Main Bar Research Articles

Fatigue Performance Evaluation of Existing Concrete Girder Bridges

Main steel bars and prestressed strands in critical parts of existing concrete girder bridges are at risk of fatigue and fracture under the combined action of heavy truck loads, increased traffic volume and the effects of environmental corrosion. Based on cumulative damage theory and fracture mechanics, this paper proposes a framework for evaluating the fatigue performance of existing concrete girder bridges. The evaluation framework contains four steps: investigation of the bridge archives; detection, monitoring and simulation; fatigue performance evaluation; and implementation of the maintenance and management recommendations. A combination of acoustic emission and weigh-in-motion (WIM) technologies was adopted to acquire vehicle information and evaluate girder performance, and a Monte Carlo method and function fitting were also applied to calculate a fatigue reliability index. The results of the evaluation indicate that the case-study bridge is extremely unlikely to fail as the result of fatigue during the design service life. In addition, the parameter analysis shows that the fatigue reliability of concrete bridges is sensitive to the combined effects of negative factors. The reliability index curve and the target value of the reliability index can be used to determine the recommended fatigue inspection intervals and the limits for the initial crack size in critical steel bars.

Numerical analysis on the behaviour of reinforced concrete frame structures in fire

Numerical approach using finite element method has been used to evaluate the behaviour of reinforced concrete frame structure subjected to fire. The structure is previously designed in accordance with Eurocode standards for the design of structures for earthquake resistance, for the ductility class M. Thermal and structural response are obtained using a commercially available software ANSYS. Temperature-dependent nonlinear thermal and mechanical properties are adopted according to Eurocode standards, with the application of constitutive model for the triaxial behaviour of concrete with a smeared crack approach. Discrete modelling of concrete and reinforcement has enabled monitoring of the behaviour at a global, as well as at a local level, providing information on the level of damage occurring during fire. Critical regions in frame structures are identified and assessed, based on temperatures, displacements, variations of internal forces magnitudes and achieved plastic deformations of main reinforcement bars. Parametric analyses are conducted for different fire scenarios and different types of concrete aggregate to determine their effect on global deformations of frame structures. According to analyses results, the threedimensional finite element model can be used to evaluate the insulation and mechanical resistance criteria of reinforced concrete frame structures subjected to nominal fire curves.

Experimental Investigation on Flexural Crack Control for High-Strength Reinforced-Concrete Beam Members

The purpose of this study is to investigate the flexural crack development of high-strength reinforced concrete (HSRC) beams and suggest the design equations of the flexural crack control for HSRC beams. This study conducts two full-size simply-supported beam specimens and seven full-size cantilever beam specimens, and collects the experimental data of twenty full-size simply-supported beams from the past researches. In addition to high-strength reinforced steel bars of specified yielding stresses of 685 and 785 MPa, these specimens are all designed with the high-strength concrete of a specified compressive stress of 70 or 100 MPa. The experimental data is used to verify the application of the flexural crack control equations recommended in ACI 318-14, as reported by AIJ 2010, as reported by JSCE 2007 and as reported by CEB-fib Model Code 2010 on HSRC beam members; then, this study concludes the design equations for the flexural crack control based on ACI 318-14. Additionally, according to the experimental data, to ensure the reparability of an HSRC beam member in a medium-magnitude earthquake, the allowable tensile stress of the main bars can be set at the specified yielding stress of 685 MPa.

