Numerical analysis of fiber composite-steel plate upgraded beam–column sub-assemblages under cyclic loading

In the present study, exterior beam–column sub-assemblage from a regular RC building has been considered. Extremely poor gravity load designed (GLD) beam–column sub-assemblage was upgraded by combinely using FRP and steel plate. Three different upgradation schemes have been proposed. Nonlinear finite element (FE) program has been employed for analysing both existing and upgraded sub-assemblages under cyclic loading. Concrete parts of the FE models were modelled using quadratic brick – and steel plates were modelled using tetrahedral – solid elements. All the FRPs were modelled as 9-noded iso-parametric multi-layered shell elements with embedded unidirectional reinforcement to represent the anisotropic material property. Contact elements and bond properties were suitably incorporated. It has been found out that the results obtained from the numerical analysis are well corroborated with those of experimental results. Further, a detailed parametric study has been carried out on type, extent and amount of flexural strengthening, and number of wrapping to identify the scopes of improvement on the proposed upgradation schemes.     

Seismic behavior of hybrid fiber reinforced cementitious composite beam–column joints

This paper presents the experimental results of six exterior beam–column joints with different concrete composites under cyclic loading. Engineered cementitious composite with polypropylene fiber and hybrid cementitious composites (HCC) using three different types of fiber namely hooked end steel fiber; brass coated steel fiber and polypropylene fiber are explored in this study. The hysteresis behavior, ductility response, energy dissipation with damping characteristics, crack patterns and damage index of all tested specimens are analyzed and compared with the cyclic response of conventional specimens. The test results indicate that HCC increases load carrying capacity and enhances energy dissipation with increased stiffness retention over conventional specimens. At higher rotation, joint specimens with HCC manifest better damage tolerance capacity over conventional specimens. This investigation implies that the use of HCC in the joint region may be an alternative solution to significantly increase the shear capacity, damage tolerance capacity and member ductility.     

Comparative performance of sub-standard interior reinforced concrete beam–column connection with various joint reinforcing details

This paper discusses the effect of some important parameters on cyclic behavior of sub-substandard interior beam–column connection. The objective is to investigate the effect of joint shear stress, anchorage bond of longitudinal beam bar within the joint and horizontal joint reinforcements on the joint performance. The experiment consisted of five half-scale beam–column specimens. The control specimen (J1) represented a typical non-ductile beam–column joint in mid-rise RC buildings constructed in low seismic zone. In specimen J2, the bond between concrete and longitudinal bars was completely removed initially. In specimen J3A and J3B, a substantial amount of horizontal joint reinforcement was provided in joint core. In specimen J4, the column size was enlarged to reduce shear stress in joint. The experimental result demonstrated brittle joint shear failure in control specimen (J1), specimens J3A and J3B, beam splitting failure in specimen J2 and ductile flexural failure in specimen J4. Based on experimental results, it was found that the initial lost of bond did not cause a substantial reduction in joint capacity. Moreover, provision of substantial horizontal joint reinforcements in specimen J3A and J3B did not produce a comparable improvement in the seismic performance. With increased column size in specimen J4, the energy dissipation characteristics were greatly improved as indicated by large spindle-shaped cyclic loops.     

Experimental study of RC beam–column joints strengthened using CFRP composites

This paper presents an experimental study to strengthen the shear capacity of non-seismic joints using Carbon Fiber Reinforced Plastic (CFRP) materials. Eight exterior RC beam–column joint specimens including a non-seismic specimen, a seismic specimen and six retrofitted specimens with different configurations of CFRP sheets were developed and tested to find out an effective way to improve the seismic performance of the joints in terms of the lateral strength and ductility. The different configurations of CFRP sheets considered were the T-shape, L-shape, X-shape and strip combinations. The research focused on the effect of using CFRP sheets for enhancing strength and increasing ductility of the non-seismic beam–column joints. The test results showed that appropriately adding CFRP composites to the non-seismic specimen significantly improved the lateral strength as well ductility of the test specimens. Especially, the X-shaped configuration of wrapping, the strips on the column and two layers of the CFRP sheets resulted in a better performance in terms of ductility and strength.     

