• Earthquakes and Structures
• /
• 제9권6호
• /
• pp.1337-1353
• /
• 2015

Seismic upgrading of existing structures is a technical and social issue aimed at risk reduction. Sustainable design is one of the most important challenges in any structural project. Nowadays, many retrofit strategies are feasible and several traditional and innovative options are available to engineers. Basically, the design strategy can lead to increase structural ductility, strength, or both of them, but also stiffness regulation and supplemental damping are possible strategies to reduce seismic vulnerability. Each design solution has different technical and economical performances. In this paper, four different design solutions are presented for the retrofit of an existing RC frame with poor concrete quality and inadequate reinforcement detailing. The considered solutions are based on FRP wrapping of the existing structural elements or alternatively on new RC shear walls introduction. This paper shows the comparison among the considered design strategies in order to select the suitable solution, which reaches the compromise between the obtained safety level and costs during the life-cycle of the building. Each solution is worked out by considering three different levels of seismic demand. The structural capacity of the considered retrofit solutions is assessed with nonlinear static analysis and the seismic performance is evaluated with the capacity spectrum method.

• 해양환경안전학회지
• /
• 제16권1호
• /
• pp.125-133
• /
• 2010

기존의 해상교량 기둥의 외부보강에 따른 연구들은 현재까지 주로 중앙점 재하에 따른 성능을 평가하였다. 하지만, 장대교량의 기둥은 정확한 중심축을 기준으로 축하중을 받는 경우와 편심으로 인한 큰 모멘트가 동시에 작용하는 경우가 많이 발생한다. 이 연구에서는 해상장대교량의 고강도 철근콘크리트 기둥의 하중재하 위치와 2가지의 보강 재료인 탄소섬유 및 고성능 유리섬유를 각각 보강하여 그 효과를 분석하였다. 실험에 사용된 12개의 기둥 실험체는 모두 같은 크기로 제작 및 실험을 하였다. 그 중 6개 실험체의 횡보강 철끈은 띠철근으로 배근하였으며, 그 외 6개의 실험체는 나선철근으로 매끈하였다. 그리고 각각 3겹의 탄소섬유 및 고성능 유리섬유를 적용하여 감싸기 방법으로 보강하였다. 실험변수는 하중재하 위치에 따른 철근의 보강행태 및 보강재료가 고려되었다. 실험결과, 편심축에 따른 하중재하 기둥부재는 중심축 하중재하에 비해 최대 파괴하중이 감소하였지만 고성능 유리섬유를 보강한 기둥부재는 축하중 및 편심하중에서 탄소섬유를 보강한 경우보다 내력과 연성이 우수하였다.

• Structural Engineering and Mechanics
• /
• 제13권1호
• /
• pp.75-90
• /
• 2002

Many existing concrete structures suffer from low quality of concrete and inadequate confinement reinforcement. These deficiencies cause low strength and ductility. Wrapping concrete by carbon fiber reinforced polymer (CFRP) composite sheets enhances compressive strength and deformability. In this study, the effects of the thickness of the CFRP composite wraps on the behavior of concrete are investigated experimentally. Both monotonic and repeated compressive loads are considered during the tests, which are carried out on strengthened undamaged specimens, as well as the specimens, which were tested and damaged priorly and strengthened after repairing. The experimental data shows that, external confinement of concrete by CFRP composite sheets improves both compressive strength and deformability of concrete significantly as a function of the thickness of the CFRP composite wraps around concrete. Empirical equations are also proposed for compressive strength and ultimate axial deformation of FRP composite wrapped concrete. Test results available in the literature, as well as the experimental results presented in this paper, are compared with the analytical results predicted by the proposed equations.

