Papers by A Gustavo Ayala
Lecture notes in civil engineering, 2023
Bulletin of Earthquake Engineering, Jul 11, 2023
Lifelines 2022, Nov 16, 2022
Numerical Methods for Partial Differential Equations, 2009
ABSTRACT This work presents a variational formulation of the material failure process, idealized ... more ABSTRACT This work presents a variational formulation of the material failure process, idealized as strain or displacement discontinuities, by weak, strong, or discrete embedded discontinuities into a continuum. It is shown that the solution of the proposed variational formulation may be approximated by different types of finite elements with embedded discontinuities. The developed displacement approximation of a finite element split by the discontinuity leads to a symmetric stiffness matrix, which considers not only the continuity of tractions but also the rigid body relative motions of the portions in which the element is split. The variational formulation of a continuum with more than one discontinuity in its interior is developed. It is shown that this formulation may lead to finite elements with embedded discontinuities that can be classified as displacement, force, mixed, and hybrid models. To show the effectiveness of the proposed formulation, the classical example of a bar under tension is solved using one and 2D finite element approximations. © 2008 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2009
This paper describes a simplified procedure for the performance based seismic evaluation of bridg... more This paper describes a simplified procedure for the performance based seismic evaluation of bridges. It is based on the definition of a non-linear response curve for a reference SDOF system corresponding to the mode which contributes the greatest to the response of these structures. This curve is obtained through non-linear modal spectral analyses taking into account the contribution of higher modes of vibration. The procedure is based on one previously used for the evaluation of multi-storey buildings where, through a multi-mode pushover analysis, the response curve of a simplified reference system is obtained and from this the seismic performance of the structure is determined. In this paper, this procedure is modified by using for the definition of the response curve of the reference system, modal spectral analyses which take into consideration in an implicit way, the displacement reversal characteristic of the earthquake action, and the participation of higher modes of vibration of importance in the evaluation of bridges whose response is governed by one mode of vibration and the transient nature of earthquake action. To illustrate the application of the procedure, the results of two bridges, one regular and the other irregular, obtained with this methodology for earthquakes of various intensities given by the design spectrum of Eurocode 8, are compared with the mean of the corresponding results from inelastic step by step dynamic analyses using an ensemble of earthquake records congruent with the design spectrum of this code.
This paper presents the formulation, evaluation and comparison of two newly developed displacemen... more This paper presents the formulation, evaluation and comparison of two newly developed displacement based design procedures for reinforced concrete bridges. The foundations of both methods are established within the framework of the performance based design philosophy, however they are different inasmuch as the first one is an iterative linear method based on the concepts of the substitute structure, proposed more than three decades ago, and the use of seismic demands given by damping reduced design spectra and the other is a direct non-iterative non-linear procedure based on the concepts of a non-linear SDOF reference system and seismic demands given by uniform hazard design spectra for an assumed rate of exceedence of the target performance. To understand the potential of application of both methods, the issue of bridge regularity is explicitly examined showing that, further to the concept that regularity of a bridge is closely related to the expected seismic performance under design actions, it is also linked to the used performance based evaluation/design method. It is shown that when a bridge structure is irregular, both proposed procedures may lead to incorrect evaluations/designs unless some additional considerations are introduced in the procedures. The results obtained from both methods are illustrated by applying them to five bridges. SOMMARIO In questa memoria si presenta una procedura per la progettazione sismica dei ponti, avente come obiettivo il conseguimento di una prefissata prestazione. Tale procedura si basa sull’idea che la prestazione di una struttura possa essere approssimata con quella di un oscillatore di riferimento ad 1 grado di liberta non lineare, definito sulla base del modo del ponte che contribuisce maggiormente alla sua risposta. Si mostra come il modo piu conveniente per calcolare la curva di risposta dell’oscillatore di riferimento sia quello di ripetere consecutivamente una serie di analisi modali con spettro di risposta, durante le quali le proprieta del ponte evolvono in accordo con il livello della domanda sismica. L’impiego dell’analisi modale con spettro di risposta, mentre da un lato e semplice, dall’altro porta in conto, in modo implicito, la natura oscillatoria dell’azione sismica ed il contributo dei modi superiori, contributo che, per alcuni ponti, puo essere significativo. La procedura proposta si articola in due fasi: nella prima la struttura e considerata integra e nella seconda e soggetta ad una distribuzione di danno suggerita dal progettista. Si mostra, inoltre, come il metodo di progettazione proposto cessi di fornire risultati corretti, quando l’ordine dei modi che contribuiscono maggiormente alla risposta della struttura cambia passando dalla struttura integra alla struttura danneggiata. La procedura e illustrata mediante l’esempio della progettazione di due ponti, uno regolare e l’altro irregolare, svolta utilizzando come domanda sismica lo spettro di progetto contenuto nell’EC8. La validita della procedura e mostrata confrontando i risultati da essa forniti con le statistiche dei primi due ordini della risposta in termini di spostamento ottenute da una serie di analisi dinamiche non lineari che utilizzano come ingresso accelerogrammi artificiali.
