factors  and  for  an  intermediate  value of the  isolation degree. Using Incremental Dynamic Analyses (IDA) and assuming different values of the limit state thresholds for the single concave sliding bearings and for the superstructure, the seismic fragility curves are  evaluated.  Finally,  the  reliability  curves  of  the  inelastic base-isolated structural systems, with a design life of 50 years, are derived and represent seismic reliability-based design (SRBD) abacuses, useful to define the system properties.

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The study moves from the current debate about the suitability of the unidirectional tests regulated in the standards, and aims at investigating the effect of the displacement trajectory on the evaluation of seismic isolators. A 3D finite  element  thermal-mechanical  model  of  a  Curved Surface Sliders is formulated, and numerical analyses are performed  considering  unidirectional  and  bidirectional  displacement-controlled orbits. The temperature rise at the sliding surface is calculated from  the  software  and  used  to adjust at each iteration step the coefficient of friction of the bearing. The results of the analyses examining  different  orbits  are  compared  in  terms  of  maximum  shear  force, dissipated energy and temperature rise on the surface of the thermoplastic pad. The conclusions point to the fact that the unidirectional  tests  provide a conservative evaluation of the bearing performance, but are not suitable for determining the bearing properties that  are  needed for accurate nonlinear   response   history   analyses.  Furthermore,   unidirectional   tests   tend   to   underestimate   the  temperature  rise  induced  from bidirectional  trajectories.

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Two different base isolation retrofit strategies for older elevated water tanks with reinforced concrete structure are presented in this paper. The mutual objective consists in minimizing the impact of the interventions, in view of the architectural and historical value of these plants. The two strategies incorporate double curved sliding surface isolators, and a combined system of high damping rubber bearings and steel-Teflon sliders, respectively. A representative case study is examined for a demonstrative application of the two base-isolation technologies, i.e. the water tower of S. Salvi ex-psychiatric hospital in Florence. The  tower  was  erected  in  1905  with  a  braced frame staging structure, characterized by a set of bracing trusses with equal inclination. This unconventional layout determines  an  asymmetrical  behaviour, and a rather poor performance with respect to seismic action. The design criteria followed  for  the  two retrofit interventions  are  presented  by a step-by-step procedural description. An  assessment  analysis of their  performance  in  comparison  to  the  response  evaluated  in  current conditions is offered, along with technical installation details of the two protective systems.

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