• Steel and Composite Structures
• /
• 제23권2호
• /
• pp.187-194
• /
• 2017

To reuse a broken plain concrete (PC) arch, a retrofitting method was proposed to ensure excellent structural performances, in which carbon fiber reinforced polymers (CFRPs) were applied to repair and strengthen the damaged PC arch through bonding and wrapping techniques. Experiments were carried out to reveal the deformation and the load carrying capacity of the retrofitted composite arch. Based on the experiments, repairing and strengthening effects of the CFRP retrofitted broken arch were revealed. Simplified analysing model was suggested to predict the peak load of the CFRP retrofitted broken arch. According to the research, it is confirmed that absolutely broken PC arch can be completely repaired and reinforced, and even behaves more excellent than the intact PC arch when bonded together and strengthened with CFRP sheets. Using CFRP bonding/wrapping technique a novel efficient composite PC arch structure can be constructed, the comparison between rebar reinforced concrete (RC) arch and composite PC arch reveals that CFRP reinforcements can replace the function of steel bars in concrete arch.

• Advanced Composite Materials
• /
• 제17권3호
• /
• pp.277-299
• /
• 2008

High quality and expedient processing repair methods are necessary to enhance the service life of bridge structures. Deterioration of concrete can occur as a result of structural cracks, corrosion of reinforcement, and freeze.thaw cycles. Cost effective methods with potential for field implementation are necessary to address the issue of the vulnerability of bridge structures and how to repair them. Most infrastructure related applications of fiber-reinforced plastics (FRPs) use traditional hand lay-up technology. The hand lay-up is tedious, labor-intensive and relies upon personnel skill level. An alternative to traditional hand lay-up of FRP for infrastructure applications is Vacuum Assisted Resin Transfer Molding (VARTM). VARTM uses single sided molding technology to infuse resin over fabrics wrapping large structures, such as bridge girders and columns. There is no work currently available in understanding the interface developed, when VARTM processing is adopted to wrap fibers such as carbon and/or glass over concrete structures. This paper investigates the interface formed by carbon fiber processed on to a concrete surface using the VARTM technique. Various surface treatments, including sandblasting, were performed to study the pull-off tensile test to find a potential prepared surface. A single-lap shear test was used to study the bond strength of CFRP fabric/epoxy composite adhered to concrete. Carbon fiber wraps incorporating Sikadur HEX 103C and low viscosity epoxy resin Sikadur 300 were considered in VARTM processing of concrete specimens.

• Earthquakes and Structures
• /
• 제10권2호
• /
• pp.313-328
• /
• 2016

Beam-column joints are recognized as one of the most critical and vulnerable zones of a Reinforced Concrete (RC) moment resisting structure subjected to seismic loads. The performance of the deficient beam-column joints can be improved by retrofitting these joints by jacketing them with varied materials like concrete, steel, FRP and ferrocement. In the present study strength behavior of RCC exterior beam-column joints, initially loaded to a prefixed percentage of the ultimate load, and retrofitted using ferrocement jacketing using two different wrapping schemes has been studied and presented. In retrofitting scheme, RS-I, wire mesh is provided in L shape at top and at bottom of the beam-column joint, whereas, in scheme RS-II along with wire mesh in L shape at top and bottom wire mesh is also provided diagonally to the joint. The results of these retrofitted beam-column joints have been compared with those of the controlled joint specimens. The results show an improvement in the ultimate load carrying capacity and yield load of the retrofitted specimens. However, no improvement in the ductility and energy absorption has been observed.

• Structural Engineering and Mechanics
• /
• 제73권1호
• /
• pp.53-64
• /
• 2020

In different high seismic regions around the world, many non-ductile existing reinforced concrete frame buildings, built without adequate seismic detailing requirements, have been damaged or collapsed after past earthquakes. The assessment and the retrofit of these non-ductile concrete structures is crucial theme of research for all the scientific community of engineers. In particular, a careful assessment of the existing building is fundamental for understanding the failure mechanisms that govern the collapse of the structure or the achievement of the recommended limit states. Based on the seismic assessment, the best retrofit strategy can be designed and applied to the structure. A school building located in Avellino province (Italy) is the case study. The analysis of seismic vulnerability carried out on the mentioned building has highlighted deficiencies in both static and seismic load conditions. The retrofit of the building has been designed based on different retrofit options in order to show the real retrofit design developed from the engineers to achieve the seismic safety of the building. The retrofit costs associated to structural operations are calculated for each case and have been summed up to the costs of the in situ tests. The paper shows a real retrofit design case study in which the best solution is chosen based on the results in terms of structural performance and cost among the different retrofit options.

