• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.31 no.5A
• /
• pp.389-397
• /
• 2011

In this study, an experiment for the biaxial behavior of specimens was carried out to identify whether the isotropic flexure tensile stress of concrete in the BFT method is feasible. Another experiment for the improvement of the BFT method was conducted to ensure the isotropic flexure tensile stress of BFT specimens during the test. In addition, the biaxial flexure strength of concrete given by the improved BFT method was compared to the uniaxial flexure strength by the four-point bending test. Test results show that the isotropic flexure tensile stress of concrete using the BFT method was highly influenced by the surface conditions and warping of the specimens. Using improved BFT method, we could obtained the isotropic flexure tensile stress of concretes. The biaxial flexure strength of BFT was about 32% greater than the uniaxial flexure strength of the four-point bending test. In the experiment, with the smaller scatter, the improved BFT method gave a reliable biaxial flexure strength like the four-point bending test.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2010.04a
• /
• pp.441-444
• /
• 2010

대공간 구조물과 초고층 빌딩에 있어 건축물의 자중 감소에 대한 요구가 늘어나고 있으며 이에 대한 가장 효과적인 방법 중 하나는 경량 콘크리트를 사용하는 것이다. 본 연구는 최외단 철근의 순인장 변형률에 따른 경량콘크리트 보의 휨 거동 및 휨 성능을 평가하는 것에 그 목적이 있다. 크기와 형상이 동일한 보통중량 콘크리트 보 1개와 경량 콘크리트 보 4개의 총 5개 시험체를 제작하여 최외단 철근의 순인장 변형률을 변수로 실험을 수행하였으며 이를 통해 순인장 변형률에 따른 경량콘크리트 보의 강도와 연성의 변화를 분석하였다. 실험 결과 최외단 철근의 순인장 변형률이 증가할수록 시험체의 연성비는 증가하였으며 최대하중과 강성은 감소하였다. 특히 순인장 변형률 0.005 이상에서 연성지수 2 이상을 확보할 수 있었다.

• Journal of the Korean Wood Science and Technology
• /
• v.46 no.1
• /
• pp.85-92
• /
• 2018

In order to use glued built up timber beam as a structural member for post and beam construction, it must be possible to manufacture long-span lumber. In this study, the researchers conducted a performance evaluation for longitudinal bonding of lumber (cross-section $89{\times}120mm$) made from larch. The specimens were prepared in six different forms using the longitudinal bonding method. The bonding strength of these specimens was tested through tensile strength tests and bending strength tests. The tensile strength test result of the longitudinally bonded parts was better than that of the double lap specimens. And, the tensile strength value of the scarf specimen was better than that of the hooked scarf specimen. The tensile strength of the GFRP (Glass Fiber Reinforced Plastic) rod insertion bonding specimen was 3.6 MPa, which was the highest. As for the bending strength test result of the longitudinally bonded part, the average MOR (modulus of rupture) of the specimen where a GFRP rod was inserted and bonded measured 29 MPa, while the specimens of other bonded parts showed a MOR no more than 11 MPa. Toughness destruction was observed in specimens where a GFRP rod was insertion-bonded. The rest of the specimens showed brittle destruction. The average MOR strength of the Rod + Lap specimen was 30.5 MPa, which was the highest among all longitudinally bonded specimens. The bending strength of the Rod + Lap specimens showed an effective strength that was 66% of that of the control group which were not longitudinally bonded.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.04a
• /
• pp.693-696
• /
• 2008

The biaxial tensile strength of concretes was measured by the Biaxial Flexure Test(BFT) which was recently developed to measure the biaxial tensile strength of concretes. From the test result, The circular specimen is generally fractured after 1${\sim}$3 of the initial crack were formed on the top of specimen. The direction and number of the initial crack was completely arbitrary. As the specimen was larger, the number of the crack increased. And, the strengths of the different radii and thickness of specimens were calculated by the commercial finite element program to study the size effect of the biaxial tensile strength like the uniaxial tensile strength. The parameters such as radii to the support and to the load point, were studied using the program. The results of the FE analysis were entirely consistent with the predictive solution, when b/a>0.4, and the thickness of the specimens were increased. On the other hands, those with lesser free length showed good results.

• Magazine of the Korea Concrete Institute
• /
• v.5 no.3
• /
• pp.187-194
• /
• 1993

본 논문에서는 유리섬유의 적층수, 유리섬유의 배향각도에 대한 유리섬유 강화 플라스틱(Glass Fiber Reinforced Plastics ; GFRP)의 인장거동 변화를 고찰하고, 이들의 상관관계를 규명하기 위하여 일련의 GFRP 시험체에 대하여 인장실험을 수행하였다. 시험체는 폭12.5mm, 길이 60mm크기로 일정하게 제작하였으며, 시험체에 대하여 인장실험을 수행하였다. 시험체 제작시 유리섬유로 적층수는 14, 22, 30층, 유리섬유의 배향각도는 0$^{\circ}$, 30$^{\circ}$, 45$^{\circ}$로 하였다. 인장실험시 각 시험체의 파괴양상, 극한하중 및 하중변화에 대한 인장변형율을 조사하였고, 이들 결과를 토대로 유리섬유의 적층수와 배향각도에 따른 GFRP의 극한하중, 응력-변형율 선도 및 탄성계수 등을 비교 분석하였다. 한편 본 논문에서는 유리섬유의 적층수, 직경 변화에 따른 GFRP관의 파괴거동을 고찰하기 위하여 4점 재하법에 의한 GFRP관의 휨파괴실험을 수행하였다. 실험에 사용된 시험체는 길이 1200mm로 하였으며, 유리섬유의 적층수를 30, 35, 40층, 관의 직경을 50, 100, 150mm로 하였다. 파괴실험시 각 시험체의 하중변화에 대한 휨 변형율, 중앙점 처짐량 및 항복하중을 측정하였고, 이들 결과를 토대로 유리섬유으 적층수와 관의 직경에 따라 GFRP관의 항복하중 및 파괴에너지를 비교 분석 하였으며, 항복시 파괴에너지를 추정할 수 있는 제안식을 유도하였다.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.35 no.2
• /
• pp.299-306
• /
• 2015

