RC Elements Research Articles

A Review on the Sway of Using Shape Memory Alloys on Enhancing the Behavior of RC Elements under Cyclic Loading

A Review on the Sway of Using Shape Memory Alloys on Enhancing the Behavior of RC Elements under Cyclic Loading

Rapid time-domain simulation of fractional capacitors with SPICE

Fractional capacitors, commonly called constant-phase elements or CPEs, are used in modeling and control applications, for example, for rechargeable batteries. Unfortunately, they are not natively supported in the well-used circuit simulator SPICE. This manuscript presents and demonstrates a modeling approach that allows users to incorporate these elements in circuits and model the response in the time domain. The novelty is that we implement for the first time a particular configuration of RC elements in parallel in a Foster-type network with SPICE in order to simulate a constant-phase element across a defined frequency range. We demonstrate that the circuit produces the required impedance spectrum in the frequency domain, and shows a power-law voltage response to a step change in current in the time domain, consistent with theory, and is able to reproduce the experimental voltage response to a complicated current profile in the time domain. The error depends on the chosen frequency limits and the number of RC branches, in addition to very small SPICE numerical errors. We are able to define an optimum circuit description that minimizes error while maintaining a short computation time. The scientific value is that the work permits rapid and accurate evaluation of the response of CPEs in the time domain, faster than other methods, using open source tools.

Experimental Study on the Effect of Steel Reinforcement Ration on the Cracking Behaviour of FRP-Strengthened RC Elements

This paper examines the cracking behaviour of reinforced concrete beams strengthened by externally bonded fiber-reinforced polymer. The crack opening of RC structures is a key parameter for the durability of concrete structures. It is of vital importance for designers to be able to make correct estimations of the crack opening values of strengthened structures. FRP strengthening affects the cracking behaviour of RC beams with different steel percentages. Beams have been tested under four-point bending mechanical tests until failure with three steel ratios and two layers of externally bonded wet carbon fibers (CFRP). In order to measure the crack opening during loading, Digital Image Correlation is used to obtain the crack opening along the beam during load functioning. The results allow for a comparison of the RC beams with and without FRP and enhance the effect of FRP on crack opening. The crack width was compared with the theoretical values obtained based on the relation proposed by Eurocode 2 (EC2). The comparison enhanced the need to propose a modified relation. Subsequently, an empirical model was established as a modification of EC2, considering the presence of a CFRP system. The corresponding results were compared and discussed to validate the model. For the same level of loads, the crack opening can be reduced by 20 to 50% depending on the level of steel ratio.

Computationally-efficient high-fidelity nonlinear FEA of seismically isolated post-tensioned RC bridges

This study presents a novel computationally efficient high-fidelity nonlinear FEA (NLFEA) methodology for prestressed RC bridges constructed in the UAE and seismically isolated with elastomeric bearings. Specifically, the presented NLFEA methodology, using 3D solid brick elements, is shown to overcome traditional prohibitive numerical burdens. This is demonstrated without compromising accuracy or upscaling applicability and appropriateness. The proposed NLFEA approach is highlighted through detailed modeling of RC bridges’ non-traditional structural components and loading aspects (elastomeric bearings and post-tension prestressing cables). The mechanical behavior of elastomeric isolators and the RC continua, including cracking and other nonlinear phenomena, are captured via 3D solid brick elements. Moreover, the modeling procedure accurately represents the post-tension tendons’ prestressing forces and the associated effects on the RC elements. The prestressing forces are incorporated within the tendon elements via insightful manipulations of stepwise initial conditions and internal force adjustments. Additionally, load-carrying capacity determination for the elastomeric bearings was achieved by conducting a parametric investigation to capture their mechanical behavior adequately. Eventually, the analysis of a full-scale bridge is presented in this paper. The post-tensioned RC bridge understudy spans 100 m over eight elastomeric (natural rubber) seismic isolator bearings. Twelve post-tension prestressing cables are utilized to provide the bridge with continuous internal tension-balancing forces. A high-fidelity detailed FEA model of the complete bridge is developed and validated against a SAP2000 FEA model. It is shown that reasonable computational efforts can be expected without compromising the accuracy of the results.

