Jacket Thickness Research Articles

Effect of Fibrous Jacket on Behavior of RC Columns

This paper presented an extensive study about the strengthening of RC square short columns with high strength concrete jackets reinforced with steel fiber. The aim of this study is to investigate the effect of confinement by fibrous jacket on the behavior of RC column. A comparative study is performed on 23 square columns (six of them were unconfined columns where the remaining seventeen were confined columns) with varied parameters such as steel fibers ratio and type, jacket thickness, partial and full strengthening, type of confining jacket (hoop and composite), use of epoxy as bond material between the concrete column and strengthening jacket, and length parameter. The test results showed that the strengthened columns showed a significant improvement in the ultimate stress, load-carrying capacity, maximum strain, ductility, and energy absorption. Increase the steel fibers ratio (1, 1.5 and 2%) increased the ultimate stress by (22.5, 12.3 and 12.5%) respectively. The use of epoxy as bond material enhanced the ultimate stress by an average improvement by (55%). Composite case in the strengthening enhanced the load-carrying capacity larger than hoop case by (28.7 and 42%) for FRC jackets with hooked and straight fibers respectively but in case of stress capacity, hoop jacket carries stresses more than composite according to the stressed cross-sectional area. Increase jacket thickness (25 and 35 mm) enhanced the ultimate stress by (28.7 and 15.5%) respectively. Partial strengthening has a good enhancement in the ultimate load but was less than full strengthening. Increase the length by (25 cm) decreased the enhancement in load capacity of the column with hoop jacket by (45.3%). Concrete jackets enhanced Energy absorption and ductility which improved the deformation capacity. The compressive behavior of stub concrete columns was also modeled, simulated, and analyzed numerically by a 3D nonlinear finite element model. The verification process was performed against the reported data of the experimental test which proved the results of experimental results and showed a good agreement between experimental and numerical outcomes.

Mechanical performance of CFRP-confined sustainable geopolymeric recycled concrete under axial compression

Sustainable geopolymeric recycled aggregate concrete (RAC) by utilizing environmentally-friendly binder-geopolymer and constructional solid waste-recycled aggregate (RA) will facilitate the sustainability in concrete industry. This study investigated the compressive behavior of sustainable geopolymeric RAC confined by carbon fiber-reinforced polymer (CFRP) jackets. A total of 72 cylindrical fly ash/slag-based geopolymeric concrete specimens, including 48 CFRP-confined specimens and 24 unconfined specimens were fabricated and tested. The testing variables included: coarse aggregate type (i.e., natural aggregate and RA), thickness of CFRP jackets (i.e., 1, 2, and 3 layers) and (iii) slag content (i.e., 0, 10%, 20% and 30% of the total binder by mass). The results indicate that the CFRP confinement remarkably enhances the compressive strength and ultimate strain of geopolymeric concrete, and the enhancement is more pronounced with the increase of CFRP jacket thickness. Moreover, the RA replacement and the inclusion of slag have minor influences on the CFRP confinement performance for the compressive strength, but have obvious effects on the CFRP confinement performance for the ultimate axial strain. Based on the test results, empirical stress and strain models were proposed to predict the ultimate condition of the CFRP-confined geopolymeric concrete.

Experimental Study of Strengthening of RC Columns with Steel Fiber Concrete

This study introduces an experimental program to investigate the performance of concrete wrapping jackets reinforced by steel fibers used for retrofitting of the square and circular RC columns under axial loads. Ten columns divided into two groups; the first group included seven square columns while the second group involved three circular columns. The experimental study included testing the columns with varied parameters such as cross-section shape, type and aspect ratio of steel fibres, jacket thickness, and using several techniques for retrofitting the column such as strengthening by plain and reinforced concrete jackets. The selected parameters affected the compressive behavior of confined columns high strength concrete jackets. The obtained results revealed that all strengthened columns with square cross-section appeared maximum strength greater than a circular one. Using several types of concrete jacketing promotes the load-capacity of the column with a clear improvement in the ductility. Increasing thickness appeared increasing in the load-carrying capacity in comparison with the reference column. Using the straight fibres showed better enhancement in the load capacity than the hooked ones. The main result was the failure mode was different from unstrengthen columns which showed more crushing in the concrete core with an increase in thickness.

