• Restorative Dentistry and Endodontics
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• 제48권3호
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• pp.30.1-30.11
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• 2023

Objectives: This study verified the possibility of cementing fiberglass-reinforced posts using a flowable bulk-fill composite (BF), comparing its push-out bond strength and microhardness with these properties of 3 luting materials. Materials and Methods: Sixty endodontically treated bovine roots were used. Posts were cemented using conventional dual-cured cement (CC); self-adhesive cement (SA); dual-cured composite (RC); and BF. Push-out bond strength (n = 10) and microhardness (n = 5) tests were performed after 1 week and 4 months of storage. Two-way repeated measures analysis of variance (ANOVA), 1-way ANOVA, t-test, and Tukey post-hoc tests were applied for the push-out bond strength and microhardness results; and Pearson correlation test was applied to verify the correlation between push-out bond strength and microhardness results (α = 0.05). Results: BF presented higher push-out bond strength than CC and SA in the cervical third before aging (p < 0.01). No differences were found between push-out bond strength before and after aging for all the luting materials (p = 0.84). Regarding hardness, only SA presented higher values measured before than after aging (p < 0.01). RC and BF did not present 80% of the maximum hardness at the apical regions. A strong positive correlation was found between the luting materials' push-out bond strength and microhardness (p < 0.01, R² = 0.7912). Conclusions: The BF presented comparable or higher push-out bond strength and microhardness than the luting materials, which indicates that it could be used for cementing resin posts in situations where adequate light curing is possible.

• 한국강구조학회 논문집
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• 제14권1호
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• pp.113-120
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• 2002

프리캐스트 바닥판 합성형 교량의 전단연결부는 전단포켓과 베딩층이 존재하여 현장타설 강합성 교량과는 다른 구조적 특징을 갖고 있다. 따라서 프리캐스트 바닥판의 전단연결재 설계의 기초를 수립하기 위해서는 실험을 통한 연구가 수행되어야 한다. 프리캐스트 바닥판 합성형 교량의 전단연결재의 피로수명을 평가하기 위하여 베딩층의 두께를 변수로 한 전단연결재의 push-out 피로 시험을 수행하였다. push-out 피로 시험의 수행 결과, 전단연결재의 파괴모드를 확인하였고, 이를 통해 프리캐스트 바닥판 합성형 교량의 전단연결재의 피로수명 곡선식을 유도하였다.

• Steel and Composite Structures
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• 제27권5호
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• pp.537-543
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• 2018

Mechanical shear connectors are commonly used to transfer longitudinal shear forces across the steel-concrete interface in composite beams. Steel pipe as a new shear connector is proposed in this research and its performance to achieve composite strength is investigated. Experimental monotonic push-out tests were carried out for this connector. Then, a nonlinear finite element model of the push-out specimens is developed and verified against test results. Further, the finite element model is used to investigate the effects of pipe thickness, length and diameter on the shear strength of the connectors. The ultimate strengths of these connectors are reported and their respective failure modes are discussed. This paper comprises of the push-out tests of ten specimens on this shear connector in both the vertical and horizontal positions in different reinforced concretes. The results of experimental tests are given as load-deformation plots. It is concluded that the use of these connectors is very effective and economical in the medium shear demand range of 150-350 KN. The dominant failure modes observed were either failure of concrete block (crushing and splitting) or shear failure of pipe connector. It is shown that the horizontal pipe is not as effective as vertical pipe shear connector and is not recommended for practical use. It is shown that pipe connectors are more effective in transferring shear forces than channel and stud connectors. Moreover, based on the parametric study, a formula is presented to predict the pipe shear connectors' capacity.

