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A nonlinear model for multilayered rubber isolators based on a co-rotational formulation
(01/01/2017) Maureira, N.; Llera, J. de la; Oyarzo, C.; Miranda, S.
This article proposes a geometrically nonlinear co-rotational model aimed to characterize the mechanical behavior of elastomeric seismic isolators. The model is able to capture the axial and lateral coupling in both axial directions, i.e. compression and tension of the isolator. Also reproduces the instability the loads in tension as well as in compression, and provides theoretical evidence of the non-symmetric behavior of the isolator in these two directions. To validate model results, a quasistatic analysis was performed on a typical isolator with many different shape factors. From the parametric analysis performed, it is observed that buckling loads are higher in tension than in compression. However, as the shape factor of the isolator increases, the behavior in compression and tension becomes symmetric. It becomes apparent that significant differences in normal stresses and strains under tensile and compressives loads are observed for axial loads smaller than 10% of the nominal buckling load. The example presented shows that lateral displacements of about 25% of isolator radius and tension forces up to 10% of the buckling load are possible without inducing cavitation in the rubber. Accuracy of the model was also tested against finite element model results and experimental data showing satisfactory results. Furthermore, a response-history analysis of an isolated structure is presented and compared for two isolator models: the two-spring model and the model proposed herein. Finally, material nonlinearity was introduced in the dynamic analysis using a Bouc-Wen type element in parallel with the isolator. The responses are similar between models; however, significant differences occur locally in the isolator for high axial loads and/or large lateral displacements. (C) 2016 Elsevier Ltd. All rights reserved.
A combined photovoltaic and novel renewable energy system: An optimized techno-economic analysis for mining industry applications
(01/04/2017) Vyhmeister, Eduardo; Muñoz, Cristina Aleixendri; Bermúdez, José Miguel; Pina Moya, Javier; Fúnez Guerra, Carlos; Rodríguez Mayor, Lourdes; Godoy Faúndez, Alex; Higueras, Pablo; Clemente-Jul, Carmen; Valdés-González, Héctor; Reyes-Bozo, Lorenzo
The productivity of the mining industry in Chile, currently the main driver of Chilean economy, is closely tied to foreign demand for ores. Ore-processing is known for involving energy–intensive processes, such as comminution, concentrating and cathodic processes. As mining activities take place in the arid north of Chile, they are affected by water scarcity. Water shortage has forced the industry to pump desalinated seawater up to mining sites over 2000 m above sea level, further increasing electricity consumption. Given these energy needs, and the fact that electrical energy supply in the north of Chile is based on fossil fuels, it is important to consider the use of renewable energies as environment-friendly and economic alternatives. The aim of this work is to evaluate, by an optimized techno-economic analysis, the use of photovoltaic and a novel wind-based technology to supply at least 10% of the current and the predicted electrical energy requirements of the mining industry in the Antofagasta region. A combination of an optimization problem and technical evaluation was performed using Matlab to obtain the optimal number of solar and wind-based technology units in a case study. Total energy generation from a novel wind-based technology unit is 67,616 MWh/y, corresponding to 14.45·106 Nm3 (1298 t) of hydrogen and 7.41·106 Nm3(10,323 t) of oxygen after electrolytical transformation. Considering a 65% efficiency of the combined cycle fed with hydrogen and oxygen, 28,133 MWh/y of electrical energy would be obtained. For the cases studied the cost of energy from the combined system was estimated to be between 0.255 US$/kWh and 0.273 US$/kWh, slightly higher than the average energy regional cost. According to the analysis, the renewable energy system could be a sustainable alternative to supply economic green energy to the mining industry in Chile.
