Main Bar Research Articles

Anchorage of Longitudinal Column Reinforcement in Bridge Monolithic Connections

Most of the existing mechanical models for shear strength and strain calculation of beam-column joints do not explicitly account for bond conditions of the longitudinal reinforcement of the connected members that are anchored inside the joint region. When considered, bond is accounted for through empirical parameters. In this paper, an analytical method for the definition of the strain distribution along the anchorage of the column longitudinal reinforcement inside a bridge monolithic connection is proposed. The anchorage capacity of the main column reinforcement is considered to be affected by two independent mechanisms. The capacity of the first mechanism depends on the average bond stress along the elastic part of the anchorage that is calculated by a mathematical solution without taking into account the beneficial effect of the transverse reinforcement. The capacity of the second mechanism depends on the coefficient of friction arising between main column bars and transverse reinforcement that encloses and restrains the anchorage. The coefficient of friction is empirically set in relation to the position of the transverse bar; either along the elastic part of the anchorage or in the part where yielding penetrates inside the joint. A parametric evaluation of the main design parameters affecting the anchorage capacity is conducted next. The proposed model is finally used in calculating the joint shear response of selected bridge connection specimens for which reported data of strain distribution along anchorages exist. The calculated values correlate successfully with the associated experimental data.

Stress analysis of helicopter main rotor torsion bar

The results of stress analysis for the main rotor torsion bar of the ANSAT helicopter based on the finite element method are presented. The analysis was performed for the base types of loading in the linear statement. The analysis results agree well with the experimental data.

Flexural response of FRC corbels

Abstract A strut-and-tie macro-model is proposed to determine the flexural response of fiber reinforced concrete (FRC) corbels, reinforced with longitudinal bars and subjected to vertical load. The effects of the corbel geometry, the percentage of steel fibers, and grades of concrete and steel bars are also included. The model, which is specific for FRC corbels with hooked steel fibers, allows the determination of load levels, and corresponding displacements, associated with the first cracking, yielding of the main steel bars and crushing of the concrete strut. The sequential occurrence of these phenomena is established, depending on the amounts of steel fibers and reinforcing steel. The simplified flexural response of corbels, in terms of load–deflection curves, is in good agreements with experimental data collected from the literature. In addition, prevision of bearing capacity and failure modes (yielding of main steel or crushing of concrete strut) is obtained with reference to other experimental data collected from the literature. Finally, some recommendations on the design of FRC corbels are given.

Experiment and Analysis of Smart Concrete Beam Strengthened Using Shape Memory Alloy Wires

Shape memory alloy (SMA) has many potential applications as an actuator in smart material systems due to its abilities of shape memory, pseudo-elasticity, high damping and wear resistant. In this paper, a smart concrete beam has been developed by taking advantage of the shape memory effect of SMA and the characteristic of applying large forces on the resisting member in the transformation of SMA on heating. Deformation behavior and influence of factors on the deformation behavior of SAM smart concrete beam were investigated experimentally. Actuation mechanics of SMA was analyzed. Experimental results show that SMA wires significantly increase structural survivability and allow structural to recover from residual deformation by damaged earthquake and typhoon, and the crack almost closes completely after electrically heating the SMA wires. The number or areas of SMA wires has no influence on the tendency of deformation during loading and the tendency of reversion by heating. An increasing of the initial pre-strain of SMA wire can significantly improve the capacity of self-restoration of SMA concrete beams, but the steel main bars play a very negative role in reducing residual deformation.

