• Journal of the Korea Institute of Building Construction
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• v.13 no.6
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• pp.627-633
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• 2013

This paper presents the result of a mock-up test and field application of concrete that is black in color thanks to the application of superplasticizer containing carbon amino silica black (CASB-SP). Mock-up specimen with a size of $3000{\times}1500{\times}40$ mm was fabricated with black concrete applying 0.5% of CSAB-SP with 27 MPa. After dividing the zone in wall mock-up specimen, three different water repelling agents were applied to verify its effect of efflorescence prevention. It was found that the use of CASB-SP with 0.5% made the black concrete develop a highly clear black color, and the epoxy type water repelling agent had better performance in efflorescence prevention. Based on mock-up test, field application was conducted with bridge member. It was also found that the application of CASB-SP showed favorable results in black color development.

• Journal of Welding and Joining
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• v.17 no.1
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• pp.88-96
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• 1999

The effects of root gap on welding residual stress and deformation are dealt with the multi-pass weldment with three kinds(0, 6, 30mm) of root gap by F.E.M common code, and then compared with experiment data. In this analysis, an 100% ramp heat input model was used to avoid numerical convergence problem due to an instantaneous increase in temperature near the fusion zone, and the effect of a moving arc in a two dimensional plane was also included. During the analysis, a small time increment was applied in a period with instantaneous temperature fluctuation while a large time increment was used in the rest period. The residual stress is distributed as symmetric types and maximum value is also equivalent when the weldment with 0mm and 6mm root gap is welded. In the case of 30mm root gap welding, the distribution of the residual stress extends over a wide range as asymmetric types due to the built-up weld, and most of the residual stress is biased in the side of a built-up weld part. In case of 0mm gap welding and 6mm gap welding, a little angular distortion occurs, but the level of deformation is small. When the weldment with 30mm root gap is welded, the angular deformation of the asymmetric types, however, occurs larger than the other specimens. The experimental and the analytic results show good coincidence and indicate that the welding residual stress and deformation distribution of 30 mm root gap specimen may be asymmetric and the amplitude is larger than those of root gap specimen under standard.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.4
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• pp.99-106
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• 2014

In order to study the reasonable design thermal loads, the steel box girder bridge specimen which have no concrete slab was manufactured with the real size dimension. The temperature data were measured for 5 month at the 18 thermo gauges which were attached according to height. The temperature differences between the top and bottom flange in steel box girder specimen were calculated and the temperature gradient models were proposed by the probabilistic method. This proposed model showed a correlation of approximately 97% when compared with the similar model of Euro Code. Thus, the temperature gradient models which were suggested in this study may be used as the basis data in calculating the design load temperature.

• Smart Structures and Systems
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• v.12 no.2
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• pp.97-119
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• 2013

This paper presents numerical and experimental results on the use of guided waves for structural health monitoring (SHM) of crack growth during a fatigue test in a thick steel plate used for civil engineering application. Numerical simulation, analytical modeling, and experimental tests are used to prove that piezoelectric wafer active sensor (PWAS) can perform active SHM using guided wave pitch-catch method and passive SHM using acoustic emission (AE). AE simulation was performed with the multi-physic FEM (MP-FEM) approach. The MP-FEM approach permits that the output variables to be expressed directly in electric terms while the two-ways electromechanical conversion is done internally in the MP-FEM formulation. The AE event was simulated as a pulse of defined duration and amplitude. The electrical signal measured at a PWAS receiver was simulated. Experimental tests were performed with PWAS transducers acting as passive receivers of AE signals. An AE source was simulated using 0.5-mm pencil lead breaks. The PWAS transducers were able to pick up AE signal with good strength. Subsequently, PWAS transducers and traditional AE transducer were applied to a 12.7-mm CT specimen subjected to accelerated fatigue testing. Active sensing in pitch catch mode on the CT specimen was applied between the PWAS transducers pairs. Damage indexes were calculated and correlated with actual crack growth. The paper finishes with conclusions and suggestions for further work.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.2
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• pp.98-104
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• 2018

Nondestructive strength Equations are commonly used to determine the strength of concrete. However, the application of the existing equations may include many errors because this method is proposed on the basis of limited experimental parameters while actual bridges have various parameters such as conditions of concrete mixtures, properties of concrete strength, etc. Also, the error among the existing equations causes the confusion when engineers select the proper estimation equation for the concerned bridge. In this study, a series of the field inspection and the test have been performed on 297 existing bridges, in order to evaluate the bridges, based on the test results of the in-depth inspection, and the estimated strengths by means of the nondestructive strength equations are analyzed and compared with results of the core specimen strengths. According to results of analyses, the nondestructive strength equation proposed by CNDT Committee of Architectural Institute of Japan had high relationship with core strength. However, the strengths predicted by this equation, are underestimated when concrete's strengths are over 30 MPa, otherwise, they are overestimated. Also in this paper, based on the relationship between the estimated nondestructive concrete strengths and the core specimen strengths the modified strength equation through simple correlation analysis is proposed.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.794-797
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• 2004