Geotechnical Aspects of the 20115 M-w 8.3 Illapel Megathrust Earthquake Sequence in Chile
(01/05/2017) Candia, Gabriel; Pascale, Gregory de; Montalva, Gonzalo; Ledezma, Christian
The 2015 Illapel earthquake sequence in Central Chile, occurred along the subduction zone interface in a known seismic gap, with moment magnitudes of M-w 8.3, M-w 7.1, and M-w 7.6. The Main event triggered tsunami waves that damaged structures along the coast, while the surface ground motion induced localized liquefaction, settlement of bridge abutments, rockfall, debris flow, and collapse in several adobe structures. Because of the strict seismic codes in Chile, damage to modern engineered infrastructure was limited, although there was widespread tsunami-induced damage to one-story and two-stories residential homes adjacent to the shoreline. Soon after the earthquake, shear wave measurements were performed at selected potentially liquefiable sites to test recent Vs-based liquefaction susceptibility approaches. This paper describes the effects that this earthquake sequence and tsunami had on a number of retaining structures, bridge abutments, and cuts along Chile's main highway (Route 5). Since tsunami waves redistribute coastal and near shore sand along the coast, liquefaction evidence in coastal zones with tsunami waves is sometimes obscured within minutes because the tsunami waves entrain and deposit sand that covers or erodes evidence of liquefaction (e.g., lateral spread or sand blows). This suggests that liquefaction occurrence and hazard may be under estimated in coastal zones. Importantly, the areas that experienced the greatest coseismic slip, appeared to have the largest volumes of rockfall that impacted roads, which suggests that coseismic slip maps, generated immediately after the shaking stops, can provide a first order indication about where to expect damage during future major events.
Low-temperature curing strength enhancement in cement-based materials containing limestone powder
(01/06/2017) Bentz, Dale P.; Stutzman, Paul; Zunino, Franco
With the ongoing sustainability movement, the incorporation of limestone powder in cementitious binders for concrete in the U.S. has become a subject of renewed interest. In addition to accelerating the early age hydration reactions of cementitious systems by providing additional surfaces for nucleation and growth of products, limestone powder is also intriguing based on its influence on low-temperature curing. For example, previous results have indicated that the utilization of limestone powder to replace one quarter of the fly ash in a high volume fly ash mixture (40-60% cement replacement) produces a reduction in the apparent activation energy for setting for temperatures below 25 degrees C. In the present study, the relationship between heat release and compressive strength of mortars at batching/curing temperatures of 10 and 23 degrees C is investigated. For Portland-limestone cements (PLC) with limestone additions on the order of 10%, a higher strength per unit heat release is obtained after only 7 d of curing in lime water. Surprisingly, in some cases, the absolute strength of these mortar cubes measured at 7 d is higher when cured at 10 degrees C than at 23 degrees C. Solubilities vs. temperature, reaction stoichiometries and enthalpies, and projected phase distributions based on thermodynamic modeling for the cementitious phases are examined to provide some theoretical insight into this strength enhancement. For a subset of the investigated cements, thermogravimetric analysis, quantitative X-ray diffraction, and scanning electron microscopy are conducted on 7-d paste specimens produced at the two temperatures to examine differences in their reaction rates and the phases produced. The strength enhancement observed in the PLC cements is related to the cement hydration products formed in the presence of carbonates as a function of temperature.
Parallel construction of wavelet trees on multicore architectures
(01/06/2017) Fuentes-Sepúlveda, José; Elejalde, Erick; Ferres, Leo; Seco, Diego
The wavelet tree has become a very useful data structure to efficiently represent and query large volumes of data in many different domains, from bioinformatics to geographic information systems. One problem with wavelet trees is their construction time. In this paper, we introduce two algorithms that reduce the time complexity of a wavelet tree's construction by taking advantage of nowadays ubiquitous multicore machines. Our first algorithm constructs all the levels of the wavelet in parallel with O(n) time and bits of working space, where n is the size of the input sequence and is the size of the alphabet. Our second algorithm constructs the wavelet tree in a domain decomposition fashion, using our first algorithm in each segment, reaching time and bits of extra space, where p is the number of available cores. Both algorithms are practical and report good speedup for large real datasets.
Modeling Lean and Agile Approaches: A Western Canadian Forest Company Case Study
(01/09/2018) Vergara, Francisco P; Palma, Cristian D.; Nelson, John D.
