1,720,988 research outputs found
An analytical formulation of q-factor for mid-rise CLT buildings based on parametric numerical analyses
No full textThe seismic response of cross-laminated timber buildings is analysed with the aim of assessing the correlation between the dissipative capacity (i.e., q-factor) and the assembling methodologies and geometrical properties. A parametric study was performed by means of incremental dynamic analyses on various building configurations with varying constructive features such as density of panel-to-panel joints and building slenderness. The results are firstly used to define parameters representative of the building geometry and assembling methodology and then to develop an analytical relationship to compute their most suitable q-factor starting from such parameters. The proposed method is finally validated referring to significant case studies available in literature
Seismic design of floor–wall joints of multi-storey CLT buildings to comply with regularity in elevation
No full textThe effects of irregularity in elevation of cross-laminated timber buildings have not been fully analysed in literature to provide useful information for the design. In this work, a number of building configurations, regular or irregular in elevation, characterized by a different arrangement per storey of the floor–wall joints have been analysed by means of non-linear dynamic analyses. Comparative results in terms of ratio between the behaviour q-factor of the investigated irregular configurations and that of reference regular ones, show that less dissipative capacity can be expected if the building is irregular due to a disequilibrium among storeys between the actual and the required strength provided by the floor–wall joints. A correlation method to estimate the behaviour q-factor for perfectly regular cross-laminated timber buildings is here presented and extended to in-elevation irregular ones. A new empirical formulation to assess the reliable corrective factor accounting for the irregularity in elevation of cross-laminated timber buildings, according to Eurocode 8 provisions, is also proposed. A final discussion about the implications of in elevation irregularity on the building design is reported
Reinforced concrete structural elements cast into wood-chip cement formworks subjected to compression and out-of-plane bending
No full textThe mechanical response of reinforced concrete walls cast into permanent woodchip-cement formworks and subjected to eccentric compression has been assessed with experimental tests of full-scale panels and an analytical approach has been proposed. The load-bearing capacity of the wall panel is assured by the inner reinforced concrete grid structure, composed of vertical columns and horizontal ribs, reinforced with vertical and horizontal steel bars. The experimental specimens were realized varying the concrete cross-section and tested varying the eccentricity of the applied vertical load. Both reinforced and non-reinforced panels were tested. An analytical model is proposed to evaluate the load-bearing capacity, based on dimensionless curves, which provide reduction coefficients of strength based on eccentricity and slenderness, considering second-order effects. The analytical model demonstrates a reliable prediction of the experimental peak loads
A study about optimal stiffening of timber floors in URM buildings
No full textTimber floors in traditional masonry buildings normally have limited in-plane stiffness, which may be not
sufficient to avoid out-of-plane failure of walls or to transmit efficiently seismic forces among walls. Therefore,
various stiffening techniques of timber floors have been developed with the aim of improving the global behaviour
of the building. The evaluation of the efficiency of the stiffening intervention needs adequate numerical modelling
strategy, taking into account the nonlinear in-plane behaviour of masonry piers and spandrels, the out-of-plane
stiffness and strength of walls, the actual stiffness and hysteretic behaviour of timber floors. The macro-element
modelling can be considered an intermediate strategy in terms of model complexity, as it requires experimental
data for its calibration, but can be quite easily adapted to the building geometry. Nonlinear incremental dynamic
analyses of different case-study buildings are presented, varying the type of floor, the seismic signal and the
modelling criteria as the complexity and accuracy of the adopted technique, with the aim of analysing the effects
of the stiffening techniques on the building response. The comparative analyses show that the seismic capacity of
a traditional masonry building may decrease if a retrofitting method leading to excessive floor stiffening and/or
mass increase is adopted, depending on the geometry and mechanical characteristics of walls and floors. This
means that the need of increasing the in-plane stiffness of floors should be evaluated on a case-by-case basis,
comparing the actual capacities of floors and walls
Capacity design of traditional and innovative ductile connections for earthquake-resistant CLT structures
Full text linkTraditional connections in earthquake-resistant cross-laminated timber buildings are susceptible of brittle failures, even when buildings are designed and supposed to be ductile. This is mainly due to the large underestimation of the actual strength of the ductile components, with consequent increased strength demand for the brittle parts, which may fail if designed with insufficient overstrength. Recent studies demonstrate that the use of steel connections characterized by a well-defined mechanical behaviour can improve significantly ductility and dissipative capacity of cross-laminated timber structures and the reliability of the capacity design. In this paper, the conceptual model of capacity design is discussed, proposing some modifications to improve its reliability for traditional and high-ductility connections for CLT structures. Results from quasi-static cyclic-loading tests of an innovative ductile bracket are presented and the corresponding overstrength factors are computed using the proposed conceptual method and compared with values available in the literature for traditional connections. Finally, a comparative application of the capacity criteria to the design of the innovative bracket and of a traditional nailed connection is presented and discussed