• Steel and Composite Structures
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• 제43권4호
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• pp.511-522
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• 2022

An experimental investigation to study the behaviour of connections between cold-formed steel (CFS) joist and plywood structural panel is presented in this paper. Material testing on CFS and plywood was carried out to assess their mechanical properties and behaviour. Push-out tests were conducted to determine the slip modulus and failure modes of three different shear connection types. The employed shear connectors in the study were; size 14 (6mm diameter) self-drilling screw, M12 coach screw, and M12 nut and bolt. The effective bending stiffness of composite cold-formed steel and plywood T-beam assembly is calculated based on the slip modulus values computed from push-out tests. The effective bending stiffness was increased by 25.5%, 18% and 30.2% for self-drilling screw, coach screw, nut and bolt, respectively, over the stiffness of cold-formed steel joist alone. This finding suggests the potential to enhance the structural performance of composite cold-formed steel and timber flooring system by mobilisation of composite action present between timber sheathing and CFS joist.

• Steel and Composite Structures
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• 제35권4호
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• pp.475-494
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• 2020

Presented are experimental results from 24 full-scale push test specimens to study the behaviour of composite beams with trapezoidal profiled sheeting laid transverse to the beam axis. The tests use a single-sided horizontal push test setup and are divided into two series. First series contained shear loading only and the second had normal load besides shear load. Four parameters are studied: the effect of wire mesh position and number of its layers, placing a reinforcing bar at the bottom flange of the deck, normal load and its position, and shear stud layout. The results indicate that positioning mesh on top of the deck flange or 30 mm from top of the concrete slab does not affect the stud's strength and ductility. Thus, existing industry practice of locating the mesh at a nominal cover from top of the concrete slab and Eurocode 4 requirement of placing mesh 30 mm below the stud's head are both acceptable. Double mesh layer resulted in 17% increase in stud strength for push tests with single stud per rib. Placing a T16 bar at the bottom of the deck rib did not affect shear stud behaviour. The normal load resulted in 40% and 23% increase in stud strength for single and double studs per rib. Use of studs only in the middle three ribs out of five increased the strength by 23% compared to the layout with studs in first four ribs. Eurocode 4 and Johnson and Yuan equations predicted well the stud strength for single stud/rib tests without normal load, with estimations within 10% of the characteristic experimental load. These equations highly under-estimated the stud capacity, by about 40-50%, for tests with normal load. AISC 360-16 generally over-estimated the stud capacity, except for single stud/rib push tests with normal load. Nellinger equations precisely predicted the stud resistance for push tests with normal load, with ratio of experimental over predicted load as 0.99 and coefficient of variation of about 8%. But, Nellinger method over-estimated the stud capacity by about 20% in push tests with single studs without normal load.

• The Journal of Advanced Prosthodontics
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• 제7권1호
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• pp.15-20
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• 2015

PURPOSE. The aim of this study was to evaluate whether the push-out bond strength varies between oval and circular fiber posts, and to examine the effect on the resin cement thicknesses around the posts. MATERIALS AND METHODS. Eighteen mandibular premolar roots were separated into two groups for oval and circular fiber posts systems. Post spaces were prepared and fiber posts were luted to the post spaces. Roots were cut horizontally to produce 1-mm-thick specimens. Resin cement thicknesses were determined with a metallographic optical microscope and push-out tests were done. RESULTS. No significant differences were observed in terms of push-out bond strength between the oval and circular fiber posts (P>.05) The resin cement thicknesses of the oval posts were greater than those of the circular posts group in the coronal, middle and apical specimens (P<.05). CONCLUSION. In the light of these results, it can be stated that resin cement thickness does not affect the push-out bond strength.

• Steel and Composite Structures
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• 제7권5호
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• pp.391-404
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• 2007

This paper presents push-out tests of stud shear connectors to examine their fatigue behavior for developing a new composite bridge deck system. The fifteen push-out specimens of D16 mm stud welded on 9 mm steel plate were fabricated according to Eurocode-4, and a series of fatigue endurance test and residual strength test were performed. Additionally, the stiffness and strength variations by cyclic loading were compared. The push-out test, when the stiffness reduction ratio of the specimens was 0.95 under cyclic load, resulted in the failure of the studs. The stiffness variation of the push-out specimens additionally showed that the application of cyclic loads reduced the residual strength. The fatigue strength of the shear connectors were compared with the design values specified in the Eurocode-4, ASSHTO LRFD and JSSC codes. The comparison result showed that the fatigue endurance of the specimens satisfies the design values of these codes.

