Engaging soft computing in material and modeling uncertainty quantification of dam engineering problems

Due to complex nature of nearly all infrastructures (and more specifically concrete dams), the uncertainty quantification is an inseparable part of risk assessment. Uncertainties might be propagated in different aspects depending on their relative importance such as epistemic and aleatory, or spatial and temporal. The objective of this paper is to focus on the material and modeling uncertainties, and to couple them with soft computing techniques aiming to reduce the computational burden of the conventional Monte Carlo-based finite element simulations. Several scenarios are considered in which the concrete and foundation material properties, the water level, and the dam geometry are assumed as random variables. Five soft computing techniques (i.e., random forest, boosted regression trees, multi-adaptive regression splines, artificial neural networks, and support vector machines) are employed to predict various quantities of interest based on different training sizes. It is argued that the artificial neural network is the most accurate algorithm in majority of cases, with enough accuracy as to be useful in reliability analysis as a complement to numerical models. The results with 200 samples in the training set are enough for reaching useful accuracy in most cases. For the simple prediction tasks, the results were predicted with less than 1% error. It is observed that increasing the number of input parameters increases the prediction error. The partial dependence plots provided most sensitive variables in dam design, which were consistent with the physics of the problem. Finally, several practical recommendations are provided for future applications

Performance Based Earthquake Engineering of Concrete Dams

The main objective of this thesis is to develop a framework for performance based earthquake engineering (PBEE) of concrete dams. To pursue this goal, this study first develops an extended and quantitative version of potential failure mode analysis (PFMA) for concrete dams. Different failure modes are investigated for all types of concrete dams. A Matlab-based code is developed for probabilistic performance assessment of concrete dams (PPACD). This code is used for assessment of concrete dams within the context of PBEE. A probabilistic seismic demand model (PSDM) is proposed for concrete dams based on cloud analysis methodology. The outcome of PSDM is selection of optima intensity measure (IM) parameters for gravity dams. Then, the sensitivity and uncertainty of dam-foundation system is quantified under the mixed-mode fracture of zero-thickness interface joint element. Capacity and fragility curves are derived for most sensitive random variables. This research also examined the performance of the dam under incremental dynamic analysis (IDA). First, the anatomy of a single-record IDA is studied and contrasted by framed structures. Then, the collapse fragility curves are derived for single and multiple-component ground motions. The impact of epistemic uncertainty is investigated in addition to the aleatoric one. Finally, a multi-scale damage index (DI) is proposed for gravity dams which is a function of crest displacement, crack ratio, and dissipated energy. Using this hybrid DI, a computationally simple but effective methodology is proposed for progressive failure analysis of dams. In all cases, first the methodology is discussed and then, a numerical example illustrates the details

Optimal FRP Jacket Placement in RC Frame Structures Towards a Resilient Seismic Design

This paper proposes an optimal plan for seismically retrofitting reinforced concrete (RC) frame structures. In this method, the columns are wrapped by fiber-reinforced polymer (FRP) layers along their plastic hinges. This technique enhances their ductility and increases the resiliency of the structure. Two meta-heuristic algorithms (i.e., genetic algorithm and particle swarm optimization) are adopted for this purpose. The number of FRP layers is assumed to be the design variable. The objective of the optimization procedure was to provide a uniform usage of plastic hinge rotation capacity for all the columns, while minimizing the consumption of the FRP materials. Toward this aim, a single objective function containing penalty terms is introduced. The seismic performance of the case study RC frame was assessed by means of nonlinear pushover analyses, and the capacity of the plastic hinge rotation for FRP-confined columns was evaluated at the life safety performance level. The proposed framework was then applied to a non-ductile low-rise RC frame structure. The optimal retrofit scheme for the frame was determined, and the capacity curve, inter-story drift ratios, and fragility functions were computed and compared with alternative retrofit schemes. The proposed algorithm offers a unique technique for the design of more resilient structures.Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Orthotropic Material and Anisotropic Damage Mechanics Approach for Numerically Seismic Assessment of Arch Dam-Reservoir-Foundation System

