4,505 research outputs found
Effect of fiber-reinforced polymer confinement on bond strength of hooked bars in high-strength concrete
No full textTo assess the viability of the external confinement of high-strength concrete beam-column joints with carbon fiber-reinforced polymer (CFRP) sheets in increasing the bond strength of hooked bars anchored in the joints, 12 hooked bar specimens were tested. The specimen simulated the rigid connection of a cantilever beam to a column. The variables were the beam tensile bar size, anchorage length, mode of confinement of the beam hooked bars in the beamcolumn joint, and presence or absence of fiber-reinforced polymer (FRP) wraps. The nominal or intended concrete compressive strength was 60 MPa (8.7 ksi). Test results of the study were analyzed and the effect of FRP was assessed by comparing performance of specimens whose beam-column anchorage zones were wrapped with FRP sheets with analogous specimens with no FRP. FRP sheets were found effective in increasing the anchorage capacity and the ductility of the load-deflection history. © 2009, American Concrete Institute.[Anonymous], 2005, 318 ACI COMM; *ASTM INT, 2003, A615A615M03A ASTM IN; Hamad BS, 2004, J COMPOS CONSTR, V8, P14, DOI 10.1061-(ASCE)1090-0268(2004)8:1(14); Hamad BS, 2004, ACI STRUCT J, V101, P747; Hamad BS, 2004, J COMPOS CONSTR, V8, P248, DOI 10.1061-(ASCE)1090-0268(2004)8:3(248); HAMAD BS, J COMPOSITES CONSTRU, V9, P440
Effect of FRP confinement on bond strength of hooked bars: Normal-strength concrete structures
No full textTo assess the viability of the external confinement of normal-strength concrete beam-column joints with carbon fiber-reinforced polymer (CFRP) sheets in increasing the bond strength of hooked bars anchored in the joints, 12 hooked bar specimens were tested. The variables were beam tensile bar size, anchorage length, mode of confinement of the beam hooked bars in the beam-column joint (whether the hooked bars were anchored within or outside the column reinforcement cage, denoted as confined specimens or unconfined specimens), and presence or absence of FRP wraps. The specimen simulated the rigid connection of a cantilever beam to a column. The tensile beam reinforcement consisted of two bars anchored in the base column using hooked-bar anchorages. Test results indicated that FRP sheets were effective in increasing the anchorage capacity and the ductility of the load-deflection history for both unconfined and confined specimens. However, FRP sheets had a more significant influence on unconfined specimens than companion confined specimens. As compared with unconfined specimens without FRP wrapping, unconfined FRP specimens had an average of a 23percent increase in bond strength, confined non-FRP specimens had an average 30percent increase in bond strength, and confined FRP specimens had an increase of 54percent. © 2009 ASCE.*ACI, 2005, ACI31805ACI318R05; ASTM, 2004, 2004 ANN BOOK ASTM S, V04.08; Ghobarah A, 2005, J COMPOS CONSTR, V9, P408, DOI 10.1061-(ASCE)1090-0268(2005)9:5(408); Hamad BS, 2004, J COMPOS CONSTR, V8, P14, DOI 10.1061-(ASCE)1090-0268(2004)8:1(14); Hamad BS, 2004, ACI STRUCT J, V101, P747; Hamad BS, 2005, J COMPOS CONSTR, V9, P44, DOI 10.1061-(ASCE)1090-0268(2005)9:1(44); Hamad BS, 2004, J COMPOS CONSTR, V8, P248, DOI 10.1061-(ASCE)1090-0268(2004)8:3(248); Kono S, 1998, P 2 INT C COMP INFR, P343; Pantelides CP, 2008, J COMPOS CONSTR, V12, P435, DOI 10.1061-(ASCE)1090-0268(2008)12:4(435)1
Comparison of roles of FRP sheets, stirrups, and steel fibers in confining bond critical regions
No full textBased on experimental data of tension lap splices confined with fiber reinforced polymer (FRP) sheets in normal and high strength concrete (HSC) specimens, a new FRP confinement parameter, Ktr,f was recommended. It accounts for the increase in bond strength due to the presence of FRP sheets. In this paper, a correlation is presented between the confining effects of FRP flexible sheets, transverse reinforcement, and steel fibers to improve the bond capacity and ductility of the mode of failure of tension lap splices. The correlation is based on research programs conducted at the American University of Beirut in recent years using identical specimens except for the confinement method used: FRP sheets, transverse steel stirrups, or steel fibers. Other variables included the amount of confinement provided and concrete strength. Analysis of test results indicated that an equivalent improvement in bond strength of tension lap splices in normal and high strength concrete specimens is provided by an amount of FRP sheets corresponding to a Ktr,j value of 2.5, or an amount of transverse reinforcement corresponding to K tr of 1.0db. For HSC specimens, an amount of steel fibers corresponding to a volume fraction of 1percent would provide an equivalent improvement in bond strength. © ASCE.*ACI COMM, 2005, 31805ACI; AZIZINAMINI A, 1993, ACI STRUCT J, V90, P554; Azizinamini A, 1999, ACI STRUCT J, V96, P826; Darwin D, 1996, ACI STRUCT J, V93, P347; Hamad BS, 2004, J COMPOS CONSTR, V8, P14, DOI 10.1061-(ASCE)1090-0268(2004)8:1(14); Hamad BS, 2001, ACI STRUCT J, V98, P638; Hamad BS, 2002, MATER STRUCT, V35, P219, DOI 10.1007-BF02533083; Hamad BS, 2003, ACI STRUCT J, V100, P19; Hamad BS, 2004, ACI STRUCT J, V101, P747; Hamad BS, 2004, J COMPOS CONSTR, V8, P248, DOI 10.1061-(ASCE)1090-0268(2004)8:3(248); SALWAN BR, 2003, THESIS AM U BEIRUT B55