Flume experiments on vegetated alternate bars

The planform morphology of a river reach is the result of the combined actions of sediment motion (erosion, transport and deposition), hydrological regime, development and growth of vegetation. However, the interactions among these processes are still poorly understood and rarely investigated in laboratory flume experiments. In these experiments and also in numerical modelling, vegetation is usually represented by rigid cylinders, although it is widely recognized that this schematization cannot reproduce the effects of root stabilization and binding on riverbed sediment. In this work, we focus on the effects of added vegetation on morphological dynamics of alternate bars in a straight channel by means of flume experiments. We performed laboratory experiments reproducing hydraulic conditions that are typical of gravel bed rivers, in terms of water depth, bed slope and bed load; these conditions led to the formation of freely migrating alternate bars. We then employed rigid vegetation that was deployed on the reproduced alternate bars according to field observations. Various vegetation scenarios, in terms of density and spatial arrangement, were deployed in the flume experiments such to mimic different maintenance strategies. Results show the effects of rigid vegetation on the alternate bar configuration on the overall topographic pattern, the main alternate bar characteristics (such as amplitude and wavelength) and migration rate.

Analisis tegangan pada batang utama mekanisme bukaan payung raksasa

Spacious areas as venues for events such as weddings, gatherings, musical performances, bazaars even as parking lots, need to be protected from climate change. Therefore, it is necessary to develop the design of a giant umbrella axle mechanism measuring 12 x 12 meters with a height of 8 meters. This paper describes and stresses the stress analysis on the main bar of the giant umbrella opening mechanism. The result of modeling on the stem is presented in the form of stress contour, factor of safety (FOS), and displacement. The largest working voltage is 2 MPa in the connection area, but this voltage is still low when compared with ASTM A36 rod material structure or equivalent to SS-41 which has a yield strength of 100 MPa. The low voltage von misses are relevant to FOS values that generally reach 100 or more. The largest displacement value is in the center of the stem, which is 0.3 mm. Thus, the modeling results are able to withstand a load of 1 ton.

The influence of main bar corrosion on bond strength in selfcompacting concrete

The experimental study was conducted to determine the influence of main bar corrosion on bond strength in self-compacting concrete (SCC). A total 16 tension pullout tests specimens reinforced with 10 mm and 14 mm diameter bar were used for the bond strength test. The properties of SCC were determined from the slump flow, T50cm, V-funnel and L box test. Reinforcing bars in the concrete were submitted to impressed current to accelerate the corrosion of the bar. It was found that the relationship between bond strength and concrete strength in un-corroded specimens differed from that of corroded specimens set in high-strength concrete because of brittleness in the corroded specimens, which caused a sudden loss of bond strength. The results revealed that specimens of un-corroded and corroded showed a higher percentage of bond strength degradation during the pullout tests.

Evaluation of the seismic performance of reinforced concrete frames strengthened with CFRP fabric and NSM bars

An experimental program was conducted to evaluate the seismic performance of rigid frames strengthened with externally bonded CFRP fabric and near-surface mounted (NSM) CFRP bars. Three rigid frame specimens were subjected to cyclic loading. The three specimens were identical in size and internal reinforcement. One specimen served as control while the other two specimens were strengthened using CFRP fabric and NSM bars such that they have equivalent capacity at first yielding. CFRP wraps were used on the strengthened specimens to anchor the main CFRP sheets and NSM bars and to prevent/delay debonding of the FRP reinforcement. Test results indicated that both techniques delay the yielding of the internal steel reinforcement and result in an increase in the flexural strength of the members, an increase in energy dissipation, and a decrease in stiffness degradation. However, the load-deflection response for both strengthening techniques flattens shortly after yielding of internal steel due to localized debonding of the fabric and the bars, unlike monotonic loading which typically shows post-yielding stiffness. Results also showed that strengthening with CFRP fabric results in fewer cracks, more energy dissipation, and less strength degradation after yielding than strengthening with NSM bars where the latter results in higher ultimate strength.

