366,898 research outputs found
Effect of reconstituted method on shear strength properties of peat
Peat is an organic soil contains more than 75% organic content. Shear strength of the
soil is one of the most important parameters in engineering design, especially during
the pre-construction and post-construction periods, since used to evaluate the
foundation and slope stability of soil. Peat normally known as a soil that has very
low shear strength and to determine and understand the shear strength of the peat is
difficult in geotechnical engineering because of a few factors such as the origin of
the soil, water content, organic matter and the degree of humification. The aim of this
study was to determine the effective undrained shear strength properties of
reconstituted peat. All the reconstituted peat samples were of the size that passing
opening sieve 0.425mm, 1.000mm, 2.360mm and 3.350mm and were preconsolidated
at pressures of 50 kPa, 80 kPa and 100 kPa. The relationship deviator
stress- strain, σdmax and excess pore water pressure, Δu, shows that in both of
reconstituted and undisturbed peat gradually increased when confining pressure, σ’
and pre- consolidation pressure, σc increased. As a conclusion, the undrained shear
strength properties result obtained shows that the RS3.350 has higher strength than
RS0.425, RS1.000 and RS2.360. However, the entire reconstituted peat sample
shows the increment value of the shear strength with the increment of peat size and
pre- consolidation pressure. For comparison purposes, the undrained shear strength
properties result obtained shows that the reconstituted peat has higher strength than
undisturbed peat. The factors that contributed to the higher shear strength properties
in this study are segregation of peat size, pre- consolidation pressure, initial void
ratio and also the physical properties such as initial water content, fiber content and
liquid limit
Shear tests of litesteel beams with web openings
This paper presents the details of experimental studies on the shear strength of a recently developed, cold-formed steel beam known as LiteSteel Beam (LSB) with web openings. The innovative LSB sections have the beneficial characteristics of torsionally rigid closed rectangular flanges combined with economical fabrication processes from a single strip of high strength steel. They combine the stability of hot-rolled steel sections with the high strength to weight ratio of conventional cold-formed steel sections. The LSB sections are commonly used as flexural members in the building industry. Current practice in flooring systems is to include openings in the web element of floor joists or bearers so that building services can be located within them. Shear behaviour of LSBs with web openings is more complicated while their shear strengths are considerably reduced by the presence of web openings. However, limited research has been undertaken on the shear behaviour and strength of LSBs with web openings. Therefore a detailed experimental study involving 26 shear tests was undertaken to investigate the shear behaviour and strength of different LSB sections. Simply supported test specimens of LSBs with an aspect ratio of 1.5 were loaded at midspan until failure. This paper presents the details of this experimental study and the results. Experimental results showed that the current design rules in cold-formed steel structures design codes (AS/NZS 4600) [1] are very conservative for the shear design of LSBs with web openings. Improved design equations have been proposed for the shear strength of LSBs with web openings based on experimental results from this study
Influence of ceramic (feldspathic) surface treatments on the micro-shear bond strength of composite resin
Objective:
To test the null hypothesis that surface treatment has no influence on the micro-shear bond strength between orthodontic composite resin cement and ceramics (feldspathic porcelain).
Materials and Methods:
Circular specimens of feldspathic porcelain were fabricated and randomly divided into six groups: (1) no treatment; (2) treatment with a mixture of acidic primer and silane agent for 20 seconds; (3) etching with 9.5% hydrofluoric acid; (4) etching with 9.5% hydrofluoric acid and coating with a mixture of acidic primer and silane agent for 20 seconds; (5) airborne-particle abrasion with 50-μm aluminum oxide; and (6) airborne-particle abrasion and coating with a mixture of acidic primer and silane agent for 20 seconds. The porcelain disks were then bonded to resin cylinders with composite resin cement. A micro-shear bond test was carried out to measure the bond strength. Moreover, each ceramic surface was observed morphologically by scanning electron microscopy. One-way analysis of covariance was used to compare the groups for differences in micro-shear bond strength.
Results:
The mean micro-shear bond strength varied as a function of surface treatment. It ranged from 3.7 to 20.8 MPa. The highest values for micro-shear bond strength were found when the surface was acid-etched with hydrofluoric acid and coated with silane. On the other hand, the control group (no treatment) had significantly lower micro-shear bond strength than all the other groups.
