1,721,227 research outputs found
Multiphysics-Lattice Discrete Particle Model: possible strategies for upscaling
Full text linkThe optimization of civil infrastructure maintenance and management is a challenging task, littered of open issues requiring the synergic development of effective structural health monitoring systems and reliable models to be addressed. Relevant to concrete structures, models cannot disregard the multi-physics nature of the problem: moisture and heat transport phenomena in uncracked and cracked conditions, the ingress of aggressive agents, and the ensuing chemical reactions - that the latter may trigger - heavily affect the mechanical performance. Most of the mentioned processes happen at a scale typically smaller than the structural one. Then, it is also necessary to perform multiscale analysis, capable of adapting structural models to the insights resulting from lower scale analyses. In the last decade, Multiphysics-Lattice Discrete Particle Model (M-LDPM) has been successfully adopted to model a wide range of phenomena in civil engineering involving concrete structural members: ageing, environment-induced degradation, shrinkage, creep, and usage of advanced construction materials. Furthermore, the discrete nature of the model has shown the capability of predicting the cracking patterns accurately. However, such a comprehensive and accurate model simulates the material at the mesoscale, and the path towards the exploitation of the insights resulting from lower-scale modelling at the structural level is paved of computational and theoretical burdens. In this work, a review of the state-of-the-art concepts that allow upscaling M-LDPM is presented. The aim is to explore alternatives for the formulation of computationally efficient macroscale models that leverage on both the predictive quality of M-LDPM in capturing and predicting the material constitutive behaviour, and the computational affordability that features the classical Finite Element Method for the structural analysis of complex systems
Coupled mesoscale analysis of concrete shrinkage
No full textCracking, driven by shrinkage and thermal strains, strongly influences the serviceability and durability of concrete structures. After several decades of use, cracking can cause structural deterioration and damage. Concrete shrinkage is sensitive to temperature and humidity variations in a complex hygrothermal environment. Therefore, an efficient numerical framework is essential to predict the structural response for all potential geometries and environmental conditions. This work presents a new multi-physics simulation framework coupling the mechanical behavior with chemical/physical processes of concrete while considering the meso-structure of concrete. The Lattice Discrete Particle Model (LDPM) is used the describe the mechanical response. The Hygro-Thermo-Chemical (HTC) model, which describes the moisture transport, heat transfer, and curing reaction, is solved using a flow lattice element (FLE) system dual to the mechanical mesh. The development of mechanical characteristics, as well as thermal and hygral eigenstrains owing to continued curing, is driven by the HTC model. In addition, a newly proposed 2-phase formulation for concrete shrinkage is introduced, considering the effect of aggregate volume and stiffness on concrete shrinkage. The results give robust predictions of macroscopic shrinkage for concretes with different mix proportions and indicate a better representation of meso-structural features than the previously proposed 1-phase formulation. To ensure the reliability of the results, five experimental campaigns from the literature were selected to calibrate and validate the numerical model. The model agrees well with the experimental data and offers new insights into local strain distribution and cracking behavior in heterogeneous materials at an acceptable computational cost
Discrete element framework for modeling tertiary creep of concrete in tension and compression
Full text linkIn this contribution, a computational framework for the analysis of tertiary concrete creep is presented, combining a discrete element framework with linear visco-elasticity and rate-dependency of damage. The Lattice Discrete Particle Model (LDPM) serves as constitutive model. Aging visco-elasticity is implemented based on the Micro-Prestress-Solidification (MPS) theory, linking the mechanical response to the underlying physical and chemical processes of hydration, heat transfer and moisture transport through a multi-physics approach. The numerical framework is calibrated on literature data, which include tensile and compressive creep tests, and tests at various loading rates. Afterwards, the framework is validated on time-to-failure tests, both for flexure and compression. It is shown that the numerical framework is capable of predicting the time-dependent evolution of concrete creep deformations in the primary, secondary but also tertiary domains, including very accurate estimates of times to failure. Finally, a predictive numerical study on the time-to-failure response is presented for load levels that are difficult to test experimentally, showing a deviation from the simple linear trend that is commonly assumed. Ultimately, two alternative functions for time-to-failure curves are proposed that are mechanically justified and in good agreement with both, experimental data and numerical simulations
Insights on Lattice Discrete Particle Model Calibration and Validation Procedure to Simulate Polypropylene and Steel Fibre-Reinforced Concrete
No full textThe use of fibre-reinforced concrete (FRC) has been substantially increasing in the last few years, in different fields of the construction industry. Recently, many experiments have been performed to observe the short- and long-term mechanical behaviour of FRC, and several models have been formulated to capture its mechanical response. In this work, the mechanical behaviour is simulated through the Lattice Discrete Particle Model (LDPM) and its extension to fibre-reinforced cementitious composites (LDPM-F). This paper aims to provide insights into the calibration process and potential pitfalls in a case where only limited experimental data are available—in this case, unconfined uniaxial compression and three-point bending tests on different mixes of polypropylene and steel fibre-reinforced concretes. As a first step, a sensitivity analysis is performed to weight the effect of each governing mesoscale parameter on the simulated macroscale behaviour. Then, for each mix at issue, different sets of model parameters are identified as capable of accurately matching the experimental evidence. As a validation, each calibrated set is used to simulate energy absorption tests on round panels. The validation stage shows that one of the identified sets, for the FRC with polypropylene fibres, accurately matches the round panels’ response, while the others result in acceptable predictions. For the mix with steel fibres, instead, none of the sets captures the experimental results, likely due to the different post-cracking behaviour detected in fracture and energy absorption tests. Finally, a parametric study showcases how the LDPM-F might serve as tool to optimise the mix design without extensive experimental investigations