Behavior of large-scale FRP-confined rectangular RC columns under eccentric compression

Fiber-reinforced polymer (FRP) composites have become widely accepted in the strengthening or seismic retrofitting of reinforced concrete (RC) columns in practice. FRP-confined rectangular concrete columns under concentric axial compression have been extensively studied, leading to many stress-strain models (i.e., concentric-loading stress-strain models). Although RC columns in practical structures are commonly subjected to combined axial compression and bending (i.e., eccentric compression), existing research on eccentrically-loaded FRP-confined rectangular RC columns has been much more limited. More specifically, the limited research available has generally been concerned with small-scale RC columns, and the applicability of existing concentric-loading stress-strain models for FRP-confined concrete in the analysis of large-scale eccentrically-loaded rectangular RC columns has not been properly clarified. This paper presents the results of an experimental study including eight large-scale FRP-confined rectangular RC columns tested under eccentric compression. The following key test variables were carefully examined in the experimental program: the load eccentricity, the direction of bending, and the FRP jacket thickness. A theoretical column model is then presented for predicting the responses of the test columns. It is shown that the direct use of a concentric-loading stress-strain model for FRP-confined concrete in the column model leads to significant errors in predicting the ultimate deformation of the test columns.

Behavior and new strength model of FRP square columns based on the FRP effective circumferential failure and the effective lateral confining pressure

This paper presents an experimental investigation of the effect of concrete compressive strength, strengthening ratio and corner radius on the behavior of small-scale square columns wrapped with carbon fiber-reinforced plastic (CFRP) materials. A total of 39 specimens (150 × 150 × 300 mm) wrapped with one, two, and three plies of CFRP wraps were tested. In addition to the FRP jacket thickness, the effect of three different concrete mixes and four cases of corner radius were examined. The effective circumferential CFRP failure strain and the effect of the effective lateral confining pressure were investigated. The obtained results show that the CFRP reinforced columns provide a significant increase in ultimate conditions (strength and ductility) compared to the case of the unconfined specimens. It can be seen that higher concrete compressive strength and lower strengthening ratio reduce the effect of confinement with CFRP material. The test results demonstrated that the corner radius ratio is in direct proportion to the increase in confined concrete strength. A new model is presented to predict the compressive axial strength and corresponding strain of CFRP-confined columns based on the effective lateral strain of FRP material.

FRP-confined recycled glass aggregate concrete: Concept and axial compressive behavior

In this study, the axial compressive behavior of fiber-reinforced polymer (FRP)-confined recycled glass aggregate concrete (RGAC) was experimentally investigated. In the FRP-confined RGAC, the FRP, a high performance material with high strength and excellent corrosion resistance, is utilized both as confinement and cover to the core concrete in order to increase mechanical performance (strength and deformability) and durability resistance to harsh environmental attack, respectively. Axial compression tests were carried out on a series of RGAC cylindrical columns, including 21 unconfined RGAC specimens and 42 CFRP-confined RGAC specimens. The key test variables examined in this study include the FRP jacket thickness and replacement ratio of aggregates. The test results showed that the compressive behavior (e.g. strength and elastic modulus) of FRP-confined RGAC is comparable to that of FRP-confined normal concrete when the replacement ratio of RGAs is not large than 50%, although the compressive behavior of RGAC has a notable decrease with increasing replacement ratio of recycled glass aggregates (RGAs). The test results also demonstrated that a combined use of coarse and fine RGAs slightly improved the compressive behavior of both confined and unconfined RGAC. Based on this study, an effective way of re-using glass waste can be developed.

