• Journal of the Korean Wood Science and Technology
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• 제48권2호
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• pp.136-153
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• 2020

In this paper, the influence of initial formaldehyde/urea (F/U) molar ratios on the performance of low molar ratio (1.0) urea-formaldehyde (UF) resin adhesives has been investigated. Two initial F/U molar ratios, i.e., the first and second initial molar ratios were used for the alkaline addition reaction. Three levels of the first initial F/U molar ratios (2.0, 3.0, and 4.0) and two levels of the second initial molar ratios (2.0 and 1.7) were employed to prepare a total of six UF resins with an identical final molar ratio (1.0). The basis properties, functional groups, molecular weight, crystallinity, and thermal curing properties of the UF resins were characterized in detail. Higher levels (3.0 and 4.0) of the first initial F/U molar ratio provided the UF resins with better properties (non-volatile solids content, viscosity, gelation time, pH, and specific gravity) than those of the resins prepared with the conventional level F/U molar ratio of 2.0. Statistical analysis suggested that combining the first and second initial molar ratio of 4.0 with 1.7 would result in UF resins with greater adhesion strength and lower formaldehyde emission than those of the resins prepared with other molar ratios. The results showed that higher levels of the first initial molar ratio resulted in a more branched structure, as indicated by GPC, FTIR, DSC, XRD, and greater adhesion strength than those of the other UF resins with an identical final molar ratio of 1.0.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 가을 학술발표회논문집(I)
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• pp.11-30
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• 2000

Structural properties of reinforced concrete, such as bond and shear strength, that depend on the tensile properties of concrete are much lower for high-strength concrete than would be expected based on relationships developed for normal-strength concretes. To determine the reason for this behavior, studies at the University of Kansas have addressed the effects of aggregate type, water-cementitious material ratio, and age on the mechanical and fracture properties of normal and high-strength concretes. The relationships between compressive strength, flexural strength, and fracture properties were studied. At the time of test, concrete ranged in age from 5 to 180 days. Water-cementitious material ratios ranged from 0.24 to 0.50, producing compressive strengths between 20 MPa(2, 920 psi) and 99 MPa(14, 320psi). Mixes contained either basalt or crushed limestone aggregate, with maximum sizes of 12mm(1/2in). or 19mm(3/4in). The tests demonstrate that the higher quality basalt coarse aggregate provides higher strengths in compression than limestone only for the high-strength concrete, but measurably higher strengths in flexure, and significantly higher fracture energies than the limestone coarse aggregate at all water-cementitious material ratios and ages. Compressive strength, water-cementitious material ratio, and age have no apparent relationship with fracture energy, which is principally governed by coarse aggregate properties. The peak bending stress in the fracture test is linearly related to flexural strength. Overall, as concrete strength increases, the amount of energy stored in the material at the peak tensile load increases, but the ability of the material to dissipate energy remains nearly constant. This suggests that, as higher strength cementitious materials are placed in service, the probability of nonductile failures will measurably increase. Both research and educational effort will be needed to develop strategies to limit the probability of brittle failures and inform the design community of the nature of the problems associated with high-strength concrete.

• Structural Engineering and Mechanics
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• 제64권5호
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• pp.621-640
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• 2017

This paper reports the numerical investigation conducted to study the influence of Local-Distortional (L-D) interaction mode buckling on post buckling strength erosion in fixed ended lipped channel cold formed steel columns. This investigation comprises of 81 column sections with various geometries and yield stresses that are carefully chosen to cover wide range of strength related parametric ratios like (i) distortional to local critical buckling stress ratio ($0.91{\leq}F_{CRD}/F_{CRL}{\leq}4.05$) (ii) non dimensional local slenderness ratio ($0.88{\leq}{\lambda}_L{\leq}3.54$) (iii) non-dimensional distortional slenderness ratio ($0.68{\leq}{\lambda}_D{\leq}3.23$) and (iv) yield to non-critical buckling stress ratio (0.45 to 10.4). The numerical investigation is carried out by conducting linear and non-linear shell finite element analysis (SFEA) using ABAQUS software. The non-linear SFEA includes both geometry and material non-linearity. The numerical results obtained are deeply analysed to understand the post buckling mechanics, failure modes and ultimate strength that are influenced by L-D interaction with respect to strength related parametric ratios. The ultimate strength data obtained from numerical analysis are compared with (i) the experimental tests data concerning L-D interaction mode buckling reported by other researchers (ii) column strength predicted by Direct Strength Method (DSM) column strength curves for local and distortional buckling specified in AISI S-100 (iii) strength predicted by available DSM based approaches that includes L-D interaction mode failure. The role of flange width to web depth ratio on post buckling strength erosion is reported. Then the paper concludes with merits and limitations of codified DSM and available DSM based approaches on accurate failure strength prediction.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 가을 학술발표회 논문집
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• pp.147-152
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• 2001

The purpose of this study is to ascertain the strength properties of water-permeable polymer concretes with SBR latex and redispersible polymer powder. The water-permeable polymer concretes using SBR latex and redispersible polymer powder with water-binder ratio of 29%, polymer-cement ratios of 0, 5, 10, 15 and 20% are prepared, and tested for compressive strength, tensile strength, flexural strength, water permeability. From the test results, improvements in the strength properties of the water-permeable polymer concretes due to the addition of the SBR latex and redispersible polymer powder are discussed.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.494-497
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• 2004

This paper presents the analysis results predicted by the upper bound approach in the limit analysis of concrete incorporating the original plastic and crack sliding solutions for short high-strength concrete beams that varied the compressive strength of concrete, and the shear span-to-depth and vertical shear reinforcement ratios. The significance of the distance away from the support to define the location where the yield line starts and the properties of cracked concrete, particularly related to high-strength concrete, is identified.

