Conventional RC Research Articles

Flexural Behaviour of Geopolymer RC Beam with Scrap Steel Slag Coarse Aggregate

This research work aims adding further sustainability to the cement - less geopolymer concrete by replacing its natural gravel coarse aggregate by an industrial by-product, scrap steel slag. Geopolymer RC beam of grade M40 with 100% scrap steel as coarse aggregate was studied for its flexural behavior and compared with conventional reinforced cement concrete beam with gravel coarse aggregate. The specimens were tested under two-point static loading. The analysis was also carried out using ANSYS software. The study derived that in all stages, the performance of the geopolymer beam with scrap steel slag was marginally better than the conventional beam with gravel coarse aggregate. The ultimate load carrying capacity, deflection, service load and ductility factor of geopolymer RC beam with scrap steel slag coarse aggregate was comparable to the conventional cement concrete RC beam and is marginally higher. It is also found that conventional RC theory can be used in the calculation of moment capacity, deflection and crack width of the geopolymer beam of study and FE modeling and analysis using ANSYS were comparable to the experimental results.

Experimental study on the seismic performance of composite columns with an ultra-high-strength concrete-filled steel tube core

The ultra-high-strength concrete-encased concrete-filled steel tube column consists of a concrete-filled steel tube core and a rectangle-shaped reinforced concrete encasement. This article presents the seismic performance analysis of ultra-high-strength concrete-encased concrete-filled steel tube columns subjected to cyclic loading. Based on the measured load-lateral displacement hysteresis curves of six ultra-high-strength concrete-encased concrete-filled steel tube columns and two conventional RC columns, the seismic behaviours, such as the ductility, energy dissipation, stiffness and load-bearing capacity, were analysed. The effects of the arrangement of the stirrups and the layout of the prestressed steel strips on the seismic performance of the composite columns were critically examined. The test results indicated that the ductility and energy dissipation performance of the ultra-high-strength concrete-encased concrete-filled steel tube columns were increased by 74.8% and 162.7%, respectively, compared with the conventional columns. The configuration of the prestressed steel strip increased the ductility of the composite column by 28.9%–63% and increased the energy consumption performance by 160.2%–263.3%. By reducing the stirrup spacing and using prestressed steel strips, the concrete-filled steel tube core columns could be effectively confined, leading to a great enhancement in ductility, energy dissipation, stiffness and load-bearing capacity.

A novel active AC coupled input stage of instrumentation amplifier for bioelectrical applications

For recording bioelectrical signals using Instrumentation Amplifiers (INA), capacitive AC coupling of the differential inputs is necessary for two major reasons, providing DC electrical isolation of the subject to avoid hazards of tissue burn, and to block DC or very low frequency skin-electrode contact potentials. The latter, when met, allows high admissible differential gain of the INA, which in turn, is expected to give a desirable high Common Mode Rejection Ratio (CMRR). However, the use of conventional passive RC high pass filters at the input greatly reduces CMRR. This work intends to design an improved AC coupled input circuitry for INA giving high CMRR and high input impedance. A differential RC high-pass input circuit has been developed using an active element. It creates an effective high resistance for the common mode current but provides a low resistance path to input bias currents for normal operation of the INA. Between 1 Hz and 100 Hz, CMRR of the DC coupled INA (LT1167) was 115 dB, using a well matched traditional RC coupling, 55 to 95 dB, while it was 110 dB using the improved active AC coupled circuit. This improvement was practically demonstrated through Electrocardiogram measurements from a human subject. A novel active AC coupling circuitry has been proposed and developed giving high CMRR, very close to the maximum of an INA, which is non-varying within the frequency band of interest of Bioelectrical amplifiers. The developed input circuit will improve all bioelectrical measurements in the future.

Static load test on progressive collapse resistance of fully assembled precast concrete frame structure

The progressive collapse behavior of fully assembled PC structures using dry connections under explosion, uncontrolled fire, and vehicle impact loads has seldom been studied. In the present study, three half scale moment sub-structures including a conventional RC specimen and two PC specimens using dowel bars and corbel were tested to investigate the progressive collapse performance. Collapse of the moment frame specimens with two spans was generated by the mid-column removal scenario under static loading. The test result showed that the peak strength of the PC specimens was only 76–81% of that of the RC specimen in compressive arch action and the ultimate displacement of the mid-column was 72–77% of that of the RC specimen. Unlike the RC specimen, catenary action was not completely developed in the PC specimens showing lower ductility. The load-displacement relationship and failure modes of the specimens agreed well with the prediction by finite element analysis, and a parametric study was conducted addressing various connection details to improve the progressive collapse performance of the PC moment sub-structure.

