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Experimental and numerical characterization of the cyclic behaviour of unreinforced and reinforced mansonry structures
No full textCyclic behavior of masonry walls strengthened by tie rods
No full textThis preliminary work is aimed at investigating numerically the behaviour of unreinforced masonry walls strengthened through the use of metallic tie rods. In the first part, the improvement of strength is studied by evaluating the increase in shear resistance for low vertical action values, which is the most critical state for unreinforced masonry. Tie rods are placed along diagonals of the walls, as to maximize their effect on the overall strength and on recentering capabilities of piers. Subsequently, by using non-linear dynamic analyses carried out on a masonry wall, the importance of the axial forces acting on retrofitted piers during a seismic event is highlighted. It is shown that this becomes particularly important in the presence of a significant vertical component due to seismic actions. All the analyses are carried-out with non-linear material models, as to investigate the capacity in post-elastic field. Finally, the recentering capabilities and cyclic response of strengthened piers using tie rods are evaluated, on the basis of the residual transversal displacements measured at the end of numerical simulations. Results show improvements on the shear-displacements cyclic behaviour of reinforced piers, including better recentering capabilities, enhancing masonry performance under seismic conditions
Experimental and numerical characterization of the cyclic behaviour of unreinforced and reinforced masonry spandrels
No full textThe mechanical behaviour of unreinforced and reinforced masonry spandrels is
studied, using the results of several experimental tests carried out on H-shaped full-scale specimens.
In particular, four unreinforced masonry specimens in different configurations, were built by varying
the masonry material (bricks and stones) and lintel supports (wooden lintel, masonry arch) are
considered. Each specimen was then reinforced with different strengthening techniques (tensioned
bars, steel profiles and CFRP strips) and re-tested. The mechanical behaviour of the spandrel
involves typically two types of failure: shear and flexural collapse. Starting from the experimental
behaviour of the tested specimens, a numerical model able to predict the cyclic response of a
spandrel subjected to seismic loading is presented and validated with the experimental results. The
numerical model allows one to evaluate the energy dissipation that occurs in a masonry spandrel
during a quasi-static cyclic test or a dynamic analysis
A TOOL FOR NON-LINEAR DYNAMIC INVESTIGATION OF URM STRUCTURES
No full textIn this work, an effective modelling strategy for describing the non-linear behaviour of unreinforced masonry (URM) structures is presented. The approach uses the equivalent frame modelling and represents each masonry wall with macroelements, which are formed by zero-length multi-spring elements connected each other via elastic links. Each macroelement has two rotational springs, one at both ends and a shear spring in the middle of the length. Two specific hysteretic rules are used in the springs, describing the shear and the rotational hysteretic cycles. The employed laws account for stiffness and strength degradation, and the strength of each panel is calculated on the base of the axial load detected in the wall. Some numerical-experimental comparisons are presented to demonstrate the potential and the accuracy of the actual modelling
Experimental and numerical characterization of the cyclic behaviour of unreinforced and reinforced mansonry structures
No full textInvestigation on the accuracy of the N2 method and the equivalent linearization procedure for different hysteretic models
No full textIn this paper, an extensive parametric study was carried out to evaluate the dynamic response of single degree of freedom (SDOF) systems with elasto-plastic and flag-shape hysteretic behaviour for three different dissipation capacities. Three sets of natural accelerograms were used, each one composed by at least 7 records which are on average spectrum-consistent in pseudo-acceleration, spectral displacement or both of them. All sets were also employed to draw the inelastic spectra for different ductility values. Such rigorous spectra were then compared with the approximated curves calculated using the N2 method and the Equivalent Linearization Procedure (ELP) based on the use of overdamped elastic spectra. The analyses demonstrate a general accuracy of the N2 method, which is mostly based on the ductility of the system, even for the hysteretic behaviour characterised by reduced energy dissipation. Larger discrepancies were found for systems with lower damping ratios and reduced fundamental periods. The ELP, which mainly depends upon the dissipated energy, led instead to overall slightly larger discrepancies than the N2 method, particularly for not dissipative and ductile systems, whereas the approximation is generally acceptable for elasto-plastic systems
Partitioned Modelling for Nonlinear Dynamic Analysis of Reinforced Concrete Buildings for Earthquake Loading
No full textNon-linear modelling of the in-plane seismic behaviour of timber Blockhaus log-walls
No full textThis paper investigates the non-linear modelling of the cyclic behaviour of Blockhaus timber log-walls under in-plane lateral loads. The structural behaviour of Blockhaus log-walls in the examined loading condition strictly depends on the geometry – thus on the deformability and ultimate resistance – of the adopted corner joint, namely the joint between perpendicular log-walls. The presence of metal fasteners is in fact minimized and the structural interaction between the basic timber components is provided by simple mechanisms such as notches, tongues and grooves, multiple surfaces in contact. In this paper, a computationally effective FE-model is developed, in order to predict the cyclic behaviour of an entire Blockhaus log-wall once the cyclic behaviour of the adopted corner joint is known. The model uses non-linear hysteretic springs to describe the joint behaviour, where all typical features such as pinching behaviour, strength and stiffness degradation can be considered. By comparing the numerical and the experimental predictions of the cyclic response of full-scale Blockhaus log-walls, a general good agreement is found. Simulations confirmed the high flexibility of the studied structural systems, as well as the significant effect of possible openings such as doors and windows on their global resistance to in-plane lateral loads. In conclusion, the presented study confirmed that the proposed modelling approach can be used to estimate the load-carrying capacity and vulnerability to seismic events of Blockhaus shear walls, and that the same model could be extended to full Blockhaus buildings.This paper investigates the non-linear modelling of the cyclic behaviour of Blockhaus timber log-walls under in-plane lateral loads. The structural behaviour of Blockhaus log-walls in the examined loading condition
strictly depends on the geometry – thus on the deformability and ultimate resistance – of the adopted corner joint, namely the joint between perpendicular log-walls. The presence of metal fasteners is in fact minimized and the structural interaction between the basic timber components is provided by simple mechanisms such as notches, tongues and grooves, multiple surfaces in contact. In this paper, a computationally effective FE-model is developed, in order to predict the cyclic behaviour of an entire
Blockhaus log-wall once the cyclic behaviour of the adopted corner joint is known. The model uses non-linear hysteretic springs to describe the joint behaviour, where all typical features such as pinching behaviour, strength and stiffness degradation can be considered. By comparing the numerical and the experimental predictions of the cyclic response of full-scale Blockhaus log-walls, a general good agreement is found. Simulations confirmed the high flexibility of the studied structural systems, as well as the significant effect of possible openings such as doors and windows on their global resistance to in-plane lateral loads. In conclusion, the presented study confirmed that the proposed modelling approach
can be used to estimate the load-carrying capacity and vulnerability to seismic events of Blockhaus shear
walls, and that the same model could be extended to full Blockhaus buildings
"Non-linear springs for cyclic analysis of wooden structures"
No full textA non-linear spring for modelling of wooden structures under seismic loading condition has been implemented as an external library in OpenSees framework. This element, previously used in the FE code ABAQUS and written in Fortran 77 language, has been interfaced with OpenSees via an ad-hoc routine. The proposed element is used in static and dynamic non-linear models of wooden structures to represent the dissipative capacity of steel connections. An example of a X-lam (cross-lam) wall is presented and a comparison with available experimental results is shown. The model is built with non-linear springs elements and quad elements characterized by linear-elastic behaviour
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