Capacity design of CLT structures with traditional or innovative seismic-resistant brackets
No full textCapacity design of typical earthquake-resistant connections for CLT structures
No full textEarthquake-resistant CLT structures can be designed in accordance with the concept of non-dissipative or dissipative
structural behaviour. In the second case, modern Italian and European seismic codes require the compliance with the
capacity design, to assure the development of plastic deformations in the dissipative components before failure of the
non-dissipative ones. For timber structures, this requirement is crucial, because no regions outside the defined nonlinear
zones, i.e., steel connections, exhibit dissipative capacity. The load-bearing capacity of connections with
dowel-type fasteners is currently estimated according to conservative design methods for static actions, which do not
take advantage of their entire strength in the seismic design. Such underestimation of their actual capacity, the high
scattering of their mechanical parameters demonstrated by experimental tests and the use of different partial factors
for material properties for each component of the same connection, introduce indecisions in the capacity design and
in the overstrength factors to be used. Additionally, the recent diffusion of multi-storey CLT buildings in earthquakeprone
areas like Italy, makes these issues particularly relevant. In this work, the concept of capacity design and its
application in the seismic deign of CLT buildings are discussed, also in terms of suitable values of overstrength
factors for this structural system. Moreover, an overview of capacity-design rules for timber structures introduced by
the latest reviews of Italian and European Codes and Standards is given. Finally, an applicative example of capacity
design of a typical connection for CLT buildings and main outcomes are analysed
Seismic capacity of steel frames braced with cross-concentric rectangular plates: Non-linear analyses
No full textThe use of cross-concentric braced steel frames is still an effective way to realize earthquake-resistant buildings, thanks to the simplicity in the design and realization, assuring good strength, stiffness and ductility, provided that capacity design be fulfilled. Results from non-linear static and dynamic analyses of steel frames braced with cross-concentric rectangular plates are presented to discuss some significant design aspects that play a key role in the definition of the hysteretic dissipative response of such structures. Parametric cyclic analyses were performed to assess the peak- and post-buckling lateral strength and the dissipative capacity of a small- and a full-scale frame, varying the non-dimensional slendemess of the bracing plates. Then, results of incremental dynamic analyses of a one-, three-, six- and ten-storey building are discussed to evaluate the behaviour factor for this structural typology, as function of inter-storey drift. Results from the parametric and incremental analyses give the optimal range of non-dimensional slenderness of the bracing plates as a compromise between limited overstrength and good dissipative capacity and confirm the behaviour factor currently provided by Eurocode, relating it with an expected inter-storey lateral drift. (C) 2019 Elsevier Ltd. All rights reserved
Effects of in-plane strengthening of timber floors in the seismic response of existing masonry buildings
No full textIn this work, the influence of two in-plane stiffening and strengthening techniques of traditional timber floors realized with single layer of boards in the seismic response of existing masonry buildings is investigated via numerical approach. Two retrofitting methods have been considered: addition of 45° inclined timber boards and addition of a RC slab. The dynamic behaviour of a two-storey case-study building subjected to various seismic shocks has been analysed via non-linear finite-element modelling, in order to compare the effects of the adopted retrofitting methods. All the mechanical parameters introduced in the model were calibrated from experimental data obtained from literature. The 3D model takes into account the hysteretic behaviour of masonry and floors and allows to estimate the type of failure and the corresponding PGA
Macro-element modelling of a dissipative connection for CLT structures
No full textDissipative steel connections for cross-laminated timber buildings are often characterized by biaxial tension-shear interaction in strength and displacement capacity. Detailed continuum models with nonlinear finite elements provide faithful results in simulating the hysteretic response of complex structural systems but generally require too much computational effort. The use of nonlinear macro-elements can strongly increase the efficiency of the analysis with limited decrease of accuracy of the results. In this work, the hysteretic response of a dissipative connection for cross-laminated timber structures was simulated in the OpenSees framework with a macro-element model and compared with results from tests and a continuum finite-element model developed in the Ansys® framework. The accuracy of the macro-element in reproducing the tension-shear interaction has been evaluated in terms of displacement and force domains of the connection. A further comparison between the macro-element and the continuum finite-element modelling was provided analysing the seismic response of cross-laminated timber shear walls with different arrangement of the dissipative connections. Results show that the proposed macro-element can simulate the nonlinear biaxial behaviour of the dissipative bracket and predict the force-displacement response of CLT shear walls with slight conservative underestimation of hysteretic energy dissipation. The macro-element could be implemented in models of buildings for prediction of their dynamic response with a limited computational effort
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