Behaviour of steel-fibre-reinforced concrete beams under high-rate loading

The present study focuses on examining the structural behaviour of steel-fibre-reinforced concrete (SFRC) beams under high rates of loading largely associated with impact problems. Fibres are added to the concrete mix to enhance ductility and energy absorption, which is important for impact-resistant design. A simple, yet practical non-linear finite-element analysis (NLFEA) model was used in the present study. Experimental static and impact tests were also carried out on beams spanning 1.3 meter with weights dropped from heights of 1.5 m and 2.5 m, respectively. The numerical model realistically describes the fully-brittle tensile behaviour of plain concrete as well as the contribution of steel fibres to the post-cracking response (the latter was allowed for by conveniently adjusting the constitutive relations for plain concrete, mainly in uniaxial tension). Suitable material relations (describing compression, tension and shear) were selected for SFRC and incorporated into ABAQUS software Brittle Cracking concrete model. A more complex model (i.e. the Damaged Plasticity concrete model in ABAQUS) was also considered and it was found that the seemingly simple (but fundamental) Brittle Cracking model yielded reliable results. Published data obtained from drop-weight experimental tests on RC and SFRC beams indicates that there is an increase in the maximum load recorded (compared to the corresponding static one) and a reduction in the portion of the beam span reacting to the impact load. However, there is considerable scatter and the specimens were often tested to complete destruction and thus yielding post-failure characteristics of little design value and making it difficult to pinpoint the actual load-carrying capacity and identify the associated true ultimate limit state (ULS). To address this, dynamic NLFEA was employed and the impact load applied was reduced gradually and applied in pulses to pinpoint the actual failure point. Different case studies were considered covering impact loading responses at both the material and structural levels as well as comparisons between RC and SFRC specimens. Steel fibres were found to increase the load-carrying capacity and deformability by offering better control over the cracking process concrete undergoes and allowing the impact energy to be absorbed more effectively compared to conventional RC members. This is useful for impact-resistant design of SFRC beams.

Behaviour and analysis of ultra high performance fibre reinforced concrete (UHPFRC) skew slabs

This study presents an experimental and theoretical investigation of the performance of ultra-high performance fibre reinforced concrete (UHPFRC) skew bridge decks. Five simply-supported UHPFRC slabs with different skew angles were tested under monotonically increasing concentrated load. It was observed that an increase in the skewness of a slab led to a more unsymmetrical vertical deflection profile, and also resulted in a decrease in the magnitude of reaction forces at the acute corners and a corresponding increase in the reaction forces at the obtuse corners. The test results also show that, although some reduction in ductility was seen with increasing skewness of a slab, the specimen with over 25° skew angle still maintained a desirable load carrying capacity and ductility compared to those of a conventional RC straight slab. In addition to the experimental investigations, a fundamental mechanics based closed-form model was developed based on strain energy theorem to predict the performance of a UHPFRC skew slab under linear elastic material condition. At its ultimate limit state, a novel yield-line analysis using a numerically-generated mechanics based moment-rotation relationship was adopted to predict the ultimate load carrying capacity of a skew UHPFRC slab. Both the generic analytical procedures were compared and against test results obtained from this study, as well as those reported in literature, and the results show that the models developed can be applied to UHPFRC skew slabs.

Comparative Analysis of Seismic Behaviour of Multi-Storey Composite, Steel and Conventional RC Structure

Comparative Analysis of Seismic Behaviour of Multi-Storey Composite, Steel and Conventional RC Structure

Transient Response of RC Panel Protected with Slurry Infiltrated Micro Reinforced Concrete Jacket Under Blast Loading

