Sergio Reyes

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Reyes

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Sergio

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0000-0002-0450-6880

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Publications 1 - 10 of 27

Buckling of steel tanks under earthquake loading: Code provisions vs FEM comparison
Moreno, Matías; Colombo, José; Wilches, José; et al. (2023)
Journal of Constructional Steel Research
A poor seismic design of liquid storage tanks may result in large economic losses or environmental impacts due to the spillage of their contents; therefore, an effective seismic design of these tanks is of vital importance. Moreover, many liquid storage tanks have suffered severe damage during recent earthquakes worldwide due to the buckling of their wall, which is one of the most common failures. In continuously supported tanks, anchors are an essential part of the seismic design; however, the effectiveness of incorporating them and the predictive ability of design codes on the behavior of these structures has not been extensively studied. This research evaluates the design recommendations (API-650 and NZSEE) through a comparison with nonlinear 3D finite element models. In particular, the compressive stress and the buckling capacity of the tank wall are evaluated. Three anchorage conditions are analyzed: (i) tank with a fully anchored base, (ii) tank with flexible anchors at the periphery of the base (bolted anchorage), and (iii) unanchored. Four tank geometries, two materialities (stainless steel and carbon steel), and different amounts of anchors for each geometry were analyzed. In total, 24 nonlinear 3D finite element models were developed and analyzed. The presented results provide a better understanding of the effectiveness of including anchors depending on the tank slenderness and the predictability capacity of design codes for these structures. Finally, some code guidelines for flat tanks are validated, and the need for additional detailed guidelines for slender tanks is highlighted.
Experimental and numerical assessment of grout-filled tennis balls as seismic isolation bearings
Katsamakas, Antonios A.; Del Giudice, Lorenzo; Reyes, Sergio; et al. (2023)
Engineering Structures
This paper describes the behavior of a low-cost seismic isolator comprising a grout-filled tennis ball rolling on concrete plates. The isolator could be used for isolating lightweight structures. Initially, the axial response of the system was characterized. Subsequently, full-scale isolators were tested in combined compression and lateral cyclic loading. Parameters of investigation were the testing velocity (frequency), the bearing load, the degradation due to consecutive loading, the bearing temperature, the specimen-to-specimen variability, and the engagement of the displacement restrainer. Finally, a three-dimensional finite element model was developed to model in detail the response of the isolator and to explore the influence of the rubber thickness. This is the first study to characterize the above effects and to propose a finite element model of these isolators. Results showed that the lateral cyclic response of the isolators is bilinear and can be approximated by rigid-body equations, whereas the values of the rolling friction coefficient and the yield displacement are suitable for seismic isolation applications. The specimen-to-specimen variability was minimal. Unlike sliding isolation systems, an increased bearing compressive load leads to a higher rolling friction coefficient. Analytical equations are offered to describe this effect. The rolling friction coefficient does not depend on velocity (frequency) or temperature, and the isolators did not deteriorate under consecutive loading. The proposed displacement restrainer effectively limits the motion of the isolator. The developed finite element model accurately captures the experimental response. It was used to study the influence of the thickness of the rubber layer on the lateral response, to conclude that it is minimal, for rubber layers ranging from 3.4 to 7 mm.
Analysis of Energy Dissipation in Series and Parallel
Ramirez Marquez, Victor; Guzman Lucatero, Erik; Macias Jaime, Jesus; et al. (2021)
WCEE Online Proceedings ~ Proceedings of the Seventeenth World Conference on Earthquake Engineering Japan 2021
The seismic response of a cinema structure located in a high seismic zone of Mexico structured based on steel frames and composite slabs is analyzed. The response of the structure was analyzed using viscous fluid dampers with a 18.9-meter span, and the response is obtained through nonlinear time-history analysis. The results show that there were problems with a single viscous fluid damper due to the long span of the diagonal, resulting in large dimensions and also its connection. The damper resulted in difficult capacities to manufacture and test in the laboratory. As an alternative, the frame was studied with viscous fluid and frictional dampers placed in series and parallel, analyzing their response for twenty fully reversed cycles at the maximum expected displacement, with a frequency ω equal to the fundamental of the structure-damping system, comparing the energy dissipation and its equivalent linear properties. The equivalent system of viscous fluid dampers connected in series is incorporated into the cinema project, resulting in smaller dimensions and capacities, as well as its steel connecting elements. The proposal of parallel energy dissipation was viable with fluid viscous dampers connecting them with steel elements generating the necessary stiffness so that they behave axially, reducing the cost of the dampers and achieving the energy dissipation necessary for the project.
