Steel Jacket Research Articles

State-of-the-art of fatigue performance and estimation approach of orthotropic steel bridge decks

The structural service behaviors and fracture failures of orthotropic steel bridges are significantly depended on its anti-fatigue performance. Therefore, an urgent requirement is needed for a state-of-the-art summary of the fatigue failure mechanism and life evaluation is needed, to sort out research focuses and development direction, such as to establish the whole-life anti-fatigue theory of steel bridges. The fatigue failure mechanism of cracks observed at U-rib-to-deck joints is revealed with a higher appearance rate of 50.0 %, compared to U-ribs and U-rib-to-crossbeam joints. Fatigue cracks are validated to originate at weld toe or root of U-rib-to-deck joints, and propagated along the deck thickness direction. Then the fatigue performance of deck plates is improved using advanced techniques, such as steel jacketing and polymer rebars. A suitable S-N curve-based anti-fatigue design approach can be adopted based on the application scope, stress amplitude and joint types. Advanced techniques have been implemented to monitor the health state of steel bridge components, and detect the potential appearance of fatigue cracks. Further, the fatigue failure life of orthotropic steel bridges is extended by 1 to 12 times at most, and the fatigue strength of vulnerable positions is correspondingly reduced by 20 % to 80 %.

A Restoring Force Correction Model for Enveloped Steel Jacket-Confined Seismic-Damaged Rectangular Recycled Aggregate Concrete-Filled Steel Tubular Columns

In order to establish a suitable restoring force correction model for enveloped steel jacket (ESJ)-confined seismic-damaged rectangular recycled aggregate concrete-filled steel tubular (RRACFST) columns, based on experimental research, a study of the seismic performance and parameters of ESJ-confined seismic-damaged RRACFST columns was carried out. The restoring force theory, model test, and OpenSees simulation of ESJ-confined seismic-damaged RRACFST columns were conducted. Firstly, a trilinear model of the skeleton curve and a suitable restoring force model for ESJ-confined seismic-damaged RRACFST columns were established. The results were compared with the model test results, and it was found that the two results had good consistency. Secondly, the initial damage of the RRACFST column was simulated by the reducing material properties method, and a correct numerical model for ESJ-confined seismic-damaged RRACFST columns was proposed. The influence mechanism of seismic parameters of the RRACFST column was clarified. Finally, the seismic parameter combination with the best seismic performance for ESJ-confined seismic-damaged RRACFST columns was established; namely, the replacement rate of recycled coarse aggregate is 50%, the concrete strength is C40, the axial compression ratio is 0.3, the strength of the rectangular steel tube is Q345, the wall thickness of the steel tube is 4 mm, and the slenderness ratio is 7.5.

Experimental study on seismic performance of seismic-damaged precast steel reinforced (recycled) concrete frame structure after strengthened and repaired

In order to understand the seismic performance and failure mechanism of the seismic-damaged prefabricated steel (recycled) concrete frame after strengthening and repairing, this paper uses four different strengthened methods, including carbon fiber reinforced polymer (CFRP), high-strength steel wire cloth (HSSWC), oblique support and enveloped steel jacket. Four seismic-damaged prefabricated steel (recycled) concrete frames were strengthened by single or composite strengthening, and low-cycle reciprocating failure tests were carried out on all frame specimens. The final failure mode of the reinforced specimens under simulated seismic load was observed. The seismic performance indexes such as load-displacement (P-Δ) hysteresis curve, skeleton curve, and stiffness degradation of each specimen before and after strengthening were compared and analyzed. The test results show that the strengthening methods used in this test can effectively restore the seismic performance of the seismic-damaged prefabricated steel (recycled) concrete frame. The specimens show a typical ductile failure mode, and the P-Δ hysteresis curve of the specimens is relatively full. For a single strengthened form, CFRP strengthened can more significantly restore and improve the ductility of the specimen than HSSWC strengthened, but the cumulative energy dissipation capacity of the specimen after HSSWC strengthened is stronger. The bearing capacity of the specimens after composite-strengthened is significantly improved, and the damage degree of the structure is reduced. The addition of oblique support and an enveloped steel jacket can provide greater lateral stiffness for the specimens and improve the failure mode of the specimens. The results of this paper can provide a scientific basis for the selection and design of strengthened methods for prefabricated steel-reinforced concrete structures after earthquake damage.