Review of Punching Shear Behaviour of Flat Slabs Reinforced with FRP Bars

Using Fibre Reinforced Polymer (FRP) bars to reinforce two-way concrete slabs can extend the service life, reduce maintenance cost and improve-life cycle cost efficiency. FRP reinforcing bars are more environmentally friendly alternatives to traditional reinforcing steel. Shear behaviour of reinforced concrete structural members is a complex phenomenon that relies on the development of internal load-carrying mechanisms, the magnitude and combination of which is still a subject of research. Many building codes and design standards provide design formulas for estimation of punching shear capacity of FRP reinforced flat slabs. Building code formulas take into account the effects of the axial stiffness of main reinforcement bars, the ratio of the perimeter of the critical section to the slab effective depth, and the slab thickness on the punching shear capacity of two-way slabs reinforced with FRP bars or grids. The goal of this paper is to compare experimental data published in the literature to the equations offered by building codes for the estimation of punching shear capacity of concrete flat slabs reinforced with FRP bars. Emphasis in this paper is on two North American codes, namely, ACI 440.1R-15 and CSA S806-12. The experimental data covered in this paper include flat slabs reinforced with GFRP, BFRP, and CFRP bars. Both ACI 440.1R-15 and CSA S806-12 are shown to be in good agreement with test results in terms of predicting the punching shear capacity.

Design of transverse reinforcement to avoid premature buckling of main bars

SummaryThis paper proposes an enhancement to the current strength and confinement‐based design of transverse reinforcement in rectangular and circular reinforced concrete members to ensure that the flexural strength of reinforced concrete sections does not degrade excessively due to buckling of longitudinal bars until the desired level of plastic deformation is achieved. Antibuckling design criteria are developed based on a popular bar buckling model that uses a bar buckling parameter (combining the bar diameter, yield strength, and buckling length) to solely describe the bar buckling behavior. The value of buckling parameter that limits the buckling‐induced stress loss to 15% in compression bars at the strain corresponding to the design ductility is determined. For a bar of known diameter and yield strength, the maximum allowable buckling length can then be determined, which serves as the maximum limit for the tie/stirrup/hoop spacing. Lateral stiffness required to restrain the buckling tendency of main bars at the locations of the ties/stirrups/hoops depends on the flexural rigidity of the main bars and the buckling length (equal to or multiple of tie/hoop/stirrup spacing), whereas the antibuckling stiffness (ie, resistance) provided by the ties/stirrups/hoops depends on their size, number, and arrangement. Using the above concept, design recommendations for the amount, arrangement, and spacing of rectangular and circular ties/stirrups/hoops are then established to ensure that the antibuckling stiffness of the provided transverse reinforcement is greater than the stiffness required to restrain the buckling‐prone main bars. Key aspects of the developed method are verified using experimental tests from literature.

Ultra-high performance steel fibers concrete corbels: Experimental investigation

In the present paper, results of testing eleven ultra-high performance steel fibers concrete (UHPSFC) corbels with concrete compressive strength 150MPa and under vertical loading are reported. The main test variables were shear span-to depth ratio, main tension reinforcement ratio and the provision of secondary reinforcement (closed stirrups). In all corbels, except one, the main steel bars yielded before failure and corbels failed in a consistent manner. Whereas the validity from provision the secondary reinforcement in the UHPSFC corbels represents by a significant increase in the corbels stiffness with taking into consideration the corbels failure modes. The test results in terms of load versus deflection curves, stiffness, ductility and crack patterns show the effectiveness of using ultra high performance steel fibers concrete to ensure a superior strength and deformation capacity in reinforced concrete corbels. Experimental results have been compared with diverse prediction methods. The truss model can provide accurate strength predictions in comparison with the ACI 318-14 cod’s procedure.

The Effect of Micro-reinforcement Steel Fibers Addition on the Size of the Shrinkage of Concrete and Corrosion Process of the Main Reinforcement Bars

Steel fiber reinforced concrete (SFRC) is used for concrete repair and rehabilitation. Randomly distributed steel fibers allow to obtain the composite better than plain concrete. The steel fibers increase the consistency of concrete, which may affect the reduction of shrinkage and improve the protective properties of concrete as a coating for reinforcing steel. This article presents a study which main objective was to determine the effect of the micro-reinforcement steel fibers addition on the process of corrosion of the main reinforcement bars. Completed studies included measurement of shrinkage and the main reinforcement corrosion measurement. The results were used to conduct a comparative analysis. Experiments were carried out on the concrete and the fiber reinforced concrete specimens. Corrosion tests were used for non-destructive electrochemical method for measuring galvanostatic pulse. Based on the measurements it can be concluded that the addition of 1% steel fibers to the concrete reduced the progress of corrosion of the main reinforcement bars by ∼ 33%. The addition of 1% of the micro reinforcement steel fibers to the concrete reduced the shrinkage progress in the concrete specimens.

