Minkwan Ju

New Suggestion of Effective Moment of Inertia for Beams Reinforced with the Deformed GFRP Rebar

To fundamentally solve the problem of deterioration of concrete structures, it has been researched that the high durable concrete structure reinforced with the FRP rebar can be one of major solution to the newly-developed concrete structure. FRP rebar has lots of advantages such as non-corrosive, high performance and light weight against the conventional steel rebar. Among these kinds of FRP rebars, GFRP rebar has usually been considered as the best reinforcement because of its economic point of view. Even though the material capacity of the GFRP rebar was already investigated, there are some problems such as low modulus of elastic that will be cause for degrade of the serviceability of flexural concrete member reinforced with the GFRP rebar. Thus, the deflection characteristics of the GFRP rebar reinforced concrete structure should be considered then investigated. In this study, ACI 440 guideline (2003), ISIS Canada Design Manual (2001) and Toutanji et al. (2000) was considered for predicting the moment of inertia of the concrete beam reinforced with the GFRP rebar. And it was also evaluated that load-deflection relationship had a good accordance with the test and analysis result. In the result of this study, it could be estimated that the load-deflection relationship using the suggested equation of moment of inertia in this study indicated better accordance with the test result than that of the others until failure.

Static and fatigue performance of the bolt-connected structural jointed of deep corrugated steel plate member

Corrugated steel plate culvert bridge has been more commonly used as soil steel bridges because it is the cost-effective alternative for railway-highway crossings. The corrugated steel plate culvert bridge is considered the most suitable for quick rebuilding of bridges compared with the conventional bridges. This study intends to experimentally investigate the static and fatigue performance of the bolted connection of deep corrugated steel plate. Test variables are the thickness of deep corrugated steel plate and the types of bolted connection such as bolted-only, gasket, slot hole, and washer. For static test, the failure is mainly caused by a local buckling of deep corrugated steel plate member and bearing failure of bolts. Type of gasket and slot hole showed the largest stiffness so that they may be recommended for structural safety and redundancy under a static flexural behavior. For fatigue test, the bolted-only specimen exhibited no increase in the strain until failure and the highest fatigue life among the test variables. For structural safety under cyclic loading, bolted-only connection is recommended. According to AASHTO LRFD Bridge Design Specification, fatigue life category can be determined as category D level and the fatigue limit was estimated to be 48.3 MPa. The deep corrugated steel plate members tested in this study can provide a sufficient fatigue performance in compliance with the design specification.

Experimental Assessment on the Flexural Bonding Performance of Concrete Beam with GFRP Reinforcing Bar under Repeated Loading

This study intends to investigate the flexural bond performance of glass fiber-reinforced polymer (GFRP) reinforcing bar under repeated loading. The flexural bond tests reinforced with GFRP reinforcing bars were carried out according to the BS EN 12269-1 (2000) specification. The bond test consisted of three loading schemes: static, monotonic, and variable-amplitude loading to simulate ambient loading conditions. The empirical bond length based on the static test was 225 mm, whereas it was 317 mm according to ACI 440 1R-03. Each bond stress on the rib is released and bonding force is enhanced as the bond length is increased. Appropriate level of bond length may be recommended with this energy-based analysis. For the monotonic loading test, the bond strengths at pullout failure after 2,000,000 cycles were 10.4 MPa and 6.5 MPa, respectively: 63–70% of the values from the static loading test. The variable loading test indicated that the linear cumulative damage theory on GFRP bonding may not be appropriate for estimating the fatigue limit when subjected to variable-amplitude loading.

