Search Results (34)

The sloshing in storage tanks can exert negative influences on the safety and stability of tank structures undergoing earthquake excitation. An analytical mechanical model is presented here to investigate the seismic responses of a base-isolated cylindrical tank resting on soil. The continuous liquid sloshing is modeled as the convective spring–mass, the impulsive spring–mass, and the rigid mass. The soil impedances are equivalent to the systematic lumped-parameter models. The bearing isolation is considered as the elastic–viscous damping model. A comparison between the present and reported results is presented to prove the accuracy of the coupling model. A parametric analysis is carried out for base-isolated broad and slender tanks to examine the effects of the isolation period, isolation damping ratio, tank aspect ratio, and soil stiffness on structural responses. The results show that the interaction between soft soil and the base-isolated tank exerts significant influence on earthquake responses. Full article

This paper presents the development and analysis of a bridge bearing database consistent with the 2020 Italian Guidelines (LG2020), currently enforced by the Italian law for risk classification and management of existing bridges. The database was developed by putting together the contribution of 24 research teams from 18 Italian universities in the framework of a research project foreseen by the agreement between the High Council of Public Works (CSLP, part of the Italian Ministry of Transportation) and the research consortium ReLUIS (Network of Italian Earthquake and Structural Engineering University Laboratories). This research project aimed to apply LG2020 to a set of about 600 bridges distributed across the Italian country, in order to find possible issues and propose modifications and integrations. The database includes almost 12,000 bearing defect forms related to a portfolio of 255 existing bridges located across the entire country. This paper reports a preliminary analysis of the dataset to provide an overview of the bearings installed in a significant bridge portfolio, referring to major highways and state roads. After a brief state of the art about the main bearing types installed on the bridges, along with inspection procedures, the paper describes the database structure, showing preliminary analyses related to bearing types and defects. The results show the prevalence of elastomeric pads, representing more than 55% of the inspected bearings. The remaining bearings are pot, low-friction with steel–Teflon surfaces and older-type steel devices. Lastly, the study provides information about typical defects for each type of bearing, while also underscoring some issues related to the current version of the LG2020 bearing inspection form. Full article

This paper investigates the use of glass and carbon fiber-reinforced polymer composites with epoxy matrices for non-pneumatic tires (NPTs), as an alternative to conventional elastomer-based designs. A novel NPT design approach was developed in three steps: (i) a finite element model with isotropic material properties was constructed to identify suitable spoke geometries; (ii) an anisotropic parametric study quantified key parameters influencing the load-bearing capability of two selected concepts from step (i); and (iii) a preferred version was chosen from step (ii) and evaluated under multiple load cases to ensure it met all requirements. The final tire design incorporates thick spiral spokes superimposed with a cosine-like function, showcasing the strengths and limitations of non-elastomeric reinforced polymers for NPT design. This study provides innovative insights into reducing the mass of NPTs and demonstrates the potential of fiber-reinforced polymer composites to achieve more lightweight, durable, and efficient NPT designs in comparison to pneumatic ones. Full article

A one-pot, two-step process was developed for the preparation of pyrrole compounds from 2,5-dimethylfuran. The first step was the acid-catalyzed ring-opening reaction of 2,5-dimethylfuran (DF), leading to the formation of 2,5-hexanedione (HD). A stoichiometric amount of water and a sub-stoichiometric amount of sulfuric acid were used by heating at 50 °C for 24 h. Chemically pure HD was isolated, with a quantitative yield (up to 95%), as revealed by ¹H-NMR, ¹³C-NMR, and GC-MS analyses. In the second step, HD was used as the starting material for the synthesis of pyrrole compounds via the Paal–Knorr reaction. Various primary amines were used in stoichiometric amounts. ¹H-NMR, ¹³C-NMR, ESI-Mass, and GC-Mass analyses confirmed that pyrrole compounds were prepared with very good/excellent yields (80–95%), with water as the only co-product. A further purification step was not necessary. The process was characterized by a very high carbon efficiency, up to 80%, and an E-factor down to 0.128, whereas the typical E-factor for fine chemicals is between 5 and 50. Water, a co-product of the second step, can trigger the first step and therefore make the whole process circular. Thus, this synthetic pathway appears to be in line with the requirements of a sustainable chemical process. A pyrrole compound bearing an SH group (SHP) was used for the functionalization of a furnace carbon black (CB). The functionalized CB (CB/SHP) was utilized in place of silica, resulting in a 15% mass reduction of reinforcing filler, in an elastomeric composite based on poly(styrene-co-butadiene) from solution anionic polymerization and poly(1,4-cis-isoprene) from Hevea Brasiliensis. Compared to the silica-based composite, a reduction in the Payne effect of about 25% and an increase in the dynamic rigidity (E’ at 70 °C) of about 25% were obtained with CB/SHP. Full article