With increase in terrorist attacks, there are definite priority to protect the important infrastructure facilities against possible terrorist attacks. In order to improve blast resistance capacity of RCC panel, in present study, it was strengthened with Slurry Infiltrated Micro Reinforced Concrete (SIMRC) jacket. . The SIMRC jacket strengthened RC panel was analyzed under blast load scenario using finite element method based application, ABAQUS. The dynamic behavior of concrete and grout of SIMRC was modeled using concrete damaged plasticity model. The structural response of RC panel without any strengthening was compared with SIMRC strengthened RC panel to investigate effectiveness of SIMRC jacketing to resist blast load. Parametric study was carried out considering SIMRC jacket on single side or both side of RC panel, with different ratio of thickness of jacket to thickness of RC panel (t/D) and different percentage of wire mesh reinforcement for jacket. Simulation of various analysis results were presented in form of displacement time history, distribution of tensile/compressive damage variable explaining the pattern of failure in the RC panel, comparison of distribution of tensile damage variable on front and back jacket, compression damage variable of RC panel. It was observed that for panels with strengthening displacement and damaged areas are reduced as compared to conventional RC panel. The increase in thickness ratio (t/D), percentage of wire mesh reinforcement in jacket also contribute to increase blast resistance capacity of SIMRC Jacket. It was also observed that the jacketing on both side of RC panel is more effective in reducing the displacement and the damage is observed to be spread over the support areas. Obtained results through present study demonstrate the effective use of SIMRC jacketing as blast mitigation measure.

Seismic performance of full-scale RC columns containing high proportion recycled aggregate

The potential for utilizing high proportion recycled aggregates sourced from low strength waste concrete in new concrete construction is investigated in this paper. A comprehensive experimental program, consisting of ten full-scale, flexure critical reinforced concrete columns, five of which were constructed of natural concrete aggregate and five of which contained approximately 50% recycled concrete aggregate replacing the mid-sized coarse natural aggregate, was conducted to determine the effects of different axial loads and different spacings of transverse reinforcement on the seismic characteristics of columns incorporating recycled concrete aggregates. Seismic characteristics were quantified by analysis of hysteretic response, energy dissipation capacities, damage progression, residual displacement, and strain distribution of the longitudinal reinforcement. The test results indicate that the reinforced concrete columns constructed of natural aggregate concrete and those constructed of recycled aggregate concrete exhibit similar seismic performance, despite the fact that the compressive strength of the recycled aggregate concrete was slightly lower than that of the natural aggregate concrete. A theoretical study was then conducted to predict the load–displacement response of the columns. The comparison of the experimental data with the results of these theoretical calculations indicated that conventional RC design theory applied to columns incorporating natural aggregate is also valid for columns incorporating recycled aggregate. Finally, the confinement effect of the transverse reinforcement in columns subjected to low axial load were also critically evaluated for columns built with recycled aggregate concrete.

Experimental understanding of polarization switching in PZT ferroelectric capacitor

In this study, the transient responses of polarization switching in a Pb(Zr0.52Ti0.48)O3 (PZT) ferroelectric capacitor are experimentally investigated. In order to measure the transient response of polarization switching in the ferroelectric capacitor, a conventional RC circuit consisting of a resistor and the PZT ferroelectric capacitor is first built. Then, to investigate the impact of the number of domains in the ferroelectric capacitor on the transient response, the three different sizes of top electrodes of the capacitor are chosen. The results show that the ferroelectric capacitor with a small-sized electrode is charged faster than the other capacitors with medium/large-sized electrodes. It is concluded that the number of domains affects the charging behavior, i.e., the ferroelectric capacitor is charged faster as the number of domains decreases. The effect of static terms (i.e., the alpha and beta parameters) on the transient responses is also studied. From the experimental data obtained above, the differential voltage amplification due to the polarization switching is observed. Using the multidomain Landau-Khalatnikov model, a circuit-level simulation is provided to support the experimental evidence. The simulation results show that the differential voltage amplification increases as the value of rho (ρ) coefficient decreases.

A 25-Gb/s Avalanche Photodetector-Based Burst-Mode Optical Receiver With 2.24-ns Reconfiguration Time in 28-nm CMOS

This paper describes an avalanche photodetector (APD)-based optical receiver, applicable to the burst-mode operation, in 28-nm CMOS technology. With the aims of benefiting the overall optical link power efficiency and link bandwidth, the optical receiver is designed to have high sensitivity and high reconfiguration speed for burst-mode operation. The sensitivity of the receiver is optimized by adjusting the responsivity of APD via its reverse bias voltage, which leads to the highest signal-to-noise ratio (SNR) at the front end. The two-tap feed-forward equalization (FFE), along with two-tap decision feedback equalization, is implemented in a current-integrating fashion to further improve the sensitivity with superior power efficiency to their resistively loaded counterparts. Integrating dc comparator and integrating amplitude comparator are proposed to replace the conventional RC low-pass filters and peak detectors, respectively, in extracting the information of dc offset and signal amplitude within two unit intervals (UIs), empowering significant acceleration of the burst-mode reconfiguration. When the APD is biased at −16 V, its overall responsivity at 1310 nm is 4 A/W, and the optical receiver achieves bit-error-rate (BER) better than 10−12 at −16-dBm optical modulation amplitude, 2.24-ns reconfiguration time with 5-dB dynamic range, and 1.37-pJ/b energy efficiency at 25 Gb/s.