Application of wavelet transform techniques for corrosion assessment of embedded rebars in RC elements using electromechanical impedance

Corrosion of steel reinforcement embedded in concrete significantly influences the integrity and durability attributes of reinforced concrete structures. Monitoring of the early age corrosion of the reinforcements can contribute to an effective planning of structural maintenance and restoration. This paper demonstrates an innovative approach of monitoring the rate of corrosion (mass loss due to corrosion) of steel bars embedded in concrete by capturing conductance signature using Piezoelectric sensors (PZT) by Electromechanical Impedance Technique. In the recent times Wavelet Transform (WT) based different techniques have been proved to be promising techniques for different structural health monitoring assessment. This study aims to comprehensively use the WT techniques based on EMI signals to assess the corrosion levels in the reinforcement embedded in RC members. Specifically, the study focuses on capturing the progression of corrosion levels using the RMSD index derived from the DWT, CWT and WPT analysis of conductance signatures. WT techniques provides energy values of conductance signatures. Energy level of the signatures decreases with the increase of corrosion levels and deviation of energy level between current and pristine stage is measured using statistical index Root Mean Square Deviation (RMSD). Robust relationship between the RMSD index and the corrosion mass loss ratio through nonlinear curve fitting have been derived and presented using data captured from the 48 specimens of concrete cylinders with embedded reinforcement. At last, the comparison between the actual mass loss ratio and the predicted mass loss ratio derived from these techniques have been made for the validation of the proposed relation of predicted mass loss due to corrosion.

A Gallium Nitride (GaN) Doherty power amplifier chip design based on series RC stability network

SummaryThis paper presents Doherty power amplifier (DPA) based on gallium nitride (GaN) technology, incorporating a parallel grounded network with series RC elements in front of the carrier and peaking amplifiers to enhance circuit stability. In comparison to the traditional series network with parallel RC structure, this configuration effectively reduces the sensitivity of the stability factor K to the capacitance value within the stability network. Consequently, it mitigates the impact on various performance indicators such as gain and drain efficiency, addressing the issue of measurement performance deviation caused by inaccurate capacitance models in the simulation files, which is particularly crucial for DPA. As a result, the circuit exhibits improved consistency in design and processing. With full band stability, the DPA achieves a saturation output power of approximately 29.8 dBm at 28 GHz, a saturation efficiency of 38.2%, and a 6‐dB back‐off efficiency of 29.6%.

Flexural Behaviour of FRC Beams Wrapped With FRP

Structural elements such as beams, slabs and columns may require strengthening during their service life period. A concrete structure may need strengthening for many reasons such as to increase live load capacity, to add reinforcement to a member that has been unsigned or wrongly constructed. The FRPs have various advantages like, high strength to weight ratio, corrosion resistance and ease of installation and flexibility in its use. FRP material which are available in the form of sheet are being used to strengthen a variety of RC elements to enhance the flexural, shear and axial load carrying capacity of these elements. The objective of this experiment is to strengthen the RC beams using fibres and FRP sheets in flexure. In this experimental program CFRP and GFRP sheets were applied to the bottom surface and sides of the concrete beam with different configuration and their performance in flexure were studied. In this experimental program eight RC beams of size 1500 x 150 x 200mm were casted with two 10mm dia. bars as tension zone, two 8mm dia. bars as compression zone and 8mm dia. bars @ 200mm c/c spacing as shear reinforcement. The experimental result shows that the flexural strength of FRP wrapped beams were increased in the range of 23.49% to 67.9% in comparison with the flexural strength of the control beam (unwrapped). The flexural strength of the beam wrapped with the single layer CFRP at the soffit and around the sides (for full depth of the beam) and beam wrapped with the single layer GFRP at the soffit and around the sides (for full depth of the beam) exhibits better performance compared with other FRP beams and increase in flexure was 67.9% in comparison with the capacity of the control beam.

Finite element simulation of expansion and damage in RC elements affected by alkali‐aggregate reactions

AbstractAlkali‐aggregate reaction (AAR) is a detrimental reaction between alkalis originating from cement and aggregates that contain reactive minerals. This reaction produces an expansive gel in hardened concrete that may cause internal stresses and cracking, after which it would be critical to evaluate the safety of the AAR‐affected structure. This paper presents a calculation framework primarily using the finite element method to simulate the structural behavior of reinforced concrete members affected by AAR. Numerical subroutines are used to calculate the anisotropic distribution of AAR‐induced expansions at each integration point, considering the stress field at each time step, whereas changes in the properties of concrete due to the progression of AAR are also considered. The modeling approach is successfully validated based on experimental data from several studies on AAR‐affected members that were reinforced in 1, 2, and 3 orthogonal directions in terms of load–deflection behavior and damage patterns. The mechanical properties of concrete were found to negligibly affect the distribution of AAR expansions. A better correlation was observed with experimental data if compressive and tensile strengths of concrete are assumed unchanged and only the modulus of elasticity of concrete is reduced as a function of AAR‐induced expansion.