Bond strength of hot-dip galvanized hooked bars in normal strength concrete structures
No full textIn 2001, a multi-phase research program was started at the American University of Beirut (AUB) to evaluate experimentally the effect of hot dip galvanizing on bond strength of reinforcement in concrete structures. In the first two phases, 24 full-scale beam specimens were tested in positive bending to evaluate the effect of galvanizing on bond strength of tension lap splices in normal and high strength concrete specimens. The variables were bar size, concrete strength, the amount of transverse reinforcement confining the splice region, and whether the bars were galvanized or not. Test results indicated that galvanizing had a negligible effect on bond strength of reinforcement in normal strength concrete. However, galvanizing caused an average of 20percent decrease in bond strength of reinforcement in high strength concrete regardless of the amount of transverse reinforcement confining the splice region. This paper reports on a third phase of the AUB program, designed to evaluate the effect of galvanizing on anchorage performance of hooked bars in normal strength concrete structures. Up to date there has been no research work done in this area. Twelve specimens were tested. The specimen simulated the rigid connection of two cantilever beams to a column. The variables were bar size, the confinement mode of the beam bars anchored in the column, and whether the bars were galvanized or not. The effect of galvanizing was evaluated by comparing the performance of galvanized bars with black bars based on the mode of failure, ultimate load, and the general load-deflection behavior. Test results indicated that effect of galvanizing on the bond strength of hooked bars in normal strength concrete was not significant. © 2007 Elsevier Ltd. All rights reserved.[Anonymous], 2002, 318 ACI COMM; *ASTM, 2004, A615A615M03A ASTM; Azizinamini A, 1999, ACI STRUCT J, V96, P826; Hamad BS, 2005, CONSTR BUILD MATER, V19, P275, DOI 10.1016-j.conbuildmat.2004.07.008; HAMAD BS, 1993, ACI STRUCT J, V90, P210; Hamad BS, 2006, ACI STRUCT J, V103, P48; Hamad BS, 2003, ACI STRUCT J, V100, P465; LIEBER W, 1967, ZEM-KALK-GIPS, P912
Effect of fiber-reinforced polymer confinement on bond strength of reinforcement in beam anchorage specimens
No full textThis paper reports on the fourth phase of a multiphase study undertaken at the American University of Beirut (AUB) to examine the effect of fiber-reinforced polymer (FRP) sheets in confining bond-critical regions in reinforced concrete beams. Results of the first three phases showed that glass- and carbon-fiber-reinforced polymer (GFRP and CFRP) sheets were effective in increasing the bond strength and improving the ductility of the mode of failure of tension lap splices in high-strength concrete (HSC) and normal-strength concrete (NSC) beams. The main objective of the fourth phase of the AUB study was to assess the effect of CFRP sheets in improving the serviceability and ultimate response of beam anchorage specimens. The added experimental data and the improved knowledge of the bond behavior of FRP confined concrete members will encourage the use of FRP technology to strengthen and retrofit bond anchorage zones. Ten beam anchorage specimens were tested in positive bending in two series. The variables were bar size, anchorage length, and concrete strength. For each bar size, anchorage length, and concrete strength, two companion specimens - identical except for whether the anchorage zone was wrapped with FRP sheets or not wrapped - were tested. The test results demonstrated that CFRP sheets were effective in enhancing the bond strength and ductility of anchorage zones in beam anchorage specimens where splitting failures were imminent.*ACI, 2002, 440R96 ACI; Darwin D, 1996, ACI STRUCT J, V93, P347; Hamad BS, 2004, J COMPOS CONSTR, V8, P14, DOI 10.1061-(ASCE)1090-0268(2004)8:1(14); Hamad BS, 2004, ACI STRUCT J, V101, P747; Hamad BS, 2004, J COMPOS CONSTR, V8, P248, DOI 10.1061-(ASCE)1090-0268(2004)8:3(248)107
Efficient route discovery for reactive routing
No full textThis thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.Information on the location of mobile nodes in Mobile Ad-hoc Networks (MANETs) has
the potential to significantly improve network performance. This thesis uses node location information to develop new techniques for route discovery in on-demand routing protocols such as the Ad-hoc On-Demand Distance Vector (AODV), thus making an important contribution to enhancing the experience of using mobile networks.
