소조사면 전량분포의 특성에 관한 고찰

조정희,이상규,안승권,박재일,Cho JeongHee,Lee SangKyu,An SeungKwon,Park Jell 대한방사선치료학회 2004 大韓放射線治療技術學會誌 Vol.16 No.1

목적 : 본 연구의 목적은 소조사면의 선량특성을 측정하며 콜리메이터의 위치에 따른 반음영의 변화와 중심선량의 분포양상을 측정하며 측외측정선량점의 변화에 따른 선량분포의 특성을 측정하여 최근 대두되고 있는 소조사면 방사선치료에 유용한 정보를 제공하는데 그 목적이 있다. 대상 및 방법 : 지멘스의 Primart 선형가속기의 6MV에너지를 이용하였으며 측정은 Farmer chamber와 Pinpoint chamber를 이용하여 심부선량율과 beam profile, 중심출력선량의 변화를 측정하였다. 중심선속의 변화에 따른 에너지의 특성과 반음영의 변화를 외측으로 2cm 간격으로 측정하였다. 측정은 $1{\times}1cm,\;3{\times}3cm,\;5{\times}5cm,\;10{\times}10cm$에서 측정하였으며 결과는 표준조건하의 측정값과 비교, 분석하였다. 결과 : Farmer chamber와 Pinpoint chamber를 이용해 $1{\times}1cm$, 10cm깊이에서 측정한 결과 두 측정기간에 소조사면에서는 $30\%$ 이상의 차이를 보였으며 조사면의 크기가 증가함에 따라 두 측정기간의 차이는 급격히 감소했다. 측외측정점의 변화에 따른 선량분포는 큰 차이가 없었으나 조사야의 크기가 감소함에 따라 $1{\times}1cm$에서는 약 $13\%$의 차이를 보여 조사야 크기에 따른 변화가 큰 것으로 측정되었다. 전체조사면에서 반음영이 차지하는 비율도 조사면이 적어짐에 따라 높게 나타났으며 $1{\times}1cm$의 조사면에서는 약 $50\%$가 반음영이 점유하는 것으로 측정되었다. 결론 : 세기조절방사선 치료를 위해서는 각기 다른 에너지 분포를 갖는 여러 각도에서 다수의 조사면를 필요로 하며 여러 복잡한 인자들이 관여하게 된다. 여러 인자들 중에서도 콜리메이터의 형태 및 위치에 따른 출력선량의 변화 양상을 정확히 측정하는 것은 매우 중요하다. 실험결과에서도 알 수 있듯이 측정깊이와 조사면의 크기 및 측정기의 종류에 따른 측정값의 변화가 매우 크게 나타나므로 양질의 세기조절방사선 치료를 제공하기 위해서는 특히 소조사면의 선량분포에 대한 특성을 정확히 측정하는 것이 매우 중요하다. Purpose : The aim of this study is to investigate the properties of small field size and to measure the penumbra and central axis depth dose varying to the jaw setting and off axis distance for indicate this data to small field sizes radiation therapy. Material and methods : The percentage depth dose, beam profile and central axis output dose was measured by farmer type ion chamber and pinpoint chamber using Primart linac with 6MV energy. Beam quality and penumbra variations according to the central axis shift, from center to every 2cm outside increment, and field size, from $1{\times}1cm$ to $10{\times}10cm$ was investigated and compared with that of the standard geometrical condition's results Results : The differences of measured values between two ion chamber was about $37\%$ at 10cm depth with $1{\times}1cm$ field sizes but as field size increased this differences was diminished gradually. Measured data from various off axis distance with the different asymmetric collimations are not changed significantly but as size decreased the dose variation was increased and at $1{\times}1cm$ field size dose difference among off axis distance was as much as $13\%$, and as shallower the measured depth the central axis dose variations among the OAD was increased, penumbra was not changed noticeably depending on off axis distance but the percentage of penumbra from its initial field sizes was strongly dependant on field sizes and penumbra occupation rates of its own field sizes ranging from $6\%$ at $10{\times}10cm$ to $50\%$ at $1{\times}1cm$ field size. Conclusion : For imrt treatment, there are several numbers of different gentry angles with beams of nonuniform fluences are required and several complex factors involved. Among them the characteristics of beam output varying to the geometrical setting and design of collimators are of important to attaining a good treatment results. As mentioned in results the differences of measured values are changed significantly depends on ion chamber volume, depths and field size. For providing quality radiation treatment, especially at small field size, those factor's should have considering deliberately.

