Anti-seismic devices are employed to implement the best performance of the structures under earthquakes. In this paper, semi-active tuned mass dampers (SA-TMDs) are studied by considering several ...combinations of variable friction forces and external disturbances. The variable damping model is used, where the goal consists in estimating the external actions to find the best friction force for system dampening. In particular, general, sinusoidal, and Gaussian dynamic loadings are considered. To obtain the response of the structure and dampers, several numerical solutions have been implemented. Probabilistic and determines analyses have been also developed to study different damper characteristics. Results show that a SA-TMD can reduce the structure displacements up to ~ 70.0% indicating a good performance in controlling different oscillations. This technology not only preserves the integrity of a structure mitigating its vibrations but also improves the life of occupants and their safety and comfort. This is beneficial from the perspective of practical application, and it is an advancement with respect to this theme.
The attack of chloride ions is one of the most important factors affecting reinforced concrete (RC) durability. Chloride ingress into concrete is usually studied by assuming constant diffusivity and ...constant surface chloride concentration. However, these two approximations could badly estimate the chloride concentration in RC structures and then the lifetime assessment. Several factors influence the chloride concentration and ingress mechanisms in the convection area. In this paper, a new multifactorial and multiphase model to account for some effects on chloride surface concentrations in the convection zone is proposed. 136 values have been collected to identify the position and the chloride concentration in the border between the diffusion and convection zones. In addition, a time-dependent multifactorial diffusivity is considered. Diffusivity, which is the key parameter of the mechanical diffusion accounts in this paper for the water/cement ratio, chloride binding, temperature, concrete age, internal humidity, concrete deformation, and damage. The surface chloride model considers environment humidity, temperature, superficial concrete irregularities, and convection area of concrete. Advanced numerical solutions have been carried out to consider space and time dependencies in the model. Results show that the error function-based solutions could underestimate the chloride concentration C for periods < 10 years and for concrete depths > 4.0 cm in comparison with the proposed model.
The diffusion of chloride ions in reinforced concrete (RC) varies in space and time, depending on many uncertain factors as material properties, temperature, aging, humidity and external loadings. In ...this paper, the goals are to provide different scenarios to probabilistic assessing of the corrosion initiation time and chloride ions content inside concrete considering different fluctuations. For the former, stochastic analyses helps to estimate the service life in RC; for the latter, the focus is on the nature of loading variation due to location and structural constraints that usually are not considered. The approach consist in studying the trend of chloride ion particles regarding the action of the external loadings by incorporating a function with random values. The governing equations are modified to account for the non-constant diffusivity under transient conditions. Results show that the chloride content for random diffusivity assumes lower values than for constant diffusivity. Moreover, in 2D analysis the chloride content is lesser of 78% than in 3D analysis.
Mechanical diffusion of chloride ions in reinforced concrete (RC) structures varies in time and space, and depends on uncertain factors such as material properties, temperature, humidity, and aging. ...In this paper, different scenarios considering the time of corrosion initiation and the influence of the chloride diffusion coefficient for different loadings (i.e., constant, sinusoidal, Gaussian, and random) were proposed. Stochastic analyses were carried out to estimate the probability of failure of steel bars, and to evaluate the influences of the internal and external factors. Advanced numerical solutions were developed to account for these influences under non-constant diffusion coefficient and non-steady-state condition. Results show that the chloride content can assume low values by using the oscillations of the generic function (e.g., sinusoidal and general) instead of constant function. The influence of the temperature appears relevant. The 3D analyses, considering the random variability, show that chloride content can be higher than ~1.50 compared to chloride content using traditional approaches. Stochastic approaches plus advanced solutions allow, in a more complete way, the sustainability decision-making process during the design phase, maintenance, inspections, and repair.
Probabilistic seismic hazard analysis (PSHA) is nowadays the more complete analysis method to estimate the seismic input for structural analysis. However, it is strongly influenced by seismogenic ...parameters and attenuation equations. Here PSHA using empirical Green’s functions (EGFs) with 2 + 2 variables is carried out, which, as proposed, are related to each other through the moment magnitude. This combination, already known as “physically based PSHA (pb-PSHA),” is an approach that should be disseminated since it could provide a good alternative in countries where the seismogenic zones and/or attenuation equations are not well established. The proposed model, using differential equations, is based on a linear fault, random/periodic/impulsive/linear source functions, and punctual hypocenter. Results are shown in terms of new seismic parameters, specific return periods, and ground accelerations. The studied country is Portugal since it appears to the authors that no study has been published about pb-PSHA for Portugal. In this sense, the model could be of importance for hazard analyses to incentivize more research on the earthquake source physics.
