• 복합신소재구조학회 논문집
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• 제4권1호
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• pp.33-39
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• 2013

Structural insulated panels, structurally performed panels consisting of a plastic insulation bonded between two structural panel facings, are one of emerging products with a viewpoint of its energy and construction efficiencies. These components are applicable to fabricated wood structures. In Korea, there are few technical documents regulated structural performance and engineering criteria in domestic market. This study was conducted to identify fundamental performance of both monotonic load and quasi static cyclic load for SIPs in shear wall application. Static test results showed that maximum load was 44.3kN, allowable shear load was 6.1kN/m, shear stiffness was 1.23 M N/m, and ductility ratio was 3.6. Cyclic test was conducted by two kinds of specimens : single panel and double panels. Cyclic test results, which were equivalent to static test results, showed that maximum load was 45.42kN, allowable shear load was 6.3kN/m. Furthermore the accumulated energy dissipation capability for double panels was as 2.3 times as that for single panel. From performance of structural tests, it was recommended that the allowable shear load for panels was at least 6.1kN/m.

• Earthquakes and Structures
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• 제7권5호
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• pp.647-665
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• 2014

Squat reinforced concrete walls require enough shear strength in order to promote flexural yielding, which creates the need for designers of an accurate method for strength prediction. In many cases, especially for existing buildings, strength estimates might be insufficient when more accurate analyses are needed, such as pushover analysis. In this case, estimates of load versus displacement are required for building modeling. A model is developed that predicts the shear load versus shear deformation of squat reinforced concrete walls by means of a panel formulation. In order to provide a simple, design-oriented tool, the formulation considers the wall as a single element, which presents an average strain and stress field for the entire wall. Simple material constitutive laws for concrete and steel are used. The developed models can be divided into two categories: (i) rotating-angle and (ii) fixed-angle models. In the first case, the principal stress/strain direction rotates for each drift increment. This situation is addressed by prescribing the average normal strain of the panel. The formation of a crack, which can be interpreted as a fixed principal strain direction is imposed on the second formulation via calibration of the principal stress/strain direction obtained from the rotating-angle model at a cracking stage. Two alternatives are selected for the cracking point: fcr and 0.5fcr (post-peak). In terms of shear capacity, the model results are compared with an experimental database indicating that the fixed-angle models yield good results. The overall response (load-displacement) is also reasonable well predicted for specimens with diagonal compression failure.

• 대한토목학회논문집
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• 제32권5C호
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• pp.199-210
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• 2012

본 연구에서는 3차원 탄-소성 유한차분해석을 통해 기존재하는 단독말뚝, $3{\times}3$및 $5{\times}5$ 군말뚝의 바로 아래 풍화암 지반에서 실시된 터널시공으로 인한 말뚝의 거동을 분석하였다. 수치해석에서는 터널굴착으로 인한 말뚝의 거동을 규명하기 위하여 지반/말뚝의 침하 및 전단응력전이(shear stress transfer) 메커니즘을 심도있게 분석하였다. 터널굴착으로 유발된 지반의 침하와 말뚝-지반 사이 경계면에서의 상대변위 발생으로 인해 말뚝에 작용하는 전단응력 및 축력의 분포가 매우 크게 변화하였다. 계산된 결과에 의하면 터널굴착으로 인해 말뚝의 두부로부터 말뚝길이의 약 80%에 해당되는 위치까지는 상향의 전단응력이 발생하였고, 그 하부에서는 하향의 전단응력이 발생하였다. 이로 인해 말뚝의 축력이 터널의 굴착에 따라 지속적으로 감소하고, 순수한 터널의 시공으로 인하여 말뚝에는 인장력이 발생하였는데 이로 인해 말뚝에는 최대 $0.36P_a$의 인장력이 발생하였다, 여기서 $P_a$는 터널굴착이전에 말뚝두부에 작용하는 설계하중이다. 말뚝의 거동은 경계면에서의 전단강도 발현 정도에 가장 큰 영향을 받는 것으로 나타났다. 군말뚝의 경우 일반적으로 말뚝의 숫자가 증가할수록 터널의 시공에 의해 말뚝의 침하가 증가하는 것으로 나타났으며, 이와는 반대로 말뚝의 축력변화는 군효과(shielding effect)로 인해 단독말뚝의 경우에 비해 작은 것으로 분석되었다. 터널굴착으로 인한 말뚝침하의 증가로 인한 겉보기지지력(apparent pile capacity) 감소는 단독말뚝에 비해 군말뚝에서 두드러지는 것으로 분석되었다.

