• Structural Engineering and Mechanics
• /
• v.83 no.4
• /
• pp.415-433
• /
• 2022

Eighteen (18) (120×300×2200 mm) beams were prepared and tested to evaluate the shear strength of Glass Fiber Reinforced Concrete (GFRC) beams with no shear reinforcement, and evaluate the effectiveness of various innovative strengthening systems to increase the shear capacity of the GFRC beams. The test variables are the amount of discrete glass fiber (0.0, 0.6, and 1.2% by volume of concrete) and the type of longitudinal reinforcement bars (steel or GFRP), the strengthening systems (externally bonded (EB) sheet, side near-surface mounted (SNSM) bars, or the two together), strengthening material (GFRP or steel) links, different configurations of NSM GFRP bars (side bonded links, full wrapped stirrups, side C-shaped stirrups, and side bent bars), link spacing, link inclination angle, and the number of bent bars. The experimental results showed that adding the discrete glass fiber to the concrete by 0.6%, and 1.2% enhanced the shear strength by 18.5% and 28%, respectively in addition to enhancing the ductility. The results testified the efficiency of different strengthening systems, where it is enhanced the shear capacity by a ratio of 28.4% to 120%, and that is a significant improvement. Providing SNSM bent bars with strips as a new strengthening technique exhibited better shear performance in terms of crack propagation, and improved shear capacity and ductility compared to other strengthening techniques. Based on the experimental shear behavior, an analytical study, which allows the estimation of the shear capacity of the strengthened beams, was proposed, the results of the experimental and analytical study were comparable by a ratio of 0.91 to 1.15.

• Journal of the Korea Concrete Institute
• /
• v.14 no.1
• /
• pp.110-117
• /
• 2002

In a strengthened bridge deck which received increased service loads, failure patterns of bridge deck vary depending on deck thickness, compressive strength of concrete, yielding strength of reinforcement, reinforcement ratio and additional strengthening ratio. General failure pattern that is most commonly reported as punching shear failure after the main rebar yields, followed by yielding of distributing rebar. In this paper, by Proposing a limit to the amount of strengthening material, a brittle failure can be prevented and a ductile failure mode similar to that developed in unstrengthened deck is derived. In order to calculated the limit strengthening ratio, the yield line theory and previously proposed plastic punching shear model have been used

• Journal of Korea Technical Association of The Pulp and Paper Industry
• /
• v.46 no.5
• /
• pp.35-42
• /
• 2014

Many historical archives have been deteriorated by aging with time. Various kinds of defects such as worm-hole, yellowing, brittleness are observed and their severity was dependent on raw material type, storage condition, and so on. For a long-term use and storage, a proper preservation treatment is required. Many studies on preservation and conservation have been carried out on hanji which was made from mulberry fiber, but there are few concerns on foreign paper. Therefore, aging and chemical strengthening treatment was done on paper made of bamboo and wood fibers depending on aging condition, the type and pickup weight of chemicals and treatment method. When methyl cellulose was treated with impregnation or brushing, the aged paper was strengthened effectively. The strengthening effect by chemicals was dependent on the aged condition of the paper.

• Steel and Composite Structures
• /
• v.23 no.4
• /
• pp.385-397
• /
• 2017

Currently, CFRP (Carbon Fiber Reinforced Polymer) plate bonding is used quite extensively as a strengthening method. In this technique, a composite CFRP plate or sheet of relatively small thickness is bonded with an adhesion material to steel or concrete structure in order to improve its structural behavior and strength. The sheets or plates do not require much space and give a composite action between the adherents. In this study, the rotation capacity of CFRP-strengthened cold-formed steel (CFS) beams has been evaluated through numerical investigation. Studies on different structural levels have been performed. At the beam level, C-section has been adopted with different values of profile thickness, web height, and flange width. At the connection level, a web bolted moment resistant type of connection using through plate has been adopted. In web-bolted connections without CFRP strengthening, premature web buckling results in early loss of strength. Hence, CFRP sheets and plates with different mechanical properties and geometric configurations have been examined to delay web and flange buckling and to produce relatively high moment strength and rotation capacity. The numerical results reveal that CFRP strengthening may increase strength, initial stiffness, and rotation capacity when compared with the case without strengthening.