Embeddable corrosion rate-measuring sensor for assessing the corrosion risk of steel in concrete structures

New and rehabilitated concrete structures need assessment of corrosion rate (CR) of rebars more precisely to ensure efficiency of protection against corrosion. For assessing the corrosion status, different sensors have been developed to reduce the risk of undetected corrosion problems. An embeddable CR-measuring sensor is embedded either closer to the rod during the construction of a new structure or in drilled holes in old structures so as to generate reliable data. In the present paper, the accuracy in predicting the corrosion current (Icorr) by embeddable sensor was assessed by comparing with other conventional electrode arrangements. Icorr was assessed under passive and active conditions of rebar. The presence of a cross bar and the effect of cover on Icorr were also studied. Using linear polarization resistance (LPR) technique and electrochemical impedance spectroscopic (EIS) technique, the CR was determined and compared with the weight-loss method. Results concluded that by using electrochemical impedance technique, developed embeddable sensor is able to predict the CR very close to the CR determined from gravimetric method. The deviation from an ideal linear curve and the higher interfacial capacitance of steel in concrete caused the LPR method to underestimate the CR of rebar. The presence of the cross bar increases the Icorr of the main bar by 4 times in a passive state of the rebar and it has no effect if the rebar is in an active state. The embedded sensor, though having smaller counter electrode (CE), polarizes the rebar up to 2 times the length of CE under both active and passive states. Copyright © 2008 John Wiley & Sons, Ltd.

Where are the stars of the bar of NGC 1530 forming?

Aims. NGC 1530 has one of the strongest bars ever observed and recent star formation sites are distributed across its bar. Our ai m is to study the photometric properties of the bar and its Hii regions, to elucidate the conditions under which Hii regions form and their spatial relation to the principal dynamical features of the bar. Methods. We obtained BVRK s and Hphotometry of the Hii regions of the bar in NGC 1530. Broad-band integrated colours and Hequivalent widths were carefully measured and analysed as a function of position with respect to the main dust-lanes of the bar. Results. We measured differences in the Hequivalent widths of the Hii regions that are located in the trailing and leading sides of the bar dust-lane. The possible factors that could produce this difference, such as (Nii) contamination, Lyman-continuum-photon dust-extinction, escape of ionizing radiation, metallici ty, IMF and age, were carefully analysed. Age differences were confirmed to be the most plausible explanation. This implies that Hii regions that are located further away from the bar dust-lane in its leading side, downstream from the main bar dust-lane, are older than the rest by∼ 1.5− 2.5 Myr. In addition, a clear spatial correlation has been found between: location of Hii regions, dust spurs on the trailing side of the bar dust-lane , and the loci of maximum velocity gradients parallel to the bar major axis (possibly tracing g as flow towards the main bar dust-lane).These results suppor t the hypothesis that massive stars are forming on the trailing side of the bar dust-lane, and age as they cross the bar, on a timescale that i s compatible with the bar dynamics timescale.

Improvement of residual compressive strength and spalling resistance of high-strength RC columns subjected to fire

This paper investigates the spalling properties of high-strength concrete in order to improve the residual compressive strength and spalling resistance in specimens subjected to 3 h of unloading fire conditions. This study consists of three series of experiments with eighteen different specimens varying in fiber type and content, finishing material and simultaneous fiber content and lateral confinement. They were fabricated to a 300 × 300 × 600 mm mock-up size. Results of the fire test showed that the control concrete was explosive, while the specimens that contained more than 0.1 vol% of polypropylene (PP) and polyvinylalcohol (PVA) fibers were prevented from spalling. One specimen, finished by a fire endurance spray, exhibited even more severe spalling than the control concrete. The specimen containing 0.1 vol% of PP fiber and using a confining metal fabric at the same time, showed the most effective spalling resistance; in particular, the residual compressive strength ratio was even higher than that of the control concrete before the fire test. It was demonstrated that adding fibers in concrete prevented the spalling occurrence and confining metal fabric around the main bars of concrete specimens can secure the strength of structures during the conditions of elevated temperature.

