FRP 시트(Sheet)를 활용한 보강 공법은 제작 과정에서의 간편함과 시공의 용이성으로 현장에서 다수 적용되고 있으며, 기존 연구자들은 FRP 시트로 보강한 철근콘크리트의 휨강도를 예측하기 위한 연구를 진행하였다. 그러나 이는 주로 탄소 섬유와 유리 섬유에 한정되어 있었다. 이 연구에서는 바잘트 섬유시트의 역학적 성질을 파악하기 위하여 물성 시험을 수행하였으며, 바잘트 섬유시트로 보강한 철근콘크리트 보의 휨실험을 수행하였다. 또한 그 결과 값을 비교 분석하여 기존 연구를 바탕 으로 바잘트 섬유 시트로 보강한 철근콘크리트 보의 휨모멘트 예측식을 제안하였다. 강도설계법, ACI440.2R (2017) 그리고 Park et al. (2005)의 예측값을 검토한 결과, 강도설계법은 실험값과 예측값의 비가 0.88로 나타났으며, ACI440.2R (2017) 설계식은 0.92, Park et al. (2005)은 0.97로 나타나 기존의 해석 방법은 휨모멘트를 과대평가하는 것으로 나타났다. 본 연구의 제안식은 실험값과 예측값의 비가 1.00으로 나타나 휨모멘트를 안전측으로 예측하는 것으로 나타났다.

한본 연구에서는, 철근콘크리트 보 구조물의 동결융해에 따른 장기거동특성 및 최종 파괴형태를 비교 분석하고자 하였다. 철근콘크리트 보 시험체와 재료 시험체를 제작하여, 동결융해 챔버를 이용하여 동결과 융해를 반복적으로 수행하였다. 동결융해를 위하여 기존의 시험법을 참고하여 철근콘크리트 구조물에 대한 시험을 수행 하였다. 동결융해에 따른 콘크리트의 재 료특성 변화와 철근콘크리트 보 구조물의 거동특성 변화를 통하여 동결융해에 대한 영향을 평가하였다. 제안된 동결융해 시험법을 통하여 콘크리트 공시체의 압축강도가 약 19%감소하였다. 철근콘크리트 보 시험체의 경우, 콘크리트의 표면 강도가 동결 융해에 의하여 감소되어 사인장 균열이 발생하여, 재료적 강도 감소에 의한 구조물의 성능이 감소함을 확인하였다. 또한, 사인장 균열이 발생한 동결융해 시험체의 에너지 소산능력이 동결융해를 거치지 않은 시험체와 비교하여 적게 발생하였다.

In this study, the design of anchorage zone for unbonded post-tensioned concrete beam with single tendons of ultimate strength 2400MPa was evaluated to verify that the KDS 14 20 60(2016) and KHBDC 2010 codes are applicable. The experimental results showed that the bursting force equation of current design codes underestimated bursting stress measured by test, because the KDS 14 20 60(2016) and KHBDC 2010 propose the location of the maximum bursting force 0.5h which is the half of the height of member regardless of stress contribution. Although the allowable bearing force calculated by current design codes was not satisfied the prestressing force, the cracks and failure in anchorage zone was not observed due to the strengthening effect of anchorage zone reinforcement.

This paper discusses the influence of transverse reinforcement spacing and support width of concrete wide beam on shear performance. In order to evaluate the shear performance, a total of thirteen specimens were constructed and tested. The transverse reinforcement spacing, the number of legs and support width were considered as variables. From the test results, the shear strength equation of concrete wide beam is proposed for prediction of shear strength of concrete wide beam to consider the transverse reinforcement spacing and support width. It is shown that the proposed equation is able to predict shear strength reasonably well for concrete wide beam.

본 연구는 FRP-콘크리트 합성구조의 휨/전단에 대한 구조적 성능 및 거동 특성을 해석적으로 규명하고자 휨/전단 저항성능에 대해 외연적 유한요소해석을 이용하여 FRP 합성보의 휨/전단파괴거동 해석을 실시하여 기 수행한 실험과 비교분석 하고, 적용된 콘크리트손상소성모델의 각각의 인자들의 영향에 대해 매개분석하고 최적화된 안을 제시하고자 하였다. 기하학적 및 재료적 비선형성 큰 경우 유한요소해석 중 내연적 해석의 경우 수렴에 많은 문제점을 내포함으로 외연적 유한요소 접근법이 보다 합리적임을 수치해석을 통해 보였다. 본 연구의 경우 콘크리트손상소성모델의 여러 인자들에 대한 매개변수 해석을 수행한 결과, 다이레이션각의 경우는 26°, 파괴에너지 값으로 100Nm/m2, 인자 Kc의 값으로는 0.667 그리고 손상계수는 감안하는 것이 합리적이다.