Corrosion Rate-Based Adjustment of Plastic Hinge Parameters of Corroded RC Elements

In line with the trend towards predictive seismic codes adopting the performance-based design method, this paper presents an integrated protocol to determine the degraded hysteresis parameters of corroded RC hinges based on relationships developed for this purpose together with a calibration procedure using the random-mutation hill-climbing algorithm. The adjustment procedure is integrated into the material library of the OpenSees software and used to perform nonlinear dynamic analyses to investigate the seismic performance of a typical bridge with affected piers at different corrosion levels. In practice the proposed procedure permits to assess the seismic performance of existing or new structures for a given corrosion rate distribution.

Experimental behavior of lintels for AAC masonry buildings: Comparison among different solutions

AbstractThe paper investigates the experimental behavior up to failure of different types of lintels for AAC masonry buildings. At first, precast highly‐reinforced AAC lintels, that are quite widespread on the European and Turkish market, were tested in flexure, by considering different reinforcement type and arrangement. The second analyzed solution is represented by RC lintels cast within three juxtaposed special AAC elements with U section, acting as formwork and final external finishing. Also in this case, the effect of reinforcement type (lattice girders, ordinary rebars, or a combination of them) and reinforcement amount on the bearing capacity and mode of failure was analyzed. The experimental results highlight that precast AAC lintels available on the market are very light and are characterized by high stiffness in bending; however, being usually over‐reinforced, their failure is quite brittle. On the contrary, RC lintels cast within U‐shaped AAC blocks (“combined AAC‐RC” specimens) are heavier but can be easily designed to have a ductile behavior, by simply following design Standard recommendations for ordinary RC elements.

Performance criteria expressed by means of relative displacements for a retrofitted masonry school building

In order to study how retrofitting techniques applied to URM structures influence the failure modes and the displacement capacity of the buildings, a school building from Bucharest was modelled using 3DMacro software. The mixed structural system required a particular approach for the calculation model, in a software able to capture the interaction between the reinforced concrete elements (columns and tie beams) and the URM masonry panels.Damage pattern evolution was analyzed for the three models capturing the gradual seismic improvements done in the past century, transforming the unreinforced masonry structure into a confined masonry one, with few RC elements, and eventually into a fully jacketed structure with densely spaced RC columns. The results obtained from the nonlinear static analyses were validated by means of global and local displacement limits associated with specific damage criteria.The damage suffered after 1977 Vrancea earthquake and the current performance requirements in terms of seismic safety led to structural changes aimed at improving the behavior of masonry structures by means of interventions that marked the transition from an unreinforced masonry structural system to a retrofitted masonry structural system. The comparative analyses carried out between the behavior of the initial and the strengthened structure of the school intend to highlight the benefits of the retrofitting interventions performed, but also the situations in which the applied strengthening measures might prove to be excessive. Considering the case study is representative for the existing building stock in the education sector in Romania which needed subsequent seismic retrofitting in order to reach the required seismic safety, the results highlight the improved behavior after these interventions. The present works represent a topic of interest at national level, since it targets a large part of the existing building stock subjected to losses in case of an earthquake. Moreover, the past retrofitting interventions assessed in this paper represent a typical intervention done for similar structures, and therefore, the results obtained are representative for the Romanian building stock.

A New Bond Degradation Model for Freeze–Thaw-Damaged Reinforced Concrete

Freeze–thaw cycles (FTCs) are one the most serious causes of damage in RC structures in cold regions affecting both concrete and bond behavior. In this paper, after a comprehensive review on the effects on concrete and bond of freeze–thaw degradation for ordinary concrete, a new constitutive bond stress-slip law is formulated in the framework of a coupled mechanical-environmental damage model. This law is developed exploiting the versatility of Bezier curves and using an optimization process based on genetic algorithms to select the best form among some options (composite quadratic, composite cubic, and a single fourth-order curve). Moreover, a comprehensive enhanced freeze–thaw degradation (E-FTD) model is developed including the effect of FTCs on bond behavior, by means of a new environmental damage parameter included in the proposed bond stress-slip law. The whole model is formulated, calibrated, and validated referring to all the available experimental data to the authors’ knowledge both for compressive and pull-out tests for ordinary concrete. The comparison with the experimental results showed the proposed E-FTD model is able to predict bond strength degradation fairly well and generally on the safe side, capturing also the overall bond-slip curves, making it particularly appealing for the structural analysis of RC elements subjected to FTCs according to an engineering-oriented approach.