In contrast with modeling of the contraction joints, the performance and influence of lift joints are usually neglected in numerical analysis of concrete arch dams. In this paper, the seismic nonlinear response of a concrete arch dam– reservoir–foundation system is investigated with considering the effects of lift joints using orthotropic-based material. An anisotropic damage mechanics approach is introduced and modified to take into account the effects of weak horizontal planes between concrete lifts during the construction phase. This model is capable to consider the pre-softening behavior, the softening initiation criterion and anisotropic cracking behavior in mass concrete. The coupled equation of motion in dam–reservoir system is solved by staggered displacement method while the foundation rock is assumed as a mass-less and rigid mediums. The coupled system is excited using three-component ground motion in the maximum credible level. It is found that using orthotropic-based material increases crest displacements and also leads to more damage in the dam body in comparison with the case using the common isotropic-based material.В отличие от моделирования усадочных швов, при численном анализе бетонных арочных плотин работа и влияние строительных швов обычно не учитываются. Исследуется сейсмическая нелинейная реакция системы (бетонная) арочная плотина–резервуар–основание с учетом действия строительных швов на основе ортотропного материала. Представленный анизотропный подход к механике повреждения изменен для учета слабых горизонтальных плоскостей между слоями бетона в процессе строительства. Эта модель допускает учет характеристики предварительного размягчения, критерия возникновения размягчения и характеристики анизотропного растрескивания. С помощью метода ступенчатых перемещений, предполагая, что скальное основание состоит из невесомых жестких тел, решена система связанных уравнений движения в системе плотина–резервуар. Движение грунта по трехкомпонентной технологии возбуждает данную систему на максимально вероятном уровне. Обнаружено, что использование ортотропного материала увеличивает смещение гребня плотины и, как следствие, повреждение тела плотины в большей степени по сравнению с использованием распространенного изотропного материала.На відміну від моделювання усадкових швів, при чисельному аналізі бетонних арочних гребель робота і вплив будівельних швів зазвичай не враховуються. Досліджується сейсмічна нелінійна реакція системи (бетонна) арочна гребля–резервуар–основа з урахуванням дії будівельних швів на основі ортотропного матеріалу. Представлений анізотропний підхід до механіки руйнування змінено для урахування слабких горизонтальних площин між шарами бетону в процесі будівництва. Ця модель допускає урахування характеристики попереднього розм’якшення, критерію виникнення розм’якшення і характеристики анізотропного розтріскування. За допомогою методу східчастих переміщень, припускаючи, що скельову основу складають невагомі жорсткі тіла, розв’язано систему зв’язаних рівнянь руху в системі гребля–резервуар. Рух ґрунту за трикомпонентною технологією збуджує дану систему на максимально імовірному рівні. Установлено, що використання ортотропного матеріалу збільшує зміщення гребеня греблі і, як наслідок, пошкодження тіла греблі в більшій мірі порівняно з використанням розповсюдженого ізотропного матеріалу

Seismic risk prioritization of a large portfolio of dams: Revisited

The development of potential failure mode analysis and risk analysis has greatly improved the state-of-practice for the safety of dams. Risk analysis are well developed in many industries (such as building design, medicine, and insurance) and has greatly advanced in the dams industry over the last 40 years. Engineers and scientists are now deeply investigating and thinking about failure mechanisms associated with operating dams and the probabilities of dam failures. As such, the condition of dams and the risks associated with their operation are now being portrayed better than ever before to dam safety officials and decision-makers. Accurate and adequate risk analyses for a portfolio of dams is extremely important in today’s environment to manage limited budgets and potentially save (or redirect) expensive rehabilitations to identified and critical needs. The goal is to reduce risks of a portfolio of dams in an efficient and cost-effective manner. This article provides a review on risk-based dam terminology and bridging the semi-quantitative and numerical simulation. Moreover, a review of the current state-of-practice for prioritizing a large portfolio of dams subjected to seismic loadings and potential risks is provided. As a potential application, the seismic risk of the 18 dams (which have been experienced relatively large earthquakes) all over the world is evaluated. The semi-quantitative approach is contrasted with finite element model for one of the selected dams

On the Dynamic Capacity of Concrete Dams

The purpose of this joint contribution is to study the maximum dynamic load concrete dams can withstand. The so-called "dynamic capacity functions" for these infrastructures seems now technically and commercially feasible thanks to the modern finite element techniques, hardware capabilities, and positive experiences collected so far. The key topics faced during the dynamic assessment of dams are also discussed using different point of view and examples, which include: the selection of dynamic parameters, the progressive level of detail for the numerical simulations, the implementation of nonlinear behaviors, and the concept of the service and collapse limit states. The approaches adopted by local institutions and engineers on the subject of dam capacity functions are discussed using the authors' experiences, and an overview of time and resources is outlined to help decision makers. Three different concrete dam types (i.e., gravity, buttress, and arch) are used as case studies with different complexities. Finally, the paper is wrapped up with a list of suggestions for analysts, the procedure limitations, and future research needs

Developing a Library of Shear Walls Database and the Neural Network Based Predictive Meta-Model

There is a large amount of useful information from past experimental tests, which are usually ignored in test-setup for the new ones. Variation of assumptions, materials, test procedures, and test objectives make it difficult to choose the right model for validation of the numerical models. Results from different experiments are sometimes in conflict with each other, or have minimum correlation. Furthermore, not all these information are easily accessible for researchers and engineers. Therefore, this paper presents the results of a comprehensive study on different experimental models for steel plate and reinforced concrete shear walls. A unique library of up to 13 parameters (mechanical properties and geometric characteristics) affecting the strength, stiffness and drift ratio of the shear walls are gathered including their sensitivity analysis. Next, a predictive meta-model is developed based on artificial neural network. It is capable of forecasting the responses for any desired shear wall with good accuracy. The proposed network can be used to as an alternative to the nonlinear numerical simulations or expensive experimental test.</p

Vibration and Control in Structures under Single and Multiple Hazards

Vibrations in civil engineering structures and mechanical systems arise from different sources of excitations including natural hazards induced loadings of structures, machineries and devices, rotating unbalance, and fault bearings. The field of vibration and control is developed into a multidisciplinary thematic which encompasses knowledge from structural dynamics, modelling, modal analysis, electrical engineering, computer sciences, and control theory, crucial for the understanding and treatment of the issues raised from occurrence of excessive vibrations