Comparative Analysis of Seismic Behaviour of Flat Slab and Conventional RC Framed Structure

Comparative Analysis of Seismic Behaviour of Flat Slab and Conventional RC Framed Structure

Experimental and numerical study on low-velocity lateral impact behaviors of RC, UHPFRC and UHPFRC-strengthened columns

This paper aims to develop a strengthening method based on ultra-high performance fiber reinforced concrete (UHPFRC) to improve the performance of a column under impact loading. Impact performances of UHPFRC columns were first examined by using the drop-hammer impact test system. The impact-resistant performance of an axially-loaded UHPFRC column was experimentally confirmed to be superior to that of the conventional RC column. The importance of exerting an axial load was highlighted and addressed by comparing the experimental data of UHPFRC columns with and without axial loads. Subsequently, three different types of UHPFRC-strengthened RC columns were experimentally investigated in detail. Superior performances were observed for the strengthened column with two-end (i.e., potential plastic hinge zone) UHPFRC jackets in comparisons with the other strengthening schemes. Impact strengths could be improved when adding a UHPFRC jacket in the contact zone, but significant increases in impact forces would be induced simultaneously. The column with UHPFRC jackets in both the contact zone and the two ends was shown to be the worst configuration because shear (or punching) failure is prone to occur in the remaining RC portions. A finite element (FE) modeling method was proposed and demonstrated as being capable of reasonably predicting impact responses of UHPFRC columns and UHPFRC-strengthened columns. The findings drawn from the experimental and numerical studies can facilitate the strategic application of UHPFRC for improving the impact-resistant performance of bridge and building columns.

A 3D Thermal Network Model for Monitoring Imbalanced Thermal Distribution of Press-Pack IGBT Modules in MMC-HVDC Applications

In this paper, the impact of a double-sided press-pack insulated-gate-bipolar-transistor (PP IGBT) cooling structure on its thermal impedance distribution is studied and explored. A matrix thermal impedance network model is built by considering the multi-chip thermal coupling effect for the collector side of the PP IGBT. Moreover, a verification has been made by comparing the proposed matrix thermal network model and the conventional lumped RC network model provided by the manufacturer. It is concluded that the collector side has lower thermal resistance and dissipates about 88% of the heat generated by the IGBT chips inside the module. Then, a modular-multilevel-converter high-voltage-direct-current (MMC-HVDC)-based type test setup composed of the press-pack IGBT stacks is established and the junction temperature is calculated with the proposed thermal model and verified by temperature measurements.

Comparison between cyclic response of RC columns transversely reinforced with FRP strips and carbon steel

This study investigates the effects of different confinement methods for longitudinal reinforcement bars in reinforced concrete, RC columns. Comparison is made between three RC columns; two were transversely reinforced with carbon steel in single tie and continuous spiral form, and the third sample were transversely reinforced with Fibre Reinforced Polymer, FRP strips in continuous spiral form. Numerical simulation is conducted using validated numerical models. All three RC column models were subjected to a constant axial load and cyclic loading. Hysteresis curves and backbone curves were used to analyse cyclic behaviour of each samples. Comparisons between the RC columns were made based on the ultimate load capacity and energy dissipation capacity ratio. Results show that, RC column transversely reinforced with FRP strips exhibits the highest ultimate load and energy dissipation capacity. The ultimate load capacity is 15% and 10% higher than the RC column transversely reinforced with carbon steel in single tie and continuous spiral form respectively. The FRP strips also increases the energy dissipation capacity up to 35% and 22% compared to the one transversely reinforced with carbon steel in single tie and spiral form respectively. It can be concluded that the usage of FRP strips as transverse reinforcement in RC column is able to improve the cyclic responses of the conventional RC columns.