Effect of tuning of charge defects by K, Ba, La doping on structural and electrical behaviour of NaNbO3

The aim of this study is to highlight the impact of monovalent, divalent and trivalent substitutions on structural, and electrical properties. Creation of defects and its impact on phase transition behaviour reflected in dielectric properties makes it more interesting. Compositions (x) in the material system Na1-xAxNbO3 (where, x = 0.0 abbreviated as S0, and x = 0.05 for K1+, Ba2+, and La3+ doped samples abbreviated as S1, S2, and S3 respectively) are prepared by the conventional solid-state reaction method. Rietveld refinement of diffraction data has confirmed single-phase formation with an orthorhombic structure having Pbcm space group symmetry. FTIR spectra show the shifting of vibrational modes towards higher wave number sides with increasing valence states of dopants. SEM images of these samples show a decrease in average grain size for S1, S2, and S3, respectively. Dielectric plots from room temperature to 773K at 1 kHz, 10 kHz, and 100 kHz for x = 0.0 have shown two prominent anomalies, one at 404K and the other one at 610K. The low-temperature anomaly has disappeared in samples S1, S2, and S3, whereas the high-temperature sharp anomaly at 610K for sample S0 has shifted to 618K for sample S1 and vanished for samples S2 and S3. Tanδ with temperature plots show two anomalies for samples S0, S1, and S2, whereas for S3, only one broad anomaly is observed. Conductivity has been found to increase with doping through the equivalent concentration of iso-valent K1+ and graded off-valent Ba2+ and La3+ cations. Impedance analysis has proposed an electronic circuit model containing two parallel equivalent RC elements.

Structural performance of Nano alumina-based RC element with polypropylene fibre and GGBS: An experimental assessment

In today's scenario, the essential ingredients of concrete, such as cement, and fine and coarse aggregate will vanish completely in a few decades due to its overexploitation and unscaled utilization. Similarly, cement has contributed to more emissions of carbon dioxide into the atmosphere during its stage of manufacturing, and it’s become a major influencer of increasing global temperatures. Recent researchers are finding alternative sources of materials that replace fully or partially the role of conventional concrete materials. Several industrial and agricultural solid residues are under investigation to be utilised nowadays to alter the place of conventional concrete materials and to control the impact of environmental problems. In this study, the performance of structural RC elements of M35 grade was evaluated by replacing the Nano alumina in a fixed proportion of 1% with the inclusion of ground granulated blast furnace slag and Polypropylene fibre at definite proportions in place of cement as per mix design. Engineering parameters such as compression, modulus of rupture and elasticity, crack width, and rate of deflection was examined. Based on the results of experiments, it was found that the cement proportion CAG1 and CAGP4 have provided the promotable result when compared to conventional concrete and led to using these materials instead of cement has made RC elements stronger than when they were made with regular cement.

From Multi-Physics to Electrical Circuit Models of Aged Graphite Electrodes of Lithium-Ion Battery

A two-step up-scaling methodology is established to determine a temporal Electric Equivalent Circuit (EEC) model of aged graphite electrodes. The methodology is fed with original experimental results of graphite impedance spectra obtained upon aging on graphite-NMC pouches instrumented with reference electrodes. An analytical expression is first derived which includes the impedance contributions from interfacial kinetics, double-layer adsorption, solid-phase diffusion processes in the graphite particles as well as lithium diffusion through the SEI layer. The derivation of the temporal EEC model from this analytical expression using Foster series allows to link the EEC model parameters to materials properties and to tune the accuracy of the model by choosing the number of RC elements in the series. The validity of the model is ascertained by comparison with the experimental data obtained at different aging time and for two cycling temperature conditions. In particular, accounting for lithium diffusion through the SEI is necessary to capture the evolution of the impedance spectra of significantly aged graphite electrodes.

Realization of the TOW-THOMAS Biquad Active Filter

The Tow-Thomas Biquad Circuit provides the filter designers with a valuable building block for building higher order active filters. It is a flexible circuit structure in which the transfer function properties are easily manipulated by modifying the passive RC elements that connect the operational amplifiers. It can be easily defined in its low-pass and bandpass operations. Above all, we can easily fabricate the possible filters inside a single chip with very slight modification of the standard Tow-Thomas Circuit.

Electrical Transport Mechanisms in Graphene Nanoplatelet Doped Polydimethylsiloxane and Application to Ultrasensitive Temperature Sensors.