Local and global integrative retrofitting of reinforced concrete frames using in‐plane buckling steel braces

AbstractTwo large‐scale, single‐storey, single‐bay reinforced concrete (RC) moment frames, designed as per an outdated seismic code to represent a typical framing detail of a four‐storey building, have been tested under displacement‐controlled quasi‐static loading protocol as per ACI 374.1‐05. The RC frames include a plinth beam with brick infill underneath, a slab monolithically cast with the top beam and provision for applying axial load to the column to simulate real construction scenario. One of the frames has been tested as a bare frame, and the second one has been retrofitted with conventional steel braces designed to undergo in‐plane buckling. The size of the brace has been selected based on the result of a nonlinear time history analysis of representative low‐ to mid‐rise open‐ground storey RC buildings. Post‐installed chemical anchors have been utilized to connect the steel braces to the narrow RC frame members following the outcomes of an experimental investigation by the same authors. Local‐level retrofitting by steel jacketing using adhesives has been designed and utilized on columns and beams to achieve the desired seismic response. The seismic performance of the retrofitted frame has been compared with the bare frame in terms of strength, stiffness, ductility, energy dissipation and hysteretic damping. The tests provide insight into the role of the plinth beam, effect of RC slab on the strong‐column weak‐beam aspect and the achievement of the desirable hinge mechanism through a precise design and detailing of global and local level retrofitting technique.

Development of a high current density, high temperature superconducting cable for pulsed magnets

Abstract A low AC loss Rare Earth Barium Copper Oxide (REBCO) cable, based on the VIPER cable technology has been developed by Commonwealth Fusion Systems for use in high field, REBCO based tokamaks. The new cable is composed of partitioned and transposed copper ‘petals’ shaped to fit together in a circular pattern with each petal containing a REBCO tape stack and insulated from each other to reduce AC losses. A stainless steel jacket adds mechanical robustness—also serving as a vessel for solder impregnation—while a tube runs through the middle for cooling purposes. Additionally, fiber optic sensors are placed under the tape stacks for quench detection. To qualify this design, a series of experiments were conducted as part of the SPARC tokamak Central Solenoid Model Coil program—to retire the risks associated with full scale, fast ramping, high flux HTS Central Solenoid (CS) and Poloidal Field (PF) coils for tokamak fusion power plants and net energy demonstrators. These risk study and risk reduction experiments include (1) AC loss measurement and model validation in the range of ~5 T/s, (2) an IxB electromagnetic loading of over 850 kN/m at the cable level and up to 300 kN/m at the stack level, (3) a transverse compression resilience of over 350 MPa, (4) manufacturability at tokamak relevant speeds and scales, (5) cable to cable joint performance, (6) fiber optic based quench detection speed, accuracy, and feasibility, and (7) overall winding pack integration and magnet assembly. The result is a cable technology, now referred to as PIT VIPER, with AC losses that measure fifteen times lower (at ~5 T/s) than its predecessor technology; a 2% or lower degradation of critical current (Ic) at high IxB electromagnetic loads; no detectable Ic degradation up to 570 MPa of transverse compression on the cable unit cell; end to end magnet manufacturing, consistently producing Ic values within 7% of the model prediction; cable to cable joint resistances at 20 K on the order of ~15 nΩ; and fast, functional quench detection capabilities that do not involve voltage taps. This cable technology will be tested comprehensively in a Central Solenoid Model Coil to prove its readiness for compact, high field tokamak operation.