Multi-physics Modelling of Moisture Diffusion in the FRP-Concrete Adhesive Joints
No full textFRP-to-concrete adhesive joints are being used increasingly often across a wide range of structural problems, as they provide the possibilities to overcome the uneven stress transfer and stress concentration often found in conventional mechanical anchor systems. For hybrid FRP/concrete substrates, however, the interfacial bond strength is mainly affected by the behavior of adhesive joints, which are known to be highly sensitive to environmental conditions such as moisture uptake and temperature variations. More specifically, polymers are perceptible to moisture ingress, which diffuses out of concrete. The related water uptake leads to a series of changes in mechanical properties, summarized as hydrolytic degradation. A nonlinear FEM-based model was used to simulate the moisture diffusion into the adhesive, which was then coupled with a mechanical degradation model for thermoset polymers. The multi-physics computational framework is able to capture the moisture transport between concrete and adhesive, and adhesive and air. Also, the associated local changes in mechanical response can be obtained. An experimental test campaign in different humidity conditions was selected to calibrate and validate the numerical model, which shows good agreement. The load-slip curves of the single-lap shear test were predicted. The results provide valuable insights regarding the underlying moisture diffusion and interface degradation mechanisms
Numerical modeling on the short-term response of fiber-reinforced concrete round panels
No full textFiber-reinforced concrete is a composite material consisting of discrete, discontinuous, and uniformly distributed fibers in plain concrete primarily used to enhance the tensile
properties of the concrete. FRC performance depends upon the fiber, interface, and matrix properties. The use of fiber-reinforced concrete has been increasing substantially in the past few years in different fields of the construction industry such as ground-level
application in sidewalks and building floors, tunnel lining, aircraft parking, runways, slope stabilization, etc. Many experiments have been performed to observe the short-term and long-term mechanical behavior of fiber-reinforced concrete in the last decade and numerous numerical models have been formulated to accurately capture the response of fiber-reinforced concrete.
The main purpose of this dissertation is to numerically calibrate the short-term response of the concrete and fiber parameters in mesoscale for the three-point bending test and cube compression test in the MARS framework which is based on the lattice
discrete particle model (LDPM) and later validate the same parameters for the round panels. LDPM is the most validated theory in mesoscale theories for concrete.
Different seeds representing the different orientations of concrete and fiber particles are simulated to produce the mean numerical response. The result of numerical simulation shows that the lattice discrete particle model for fiber-reinforced concrete can
capture results of experimental tests on the behavior of fiber-reinforced concrete to a great extent
Aging concrete structures: a review of mechanics and concepts
Full text linkThe safe and cost-efficient management of our built infrastructure is a challenging task considering the expected service life of at least 50 years. In spite of time-dependent changes in material properties, deterioration processes and changing demand by society, the structures need to satisfy many technical requirements related to serviceability, durability, sustainability and bearing capacity. This review paper summarizes the challenges associated with the safe design and maintenance of aging concrete structures and gives an overview of some concepts and approaches that are being developed to address these challenges
Assessment of bridges based on stiffness identification using modal bending lines
No full textAll Engineering structures are subjected to time-dependent degradation processes. In order to allow for cost effective maintenance, it is necessary to be able to determine the current structural condition and reliability profile respectively and to extrapolate the acquired assessment indices into the future. Based on this information maintenance planning then can be optimized.
At the moment still visual inspection is the tool of choice for the inspection of structures although many other different methods based on local or global measurements have been developed. However the basis for the combination of results of classical visual inspection and more sophisticated tools still is missing. In this contribution a practically feasible approach for the identification of the actually present bending stiffness is being presented and the
methodology for the assessment of the structure’s reliability level with respect to the ultimate limit state (ULS), the serviceability limit state (SLS) and the durability limit state (DLS) will be discussed as well as a correlation with condition levels defined by codes
A simulation approach of experimental design for concrete compressive strength
No full textThe material properties of concrete play an important role in most mechanical and numerical models that describe the behaviour of a concrete structure. Since those properties do not remain constant, an experimental procedure is needed in order to obtain the parameters that express their development in time. Apart from point estimates for the parameters of the ageing models obtained from experimental data, the followed procedure should also be able to provide uncertainty estimates required for inference and reliability computations. These considerations have been rather overlooked to date. In this context, decisions on the days of testing, the number of tested units and the regression methods need to be taken within some physical constraints. In the present paper, we provide an analysis aiming to yield practical recommendations for optimal testing design. The confidence intervals for the parameters of interest related to the compressive strength of concrete are obtained through a Monte Carlo simulation. Furthermore, we investigate whether a resampling procedure can be used to reconstruct these confidence intervals upon single experimental realisations with no prior information on the parameters. Based on the analysis results and the desired precision, a design of experiments for obtaining the development of concrete compressive strength in time
is possible
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