Force- and Displacement-Controlled Non-linear FE Analyses of RC Beam with Partial Steel Bonded Length

The current work deals with the comparison between two different computer formulations, namely, force- and displacement-controlled approaches for non-linear FE analyses of an RC beam in flexure with partially developed and asymmetric steel reinforcement. Instead of inputting load–slip data of direct tension pullout test to ANSYS code for defining the bond property, a different approach is adopted. In the study, load slip data are extracted from bond stress model of Yousaf (Performance of self-compacting concrete in bond at beams intersection. PhD dissertation, 2015) where the model was developed using data of digital strain gauge mounted on main steel bar in flexural beam testing. The load slip data are fed to computer as a set of real contestants choosing large-deformation non-linear plastic analysis scheme, discrete modeling approach for material modeling and program-chosen incremental scheme following the Newton–Raphson method. Complete harmony is found in computer and experimental results advocating the correctness and validation of the approach adopted for computer analysis. Among both formulations adopted for ANSYS analysis, the results reveal that the displacement-controlled approach is easy and efficient in terms of time-saving and less disk space requirement along with the ability to give falling branch of load–deflection response, if element displacement capacity still exists. Furthermore, it gives an early estimate of the load carrying capacity of the structural element along with suitable values of convergence and non-linear solution parameters. On the other hand, force-based analysis for a beam with unsymmetrical reinforcement detailing seems to yield more realistic and practical results in terms of mid-span deflection and beam cracking behavior compared with assumed symmetric displacement-controlled technique. From the study, the superiority of the force-controlled approach in comparable conditions is established through observed performance simulation with that of practical beam results along with the applicability of the approach adopted in the study. A comparison of ANSYS and experimental stress of partially developed rebar shows that the used bond model performs extremely well.

Fiscal policy options ahead of the Autumn Statement

Economic OutlookVolume 40, Issue 4 p. 18-24 Feature articles Fiscal policy options ahead of the Autumn Statement† First published: 05 December 2016 https://doi.org/10.1111/1468-0319.12245 † By Andrew Goodwin, Lead UK Economist, agoodwin@oxfordeconomics.com AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Abstract In our view the case for a fiscal stimulus is incontrovertible. The vote to leave the EU has dampened the outlook for growth, while there is limited scope for monetary policy to offer more support. The existing fiscal plans will exert a sizeable drag on growth and with borrowing costs so low, there is a strong case for relaxing the squeeze. Scenarios run on the Oxford Global Model suggest that raising capital spending by 1% of GDP in each of the next two fiscal years could boost GDP growth by 0.7% a year over that period. We also find that the package would, in some respects, pay for itself, with the public sector net debt-to-GDP ratio peaking at a lower level. The main bar to this package would be whether there are sufficient ‘shovel ready’ projects available. Political considerations might encourage the government to opt instead for packages geared towards boosting current spending – perhaps on the NHS – or cutting taxes. But our modelling suggests that this would offer a smaller boost to activity and would also generate poorer fiscal outcomes than an infrastructure-led package. While the case for a stimulus package is very strong, our expectations for delivery are fairly low. The Conservatives have enjoyed electoral success on the back of a strong austerity message and suggestions that they might loosen fiscal policy appear to be aimed at averting a worst-case scenario, rather than a conviction that this would be a positive policy to boost both short- and long-term growth prospects. So if the economic data remains firm, the prospects of a sizeable stimulus package will recede. And if a package is implemented, the temptation to favour crowd-pleasing tax cuts over higher investment may prove to be irresistible. Therefore, we view a large, infrastructure-focused, stimulus package as an upside risk to our forecast, not a core assumption. Volume40, Issue4October 2016Pages 18-24 RelatedInformation