The air and structural loads of a 5-ton class light helicopter (LH) rotor in a 2.24 g pull-up maneuver are investigated using a coupling between the computational structural dynamics (CSD) and computational fluid dynamics (CFD) methods. The LH rotor is characterized by a five-bladed system with elastomeric bearings and inter-bladed dampers. The periodic trim solution along with the converged CFD/CSD delta airloads obtained in steady-level flight (advance ratio of 0.287) are used to perform the transient CSD maneuver analysis. The resulting vehicle attitude angles and velocity profiles of the aircraft are then prescribed in the quasi-static (QS) CFD maneuver analysis. It is demonstrated that the present QS approach provides an effective means for the maneuver loads’ analysis. The important flow behaviors such as BVI (blade–vortex interaction)-induced oscillations and the negative pitching moment peaks met in maneuver flight are captured nicely with the proposed method. Either the vortex trajectories or the surface pressure distributions are examined to identify the sources of the oscillations. A loose CFD/CSD coupling (LC) is used to predict the blade elastic motions, structural moments, and pitch link loads at the specified maneuver revolution of the rotor and also to correlate these with the transient CSD-based predictions. A reasonable correlation is obtained. The LC results show more pronounced 5P (five per revolution) oscillations on the structural response than those of the CSD-based methods. Full article

This paper examines the initial sizing theory of elastomeric bearings. In addition, the manufacturing process of the elastomeric bearing was analyzed to define the essential contents necessary to manufacture reliable elastomeric bearings. Mooney-Rivlin parameters were presented based on the test results to predict the characteristics of metal materials and rubber stacked. Mooney-Rivlin parameters were inputted to determine whether the structure was abnormal, by constructing a finite element model for the elastomeric bearing. A modeling technique was established to meet the structural rigidity and strength requirements of full elastomeric bearings, critical components of the helicopter main rotor system. In addition, the flight situation in which the maximum load of an actual helicopter equipped with an elastomeric bearing can be applied was selected, and linear structural analysis and nonlinear analysis were performed to confirm the behavior of the elastomeric bearing. As a result of performing linear static analysis, a negative margin was generated, but when nonlinear analysis was performed again, it was confirmed that there was a sufficient safety margin. It was shown that design reliability for the molding and manufacturing process of elastomeric bearings could be improved in terms of strength. Full article

Lifeline structures such as hospital buildings need to be specifically designed such that they experience reduced vibrations when subjected to earthquake excitations because it will be difficult to vacate hospital buildings under the event of any earthquake. Therefore, to ensure operational condition under earthquake excitations in an existing hospital building, the present study utilizes flexible unbonded fiber-reinforced elastomeric isolators (UFREIs) for its seismic isolation. The UFREI-based isolation system is designed to restrict the structural acceleration within the tolerable limits for the building inhabitants even during earthquake hazards. However, the use of such flexible isolators results in excessively large bearing displacements, which either may not be practical and/or pose several serviceability issues. Therefore, tuned mass damper (TMD) is attached to the base floor of the UFREI-isolated hospital building to reduce the large isolator displacements. Properties of the hybrid vibration control system are designed according to the site-specific scenario in New Delhi, India. Further, nonlinear time-history analyses of the UFREI-isolated hospital building with the TMD are carried out, and responses are compared with its uncontrolled response. Results show that the peak bearing displacement response of the UFREI-isolated hospital building is reduced by 9% to 27%, due to the addition of the TMD. Importantly, the required design displacement of the UFREI-based isolation system is decreased by 27%, without compromising the effectiveness of base isolation. In fact, the performance of the hybrid vibration control system is superior to the base isolation system alone. Full article

