177,030 research outputs found
A Comparative Study of Models on Confinement of Concrete Cylinders with FRP Composites. Part I: Review of experiments and models
No full textA Comparative Study of Models on Confinement of Concrete Cylinders with FRP Composites. Part II: Performance Assessment of Models
No full text
Behaviour and capacity of CFRP-confined concrete cylinders subjected to monotonic and cyclic axial compressive load
No full textConcrete Cylinders Confined by Prestressed CFRP Filament Winding under Axial Load
No full textDuring last decades, most R&D and field application projects have concentrated on concrete columns repair and reinforcement using composite materials, which result in considerable enhancement in strength and ductility of axially in compression loaded concrete. The use of composite materials could upgrade civil engineering structures and be the most effective steps to introduce composites into widespread civil engineering use.
Experimental study of concrete cylinders confined by CFRP sheet displays a distinct bilinear stress-strain response with transition zone around the ultimate strength of unconfined concrete. The slope of the branches after transition zone and confining pressure depend on the volumetric ratio of the confining device and has lower modulus than the initial branch. The use of wrapped concrete columns above the transition zone is questionable because of internal damage of concrete and low tangential slope of loaddisplacement curve. The lower modulus may create problems to take favor of increased strength by confinement due to reduced Euler stability load. Therefore it would be favorable to raise the load level of the transition zone to be able to use the higher modulus of this initial branch to achieve better stability at least up to this load level. This function could be achieved by prestressing the confinement.
The investigations were executed loading concrete cylinders with diameter 150mm and height 300mm with compressive load. Five different concrete series with cube strengths 34.2; 60.5; 76.2; 81.4 and 104.1MPa, that cover nearly the whole range in practice, were investigated. The parameters taken under consideration for the confinement were three levels of prestress enabled by the prestressing device 300, 600 and 800 N on yarn, which resulted in prestress in carbon filaments equal to 80; 160 and 210MPa (Carbon filaments had the tensile strength 3800 MPa and modulus 228 GPa). The confining reinforcement ratio was 2.48%. The friction between steel loading plates and concrete surface was reduced by three layers of teflon sheet. The specimens were fully instrumented and apart from load, axial and lateral strains were measured with LVDTs and strain gauges.
The confining action of carbon filaments with prestress was effective enough to obtain a longer first elastic branch of stress-strain relation, showing stiff load-unload behaviors. The confining action was engaged from this early loading stage by the prestress of confinement, which delayed the formation of internal cracks. More restricting action by the prestressed confinements makes it difficult for the internal crack to propagate so the large crack was prevented to form. Theoretical prediction showed that prestress of confinement could elevate the transition zone with 20 to 30 percents. The higher the concrete strength, the less effective the confinement action was. However, a higher elastic limit in concrete behavior was obtained.
Cyclic load caused no degradation in confining action. On the contrary, the ultimate strength could be higher, when load was increased after cycling. Stress-strain relationships of the monotonic load act like an envelope of that of cyclic load since they have similar loading paths.
For the satisfactory prediction of strength, the stress analysis of crack growth inside concrete after transition zone should be accompanied by the analysis of confinement and its interaction with the damaged concrete
Lapped joints in reinforced concrete
No full textThis thesis is concerned with an experimental investigation of the behaviour of lapped joints in reinforced concrete. A review of existing literature highlights the need to establish the longitudinal strain distribution along lap joints. This has been achieved experimentally, with detailed strain measurements being taken using a technique of internally gauging the reinforcing rods. In some specimens, strain concentration gauges were installed at the tip of the lap to permit the acquisition of particularly localised information. Computer programs were developed to process the substantial amounts of data generated during the course of each test. Two series of tests were undertaken, both using axially loaded specimens, and dealing with tension and compression lap joints respectively. The laps ranged in length from 125 to 750 mm, and comprised bars of either 12 or 20 mm diameter. Transverse reinforcement was provided in two of the tension specimens. Greater emphasis was placed on the first series, with fifteen tension specimens being tested. Thirteen of these tests were each completed within a single day but, additionally, two long-term tests were undertaken. In the latter, a constant load was sustained for up to 81 days. The measurements clearly showed the changing behaviour of the specimens, first as transverse cracks developed and subsequently as failure of the lap joint was approached. The comprehensive analysis of the test results includes a comparison of the ultimate behaviour of these joints with existing design proposals and regulations. The detailed information provided by the strain measurements enables the justification of design assumptions regarding lap joint behaviour, and thus lends greater confidence to existing design regulations. The results from five compression specimens were analysed and compared with the tension tests. The significant contribution to force transfer made by the bearing of the free end of the steel against the concrete was evident. The specimens were loaded to the rig capacity without failing. Additional strain measurements were taken in one tension and one compression specimen by casting embedment gauges within the concrete. These gauges were arranged to measure the circumferential strains in the specimen, and were complemented by strain gauges mounted on the surface of the concrete. The data thus obtained permitted a comparison of the bursting forces set up inside and outside the lap joints. The work showed that some aspects of lap joint behaviour require clarification. Suggestions for further work are included
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
No full textBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
- …