Conclusion:
The null hypothesis that the surface treatment has no influence on the micro-shear bond strength of orthodontic composite resin was rejected. The bond strength between ceramics and orthodontic resin cement is affected by the ceramic surface treatment. The bond failure was of the adhesive type, except with the hydrofluoric acid + silane group, where it was a cohesive bond failure
Nucleation in a sheared Ising model: effects of external field
Simulations using the Forward Flux Sampling method have shown a nonmonotonic
de- pendence of the homogeneous nucleation rate on the shear rate for a sheared
two dimensional Ising model [R. J. Allen et al, arXiv cond-mat/0805.3029]. For
quasi-equilibrium systems (i.e. in the absence of shear), Classical Nucleation
Theory (CNT) predicts the dependence of the critical cluster size and the
nucleation rate on the external magnetic field. We investigate the behaviour of
the sheared Ising model as a function of the external field. At low exter- nal
field strength, the same nonmonotonic behaviour holds and the peak in the
nucleation rate is remarkably insensitive to the field strength. This suggests
that the same external field-dependence holds for the enhancement of nucleation
by shear at low shear rates and the suppression of shear at high shear rates.
At high field strength, the nucleation behaviour is qualitatively different. We
also analyse the size and shape of the largest cluster in the transition state
configurations, as a function of the external field. In the sheared system, the
transition state cluster becomes larger and more elongated as the field
strength decreases. We compare our results for the sheared system to the
predictions of the CNT for the quasi- equilibrium case, and find that the CNT
cannot easily be used to describe nucleation in the system under shear
Finite element analyses of lipped chanel beams with web openings in shear
Cold-formed steel members are increasingly used as primary structural elements in buildings due to the availability of thin and high strength steels and advanced cold-forming technologies. Cold-formed lipped channel beams (LCB) are commonly used as flexural members such as floor joists and bearers. Shear behaviour of LCBs with web openings is more complicated and their shear capacities are considerably reduced by the presence of web openings. However, limited research has been undertaken on the shear behaviour and strength of LCBs with web openings. Hence a numerical study was undertaken to investigate the shear behaviour and strength of LCBs with web openings. Finite element models of simply supported LCBs with aspect ratios of 1.0 and 1.5 were considered under a mid-span load. They were then validated by comparing their results with test results and used in a detailed parametric study. Experimental and numerical results showed that the current design rules in cold-formed steel structures design codes are very conservative for the shear design of LCBs with web openings. Improved design equations were therefore proposed for the shear strength of LCBs with web openings. This paper presents the details of this numerical study of LCBs with web openings, and the results
Shear strength analysis of concrete beams reinforced with GFRP bars using strut and tie model
This dissertation presents an experimental investigation on the behavior and
ultimate shear strength of reinforced concrete beam. Sixteen reinforced concrete beams
was design and tested to failure. This study consists of two series of beams, which are
conventional steel reinforced beams (BSN) and reinforced concrete beams with Strut and
Tie Model (STM) using StaadPro software and both result were compared in term of
shear strength. The main test variables were shear span-to-depth ratio (2.1 and 2.9),
percent of longitudinal reinforcement ratio (tension) steel and GFRP (0.6% and 0.9%),
and shear reinforcement ratio (1.5% and 0.6%). The test results revealed that the mode of
failure for all beam is flexural with shear reinforcement characteristics and longitudinal
reinforcement ratio play a critical role in controlling the mode of failure. The
experimental approved that the spacing between shear cracks for the specimens with
larger shear span to depth ratio is greater than the smaller shear span to depth ratio and
while the shear span to depth ratio (a/d) decreases, the shear strength increase. For
longitudinal reinforcement ratio it can be inferred that the higher longitudinal
reinforcement ratio brings the smaller diagonal crack. Also, greater stirrup spacing leads
to the greater diagonal crack, confirming that there is a significant influence of the stirrup
spacing on the spacing between shear cracks. The reason for this behavior is the
decreasing effective concrete area, in which shear crack width is controlled by the stirrup,
and hence the increasing bond effect between the stirrup and the surrounding concrete
Longitudinal shear behavior of several oxide dispersion strengthened alloys
Two commercial oxide dispersion strengthened (ODS) alloys, MA-753 and MA-754, and three experimental ODS alloys, MA-757E, MA-755E, and MA-6000E, were tested in shear at 760 C. Comparisons were made with other turbine blade and vane alloys. All of the ODS alloys exhibited less shear strength than directionally solidified Mar-M 200 = Hf or then conventionally cast B-1900. The strongest ODS alloy tested, MA-755E, was comparable in both shear and tensile strength to the lamellar directionally solidified eutectic alloy gamma/gamma prime - delta. Substantial improvements in shear resistance were found for all alloys tested when the geometry of the specimen was changed from one generating a transverse tensile stress in the shear area to one generating a transverse compressive stress. Finally, 760 C shear strength as a fraction of tensile strength was found to increase linearly with the log of the transverse tensile ductility
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