1,721,003 research outputs found
Non-linear simulation of shaking-table tests on 3- and 7-storey X-Lam timber buildings
No full textAbstract This paper presents an advanced \FE\ modelling of cross-laminated (X-Lam) timber buildings for non-linear dynamic analyses. The model has been used to reproduce the experimental results of the shaking table tests carried out in Japan within the \SOFIE\ project on the 3- and 7-storey full-scale timber buildings. The X-Lam timber panels have been schematized with linear-elastic shell elements, whereas all metal connectors (hold-downs, angle brackets, screws) have been described with 3-DOFs non-linear hysteretic springs. The hysteretic law has a trilinear backbone curve, and is characterised by pinching, post-peak softening, strength and stiffness degradation. The approximating hysteretic laws of the springs have been calibrated on the experimental cyclic tests carried out on each single metal connector. Additional features of the model are the possibilities to account for friction at the interface between upper and lower X-Lam panels, and for a strength domain between shear and tensile force in the metal connectors. Due to the lack of experimental results, these variables have been identified via parametric study so as to reduce the difference between the numerical prediction and the experimental result of X-Lam single walls loaded with cyclic horizontal load. The experimental–numerical comparisons of the shaking table tests demonstrate the capacity of the model to capture the seismic responses of both buildings with errors within 20% in relative acceleration and 7% in roof displacement. Friction has been found to significantly affect the seismic response as it reduces the peak top displacement up to 31%
A macroelement for the cyclic analysis of masonry structures
No full textIn this work, a macroelement for the cyclic analysis of masonry structures is presented. The proposed model is based on the equivalent frame method to represent the structure, in which each masonry pier or spandrel is schematised by a beam-type macroelement containing two flexural nonlinear springs at both ends, a shear nonlinear spring in the middle and two Euler-Bernoulli elastic beams connecting them. Each springs have a length conventionally chosen by the user in percentage of the macroelement height, and their characteristics are calculated automatically. The springs exhibit a cyclic behaviour, different for flexure and shear. Stiffness and strength degradation are implemented in both hysteretic laws; moreover, the strength is calculated during the analysis as a function of the axial compressive load. All parameters governing degradations and hysteretic cycles are obtained on the base of the results of experimental tests on masonry piers.
The macroelement, implemented as User Element (UEL) in the general FE code Abaqus is formulated using the static condensation method, and it supplies the tangent stiffness matrix and the force vector as output. The force vector is obtained assembling the contribution of each element and performing some simple Newton-Raphson iterations to ensure the internal equilibrium.
To validate the proposed cyclic behaviour, two cyclic experimental tests on masonry piers have been reproduced numerically. It is shown that the macroelement is able to change the amount of dissipated energy on the base of the slenderness of the masonry wall thanks to the stiffness ratios of the non-linear springs. For a slender pier, which mostly has a flexural collapse, the rotational springs will mainly influence the whole response, while for a squat wall, that presents a shear failure, the shear spring will be more stressed.
A comparison between experimental and numerical results is also performed on a 2-storey perforated façade subjected to a cyclic test, evidencing the validity of the presented approach in real models
“Advanced models for seismic analyses of timber buildings.”
No full textThe paper discusses the seismic analysis of multi-storey buildings made from cross-laminated timber panels ('crosslam'). The different analysis procedures allowed by the Eurocode 8 for seismic design, namely: (i) linear static ('lateral force'); (ii) linear dynamic ('modal response spectrum'); (iii) non-linear static ('push-over'); and (iv) non-linear ('time-history') analyses, are introduced. Some recommendations are given for an effective modelling of the building. Cross-laminated panels are schematized with two-dimensional Finite Elements with linear-elastic behaviour. Connections are modelled using linear elastic, non-linear elastic, and hysteretic springs for (i) and (ii), (iii), and (iv) analysis methods, respectively. Some suggestions on how to model non-symmetric connections such as hold-downs and angle brackets loaded in tension/compression using an elastic spring are given, as well as on how to approximate the actual non-linear behaviour with a linear elastic or an elasto-plastic equivalent behaviour. Information on push-over analyses and the N2 method for the seismic design of timber buildings is also provided. An advanced numerical model to describe accurately the features of the connection cyclic behaviour, namely: pinching effects, strength and stiffness degradation, and softening after the attainment of the peak strength is also introduced. This model allows the user to correctly characterize the non-linear behaviour of the connections, and to calculate the dissipated energy for single fasteners and also for more complex structures. A case study cross-lam multi-storey building analysed using the linear-dynamic and the non-linear static is also presented, together with the non-linear analysis of a wall panel subjected to cyclic tests, demonstrating the excellent approximation achievable using the proposed advanced model
“Effectiveness of the N2 method for the seismic analysis of structures with different hysteretic behaviour.”