Battery aging assessment and parametric study of lithium-ion batteries by means of a fractional differential model

An extensive parametric study of an alternative battery model, the fractional differential model (FDM), is presented for the first time over the entire lifetime of 20Ah NMC cells. The evolution of the FDM's model parameters, identified in the time-domain, is compared to electrochemical impedance spectroscopy results to assess their physico-chemical significance. This comprehensive parametric analysis shows that the FDM is able to capture relevant physico-chemical information with regards to the ohmic resistance over the entire SoC range and battery lifetime. Furthermore, the FDM's electrical performance is compared to the conventional first order RC battery model over the entire battery lifetime. Thanks to the FDM's non-integer derivatives for system states, it is able to capture intrinsic fractional derivative properties such as diffusion dynamics, charge transfer and memory hysteresis, which results in an improved simulation accuracy compared to the RC model. The comparative study showed an improved simulation accuracy of the FDM up to 85% in the lowest SoC range and a minimum improvement of 40% over the entire SoC range, considering the entire battery lifetime. Inherently proving that the FDM's ability to capture highly nonlinear battery behavior in the low SoC region persists over battery lifetime.

Frequency‐dependent empirical modeling for intrinsic output capacitance and conductance of HR PD‐SOI MOSFETs

AbstractA high resistivity PD‐SOI MOSFET equivalent circuit model including a parallel connection of intrinsic output capacitance and conductance with frequency‐dependent empirical equations is newly proposed to accurately simulate their abrupt change in the low‐frequency region. This new empirical model is superior to a conventional RC one, because equivalent circuit structure and parameter extraction process are simpler. Better agreements with measured Y22‐parameter are obtained for the new model than the conventional one.

Secondary Cracks and Mechanical Behavior Prediction of Concrete Segments After FRP Confinement

It is quite challenging to use tunnel segment as a repair experiment object due to its large size, the difficulty of installation, and loading inconvenience. To tackle this problem, a 45° symmetrical-bevel RC plate has been employed to substitute segment and conventional RC plate, and to investigate the mechanical behavior of secondary crack problems for concrete segments after repair by polymeric matrix and fiber reinforcement polymers (FRPs). Moreover, elaborate five numerical models of segments were established by means of experiments and 3D finite element method. The prediction results indicated that the mechanical properties of using 45° symmetrical-bevel RC plate were in good agreement with the concrete segments (81.30%). In contrast, those using conventional RC plate showed a larger disagreement (57.49%). Versus and after repair by PM and FRPs, the secondary cracks of concrete segments were improved by 2.86–29.52% of compressive strength compared with the primary cracks. It demonstrated that the experimental results and the simulation results matched well (close to min. 87.89%).

A numerical and experimental study on the dynamical behavior of 3D-Panel Wall on Piloti RC Frame

PurposeThe purpose of this paper is to examine the dynamical behavior of a combined three-story building with a 3D panel wall system including a soft story irregularity at the very first floor by doing a shaking table test. The upper two stories of the model were made out of the 3D panel system, while the first story was constructed only with moment-resisting RC frames.Design/methodology/approachBesides the experimental program, the numerical finite element method was implemented for the verification of the experimental results. In the experimental study, the building responses including the floors’ accelerations and drifts were considered, and the seismically vulnerable zones were reported and compared with that provided by the implemented FEM-based program.FindingsAfter the shaking table test, the major cracks appeared at the end of each column and beam-column connections. Some negligible cracks were also visible around the beam-panel connections. However, no crack was seen in the upper stories. The lateral deformation of the studied building was investigated under the applied ELC25 and NGH135 earthquakes. Under the both aforementioned ground motion records, the first story drift was larger than two upper stories, since the moment-resisting frame was a soft story. The hysteretic relation between the shear and displacement for each story was studied. Under the applied ELC25 earthquake, the system remains linear and the stiffness of each story is obtainable as well.Originality/valueThis is the first time when the dynamical behavior of a combined system is studied and tested experimentally and numerically for data validation. Regarding the response of the assumed combined structure, the 3D panel system has a remarkable rigidity with respect to the conventional RC frames, also 3D panels have less weight than the moment-resisting frames.

MOS-only polyphase filter with small chip area

In this paper, it is aimed to realize a systematic approach for the realization of the MOS only complex polyphase filters which occupy small chip area. For this purpose, we used a technique based on adding cross-coupled transistors realizing local positive feedback, which, in turn, increases filter time constants. Thanks to this method, a substantial reduction in the filter chip area is achieved without having to use bulky on chip capacitors. The usefullness of the approach is validated by comparing the layouts of the designed CMOS circuit with the conventional RC polyphase filter. Post-layout simulation results using SPECTRE in CADENCE design environment are provided to verify feasibility of the proposed complex filter.