ng-Jun You

Durability of GFRP composite exposed to various environmental conditions

This paper presents a short-term durability test program for E-glass/vinylester composite exposed to various environmental conditions. The main objective of this study is to investigate the degradation of GFRP composite and its influence on the tensi le strength. A total of 530 strand-type E-glass/vinylester specimens were fabricated and exposed to six different environmental conditions for up to 150 days. To examine the degradation of conditioned specimens, the weight gain was measured and scanning electronic microscope images were taken at fractured section. Also, the tensile strength of the specimens was tested. From the test results, it is clear that the tensile strength of the conditioned specimens was significantly reduced due to the degradation of GFRP under the environmental conditions considered.

Experimental Investigation for Tensile Performance of GFRP-Steel Hybridized Rebar

Tensile performance of the recently developed “FRP Hybrid Bar” at Korea Institute of Civil Engineering and Building Technology (KICT) is experimentally evaluated by the authors. FRP Hybrid Bar is introduced to overcome the low elastic modulus of the existing GFRP bars to be used as a structural member in reinforced concrete structures. The concept of material hybridization is applied to increase elastic modulus of GFRP bars by using steel. This hybridized GFRP bar can be used in concrete structures as a flexural reinforcement with a sufficient level of elastic modulus. In order to verify the effect of material hybridization on tensile properties, tensile tests are conducted. The test results for both FRP Hybrid Bar and the existing GFRP bars are compared. The results indicate that the elastic modulus of FRP Hybrid Bar can be enhanced by up to approximately 250 percent by the material hybridization with a sufficient tensile strength. To ensure the long-term durability of FRP Hybrid Bar to corrosion resistance, the individual and combined effects of environmental conditions on FRP Hybrid Bar itself as well as on the interface between rebar and concrete are currently under investigation.

Tensile Strength of GFRP Reinforcing Bars with Hollow Section

Fiber reinforced polymer (FRP) has been proposed to replace steel as a reinforcing bar (rebar) due to its high tensile strength and noncorrosive material properties. One obstacle in using FRP rebars is high price. Generally FRP is more expensive than conventional steel rebar. There are mainly two ways to reduce the cost. For example, one is making the price of each composition cost of FRP rebar (e.g., fibers, resin, etc.) lower than steel rebar. Another is making an optimized design for cross section and reducing the material cost. The former approach is not easy because the steel price is very low in comparison with component materials of FRP. For the latter approach, the cost could be cut down by reducing the material cost. Therefore, an idea of making hollow section over the cross section of FRP rebar was proposed in this study by optimizing the cross section design with acceptable tensile performance in comparison with steel rebar. In this study, glass reinforced polymer (GFRP) rebars with hollow section and 19 mm of outer diameter were manufactured and tested to evaluate the tensile performance in accordance with the hollowness ratio. From the test results, it was observed that the tensile strength decreased almost linearly with increase of hollowness ratio and the elastic modulus decreased nonlinearly.

Structural Analysis of a Hybrid Substructure With Multi-Cylinder for 5MW Offshore Wind Turbines

The substructure for offshore wind turbines is strongly influenced by the effect of wave forces as the size of substructure increases. Therefore, it is very important to reduce the wave force acting on substructures. In the present study the hybrid substructure, which is composed of a multi-cylinder having different radius near free surface and a gravity substructure at the bottom of multi-cylinder, is suggested to reduce the wave forces. The fluid domain is divided into two regions to calculate the wave forces acting on the hybrid substructure with multi-cylinder and the scattering wave in each fluid region is expressed by an Eigen-function expansion method. The comparison between the mono pile and the hybrid substructure is made for wave forces. Using the wave forces obtained from this study, the structural analysis of hybrid substructure is carried out through ANSYS mechanical. In order to investigate the resonance between the wind turbine and the hybrid substructure, the modal analysis is also carried out.Copyright

Creep Behavior of Pultruded Ribbed GFRP Rebar and GFRP Reinforced Concrete Member

Fiber reinforced polymer (FRP) has been gathering interest from designers and engineers for its possible usage as a replacement reinforcement of a steel reinforcing bar due to its advantageous characteristics such as high tensile strength, non-corrosive material, etc. Since it is manufactured with various contents ratios, fiber types, and shapes without any general specification, test results for concrete members reinforced with these FRP reinforcing bars could not be systematically used. Moreover, since investigations for FRP reinforced members have mainly focused on short-term behavior, the purpose of this study is to evaluate long-term behaviors of glass FRP (GFRP) reinforcing bar and concrete beams reinforced with GFRP. In this paper, test results of tensile and bond performance of GFRP reinforcing bar and creep behavior are presented. In the creep tests, results showed that 100 years of service time can be secured when sustained load level is below 55% of tensile strength of GFRP reinforcing bar. A modification factor of 0.73 used to calculate long-term deflection of GFRP reinforced beams was acquired from the creep tests for GFRP reinforced concrete beams. It is expected that these test results would give more useful information for design of FRP reinforced members.

