• Journal of the Korean Society for Advanced Composite Structures
• /
• v.6 no.3
• /
• pp.41-49
• /
• 2015

The repair of manhole raise has been caused much construction times and disruption of traffic flow, serious environmental pollution from crushed construction wastes, and budget waste due to the repeated repair construction works. In order to overcome such problems, we have developed the new manhole repairing composite structures by using a glass fiber-reinforced polymer (GFRP) pipe, which can raise manhole to the regular height of the overlayed road pavement with rapid construction and minimum traffic jams. This environmental-friendly technology is method completed by the methyl methacrylate monomer (MMA) double wide flanged GFRP pipe composite structures in order to raise manhole to the regular height. In this paper, two kinds of the compressive strength tests of MMA mortar composites were conducted and evaluated by a general compressive strength test, and compressive strength test after freezing-thawing resistance test. It was found that this MMA mortar composites will be used for the application of the double wide flanged GFRP pipe composite structures.

• Journal of The Korean Society of Agricultural Engineers
• /
• v.47 no.5
• /
• pp.27-39
• /
• 2005

In the recent design of high ductile fiber-reinforced ECC (engineered cementitious composite), optimizing both processing and mechanical properties for specific applications is critical. This study presents an innovative method to develop new class ECCs, which possess the different fluid properties to facilitate diverse types of processing (i.e., self-consolidating or shotcrete processing) while maintaining ductile hardened properties. In the material design concept, we employ a parallel control of fresh and hardened properties by using micromechanics and cement rheology. Control of colloidal interaction between the particles is regarded as a key factor to allow the performance of the specific processing. To determine how to control the particle interactions and the viscosity of cement suspension, we first introduce two chemical admixtures including a highly charged polyelectrolyte and a non-ionic polymer. Optimized mixing steps and dosages we, then, obtained within the solid concentration predetermined based on micromechanical principle. Test results indicate that the rheological properties altered by this approach were revealed to be highly effective in obtaining the desired function of the fresh ECC, allowing us to readily achieve hardened properties, represented by pseudo strain-hardening behavior in uniaxial tension.

• Journal of Electrical Engineering and Technology
• /
• v.3 no.1
• /
• pp.115-120
• /
• 2008

Use of the carbon nanotube is superior to general powder state materials of mechanical and electrical properties. Because its ratio of diameter and length (aspect ratio) is very large, it has been known as a type of ideal nano-reinforcement material. Based on this advantage, the existing carbon black of semiconductive shield materials used in power cables can acquire excellent properties by using a small amount of carbon nanotubes. Thus, we investigated the thermal properties of the carbon nanotube, such as thermal conductivity, specific heat, and DSC (Differential Scanning Calorimetry). We found that a high thermal resistance level is demonstrated by using a small amount of carbon nanotubes. As a result, this tendency confirms high cross-linking density in a new network in which the carbon nanotube between carbon black constitute molecules shows a bond by similar constructive properties.

• Journal of the Korean Society of Safety
• /
• v.25 no.3
• /
• pp.71-77
• /
• 2010

This paper presents the results of a study on flexural capacity of large size RC slabs strengthened with carbon fiber reinforced polymer(CFRP) plates. A total of 5 specimens of 6.0m length were tested in four point bending after strengthening them with externally bonded CFRP plates. The CFRP plates were bonded without prestress and with two prestress levels, 0.4% and 0.6% of CFRP plate strain. Test variables included the type of strengthening, prestressing level, and the effects according to each test variables are analysed. The experimental results show that proposed methods can increase significantly the flexural capacity such as strength, stiffness of the beam and the increase ranged between 36.2% and 63.2% of the load-carrying capacity of the control beams. The non-prestressed specimen failed by separation of the plate from the beam due to premature debonding while most of the prestressed specimens failed by CFRP plate fracture. And the cracking loads and maximum loads were increased proportionally to the prestress level.

• Smart Structures and Systems
• /
• v.3 no.2
• /
• pp.133-146
• /
• 2007

This paper addresses a new type of broad and stage-based hybrid carbon fiber reinforced polymer (HCFRP) sensor that is suitable for the sensing of infrastructures. The HCFRP sensors, a type of composite sensor, are fabricated with three types of carbon tows of different strength and moduli. For all of the specimens, the active materials are carbon tows by virtue of their electrical conductivity and piezoresistivity. The measurement principles are based on the micro- and macro-fractures of different types of carbon tows. A series of experiments are carried out to investigate the sensing performances of the HCFRP sensors. The main variables include the stack order and volume fractions of different types of carbon tows. It is shown that the change in electrical resistance is in direct proportion to the strain/load in low strain ranges. However, the fractional change in electrical resistance (${\Delta}R/R_0$) is smaller than 2% prior to the macrofractures of carbon tows. In order to improve the resistance changes, measures are taken that can enhance the values of ${\Delta}R/R_0$ by more than 2 times during low strain ranges. In high strain ranges, the electrical resistance changes markedly with strain/load in a step-wise manner due to the gradual ruptures of different types of carbon tows at different strain amplitudes. The values of ${\Delta}R/R_0$ due to the fracture of high modulus carbon tows are larger than 36%. Thus, it is demonstrated that the HCFRP sensors have a broad and stage-based sensing capability.