In the forest supply chain of the coast of British Columbia, the material flows are directed toward the push production of commodity products. This industry has not adopted lean and agile principles due to unclear economic impacts on the supply chain in changing market conditions. We tested the ability of lean and agile principles to improve performance in the coastal integrated forest industry. Mixed integer programming formulations were subject to over-under production capacity, and over-under demand fulfillment penalties to emulate agile, lean, and hybrid manufacturing environments, when solving the planning problem. Assuming that the coastal integrated forest industry performs as a hybrid environment, the profit results of each manufacturing environment were judged. The results show that, opportunities for profit improvement were 11% for adopting an agile environment when demand was stable with low variation and large batches of production. However, profit improvement was non-existent when the same demand attributes apply but with high variation. The opportunities for profit improvement were 12% when an agile environment or lean environment was adopted when demand was stable with low variation and small batches of production. However, opportunities for profit improvements of 15% existed for adopting an agile environment when demand was unstable with high variation and small batches of production
Multiperiod Optimisation of Irrigated Crops under Different Conditions of Water Availability
(01/10/2018) Kuschel-Otarola, Mathias; Rivera, Diego; Holzapfel, Eduardo; Palma, Cristian D.; Godoy Faúndez, Alex
We propose a nonlinear optimisation model which maximises profits by resource allocation on a monthly time scale, considering a monthly crop yield model. The proposed model was applied to six management scenarios (two seasonal and four monthly), nine conditions of water availability, and two situations of resource availability under Chilean conditions. These situations provided the same seasonal amount of resources, but different distributions over time. The model included improvements in water resource management such as water storage and water transactions, being the latter a monthly decision variable that can increase farmers’ profits. According to our results, monthly scenarios gave high profits, even better with appropriate resource distribution. When water costs are high, water transactions allow loss reduction of up to 50%. Regarding labour, the lack of availability is more critical than the wages
Seismic Vulnerability of Wine Barrel Stacks
(01/11/2016) Candia, Gabriel; Jaimes, Miguel A.; Arredondo, César; de la Llera, Juan Carlos; Favierc, Philomène
Recent earthquakes have shown that wine barrel stacks are highly susceptible to collapse, leading to large economic losses, downtime, and longer recovery periods. This study presents a methodology using a probabilistic approach for estimating the fragility functions and economic losses in barrel stacks. The seismic response of these systems was determined from the dynamic equilibrium equations that describe the position and orientation of each element. The analysis considered ground motions scaled at different intensity levels and different barrel stack configurations; the simulations enabled reproducing the most common collapse mechanisms observed in the field and in shaking table experiments. From a statistical analysis of the results, vulnerability functions were evaluated as the probability of being within a specific damage state for a given ground motion intensity. Additional numerical simulations were performed to study the effects of the inherent uncertainty of the interface parameters controlling the dynamic response and collapse sequence of the barrel stacks. Furthermore, this methodology was used to evaluate the impact effect and improvement of a base isolation solution as a damage mitigation measure
Beneficios de utilizar modelos ad-hoc de gestión de inventarios en presencia de flujos de retorno
(2010) Sepúlveda Rojas, Juan Pedro; Baesler Abufarde, Felipe; Núñez Morales, Domingo Antonio
En este trabajo se analiza el impacto de la logística reversa en los modelos de gestión de inventarios a través del análisis de las implicancias y extensiones de algunos modelos estudiados en la literatura. A través de experimentación con modelos de inventario determinísticos encontramos que en gran parten de los escenarios estudiados, los costos de utilizar modelos clásicos de gestión de inventarios son superiores a modelos que toman en cuenta los flujos de retorno. Solo en casos muy particulares en donde el costo de mantención de stocks en el taller de reparables era muy elevado, se observaba la conveniencia del uso de los modelos tradicionales en detrimento de los que consideran flujos de retorno. Se puede observar además que no existen comparaciones cuantitativas entre una gestión tradicional de inventarios y una que considere los flujos de retorno.