Reliability Evaluations of an Offshore Platform With Partial Porous Cylinders due to Wave and Seismic Forces

In the present study, the partial porous cylinder, which is composed of a porous part located near free surface and a rigid part bounded top and bottom by impermeable end caps, is suggested to reduce the effect of wave forces. In order to calculate the wave force acting on the partial porous cylinder the fluid domain is divided into three regions, and the scattering wave in each fluid region is expressed by an Eigen-function expansion method. Applying Darcy’s law to the porous boundary condition, the effect of porosity can be simplified. Using the wave and the seismic forces, the dynamic response evaluations of the offshore platform with partial porous cylinders are carried out through the modal analysis and the substructure method based on the effect of soil-structure interaction. The displacement and the bending stress at critical structure members are computed using the Monte Carlo Simulation (MCS). Using the reliability index based on the results from MCS, the reliability evaluations of the offshore platform with partial porous cylinders are examined.Copyright

Structural Performance of the Optimum Floating Structure for Reduced Motion

In order to design a reliable floating structure, the hydrodynamic motion and structural performance under wave loadings should be reduced with the effects of wave-induced hydraulic pressure acting on the floating structure. In this study, analytical studies were carried out for optimum type to reduce the hydrodynamic motion and pressure of concrete floating structure. The optimum floating structure is combined with pontoon-type and hybrid-type floating structures, called combination-type floating structure. In order to verify reducing motion and improving structural performance of combination-type floating structure, analytical studies were carried out for the floating structures. After hydrodynamic analysis, the six degree motions of structure are investigated for fifth periods in shallow water. The hydrodynamic motions of combination-type are lower than other type of floating structures. It meant that the combination-type floating structure can be very efficient to reduce the wave forces acting on structures and be slightly influenced by the incident waves. In addition, to evaluate structural performance of floating structures under the critical wave load that presents maximum motion of floating structure. As the results of this study, the combination-type floating structure identified reducing hydrodynamic motion and excellent structural performance than other floating structures. However, high concentrated stress occurred at the edge of the bottom slab of the bow and stern parts where cylinder wall was connected to the bottom slab. Therefore, some alternatives which can be easily obtained from a simply modification of structural details are proposed to overcome these problems.Copyright

Development of Optimum Grip System in Developing Design Tensile Strength of GFRP Rebars

Previous test results showed that the current ASTM(American Standard for Testing and Materials) grip adapter for GFRP(Glass Fiber Reinforced Polymer) rebar was not fully successful in developing the design tensile strength of GFRP rebars with reasonable accuracy. It is because the current ASTM grip adapter which is composed of a pair of rectangular metal blocks of which inner faces are grooved along the longitudinal direction does not take into account the various geometric characteristics of GFRP rebar such as surface treatment, shape of bar cross section as well as physical characteristics such as poisson effect, elastic modulus in the transverse direction and so on. The objective of this paper is to provide how to proportion the optimum diameter of inner groove in ASTM grip adapter to develop design tensile strength of GFRP rebar. The proportioning of inner groove in ASTM grip adapter is based on the force equilibrium of GFRP rebar between tensile capacity and minimum frictional resistance required along the grip adapter. The frictional resistance of grip adapter is calculated based on the compressive strain compatibility in radial direction induced by the difference between diameter of GFRP rebar and inner groove In ASTM grip. All testing procedures were made according to the CSA S806-02 recommendations. From the preliminary test results on round-type GFRP rebars, it was found that maximum tensile loads acquired under the same testing conditions is highly affected by the diameter of inner groove in ASTM grip adapter. The grip adapter with specific dimension proportioned by proposed method recorded the highest tensile strength among them.

An Estimate of Flexural Strength for Reinforce Concrete Beams Strengthened with CFRP Sheets

Carbon fiber reinforced polymer (CFRP) sheets are becoming increasingly popular for strengthening deteriorated concrete bridges due to their excellent strength and stiffness-to-weight ratio, corrosion resistance, and convenience of construction work. The purpose of this study is to compare the performance of CFRP-strengthened reinforced concrete (RC) beams and to develop a new design formula. Simple beams with 3 m span length were tested to investigate the effect of reinforcing steel ratio and CFRP-reinforcing ratio on the flexural behavior of strengthened RC beams. The test results were analyzed with the special emphasis on the failure mode, the maximum load, and the strain distribution in the section. It is shown that the strain of the strengthened beams is not linearly distributed in the section. A new design formula based on the non-linear distribution of the strain has been derived and showed that it has a good agreement with the various domestic and foreign test results.

Numerical Analysis of Interlocking Caisson Breakwater using Modular System

Sunghoon Song, Korea Institute of Civil Engineering and Building Technology, songsunghoon@kict.re.kr Minsu Park, Korea Institute of Civil Engineering and Building Technology, mspark@kict.re.kr Youngjun You, Korea Institute of Civil Engineering and Building Technology, yjyou@kict.re.kr Younju Jeong, Korea Institute of Civil Engineering and Building Technology, yjjeong@kict.re.kr Yoonkoog Hwang, Korea Institute of Civil Engineering and Building Technology, ykhwang@kict.re.kr