단면증대공법은 경제성과 시공상 보편적으로 사용되는 공법으로 우리나라의 철근콘크리트 기둥을 보강하기 위한 공법으로 널리 사용되어 왔다. 이와 관련하여 단면증대된 부재의 성능에 관한 실험적 또는 해석적 연구는 수행된 사례가 있으나, 휨성능과 단면증대 부분의 표면거칠기 범위의 상관관계에 대한 연구는 수행되지 않았다. 따라서, 본 연구에서는 단면증대된 보의 휨성능을 평가하기 위해 표면거칠기의 범위를 변수로 한 단면증대보의 휨실험을 수행하였다. 그 결과는 다음과 같다. (1) 시공에서 사용되는 방법에 따라 거칠기 처리가 된 표면의 거칠기 이력을 분석한 결과 인접 산과 골의 차이는 6mm를 초과하였다. (2) 거칠기 이력이 측정된 거리가 600mm를 초과하연, 거칠기 지표는 일관된 결과를 나타내었다. (3) 표면거칠기처리를 하지 않은 보의 휨성능과 비교할 때, 표면거칠기가 된 보의 휨강성은 25%증가하고, 항복강도는 9%, 최대강도는 6%증가하였다. (4) 모든 시험편은 표면거칠기 처리의 유무에 상관없이 단면해석결과 나타난 항복강도보다 높은 강도를 나타내었다.

Experimental evaluation of torsional behavior, which is possible behavior of seismic beams of RC structures, was carried out. Concrete strength and stirrup spacing were set as experimental variables to investigate the torsional strength of RC beams. Based on the experimental results, the torsional strength of RC beams was compared and analyzed. From the experimental results, the concrete strength was caused a difference of about 30% in the torsional strength of the maximum torque of the RC beam specimen, and the stirrup spacing was found to be about 2.8 times and 5 times that of the peak torque. Therefore, this study will be an important study to understand the effect of both concrete strength and stirrup spacing for the torsional strength or torsional behavior of RC beams.

In the seismic design of building structural members, due to the complexity of the placement of PC steels in prestressed concrete members, it is necessary to review and define the definition of member damage in comparison with reinforced concrete members.In this study, the results of past experiments compared with the calculation results by ‘section Analysis Method’, with the aim of reviewing the precision of calculation results when member damage evaluation is performed using the section analysis method. Furthermore, it is also compared with the calculation results by the ‘split Element Method’.In addition, parametric studies were carried out, and the influence of the difference between the amount of PC steels and reinforced bar on the residual strain was examined.

In order to evaluate a stress state of concrete according to the change of tensile force of prestressed beam, improved nonlinear resonant ultrasonic spectroscopy(NRUS) method is proposed. This technique is advantageous to evaluate the stress state in initial state because the method shows much higher sensitivity than existing linear ultrasonic methods. The NRUS technique measure a nonlinearity parameter, which is calculated from the resonant frequency shift of ultrasonic wave related to the medium state, and the result is also closely related to the stress state of concrete. In this study, the nonlinearity parameter was measured with the change of tensile force to verify the close relationship between the two factors, and the effect of repetitive load cycle on the change of nonlinearity parameter was analyzed. In addition, sensitivity comparison with the linear ultrasonic pulse velocity method was performed. Through the experimental results, the possibility of NRUS technique for the evaluation of stress state in prestressed beam was confirmed.

A tensile failure criterion that can minimize the mesh-dependency of simulation results on the basis of the fracture energy concept is introduced, and conventional plasticity based damage models for concrete such as CSC model and HJC model, which are generally used for the blast analyses of concrete structures, are compared with orthotropic model in blast test to verify the proposed criterion. The numerical prediction of the time-displacement relations in mid span of the beam during blast loading are compared with experimental results. Analytical results show that the numerical error is substantially reduced and the accuracy of numerical results is improved by applying a unique failure strain value determined according to the proposed criterion.