Shaking table test on full-scale legged liquid storage tanks protected with a vertical-rocking isolation system
Reyes, Sergio; Almazán, José L.; Colombo, José I.; et al. (2021)
WCEE Online Proceedings ~ Proceedings of the Seventeenth World Conference on Earthquake Engineering Japan 2021
Legged thin-walled liquid storage tanks have shown in many cases poor seismic performance during several strong earthquakes around the world. The damage and collapse of these containment structures lead to the loss of the liquid, such as milk, wine, and others, thus generating significant economic losses. This damage may also affect components along the production line of other food products, and hence, it is relevant to develop solutions to seismically protect these structures and ensure continuous operation. Consequently, this paper presents the dynamic performance evaluation of a new Vertical-Rocking Isolation system. This evaluation is done by shaking table tests performed on a full-scale legged storage tank. A comparison is presented between the numerical seismic behavior of the fixed-to-the-base configuration of the tank and the experimental one with vertical rocking isolation. The isolation system setup consisted of four ISO3D-2G devices, each one placed on each leg of the tank. The ISO3D-2G device is vertically flexible and laterally stiff, which enables the isolation mechanism of the rocking motion of the tank. The experiments were carried out using a white noise input and three ground motions. The measurements included the acceleration and lateral displacement at the center of mass of the tank. Experimental results confirm the beneficial effects of using a vertical-rocking isolation system in this legged storage tank. Base shear reduction ratios between 5.5 and 8.4 were obtained, which demonstrates that the lateral isolation effect is satisfactory. The use of this device can also be extended to other systems sensitive to rocking motions.
Best retrofit based on energy dissipation for a building subjected to various strong earthquake
Guzman Lucatero, Erik; Ramirez Marquez, Victor; Macias Jaime, Jesus; et al. (2021)
WCEE Online Proceedings ~ Proceedings of the Seventeenth World Conference on Earthquake Engineering Japan 2021
A Mexico City building built in 1958 located on soft soil is analyzed, which has been damaged by the 1985 Mw 8.1 and 2017 Mw 7.1 earthquakes. Buildings in the same area and similar structural systems collapsed in these earthquakes (210 in 1985 and 38 in 2017). To perform the mathematical model, a structural identification was carried out using a rebar locator and a concrete rebound hammer. The response of the building subjected to these earthquakes was analyzed, finding the changes of the stiffness of the building when plastic hinges were formed, as well as the adjustment in the period of the structure. The analysis performed are nonlinear time-history. The response of the structure shows considerable damage to several elements being at risk of collapse with another earthquake, the reason why the building is uninhabited. Therefore, reinforcements are proposed with energy dissipation which gives the building the capability to resist another earthquake like the experienced in 1985 or 2017. To determine which system is the most convenient in this case, the response of the building is compared using several energy dissipation systems; those that only provide damping to the structure, and those that provide damping and also stiffness. An important point observed was that systems that provide stiffness and damping can lead the period of the structure to coincide with the site period (2 seconds), which would cause a resonance effect, the main reason of why many near-2-second period buildings collapsed in 1985 earthquake. Therefore, it is highly recommended to carry out an analysis of this type on all buildings that have been affected by more than one strong earthquake in Mexico City.
Vibration Isolation Capabilities of a Low-Cost Seismic Isolation System Based on Elastomeric Rolling Spheres for Masonry Structures
Reyes, Sergio; Katsamakas, Antonios A.; Vassiliou, Michalis F. (2024)
RILEM Bookseries ~ Structural Analysis of Historical Constructions
In recent years, seismic isolation has been used as an effective retrofit technique to protect historical buildings and structures against earthquakes. However, for some isolation devices, man-induced low-amplitude vibrations (e.g., construction activities, vehicle, and rail traffic) can still be directly transmitted to the structure. These vibrations can cause damage and deteriorate structural elements if they persist during extended periods of time, especially on masonry or unreinforced structures. This paper explores the horizontal low-amplitude vibration isolation capabili-ties of a low-cost seismic isolation system based on elastomeric rolling spheres for low-rise structures. The isola-tion system consists of elastomeric spheres placed underneath the structure, providing lateral isolation through rolling and still providing vertical flexibility and damping through the deformability of the spheres. Experimental tests were performed to characterize the sphere’s rolling mechanical behavior under relatively small deformation amplitudes, calibrating a simple yet effective nonlinear model to perform further numerical analyses under other inputs that the shake table could not reproduce. The vibration isolation performance of the spheres was addressed through its transfer function. The results showed that the proposed isolation system based on rolling elastomeric spheres has the potential to serve as a dual isolation system, i.e., protect the structure against earthquake events and long-term ambient vibrations. Further experimental tests need to be performed to validate the conclusions pre-sented herein and extend the applicability of such isolation system to industrial machinery or sensitive equipment where traditional vibration isolators are required but do not protect against earthquakes.