Modelo de aprendizaje para la selección de un proyecto diseñoconstrucción (llave en mano) en el sector público
(2010) Bastías, Alfonso; Keith R. Molenaar
El método primario de ejecución de proyectos en el sector público en los Estados Unidos (U.S.), tradicionalmente ha sido la ejecución diseño-licitaciónconstrucción. El sector público históricamente ha separado los contratos de diseño y construcción. En la década de los 90, el sector público norteamericano comenzó a experimentar con la ejecución de proyectos diseño-construcción (llave en mano), que combina el diseño y la construcción en un solo contrato. En 1997 se estableció un sistema de apoyo a la toma de decisiones, con el fin de entregar un modelo se selección formal para la ejecución de proyectos en el sector público. El modelo apoya a los propietarios del sector público a determinar cuáles son los proyectos adecuados para la ejecución diseñoconstrucción (llave en mano). Este modelo inicial por naturaleza era estático y estaba basado en un análisis de regresión de 104 proyectos. El análisis produjo un modelo predictivo con cinco criterios de rendimiento: satisfacción general, carga administrativa, cumplimiento de expectativas, variación del programa, y variación del presupuesto. Desde 1997, el número de proyectos diseño-construcción ha aumentado dramáticamente y los métodos diseñoconstrucción del sector público han evolucionado. El modelo original puede ser mejorado con nuevos datos y una estructura que se traduce en un modelo adaptativo, mientras la industria continúa evolucionando. Este documento presenta una aplicación formal y el uso de capacidades para complementar el modelo estático original. Este modelo se ajusta a parámetros y funciones a través del empleo de inteligencia artificial, como principal motor de conocimiento. Este enfoque puede ser adaptado a muchas aplicaciones de apoyo a la toma de decisiones en la industria del diseño y construcción
Base Station Location Optimization for Minimal Energy Consumption in Wireless Networks
(Vehicular Technology Conference, 2011) González-Brevis, P; Gondzio, J; Fan, Y; Poor, H.; Thompson, J.; Krikidis, I; Chung, P.
This paper studies the combined problem of base station location and optimal power allocation, in order to optimize the energy efficiency of a cellular wireless network. Recent work has suggested that moving from a network of a small number of high power macrocells to a larger number of smaller microcells may improve the energy efficiency of the network. This paper investigates techniques to optimize the number of base stations and their locations, in order to minimize energy consumption. An important contribution of the paper is that it takes into account non-uniform user distributions across the coverage area, which is likely to be encountered in practice. The problem is solved using approaches from optimization theory that deal with the facility location problem. Stochastic programming techniques are used to deal with the expected user distributions. An example scenario is presented to illustrate how the technique works and the potential performance gains that can be achieved.
Proceso logístico productivo de un centro de sangre regional: modelamiento y análisis
(2011) Baesler, Felipe; Martínez, Cristina; Yaksic, Eduardo; Herrera, Claudia
Background: The blood supply chain is a complex system that considers different interconnected elements that have to be synchronized correctly to satisfy in quality and quantity the final patient requirements. Aim: To determine the blood center maximum production capacity, as well as the determination of the necessary changes for a future production capacity expansion. Material and Methods: This work was developed in the Blood Center of Concepcion, Chile, operations management tools were applied to model it and to propose improvement alternatives for the production process. The use of simulation is highlighted, which permitted the replication of the center behavior and the evaluation of expansion alternatives. Results: It is possible to absorb a 100% increment in blood demand, without making major changes or investments in the production process. Also it was possible to determine the subsequent steps in terms of investments in equipment and human resources for a future expansion of the center coverage. Conclusions: The techniques used to model the production process of the blood center of Concepcion, Chile, allowed us to analyze how it operates, to detect "bottle necks", and to support the decision making process for a future expansion of its capacity (Rev Med Chile 2011; 139: 1150-1156).
Desarrollo de un algoritmo para la generación y elección de soluciones de corte en la operación de canteo y despuntado en aserraderos
(2011) Vergara, Francisco P.; Baesler, Felipe; Ramos, Mario
In this research work an algorithm that gathers the best procedures applied in sawmills was developed, along with a methodology based on cutting geometrical line analysis. This application was programmed under the C(++) language, sizes objective board and its prices, and the 2-D slab geometry are the input data, obtaining length and width solutions for every slab. Its outcomes have been compared with a pattern that matches the solutions provided by an "optimized" cutting machine in a southern sawmill in Chile. Four types of solutions were obtained when inputting slabs geometry, which was captured with four different reading steps. Outcomes show that solutions achieved with a reading width of 100 mm were 4% better in average than the pattern, and far better to other solutions achieved with the remaining 3 steps. Leaving aside the particular operating conditions of either method; a theoretical comparison of time by solution method, indicates that the 77 milliseconds SISCORMAD employed are significantly lower than those obtained with dynamic programming 320 milliseconds, 890 milliseconds with total enumeration, and 140 milliseconds obtained with geometric heuristic as solution times reported by [6]. This feature makes the developed algorithm very attractive for future applications. However, given the heuristic nature SISCORMAD, it is just a high quality solution, but not optimal.
