Effects of Deformation Properties on the Bond of Reinforcing Bars

The effects of deformation properties on the bond of steel reinforcing bars to concrete are studied to develop guidelines for commercially produced high relative rib area deformation patterns and accurate equations to predict bond strength. The fundamental behavior of bond is studied using finite element analysis. Beam-end tests are used to investigate the effects of bar size, relative rib area, and the ratio of rib width (measured parallel to the longitudinal axis of the bar) to center-to-center rib spacing on bond strength. 139 specimens containing bars with relative rib areas, R" ranging from 0.05 to 0.28 were tested both with and without transverse stirrups confining the test bar. Bond strength is not affected by Rr for bars not confined by transverse stirrups, but increases as bar size and Rr increase for bars confined by transverse stirrups. Bond strength decreases when the ratio of rib width to center-to-center rib spacing is greater than 0.45. Splice tests are used to investigate the effects of bar size, relative rib area, epoxy coating, and the amount of transverse reinforcement confining the bars on splice strength. Thirty tests of beams containing No. 5 and No. II (16 and 36 mm) bars are combined with sixty-three previously reported tests of beams containing No. 8 (25 nun) bars. The combined results include tests for bars with Rr ranging from 0.065 to 0.140. The results show that splice strength is unaffected by Rr for splices not confined by transverse reinforcement, but increases as bar size and Rr increase for splices confined by transverse reinforcement. Under all conditions of confinement, epoxy coating has a less detrimental effect on the splice strength of high relative rib area bars than on the splice strength of conventional bars. Accurate splice strength equations, that account for the effects of bar size, relative rib area, and epoxy coating on bond strength, are combined with a reliability-based strength reduction factor

Splice Strength of Epoxy-Coated High Relative Rib Area Bars

The effect of epoxy coating on the splice strength of high relative rib area bars with and without confining transverse reinforcement is described. Test results for 47 beam splice specimens containing No. 5, No. 8, or No. 11 (16, 25 or 36 mm) bars with relative rib areas ranging from 0.101 to 0.141 and seven deformation patterns are included in the analysis. Twenty seven of the 47 beam splice tests are reported for the first time. Average coating thickness ranged from 7.1 to 16.8 mils (0.18 to 0.43 mm). Fortythree specimens were bottom-cast and four were top-cast. The test results for the high relative rib area bars are combined with 44 previous splice tests using conventional bars. Epoxy coating was found to have a much less detrimental effect on splice strength for high relative rib area bars than for conventional bars. The average splice strength ratio of coated to uncoated bars C/U is 0.89, compared to 0.74 for conventional reinforcement. C!U is approximately the same for splices with and without transverse reinforcement. The test results of the current study indicate that the development length modification factor required by the ACI Building Code (318-95) and the AASHTO Bridge Specifications (1992) can be reduced from 1.5 to 1.2 for epoxy-coated high relative rib bars

Reliability-Based Strength Reduction Factor For Bond

The formulation and calculation of a reliability-based strength-reduction ( <P) factor for developed and spliced bars is described. Conventional and high relative rib area bars, both with and without confining reinforcement, are considered. The cp-factor is determined using statistically-based expressions for development/splice strength and Monte Carlo simulations of a range of beams. A strength-reduction factor of 0.9 is obtained for the design expressions for development/splice length, based on a probability of failure in bond equal to about one-fifth of the probability of failure in bending or combined bending and compression. <P = 0.9 is incorporated into two expressions for development/splice length in a manner that is transparent to the user. A major advantage of each of the final expressions is that they provide identical values for development and splice length, removing the need to multiply development length by 1.3 or 1.7 to obtain the length of most splices