Design of Smooth Aluminum Bonded Sheaths in HV XLPE Cables Based on the Bending Performance Research

In China, recent ablation failures of water-blocking buffer layer occurred in high voltage (HV) cross-linked polyethylene (XLPE) cables with corrugated aluminum sheath have stimulated the product development of cables with smooth aluminum bonded sheath. Despite the many advantages, bending performance is one of the few weaknesses of smooth aluminum bonded sheath. In this paper, a three-dimensional model of a cable with smooth aluminum bonded sheath in a four-point bending test was set up, where the cohesive zone model was applied to simulate the mechanical behavior of the adhesive layer (bonding interface). The influence on the bending performance of the bonded sheath by the thickness of aluminum layer, the parameters of hot melt adhesive, the thickness and material parameters of outer jacket, as well as the cable specification was investigated, together with the stress distribution and damage analysis of the adhesive layer. Based on the research, the material selection and structural design of smooth aluminum bonded sheath were recommended for HV XLPE cables, including an additional requirement for the shear strength of hot melt adhesive besides those already in IEC and IEEE standards. Finally, a 110 kV XLPE cable with smooth aluminum bonded sheath was manufactured and type tested.

Tailoring Confining Jacket for Concrete Column Using Ultra High Performance-Fiber Reinforced Cementitious Composites (UHP-FRCC) with High Volume Fly Ash (HVFA)

Ultra-High Performance Fibre-Reinforced Cementitious Composites (UHP-FRCC) show excellent mechanical performances in terms of strength, ductility, and durability. Therefore, these cementitious materials have been successfully used for repairing, strengthening, and seismic retrofitting of old structures. However, UHP-FRCCs are not always environmental friendly products, especially in terms of the initial cost, due to the large quantity of cement that is contained in the mixture. Different rates of fly ash substitute herein part of the cement, and the new UHP-FRCCs are used to retrofit concrete columns to overcome this problem. To simulate the mechanical response of these columns, cylindrical specimens, which are made of normal concrete and reinforced with different UHP-FRCC jackets, are tested in uniaxial compression. Relationships between the size of the jacket, the percentage of cement replaced by fly ash, and the strength of the columns are measured and analyzed by means of the eco-mechanical approach. As a result, a replacement of approximately 50% of cement with fly ash, and a suitable thickness of the UHP-FRCC jacket, might ensure the lowest environmental impact without compromising the mechanical performances.

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.

Parametric study of medium span bridges retrofitted with reinforced concrete jacketing

Most reinforced concrete (RC) bridges in many countries are medium-span length structures built in the last decades and designed for very low seismic forces. The evolution of seismic codes and the average age of the bridges require the evaluation of their seismic vulnerability. This study assesses the expected capacity, demand and damage of seismically deficient medium-length highway bridges, supported in frame-type piers using dynamic nonlinear methodologies. A parametric study of reinforced concrete retrofitted bridges with RC jacketing was conducted. The non-retrofitted structures are 30 m span simple supported bridges with pier heights in the range of 5–25 m. The main emphasis of the study is the assessment of the jacket parameters’ contribution to the seismic vulnerability of bridges. Particularly, it is quantified how jacket thickness and reinforcement ratio affect the probability of reaching a particular damage limit state. The retrofitted scheme includes three jacket thicknesses and three different longitudinal steel ratios. The results evaluate bridge demands and fragility curves to quantify the influence of RC jacketing on the seismic response of structures and allow to select the best jacket parameters that improve the expected seismic behavior of the bridge models. Additionally, the influence of model hysteresis degradation on the expected damage of retrofitted bridges was also determined.