• Steel and Composite Structures
• /
• 제30권3호
• /
• pp.231-251
• /
• 2019

In the present study, a numerical and experimental investigation has been carried out on the seismic behavior of RC columns of a bridge which damaged under corrosive environments and retrofitted by various techniques including combined application of CFRP sheets and steel profiles. A novel hybrid retrofitting procedure, including the application of inner steel profiles and outer peripheral CFRP sheets, has been proposed for strengthening purpose. Seven large-scale RC columns of a Girder Bridge have been tested in the laboratory under the influence of simultaneous application of constant axial load and the lateral cyclic displacements. Having verified the finite element modeling, using ABAQUS software, the effects of important parameters such as the corrosion percentage of steel rebars and the number of CFRP layers have been evaluated. Based on the results, retrofitting of RC columns of the bridge with the proposed technique was effective in improving some measures of structural performance such as lateral strength degradation and higher energy absorption capability. However, the displacement ductility was not considerably improved whereas the elastic stiffness of the specimens has been increased.

• Steel and Composite Structures
• /
• 제47권6호
• /
• pp.781-794
• /
• 2023

In order to directly apply seawater and sea sand in construction without desalination, a type of square concrete-filled steel tube (CFST) encased with prefabricated seawater sea-sand concrete filled Polyvinyl Chloride (PVC)/Glass Fiber Reinforced Polymer (GFRP) tube column was proposed. Twenty short columns were tested under uniaxial loads, and the test parameters included inner tube types, seawater sea-sand concrete replacement ratios, concrete strength, the wrapping area of Carbon Fiber Reinforced Polymer (CFRP) strips and the thickness of GFRP tube. The effects of the parameters on failure modes, loading capacity, ductility and strain responses were discussed. All the tested specimens failed with serious buckling of the steel tubes and fracture of the inner tubes. The specimens had good residual bearing capacity corresponding to 64% to 88.9% of the peak capacity. The inner GFRP tubes and PVC tubes wrapped by CFRP strips provided stronger confinement to the core concrete, and were good choices for the proposed columns. Moreover, an analytical model for the composite column with different inner tube types was proposed.

• Earthquakes and Structures
• /
• 제12권2호
• /
• pp.237-250
• /
• 2017

There has been increasing attention in many countries on seismic retrofit of old fashioned RC structures in recent years. In such buildings, the joints lack transverse reinforcement and suffer inadequate seismic dimensional requirements and the reinforcement is plain bar. The behavior of the joints is governed by sliding of steel bars and diagonal shear failure is less influential. Different methods to retrofit beam-column joints have been proposed in the literature such as wrapping the joint by FRP sheets, enlargement of the beam-column joint, and strengthening the joint by steel sheets. In this study, an enlargement technique that uses external prestressed cross ties with steel angles is examined. The technique has already been used for substructures reinforced by deformed bars and has advantages such as efficient enhancement of seismic capacity and lack of damage to the joint. Three reference specimens and two retrofitted units are tested under increasing lateral cyclic load in combination with two levels of axial load. The reference specimens showed relatively low shear strength of 0.150${\surd}$($f_c$) and 0.30${\surd}$($f_c$) for the exterior and interior joints, respectively. In addition, relatively brittle behavior was observed and large deformations extended into the panel zone of the joints. The retrofit method has increased ductility ratio of the interior beam-column joints by 63%, and energy dissipation capacity by 77%, relative to the control specimen; For external joints, these values were 11%, and 94%. The retrofit method has successfully relocated the plastic joints far from the column face. The retrofit method has improved shear strength of the joints by less than 10%.