Splice Strength of High Relative Rib Area Reinforcing Bars

This paper describes the testing and analysis of83 beam-splice specimens containing No. 5, No. 8, and No. 11 ( 16, 25, and 36 mm) bars with relative rib areas (ratio ofprojected rib area nonnal to bar axis to the product of the nominal bar perimeter and the center-to-center rib spacinJ?) ranJ?inJ? from 0.065 to 0.140. Concretes containing two different coarse aggregates were used to evaluate the effect of'ag1veJ?ate properties on bond strength. Sixty specimens contained uncoated bars with confining transverse reinforcement. Thirteen specimens contained uncoated bars without confining reinforcement, and 10 specimens contained epoxv-coated bars, nine without confining reinforcement and one with confining reinfiJrcement. The tests are analyzed to detennine the effect of relati1·e rib area and bar diameter on the increase in bond strength provided by confining reinfiJrcement. The tests also provide a preliminary indication of the effect of high relati1·e rib area on the splice strength of epoxv-coated bars. The splice streni;th of uncoated reinforcement confined by transverse reinf( Jrcement increases with an increase in the relative rib area and the bar diameter of the spliced bars. The increase in splice strength provided by transverse reinforcement increases as the strength of the coarse aggregate increases. The use of reinforcinJ? bars with an averai;e relative rib area of 0.1275, an increase ff-om the average value for conventional bars of'0.0727, can provide up to a 26 percent decrease in splice lenJ?th compared to conventional reinf'orcement when confininJ? reinforcement is used. The savings obtainable with high relative rib area bars is highestf(Jr low covers and bar spacings. Epoxy coating appears to have a less detrimental effect on splice strength for high relative rib area bars than for conventional bars. The results indicate that the maximum development length modification factor used for epoxy-coated reinforcement may be reduced by 20 percent

Development Length Criteria for Conventional and High Relative Rib Area Reinforcing Bars

Statistical analyses of 133 splice and development specimens in which the bars are not confined by transverse reinforcement and 166 specimens in which the bars are confined by transverse reinforcement are used to develop an expression for the bond force at failure as a function of concrete strength, cover, bar spacing, development/splice length, transverse reinforcement, and the geometric properties of the developed/spliced bars. Results are used to formulate design criteria that incorporate a reliability-based strength reduction (f) factor that allows the calculation of a single value for both development and splice length for given material properties and member geometry. As with earlier studies, the analyses demonstrate that the relationship between bond force and development or splice length ld is linear but not proportional. Thus, to increase the bond force (or bar stress) by a given percentage requires more than the percentage increase in ld . f ¢ c 1/2 does not provide an accurate representation of the effect of concrete strength on bond strength over the full range of concrete strengths in use today; development/splice strengths are underestimated for low-strength concretes and overestimated for high-strength concretes. f¢ c 1/4 provides an accurate representation of the effect of concrete strength on bond strength for concretes with compressive strengths between 2500 and 16,000 psi (17 and 110 MPa). The most accurate representation of the effect of transverse reinforcement on bond strength obtained in the current analysis includes parameters that account for the number of transverse reinforcing bars that cross the developed/spliced bar, the area of the transverse reinforcement, the number of bars developed or spliced at one location, the relative rib area of the developed/spliced bar, and the size of the developed/spliced bar. The yield strength of transverse reinforcement does not play a role in the effectiveness of the transverse reinforcement in improving development/splice strength. Depending on the design expression selected, for conventional and high relative rib area bars that are not confined by transverse reinforcement, development lengths average 2 to 14 percent higher and splice lengths 12 to 22 percent lower than those obtained using ACI 318-95. For conventional reinforcing bars confined by transverse reinforcement, development lengths average 5 percent lower to 16 percent higher than those obtained using ACI 318-95, while splice lengths average 11 to 27 percent lower than those obtained using ACI 318-95. For high relative rib area reinforcing bars confined by transverse reinforcement, development lengths average 3 to 17 percent lower than those obtained using ACI 318 95, while splice lengths average 25 to 36 percent lower than those obtained using ACI 318-95. When confined by transverse reinforcement, high relative rib area bars require development and splice lengths that are 13 to 16 percent lower than required by conventional bars

