• Journal of Korean Tunnelling and Underground Space Association
• /
• v.8 no.3
• /
• pp.227-235
• /
• 2006

The problematic issue of cracking, water shedding in tunnel is recently coming out in the view of the structural stability. Hence, the assessment is required for the existing tunnels to achieve the structural soundness of tunnels, and their safety and maintenance. In this study, fracture behaviour and displacement of a tunnel concrete lining using steel fiber reinforcement concrete was investigated. The specimens were fabricated in single lining for a model of real road tunnel. As parameters, load condition, thickness of lining, whether or not rear cavity in crown, and a ratio of steel fiber in concrete were taken. From these factors, the load for crack and fracture, displacement, and the pattern of crack were looked into for the structural stability of a tunnel concrete lining.

• Proceedings of the KSR Conference
• /
• 2007.11a
• /
• pp.1370-1378
• /
• 2007

High speed railway bridge is affected on safety of bridge by dynamic amplification effect, when dynamic response of bridge is equal to effect cycle load for rolling stock axle according to high speed operation train. And excessive deformation of structure has negative effect on operation safety of train and comfort of passenger due to fluctuation of wheel load by torsion of track etc. and decrease of contact force on vehicle wheel-rail. To ensure the safety of track and train operation safety, it is have to perform the study on resonance and deformation of structure. That criteria and requirement of railway bridge is limitation of vertical acceleration on deck for dynamic behavior of structure, contact of vehicle wheel and rail, limitation of face distortion and rotation angle of end deck, and limitation of vertical displacement by train. Unlike KYEONGBU High Speed Railway, New constructed HONAM High Speed Railway have to applied the new requirement for dynamic behavior safety according to change of condition which is type of ballast (slab ballast), interval of track, and actual rolling stock load. Therefore, in this paper, it was conformed the dynamic characteristic due to parameter, which related with above mentioned criteria, for steel composite bridges.

• Journal of Korean Society of Steel Construction
• /
• v.18 no.6
• /
• pp.769-782
• /
• 2006

As the ambient vibration test (AVT) of railway bridges has a limited range of speed, it has a limitation in examining the dynamic behavior of bridges accordingto speed. Thus, in order to analyze the correlation between the speed of a train passing over a bridge and the bridge's dynamic response, we conducted a speed-increasing experiment using a real diesel locomotive. To analyze the acceleration response characteristics, we attached seven vertical accelerometers at equal intervals throughout the entire section of the bridge except the supports, and one horizontal accelerometer to the middle span. Linear variable differential transformers (LVDT) were installed at the bridge's center in both vertical and horizontal directions to investigate the vertical and horizontal behaviors. The test train was statically loaded at the center and at the end of the bridge. And its speed was increased from 5 km/h to 90 km/h. With data obtained from the experiment, the vibration level was evaluated in each direction by the filtering frequency, and the level of horizontal vibration was examined in comparison with vertical vibration. The displacement and wheel load variation was analyzed by speed.

• Magazine of the Korea Concrete Institute
• /
• v.11 no.1
• /
• pp.221-230
• /
• 1999

A study was conducted to investigate the flexural behavior of reinforced high-strength concrete beams using Belite cement. In this study, fourteen reinforced Belite and control beams were tested. The major experimental variables are compressive strength(350kgf/$cm^2$ and 600kgf/$cm^2$)of concrete and reinforcement ratios(0.0086~0.0345). They were tested by three point loading method. Comparing with flexural behavior of normal reinforced concrete beams, the investigation were to : (1) determine experimentally the load-displacement relationships and the strain distribution on the section of test beams : (2) determine experimentally the moment-curvature and the load-neutral axis relationship of Belite ; (3) investigate the flexural ductility of Belite ; (4) estimate the ratio of the capacities of nominal moment strength as a function of ACI to as a experiment. From the test results, the flexural behavior of reinforced high-strength concrete beams using Belite cement are similar to flexural behavior of normal reinforced concrete beams.