Effect of the Laser Beam Size on the Cure Properties of a Photopolymer in Stereolithography

Jae-Hyung Sim,Eun-Dok Lee,Hyeog-Jun Kweon 한국정밀공학회 2007 International Journal of Precision Engineering and Vol.8 No.4

Stereolithography (SLA) is a technique using a laser beam to cure a photopolymer liquid resin with three-dimensional computer-aided design (CAD) data. The accuracy of the prototype, the build time, and the cured properties of the resins are controlled by the SLA process parameters such as the size of the laser beam, scan velocity, hatch spacing, and layer thickness. In particular, the size of the laser beam is the most important parameter in SLA. This study investigated the curing properties of photopolymers as a function of the laser beam size. The cure width and depth were measured either on a single cure line or at a single cure layer for various hatch spacings and laser beam sizes. The cure depth ranged from 0.23 to 0.34 mm and was directly proportional to the beam radius, whereas the cure width ranged from 0.42 to 1.07 mm and was inversely proportional to the beam radius. The resulting surface roughness ranged from 1. 12 to 2.23 ㎛ for a ratio of hatch spacing to beam radius in the range 0.5-2.0 at a beam radius of 0.17 mm and a scan velocity of 125 mm/sec.

Size Effect in Shear Failure of High Strength Concrete Beams without Stirrup reinforced with Basalt FRP Bars

Ghazi Bahroz Jumaa,Ali Ramadhan Yousif 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.4

This study investigates the size effect in shear failure of high strength concrete beams without stirrup reinforced with basalt Fiber Reinforced Polymer (FRP) bars. The experimental works include constructing and testing twelve large-scale simply supported beams. The main considered parameters were beam depth (300, 500 and 700 mm), flexural reinforcement ratio and concrete compressive strength. The test results show that there is a considerable size effect in normalized shear strength with average reductions in shear strength of 32.8 and 43.6% when the beam effective depth was increased from 252 to 452 and 635 mm respectively. With increasing beam depth the ultimate deflection and ductility reduced substantially and the shear failure become more brittle. Comparing the experimental with predicted shear strength by seven codes and nine proposed equations from literature showed that the most accurate design equations, are those of Alam and Hussein (2013), Razaqpur and Spadea (2010), Lee and Lee (2014), and CSA (2010, 2012), however in most of the considered equations the degree of conservatism decreased with increasing beam depth. Moreover, comparing the size effect in this study with others from the literature indicated that the size effect is larger in beams reinforced with basalt FRP rebar than glass and carbon FRP rebar, however more studies are needed to confirm this.

Two-dimensional SR Interferometer for PLS-II

김창범,황일문,최효진,박성주,Jung-Yun Huang,박용운,고인수,류진영,황지광 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.58 No.4

A synchrotron radiation (SR) interferometer was used for beam size measurements at the Pohang Light Source (PLS). It was an one-dimensional (1D) interferometer, and the horizontal beam size was only available for real time measurements of the user service. In the PLS upgrade project (PLS-II), a 2D interferometer was tried for simultaneous measurements of the horizontal and the vertical beam sizes. Various sizes of the 2D slits were tried to find an optimum condition by considering the SR characteristics and the instrument’s limitations. Measurement results of the beam size were cross-checked in three different ways and showed good agreements with each other. After optimization, the measurement accuracy of the beam size was improved significantly, and a vertical beam size change was noticed when the gap distance of the elliptically polarized undulator (EPU) was changed.