Analytical investigation on the behavior of circular and square RC columns strengthened with RPC and wrapped with FRP under uniaxial compression

This paper presents an analytical approach to predict the uniaxial compression behavior of circular and square reinforced concrete (RC) columns strengthened with reactive powder concrete (RPC) jackets and wrapped with fiber reinforced polymer (FRP). The analytical axial load-axial strain responses of the strengthened RC columns were compared with experimental axial load-axial strain responses. The analytical approach presented in this study conservatively predicted the ultimate axial load of the strengthened RC columns. Also, a parametric study was carried out to investigate key factors that influence the axial load-axial strain response of the strengthened RC columns. It was found that the ratio of the RPC jacket thickness to the diameter or side length of the base RC column significantly influenced the service axial load, ultimate axial load and ductility of a strengthened RC column.

Flexural Behavior of Composite Concrete–Epoxy–Reinforced Concrete Beams

This paper deals with the structural performance of composite reinforced concrete beams made of two different concretes, bonded together using epoxy resin. The fabricated beam section consists of low-strength reinforced concrete core and relatively large thickness outer skin concrete jacket without reinforcement. The results confirm that the bonding technique used for constructing the composite section is effective. Flexural strength of the tested beam is mainly governed by the outer jacket thickness followed by the compressive strength of concrete. A simple flexural analytical model was developed to calculate moment capacity of composite sections. The predictions were found accurate and can be utilized for the flexural analysis and design of composite reinforced concrete beams. A parametric study was made to investigate the effects of core reinforcement and both composite section geometry and material properties on the depth of compression zone and moment capacity of the section.

Effects of cable insulations’ physical and geometrical parameters on sheath transients and insulation losses

This paper investigates the influence of insulations’ physical and geometrical parameters on cable sheath transients and insulation losses considering power cables for high voltage alternating current (HVAC) applications. The study is based on theoretical analysis, Electromagnetic Transient Program (EMTP) simulations, and finite element (FE) simulations. Special attention is paid to the effects of the insulations’ relative permittivities and the protective jacket thickness on cable capacitance, transient voltages, and dielectric losses for different possible conditions including the variations in insulation permittivity and ground resistivity. The cable model used in this work is a single core (SC) underground coaxial cable with an AC voltage supply of 220 kV and 60 Hz frequency. A method for calculating the dielectric losses in cable insulations due to transient voltages was developed. The proposed method is based on the numerical calculations of the flowing electric currents through insulations using FE model. In addition, the relation of the dielectric loss and the maximum sheath overvoltage as a function of permittivites and as a function of protective jacket thickness was explored to obtain an optimum protective jacket relative permittivity from the viewpoint of both the overvoltage and the loss. For given cable system parameters, the transient voltage waveforms within a time period of t = 0–2 ms obtained on the core and the sheath produced dielectric losses 34.362 [W/m] and 3.365 [W/m] at insulation and protective jacket, respectively.Results and conclusion provide a useful background for the ongoing power cable design process and application studies.

Compressive behaviour of stub concrete column strengthened with ultra-high performance concrete jacket

This paper firstly performed compressive tests on 18 stub concrete columns with externally confined ultra-high performance concrete (UHPC) jacket. The studied parameters in this testing programme were the thickness of UHPC jacket and the shapes of specimens. The influences of these parameters on the compressive behaviour of stub concrete columns confined by UHPC jacket were reported and discussed. The test results revealed that increasing the thickness of confining UHPC jacket significantly improved the compressive behaviours of concrete stub columns for cylindrical shaped column. However, this influence on that of square shaped stub columns was less significant. An analytical model was proposed to predict the compressive stress-strain behaviour of stub concrete columns with externally strengthening UHPC jacket. The validations of the predictions against the reported test results confirmed the accuracy of the analytical model. The compressive behaviour of stub concrete columns with UHPC jacket was also simulated by 3D nonlinear finite element model (FEM). Validations against the reported test data proved that the FEM simulated well compressive behaviour of concrete stub columns with UHPC jacket.