Spiral Inflow Feeding the Nuclear Starburst in M83, Observed in Hα Emission with the GHαFaS Fabry-Perot Interferometer

We present observations of the nearby barred starburst galaxy M83 (NGC 5236), with the new Fabry-Perot interferometer GHαFaS mounted on the 4.2 m William Herschel Telescope on La Palma. The unprecedented high-resolution observations, of 16 pc FWHM−1, of the Hα-emitting gas cover the central 2 kpc of the galaxy. The velocity field displays the dominant disk rotation with signatures of gas inflow from kpc scales down to the nuclear regions. At the inner inner Lindblad resonance radius of the main bar and centered at the dynamical center of the main galaxy disk, a nuclear (5.5 ± 0.9) × 108 M☉ rapidly rotating disk with scale length of 60 ± 20 pc has formed. The nuclear starburst is found in the vicinity as well as inside this nuclear disk, and our observations confirm that gas spirals in from the outer parts to feed the nuclear starburst, giving rise to several star formation events at different epochs, within the central 100 pc radius of M83.

STRUCTURAL PERFORMANCE OF PRECAST CONCRETE BEAMS WITH SPLICE-BAR JOINTS OF LONGITUDINAL BARS AT THE MIDSPAN

In this study, bending and shear tests were conducted to understand the seismic performance of reinforced concrete beams formed by joining together two precast beam-end elements at the midspan using cast-in-place concrete with splice-bar joints of main bars. A total of 11 specimens were used, and the parameters were the strength of main bars and cast-in-place concrete, transverse reinforcement spacing and the amount of U-shaped reinforcement in the lap splices region. As a result of the test, a design method for splice-bar joints necessary for flexural yielding of beam ends was developed. Also, a bond splitting strength evaluation method taking into account the effect of U-shaped bars and the influence of the stress gradient, developed by modifying evaluation formulas currently in use, was proposed.

Structural behaviour of three-pile caps subjected to axial compressive loading

This work presents a comparative analysis about the behaviour of pile caps supported by 3 piles subjected to axial loading. Piles with 20 cm and 30 cm diameters were analysed. The main reinforcement was maintained in all the specimens, however, the arrangement of the secondary reinforcement varied. The main reinforcement consisted of steel bars connecting the piles. The secondary reinforcement was made up of: (a) bars going through the piles and through the projection of the column, (b) bars forming a network, and (c) vertical and horizontal stirrups. The main objective was the observation of the pile cap behaviour regarding the cracks and the modes of rupture. The real scale specimens were subjected to experimental tests until failure by rupture. Instruments were placed with the aim to obtain the displacement of the bases, the strains in the main and secondary reinforcement bars, in the compression struts, in the lower and upper nodal zones and in the sides of the caps. None of the caps reached failure by rupture with a load less than 1.12 times the theoretical load. The specimens ruptured due to the cracking of the compression strut and/or the yielding of the reinforcement bars in one direction.

Cruising Tourism - Development Chance of Kotor

Diversification and specialization of the nautical tourism offer, initiated by more and more turbulent changes within the domain of demand preferences in nautical tourism, resulted in the appearance of the types of this aspect of selective tourism, the most prominent of which is cruising tourism. The issue is about new industry on the global tourist market, within which 20 mil. passengers are to be carried in the year 2011. Development of cruising tourism is particularly interesting for Kotor, the tourist destination with valuable natural and anthropogenic tourist resources on the Montenegrin coast. It can become one of the main bars of its economic development in future. However, realization of such scenario requires intensive structural changes in the domain of local and regional tourist product.