Computation of stress-deformation of deep beam with openings using finite element method

Senthil, K.,Gupta, A.,Singh, S.P. Techno-Press 2018 Advances in concrete construction Vol.6 No.3

The numerical investigations have been carried out on deep beam with opening subjected to static monotonic loading to demonstrate the accuracy and effectiveness of the finite element based numerical models. The simulations were carried out through finite element program ABAQUS/CAE and the results thus obtained were validated with the experiments available in literature. Six simply supported beams were modelled with two square openings of 200 and 250 mm sides considered as opening at centre, top and bottom of the beam. In order to define the material behaviour of concrete and reinforcing steel bar the Concrete Damaged Plasticity model and Johnson-Cook material parameters available in literature were employed. The numerical results were compared with the experiments in terms of ultimate failure load, displacement and von-Mises stresses. In addition to that, seventeen beams were simulated under static loading for studying the effect of opening location, size and shape of the opening and depth, span and shear span to depth ratio of the deep beam. In general, the numerical results accurately predicted the pattern of deformation and displacement and found in good agreement with the experiments. It was concluded that the structural response of deep beam was primarily dependent on the degree of interruption of the natural load path. An increase in opening size from 200 to 250 mm size resulted in an average shear strength reduction of 35%. The deep beams having circular openings undergo lesser deflection and thus they are preferable than square openings. An increase in depth from 500 mm to 550 mm resulted in 78% reduced deflection.

FE Analysis on Size Effect in Torsional Behavior of Rectangular RC Beams with and without FRP Strengthening

Mojtaba Shokri,Mahmoud Edalati,S. Mohammad Mirhosseini,Ehsanollah Zeighami 대한토목학회 2024 KSCE Journal of Civil Engineering Vol.28 No.5

Although torsion is usually considered a secondary consideration in structural design, it can lead to failures, especially in structures with irregular geometry exposed to seismic forces or in unique situations. While some studies have explored the size effect on the torsional behavior of RC beams, none have addressed the impact of reinforcement. This paper investigates the size effect on the torsional behavior of RC beams with varying reinforcement ratios, including both FRP sheets and steel rebars. In this study, the torsional behavior of reinforced concrete (RC) beams with and without FRP strengthening was investigated numerically. Modeling was carried out by Finite element (FE) software ABAQUS and validated using experimental data from literature. The torsional behavior of 24 models with differences in cross-section size and reinforcement ratio were investigated. Concrete damage plasticity, Hashin damage criteria, and von Mises stress were used to investigate the damage in concrete, FRP, and steel, respectively. The cracking torsional moment, ultimate torsional moment, and torque-twist curve of the beams were evaluated and presented. The results indicated the presence of a significant size effect in the torsional strength of beams. After reinforcing the beams with FRP fabrics, the average cracking moment increased by a range of 1.72% to 36% across different groups of beams. An 8.2% increase in ultimate strength is observed with just a 0.4% rise in the FRP strengthening ratio. Post-cracking behavior was seen in 8 models with adequate steel and FRP reinforcement ratio.

크기효과를 고려한 강섬유 콘크리트 보의 전단강도 분석

오경수(Gyeong-Su Oh),손동희(Dong-Hee Son),최현기(Hyun-Ki Choi),배백일(Baek-Il Bae),최창식(Chang-Sik Choi) 한국콘크리트학회 2024 콘크리트학회논문집 Vol.36 No.4

본 연구는 전단보강이 없는 일반 콘크리트(PC)와 강섬유 콘크리트(SFRC) 보의 전단강도 및 크기효과를 실험적으로 비교 평가하였다. 이를 위해 높이 350, 650, 950 mm 크기의 보 실험체를 제작하였고 강섬유 혼입률을 0, 1 %로 설정하여 실험을 수행하였다. 실험 결과, SFRC 보는 PC 보에 비하여 높은 전단강도를 보였으며 크기 증가에 따른 전단강도의 감소가 상대적으로 낮게 나타났다. 이는 SFRC의 강섬유가 균열면에 가교하여 균열을 효과적으로 제어하기 때문이다. 그러나 현행 설계기준은 이러한 강섬유의 향상된 전단강도와 저감된 크기효과를 충분히 반영하지 못하고 있다. 따라서 SFRC 보의 크기효과를 적절히 반영할 수 있는 새로운 전단강도 제안식이 필요하다. This study experimentally compares the shear strength and size effect of plain concrete (PC) beams and steel fiber-reinforced concrete (SFRC) beams without shear reinforcement. Beam specimens with heights of 350, 650, and 950 mm were fabricated, and steel fiber volume ratios were set at 0 % and 1 %. The experimental results indicated that SFRC beams exhibited higher shear strength compared to PC beams, and the reduction in shear strength due to size increase was relatively lower. This was attributed to the bridging effect of steel fibers across crack faces, effectively controlling crack propagation. However, current design standards do not adequately reflect the enhanced shear strength and reduced size effect provided by steel fibers. Therefore, there is a need for a new shear strength formulation that properly accounts for the size effect in SFRC beams.