Strengthening of non-seismically detailed reinforced concrete beam–column joints using SIFCON blocks

This article aims to propose a novel seismic strengthening technique for non-seismically detailed beam–column joints of existing reinforced concrete buildings, typical of the pre-1975 construction practice in Turkey. The technique is based on mounting pre-fabricated SIFCON composite corner and plate blocks on joints with anchorage rods. For the experimental part three 2/3 scale exterior beam–column joint specimens were tested under quasi-static cyclic loading. One of them was a control specimen with non-seismic details, and the remaining two with the same design properties were strengthened with composite blocks with different thickness and anchorage details. Results showed that the control specimen showed brittle shear failure at low drift levels, whereas in the strengthened specimens, plastic hinge formation moved away from column face allowing specimens to fail in flexure. The proposed technique greatly improved lateral strength, stiffness, energy dissipation, and ductility.     

Pavement performance evaluation of recycled styrene–butadiene–styrene-modified asphalt mixture

More and more styrene–butadiene–styrene (SBS)-modified asphalt waste materials are being discarded with the increase in road service life. The recycling of these waste pavement materials can reduce environmental pollution and help save resources. However, the low-temperature performance and the fatigue resistance of recycled asphalt mixture are significantly affected by the addition of reclaimed asphalt pavement (RAP). In order to evaluate the low-temperature performance and the fatigue resistance of recycled SBS-modified asphalt mixture, three points bending test, Fénix test and Ensayo de BArrido de DEformaciones test were conducted. Additionally, the differences of recycling between SBS-modified RAP with different ageing conditions and ordinary unmodified RAP were compared. The results showed that fatigue resistance of modified recycling of asphalt mixture with different RAPs did not vary much under low temperature (?5 °C) while displaying an obvious difference under higher temperature. SBS-modified RAP under light ageing condition was suitable for modified recycling. However, the SBS-modified asphalt from RAP under serious ageing condition would lose modification effect resulting in a great reduction of the low-temperature crack resistance and the fatigue resistance. Therefore, it is necessary to evaluate the ageing degree of RAP before recycling SBS-modified asphalt mixture. The SBS-modified RAP under serious ageing condition (SM-RAP) is not recommended for directly modified recycling. But considering for further utilisation, the SM-RAP used for unmodified recycling as ordinary unmodified RAP can be regarded as a good choice and the RAP content should be restricted to less than 30%.     

Behaviour of hybrid fibre reinforced concrete beam–column joints under reverse cyclic loads

An experimental investigation was carried out to study the effect of hybrid fibres on the strength and behaviour of High performance concrete beam column joints subjected to reverse cyclic loads. A total of 12 reinforced concrete beams column joints were cast and tested in the present investigation. High performance concrete of M60 grade was designed using the modified ACI method suggested by Aïtcin. Crimped steel fibres and polypropylene fibres were used in hybrid form. The main variables considered were the volume fraction of (i) crimped steel fibres viz. 0.5% (39.25 kg/m³) and 1.0% (78.5 kg/m³) and (ii) polypropylene fibres viz. 0.1% (0.9 kg/m³), 0.15% (1.35 kg/m³), and 0.2% (1.8 kg/m³). Addition of fibres in hybrid form improved many of the engineering properties such as the first crack load, ultimate load and ductility factor of the composite. The combination of 1% (78.5 kg/m³) volume fraction of steel fibres and 0.15% (1.35 kg/m³) volume fraction of polypropylene fibres gave better performance with respect to energy dissipation capacity and stiffness degradation than the other combinations.     

Strength and ductility of FRP web-bonded RC beams for the assessment of retrofitted beam–column joints

It is generally accepted that beam–column joints are critical elements of reinforced concrete (RC) buildings subjected to lateral loads, and that they may require specific design treatment following the accepted design philosophy of the strong-columnweak-beam. In earthquake-prone regions, the joints must be designed to allow the dissipation of large amounts of energy into the neighbouring elements without a significant loss of strength and ductility. The frames are often designed carefully based on the strong-column–weak-beam concept and their joints detailed accordingly. Sometimes, though, the detailing is inadequate (example, RC joints designed to earlier codes have insufficient lateral resistance). Web-bonded FRP (fibre reinforced plastic) is one of the few possible strengthening methods that can be used when an inadequately detailed joint is damaged causing severe degradation of the joint’s structural strength. In this paper, the results of some tests on FRP strengthened specimens are presented. The results show that the method is effective and capable of restoring or even upgrading the strength of the system. In addition, using the basic principles of equilibrium and compatibility, an analytical model is presented that simplifies the analysis and design of this strengthening scheme. Based on the model, a range of design graphs are presented for selection of the type and the amount of FRP required upgrading an existing joint to a specified moment capacity and curvature ductility.     