Optimum Mix Proportions of In-fill Slurry for High Performance Steel Fiber Reinforced Cementitious Composite

Seung-Won Kim･Cheol-Woo Park*･ Seong-Wook Kim･ Hyun-Myung Cho･ Sang-Pyo Jeon･Min-Kwan Ju(Received August 5, 2014 / Revised September 23, 2014 / Accepted September 25, 2014)As political circumstances in oversea countries and Korea varies, the risk of vulnerability from unexpected extreme loading con ditions,such as explosions or extreme impacts, also increased. In additi on, construction companies in Korea recently have taken chances of overseas expansion to countries where their domestic situations are not in rest. Therefore, the resistance of construction mate rials forblast or impact loading become taking more consideration from engineering field. This study is a part of the research to develo p a highperformance fiber reinforced cementitious composite materials with high volume steel fibers and primary purpose of this study i s to find an optimum mix proportions of in-fill slurry. In order to accomplish the tasks this study performed experimental investiga tions onthe slurry for consistency, compressive strength, flowability, J-penetration, bleeding and rheology properties as well as mecha nical properties, compressive and flexural strength, with respect to different mix proportions.키워드 : 강섬유보강 시멘트 복합체, 폭발 및 충격하중, 최적배합, 충전슬러리Keywords : Steel fiber reinforced cementitious composite, Blast and Impact loading, Optimum mix proportions, In-fill slurry* Corresponding author E-mail: tigerpark@kangwon.ac.kr

A Modified Model for Deflection Calculation of Reinforced Concrete Beam with Deformed GFRP Rebar

The authors carried out experimental and analytical research to evaluate the flexural capacity and the moment-deflection relationship of concrete beams reinforced with GFRP bars. The proposed model to predict the effective moment of inertia for R/C beam with GFRP bars was developed empirically, based on Branson’s equation to have better accuracy and a familiar approach to a structural engineer. For better prediction of the moment-deflection relationship until the ultimate strength is reached, a nonlinear parameter () was also considered. This parameter was introduced to reduce the effect of the cracked moment of inertia for the reinforced concrete member, including a lower reinforcement ratio and modulus of elasticity of the GFRP bar. In a comparative study using six equations suggested by others, the proposed model showed better agreement with the experimental test results. It was confirmed that the empirical modification based on Branson’s equation was valid for predicting the effective moment of inertia of R/C beams with GFRP bar in this study. To evaluate the generality of the proposed model, a comparative study using previous test results from the literature and the results from this study was carried out. It was found that the proposed model had better accuracy and was a familiar approach to structural engineers to predict and evaluate the deflection behavior.

Evaluating rating factor for prestressed concrete girder bridges by nonlinear finite element analysis

This study provides a new approach to evaluate the load carrying capacity in rating factor (RF) of prestressed concrete I type girder bridges utilising nonlinear finite element (FE) analysis. RF has been conventionally calculated either by ultimate strength design (USD) or allowable stress design methods in terms of live load effects. This study introduces nonlinear FE analysis as a new approach to estimate the RF. In general, nonlinear FE analysis is considered as one of the most efficient methods to simulate structural behaviour. This method can also simulate a live load effect, which is very important for the load carrying capacity of structures. To apply nonlinear FE analysis, an FE live load constant was conceptually suggested to estimate the RF. On comparing the RF obtained via the conventional method of USD, it was found that the RF estimated by nonlinear FE analysis approach has almost the same value. Hence, the nonlinear finite element method-based RF methodology can be efficiently used to estimate the load carrying capacity of bridges.

Experimental Verification of Flexural Response for Strengthened R/C Beams by Stirrup Partial-Cutting Near Surface Mounted Using CFRP Plate

The near surface mounted (NSM) FRP strengthening method has been conventionally applied for strengthening the deteriorated concrete structures. The NSM strengthening method, however, has been issued with the problem of limitation of the cutting depth which is usually considered as concrete cover depth. This may be related with degradation of bonding performance in long-term service state. To improve the debonding problem, in this study, the Stirrup partial-cutting NSM (SCNSM) strengthening method using CFRP plate was newly developed. SCNSM strengthening method can be effectively applied to the deteriorated concrete structure without any troubles of insufficient cutting depth. To experimentally verify the structural behavior, the flexural test of the concrete beam by using the SCNSM strengthening method was conducted with the test variable as the strengthening length (32%, 48%, 70%, 80%, 96% of span length). In the result of the test, the NSM and SCNSM strengthened specimen showed similar structural behavior with load-deflection, mode of failure. Additionally, there was no apparent structural degradation by the stirrup partial-cutting. Consequently, it was evaluated that the SCNSM strengthening method can be useful for seriously damaged concrete structures that is hard to apply the conventional NSM strengthening method for increasing the structural capacity.