Design for shear strength of concrete beams longitudinally reinforced with GFRP bars

Thomas, Job,Ramadassa, S. Techno-Press 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.53 No.1

In this paper, a model for the evaluation of shear strength of fibre reinforced polymer (FRP)-reinforced concrete beams is given. The survey of literature indicates that the FRP reinforced beams tested with shear span to depth ratio less than or equal to 1.0 is limited. In this study, eight concrete beams reinforced with GFRP rebars without stirrups are cast and tested over shear span to depth ratio of 0.5 and 1.75. The concrete compressive strength is varied from 40.6 to 65.3 MPa. The longitudinal reinforcement ratio is varied from 1.16 to 1.75. The experimental shear strength and load-deflection response of the beams are determined and reported in this paper. A model is proposed for the prediction of shear strength of beams reinforced with FRP bars. The proposed model accounts for compressive strength of concrete, modulus of FRP rebar, longitudinal reinforcement ratio, shear span to depth ratio and size effect of beams. The shear strength of FRP reinforced concrete beams predicted using the proposed model is found to be in better agreement with the corresponding test data when compared with the shear strength predicted using the eleven models published in the literature. Design example of FRP reinforced concrete beam is also given in the appendix.

탄소섬유 시트로 휨 보강된 철근 콘크리트 보에서 보 크기와 보강 겹수가 구조 거동에 미치는 영향에 대한 실험 연구

김희선(Kim, Hee-Sun) 대한건축학회 2012 大韓建築學會論文集 : 構造系 Vol.28 No.11

The purpose of this study is to investigate beam size effect on structural behaviors of RC beams strengthened with CFRPs. Toward this goal, RC beams having different sizes are fabricated and strengthened with CFRPs. Beam lengths are 3200㎜ and 4600㎜. Amount of steel bar and CFRP (Carbon Fiber Reinforced Polymers) reinforcements are controlled in order to unify reinforcing ratios of tested beams. From the tests, structural behaviors such as cracks and beam failure modes are observed. Also, displacements and strains on FRPs and reinforcing steel bars are measured from the tests. The experimental results show that CFRP sheet is able to increase load capacity of reinforced concrete beams by 30~50%, however strengthening effect significantly decreases as number of CFRP sheets increases due to debonding failure of the CFRPs. Also, no significant influence by beam sizes can be found from beginning of normalized load-deflection curves. In relatively small sized beams, slight differences are found such that first crack is delayed and interfacial stresses is reduced.

Deep-beams with indirect supports: numerical modelling and experimental assessment

Mário Pimentel,Paulo Cachim,Joaquim Figueiras 사단법인 한국계산역학회 2008 Computers and Concrete, An International Journal Vol.5 No.2

An experimental and numerical research was conducted to gain a deeper insight on the structural behaviour of deep-beams with indirect supports and to assess the size effects in the ultimate state behaviour. The experimental campaign focused on the influence of the reinforcement tie distribution height on the compression check of the support region and on the benefits of using unbonded prestressing steel. Three reduced scale specimens were tested and used to validate the results obtained with a nonlinear finite element model. As a good agreement could be found between the numerical and the experimental results, the numerical model was then further used to perform simulations in large scale deep-beams, with dimensions similar to the ones to be adopted in a practical case. Two sources of size effects were identified from the simulation results. Both sources are related to the concrete quasi-brittle behaviour and are responsible for increasing failure brittleness with increasing structural size. While in the laboratory models failure occurred both in the experimental tests as well as in the numerical simulations after reinforcement yielding, the numerically analysed large scale models exhibited shear failures with reinforcement still operating in the elastic range.