When reinforcing an existing reinforced concrete beam-column building with a precast concrete panel, special connection between the PC member and the RC member is required to solve the time dependent deformation of the RC member and to receive the large shear forces. The aim of this study is to obtain the shear strength of upper connection between the existing RC beam-column and infilled PC wall panels in experimentally and theoretically. Thus, the static shear loading tests were conducted on the 6 specimens with the plate connection. Shear failure was resulted from the weakest portion of interior PC panel, exterior RC, and the connection, when the PC portion which located at the center of specimen was pulled upward from the bottom. T he experimental result was compared with analytical result from ACI 318M-14 Chapter 17 for the shear strength of post-installed anchor and PCI Handbook 7th edition 6.8 Structural Steel Corbel (PCI Design Handbook 7th edition, 2010) for the strength of cast-in H-beam. The analytical and experimental results show final failure at the same location. The failure loading of experiment showed larger than average 6% to that of the analysis.

최근에 요소망의 재구성이 불필요하고 균열의 가시화에 강점을 가지는 확장유한요소법(XFEM)을 이용한 균열 해석이 많이 연구되고 있지만 주로 단일재료로 이루어진 부재의 해석에 집중되어 있다. 본 논문에서는 복합재료 부재인 철근콘크리트보의 다중균열 해석에 확장유한요소법을 적용하며 그 적용성과 타당성을 살펴보았다. 확장유한요소해석 기능이 탑재된 상용해석프로그램인 ABAQUS를 사용하여 균열해석을 수행하였으며 그 결과를 실험결과와 비교하였다. 확장유한요소법에서 인접요소에 동시에 균열이 발생할 경우 균열의 불연속성이 나타나지 않은 부가자유도 잠김 현상을 발견하였고 이에 대한 원인과 그 해결방안을 제시하였다. 또한 실험결과와 유사한 다중균열 발생을 위한 모델링 기법도 제시하였다. 확장유한요소법을 이용한 해석결과는 실험결과와 유사한 균열 양상 및 균열 간격을 보여 주었으며 하중-변위 관계에 있어서도 실험에 근접한 결과를 보여 주었다.

In the moment frame subjected to earthquake loads, beam-column joint is structurally important for ductile behavior of a system. ACI Committee 352 proposed guidelines for designing beam-column joint details. The guidelines, however, need to be updated because of the lack of data regarding several factors that may improve the performance of joints. The purpose of this study is to investigate the seismic performance of reinforced concrete exterior joints with high-strength materials and unbonded tendons. Three specimens with different joint shear demand-to-strength ratios were constructed and tested, where headed bars were used to anchor the beam bars into the joint. All specimens showed satisfactory seismic behavior including moment strength of 1.3 times the nominal moment, ductile performance (ductility factor = at least 2.4), and sufficiently large dissipated energy.

This paper shows the simplified equation to predict the ultimate moment capacity and corresponding rod stress in reinforced concrete beam with external post-tensioning rods. Because the stress of external post-tensioning rod depends on the beam deflection, the previous analytical model for post-tensioned beams requires a tedious iteration process. Also, the stress equations in ACI code or other researchers’ models are suitable only for internal tendons in concrete beams. In this study, given the lack of analytical approaches to predict the nominal stress of the external unbonded rod, a simple and robust equation has been proposed for externally post-tensioned concrete beams. It is concluded that the proposed equation predicted the stress of external steel rods in post-tensioned concrete beams reasonably well.

The demand for the structural system of reduction of story height increases because buildings are getting higher. The existing structural systems are not efficiency. Thus, it is hard to reduce the story height and existing methods cannot secure economics as expected. This study aims at developing the partially concrete-filled new type composite beam, which can efficiently resist against the end negative moment and central positive moment, also reduce deflection of beams. Through case studies on loading of concentrated load and uniformly distributed load to fixed beam, we could find the most efficient ratio of moment of inertia and the ratio (end beam length to span). The gap space between middle and end beam can be used as facilities installation, consequently the suggested Omega beam system is expected to get the effect of reduction in story height as well as reduction of quantity.