Influence of steel jacket thickness on the RC bridges’ seismic vulnerability

Abstract The seismic demands of bridges subjected to strong earthquakes are mostly concentrated on piers. The main objective of this study is to assess the seismic vulnerability of retrofitted bridges with steel jackets. It analyzes the influence of the steel jacket thickness on the seismic capacity and demand of bridges. The bridges in study have two simple supported spans with superstructure composed by AASHTO type girders and a substructure formed with one circular pier over a stiff foundation. They are located on the Pacific coast of Mexico that is a zone of high seismicity. The bridges seismic capacity are evaluated through nonlinear static analyses and the shear force and displacement demands were determined using capacity spectra with a group of 10 real accelerograms from a subduction source. The response spectra were scaled to several peak ground accelerations (PGA) with the aim to estimate four damage scenarios linked each one to a probability of exceedance in a specific period, for return periods in the range of 72–3500 years that represent service level and maximum considered earthquake. Results show that the confining effect provided by the steel jackets substantially improves the seismic performance of the bridges piers. The increase of jacket thickness guides to important increments on columns base shear capacity, and the influence of the steel jacket thickness depends on the limit state and bridge slenderness ratio.

Nonlinear Finite Element Analysis of B-C Connections: Influence of the Column Axial Load, Jacket Thickness, and Fiber Dosage

The behavior of beam-column (B-C) connections received thorough investigation during the past decades focusing on critically-detailed connections before and after strengthening. Various techniques for strengthening of the B-C connection were previously evaluated using high performance concrete jackets (HPCJ), carbon-fiber reinforced polymer (CFRP) composites, or external steel plates. In this study, systematic nonlinear finite element analyses (FEA) were conducted using ANSYS to evaluate the effects of the fiber content and thickness of the HPCJ as well as the level of the column axial load, which is a parameter difficult to evaluate experimentally due to limitations in loading machines and requirement for complicated testing setups. A total of twenty nonlinear FEA models were created, calibrated and properly verified with reputable experimental literature results. The nonlinear FEA results showed that both the HPCJ thickness and fiber content significantly affect the cracks distribution, failure mode, ultimate load capacity, and ductility of the B-C connection. Column axial load levels up to 75% were advantageous to the behavior of virgin B-C connections. In strengthened B-C connections with HPCJ, column axial load levels of 50% and 75% besmirched the behavior compared with 25%. The use of 1% volumetric fiber fraction within the HPCJ results in comparable performance as 2%. The lateral load capacities, net drifts, hysteresis loops, cracks distribution, energy dissipation, stiffness degradation, and failure modes were presented.

Experimental study of CFRP-confined reinforced concrete masonry columns tested under concentric and eccentric loading

Using Carbon Fiber Reinforced Polymers (CFRP) jackets to confine existing concrete masonry columns for capacity and ductility enhancement has been approved in axial compression applications. Considering that the majority of columns in practice are loaded under a combination of axial compression load and bending moment, experimental work for testing reinforced concrete masonry columns confined by CFRP jackets under eccentric loading is needed. This paper presents the results of testing 28 half-scale fully grouted reinforced concrete masonry columns under different concentric, eccentric loading conditions and variations in CFRP jacketing. The ability of CFRP jackets to improve the structural performance is evaluated. Axial force-bending moment interaction diagrams of confined reinforced concrete masonry columns are compared against the unconfined masonry columns to quantify the enhancement in strength and moment. The results indicate that increasing the CFRP jacket thickness enhanced the performance of masonry columns regarding axial strain and strength; however, there was a noticeable reduction in strength gain under strain gradient condition upon increasing the eccentricity level. Also, axial force-bending moment interaction diagrams of confined masonry columns showed an increase in the load and the moment capacity compared to that of unconfined masonry columns.