• Composites Research
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• 제17권4호
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• pp.40-46
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• 2004

본 연구에서는 single lap 전단시험을 통해 자가치료제와 촉매의 혼합비율 및 경화온도가 자가치료용 폴리머 복합재에 적용되는 자가치료제의 접착성능에 미치는 영향을 조사하였다. 자가치료세로는 DCPD (dicyclopentadiene), ENB(5-ethylidene-2-norbornene), DCPD와 ENB가 혼합된 경우를 고려하였으며 촉매로는 bis(riclohexylphosphine) benzyllidine rethenium (IV) dichloride Grubbs' catalyst를 사용하였다. 이때 DCPD에 대한 촉매의 혼합비율은 1.0wt%와 0.5wt%, ENB에 대한 촉매의 혼합비율은 0.lwt%, DCPD와 ENB의 혼합액에 대한 촉매의 혼합비율은 0.5wt%를 적용하였으며 경화온도는 $25^{\circ}C$, $60{\circ}C$, $80^{\circ}C$를 고려하였다. 연구결과에 따르면 DCPD의 경우 안정화된 접착강도를 얻기 위해서는 많은 양의 촉매와 긴 경화시간이 요구되었다 ENB의 경우는 DCPD의 경우에 비해 촉매의 혼합비율이 낮아도 빠른 경화반응을 얻을 수 있었지만 경화시간이 증가함에 따라 접착전단강도는 DCPD와는 달리 최대 값에 도달하였다가 점차 감소하면서 안정화되는 양상을 나타내었다. DCPD와 ENB의 혼합액 경우도 ENB와 유사한 경화거동을 나타내며 DCPD에 대한 ENB의 혼합비율이 높을 수록 경화반응이 빨라지는 양상을 얻을 수 있었다. 아울러 경화온도가 높을수록 집착전단강도는 증가되며 안정화된 평탄부에 도달하는 경화시간은 짧아짐을 알 수 있었다

• 터널과지하공간
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• 제4권3호
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• pp.261-273
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• 1994

Direct shear tests were carried out on the rock joints and artificial discontinuities to investigate the influence of joint roughness on the shear strength and deformation behaviour. Single direct shear testing apparatus used in experiment was designed and manufactured. Its capacity is 200 tons of shear load, 20 tons of normal load and 50$\textrm{cm}^2$ of maximum shear area. Test samples were cement mortar with artificial discontinuity and sandstone with natural joint. Peak shear strength was increased as joint roughness or normal stress was increased, especially, linearly increased with roughness angle in cement mortar. If joint roughness angle was constant at low normal stress, shear strength was not affected by width and height of joint roughness in cement mortar. Peak shear strengths obtained from tests were larger than the values calculated by Barton's equation, and shear stiffness was increased with joint roughness coefficient.

• Structural Engineering and Mechanics
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• 제56권6호
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• pp.983-1001
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• 2015

This study focuses on the load carrying capacity and the force transfer mechanism of multi-hole perfobond shear connectors in steel-concrete composite structure. The behavior of multi-hole perfobond shear connector is more complicated than single-hole connector cases. 2 groups push-out tests were conducted. Based on the test results, behavior of the connection was analyzed and the failure mechanism was identified. Simplified iterative method and analytic solution were proposed based on force equilibrium for analyzing multi-hole perfobond shear connector performance. Finally, the sensitivity of design parameters of multi-hole perfobond shear connector was investigated. The results of this research showed that shear force distribution curve of multi-hole perfobond shear connector is near catenary. Shear forces distribution were determined by stiffness ratio of steel to concrete member, stiffness ratio of shear connector to steel member, and number of row. Efficiency coefficient was proposed to should be taking into account in different limit state.

