This study evaluated the influence of nozzle shapes in the orientation of fibers in cementitious materials. The nozzle shapes involved in the study are conventional, balded, and tapered circulars. The results showed that both the bladed and tapered nozzles increased the control performance of fiber orientation compared to the conventional nozzle. In particular, bladed nozzle was more effective in controlling the fiber orientation.

최근 철근 콘크리트 구조물에 다양한 철근 이음이 사용되고 있다. 이에 따라 커플러 이음 철근의 인장 특성에 대한 파악이 중요해졌 다. 본 연구에서는 커플러 이음 철근의 연성도에 대한 평가를 위하여 ASTM A615 기준에 따라 생산된 Grade 60 D22(#7), D29(#9), 그리고 두 종류의 커플러를 상대로 1축 인장시험을 수행하였다. 보다 정확하고 다양한 지점에서 자유로운 계측이 가능한 이미지 프로세싱 방법을 사용하 여 변형률을 계측하였다. 1축 인장시험 결과, 응력-변형률 관계와 응력 단계별 종방향 변형률 분포를 산출할 수 있었고, 이를 통하여 동일한 표 점거리 내에서 커플러 이음 부분이 많이 차지할수록 평균변형률이 낮아지는 것을 알 수 있었다. 또한 커플러 이음철근의 극한거동 및 파단 시 변형률에 대한 평가를 통해 커플러의 길이에 대한 한계상태변형률과 파단변형률과의 상관관계를 정식화하였다.

Domestic social infrastructures have been rapidly growing based on economic growth in the 1970s. Recently, the construction of various methods has been continuously being carried out in accordance with the development of construction technology. Due to these influences, Maintenance work is becoming as important as construction.

All the structures include initial imperfections that can affect the structural behavior and stability, particularly during construction. Therefore, for a concrete beam with an initial lateral deformation, creep analysis was performed to evaluate the influence of the initial imperfection on the creep deformation of the beam in the both vertical and lateral directions.

Recently, fiber-reinforced concrete has been commonly applied to floor slabs. Therefore, this study introduces a program that can determine an optimum content of fibers incorporated in concrete accounting for the flexural and punching shear capacities, as well as serviceability conditions in the design of fiber-reinforced concrete floor slabs.

Domestic social infrastructures have been rapidly growing based on economic growth in the 1970s. Recently, the construction of various methods has been continuously being carried out in accordance with the development of construction technology. Due to these influences, Maintenance work is becoming as important as construction.

This study measured the in-plane and out-of-plane deflections of a beam using image processing technology. The deflections and rotation obtained from the vision-based measurement were compared with those from the traditional, current measurement method using three wired potentiometers. The results of this study indicated that the proposed vision-based measurement system was successfully applied to evaluating the out-of-plane deflections of a beam including the vertical in-plane deflection.

Damage states of an underground tunnel structure need to be defined in the estimation of its seismic fragility. They are identified in this paper by applying pushover analyses of an typical tunnel structure. Latin Hypercube sampling (LHS) technique is used to explicitly consider uncertainties in the associated design variables.

This study evaluated the lateral thermal deformation induced by environmental factors for a precast I-girder. Lateral temperature gradients across the cross-section of the girder were calculated using analytical equations based on daily solar radiation, temperature variation, and wind speed. Then the lateral thermal deformation showed an average of approximately 40% to 71% of the tolerance for the initial lateral deformation of the girder, defined in the PCI bridge design standard.

This study was aimed to investigate the difference in strength of Carbon Nanotube (CNT) reinforced cement mortars with different types of surfactants and doses. In the experimental program, CTAB, SDBS and TX10 which were common surfactants adopted to improve CNTs dispersion in fabricating CNT composites in many industrial fields were included and superplasticizer which was revealed to be effective to disperse CNTs especially in CNT reinforced cementitious composites were added as well. Superplasticizer presented less strength reduction in cement mortar and more strength gain by adding CNTs among four types of surfactants. Higher dosage of superplasticizer caused lower strength of cement mortar. Adding CNTs of 0.4 wt.% or less to cement didn’t show strength enhancement by adding CNTs but 0.8 wt.% of CNTs resulted in strengthening effect after all. Finally, a combination of 0.1 wt.% of CNTs, superplasticizer and sonication treatment could lead to strength improvement by adding CNTs in cement mortar.

This study evaluated the fracture strength of GFRP-strengthened RC beams caused by the debonding failure of the GFRP. The fracture strength of RC beams calculated using FRP debonding strains suggested by several main design guidelines were higher than those of experiments. The result might indicate the need of some reduction in the values of the debonding strain or the strength reduction factor.

In this paper a computationally efficient methodology to establish the seismic fragility curve for underground tunnel structures is developed by integrating the response acceleration method and the maximum likelihood approach with a large set of artificial ground motion time-histories. It is elaborated with an illustrative numerical example.

An experimental study was performed to evaluate the ultimate strength of GFRP-strengthened RC beams compared to those obtained from main design guidelines. The results of this study indicated that ultimate strength method requires accounting for the stiffness of the applied FRP and the value of concrete compressive stain for its application to strengthened beams.

A pipe-rack structure exposed to various environmental conditions is one of the critical structures for the safety of a plant industry. Based on a selected, typical pipe-rack structure, this study evaluated the behavior of the pipe-rack structure accounting for the operating condition of the pipe and at the same time the effect of environmental conditions.

This study utilizes an equation proposed for the calculation of the lateral-torsional buckling moment of a reinforced concrete beam to evaluate the lateral rollover stability of a precast concrete girder particularly during construction. The result of this study showed the lateral-torsional capacity of a girder significantly decreased with an increase in the initial sweep of the girder. The capacity of a girder with the initial sweep in the order of around two times the PCI tolerance becomes smaller than its ultimate flexural capacity.

Maintenance of plant facilities are becoming important due to lots of recent plant construction. While maintenance of plant facilities are performed, maintenance of plant structures are usually not carried out properly. In this paper, measurement threshold estimation algorithm is developed for maintenance of pipe-rack structure. Currently, field verification of the developed algorithm is being performed on a real pipe-rack structure.