SUMMARY In this paper the stiffness and energy dissipation characteristics of RC hollow rectangul... more SUMMARY In this paper the stiffness and energy dissipation characteristics of RC hollow rectangular bridge piers are investigated. The work involves two different levels of model sophistication, namely: a continuous non-linear model without energy dissipation derived from non-linear finite element analyses and an equivalent linear viscoelastic model with secant to yield stiffness and equivalent damping characteristics. In all stages of the analyses the results obtained are compared and validated with those derived from existing experimental results. The potential of using this procedure for determining the linear-equivalent stiffness and dissipation characteristics of piers and ultimately of full bridges is discussed within the framework of performance based design and evaluation of RC bridges using the substitute structure method.
International Journal of Solids and Structures, Mar 1, 2004
ABSTRACT In this paper the mathematical modeling of discontinuities using the discrete approximat... more ABSTRACT In this paper the mathematical modeling of discontinuities using the discrete approximation and the continuum approximation with weak discontinuities is presented. First, the kinematics of discontinuities is discussed, then two constitutive models based on the continuum damage mechanics theory are developed. The first model is an isotropic damage model and is used in the discrete approximation. The second model is an anisotropic damage model and is used in the continuum approximation. These models are characterized for weighing the mode of failure in the failure criterion. An energy analysis is proposed to establish the equations that relate the parameters of both constitutive models; the fulfillment of the involved equations guarantee that both models are energetically equivalent. It is concluded that the proposed models are suitable to reproduce the constitutive behavior of discontinuities.
Engineering Fracture Mechanics, Mar 1, 2014
International Journal for Numerical and Analytical Methods in Geomechanics, 2005
This paper presents an alternative strategy to evaluate the stability of tunnels during the desig... more This paper presents an alternative strategy to evaluate the stability of tunnels during the design and construction stages based on a hybrid system, composed by neural, neuro-fuzzy and analytical solutions. A prototype of this system is designed using a database formed by 261 cases, 45 real and the rest synthetic. This system is capable of reproducing the displacements induced at the periphery of the tunnel before and after support installation. The stability of the excavation process is evaluated using a criterion that considers dimensionless parameters based on the shear strength of the media, the induced deformation level in the ground, the plastic radii and the advance of excavation without support. The efficiency and validity of the prototype is verified with two examples of actual tunnels, one included in the database used to train the system and the other not included. The results of both examples show a better approximation than other commonly used techniques.
Numerical Methods for Partial Differential Equations, 2006
ABSTRACT A methodology for the numerical implementation of embedded discontinuities into the fini... more ABSTRACT A methodology for the numerical implementation of embedded discontinuities into the finite element method is developed. This is applicable for the discrete and continuum approximations of discontinuities. The variational formulation of the problem of a solid with discontinuities is established for both approximations, yielding the equations used in this methodology. Three sets of equations are obtained by applying this methodology; all are suitable to be numerically implemented. To show the application potential of this method, the numerical simulation of the formation and propagation of a discontinuity in a concrete specimen is carried out and the results are compared with those from the physical experiment, demonstrating the adequacy of the methodology and its corresponding implementations to model discontinuities. © 2005 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2006
Advances in Civil Engineering, 2017
The influence of crumb-rubber on the mechanical properties of Portland cement concrete (PCC) is s... more The influence of crumb-rubber on the mechanical properties of Portland cement concrete (PCC) is studied by experimental tests and numerical simulations. The main hypothesis of the study is that replacing part of the stone aggregate with crumb-rubber in the mix modifies the energy dissipation during the cracking process and affects the concrete behaviour under monotonically increasing loads. The experimental research program characterizes the mechanical properties of PCC for three different types of concrete with a variable content of crumb-rubber. The experimental results showed that fracture energy and other properties are directly related to the rubber fineness used in the mixture. The material properties derived for these laboratory tests are used to study, by numerical models, its response through its damage evolution. The numerical model used to simulate the damage evolution of the concrete is the Embedded Discontinuity Method (EDM). One characteristic of the EDM is that it does not need to modify the mesh topology to propagate the damage through the continuum solid. For this study, the Disk-Shaped Compact Tension specimen geometry, normed by the D7313-13 of the ASTM, is used. Results showed that the numerical methods provide good approximation of the experimental curve in the elastic and softening branches.