Elastic strains, modulus and permanent deformation of foamed bitumen pavements in accelerated testing facility
(2012) González Vaccarezza, Álvaro; Cubrinovski, Misko; Pidwerbesky, Bryan; Alabaster, David
An accelerated full-scale experiment on foamed bitumen (FB) pavements was conducted at the Canterbury Accelerated Pavement Testing Indoor Facility (CAPTIF) in New Zealand. The results of the CAPTIF experiment showed that the section with 2.8% bitumen content and 1% cement content (section B28C10) had the best performance. These results were published in a previous research paper. The current paper is the continuation of the previous work and aims to provide design and performance parameters that could be used by practitioners and researchers. The pavement strains were measured at different depths and transverse locations using pavement instrumentation. The measurements showed that subgrade strains are lower in section B28C10 and that the strain distribution in the subgrade is relatively uniform, reducing the strain concentrations in this layer. Falling Weight Deflectometer (FWD) measurements were used to determine an AASHTO 93 structural coefficient of 0.20 for the FB layer of section B28C10. FWD and pavement strain measurements were used to back-calculate the average elastic modulus of 1100 MPa for the FB layer. Finally, a permanent or plastic strain model was developed for the FB layer using the pavement vertical surface deformation measurements and post-mortem data.
udpSkeduler: A web architecture based decision support system for course and classroom scheduling
(2012) Miranda, Jaime; Rey, Pablo; Robles, José
A key process for post-secondary educational institutions is the definition of course timetables and classroom assignments. Manual scheduling methods require enormous amounts of time and resources to deliver results of questionable quality, and multiple course and classroom conflicts usually occur. This article presents a scheduling system implemented in a Web environment. This system generates optimal schedules via an integer-programming model. Among its functionalities, this system enables direct interaction with instructors in order to gather data on their time availability for teaching courses. The results demonstrate that significant improvements over the typical fully manual process were obtained. (C) 2011 Elsevier B.V. All rights reserved.
Interpretation of laboratory and full-scale testing of New Zealand foamed bitumen pavements using finite-element modelling
(2012) González Vaccarezza, Álvaro; Cubrinovski, Misko; Alabaster, David; Thenoux, Guillermo
A large research project on foamed bitumen (FB) stabilisation was conducted in New Zealand. The project consisted of an extensive laboratory and full-scale testing of FB pavements. The objective of this paper is to interpret the performance of FB pavements by using finite-element (FE) modelling. The mechanical properties of the materials were calculated using testing data and used as material inputs in the FE modelling. The MohrCoulomb and DruckerPrager material models were adopted to calculate plastic deformation, which is related to pavement rutting. Results of the modelling indicate that increasing the FB content increases the tensile strength and modulus of the pavements, reducing the plastic deformations in the subgrade and the stabilised layer. In addition, adding FB reduces sensitivity to rutting when pavement is overloaded or the asphalt surface layer is cracked
Environmental outcomes: Linking social and economic issues
(2012) Godoy Faúndez, Alex; Hernando, Andrés; Correa, C; Reyes, L
Concepts like environmental convservation, sustainability and sustainable development are not currently considered primary concerns in most of Latin-America and the Caribbean. This omission can partly be attributed to the lack of environmental history in this area. By the 1950s, the concept of environmental conservation was introduced to our legal and technical vocabulary due to influences of conservationism associated with academic-intellectual national elites. These elites formed an eco-spiritual movement closer to socialism ideology than to eco-centric ideas, as a natural outcome of the late 60s and early 70s culture. The military governments, which took power during the 70s and 80s, persecuted people associated with socialist ideologies, resulting in a dispersal of members and ideas resulting in the loss of environmental concepts and ideas for over 10 years. The economic reforms of the 1980s and the adoption of the neoliberal paradigm increased the importance of the exploitation of natural resources. These reforms increased economic development yet led to the concern regarding the environmental impacts. As a response a new institutional network was created. New institutions allowed the establishment of various institutes and centers that funded research as a response to the neoliberal economic model. Introducing ecological concepts, their main concern was the indiscriminate exploitation of natural resources. The focus was mainly on profits and environmental issues related to agriculture and mining resources (Vallejos, J.P.; 1994). During the 1990s, new intellectuals associated with Non-Governmental Organisations (NGOs) emerged. The focus was for the promotion of democracy and social justice, rescuing their social influence from the original socialist thinking. This also meant a turning point in the collective conscience about the environment by introducing a social component, Nevertheless, environmental concern was often used according to their personal agendas. The "institutionalization" created by new intellectuals disappointed with the socialist approach and instrumentalization, adopted equality issues and development concern thus putting an end to its ideological use. However, it is acknowledged that these trends have set the overall development of the new legal institutions, which, since the return to democracy and the incorporation of highly technical professionals to high public positions and private management, led to the passing of laws such as Law on Environmental Framework Law No. 19,300 in Chile.