20 years of monitoring of a steel jacket offshore platform: variability of environmental and modal parameters

The fixed steel offshore platform VEGA-A has been operating in the Sicily channel since 1988. The platform, one of the largest in the Mediterranean Sea, is equipped with a monitoring system that collects environmental (by means of a current meter, a depth gauge, and a system for detecting wind speed and direction) and structural (by means of nine accelerometers) data. After a description of the recording system, this paper provides a statistical interpretation of the structural response of the platform over the last 20 years. The structural monitoring system is aimed at performing dynamic identification (i.e., evaluating main frequencies and mode shapes), and part of the acquired data is directly processed on the platform in order to constantly check their representativeness in relation to the structural control of the platform. The possible variation of main frequencies and mode shapes over time may be due to both changes in environmental loads/conditions and/or structural damage; in this respect, a data-driven approach capable of recognizing anomalies in the dynamic behavior was adopted here to assess the performances of the platform over the 20 years monitoring period.

Experimental Investigation on Axial Strength Improvement of Cold-Formed Steel Jacketed Concrete Stub Columns

This paper presents an experimental study on the behavior of low-strength concrete columns confined with cold-formed steel under axial compression. The laboratory test specimens consist of four groups of rectangular concrete stub columns in the size of 130 ×\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ imes $$\\end{document} 200 mm cross section and 300 mm height; the first group composes of the unconfined specimens, while the other three contain the confined specimens under 0%, 25% and 50% sustained axial loads. The jackets are made of two G450-grade channel cold-formed steel sections of 2.4 mm thickness welded together. No bonding material is used between the core concrete and the steel jacket. From the results, it is found that the cold-formed steel jacketing can increase the axial strengths of the unconfined concrete specimens by approximately 40-65%. The strength increase comes mainly from the confinement action, as only small axial deformation is detected in the jacket. Based on the given amount of prescribed preloads in this study, the presence of preload in the column does not have a significant effect on the increase in strength of the confined concrete columns. The measured strength enhancement ratio and the confinement ratio of the tested specimens are compared using five existing strength predictive equations. The performance of the unbonded cold-formed steel jacketing technique adopted in the stub columns is observed to closely conform with the predictive confinement model of the concrete-filled tubes.

Effects of Thermally-Assisted and High-Pressure Processing on Background Microbiota and the Listeria monocytogenes Load of a Minimally Processed Commodity.

The current study investigated the impact of treatments with elevated hydrostatic pressure (500 MPa) for inactivation of Listeria monocytogenes on smoked rainbow trout (Oncorhynchus mykiss) at high and low inoculation levels. The temperature values of the trials were set at 4.4 and 60.0 °C, adjusted with a circulating water bath connected to a stainless steel jacket surrounding the pressure processing chamber. Before pressure processing, the counts (selective counts of PALCAM, mean ± SD) of L. monocytogenes were 6.45 ± 0.1 log CFU/g and were reduced (p < 0.05) to 3.72 ± 0.3, and <1.48 ± 0.8 log CFU/g after 10 min of treatment at 4.4 and 60.0 °C, respectively. Treatments of low inoculation level samples were similarly efficacious and resulted in a reduction (p < 0.05) of the pathogen to 1.62 ± 0.3 and <0.82 ± 0.0 log CFU/g for treatments at 4.4 and 60.0 °C, respectively. At 4.4 °C, linear D-value and non-linear kmax1 were 8.68 and 0.50, and 5.81 and 2.41 for high-inoculation and low-inoculation samples, respectively. Application of hydrostatic pressure at 500 MPa at cold and elevated temperatures was efficacious for up to 5.03 log CFU/g reduction of L. monocytogenes, illustrating the potential for further adaptation of this technology.

