1,720,974 research outputs found
Validation and application of rational tying method for robustness design of post-and-beam timber buildings
No full textThe lack of reliable tying methods for the design of low and medium-rise mass timber buildings with regard to progressive collapse constitutes a strong limitation for the timber structural engineering community. In this context, the current work aims to validate and apply a recently developed rational tying force method for robustness design of post-and-beam timber buildings falling in low and medium consequence classes. This rational tying force method, which considers the requisite resistance via tying to the loss of a load-bearing member, preserves the simplicity of the prescriptive rules present in some current standards, while utilising a mechanical basis similar to that considered in alternative load path analysis. An extended example of the application of the new tying force method to a post-and-beam timber structure is reported in this work. The example highlights several critical aspects for achieving a robust design of post-and-beam timber structures. The results presented in this work show that the new tying force method represents a promising and practical strategy for robustness design of post-and-beam timber buildings
Mesoscale Modeling of a Masonry Building Subjected to Earthquake Loading
No full textMasonry structures constitute an important part of the built environment and architectural heritage in seismic areas. A large number of these old structures showed inadequate performance and suffered substantial damage under past earthquakes. Realistic numerical models are required for accurate response predictions and for addressing the implementation of effective strengthening solutions. A comprehensive mesoscale modeling strategy explicitly allowing for masonry bond is presented in this paper. It is based on advanced nonlinear material models for interface elements simulating cracks in mortar joints and brick/block units under cyclic loading. Moreover, domain decomposition andmesh tying techniques are used to enhance computational efficiency in detailed nonlinear simulations. The potential of this approach is shown with reference to a case study of a full-scale unreinforced masonry building previously tested in laboratory under pseudodynamic loading. The results obtained confirm that the proposed modeling strategy for brick/block-masonry structures leads to accurate representations of the seismic response of three-dimensional (3D) building structures, both at the local and global levels. The numerical-experimental comparisons show that this detailed modeling approach enables remarkably accurate predictions of the actual dynamic characteristics, along with the main resisting mechanisms and crack patterns
Long-term analysis of steel-concrete composite beams: FE modelling for effective width evaluation
No full textThis paper presents a finite element model suitable for long-term analysis of steel–concrete composite beams. The structure is modelled using
one-dimensional beam elements for the steel profile and two-dimensional shell elements for the concrete slab, where the two types of element are interconnected by means of special-purpose link elements. In this way, the deformability of the connection system can be taken into account, along with the shear lag phenomenon in the concrete slab. Careful consideration is taken in modelling the concrete behaviour, for which both
rheological phenomena, such as creep and shrinkage, and non-linear behaviour due to cracking are fully considered for a plane stress state. Some
preliminary analyses carried out on a composite girder bridge subjected to long-term loading demonstrate the applicability of the proposed method for evaluating the influence of different and complex phenomena, such as the shrinkage and cracking of concrete, on the effective width evaluation. These analyses also highlight potential shortcomings in current design codes of practice, the validation of which necessitates further experimental and numerical work
A robustness-oriented procedure for the design of tying reinforcement in precast concrete hollow-core floors
Full text linkBuildings may be subjected during their service life to extreme events which can trigger progressive collapse. On this front, the role played by tying reinforcement in structural members is crucial for an adequate load redistribution and the avoidance of disproportionate collapse. This work proposes a robustness-oriented procedure for the design of tying reinforcement placed in the hollow-core units and beams of precast concrete buildings, where limited studies are available in scientific literature. In particular, the aim is to provide a simple yet reliable approach for the design of concentrated and distributed ties in precast floors by adopting fundamental input parameters such as the system’s chord rotation capacity and dynamic amplification factor, which are not considered in current design codes. Firstly, a flow-chart of the design procedure is proposed and discussed. Secondly, the input parameters are calculated based on recent analytical approaches - proposed by some of the authors - to optimize the tying reinforcement design. Finally, the efficiency of the design procedure is demonstrated with an application example, and a novel detailing scheme is proposed which is aimed at a significant enhancement of structural robustness. Due to its simplicity, the proposed design procedure is contended to be applicable in robustness assessment and design of building structures with precast concrete hollow-core floors
A hybrid macro-modelling strategy with multi-objective calibration for accurate simulation of multi-ring masonry arches and bridges
No full textThis paper presents an efficient hybrid continuum-discrete macro-modelling strategy with an enhanced multiscale calibration procedure for realistic simulations of brick/block-masonry bridges. The response of these structures is affected by the intrinsic nonlinearity of the masonry material, which in turn depends upon the mechanical properties of units and mortar joints and the bond characteristics. Finite element approaches based upon homogenised representations are widely employed to assess the nonlinear behaviour up to collapse, as they are generally associated with a limited computational demand. However, such models require an accurate calibration of model material parameters to properly allow for masonry bond. According to the proposed approach, the macroscale material parameters are determined by an advanced multi-objective strategy with genetic algorithms from the results of mesoscale “virtual” tests through the minimisation of appropriate functionals of the scale transition error. The developed continuum-discrete finite element macroscale description and the calibration procedure are applied to simulate the nonlinear behaviour up to collapse of multi-ring arch-bridge specimens focusing on the 2D planar response. The results obtained are compared to those achieved using detailed mesoscale models confirming the effectiveness and accuracy of the proposed approach for realistic nonlinear simulations of masonry arch bridges