Test of Headed Reinforcement in Pullout II: Deep Embedment

A total of 32 pullout tests were performed for the multiple headed bars relatively deeply embedded in reinforced concrete column-like members. The objective was to determine the minimum embedment depth that was necessary to safely design exterior beam-column joints using headed bars. The variables for the experiment were embedment depth of headed bar, center-to-center distance between adjacent heads, and amount of supplementary reinforcement. Regular strength concrete and grade SD420 reinforcing steel were used. The results of the test the indicated that a headed bar embedment depth of <TEX>$10d_b$</TEX> was not sufficient to have relatively closely installed headed bars develop the pullout strength corresponding to the yield strength. All the experimental variables, influenced the pullout strength. The pullout strength increased with increasing embedment depth and head-to-head distance. It also increased with increasing amount of supplementary reinforcement. For a group of closely-spaced headed bars installed in a beam-column joint, it is recommended to use column ties at least 0.6% by volume, 1% or greater amount of column main bars, and an embedment depth of <TEX>$13d_b$</TEX> or greater simultaneously, to guarantee the pullout strength of individual headed bars over 125% of <TEX>$f_y$</TEX> and ductile load-displacement behavior.

A new population of planetary nebulae discovered in the Large Magellanic Cloud - II. Complete PN catalogue

This paper presents accurate homogeneous positions, velocities and other pertinent properties for 460 newly discovered and 169 previously known planetary nebulae (PNe) in the central 25-deg 2 bar region of the Large Magellanic Cloud (LMC). Candidate emission sources were discovered using a deep, high-resolution Ha map of the LMC obtained by median stacking a dozen 2 h Hα exposures taken with the UK Schmidt Telescope (UKST). Our spectroscopic follow-up of more than 2000 compact (i.e. <20 arcsec) Ha emission candidates uncovered has tripled the number of PNe in this area. All of the 169 previously known PNe within this region have also been independently recovered and included in this paper to create a homogeneous data set. Of the newly discovered PNe, we classify 291 as 'true', 54 as 'likely' and 115 as 'possible' based on the strength of photometric and spectroscopic evidence. Radial velocities have been measured using both weighted averaging of emission lines and cross-correlation techniques against high-quality templates. Based on the median comparison of the two systems, we define a measurement error of ±4 km s -1 . A new velocity map of the central 25 deg 2 of the LMC, based on results from the combined new and previously known PNe, is presented, indicating an averaged heliocentric velocity differential of 65 km s -1 perpendicular to the line of nodes for the entire PN population across our survey area. Averaged velocities of our PNe and molecular hydrogen (from the literature) across 37 x 37 arcmin 2 subareas are compared. The PNe are found to have a higher vertical velocity dispersion than the H i disc to a maximum of 10 times the spread of the Hi disc, in keeping with the findings of Meatheringham et al.. In addition, moving out from the main bar, we find that the PN population follows a plane which is somewhat warped in relation to the Hi disc. We estimate the total PN population of the entire LMC system, based on our R equiv Ha limiting magnitude of ∼22, to be 956 ± 141.

The Recent Star Formation in NGC 6822 fromHubble Space TelescopeImaging

We present Hubble Space Telescope WFPC2 and STIS imaging of the low-metallicity galaxy NGC 6822, performed as part of a study of the young stellar populations in the galaxies of the Local Group. Eleven WFPC2 pointings, with some overlap, cover two regions extending over 19 and 13 arcmin2, respectively, off the galaxy center. The filters used are F170W, F255W, F336W, F439W, and F555W. One 25'' × 25'' field observed with the STIS FUV- and NUV-MAMA includes Hodge's OB 8 association and the H II region Hubble V, contained in field 1 of Bianchi et al.; this previous study provides additional WFPC2 four-band photometry. We derive the physical parameters of the stars in the fields and the extinction by comparing the photometry to grids of model magnitudes. The environments studied in this work include one of the most luminous (in Hα) H II regions in the Local Group (Hubble V) with a compact star cluster, a typical OB association (OB 15), the sparse field population, and the outskirts of NGC 6822. In the WFPC2 fields, most of the hot massive stars are found in the Hodge OB 15 association, at about 5' (0.7 kpc) east of the galaxy center, extending ≈90'' (≈200 pc) in our imaging. The color-magnitude diagram indicates a young age, ≤10 Myr, for this association, where we measure 70 stars hotter than ~16,000 K (earlier than mid-B spectral type) according to their photometric colors. In the compact H II region Hubble V, we measure 80 stars brighter than mNUV < 22.5 mag and find most of them to have high temperatures. The density (per unit area) of hot massive stars in the core of the OB 8 association is higher than in OB 15 by a factor of 12, while the total stellar mass formed is similar (≈4 or 7 × 103 M⊙, when extrapolated to a mass range of 1-100 or 0.1-100 M⊙, respectively). In both OB 15 and OB 8 massive star candidates are found. In the general field outside of the OB 15 association, we find few hot massive stars (0.7 arcmin-2) and several A-type supergiants. No massive star candidates are found in the WFPC2 fields outside the main galaxy body (≈105-145 [1.5-2 kpc] from the galaxy center), where the population is dominated by foreground stars, at least down to V ~ 22. At fainter magnitudes, we measure in these outer fields a significantly larger number of stars than the model for Milky Way foreground objects would predict. The average extinction is found to vary among the three environments studied: E(B - V) = 0.22 in the outer regions, E(B - V) = 0.27 in the fields east of the galaxy main bar, and E(B - V) = 0.40 in the H II region Hubble V. A quantitative discussion of the applicability of the reddening-free-index method for photometric determination of stellar parameters is provided for the filters used in this work, based on our grids of stellar models.