A Candidate Neighbours to Rebroadcast the Route Request (CNRR) approach has been
proposed to reduce the deleterious impact, known as the broadcast storm, of RREQ packets
flooding in traditional on-demand routing protocols. The main concept behind CNRR is
specifying a set of neighbours which will rebroadcast the received RREQ. This is a departure from the traditional approach of all receiving nodes rebroadcasting RREQs and has the effect of reducing the problem of redundancy from which mobile networks suffer. The proposed protocol has been developed in two phases: Closest-CNRR and Furthest-CNRR. The simulation results show that the proposed algorithms have a significant effect as they reduce the routing overhead of the AODV protocol by up to 28% compared to the C-CNRR, and by up to 17.5% compared to the F-CNRR. Notably, the proposed algorithms simultaneously achieve better throughput and less data dropping.
The Link Stability and Energy Aware protocol (LSEA) has been developed to reduce the
overhead while increasing network lifetimes. The LSEA helps to control the global
dissemination of RREQs in the network by eliminating those nodes that have a residual
energy level below a specific threshold value from participation in end-to-end routes. The proposed LSEA protocol significantly increases network lifetimes by up to 19% compared with other on-demand routing protocols while still managing to obtain the same packet delivery ratio and network throughput levels. Furthermore, merging the LSEA and CNRR concepts has the great advantage of reducing the dissemination of RREQs in the network without loss of reachability among the nodes.
This increases network lifetimes, reduces the overhead and increases the amount of data
sent and received. Accordingly, a Position-based Selective Neighbour (PSN) approach has
been proposed which combines the advantages of zoning and link stability. The results
show that the proposed technique has notable advantages over both the AODV and MAAODV
as it improves delivery ratios by 24.6% and 18.8%, respectively.Funded by National Council for Training -
Sudan and the Sudan Academy of Science
Rocket Dynamics of Capped Nanotubes: A Molecular Dynamics Study
No full textThe study of nanoparticle motion has fundamental relevance in a wide range of nanotechnology-based fields. Molecular dynamics simulations offer a powerful tool to elucidate the dynamics of complex systems and derive theoretical models that facilitate the invention and optimization of novel devices. This research contributes to this ongoing effort by investigating the motion of one-end capped carbon nanotubes within an aqueous environment through extensive molecular dynamics simulations. By exposing the carbon nanotubes to localized heating, propelled motion with velocities reaching up to about 0.08 nm/ps was observed. Through systematic exploration of various parameters such as temperature, nanotube diameter, and size, we were able to elucidate the underlying mechanisms driving propulsion. Our findings demonstrate that the propulsive motion predominantly arises from a rocket-like mechanism facilitated by the progressive evaporation of water molecules entrapped within the carbon nanotube. Therefore, this study focuses on the complex interplay between nanoscale geometry, environmental conditions, and propulsion mechanisms in capped nanotubes, providing relevant insights into the design and optimization of nanoscale propulsion systems with various applications in nanotechnology and beyond
Essays in statistical arbitrage
No full textThis three-paper thesis explores the important relationship between arbitrage and price efficiency. Chapter 3 investigates the risk-bearing capacity of arbitrageurs under varying degrees and types of risk. A novel stochastic process is introduced to the literature that is capable of jointly capturing fundamental risk factors which are absent from extant specifications. Using stochastic optimal control theory, the degree to which arbitrageurs' investment behaviour is affected by aversion to these risks is analytically characterized, as well as conditions under which arbitrageurs cut losses, effectively exacerbating pricing disequilibria. Chapter 4 explores the role of arbitrage in enforcing price parity between cross-listed securities. This work employs an overlooked mechanism by which arbitrage can maintain parity, namely pairs-trading, which is cheaper to implement than the mechanism