Experimental-numerical strategies for the calibration of detailed masonry models
No full textDetailed mesoscale models enable realistic response predictions of masonry structures subjected to different loading conditions. The accuracy of the numerical predictions strongly depends upon the calibration of the model material parameters, which is usually conducted at the level of masonry constituents. However, especially for existing structures testing of individual components can be difficult or unreliable. In this work, an innovative approach for the calibration of a mesoscale masonry representation is proposed. It is based on the inverse analysis of the results of physical in situ tests performed using an innovative setup with flat-jacks. The post-processing inverse procedure comprises (i) metamodeling as a replacement of expensive nonlinear simulations, (ii) sensitivity analysis to reduce the parameters to identify to those which effectively control the recorded response, and (iii) optimisation by means of Genetic Algorithms to find the best fitting model parameter set. The potential of the proposed calibration procedure is shown considering the response of masonry components tested in laboratory following the proposed in-situ test
Comportamento non-lineare di nodi esterni trave-colonna in c.a.: modelli locali di capacità ed influenza sulla risposta sismica globale
No full textAtti del 18° Congresso C.T.E
Seismic performance of existing RC frames: influence of beam-to-column joint modelling
No full textThis paper presents the main results of numerical analyses carried out to assess the seismic performance of reinforced
concrete frames. In particular, the influence of the beam-to-column joint behaviour on the seismic response of
existing RC frames, characterized by inadequate structural detailing to effectively withstand seismic loading, has
been investigated. In the employed modelling approach for RC frames, the joint damage is represented using
nonlinear rotational springs with limited ductility and with strength and stiffness degradation. A brief overview of the
capacity models for joints in RC structures currently available in the technical literature is reported in the introductory
section of the paper. Subsequently, some analytical details of the employed joint model, which has been calibrated
considering several experimental results, are provided. Finally, the main results achieved in the numerical analyses
are presented and discussed. Nonlinear static and dynamic analyses have been carried out, considering two, three and
four-storey RC frames and accounting for material and geometric nonlinearity in beams and columns. The influence
of potential damage in beam-to-column joints has been investigated, where the results achieved with the
beam-to-column joints represented through nonlinear springs are compared against those obtained assuming rigid
joints. The outcomes of the numerical study show that the overall vulnerability of the analysed RC frames is strongly
affected by the beam-to-column joint damage
An experimental-numerical procedure for the identification of mesoscale material properties for brick-masonry
No full textThe response of unreinforced masonry is very complex because of its inherent heterogeneity and nonlinear behaviour, which is governed by the interaction between masonry units and mortar joints. Mesoscale modelling can provide a very good representation of the actual response of masonry structures when using adequate material parameters for the individual components. An attractive strategy has been recently developed by the authors for the calibration of the mesoscale material properties. This is based upon the inverse analysis of the macroscale behaviour of a part of the structure subjected to the pressures exerted by two flatjacks arranged along the mortar bed joints and the perpendicular direction. Thus far this strategy has been applied only to pseudo-experimental data, whereas in this paper it is enhanced considering the experimental results obtained in physical laboratory tests on running bond masonry walls. It is demonstrated that inverse analysis of the measured experimental displacement field allows the estimation of the elastic properties, the cohesion and the friction angle for the interface elements used in the mesoscale description to represent mortar joints
Validation of simplified tying force method for robustness assessment of RC framed structures
No full textThe robustness of reinforced concrete (RC) structures is an important ongoing research topic in the civil engineering community. Especially in the last decades, the need for structural robustness assessment methods has become urgent, and several design methods have been proposed in codes and guidelines to mitigate the progressive collapse risk of reinforced concrete structures. The most used approaches are the Tying Force and Alternate Load Path methods. The first is typically applied as an indirect and prescriptive method where the building is considered mechanically tied together and able to enhance continuity and the resistance to progressive collapse. The second is a direct method, where the capacity of the structure to sustain the applied loads is evaluated after the loss of a load-bearing element, most effectively using advanced nonlinear structural analysis methods. In the context of the Tying Force method, the Eurocode is recognised to underestimate the tie force demands required by building structures subject to the loss of a load bearing member, which are better reflected in the USA UFC Guidelines. A new Tying Force method has been proposed by Izzuddin & Sio (2021) for the next generation of the Eurocodes, which addresses the shortcomings of the present Eurocode guidance, and provides a more comprehensive treatment than considered in the UFC code. The present paper is aimed specifically at the validation of the new Simplified Tying Force method (Izzuddin & Sio, 2021) for reinforced concrete structures, considering grillage and combined beam/slab floor systems, and considering the rotational ductility of such structures, which is explicitly considered in the new method
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