The temperature effect on electronic transport mechanisms in graphene nanoplatelet (GNP) doped polydimethylsiloxane (PDMS) for temperature sensing applications has been investigated under electrical impedance spectroscopy (EIS) analysis. AC measurements showed a very prevalent frequency-dependent behavior in low filled nanocomposites due to the lower charge density. In fact, 4 wt % GNP samples showed a nonideal capacitive behavior due to scattering effects. Therefore, the standard RC-LRC circuit varies with the substitution of capacitive elements by CPEs, where a CPE is a constant phase element which denotes energy dissipation. In this regard, the temperature promotes a prevalence of scattering effects, with an increase of resistance and inductance and a decrease of capacitance values in both RC (intrinsic and contact mechanisms) and LRC (tunneling mechanisms) elements and, even, a change from ideal to nonideal capacitive behavior as in the case of 6 wt % GNP samples. In this way, a deeper understanding of electronic mechanisms depending on GNP content and temperature is achieved in a very intuitive way. Finally, a proof-of-concept carried out as temperature sensors showed a huge sensitivity (from 0.05 to 11.7 °C-1) in comparison to most of the consulted studies (below 0.01 °C-1), proving, thus, excellent capabilities never seen before for this type of application.

Effect of the strengthening patterns on the flexural performance of RC continuous beams using FRP reinforcements

Statically indeterminate RC elements such as continuous beams are the most widely used structural form. Their flexural behavior and failure modes are considerably different from those of simply supported ones. The use of FRPs for flexural strengthening and retrofitting continuous RC beams has hardly been studied. Therefore, this paper compares the impacts of NSM-FRP and EB-FRP systems in two-span beams. The overall experimental program of this study consisted of fourteen large-scale bending tests. The performance of each strengthening system is presented and discussed in terms of failure mode, yielding and load-carrying capacities, ductility, and energy absorption capacities, FRP debonding strain, and serviceability state. The experimental results showed that the failure mode is mainly dependent on the type, length, and position of the FRPs, however, a general improvement in the flexural performance of strengthened beams was observed. The NSM technique allows the FRP tensile strength to be better exploited than the EB technique.

Seismic vulnerability assessment of reinforced concrete bridge piers with corroded bars

AbstractReinforced concrete (RC) structures located in aggressive environment, for example, RC bridge piers close to the sea and experiencing chloride attacks, may be exposed to an increased seismic vulnerability. This requires practical yet effective safety assessment strategies aimed to determine the seismic behavior by incorporating corrosion deterioration phenomena. An easy‐to‐use phenomenological model is here developed to describe the seismic behavior of corroded RC elements based on a fiber hinge formulation wherein the corrosion‐induced mechanical degradation of concrete and steel is implemented through appropriate constitutive laws at the fiber level. The developed fiber hinge formulation is first validated against experimental cyclic tests of corroded RC columns from the literature. Then, the proposed approach is used for the seismic vulnerability assessment of the Zappulla multi‐span viaduct (southern Italy), whose RC bridge piers (with a box‐shaped, two‐cell hollow rectangular cross section) are exposed to carbonation and chloride‐induced corrosion. A comprehensive in‐situ testing campaign is conducted for the mechanical characterization of the materials in the RC piers. Corrosion potential mapping, carbonation tests and tensile tests on corroded bars extracted from RC piers are critically interpreted to calibrate the constitutive laws of the fiber‐hinge model. Motivated by experimental findings, numerical seismic analyses (including linear dynamic, nonlinear static and nonlinear dynamic analyses) are performed under two different corrosion scenarios to quantify the impact of corrosion on the resulting seismic vulnerability conditions of bridge piers with corroded bars. The proposed approach is characterized by low computational cost and lends itself to large‐scale seismic vulnerability assessment of other existing RC bridges placed in corrosive environment.

Seismic Risk and Finite Element Modelling Influence of an Existing One-Storey Precast Industrial Building

ABSTRACT Precast structures are widely used in Southern Europe particularly for industrial buildings. Most of such buildings have been built before the enforcement of modern anti-seismic regulations showing a poor performance during past major earthquakes. Focusing on existing one-storey precast industrial buildings, the paper investigates the influence of modelling choices on the risk assessment, direct losses, and required structure retrofit time. RC forks, cladding panels, and elements connections were specifically considered. A precast industrial building with structural details compatible with 1980s Italian regulations was selected and analysed. In general, the failure was associated with the collapse of roof elements.