The quality for the domestic pavement is evaluated based on flexural strength at the age of 28 days in accordance with KS regulation. Most specimens of the flexural tensile strength used currently are relatively large ones with a dimension of $150{\times}150{\times}550mm$. Accordingly, it is difficult to treat the specimens, and the utilization of a curing tank is low. In this paper, the study tried to resolve the problem by specimen size specified in the code. For this purpose, a flexural strength test was conducted according to the log scale within the specimen size specified by the KS. And, based on the results of this experiment, a comparative analysis was conducted using the prediction formula of Size Effect Law (SEL) proposed by Bazant to examine the correlation between specimen sizes, so as to use the result as basic data for the reduction of the specimen size in the quality evaluation of concrete pavement.

• Journal of the Korea Institute of Building Construction
• /
• v.19 no.6
• /
• pp.485-494
• /
• 2019

This study is to evaluate the effect of admixtures such as blast-furnace slag and fly ash on adhesion in flexure and tension of polymer cement mortar(PCM) using SAE emulsion. The test specimens are prepared with five polymer-cement ratios and five admixture contents, and tested for flexural strength, adhesion in flexure, tensile strength and adhesion in tension. Based on the test results, no improvement of flexural strength and adhesion in flexure caused by admixtures in PCM can be indicated, but the tensile strength and adhesion in tension is improved due to mixing of the admixtures. In particular, the maximum of adhesion in tension of PCM with P/C 20% and BF content of 10% is 3.35MPa which is about 2.36 times higher than that of ordinary cement mortar, and 1.32 times that of PCM that does not contain any admixture. The average ratio of adhesion in tension to tensile strength of PCM was 48.7%. It is apparent that admixture contents of 5% or 10% could be proposed for improvement of tensile strength and adhesion in tension of PCM.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.23 no.5
• /
• pp.551-557
• /
• 2010

The purpose of this study is to estimate experimentally the flexural behavior, capacity and validity of existing regulation of net tensile strain in lightweight concrete beams and polymer modified lightweight concrete beams. One normal weight concrete beam and four lightweight concrete beams, three polymer modified lightweight concrete beams were constructed as same figure and attempted to evaluate the difference of strength and ductility in specimens of different net tensile strain in extreme tension steel. Test results are indicated in terms of load-deflection behavior and ductility index. As the value of net tensile strain increased, the flexural strength and stiffness of specimen decreased but ductility index increased in both of lightweight concrete beams and polymer modified lightweight concrete beams. It is considered that to achieve similar ductility index of normal weight concrete, net tensile strain in extreme tension steel should exceed 0.005 for lightweight concrete beam and polymer modified lightweight concrete beam.

• Journal of the Korea Concrete Institute
• /
• v.17 no.6 s.90
• /
• pp.1033-1042
• /
• 2005

Until recently tensile stresses in concrete have not been considered, since it does not affect the ultimate strength of reinforced concrete flexural members significantly However, to verify the load-deflection relationship, the effect of tensile stresses between reinforcing bars and concrete, so-called tension stiffening effect must be taken into account. Main parameters of the tension stiffening behavior are known as concrete strength, and bond between concrete and reinforcing bars. In this study total twenty specimens subjected to bending were tested with different concrete strength, coverage, and de-bonding length of longitudinal bars. The effects of these parameters on the flexural rigidity, crack initiation and propagation were carefully checked and analyzed.

• Journal of the Korean Wood Science and Technology
• /
• v.39 no.4
• /
• pp.351-358
• /
• 2011

This study has been carried out to understand the fracture characteristics of the tension wood of Quercus mongolica under the shear and bending stress. Macroscopically, the wood fluff in the shear surface appeared more frequently in tension wood than sound wood, and more coarse wood fluffs were observed in 30% than 10% moistured shear surface. In the fractured tension wood from bending stress, more thick and long wood fiber appeared than sound wood. The observation using scanning electron microscope indicated that both sound and tension wood samples from radial shear surface showed the intrawall dominated failure and the fracture surface of the ray parenchyma cell showed the transwall dominated failure. In tangential shear surface, wood fiber surface showed the intrawall failure and short and coarse wood fiber was observed in tension wood. Ray parenchyma cell of sound and tension wood samples showed the transwall failure. The surfaces of tension wood’s ray parenchyma cell were relatively clean. The fractured tension wood from bending stress showed unsharp and flat wood fiber compared with sound wood.