Photovoltaic (PV) energy systems are considered good renewable energy technologies due to their high production of clean energy. This paper combines a PV system with wastewater treatment plants ...(WWTPs), which are usually designed separately. For this, a recent methodology was adopted, which provides direct steps to estimate the peak powers of PV plants (PVPs) by using the airflow of blowers. The goal was to reduce the energy consumption of aeration tanks in WWTPs. Analytical equations and parameters based on the air temperature, solar irradiation, biological kinetic, dissolved oxygen, and mechanical oxygenation are adopted. The key parameter in this methodology is the air temperature variation that represents an approximated temperature in the WWTP’s oxidation tanks. It is shown, through the analysis of small WWTPs, that since the temperature changes for each season, there is a peak in the function of the quantity of oxidation, which is high in the summer season. Further, the curve trends of temperature for WWRPs are similar to PVPs. Therefore, it could be possible to design the PV system with the WWTPs well. The results show that the air temperature curves increase in a directly proportional way with the consumption of energy from oxidation blowers; this could induce a more conservative PVP design. Furthermore, the results show that the mean trend of the energy consumption of the analyzed aeration systems reaches about 8.0% at a temperature of 20–25 °C, covering a good part of the oxidation tank consumption.
In this paper the negative effects of the chloride ions attack in reinforced concrete (RC) elements have been studied. For this the vertical and horizontal chloride diffusivity has been treated by ...several models to identify the more relevant factor affecting the chloride concentration. The pitting corrosion has been treated to define the resistance losses of the shear forces and bending moments. An alternative deterministic/probabilistic procedure, by a direct and systematic new model, has been proposed to estimate the total time of service life for RC elements at the design phase. Several detailing configurations of steel bars in a RC beam, water/cement ratio and level of aggressiveness have been analysed to compare the model predictions. In this sense, this paper should provide useful results for analysts in terms of probability of failure for resistance losses and time of corrosion initiation. The goal is not only to provide practical results but also to evaluate the issue in a more modern risk analysis throughout the proposed prediction model.
Quantitative analyses of structural resistance are useful during the design process to prevent the occurrence of progressive collapse. Buildings subjected to continuous instances of ...expected/non-expected loadings due to extreme events (e.g., earthquakes, explosions, floods, hurricanes) can collapse. A lack of specific knowledge from the designer and poor maintenance can affect collapse analyses. In this paper, the probability of failure for pancake collapse with respect to bending collapse for reinforced concrete (RC) multi-storey buildings is estimated. New combinations regarding the elastic/plastic behaviour of the material under distributed loadings on beams are proposed. Numerical 2D finite element method (FEM) analyses are carried out to model these buildings. Also, simplified dynamic analyses are carried out. The outputs are plotted in terms of the probability of failure for pancake collapse as a function of column compressive strength and the number of removed columns. The results show that the presence of elastic beams can influence the pancake collapse of columns, and, for buildings composed of several elements, the elimination of few elements has little impact on their stability.
One of the most relevant deterioration mechanisms of reinforced concrete (RC) structures is the corrosion of steel bars by chloride ions. The service life of structures could be extended by ...monitoring this process. The lack of correlation data between chloride ion diffusion and the electrical field has meant that alternative methods have been developed in this paper. One such method considers diffusivity and the electrical field as non-constant, although they are usually assumed constant, that is, without there being any variability of the involved factors. Therefore, a multi-factorial diffusivity that accounts for the material characteristics and environmental variations is adopted. In addition, an innovative stochastic approach to evaluate the variation of the electrical field while accounting for the non-linear voltage distortion, which considers a multispecies model, has been proposed. More complete 1D/2D electro-mechanical models that are solved by advanced numerical and analytical solutions for electro-mechanical diffusion have been developed. Results show that spatiotemporal numerical models estimate the chloride concentration well, estimating more reliable scenarios to provide information on the safety situation of the structure and make it more sustainable by employing successful preventive treatments.
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•New modular metal pallets that combine blocks and deck boards are proposed.•3D FEM, analytical, and experimental tests are carried out and results compared.•More reliable values for ...loadings and displacements are provided for steel pallets.•A comparative LCA suggests that steel pallets have a good environmental performance.
Given the huge number of products transported worldwide every day, it would be advantageous to use lightweight pallets made of readily recyclable materials that are easy to clean, durable, and cheap to maintain. However, the design process for new metal pallets does not follow any specific code, which makes the transition to products with improved characteristics more challenging. This paper describes the development of a new modular steel pallet that combines blocks and deck boards to produce a range of configurable geometries for use in transportation (forklifting) and stationary (racking, stacking) conditions alike. Analytical and numerical analyses using the 3D finite element method (FEM) were carried out. Experimental tests were performed to evaluate ultimate strengths and deformations for different loadings. The experimental results used to validate the numerical models showed that these pallets performed well in terms of stiffness, deformation, and stresses. A comparative life cycle analysis (LCA) was also carried out to identify the main environmental impacts of the life cycle of pallets made from different materials. The results of a “cradle-to-gate with options” model suggest that the new proposed pallet performs better than its wood, plastic, and aluminium counterparts.
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