No full text“Effectiveness of the N2 method for the seismic analysis of structures with different hysteretic behaviour.”
No full text"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
A macro-model with nonlinear springs for seismic analysis of URM buildings
Full text linkSeismic assessment of existing unreinforced masonry buildings represents a current challenge in structural engineering. Many historical masonry buildings in earthquake regions were not designed to withstand seismic loading, thus these structures often do not meet the basic safety requirements recommended by current seismic codes and need to be strengthened considering the results from realistic structural analysis. This paper presents an efficient modelling strategy for representing the nonlinear response of unreinforced masonry components under in-plane cyclic loading which can be used for practical and accurate seismic assessment of masonry buildings. According to the proposed strategy, a generic masonry perforated walls is modelled using an equivalent frame approach, where each masonry component is described utilising multi-spring nonlinear elements connected by rigid links. When modelling piers and spandrels, nonlinear springs are placed at the two ends of the masonry element for describing the flexural behaviour, and in the middle for representing the response in shear. Specific hysteretic rules allowing for degradation of stiffness and strength are then used for modelling the member response under cyclic loading. The accuracy and the significant potential of the proposed modelling approach are shown in several numerical examples, including comparisons against experimental results and the nonlinear dynamic analysis of a building structure
Influence of the Floor Diaphragm on the Rocking Behavior of CLT Walls
No full textIn the design of cross-laminated timber (CLT) buildings in earthquake-prone areas, a crucial role in energy dissipation is played by the panel-to-panel joint. Such a connection, theoretically, could be designed for three different types of behavior: coupled, uncoupled, and monolithic. Coupled and uncoupled behaviors provide a certain amount of energy dissipation, whereas monolithic behavior does not. Currently, no specific design rules to attain a given condition are provided in any code. Furthermore, no information on the dependency of the wall behavior upon other variables, such as the out-of-plane stiffness of the floor diaphragms or the stiffness of other metal connections (e.g., hold-downs and angle brackets) can be found in the literature. In an attempt to fill in this gap, this paper presents the results of numerical analyses carried out using a commercial software package. In these analyses, the influence of the upper floor diaphragms on the rocking behavior of a two-panel wall assembly is investigated. Fully reversed displacement-controlled cyclic tests are simulated, while varying the geometrical properties (aspect ratio of the wall panels), mechanical properties (types and number of connectors used for the panel-to-panel, wall-to-foundation and wall-to-upper floor connections, out-of-plane stiffness of the floor panels), and gravity load applied on top of the assembly. The rocking capacity of the walls is investigated, together with displacements and global behavior of the assembly. The results obtained highlight the important role played by the stiffness of wall-to-floor diaphragm joints, whereas the out-of-plane flexural stiffness of the slab has a negligible effect on the overall response of the assembly
Review of experimental cyclic tests on unreinforced and strengthened masonry spandrels and numerical modelling of their cyclic behaviour
Full text linkA reliable numerical modelling for the cyclic behaviour of unreinforced and strengthened masonry spandrels is herein presented. The proposed numerical model is adapted from Tomazevic-Lutman’s model for masonry piers in shear and it has been validated upon an experimental campaign conducted at Department of Engineering and Architecture of University of Trieste. The tests were conducted on Hshaped full-scale specimens imposing vertical displacements of increasing amplitude on one leg. Four unreinforced masonry specimens arranged with different masonry material (bricks and stones) and lintel supports (wooden lintel, masonry arch) were considered. Each specimen was then reinforced with a different strengthening technique (tensioned bars, steel profiles, CFRP laminates) and re-tested. Analytical relationships were proposed, based on those available in some Codes of Practice, to estimate the maximum shear resistance of URM and RM spandrels. These relationships provide resistance values in good agreement with the experimental results and can be correctly employed to define the cyclic model of the spandrel to be used in the numerical simulation. The cyclic shear-displacement curves obtained through the numerical model are in good agreement with those of the experimental tests and very good assessment of the dissipated energy was obtained
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