Performance of foamed bitumen pavements in accelerated testing facility
(2012) Cubrinovski, Misko; Gonzalez, Alvaro; Pidwerbesky, Bryan; Alabaster, David
One of the key principal goals of pavement asset management is to develop and implement cost-effective pavement construction and maintenance strategies that achieve the required levels of service and performance. A sustainable, cost-effective technique for rehabilitating pavements is foamed bitumen stabilization. This paper presents a study on the performance of foamed bitumen pavements tested in the Canterbury Accelerated Pavement Testing Indoor Facility (CAPTIF), for full scale testing of pavements. Six pavement sections were tested; the variables were bitumen and cement content; one control section with the untreated unbound material was tested. Results showed that surface deflections decreased at sections with higher bitumen contents. After the application of 5,710,000 Equivalent Standard Axles (ESAs), the sections stabilised with cement only, bitumen only, and the control section all showed large amounts of rutting. Conversely, little rutting was observed in the three sections stabilised with foamed bitumen and 1.0% cement, showing that cement and FB together significantly improve pavement performance. The rutting results were used to develop models to describe the stable and unstable performance of the tested pavements. The paper concludes by outlining some of the practical benefits of utilising this technology in pavement asset management.
New Developments in the Primal-Dual Column Generation Technique
(2013) Gondzio, J; González-Brevis, P; Munir, P
The optimal solutions of the restricted master problems typically leads to an unstable behavior of the standard column generation technique and, consequently, originates an unnecessarily large number of iterations of the method. To overcome this drawback, variations of the standard approach use interior points of the dual feasible set instead of optimal solutions. In this paper, we focus on a variation known as the primal–dual column generation technique which uses a primal–dual interior point method to obtain well-centered non-optimal solutions of the restricted master problems. We show that the method converges to an optimal solution of the master problem even though non-optimal solutions are used in the course of the procedure. Also, computational experiments are presented using linear-relaxed reformulations of three classical integer programming problems: the cutting stock problem, the vehicle routing problem with time windows, and the capacitated lot sizing problem with setup times. The numerical results indicate that the appropriate use of a primal–dual interior point method within the column generation technique contributes to a reduction of the number of iterations as well as the running times, on average. Furthermore, the results show that the larger the instance, the better the relative performance of the primal–dual column generation technique.
Construction Project Peer Reviews as an Early Indicator of Project Success
(2013) Molenaar, Keith R; Javernick-Will, Amy; Bastías, Alfonso; Wardwell, Meredith A; Saller, Kevin
In an effort to proactively identify and mitigate potential project management problems in construction projects, the United States General Service Administration (GSA) developed and implemented a project peer review process in conjunction with the University of Colorado at Boulder and Peter Associates. This paper discusses the peer review process and analyzes whether the questions used in the review can predict project success, as measured by cost, schedule, and the project peer rating, for 22 past projects. The data were analyzed retrospectively by using the point biserial correlation coefficient. The results indicate that project peer reviews conducted during the construction process can be used to assess and predict final project performance. Questions regarding working relationships, communication, timing, project controls, and relational approaches to project participants had significant correlations with project success. In addition, the relationship between the designer and contractor appears to be very important to the outcome of the project, regardless of project delivery method. This study suggests that companies and organizations can strategically improve projects by conducting project peer reviews early in the construction process. Future research can extend and validate these findings in more detail by analyzing additional peer review questions to determine the best indicators of project failure or success.

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