The seismic response of base-isolated structures is notably influenced by mechanical properties of isolation devices due to their essential role in structural behavior. Consequently, the variability of such properties should be accounted for in the design process. The current seismic codes prescribe a simplified approach based on structural analyses in two extreme situations resulting from the upper and lower bound design properties of bearings (upper and lower bound analyses). In the case that experimental data are not provided by manufacturers, seismic codes provide the so-called “property modification factors” or “λ-factors”, i.e., modification coefficients to be applied to the nominal dynamic properties of bearings to obtain their upper or lower design properties. The aim of this paper is to provide a historical review of values provided for such factors by the main seismic codes by highlighting the limits, as well as some clerical errors, present in some codes. In particular, the European seismic codes are illustrated in detail, i.e., the Eurocode for bridges (EN 1998-2) and product standard on anti-seismic devices (EN 15129). Both these codes account for different sources of variability, such as the bearings production and the environmental and behavioral effects. For all these effects, the same λ-factor values are provided by the two codes, deriving from the second version of the AASHTO guide specifications for seismic isolation of bridges (AASHTO 1999), which are based on limited and/or old data, especially for high damping rubber bearings (HDRBs), and were never updated in the successive versions. More recent standards are also illustrated, providing different perspectives that deserve attention, even though they require further investigations to be applied in the design practice. Full article

Elastomeric bearings are widely used in bridges to support the superstructure, to transfer loads to substructures, and to accommodate movements induced by, for example, temperature changes. Bearing mechanical properties affect the bridge’s performance and its response to permanent and variable loadings (e.g., traffic). This paper describes the research carried out at Strathclyde towards the development of smart elastomeric bearings that can be used as a low−cost sensing technology for bridge and/or weigh−in−motion monitoring. An experimental campaign was performed, under laboratory conditions, on various natural rubber (NR) specimens enhanced with different conductive fillers. Each specimen was characterized under loading conditions that replicated in−situ bearings to determine their mechanical and piezoresistive properties. Relatively simple models can be used to describe the relationship between rubber bearing resistivity and deformation changes. Gauge factors (GFs) in the range between 2 and 11 are obtained, depending on the compound and the applied loading. Experiments were also carried out to show that the developed model can be used to predict the state of deformation of the bearings under random loadings of different amplitudes that are characteristic of the passage of traffic over a bridge. Full article

Fiber-reinforced elastomeric isolators (FREIs) are rubber-based seismic devices introduced as a low-cost alternative to steel-reinforced elastomeric isolators (SREIs). They are generally used in unbonded applications, i.e., friction is used to transfer the lateral loads from the upper to the lower structure. Under combined axial and shear loads, the lateral edges of the unbonded bearings detach from the top and bottom supports resulting in a rollover deformation. Due to increasing horizontal displacement, the overlap area of the bearing decreases; thus, the vertical properties of the device are a function of the imposed lateral deformation. This paper introduces a closed-form solution to derive the vertical stiffness of the bearings as a function of the horizontal displacement. The variations of the vertical stiffness and of the effective compressive modulus of square-shaped FREIs are given in this work. The analytical results are then validated through a comparison with the outputs of a parametric finite element analysis of FREIs, including different mechanical and geometric parameters. Full article

Bridges are essential structures in the logistic chain of countries, making it critical to design them to be as resilient as possible. One way to achieve this is through performance-based seismic design (PBSD), which involves using nonlinear Finite Element (FE) models to predict the response and potential damage of different structural components under earthquake excitations. Nonlinear FE models need accurate constitutive models of material and components. Among them, seismic bars and laminated elastomeric bearings play an important role in a bridge’s response to earthquakes; therefore, properly validated and calibrated models should be proposed. Only default parameter values from the early development of the constitutive models widely used by researchers and practitioners for these components tend to be used, and low identifiability of its governing parameters and the high cost of generating reliable experimental data have prevented a thorough probabilistic characterization of their model parameters. To address this issue, this study implements a Bayesian probabilistic framework using Sequential Monte Carlo (SMC) for updating the parameters of constitutive models of seismic bars and elastomeric bearings and proposes joint probability density functions (PDF) for the most influential parameters. The framework is based on actual data from comprehensive experimental campaigns. The PDFs are obtained from independent tests conducted on different seismic bars and elastomeric bearings, to then consolidate all the information in a single PDF for each modeling parameter by means of the conflation methodology, where the mean, coefficient of variation, and correlation between calibrated parameters are obtained for each bridge component. Finally, findings show that the incorporation of model parameter uncertainty through a probabilistic framework will allow for a more accurate prediction of the response of bridges under strong earthquakes. Full article