Mid- to late-Holocene environmental evolution of the Loire estuary as observed from sedimentary characteristics and benthic foraminiferal assemblages

We used sedimentological and foraminiferal characteristics of four sedimentary cores, supported by paleogeographical and historical data, to reconstruct the depositional history of the inner Loire estuary (Near Saint-Nazaire, France) and the response of benthic foraminifera to the mid- to late-Holocene marine flooding of the incised valley. These were further used to evaluate the consequent changes in estuarine morphological and hydro-sedimentary patterns during this time period. Our results described significant changes in hydro-sedimentary dynamics over the past ~6kyrsBP. At our location, these changes expressed the combined influence of marine (e.g., tide, storm waves) and fluvial dynamics (e.g., floods), which are linked, on a broader scale, to sea-level variations and the regional climate regime. Three main periods stand out: (1) from ~6.0 to ~2.5kyrsBP, when the sea-level rise slowed down, a large brackish bay extended over and around the study area. The fine-grained tidal rythmites recorded north of the Bilho bank (the main tidal bar located in our study area) indicated a calm depositional environment, protected from the main riverine influence. The presence of thick flood deposits from ~5.4 to ~4.0kyrsBP near the Bilho bank indicates further the dominance of humid conditions. (2) From ~2.5 kyrs BP to ~1850CE (pre-industrial state), sea-level stabilized at its present value, and the pre-existing bay was progressively infilled. North of the Bilho bank, near a major mudflat (Méan), the generally homogenous sedimentation composed of silty muds rich in organic matter indicated a sheltered environment; the main water flow channel being located south of the Bilho bank. Within this overall homogenous sedimentation, foraminiferal assemblages described rather accurately the progressive infilling of the valley (indicated by a decrease in the proportions of outer estuarine species), accompanied with the channelization of the main entering marine currents (tide, storm waves) (indicated by an increase in the proportions of transported species from the adjacent upper continental shelf), and finally the buildup of the Méan mudflat and the stabilization of the environment to its present day configuration (indicated by the dominance of autochthonous inner estuarine species). (3) Since 1850CE, the human impact progressively modified the general landscape of our study area with the construction of the Saint-Nazaire shipyard, the digging of the northern navigation channel and the polderization of the northern Bay. The southern channel was progressively abandoned by the main water flow in favor of the newly dug northern channel, causing the southern migration of the Bilho sandbank and the progressive filling of the southern channel.

Acoustic emission and flexural behaviour of RC beams strengthened with UHPC overlay

Reinforced concrete beams with reinforcement ratios of 0.57%, 0.89% and 1.30% are cast and after subjecting to flexural damage strengthened with ultra high performance concrete (UHPC) overlays of thickness of 10, 15 and 20mm. The composite retrofitted beams acted monolithically under bending without debonding. The damaged beams were able to regain its origin flexural capacity with 10mm overlay. The increase in load carrying capacity of beams with 15mm and 20mm overlay is 24% and 35% for beams with reinforcement ratio of 0.57%, 11.57% and 18.45% for 0.89% reinforcement ratio and 10.60% and 15.12% for beams with 1.3% reinforcement ratio. During mechanical testing, acoustic emission (AE) parameters are analyzed for five levels of damage, which are formation of hair line crack, visible crack in UHPC overlay, yielding of main bars and finally crushing of composite beams. From parametric studies between rise angle and average frequency, it is found that AE analysis can be successfully used to determine crack movement and classify damage level of retrofitted beams.