most commonly employed in the literature on cross-listed securities. This work shows that arbitrage is successful at enforcing parity between cross-listed securities, and also documents the main limits to arbitrage in this market setting. Chapter 5 examines the extent to which arbitrage contributes to the flow of information across markets. It is shown that microscopic lead/lag relationships of the order of a few hundred milliseconds exist across three major international index futures. Importantly, these delays last long enough, and induce pricing anomalies large enough, to compensate arbitrageurs for appropriating pricing disequilibria. These results accord with the view that temporary disequilibria incentivise arbitrageurs to correct pricing anomalies
Effect of confinement on bond strength of hot-dip galvanized lap splices in high-strength concrete
No full textGalvanizing reinforcing steel is one of the methods used to protect steel bars against corrosion. In 2001, a research program was started at the American University of Beirut (AUB), Beirut, Lebanon, to experimentally evaluate the effect of hot-dip galvanizing on the bond capacity of tension lap splices anchored in full-scale beam specimens designed to fail in bond splitting mode. The test results indicated that the use of galvanized bars had a negligible effect on bond strength of reinforcement in normal-strength concrete. Galvanizing, however, caused an average of 20percent decrease in bond strength of reinforcement in high-strength concrete. The primary objective of the research reported in this paper was to find a solution to eliminate the bond reduction of galvanized bars in high-strength concrete. It was important to evaluate the potential positive effect of the addition of transverse reinforcement in the splice region. One hypothesis to be tested was that such transverse reinforcement would ensure uniform bond stress distribution over the entire splice length, thus mobilizing all bar lugs along the splice in the stress transfer mechanism between the bar and the surrounding concrete, and hence would lead to increasing the bond strength of galvanized bars. The second hypothesis to be checked was whether the aforementioned mechanism of mobilizing all bar lugs along the splice in the stress transfer mechanism would reduce the significant decrease in bond strength of galvanized bars relative to black bars in high-strength concrete. Eighteen full-scale beam specimens, designed to fail in bond-splitting mode, were tested in positive bending. Each beam was reinforced with bars spliced in a constant moment region at midspan. The main variables were bar size and the amount of transverse reinforcement in the splice region. The test results indicated that, whereas confinement increased the bond strength of galvanized bars and black bars, confinement did not have a significant positive effect on the bond strength of galvanized bars relative to black bars. Copyright © 2006, American Concrete Institute. All rights reserved.[Anonymous], 2002, 318 ACI; *ASTM A, 2003, 615615M03A ASTM A, P318; Azizinamini A, 1999, ACI STRUCT J, V96, P826; BRESLER B, 1964, 7 C INT ASS BRIDG ST; BRODBECK H, 1954, SCHWEIZ BAUZEITUNG, P256; GUKILD L, 1965, VARMAFORSINKT ARMERI, P37; Hamad BS, 2003, ACI STRUCT J, V100, P465; KAYYALI OA, 1995, CONSTR BUILD MATER, V9, P219, DOI 10.1016-0950-0618(95)00024-A; KOCH R, BETONWERK FERTIGTEIL, V54, P64; LIEBER W, 1967, ZEM-KALK-GIPS, P91; Orangun C. O., 1977, ACI J, V74, P114; SHMEER F, 1920, DTSCH AUCHUSS EISNEB, P9; SLATER WA, 1920, 173 NBS, P922
Hartmut Kohne, éd., avec les contributions de C. Becker, S. Bottema, P.J. Ergenzinger, W. Frey, W.H.E. Gremmen, H. Hopfinger, Ch. Jagiella, F. Krupp, H. Kohne, H. Korschner, D.S. Reese, W. Schneider, Die rezente Utnwelt von Tall Sēḫ Hamad und Daten zur Umweltrekonstruktion der assyrischen Stadt Dûr-Katlimmu. (Berichte der Ausgrabung Tall Sēḫ Hamad/ Dūr Katlimmu [BATSH] Bd. 1)
No full textHuot Jean-Louis. Hartmut Kohne, éd., avec les contributions de C. Becker, S. Bottema, P.J. Ergenzinger, W. Frey, W.H.E. Gremmen, H. Hopfinger, Ch. Jagiella, F. Krupp, H. Kohne, H. Korschner, D.S. Reese, W. Schneider, Die rezente Utnwelt von Tall Sēḫ Hamad und Daten zur Umweltrekonstruktion der assyrischen Stadt Dûr-Katlimmu. (Berichte der Ausgrabung Tall Sēḫ Hamad/ Dūr Katlimmu [BATSH] Bd. 1). In: Syria. Tome 70 fascicule 3-4, 1993. pp. 582-583
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