• The Journal of Advanced Prosthodontics
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• 제9권5호
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• pp.350-357
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• 2017

PURPOSE. The object of the present study was to evaluate the shear bonding strength of composite to PEKK by applying several methods of surface treatment associated with various bonding materials. MATERIALS AND METHODS. One hundred and fifty PEKK specimens were assigned randomly to fifteen groups (n = 10) with the combination of three different surface treatments (95% sulfuric acid etching, airborne abrasion with $50{\mu}m$ alumina, and airborne abrasion with $110{\mu}m$ silica-coating alumina) and five different bonding materials (Luxatemp Glaze & Bond, Visio.link, All-Bond Universal, Single Bond Universal, and Monobond Plus with Heliobond). After surface treatment, surface roughness and contact angles were examined. Topography modifications after surface treatment were assessed with scanning electron microscopy. Resin composite was mounted on each specimen and then subjected to shear bond strength (SBS) test. SBS data were analyzed statistically using two-way ANOVA, and post-hoc Tukey's test (P<.05). RESULTS. Regardless of bonding materials, mechanical surface treatment groups yielded significantly higher shear bonding strength values than chemical surface treatment groups. Unlike other adhesives, MDP and silane containing self-etching universal adhesive (Single Bond Universal) showed an effective shear bonding strength regardless of surface treatment method. CONCLUSION. Mechanical surface treatment behaves better in terms of PEKK bonding. In addition, self-etching universal adhesive (Single Bond Universal) can be an alternative bonding material to PEKK irrespective of surface treatment method.

• 한국분무공학회지
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• 제25권3호
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• pp.95-102
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• 2020

Six shear coaxial injectors for a 3 tonf-class liquid rocket engine using oxygen and methane as propellants were designed and manufactured by considering geometric design parameters such as a recess length and a taper angle. Cold-flow tests on the injectors were performed using water and air as simulants. By changing the water mass flow rate and air mass flow rate, the injection pressure drop under single-injection and bi-injection was measured. The discharge coefficients through the injector oxidizer-side and fuel-side were calculated and the discharge coefficient ratio between bi-injection and single-injection was obtained. Under single-injection, the recess served to reduce the injection pressure drop on the injector fuel-side. For the injectors without recess, the discharge coefficients under bi-injection were almost the same as those under single-injection. However, for the injectors with recess, the taper angle and bi-injection had a significant effect on the discharge coefficient.

• 한국재료학회지
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• 제27권12호
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• pp.679-687
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• 2017

A strain-gradient crystal plasticity finite element method(SGCP-FEM) was utilized to simulate the compressive deformation behaviors of single-slip, (111)[$10{\bar{1}}$], oriented FCC single-crystal micro-pillars with two different slip-plane inclination angles, $36.3^{\circ}$ and $48.7^{\circ}$, and the simulation results were compared with those from conventional crystal plasticity finite element method(CP-FEM) simulations. For the low slip-plane inclination angle, a macroscopic diagonal shear band formed along the primary slip direction in both the CP- and SGCP-FEM simulations. However, this shear deformation was limited in the SGCP-FEM, mainly due to the increased slip resistance caused by local strain gradients, which also resulted in strain hardening in the simulated flow curves. The development of a secondly active slip system was altered in the SGCP-FEM, compared to the CP-FEM, for the low slip-plane inclination angle. The shear deformation controlled by the SGCP-FEM reduced the overall crystal rotation of the micro-pillar and limited the evolution of the primary slip system, even at 10 % compression.

• Computers and Concrete
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• 제32권3호
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• pp.313-326
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• 2023

The seismic safety of the shear wall structure can be assessed through seismic fragility analysis, which requires high computational costs in estimating seismic demands. Accordingly, machine learning methods have been applied to such fragility analyses in recent years to reduce the numerical analysis cost, but it still remains a challenging task. Therefore, this study uses the ensemble machine learning method to present an improved framework for developing a more accurate seismic demand model than the existing ones. To this end, a rank-based selection method that enables determining an excellent model among several single machine learning models is presented. In addition, an index that can evaluate the degree of overfitting/underfitting of each model for the selection of an excellent single model is suggested. Furthermore, based on the selected single machine learning model, we propose a method to derive a more accurate ensemble model based on the bagging method. As a result, the seismic demand model for which the proposed framework is applied shows about 3-17% better prediction performance than the existing single machine learning models. Finally, the seismic fragility obtained from the proposed framework shows better accuracy than the existing fragility methods.