• Structural Monitoring and Maintenance
• /
• v.7 no.3
• /
• pp.233-259
• /
• 2020

Using bonded fiber-reinforced polymer laminates for strengthening wooden structural members has been shown to be an effective and economical method. In this research, properties of suitable composite materials (sika wrap), adhesives and two ways of strengthening beams exposed to bending moment are presented. Passive or slack reinforcement is one way of strengthening. The most effective way of such a strengthening was to place reinforcement laminates in the stretched part of the wooden beam (lower part in our case), in order to investigate the effectiveness of externally bonding FRP to their soffits. The model is based on equilibrium and deformations compatibility requirements in and all parts of the strengthened beam, i.e., the wooden beam, the sika wrap composite plate and the adhesive layer. The theoretical predictions are compared with other existing solutions. This research is helpful for the understanding on mechanical behaviour of the interface and design of the composite-wooden hybrid structures. The results showed that the use of the new strengthening system enhances the performance of the wooden beam when compared with the traditional strengthening system.

• Steel and Composite Structures
• /
• v.17 no.4
• /
• pp.431-452
• /
• 2014

The present study focuses on the mechanical behaviour of concrete filled double skin steel tubular (CFDST) stub columns confined by fiber reinforced polymer (FRP). A series of axial compression tests have been conducted on two CFDST stub columns, eight CFDST stub columns confined by FRP and a concrete-filled steel tubular (CFST) stub column confined by FRP, respectively. The influences of hollow section ratio, FRP wall thickness and fibre longitudinal-circumferential proportion on the load-strain curve and the concrete stress-strain curve for stub columns with annular section were discussed. The test results displayed that the FRP jacket can obviously enhance the carrying capacity of stub columns. Based on the test results, a new model which includes the effects of confinement factor, hollow section ratio and lateral confining pressure of the outer steel tube was proposed to calculate the compressive strength of confined concrete. Using the present concrete strength model, the formula to predict the carrying capacity of CFDST stub columns confined by FRP was derived. The theoretically predicted results agree well with those obtained from the experiments and FE analysis. The present method is also adapted to calculate the carrying capacity of CFST stub columns confined by FRP.

• Structural Engineering and Mechanics
• /
• v.64 no.6
• /
• pp.783-792
• /
• 2017

Carbon Fiber Reinforced Polymer (CFRP) laminates are used widely either for repairing or strengthening of existing structures. When CFRP laminates are used for strengthening of RC continuous T-beams in the Hogging Moment Zone (HMZ); above and around the intermediate supports, it is important to study the expected positions of the laminates across the width of the beam flange. Although, it is traditional to consider CFRP laminates added above the beam web, this is not practical since walls and columns are located in such positions in general. This paper examines the effect of changing the positions of CFRP laminates used for the strengthening of the hogging moment zone across the beam flange of two-span-T-section beams. The Finite Element (FE) Package ANSYS is used to create 3-D theoretical models needed for the study. It can be concluded that changing the position of CFRP strengthening across the beam flange, in the hogging moment zone, is effective upon the overall behavior. The best locations are either above the web or at the flange just beside the web, due to the presence of walls and/or columns.

• Earthquakes and Structures
• /
• v.14 no.5
• /
• pp.379-388
• /
• 2018

This study aims to identify the effect of both longitudinal reinforcement details and damage level on making a decision of repairing pre-damaged bridge columns using basalt fiber reinforced polymer (BFRP) jackets. Two RC bridge columns with improper details of the longitudinal and/or transverse reinforcement were tested under the effect of a constant axial load and increasing lateral cyclic loading. Test results showed that the lap-splice column exhibited an inferior performance where it showed rapid degradation of strength before achieving the theoretical strength and its deformation capacity was limited; however, quick restoration is possible through a suitable rehabilitation technique. On the other hand, expensive repair or even complete replacement could be the decision for the column with the confinement failure mode. After that, a rehabilitation technique using external BFRP jacket was adopted. Performance-based design details guaranteeing the enhancement in the inelastic performance of both damaged columns were addressed and defined. Test results of the repaired columns confirmed that both reparability and the required repairing time of damage structures are dependent on the reinforcement details at the plastic hinge zone. Furthermore, lap-splice of longitudinal reinforcement could be applied as a key design-tool controlling reparability and restorability of RC structures after massive actions.

• Journal of the Korean Society for Advanced Composite Structures
• /
• v.3 no.2
• /
• pp.11-18
• /
• 2012

This study proposes flexural failure design criteria of continuous slabs enhanced by a hybrid system of fiber reinforced polymer (FRP) and ultra high performance concrete (UHPC). The proposed hybrid retrofit system is designed to be placed at the top surface of the slabs for flexural strengthening of the sections in both positive and negative moment zones. The enhancing mechanisms of the proposed system for both positive and negative moment regions are presented. The neutral axis of the enhanced sections in positive moment zone at flexural failure is enforced to be in UHPC overlay for preventing the compression in FRP. From this condition, a relationship between design parameters of FRP and UHPC is established. Although the capacity of the proposed retrofit system to enhance flexural strength and ductility is confirmed through experiments of one-way RC slabs having two continuous spans, the retrofitted slabs failed in shear. To prevent this shear failure, a design criteria of flexural failure is proposed.