Experimental characterization and constitutive modeling of thermoplastic polyurethane under complex uniaxial loading
Reyes, Sergio; Vassiliou, Michalis F.; Konstantinidis, Dimitrios (2024)
Journal of the Mechanics and Physics of Solids
This paper presents the testing and constitutive modeling of a Thermoplastic Polyurethane (TPU) compound used in commercial applications. The tested specimens were extracted directly from a TPU sphere used in check valves through water-jet cutting. The tests included tensile and compression tests under complex uniaxial loading protocols to capture different nonlinear phenomena, such as stress softening, hysteresis, relaxation, creep, and rate dependence. The material is modeled assuming a nonlinear elastic equilibrium path that may exhibit stress softening (i.e., Mullins effect), and a hysteretic viscoplastic response that presents rate dependence at three different time scales. To achieve this constitutive behavior, a Parallel Rheological Framework model is used. The nonlinear elastic equilibrium path is modeled using the generalized Yeoh hyperelastic model. The stress softening of the equilibrium path is modeled using the Ogden-Roxburgh damage model on the deviatoric response. The hysteretic viscous response is further split into three viscoplastic chains to represent time dependence at three different time scales in a decoupled way. Each viscoplastic chain is modeled using the Bergstrom-Boyce model with its standard evolution law of the creep strain. The model parameters were found using a stochastic optimization scheme to simultaneously fit all the considered tests. The outstanding agreement between the model and the experimental data across a wide range of loading scenarios provides additional insight into the time-dependent behavior and deformation mechanism of TPUs. Moreover, it shows that the mechanical behavior of these materials can be represented by decoupling the nonlinear viscoplastic behavior in different time scales.
Effects of two testing protocols on the material model parameter identification for rubber-like materials
Reyes, Sergio; Vassiliou, Michalis; Agathos, Konstantinos; et al. (2022)
Proceedings of the Third European Conference on Earthquake Engineering and Seismology – 3ECEES
This paper analyzes the polyurethane material that can be used for the construction of seismic isolation devices based on rolling of elastomeric spheres. Such isolators could be used in low-income countries. Uniaxial tensile tests were performed on dumbbell-shaped polyurethane 95 ShA specimens under two different loading protocols. Protocol 1 consisted of applying a cyclic saw-tooth loading centered on a pre-imposed initial deformation, while Protocol 2 consisted of consecutive loadings followed by relaxation at three different deformation levels. Then, a material model comprising three-chains in parallel was calibrated against the tests. The model combined the Yeoh hyperelastic and Bergstrom-Boyce models. The results of the parameter calibration showed that different testing protocols could lead to different model parameter values. In terms of fitting errors, it is observed that fitting to Protocol 1 generates a good prediction on Protocol 2 with an error of 0.26%; however, when fitting to Protocol 2, the behavior observed on Protocol 1 could not be accurately predicted, resulting in an error of 9.10%. Moreover, when comparing fitting to match only Protocol 1 with considering both protocols simultaneously, the total error is only reduced from 0.32% to 0.20%, suggesting that Protocol 2 adds redundant information already contained in Protocol 1. Additional tests with different deformation rates and ranges need to be conducted to define an optimal protocol for material calibration.
Numerical and Experimental Analysis of Earthquake Protection Systems based on Elastomeric Spheres
Reyes, Sergio (2024)
Since ancient times, earthquakes have been associated with concepts such as destruction, death, and loss. Nowadays, their connotation is not so different, but engineers have arguably made paramount efforts to allow humanity to live in safer constructions by creating structural design standards and proposing new technologies. In the last century, several earthquake protection technologies have been proposed to protect constructions against ground motions, which can be broadly classified into energy dissipation systems and seismic isolation systems. The first consists of providing structures supplemental damping through additional structural fuse elements that absorb energy when the structure is deformed, thus relieving part of the seismic demand on other more important structural elements, such as columns. The second consists of providing a relatively flexible interface between the structure and its foundations, which allows large deformations under earthquake ground motions and reduces the seismic demands on the isolated part of the structure. While these technologies have been widely adopted and validated for high-importance structures where an improved performance level (e.g., continuity of operation) is desired, their implementation in normal structures is still limited because sometimes it is more expensive than the traditional earthquake-resistant prescriptive design. This makes these technologies prohibitive in developing countries where following structural design codes is unaffordable, causing disproportionate casualties and damages when major earthquakes strike. This problem also extends to other types of industrial structures and equipment that exhibit a high collapse rate during seismic events, such as electrical transmission equipment, stainless steel storage tanks, and vibratory machinery, among many others. In all these structures, the prescriptive design has been shown to be insufficient to ensure an acceptable level of performance, and the use of widely implemented earthquake protection systems is sometimes an eco-nomically inviable solution. In an effort to make earthquake protection technologies more affordable, this dissertation presents the experimental and numerical studies of a rolling seismic isolation system based on elastomeric spheres that has the potential to be less expensive