Material and Structural Characteristics of High Performance Permanent Form Using Stainless Steel Fiber

Nowadays, the general stripping work of form has brought some problems; increase of total constructing cost resulted from the man-dependent form work procedure and environmental issues by wasting the debonded form. In this study, to effectively reduce unnecessary cost and resolve the environmental problems caused by these kinds of reason, a permanent form method using stainless steel fiber was introduced then its material and structural characteristics were evaluated. In the case of material characteristic, the permanent form had a good ductile behavior in the result of flexural test of the permanent form panel and pull-out test of insert bolt which is installed in the permanent form and perfect bonding capacity with a field concrete. In the case of structural characteristic, compressive and tensile behavior of the permanent form was evaluated. It also showed a good structural behavior in the view of load-deflection relationship, crack patterns and additional strengthening effect.

Punching Shear Behavior of Two-Way Concrete Slabs Reinforced with Glass-Fiber-Reinforced Polymer (GFRP) Bars

This study investigated the punching shear behavior of full-scale, two-way concrete slabs reinforced with glass fiber reinforced polymer (GFRP) bars, which are known as noncorrosive reinforcement. The relatively low modulus of elasticity of GFRP bars affects the large deflection of flexural members, however, applying these to two-way concrete slabs can compensate the weakness of the flexural stiffness due to an arching action with supporting girders. The test results demonstrated that the two-way concrete slabs with GFRP bars satisfied the allowable deflection and crack width under the service load specified by the design specification even in the state of the minimum reinforcement ratio. Previous predicting equations and design equations largely overestimated the measured punching shear strength when the slab was supported by reinforced concrete (RC) girders. The strength difference can be explained by the fact that the flexural behavior of the supporting RC beam girders reduces the punching shear strength because of the additional deflection of RC beam girders. Therefore, for more realistic estimations of the punching shear strength of two-way concrete slabs with GFRP bars, the boundary conditions of the concrete slabs should be carefully considered. This is because the stiffness degradation of supporting RC beam girders may influence the punching shear strength.

Bond performance of GFRP and deformed steel hybrid bar with sand coating to concrete

In this study, we experimentally investigated the bond performance of a glass fiber-reinforced polymer hybrid bar with a core section comprising a deformed steel bar and a sand coating. The glass fiber-reinforced polymer and deformed steel hybrid bar (glass fiber-reinforced polymer hybrid bar) can contribute to longer durability and better serviceability of reinforced concrete members because of the increased modulus of elasticity provided by the deformed steel bar. Uniaxial tensile tests in compliance with ASTM D 3916 showed that the modulus of elasticity of the glass fiber-reinforced polymer hybrid bar was enhanced up to three times. For the bond test, a total of 30 specimens with various sand-coating and surface design parameters such as the size of the sand particles (0.6 mm and 0.3 mm), sand-coating type (partially or completely), number of strands of fiber ribs (6 and 10), and pitch space (11.4 mm to 29.1 mm) of the fiber ribs were tested. The completely sand-coated glass fiber-reinforced polymer hybrid bar exhibited a higher bond strength (90.5%) than the deformed steel bar and a reasonable mode of failure in concrete splitting. A modification parameter to the Eligehausen, Popov, and Bertero (BPE) model is suggested based on the representative experimental tests. The bond stress–slip behavior suggested by the modified BPE model in this study was in reasonable agreement with the experimental results.