Numerical simulation of concrete beams reinforced with composite GFRP-Steel bars under three points bending

Fiber reinforced polymer (FRP) applications in the structural engineering field include concrete- FRP composite systems, where FRP components are either attached to or embedded into concrete structures to improve their structural performance. This paper presents the results of an analytical study conducted using finite element model (FEM) to simulate the behavior of three-points load beam reinforced with GFRP and/or steel bars. To calibrate the FEM, a small-scale experimental program was carried out using six reinforced concrete beams with 200x200 mm cross section and 1000 mm length cast and tested under three point bending load. The six beams were divided into three groups, each group contained two beams. The first group was a reference beams which was cast without any reinforcement, the second group concrete beams was reinforced using GFRP, and the third group concrete beams was reinforced with steel bars. Nonlinear finite element simulations were executed using ANSYS software package. The difference between the theoretical and experimental results of beams vertical deflection and beams crack shapes were within acceptable degree of accuracy. Parametric study using the calibrated model was carried out to evaluate two parameters (1) effect of number and position of longitudinal main bars on beam behavior; (2) performance of concrete beam with composite longitudinal reinforcement steel and GFRP bars.

Effects of spiral confinement to the bond behavior of deformed reinforcement bars subjected to axial tension

When grouted pipe splice connections are employed, the structural performance of the connected precast concrete components is significantly influenced by the bond behavior between the main reinforcing bars and the surrounding grout. Owing to this important characteristic, the bond behavior, in particular the local bond-stress slip relationship and the bond strength, of the main steel reinforcement bars embedded in grout needs to be investigated accordingly. This paper presents the bond behavior of main deformed steel reinforcement bars confined by a grouted spiral connection. A total of 36 pullout specimens were tested under increasing axial tensile load to investigate the effects of spiral confinement to the connected main steel bars. Parameters covered in this study were spiral diameter and spiral pitch distance. The experimental results showed that the spiral configurations influence the bond performance due to the effect of confinement generated by the spiral diameter and pitch distance. As compared to spiral pitch distance, the spiral diameter provides more dominant confinement effect which subsequently increases the bond strength significantly.

The 3D Structure of the Galactic Bulge

AbstractWe review the observational evidences concerning the three-dimensional structure of the Galactic bulge. Although the inner few kpc of our Galaxy are normally referred to asthe bulge, all the observations demonstrate that this region is dominated by a bar, i.e., the bulge is a bar. The bar has a boxy/peanut (X-shaped) structure in its outer regions, while it seems to become less and less elongated in its innermost region. A thinner and longer structure departing from the main bar has also been found, although the observational evidences that support the scenario of two separate structures has been recently challenged. Metal-poor stars ([Fe/H] ≲ −0.5 dex) trace a different structure, and also have different kinematics.

部材主筋のプレート定着と機械式鉄筋継手

部材主筋のプレート定着と機械式鉄筋継手

Evaluation of an Academic Library’s Liquid Designed Website

Abstract
 
 Objective – When the Harold B. Lee Library (HBLL) at Brigham Young University released a new website with same-look capabilities for computers, tablets, and smartphones, we undertook a summative assessment to review website features and to determine baseline measures of website access via device and patron group.
 
 Methods – The study used a mixed methods approach using three levels of assessment (focus groups, an online survey, and a usability test), with each level informing the subsequent level. 
 
 Results – The website changes were well-received by the overwhelming majority of patrons. Device usage was associated with the type of task for which patrons were accessing the website. Computers were used primarily for research-related tasks (e.g., accessing journals, databases, and the main search bar). Smartphones were used primarily for on-the-go tasks (e.g., accessing personal accounts, finding library hours, and reserving group study rooms). Tablets fell between these two. Several website services were identified as being underused. Study results were moderated by time of release (i.e., only half of survey participants had viewed the new website) and access to device (i.e., many patrons did not have access to a tablet or a smartphone).
 
 Conclusions – The summative assessment of the HBLL’s new website was well-received and viewed as a positive change. While most patrons were initially unaware of the same-look feature across devices, this was considered to be a positive change. As devices become more accessible for patrons, it is believed that website access by device will change. A follow-up study is planned to assess any changes in use patterns or use of access devices.