Joint input-state estimation of structures subjected to complex loads via augmented Kalman Filter with physics informed latent force models

Joint input-state estimation algorithms such as the Augmented Kalman Filter (AKF) rely on the assumption that the distribution of the input loads follows simple spatial patterns, which are either spatially distributed or sparse. However, in many real situations the spatial distribution of the loads is complex and time-varying, which poses a significant challenge. To tackle this issue, this paper introduces a novel method named the Augmented Kalman Filter with Physics Informed Latent Force Models (AKF-PILFM), which incorporates knowledge about the physics underlying the dynamics of the input loads in the estimation based on training data. In the paper, the general formulation of the AKF-PILFM is described, followed by its tailored application to structures subjected to loads with a complex spatiotemporal behavior such as wave loads. The dominant characteristics of the wave loads are identified from training data via the Dynamic Mode Decomposition, enabling the development of a state space model of the loads that can be integrated with the AKF-PILFM. To demonstrate the effectiveness of the proposed methodology, a numerical example is provided consisting of a 3D steel jacket structure subjected to nonlinear irregular waves. The AKF-PILFM shows accurate estimation results and, in the example, outperforms an existing method based on the Gaussian Process Latent Force Models and equivalent modal loads, signifying that the load’s spatiotemporal behavior substantially influences the structural response.

Seismic retrofit of intact and damaged RC columns using prefabricated steel cage-reinforced UHPC jackets and NSM GFRP bars

The use of high-performance materials, such as ultra-high-performance concrete (UHPC) and fiber-reinforced polymer (FRP), in the seismic retrofitting and strengthening of reinforced concrete (RC) columns has attracted wide attention. In this study, a novel prefabricated steel cage-reinforced UHPC jacket (PSRUJ) was proposed to improve the retrofitting efficiency of conventional cast-in-place UHPC jackets and combine the advantages of UHPC and steel jackets. PSRUJ was further combined with the near surface-mounted (NSM) technique to develop a new method for retrofitting the seismic performance of RC columns in buildings. To investigate the effectiveness of the proposed retrofitting method, cyclic loading tests were performed on one intact RC column retrofitted with PSRUJ and two damaged RC columns retrofitted with PSRUJ and the combination of PSRUJ and NSM glass FRP (GFRP) bars. After PSRUJ retrofitting, the load-carrying capacity, deformation capacity, and stiffness of the intact and damaged RC columns increased by (30∼46)%, (54∼74)%, and (24∼40)%, respectively. The inclusion of NSM GFRP bars further increased the load-carrying capacity but reduced the residual drift ratio while having little effect on the ultimate drift ratio of the retrofitted columns. Further, a damage index was proposed to assess the damage degree of core normal concrete and develop the peak strength and strain models for PSRUJ-confined damaged concrete. Finally, a flexural strength model was proposed for damaged RC columns retrofitted with PSRUJ and NSM bars.

Numerical parametric study on ultimate load of precast concrete piers with demountable connections

To investigate the flexural capacity of precast piers with demountable steel-concrete composite connection, based on the model test, the refined finite element model was developed. The flexural capacities were compared between cast-in-place (CIP) piers and precast piers with different parameters including the thickness of base steel plate and notched perfobond connector, material strength, open-hole size of base steel plate, height of jacket, and axial compression ratio. The results show that the flexural capacity of concrete precast piers with rationally designed connections should not be lower than that of CIP piers. The cracking load and flexural moment-axial compression ratio curve can be evaluated as CIP piers. The ultimate flexural capacity is positively correlated with the base steel plate thickness and jacket height. The notched perfobond connector and the stiffeners set on the base steel plate can effectively improve the flexural capacity and optimize the shape of yielding line of base steel plate. The steel strength should be greater than 300 MPa in order to ensure that the steel connection yields later than the longitudinal reinforcement. Finally, the simplified model of base steel plate and the influence mechanism of the steel plate are discussed. This paper provides reference for the design of the proposed piers and other similar connections.