Reinforced concrete beam–column joint strengthened with carbon fiber reinforced polymer

An effective rehabilitation strategy is proposed to enhance the strength and stiffness of the beam–column joint in this study. An analytical model is proposed to predict the column shear of the joints strengthened with carbon fiber reinforced polymer (CFRP). Three full scale interior beam–column joints, including two specimens strengthened with CFRP and one prototype specimen, are tested in this study. The specimens are designed to represent the pre-seismic code design construction in which there is no transverse reinforcement. A new optical non-contact technique, digital image correlation (DIC), which can measure the full strain field of specimen, is used to measure and observe the full strain field of the joint. The experimental results show that the beam–column joints strengthened with CFRP can increase their structural stiffness, strength, and energy dissipation capacity. The rehabilitation strategy is effective to increase the ductility of the joint and transform the failure mode to beam or delay the shear failure mode. By observing the measured results, it is found that the mechanical anchorages can prevent the debonding of CFRP. Comparing the analytical and experimental results, the proposed model can accurately predict the column shear and shear strength of the joints strengthened with CFRP.     

Impact of some flexibility factors in FMSs–a performance evaluation approach

This paper investigates the relative impact of versatility as a selected physical characteristic of the resources (a design adequacy factor), versus some operating strategies (control factors), on flexible manufacturing systems performance. Systems are operated under changes in mix, in the availability of the resources (due to failures), as well as at various levels of planned machines' utilization. Versatility measures at machine and system level are discussed. The extent of the machines' workload imbalance is presented as an off-line system performance indicator, expected to provide rough cut, useful information at the design stage. Simulated experiments are designed and analysed, to offer a factorial on-line view of the problem and thus, to enable estimation of interaction effects between flexibility, environmental factors and changes. A standardized, service-orientated, on-line performance measure of the system is introduced.     

Feasibility study and performance evaluation of low capacity water–LiBr absorption cooling systems functioning in different Algerian climate zones

A performance analysis was carried out on water–LiBr absorption chillers performing in the five different climate zones in Algeria. A 17.6 kW single-effect and a 16 kW double-effect commercial absorption chillers were simulated. In climate zones E1 and E2, the single-effect and double-effect chillers supplied 37% and 91%, respectively, of their nominal capacity to produce chilled water at 7 °C. In the hot climate zones E3, E4 and E5, it was not feasible for either of the chillers to produce chilled water at 7 °C. By increasing the chilled water temperature to 12 °C both absorption chillers were able to operate in climate zones E3 and E4. The single-effect chiller reached 45% of its nominal capacity in zone E3 and 33% in zone E4. The double-effect chiller delivered 80% of its nominal capacity in both climate zones. Neither of the chillers was able to operate under the thermal conditions of climate zone E5.     

Displacement bound of beam‐column with time‐dependent boundary constraints

Abstract

A simplified explicit formula for the displacement bounds of the beam‐column subjected to time‐dependent boundary constraints is proposed. The formula is derived by means of removing time dependence from the boundary conditions. The proposed bounds provide a quick estimation of the displacements for problems with complex loading conditions.     

Formulation and performance evaluation of a novel coconut oil–based metalworking fluid

Metalworking fluid (MWF) supplies a film of lubricant to abate friction, acts as a cooling media to rebate induced heat, and prevents metal pick-ups by flushing away the chips. Hence a liquid used as a cutting fluid reduces wear on the tool, reduces the energy consumption, and produces a better surface quality on the work piece. This paper describes the formulation of a novel water-soluble MWF and its performance evaluation during straight turning and end milling experiments carried out with AISI 304 stainless steel, mild steel, and cast iron as work piece materials. The MWF was prepared by mixing water with white coconut oil as the base oil and food-grade additives as surfactants. Viscosity, pH value, and biodegradability were measured and compared with a commercially available non-vegetable oil–based MWF. The surface roughness and tool surface temperature were measured throughout the machining experiments, and better performances were observed with the coconut oil–based MWF. Tool tip geometry and flank wear for straight turning machining operation were identified by observing scanning electron microscope (SEM) images.     