• International journal of steel structures
• /
• v.18 no.5
• /
• pp.1577-1588
• /
• 2018

As the excellent mechanical performance and easy construction of concrete filled steel tubes (CFST) composite structure, it has the potential to be used to strengthen RC pier columns. Therefore, tests were conducted on 2 reinforcement concrete (RC) stub columns and 9 RC columns strengthened with circular CFST under axial loading. The test results show that the circular CFST strengthening method is effective since the mean bearing capacity of the RC columns is increased at least 3.69 times and the ductility index is significantly improved more than 30%. One of the reasons for enhancement is obvious confinement provided by steel tube besides the additional bearing capacity supplied by the strengthening materials. From the analysis of the enhancement ratio, the strengthening structure has at least an extra 20% amplification except for taking full advantage of the strength of the strengthening material. Through the analysis of confining stress provided by steel tube and the stress-strain relationship of confined concrete, it is found that the strength of the core concrete can be increased by 21-33% and the ultimate strain can be enhanced to beyond $15,000{\mu}{\varepsilon}$.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.13 no.6 s.58
• /
• pp.204-211
• /
• 2009

In this study, the optimal method is applied to strengthening of RC hollow slab bridges using external prestressing. The Queen-post and King-post shapes are considered to find the effective tendon configurations. In order to achieve the objective rating factor, the optimal configurations and tendon forces are obtained by using the Sequential Unconstrained Minimization Technique (SUMT). The object function for optimal strengthening is constituted with the dimensionless function of material costs. The constraints are formulated by design specification and the rating factor. The validity of this study is presented by the analysis of the results of strengthening of the RC hollow slab bridges.

• Advances in concrete construction
• /
• v.9 no.1
• /
• pp.1-7
• /
• 2020

Retrofitting is an alteration of existing member or component of the structure. In civil engineering point of view, it is called strengthening of the old structure. Deterioration of structures may be due to aging, corrosion, failure of joints, earthquake forces, increase in service loads, etc. Such structures need urgent repair, retrofitting and strengthening to avoid collapse, cracking and loss in strength or deflection. Advanced techniques are required to be developed for the repair of structural components to replace conventional techniques. This paper focuses exclusively on torsional behaviour of Reinforced Concrete (RC) beams and retrofitted RC beams wrapped with aramid fiber. Beams were retrofitted with aramid fiber by full wrapping and in the form of 150 mm wide strips at a spacing of 100 mm, 150 mm, 200 mm respectively using epoxy resin and hardener. A total 15 numbers of RC beams of 150 mm×300 mm×1300 mm in size were cast, 3 beams are tested as control specimens, and 12 beams are tested for torsion up to the failure and then retrofitted with aramid fiber. Experimental results are validated with the help of data obtained by finite element analysis using ANSYS. The full wrapping configuration of aramid fiber regains 105% strength after retrofitting. With the increase in spacing of fabric material, torsional strength reduces to 82% with about 45% saving in material.

• Advances in materials Research
• /
• v.6 no.4
• /
• pp.317-328
• /
• 2017

In this paper, an improved theoretical solution for interfacial stress analysis is presented for simply supported concrete beam bonded with a sandwich FGM plate. Interfacial stress analysis is presented for simply supported concrete beam bonded with a sandwich plate. This improved solution is intended for application to beams made of all kinds of materials bonded with a thin plate, while all existing solutions have been developed focusing on the strengthening of reinforced concrete beams, which allowed the omission of certain terms. It is shown that both the normal and shear stresses at the interface are influenced by the material and geometry parameters of the composite beam. A numerical parametric study was performed for different simulated cases to assess the effect of several parameters. Numerical comparisons between the existing solutions and the present new solution enable a clear appreciation of the effects of various parameters. The results of this study indicated that the FGM sandwich panel strengthening systems are effective in enhancing flexural behavior of the strengthened RC beams.

• Proceeding of KASS Symposium
• /
• 2008.05a
• /
• pp.61-65
• /
• 2008

A 4-story reinforced concrete structure built above an underground parking garage shows some slab deflections, and the deflections of the concrete floor slabs are proposed to be alleviated by the application of light-weight topping material in conjunction with localized strengthening of the slabs. The application of light-weight concrete topping on the existing slab has been simulated and its performance to anticipated loads has been analyzed. The application of light-weight topping material imposes additional weight on the exiting floor slabs. This added weight on the existing slabs causes over-stressing of the slabs. This over-stressing can be alleviated by enhancing the load carrying capacity of the existing slabs. Additional load carrying capacity in the existing slabs can be developed by localized strengthening of the slabs utilizing techniques such as the application of fiber-reinforced composites on the bottom surface of the slabs, and application of fiber-reinforced composites adequately complements the capacity of the existing slabs to bear the additional load imposed by light-weight leveling material. Additional moments in the beam and columns induced by the application of the light-weight topping material were tabulated and compared with capacity. The moment D/C ratios of the beam and columns are well the range of acceptable limits, and the beam and columns are not overstressed by the application of the surcharge.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2004.03b
• /
• pp.499-506
• /
• 2004

The use of dredged soft marine clay is increasing due to a shortage of coarse material available. This paper presents a stabilization method that can increase shear strength of the surface layer of a dredged clay deposit at dates much earlier than usual. The desiccation of the upper soft 1-2m layer can be accelerated by interrupting water seeping from its bottom with impervious geotextile. Just below the geotextile, enough pervious material is provided so that the underlying deposit can be drained through it. This scheme is proved to be effective through theoretical analysis.