than other protection systems for specific applications. The system consists of spheres made of a hard thermoplastic polyurethane (Shore A hardness of 95) to support the structure's weight and provide the rolling mechanism. The restoring force can be gravity-induced (e.g., friction pendulum systems) or provided with additional elements (e.g., springs). These spheres are massively produced with or without a steel core as a commodity for ball-check valves, with standardized manufacturing procedures, low material properties variability, and meeting the ASTM D2000 standard and the ROSH and REACH compliances. However, this material has not been properly characterized for structural applications. Moreover, the rolling behavior of the system is more complex than that of a rigid rolling ball: it creeps under the vertical weight and adopts an apparently permanent oblong shape, which affects the lateral force-deformation relationship of the isolation system. The research involved a detailed mechanical characterization of the thermoplastic material and its validation against experimental tests for its use in finite element simulations to understand the system's rolling behavior and energy dissipation mechanism. Uniaxial tensile and compressive samples were extracted directly from one of the spheres and tested under complex loading protocols to trigger several nonlinear phenomena simultaneously. A constitutive modeling approach was proposed based on the parallel rheological framework and calibrated against the uniaxial tests. The results showed that this material strongly exhibited all the typical nonlinearities expected in this type of polymer, such as the Mullins effect, hysteresis, relaxation, and rate-dependence. The Mullins effect can be accurately described using the Ogden-Roxhburg model, while all other mentioned phenomena can be represented through independent viscoelastic mechanisms representing the rate-dependence of the material at different timescales. The constitutive model was implemented in MSC Marc software and validated against experimental tests involving cyclic compression tests on a solid cylinder, solid sphere, and sphere with a steel core, all made of the same nominal material. The validated model was used to perform further analyses on the behavior of a rolling sphere with and without a steel core. It was found that during creep, most deformation is concentrated towards the center of the sphere, while during rolling, most energy dissipation comes from the material being deformed close to the surface. Therefore, the benefits of including a steel core in the sphere are threefold: (1) eliminates the oblong shape caused by creep, making the force-deformation relationship more bilinear; (2) maintains an acceptable level of energy dissipation despite the replacement of almost all the elastomeric material by steel, and (3) increases the vertical load capacity of the system. However, the steel core has to be large enough since these benefits were not observed for a 100 mm diameter sphere and a steel core size of 50 mm. For steel cores of 80- and 90-mm diameter, the system's behavior is nearly bilinear with a rolling resistance coefficient close to 0.03 for a vertical load of 8kN. This rolling isolation system is an affordable solution for lightweight structures, particularly for one- or two-story masonry or reinforced concrete structures, low-rise timber buildings, and industrial equipment. A centered steel core benefits the system in two aspects: it reduces vertical deformations while increasing vertical-loading capacity and improves the rolling mechanism's behavior. However, the centeredness of the steel core is not easily achieved during the manufacturing process, compromising the performance of the whole isolation system. Thus, an accurate and fast estimation of the core eccentricity will allow an early assessment of spheres to be applied as a seismic isolation device. Four non-invasive methods for estimating the core eccentricity of the spheres are evaluated (X-ray Computed Tomography, Camera-Based motion tracking, Tilt tests, and Average Period Estimation); of which all except X-ray Computed Tomography use the system's equation of motion to estimate the core eccentricity. All methods agreed well with the results of the Computed Tomography, identifying the core eccentricity with mean errors below 12%. This shows that these methods are good candidates for developing an easy, fast, and reliable prequalification procedure for these spheres.
Experimental and Numerical Studies on Thick Rubber Bearings under Uniaxial and Offset Tensile Loading
Zhang, Zengde; Vassiliou, Michalis F.; Zhou, Ying; et al. (2024)
Journal of Structural Engineering
Thick rubber bearings (TRBs) have been proven to be effective in mitigating horizontal shaking induced by earthquakes as well as railway-induced vertical vibration. During earthquake excitations, TRBs might be subjected to tension, which should be carefully assessed during design. This paper presents experimental and numerical studies on the behavior of TRBs under tensile loading. Four full-scale thick natural rubber bearing (TNRB) and lead thick rubber bearing (LTRB) specimens were designed and tested under tension, with and without lateral offset. The test results showed that increasing the applied lateral offset decreased the tensile stress and stiffness of the TNRBs, while the LTRBs did not exhibit any reduction. In addition, the test results were compared with design specifications in current codes for conventional rubber bearings. Finally, finite element (FE) models of TRBs were built and validated against the results of uniaxial and offset tensile experiments, and the cavitation of rubber was modeled via a two-phase model. To further estimate the damage due to previous tensile loading, damage variables under cyclic tensile loading were also taken into account. The experimental and numerical results showed that the lead core only slightly increased the initial tensile stiffness of the bearing under uniaxial testing, while it had a significant influence on the tensile properties of the LTRBs under offset displacement.

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