In this study, tensile adhesive strength(TAS) test was carreid out for evaluated the effects of temperature conditions (-20, -10, 0, 5, 10, 20, 30, $40^{\circ}C$) on the tensile adhesive characteristics about 4 type waterproofing membranes which were commercially used in bridge decks. And, failure appeariences of waterproofing systems in each temperature after TAS test were observed the sawing surfaces of waterproofing systems for whether or not damaged of waterproofing membranes. Also, correction coefficient of TAS with temperature were calculated using 4 type waterproofing membrane. It could be shown that the higher TAS and shear adhesive strength, the lower temperature, regardless of the type of waterproofing membrane. Temperature sensibility of TAS was especially remarkable in epoxy membrane. Failure type was occurred the ductile failure in $30^{\circ}C\;and\;40^{\circ}C$. From these results, it was shown that if ambient temperature above $30^{\circ}C$ maintains for a long time, waterproofing membrane will be deformed by softening. Otherwise, waterproofing membrane in temperature below $20^{\circ}C$ shown that occurred the brittle failure. From the results of visual observation of cutting surface for specimen, the thin waterproofing membranes shown indented by hot aggregate of the asphalt mixtures. Therefore, it could be known that the specification of waterproofing membrane thickness is necessary by waterproofing membrane type. As temperature change varied with pavement depth, the interface temperature was more important than ambient temperature in TAS test. Now, TAS test results were limited only in $-10^{\circ}C\;and\;20^{\circ}C$ temperature, but correction coefficient of TAS by ambient temperature could be used as a solution to deal with this problem.

• Journal of the Korea Concrete Institute
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• v.16 no.2 s.80
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• pp.213-220
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• 2004

This paper deals with an enhanced structural capacity of reinforced concrete bridge deck strengthened with carbon fiber rod (CFR) which is subjected to monotonic and cyclic loads. Strengthening variables considered in this test were evenly and unevenly strengthening type. To evaluate strengthening capacity for these two strengthening types, load-carrying capacity and crack and failure pattern from the failure test were analyzed and fatigue response were examined. According to the test results, all the strengthened specimens showed punching shear failure as a result of premature failure of bonding interface between mortar and concrete. In the case of strengthening capacity, it was observed that the strengthened specimens was more effective in strength, stiffness and fatigue endurance limit than the unstrengthened specimen. In addition, the unevenly strengthening method (CR-UE) was more effective than the evenly strengthening method (CR-E).

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.2
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• pp.217-224
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• 2008

Trusses are found in many common structures such as bridges and buildings. The truss is a fundamental design element in engineering structures and it is important for an engineer to apply the truss design to engineering structures by understanding the mechanics of truss element. In an experimental course, the experiment selves as an example of the usefulness of the Wheatstone bridge in amplifying the output of a transducer. With the apparatus described here, it is possible to obtain experimental measurements of forces in a truss member which agree within errors to predictions from elementary mechanics. The apparatus is inexpensive, easy to operate, and suitable as either a classroom demonstration or student laboratory experiment. This device is a small table-top experiment. The conventional strain measuring device is costly and complicated - it is not simple to understand its structure. Hence, strain gage and the A/D converter are assembled to come up with a load and a strain measuring device. The device was tested for measuring the strain in a loaded specimen and the results were compared to those predicted by theory of mechanics.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.3
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• pp.18-24
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• 2016

This study presents a simple method which can estimate displacement using measured strain response of simply supported girder bridges. The basic concept of the present method is derived from a relation between displacement and strain, and is generalized by introducing analytical tool. Static and dynamic laboratory test are conducted on simply supported plate which is designed to respond dynamically similar to actual bridges to experimentally verify the present method, and displacement and strain are measured at the midpoint of specimen. Displacement estimated by using measured strain is well agreed with measured one. This study demonstrates that the present method is suitable for estimating displacement of real simply supported bridge, in which the installation of a displacement transducer at the fixed reference point is difficult.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.1
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• pp.85-94
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• 2016

In this study, a non-linear FEM model is presented to predict the static flexural performance of precast bridge decks with ribbed joint and is verified with previous experiment results through comparison. The several theory of material properties were applied to each mechanical properties in FEM model and FEM model's input variables were determined through experiment result and parametric study. The FEM results showed good accuracy in predicting the structural performance of the specimens and FEM model's average error rate was 5%. Also, each specimen's cracking aspect and failure mode can be predicted through FEM's plastic strain distribution. Thus, this FEM model can be used effectively for predicting the ultimate behavior and parametric study to development of design formula for joint.