Analisis Perkuatan Kolom Lingkaran Pada Bangunan Soft-Story Menggunakan Steel Jacketing Dengan Pendekatan 2D

Collapse due to soft-story is often encountered in Indonesia. The collapse mechanism caused by soft stories is very dangerous, causing severe damage even collapse to the building structure. Steel jacketing is one of the means to strengthen the column which is considered effective in increasing the strength and stiffness of the reinforced elements hence soft story collapse in buildings can be prevented. The aim of this research is to evaluate the behavior of the existing building structure before strengthening the columns using limit analysis and pushover analysis and to determine the effect of strengthening columns with steel jacketing on the behavior and the performance of the structure. In this research, the existing structure is simulated to experience design errors and is modeled as a 2D portal with the function of a 4-story school building. From the results of the limit analysis, the existing structural model has the potential to experience a local collapse mechanism, followed by the potential for soft story collapse on the 1st floor. From the results of the pushover analysis, the existing structural model experiences the soft story mechanism and does not show performance points as required by FEMA 440. After carrying out this strengthening the column with steel jacketing, the structural model shows a better failure mechanism and the element performance obtained after strengthening is in the Immediate Occupancy (IO) range

Life cycle evaluation of seismic retrofit alternatives for reinforced concrete columns.

The critical earthquakes of the last few years highlight the urgent seismic retrofitting of existing buildings due to their aging or inadequate design. This paper aims to evaluate reinforced concrete column retrofit alternatives in a region of high seismic risk. Significant economic, environmental, and functional factors must be considered when deciding between various building retrofit options. The study uses a cradle-to-grave analysis to examine the economic and environmental impacts through life cycle assessments. Specifically, the life-cycle performance of three classic alternatives for rehabilitating columns lacking adequate confinement is compared: concrete jacketing, steel jacketing, and carbon fiber incorporation. The research adopts a holistic approach using multi-criteria decision-making methods, integrating economic, environmental, and functional criteria. A set of criteria and indicators is presented in a structured hierarchy that facilitates the orderly evaluation of alternatives. The results suggest that steel jacketing is preferred, as it presents a balanced performance in most criteria. The incorporation of carbon fiber is viable due to its low environmental and functional impact, although the high production costs of the raw materials limit it. In contrast, concrete jacketing has the highest environmental and functional impacts, making it the least favorable option. The results of this study will provide relevant information for engineers and decision-makers to select the most suitable options for building retrofit when considering several simultaneous perspectives.

Column-based programmable damper for impact protection and vibration suppression of jacket structures

Steel jacket structures subjected to environmental impacts exhibit severe dynamic responses, potentially causing local fatigue failure, plastic damage, and even catastrophic collapse. Therefore, a structure with adjustable stiffness and large damping is ideal for coping with complex environmental loads and dissipating kinetic energy. A novel programmable damper was designed by connecting N-layer coupling elements composed of a linear spring, wire ropes, and an asymmetric column. Analytical models for the elastic buckling behavior of the damper were derived and mutually verified with finite element analysis (FEA). Based on the analytical models, the dependence of the mechanical responses of the damper on the number of elements and the spring stiffness was investigated for design guidance. The results indicate that the N-layer damper has 2N different stiffnesses, and the total dissipation capacity increases by approximately 2.6N times compared with a single asymmetric column. For potential applications, the dynamic decay responses of representative jacket structures assembled with the damper were simulated using the FE software ABAQUS combined with user-defined-material (UMAT) code, which demonstrated that the programmable damper is an advanced device that simultaneously achieves adjustable stiffness and significant damping.