Advances in Civil Engineering, Nov 30, 2020
is paper investigates the variational finite element formulation and its numerical implementation... more is paper investigates the variational finite element formulation and its numerical implementation of the damage evolution in solids, using a new discrete embedded discontinuity approach. For this purpose, the kinematically optimal symmetric (KOS) formulation, which guarantees kinematics, is consistently derived. In this formulation, rigid body motion of the parts in which the element is divided is obtained. To guarantee equilibrium at the discontinuity surfaces, the length of the discontinuity is introduced in the numerical implementation at elemental level. To illustrate and validate this approach, two examples, involving mode-I failure, are presented. Numerical results are compared with those reported from experimental tests. e presented discontinuity formulation shows a robust finite element method to simulate the damage evolution processes in quasi-brittle materials, without modifying the mesh topology when cohesive cracks propagate.
Latin American Journal of Solids and Structures, 2015
The study of collapse in concrete elements is an interest topic in engineering; particularly, the... more The study of collapse in concrete elements is an interest topic in engineering; particularly, the determination of the first crack load and the crack pattern. It is well known that concrete strength under compression is from 10 to 20 times greater than the strength under tension, as shown the experimental results reported by Kupfer and Gerstle (1973). In the way to collapse of reinforced concrete elements, their behaviour at the beginning is approximately linear elastic; next, cracking occurs. Then, crushing appears and finally, plasticity in reinforcing steel initiates, although struc-Juárez-Luna G. a, 1 Tena-Colunga A.
Finite Elements in Analysis and Design, Jul 1, 2012
This paper presents a variational formulation of the mechanical behaviour of beams with strong di... more This paper presents a variational formulation of the mechanical behaviour of beams with strong discontinuities, enhanced to simulate the strain localization process. The considered strain localization zones represent the formation of dislocations and hinges in beams. The presented general formulation applies to thick beams, which takes into account the internal strain energy due to bending and shear, and also a simpler formulation which takes into account only bending induced strains which applies to thin beams. It is shown that the developed energy functional for the beams with discontinuities has as stationarity conditions the strong formulation of the associated boundary value problem. As illustration, the energy functionals for Timoshenko and Euler-Bernoulli beams with embedded discontinuities are approximated by finite elements with embedded discontinuities. The development of a local material failure (leading to hinge-like strain localization zones) is in terms of continuum constitutive models furnished with strain softening capabilities. To show the validity of this formulation and its consistency with its continuum counterpart, representative numerical examples illustrating the performance of the proposed formulation are presented.
Earthquake Spectra, Aug 1, 1990
Lecture notes in civil engineering, 2023
Sismos recientes han demostrado la importancia de evaluar el tiempo que tardarían los edificios d... more Sismos recientes han demostrado la importancia de evaluar el tiempo que tardarían los edificios dañados en ser reparados, ocupables y funcionales nuevamente, debido a que el tiempo de inactividad puede generar pérdidas económicas e implicaciones sociales importantes. En este trabajo se presenta una metodología para evaluar el tiempo de recuperación en términos probabilistas de edificios que han sido dañados por sismo. El esquema de evaluación propuesto se basa en el método PERT y es consistente con el esquema de evaluación sísmica propuesto por el PEER y con el concepto de resiliencia desarrollado por el MCEER. Se presenta la evaluación de un edificio de concreto reforzado en el que se incluyen los muros de mampostería no reforzada. Recent earthquakes have demonstrated the importance of assessing the time it would take for damaged buildings to be repaired, occupied and functional again, because downtime can lead to significant economic losses and social implications. This paper presents a methodology to evaluate the recovery time in probabilistic terms of buildings that have been damaged by earthquakes. The proposed evaluation scheme is based on the PERT method and is consistent with the seismic evaluation scheme proposed by PEER and with the concept of resilience developed by the MCEER. The evaluation of a reinforced concrete building is presented, in which the infill unreinforced masonry walls are included.Postprint (published version
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Papers by A Gustavo Ayala