Chile is exposed to the occurrence of medium- and large-magnitude earthquakes. As a result, national and international design codes have been developed, whose objectives are to grant an ideal behavior to the structures. However, in Chile, many of these structures do not comply with the design and construction standards of current regulations. Therefore, we propose to carry out a historical compilation that allows establishing the components that present the seismic vulnerability in bridges built from 1920 to 2010. We explored information gathered from the Government of Chile. We analyzed 553 bridges out of a total of 6835, considering superstructure and infrastructure components and seismic design evolution. The analysis emphasizes the elements that help improve the seismic performance of a bridge when natural or induced dynamic forces act on it, such as the length support, elastomeric bearing, seismic hold-down bars, transverse girders, seismic stoppers, bracing, and expansion joints. We identified that the most significant problems in bridges are the lack of seismic stoppers, both interior and exterior; lack of development length in the support tables; use of deficient expansion joints; and the inefficient construction of cross girders and baring support; in addition to the presence of differential settlements in elements of the infrastructure. Full article

This article presents a numerical study that aims to explore the impacts of the stiffness of elastomeric bearings on the dynamic behavior of railway bridges under train-induced vibrations. For this purpose, a finite element code that considers vehicle–bridge interaction using a coupled approach was developed. The software was validated by comparing the numerical response to the analytical solution. The numerical analysis of single- and multi-span bridges with varying bearing stiffness values under passenger trains showed the interplay between bearing stiffness, its impact on the natural frequency of the bridge and the loading frequency. It is demonstrated that the amplitude of the maximum acceleration on the bridge depends heavily on the stiffness of the bearings. Furthermore, the bearing stiffness significantly impacts the location of the maximum acceleration on the bridge. The results of the extensive numerical analyses improve the understanding of the impact of the bearing stiffness on the dynamic behavior of bridges and highlight the importance of quantifying the boundary conditions correctly for reliable estimation of dynamic response of railway bridges under train-induced vibrations. Full article

The dynamic characteristics of bridges are known to be affected by damages as well as by environmental factors such as temperature. Therefore, the changes in the dynamic characteristics caused by damages and environmental factors should be considered when evaluating the health of the structure. Accordingly, this study conducted long-term monitoring and modal identification of short-span concrete bridges, i.e., a RC (reinforced concrete) slab bridge a RC rahmen (rigid-frame) bridge. The investigation revealed that temperature is the factor having the greatest influence on the variability of the dynamic characteristics as the natural frequencies of the bridge decrease with higher temperatures. Model updating verified that such modal change resulted from the temperature dependency of the elastic modulus of concrete. The RC slab bridge showed higher temperature dependency than the RC rahmen bridge owing to the presence of elastomeric bearings. Apart from the effect of temperature, non-negligible modal changes caused by other environmental factors were also identified. The results of this study are expected to provide valuable data for the health evaluation of bridges. Full article

Poly(ethylene glycol) (PEG)-based soft elastomers, bearing tertiary amine and hydroxyl groups, were synthesized in bulk from the epoxy–amine reaction between poly(ethylene glycol) diglycidyl ether (PEGDE) and a poly(etherdiamine), Jeffamine ED600. High gel fractions (≥0.95) and low glass transition temperatures (Tg ≈ −50 °C) were attained after complete curing of the systems in bulk. The amphiphilicity of the network allowed the swelling of the materials in both aqueous solutions and a variety of organic solvents. Magnetic nanocomposites were synthesized by in situ coprecipitation of magnetic nanoparticles (MNPs) in the elastomeric matrix. The obtained materials were processed by cryogenic milling to obtain powders that were tested as potential magnetic adsorbents and that showed a fast and strong response to the action of a permanent magnet. These materials showed removal rates of at least 50% in 10 min when used in the adsorption of Cu⁺² ions from an aqueous solution, making them interesting candidates for the design of magnetically separable metal ion adsorbents. Full article