Economic Study of Strengthening of Existing RCC Building

Many structures fail or deteriorate before completion of its intended life span due to poor quality of material used, lack of mix design, poor workmanship, attacked by environmental agencies, etc. Sometimes due to slenderness of column or less reinforcement provided than actual requirements, less depth/thickness provided in flexural members, etc. feels excessive vibration during walking on floor ultimately develops cracks. Strength of such structural elements can be found by using non-destructive tests like Rebound hammer test, ultrasonic pulse velocity test, etc. If strength of existing structural elements is less than desired strength then structural consultant suggested strengthening of structural elements. There are various methods used in strengthening of existing structural elements like pressure grouting, fibre wrapping, chemical treatment, structural steel support, jacketing, etc. But these techniques are very costly and need precise quality control activity. In the present of investigation, strengthening of beam and column elements of a building by ferrocement techniques and steel jacketing were carried out and cost and cost comparison and strength results before and after strengthening are presented. It is observed that the strength og structural by ferrocement technique is cost effective than steel jacketing technique. And also has increase in the strength of RCC elements

Evaluating and strengthening low-rise reinforced concrete buildings constructed in Nepal

In Nepal, the reinforced concrete (RC) frame system is commonly used to construct low-rise buildings. In last three decades, a significant number of such buildings were proportioned and constructed in accordance with Nepal National Building Code NBC 205:1994 and NBC 205:2012—also known as the Mandatory Rule of Thumb (MRT). In the aftermath of 2015 Gorkha Earthquake (Mw 7.8) which resulted in large scale social and economic losses, the efforts to formulate improved seismic design provisions led to the development of NBC 105:2020. Considering that MRT-designed low-rise RC frame buildings still constitute a significant part of existing building stock, this study is aimed to conduct a comparative seismic performance evaluation of several case study structures under a comprehensive set of ground motions. Using the nonlinear analysis and seismic fragility assessment of four low-rise RC frame buildings (designed using all three code versions), it is shown that the structural performance and seismic losses can be significantly reduced by following NBC 105:2020 provisions. Several retrofitting solutions are also explored to improve the seismic performance of buildings designed using MRT. It is shown that the concrete or steel jacketing of RC columns can significantly increase the lateral strength and energy dissipation, and reduce the damage probability of such buildings. Lastly, based on the developed results, a machine learning approach is employed to correlate the peak ground acceleration with structural drifts for convenient practical applications.

Explainable machine learning: Compressive strength prediction of FRP-confined concrete column

Fibre reinforced polymers (FRP) are widely used for the strengthening of beams, slabs and columns due to their light weight and high strength. Compared to the traditional methods like steel cages or steel jackets, it reduces the time and economic cost significantly. This study focuses on the prediction of the compressive strength of FRP-confined concrete columns, which is influenced by multiple parameters. Initially, through experimental observations and the analysis of parameter mechanisms, the key parameters affecting compressive strength were identified. Six prediction models, namely linear regression, ridge regression, decision tree, random forest, and eXtreme Gradient Boosting, were subsequently constructed and evaluated to determine the optimal machine learning model. A comparison between the machine learning models and mathematical models was conducted. Furthermore, SHapley Additive exPlanation (SHAP) analysis was performed to ascertain the parameter importance and sensitivity of the machine learning model, and the analysis results were compared with existing models. The results indicate that compared to other machine learning and mathematical models, the eXtreme Gradient Boosting model demonstrates superior robustness and accuracy. The thickness and elastic modulus of FRP, as well as the concrete strength, are identified as crucial parameters that positively influence compressive strength. The relationships between the former two parameters and compressive strength follow a logarithmic function, while the relationship between concrete strength and compressive strength is approximately linear. These findings hold implications for the future development of codes and standards.

Seismic Retrofit of Concrete Buildings Damaged by Corrosion: A Case Study in Southern Italy