• 대한기계학회논문집B
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• 제27권7호
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• pp.920-928
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• 2003

The objective of the present study was to investigate the characteristics of flow and wall shear stress under steady and pulsatile flow in the aneurysm. The numerical simulation using the software were carried out for the diameter ratios ranging from 1.5 to 3.0, Reynolds number ranging from 900 to 1800 and Womersley number, 15.47. For steady flow, it was shown that a recirculating vortex occupied the entire bulge with its core located closer to the distal end of the bulge and the strength of vortex increased with increase of the Reynolds number and diameter ratio. The position of a maximum wall shear stress was the distal end of the aneurysm regardless of the Reynolds number and diameter ratios. For the pulsatile flow, a recirculating flow at the bulge was developed and disappeared for one period and the strength of vortex increased with the diameter ratio. The maximum values of the wall shear stress increased in proportion to the diameter ratio. However, the position of a maximum wall shear stress was the distal end of the aneurysm regardless of the diameter ratios.

• 한국구조물진단유지관리공학회 논문집
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• 제7권2호
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• pp.201-208
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• 2003

In domestic, bearing wall apartment building have not rectangular walls but irregular walls which are designed at walls of various cross-sectional shapes such as H-shaped, T-shaped, Box-shaped and L-shaped. In these irregular walls connected with rigid joint each other, one side walls of irregular walls is expected to show effective behavior for rigid-jointed the other side walls. Moreover, previous studies have focused on simplifying irregular walls into rectangular walls because of the complication in structural design and analysis. So studies for variables affecting behaviors of irregular walls, such as aspect ratios and compressive strength of concrete, are insufficient. The objective of this study is to evaluate the behaviors of T-shaped structural walls with different concrete compressive strengths and aspect ratios by experimental works. Results of this experimental study show that flange wall is contributed to increase the flexural strengths by the variation of concrete strengths and aspect ratios, and that it is needed to evaluate the effect width of flange wall for rational wall design.

• Computers and Concrete
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• 제21권3호
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• pp.231-237
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• 2018

A strain-hardening highly ductile composite based on an alkali-activated slag binder and synthetic fibers is a promising construction material due to its excellent tensile behavior and owing to the ecofriendly characteristics of its binder. This study investigated the effect of different types of synthetic fibers and water-to-binder ratios on the compressive strength and tensile behavior of slag-based cementless composites. Alkali-activated slag was used as a binder and water-to-binder ratios of 0.35, 0.45, and 0.55 were considered. Three types of fibers, polypropylene fiber, polyethylene (PE) fiber, and polyparaphenylene-benzobisethiazole (PBO) fiber, were used as reinforcing fibers, and compression and uniaxial tension tests were performed. The test results showed that the PE fiber series composites exhibited superior tensile behavior in terms of the tensile strain capacity and crack patterns while PBO fiber series composites had high tensile strength levels and tight crack widths and spacing distances.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 가을 학술발표회 논문집(I)
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• pp.1-6
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• 1998

Recently, as to destruction and renovation of aged building, waste concretes have been reclaimed near foreshore and filled up underground. Recycling demolished concrete as aggregate helps to settle economic and environmental problems of obtaining superior aggregates from natural sources and to dispose waste concretes. An experimental study was carried out to investigate the strength characteristics of no-fine concrete containing recycled aggregates. The cement-aggregate weight ratios of 1: 5, 1: 6, 1: 7 and water-cement ratios of 30, 35, 40, 45% were chosen for the mix design of no-fine concretes. The compressive and splitting tensile strength at 7 and 28 days were measured for 12 different mixes. On the basis of test results, the optimum mix proportion of no-fine concrete containing recycled aggregates was determined and applied to the production of retaining wall block.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 추계 학술발표회 제17권2호
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• pp.777-780
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• 2005

The paper presents details of an investigation into the effect of sand content upon the strength and shrinkage of mortar. This strategy was to produces more durable strength mortar with less cement. Cement mortars containing $20\;wt.\;\%$ Class F fly ash, and/or $6\;wt.\;\%$ silica fume were prepared at a water/binder ratio of 0.45 and sand/binder ratios of 2.0, 2.5, 2.7, and 3.0. The increase in sand/binder ratio caused a decrease in the mortar flow. However, the sand/binder ratio did not affect the strength development. Drying shrinkage decreased with increasing the sand contents.