Behavior of large-scale FRP-confined rectangular RC columns under axial compression

Fiber-reinforced polymer (FRP) jacketing has become an attractive technique for strengthening/retrofitting reinforced concrete (RC) columns. Extensive research has been conducted on FRP-confined rectangular columns under axial compression, leading to a significant number of stress-strain models for FRP-confined concrete in these columns. However, most of these models have been developed based on test results of small-scale columns, so their applicability to large FRP-confined rectangular RC columns has yet to be properly validated. To this end, the present paper first presents the test results of an experimental study consisting of nine large-scale rectangular RC columns, including eight FRP-confined RC columns and one RC column without FRP jacketing as the control specimen, tested under axial compression. The experimental program examined the sectional corner radius and the FRP jacket thickness as the key test variables. Five representative design-oriented stress-strain models for FRP-confined concrete in rectangular columns, identified from critical reviews of the existing literature, are then assessed using the test results to examine their validity for these large-scale columns.

Performance and sensitivity analysis of UHPFRC-strengthened bridge columns subjected to vehicle collisions

Bridge columns made of normal concrete are evidenced to be susceptible to vehicle collisions. Particularly in the United States, vehicle collision has become one of the primary causes of bridge failures. This is largely due to the low crashworthiness of a conventional reinforced concrete (RC) column. Ultra-high-performance fiber-reinforced concrete (UHPFRC) as one of advanced concrete materials has been experimentally demonstrated to possess excellent strength, durability, impact resistance and energy-absorbing capacity. Accordingly, one type of UHPFRC-strengthened columns was proposed in this study as an alternative to RC columns that may be at risk for vehicle collision incidents. High-resolution finite element (FE) models were developed to investigate the performance of UHPFRC-strengthened columns subjected to vehicle collisions. In the high-resolution FE model, a three-span simply-supported girder bridge (including girder, pier column, column cap, bearing, etc.) was adopted and modelled. Material models regarding normal concrete and UHPFRC as well as the vehicle model were carefully calibrated by experimental data. The influence of initial gravity loads on impact responses was found to be pronounced, and a damping-based method was proposed to efficiently exert permanent loads on pier columns prior to a collision. Three different simplified models, as published in current studies, were investigated to replace the whole bridge model. Two single-column models with different boundaries were shown to have low accuracy. The pier-bent model considering the superstructure gravity was demonstrated as capable of predicting collision-induced responses that are in good agreement with the high-resolution FE model. The impact resistances of both RC and UHPFRC-strengthened columns were extensively investigated using the appropriate simplified model. The crashworthiness of UHPFRC-strengthened column was found to be considerably superior to that of RC column. An extensive parametric study was performed using response surface methodology to explore the influences of reinforcement ratios, thickness of UHPFRC jacket, UHPFRC strength and initial impact speed. The impact-resistant performance is mostly sensitive to changes in the thickness of UHPFRC jacket when the impact speed is not very high. On the contrary, the residual capacity of the bridge column is hardly increased by thickening UHPFRC jacket. In addition, the developed response surface models provided easy estimation of impact-induced responses of an UHPFRC-strengthened column, which have potential use as the surrogates of time-consuming FE simulations to efficiently examine the reliability and optimization of bridge columns under impact loadings.

Getting magnetocaloric materials into good shape: Cold-working of La(Fe, Co, Si)13 by powder-in-tube-processing

The powder-in-tube (PIT) technology was applied to La(Fe, Co, Si)13 powder cladded by a thin seamless austenitic steel jacket. Wires appear to be promising in the search for alternative regenerator geometries, since they offer various possibilities of arrangements allowing to optimise heat transfer and pressure loss within the boundaries set by parallel plate and sphere beds. Here, pre-alloyed La(Fe, Co, Si)13 powder was filled in a AISI 316L austenitic steel tube and swaged to wires with an outer diameter of 1 mm. By mechanical deformation, the steel jacket thickness was reduced to about 100 μm surrounding the magnetocaloric core. A post-annealing of only 10 min at 1050 °C is sufficient to form the magnetocaloric NaZn13-type phase resulting in an entropy change close to the value of a pure reference sample. The presented technology is not limited to La(Fe, Co, Si)13/steel combination but can be extended to material pairs involving wire core materials with a first order transition, such as Fe2P-type or Heusler alloys.