• Journal of the Korea Concrete Institute
• /
• v.25 no.5
• /
• pp.555-564
• /
• 2013

An effective method was proposed in this study which can improve the strengthening effect of continuous girder bridges by external tendons. The improvement of the proposed strengthening method in comparison with conventional methods was analyzed by applying equivalent load concept. In order to verify the strengthening effect, the enhancement of load-carrying capacity achieved by external prestressing was investigated through the test of continuous beams that were or were not strengthened by the external prestressing. The continuous beams were fabricated by making the deck slab continuous according to general construction practice of an actual concrete girder bridge. The test results showed that the deflections and strains of the strengthened beam were significantly reduced when comparing with those of the non-strengthened beam for the same level of external loads, and the stiffness of the member increased by strengthening. In particular, it was verified that the proposed method can effectively reduce the tensile stresses of the deck caused by negative moment at the intermediate supports of a continuous bridge.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.33 no.3
• /
• pp.843-854
• /
• 2013

This paper presents experimental research work for the evaluation of ultimate flexural behaviors of prestressed concrete beams with a corroded tendon. In order to evaluate the effects of loss of prestress or loss of tendon area on the ultimate flexural strength of prestressed concrete beams, static load tests are conducted using five prestressed concrete beams. After exposing prestressing tendons in two test beams using 25mm drill bit, the exposed tendons were corroded using an accelerating corrosion equipment to simulate loss of tendon area. During the tests, steel strains, concrete strains and displacements at the center of test beams were measured, and acoustic emission measurements were conducted to detect wire fractures. Based on the test results, evaluation method for predicting flexural strength of prestressed concrete beams with corroded tendons is investigated. In addition, evaluation methods for predicting the existence of corroded tendons in post-tensioned prestressed concrete beams at service loads are discussed.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.16 no.10
• /
• pp.6816-6822
• /
• 2015

In this study, silica aerogel-glass wool composites were developed for improvement of thermal conductivity and overcoming the water adsorption of glass wool boards. Silica aerogel-glass wool composites were prepared by glass wool and silica aerogel with liquid binder. Mixtures with binder were composed of CMC (carboxymethyl cellulose) and silica aerogel for glass wool board. Silica aerogel-glass wool composite boards were had $0.065g/cm^3$ density by impregnation silica aerogel where from origin glass wool board at $0.048g/cm^3$ density. Thermal conductivity of silica aerogel-glass wool composites were 0.0315 W/mK (up to 7.4% thermal resistance) and fire penetration time came to 362 seconds (up to 2.7 times stronger than origin glass wool board). In addition, hydrophobic aerogel characteristics prevented the adsorption of water onto silica aerogel-glass wool composite boards that was good for lightweight.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.32 no.2D
• /
• pp.159-166
• /
• 2012

During concrete placement, the formwork structure supports the weight of concrete mass. The complexity of the operation can cause concentrated workloads, which in turn brings about a collapse of the temporary structure. As a countermeasure, the operation needs to be constantly monitored to maintain safety and prevent accidents. This paper presents a USN (Ubiquitous Sensor Network)-based safety monitoring system for formwork construction. The system takes advantage of ubiquitous technology in monitoring the behavior of the formwork structure such as deflection, load weight, and tilting. The collected data are sent to the host computer wirelessly for real time monitoring. The data can be then compared with the allowed limits on guidelines. The comparison can indicate whether the concrete placement operation is executed in a safe condition.

• Journal of the Society of Disaster Information
• /
• v.7 no.4
• /
• pp.259-265
• /
• 2011

After the commercial opening of the KTX in 2005, the high speed railroad has been rapidly emerged as the major transportation means due to its high energy efficiency. Recently, the government has announced its plan to build the future transportation system around the high speed railroad. Based on this policy, the existing lines as well as the lines under construction or design are planning to increase design speed. In this paper, the suitability of the mid-span PSC girder bridges for the high speed railroad is evaluated via dynamic analysis. IT, Precom, and WPC girder bridges are considered for the purpose of this study and, for comparison, the identical modeling method and the analysis technique are utilized. The performance indices used for dynamic performance evaluation are the natural frequency, the vertical displacement, the end axial displacement, track irregularity, etc. The KTX train is utilized as a dynamic load, and the dynamic analysis is performed up to the train speed of 420km/hr with the increment of 10km/hr.

• Journal of the Korean Society of Hazard Mitigation
• /
• v.8 no.3
• /
• pp.1-9
• /
• 2008

Fiber Reinforced Polymer (FRP) composites are used extensively in aerospace, marine, automotive, infrastructure, chemical processing and sporting good applications. A concern with using FRP composites in some engineering structures is their high flammability and poor fire resistance In this research, material properties of FRP composites at increasingly high temperatures was measured and verified. The obtained mechanical properties of FRP composites were performed according to ASTM D3039/D3039M and tested to a wide range of heat conditions with temperatures from Room-temp. to 300 for times up to 30 min. It is found that the mechanical properties of FRP composites dropped with increasing heat or temperature. The reduction to the properties was due mainly to thermal degradation and combustion of the polymer matrix.