K-band observations of boxy bulges - I. Morphology and surface brightness profiles

Kn-band images, unsharp-masked images, as well as major-axis and vertically- summed surface brightness profiles are presented for 30 edge-on spiral galaxies, most with a boxy or peanut-shaped (B/PS) bulge. Such galaxies have more complex morphologies than galaxies of other bulge types, more often showing (off-)centered X structures, secondary major-axis maxima and spiral-like structures. Those features are also observed in N-body simulations of barred discs and may trace the main bar orbit families. The surface brightness profiles of galaxies with a B/PS bulge are also more complex, with typically 3 or more clearly separated regions, including a flat intermediate region (Freeman Type II profiles). Those radial breaks offer evidence for bar-driven transfer of angular momentum and radial redistribution of material. The profiles also suggest a rapid variation of the scaleheight of the disc material, contrary to conventional wisdom but again as expected from vertical resonances and instabilities in barred discs. The steep inner region of the surface brightness profiles is often shorter than the isophotally thick part of the galaxies, itself always shorter than the flat region of the profiles. Contrary to the standard `bulge + disc' model, we thus propose that galaxies with a B/PS bulge are composed of a thin concentrated disc (a disc-like bulge) contained within a partially thick bar (the B/PS bulge) and a thin outer disc. The inner disc likely formed secularly through bar-driven processes and is responsible for the steep inner region of the surface brightness profiles, while the bar is responsible for the flat region and the thick complex morphological structures observed. Those components are strongly coupled dynamically and are formed mostly of the same (disc) material. [Abridged]

The sedimentology and alluvial architecture of the sandy braided South Saskatchewan River, Canada