A case study of a building in southern Italy, subjected to high degradation by corrosion and waiting to be assessed for retrofit interventions, is presented. The owner required modifications to the building configuration, including a new layout of the floors and retrofitting for a high level of seismic load. A double strategy of an assessment and retrofit was carried out: dynamic linear and static non-linear analyses were performed, and the results were compared. Afterwards, a global strategy of mass and stiffness redistribution was implemented together with different retrofit interventions on the foundations, columns, and beams of the framed structure, such as reinforced concrete and steel jacketing, the application of FRP plates and fabrics, new steel elements, and steel–concrete composite floors. The results of the intervention are discussed and the implications of corrosion on the structures are explored. From the results obtained, it is possible to see how the use of different techniques for strengthening and passive seismic protection strategy can allow engineers to obtain the result of structural adaptation to earthquakes with low-cost interventions. The widespread adoption of steel jackets, coupled with the construction of floors using a steel–concrete composite structure, grants a good confinement of the beam–column r.c. joints, together with the overall strengthening of the existing structure. The adoption of CFRP wrapping at the lower edge of the beams implies a limited increase in thickness and the limited interventions of partial demolition from the existing structural members. A critical review of the steel jacketing aspects in terms of bending and shear strengthening is reported by considering this technique in the form of a steel exoskeleton containing the damaged concrete structure, by confining concrete elements, and by increasing the performance for both gravitational and seismic loads.

Experimental investigation of retrofitting seismically damaged reinforced-concrete frames using steel jacketing

Retrofitting seismically damaged structures provides significant economic and social benefits. To investigate the rationality of using steel jacketing to retrofit seismically damaged reinforced concrete (RC) structures, we initially tested a half-scale single-span two-story frame structure under pseudo-static loads to achieve a severe damage state. Subsequently, the structure was retrofitted using steel jacketing and tested under another round of pseudo-static loads. The seismic performances of the original and retrofitted structures were compared. The test results indicated that both the original and retrofitted specimens sequentially developed plastic hinges at the beam ends and the bottom of the columns, indicating a generally similar damage evolution mode. Comparing to the original structure, the retrofitted specimen exhibited an increase of 33% and 78.5% in initial stiffness and strength, respectively. Although the ductility ratio of the retrofitted specimen was reduced by about 14%, the ultimate drift ratios of both specimens exceeded the threshold value (1/50), indicating an adequate deformation capacity. The retrofitted specimen exhibited a certain degree of pinching behavior on the hysteretic curve because of the presence of extensive inclined shear cracks at the mid span of the beams and the progressive failure of the anchoring of the strengthening steel angle at the beam ends and column base. Consequently, the energy-dissipation coefficients of the retrofitted specimen were lower than those of the original specimen. Based on the test, the finite element analysis modeling method for RC frame structures retrofitted using steel jacketing was also studied. By comparing the numerical simulation analysis results with the experimental ones, the reliability of the proposed numerical simulation method was verified. This study can serve as a foundation for the practical application of steel jacketing to retrofit seismically damaged RC structures.

Cracking and failure mode behavior of hybrid FRP strengthened RC column members under flexural loading

AbstractStrengthening of reinforced concrete (RC) members in bridges and buildings is often required to improve flexural performance. Strengthening using fiber‐reinforced polymer (FRP) composites has become popular as FRPs offer multiple advantages compared with conventional strengthening practices like steel jacketing and concrete enlargement. External bonding (EB) using carbon FRP (CFRP) laminates/fabric has become a common strengthening practice. The effectiveness of the EB strengthened system is reduced due to possible debonding of FRP from concrete substrate. The near‐surface mounting (NSM) of FRP laminates is efficient in reducing the debonding failure, but it is not effective under dominant compression loading. Hybrid FRP (HYB) strengthening combines the advantages of both the NSM and EB techniques. HYB strengthening can enhance the performance of RC members under all loading combinations. The main objective of this study is to understand the flexural crack opening behavior of control and hybrid FRP strengthened RC column members under pure bending. The digital image correlation (DIC) analysis shows that the crack width and its propagation are significantly reduced due to hybrid FRP strengthening. The crack widths measured using the DIC are compared with the analytical predictions based on Eurocode 2 and fib bulletin 90. HYB FRP strengthening increased the strength and post‐cracking stiffness of RC elements under flexure without compromising the ductility. In addition, the HYB strengthening distributed the damage under flexural loading, unlike localized damage observed in control RC elements.