WISE/NEOWISE Observations of Comet 103P/Hartley 2

We report results based on mid-infrared photometry of comet 103P/Hartley 2 taken during 2010 May 4-13 (when the comet was at a heliocentric distance of 2.3 AU, and an observer distance of 2.0 AU) by the Wide-field Infrared Survey Explorer. Photometry of the coma at 22 μm and data from the University of Hawaii 2.2 m telescope obtained on 2010 May 22 provide constraints on the dust particle size distribution, d log n/d log m, yielding power-law slope values of alpha = –0.97 ± 0.10, steeper than that found for the inbound particle fluence during the Stardust encounter of comet 81P/Wild 2. The extracted nucleus signal at 12 μm is consistent with a body of average spherical radius of 0.6 ± 0.2 km (one standard deviation), assuming a beaming parameter of 1.2. The 4.6 μm band signal in excess of dust and nucleus reflected and thermal contributions may be attributed to carbon monoxide or carbon dioxide emission lines and provides limits and estimates of species production. Derived carbon dioxide coma production rates are 3.5(± 0.9) × 10^(24) molecules per second. Analyses of the trail signal present in the stacked image with an effective exposure time of 158.4 s yields optical-depth values near 9 × 10^(–10) at a delta mean anomaly of 0.2 deg trailing the comet nucleus, in both 12 and 22 μm bands. A minimum chi-squared analysis of the dust trail position yields a beta-parameter value of 1.0 × 10^(–4), consistent with a derived mean trail-grain diameter of 1.1/ρ cm for grains of ρ g cm^(–3) density. This leads to a total detected trail mass of at least 4 × 10^(10) ρ kg

Bacterial Gut Symbionts Contribute to Seed Digestion in an Omnivorous Beetle

Obligate bacterial symbionts alter the diets of host animals in numerous ways, but the ecological roles of facultative bacterial residents that colonize insect guts remain unclear. Carabid beetles are a common group of beneficial insects appreciated for their ability to consume insect prey and seeds, but the contributions of microbes to diet diversification in this and similar groups of facultative granivores are largely unknown.Using 16S rRNA gene clone libraries and terminal restriction fragment (tRF) length polymorphism analyses of these genes, we examined the bacterial communities within the guts of facultatively granivorous, adult Harpalus pensylvanicus (Carabidae), fed one of five dietary treatments: 1) an untreated Field population, 2) Seeds with antibiotics (seeds were from Chenopodium album), 3) Seeds without antibiotics, 4) Prey with antibiotics (prey were Acheta domesticus eggs), and 5) Prey without antibiotics. The number of seeds and prey consumed by each beetle were recorded following treatment. Harpalus pensylvanicus possessed a fairly simple gut community of approximately 3-4 bacterial operational taxonomic units (OTU) per beetle that were affiliated with the Gammaproteobacteria, Bacilli, Alphaproteobacteria, and Mollicutes. Bacterial communities of the host varied among the diet and antibiotic treatments. The field population and beetles fed seeds without antibiotics had the closest matching bacterial communities, and the communities in the beetles fed antibiotics were more closely related to each other than to those of the beetles that did not receive antibiotics. Antibiotics reduced and altered the bacterial communities found in the beetle guts. Moreover, beetles fed antibiotics ate fewer seeds, and those beetles that harbored the bacterium Enterococcus faecalis consumed more seeds on average than those lacking this symbiont.We conclude that the relationships between the bacterium E. faecalis and this factultative granivore's ability to consume seeds merit further investigation, and that facultative associations with symbiotic bacteria have important implications for the nutritional ecology of their hosts

International Asteroid Warning Network Timing Campaign : 2019 XS

Peer reviewe

Study of Z boson production in pPb collisions at √sNN=5.02 TeV

The production of Z bosons in pPb collisions at root S-NN = 5.02 TeV is studied by the CMS experiment via the electron and muon decay channels. The inclusive cross section is compared to pp collision predictions, and found to scale with the number of elementary nucleon-nucleon collisions. The differential cross sections as a function of the Z boson rapidity and transverse momentum are measured. Though they are found to be consistent within uncertainty with theoretical predictions both with and without nuclear effects, the forward-backward asymmetry suggests the presence of nuclear effects at large rapidities. These results provide new data for constraining nuclear parton distribution functions

Measurement of differential cross sections in the kinematic angular variable phi* for inclusive Z boson production in pp collisions at root s=8 TeV

Measurements of differential cross sections d sigma/d phi* and double-differential cross sections d(2)sigma/ld phi*d/y/ for inclusive Z boson production are presented using the dielectron and dimuon final states. The kinematic observable phi* correlates with the dilepton transverse momentum but has better resolution, and y is the dilepton rapidity. The analysis is based on data collected with the CMS experiment at a centre-of-mass energy of 8 TeV corresponding to an integrated luminosity of 19.7 fb(-1). The normalised cross section (1/sigma) d sigma/d phi*, within the fiducial kinematic region, is measured with a precision of better than 0.5% for phi* <1. The measurements are compared to theoretical predictions and they agree, typically, within few percent.Peer reviewe