NOL-ring based evaluation of freeze and freeze–thaw exposure effects on FRP composite column wrap systems

Four different fiber reinforced polymer (FRP) composite column wrap systems are evaluated for durability after exposure to freeze (−15°F) and freeze–thaw conditions. Response and failure mechanisms are characterized through Naval Ordinance Laboratory-ring burst tests, short-beam-shear tests, dynamic mechanical thermal analysis and microscopy. It is shown that freeze–thaw exposure after salt soak can have a significant detrimental effect and results in reductions in both tensile strength and interlaminar shear strength. The adhesive layer used in the prefabricated adhesively bonded system is shown to be the weak link in that system with degradation and failure taking place either within the adhesive or at the adhesive–composite interface. Effects of incomplete ambient cure, pre-existing voids and process induced residual stresses are shown to be critical aspects for the other three systems. It is shown that, in comparison to the freeze–thaw conditions, sustained exposure to −15°F conditions has a much lower effect on all properties except modulus which is seen to increase due to matrix hardening and transition of material response to a predominantly brittle regime.     

Synthesis of bridged β-cyclodextrin–polyethylene glycol and evaluation of its inhibition performance in oilfield wastewater

The bridged β-cyclodextrin–polyethylene glycol (β-CD–PEG) is synthesized through reaction of β-CD with PEG, which has been characterized by Fourier transform infrared spectroscope. The inhibition efficiency of bridged β-CD–PEG on corrosion of Q235 carbon steel in 0.5 M HCl solution has been investigated by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and weight loss measurements. The results show that β-CD–PEG acted as a mixed-type inhibitor and performed excellent inhibiting effect for the corrosion of the Q235 carbon steel. The steel surface morphologies are analyzed using scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) and then an adsorption mechanism model is proposed. The high inhibitory efficiency of β-CD–PEG is related with the adsorption of polymer molecules at the steel surface and a protective film formation. Finally, these results present a novel corrosion inhibitor works in oil-gas field.     

Studies on the performance of a small reciprocating compressor with different nitrogen–hydrocarbon mixtures

The performance of Joule–Thomson refrigerators operating with mixed refrigerants depends on the composition of mixtures as well as the hardware employed. The role of mixture composition on the overall performance of the system has been well addressed in the open literature. What is not well known is the role of mixture composition on the performance of individual components such as the compressor, heat exchanger, etc. The adiabatic efficiency of a single stage Joule–Thomson refrigerator compressor was measured with thirty different nitrogen–hydrocarbon and neon–nitrogen–hydrocarbon mixtures. Our results show that the adiabatic efficiency of the compressor is independent of the mixture composition in the range of pressure ratios tested.     

Electromagnetic characteristic and microwave absorbing performance of different carbon-based hydrogenated acrylonitrile–butadiene rubber composites

Hydrogenated acrylonitrile–butadiene rubber (HNBR) was mixed with carbon fiber (CF), conductive carbon black (CCB) and multi-walled carbon nanotubes (MWCNT) to prepare microwave absorbing composites, their complex permittivity was measured in microwave frequencies (2–18 GHz), and their electromagnetic characteristics and microwave absorbing performance were studied. The real part and imaginary part of permittivity of the composites increased with increasing carbon filler loading, showing dependency on filler type. The microwave reflection loss of the composites also depended on the loading and type of fillers. The matching thickness of the absorber layer decreased with increasing permittivity, while the matching frequency decreased with increasing layer thickness. The minimum reflection loss was −49.3 dB for HNBR/MWCNT (100/10) composite, while −13.1 dB for HNBR/CCB (100/15) composite and −7.1 dB for HNBR/CF (100/30) composite. The efficient microwave absorption of HNBR/MWCNT composites is accounted from high conduction loss and dielectric relaxation of MWCNT, and strong interface scattering.