Institute of R&D in Structures and Construction

Funder

Organizational Unit

Publications

Parametric study on a Bouc-Wen model with degradation features for the study of cyclic behavior of a reinforced concrete frame

Publication . Folhento, Pedro Leonel Pamplona; Barros, Rui; Braz-César, Manuel

Non-linear behavior in building frame structures is inevitable and expected in moderate to severe seismic events. This behavior tends to be concentrated at the ends of beams and columns of moment-resisting frames. These critical regions, where plastic hinges form, are important for the global stability of the structural system. Depending on the available ductility, these mechanisms are responsible for the permanent deformations that the structure undergoes, leaving the remaining parts of the structural elements in the elastic regime, and hence in the safe zone. The importance of these mechanisms led to the search for an adequate model capable of well-capturing the non-linearity phenomena involved. The development of versatile hysteresis models with degradation features has been the aim of different studies. Hence, this paper presents a parametric study based on a smooth hysteresis model, a further modification to the well-known Bouc-Wen model, developed by Sivaselvan and Reinhorn, with a physical interpretation appropriate to the study of the non-linear behavior of civil engineering structures, particularly, building structures. Furthermore, an optimization procedure is implemented to calibrate the mentioned model’s parameters, attempting to replicate the actual cyclic response of a reinforced concrete frame structure. The effect of each parameter in the hysteresis response will help on the understanding and on the possibilities of this kind of model in simulating different types of structural systems or different materials.

2021Journal article

Open access

Tensile behavior of weathered thermally bonded polypropylene geotextiles: analysis using constitutive models

Publication . Carneiro, José Ricardo; Paula, António Miguel; Pinho-Lopes, Margarida

Weathering agents can significantly affect the mechanical response of geotextiles, particularly when long exposure periods are involved. Usually, in design, changes in the mechanical behavior of geotextiles are represented by reduction factors for their tensile strength. However, their full tensile force versus elongation response can be affected. The main aim of this work was to contribute to defining simple procedures to estimate tensile force versus elongation curves for weathered samples of geotextiles. The tensile response of two thermally bonded polypropylene geotextiles, before and after natural and artificial weathering, was assessed experimentally and analyzed using different constitutive models: polynomial (Orders 4 and 6) and hyperbolic. The influence of weathering on the mechanical response of the geotextiles was analyzed, polynomial and hyperbolic models for representing the tensile force versus elongation response were adopted and their parameters derived, and simple relations were implemented to estimate model parameters for weathered samples. Results revealed the occurrence of changes in the tensile behavior of the geotextiles, both under natural and artificial weathering conditions. Both groups of models fitted the experimental data properly. The Order 4 and 6 polynomial models are shown to have limited application, as the model parameters had no link to the tensile properties of the geotextiles. By contrast, the parameters of the hyperbolic model were linked to the tensile properties, particularly if affected by correction factors. The hyperbolic model parameters of the weathered samples were estimated using the model parameters of the reference samples and the reduction factors to allow for weathering (initial stiffness and tensile strength). These estimates proved to be adequate for representing the tensile response of weathered samples, particularly for low ranges of elongation. Finally, a simple procedure to represent the tensile response of weathered geotextiles was proposed. This procedure has shown promise in generating realistic tensile versus elongation curves.

2023Journal article

Restricted access

Effect of earthquake-induced structural pounding on the floor accelerations and floor response spectra of adjacent building structures

Publication . Folhento, Pedro; Barros, Rui; Braz-César, M.T.

The influence of earthquake-induced structural pounding among buildings is paramount in the seismic analysis and design of structures. The recognition of such a phenomenon has been growing in the last decades. The search for ways to understand and mitigate the consequences of these structural collisions in building structures is the primary goal of the investigation of earthquake-induced building pounding. This phenomenon is known for increasing the floor accelerations, mainly where pounding occurs, implying significant local damage. These collisions cause short-duration acceleration pulses that may compromise the building structure and the non-structural elements within the building’s stories. Non-structural elements supported by the structure’s floors under earthquake-induced pounding instances may present a risk to human lives and/or human activity. Hence, the influence of earthquake-induced pounding in the floor response spectra of two adjacent reinforced concrete structures with inelastic behavior is assessed by varying the number of stories and their separation distance. Pounding greatly influenced the floor acceleration spectra, increasing the spread of accelerations over a broader period range, particularly exciting low to moderate periods of vibration.

2024Journal article

Open access

Constitutive models and statistical analysis of the short-term tensile response of geosynthetics after damage

Publication . Lombardi, Giovani; Paula, António Miguel; Pinho-Lopes, Margarida

The objective of this research was to analyse the tensile response of three geosynthetics, to apply constitutive equations, and propose values for model parameters to represent the nonlinear behaviour of these materials in the short-term, supported by statistical analysis. Data for specimens of a nonwoven geotextile, a woven geogrid and a reinforcement geocomposite previously submitted to mechanical damage, abrasion damage, and mechanical damage followed by abrasion damage were analysed. Nonlinear regressions of the experimental results were performed to fit the load vs. strain curves to constitutive equations. For each geosynthetic, the results of damaged specimens were statistically compared to those of the undamaged ones to observe the influence of the induced damage on the tensile behaviour of the material. Experimental results were statistically compared with those obtained by the constitutive models to verify if the tensile properties and the model parameters were properly estimated. For the geotextile, significant changes in tensile properties were noticed only after sequential mechanical damage and abrasion damage. For the geogrid and the reinforcement geocomposite, abrasion damage was predominant due to considerable changes in the tensile properties and the shape of the load vs. strain curves. In general, the polynomial models fitted the ultimate tensile strength slightly better, while the hyperbolic-based models presented better approximation of the secant stiffness. For hyperbolic-based models, estimating curves for damaged materials from model parameters of undamaged specimens by applying adjustment coefficients and reduction factors allowing for damage was considered promising, with slight differences for average and median curves. Contrary to the literature, model parameter α was not a material constant, as it varied according to the material condition and the shape of the load vs. strain curve.

2022Journal article

Restricted access

Cyclic response of a reinforced concrete frame: comparison of experimental results with different hysteretic models

Publication . Folhento, Pedro Leonel Pamplona; Braz-César, Manuel; Barros, Rui

An accurate hysteresis model is fundamental to well capture the non-linearity phenomena occurring in structural and non-structural elements in building structures, that are usually made of reinforced concrete or steel materials. In this sense, this paper aims to numerically estimate through simplified non-linear analyses, the cyclic response of a reinforced concrete frame using different hysteretic models present in the literature. A commercial Finite Element Method package is used to carry out most of the simulations using polygonal hysteretic models and a fiber model, and additionally, a MATLAB script is developed to use a smooth hysteresis model. The experimental data is based on the experiments carried out in the Laboratório Nacional de Engenharia Civil, Portugal. The numerical outcomes are further compared with the experimental result to evaluate the accuracy of the simplified analysis based on the lumped plasticity or plastic hinge method for the reinforced concrete bare frame. Results show that the tetralinear Takeda’s model fits closely the experimental hysteresis loops. The fiber model can well capture the hysteresis behavior, though it requires knowledge and expertise on parameter calibration. Sivaselvan and Reinhorn’s smooth hysteresis model was able to satisfactorily reproduce the actual non-linear cyclic behavior of the RC frame structure in a global way.

2021Journal article

Open access