• Steel and Composite Structures
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• 제49권2호
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• pp.197-213
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• 2023

To investigate the static properties of large high strength bolt shear connector in hybrid fiber-reinforced concrete (HFRC) and normal concrete (NC), eight push-out test specimens with single/double nut and HFRC/NC slabs were designed and push-out tests were conducted. A fine 3D nonlinear finite element (FE) model including HFRC constitutive model was established by using ANSYS 18.0, and the test results were used to verify FE models of the push-out test specimens. Then a total of 13 FE models were analyzed with various parameters including fiber volume fractions of HFRC, bolt diameter and thickness of steel flange. Finally, the empirical equations considering the contribution of polypropylene fiber (PF) and steel fiber (SF) obtained from the regression of the test results and FE analysis were recommended to evaluate the load-slip curve and ultimate capacity of the large high strength bolt shear connector embedded in HFRC/NC.

• Steel and Composite Structures
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• 제33권6호
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• pp.823-836
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• 2019

Spiral welded tubes (SWTs) are fabricated by helically bending a steel plate and welding the resulting abutting edges. The cost-effectiveness of concrete-filled steel tube (CFST) columns can be enhanced by utilising such SWTs rather than the more conventional longitudinal seam welded tubes. Even though the steel-concrete interface bond strength of such concrete-filled spiral-welded steel tubes (CF-SWSTs) is an important consideration in relation to ensuring composite behaviour of such elements, especially at connections, it has not been investigated in detail to date. CF-SWSTs warrant separate consideration of their bond behaviour to CFSTs of other tube types due to the distinct weld seam geometry and fabrication induced surface imperfection patterns of SWTs. To address this research gap, axial push-out tests on forty CF-SWSTs were carried out where the effects of tube material, outside diameter (D), outside diameter to wall thickness (D/t), length of the steel-concrete interface (L) and concrete strength grade (f'_c) were investigated. D, D/t and L/D values in the range 102-305 mm, 51-152.5 and 1.8-5.9 were considered while two nominal concrete grades, 20 MPa and 50 MPa, were used for the tests. The test results showed that the push-out bond strengths of CF-SWSTs of both mild-steel and stainless-steel were either similar to or greater than those of comparable CFSTs of other tube types. The bond strengths obtained experimentally for the tested CF-SWSTs, irrespective of the tube material type, were found to be well predicted by the guidelines contained in AISC-360.

• 한국강구조학회 논문집
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• 제17권6호통권79호
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• pp.737-747
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• 2005

강재 보와 콘크리트 슬래브로 구성되어 지는 합성보에서 두 부재는 일반적으로 전단연결재에 의해 서로 합성되어져 일체적인 구조거동을 하게 된다. 현재까지 전단연결재로서는 스터드(stud)가 널리 사용되어지고 있다. 합성보의 구조적 거동은 사용된 부재의 재료적 특성 외에도 스터드에 의한 전단합성작용에 의해 많은 영향을 받게 된다. 합성보 전단연결부에서의 전단합성거동은 합성보에서가 아닌 단순화된 Push-Out 시험체(Push-Out Test Specimen)에 의해 실험적으로 결정되고 있다. 최근의 연구결과에 따르면, Push-Out 실험에서 얻은 전단 스터드의 합성거동과 실제 합성보에서의 전단합성거동에는 분명한 차이점이 존재하며, 특히 부분합성된 합성보에서는 그 차이가 매우 크다는 것이 밝혀지고 있다. 본 연구에서는 표준 Push-Out 시험체 및 합성보의 구조거동 해석을 위해, Push-Out 실험으로부터 결정되는 스터드에 대한 하중-상대변위 곡선의 도입이 필요 없는 3차원 유한요소모델을 개발하였다. 해석결과의 비교 분석으로부터 합성보 전단연결부에서의 합성거동을 평가할 수 있었고, 이를 Push-Out 실험결과와 비교하여 보았으며 전단합성거동의 차이점에 대한 구체적 원인을 찾을 수 있었다.