AbstractGround penetrating radar (GPR) surveys of unit and compound braid bars in the sandy South Saskatchewan River, Canada, are used to test the influential facies model for sandy braided alluvium presented by Cant &amp; Walker (1978). Four main radar facies are identified: (1) high‐angle (up to angle‐of‐repose) inclined reflections, interpreted as having formed at the margins of migrating bars; (2) discontinuous undular and/or trough‐shaped reflections, interpreted as cross‐strata associated with the migration of sinuous‐crested dunes; (3) low‐angle (&lt; 6°) reflections, interpreted as formed by low‐amplitude dunes or unit bars as they migrate onto bar surfaces; and (4) reflections of variable dip bounded by a concave reflection, interpreted as being formed by the filling of channel scours, cross‐bar channels or depressions on the bar surface. The predominant vertical arrangement of facies is discontinuous trough‐shaped reflections at the channel base overlain by discontinuous undular reflections, overlain by low‐angle reflections that dominate the deposits near the bar surface. High‐angle inclined reflections are only found near the surface of unit bars, and are of relatively small‐scale (&lt; 0·5 m), but can be found at a greater range of depths within compound bars. The GPR data show that a high spatial variability exists in the distribution of facies between different compound bars, with facies variability within a single bar being as pronounced as that between bars. Compound bars evolve as an amalgamation of unit bars and other compound bars, and comprise a facies distribution that is representative of the main bar types in the South Saskatchewan River. The GPR data are compared with the original model of Cant &amp; Walker (1978) and reveal a much greater variability in the scale, proportion and distribution of facies than that presented by Cant &amp; Walker (1978). Most notably, high‐angle inclined strata are over‐represented in the model of Cant and Walker, with many bars being dominated by the deposits of low‐ and high‐amplitude dunes. It is suggested that further GPR studies from a range of braided river types are required to properly quantify the full range of deposits. Only by moving away from traditional, highly generalized facies models can a greater understanding of braided river deposits and their controls be established.

Clean technologies and environmental policy WEBWATCH

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主鉄筋の位置ずれ修正がＲＣ部材の力学的挙動に及ぼす影響

It is important to place reinforcing bars accurately as specified on the drawing and secure bars against movement. Actually, bar positions move under the construction work even though the displacements are large or small. Therefore, the bar arrangements have to be modified to the accurate position by bending work of bars where the displacements are over the allowable tolerances. In this study, the effects of mending work of main bars on mechanical behavior of reinforced concrete members are investigated, and inadequate bending works that adversely affect the strength of concrete members are discussed. Where the main bars displaced from specified position are sharply bent to joint new bars at accurate position, main bars are cut by repetition of bending and rebending under alternative low cyclic fatigue load as a seismic load. When the main bars are bent in member which can sustain sufficient load by a wide margin as a foundation, the inclination of main bars for modification is recommended to be less than 1:5 (desirably 1:7) to ensure specified load capacity. Because larger inclinations make the rigidity of member low by pull out of main bars from base member. Modification of main bars from outside to inside to secure effective depth can be allowed even in column member by confirming the inclination for modification under 1:5, the sufficient tie bars at all plastic hinge zones extending to cross section where effective depth is modified to be specified value, the enough tie bars to prevent bent main bars which are going to be straight under force from pushing out concrete cover, and durability changed by thinner cover.

重ね継ぎ手方式による降伏機構分離型鉄筋コンクリート造の開発

This paper presents two types of simplified structures of reinforced concrete hinge isolated systems proposed by one of the authors. One is the splice-bar type which consists of main bars and splice bars of beams. The other is the joint-bar type which consists of joint bars fixing beams and beam-column connections, and main bars of beams. The main bars of the splice-bar type and the joint bars of the joint-bar type are un-bonded at the edge parts of beams. The seismic test results excluding those of the specimens with insufficient arrangement of lap splices of the joint-bar type verified the splendid performance of the two types of structures proposed in this paper: the specimens deformed mainly by the rotation due to the wide crack at the beam-ends without any severe damage in the beams.

耐震スリットを有する鉄筋コンクリート造無開口壁が接合した梁の剛性評価 : 梁主筋端部の抜出しおよび付着劣化が降伏時剛性に及ぼす影響を仮定した場合

In this paper, girders with wall having seismic slits were modeled and a two-dimensional static elasto-plastic finite element analysis was performed. The parameters were girder section, span, main bar, concrete strength, slit wide and wall thickness. 111 models were analyzed. Key observations include the followings:(1) The stiffness K and α_y・K of girder with wall having seismic slit was large.(2) The effect of slit wide for the relationship between shear and relative displacement was small.(3) The effect of wall thickness for the elastic and plastic increasing ratio was small.(4) The effect of concrete strength for the elastic and plastic increasing ratio was small.(5) The elastic and plastic increasing ratio was derived by using the equations (9) and (10).