100 research outputs found
On fixed points of Berinde’s contractive mappings in cone metric spaces
No full textIn this paper we establish some common fixed point theorems for two self-mappings satisfying a generalized contractive
condition. This result generalizes well known comparable results in the literature. As an application, a necessary and sufficient condition for a fixed point to be a periodic point for the mapping involved therein, without appealing to continuity, in a cone metric space is established
Optimization of Mechanical Performance of Full-Scale Precast Concrete Pipes with Varying Concrete Strengths and Reinforcement Using Factorial Design
No full textThe use of precast concrete pipes for water and sewage transportation systems is a very important element of a country’s infrastructure. The main aim of this study was to investigate the effects of concrete’s compressive strength and reinforcement levels on the mechanical performance of spun-cast full-scale precast concrete pipes in the local construction industries of developing countries. A test matrix was adopted using a full 32 factorial design. The studied concrete’s compressive strength was 20, 30, and 40 MPa, and reinforcement levels were 60%, 80%, and 100%, representing low, medium, and high levels, respectively. The medium level of reinforcement represented the reinforcement requirement of ASTM C76 in concrete pipes. A total of eighteen full-scale pipes of 450 mm diameter were cast in an industrial precast pipe unit using a spin-casting technique and were tested under a three-edge bearing load. The experimental results showed that the crack load and ultimate load of the tested pipes increased with higher levels of concrete strength and reinforcement levels. For example, an approximately 35% increase in the 0.30 mm crack load was observed when the concrete strength increased from 20 MPa to 30 MPa for all tested levels of reinforcement. Similarly, around a 19% increase in ultimate load was observed for pipes with 80% reinforcement compared to identical pipes with 60% reinforcement. It was found that the pipe class, as per ASTM C76, is highly dependent on the concrete strength and reinforcement levels. All of the pipes exhibited the development of flexural cracks at critical locations (crown, invert, and springlines). Moreover, concrete pipes cast with low-level strength and reinforcement also showed signs of crushing at the crown location near to the pipe failure. The analysis of variance (ANOVA) results showed that the main factors (compressive strength and reinforcement levels) were significantly affected by the cracking loads of precast pipes. No significant effect of the interaction of factors was observed on the crack load response. However, interaction factors, along with main factors, have significant effects on the ultimate load capacity of the concrete pipes, as indicated by the F-value, p-value, and Pareto charts. This study made an effort to illustrate and optimize the mechanical performance of pipes cast with various concrete strengths and reinforcement levels to facilitate the efficient use of materials for more resilient pipe infrastructure. Moreover, the exact optimization of concrete strength and reinforcement level for the desired pipe class will make the pipe design economical, leading to an increased profit margin for local spin-cast pipe fabricators without compromising the pipe’s quality
Analytical study of corroded steel-FRP confined concrete bond under fatigue cyclic loading
No full textThe steel-concrete bond and the cracking behaviour of concrete affect the performance of reinforced concrete structures. This is due to the fact that the transfer of forces between the steel and the concrete are accomplished through the bond. The bond between the steel and the concrete is affected by many factors such as corrosion of reinforcement, type of applied loading, and the confinement level. Reinforcement corrosion is one of the primary causes of the loss of steel-concrete bond. On the other hand, an accumulation of bond damage occurs due to the application of fatigue cyclic loading, as in the case of bridges and marine structures. It is known that fibre reinforced polymer (FRP) confinement improves the bond strength, even in the case of corroded reinforcing steel bars.
The objective of this thesis was to develop an analytical tool for structural engineers to evaluate the corroded steel-FRP confined concrete bond under fatigue cyclic loading. Two models have been developed; 1) slip-fatigue model; and 2) bond stress-slip model. These models considered the effect of corrosion of reinforcement, the external confinement provided by the FRP sheets, and the fatigue cyclic loading.
Slip after ‘N’ number of cycles for unwrapped and FRP wrapped cases were developed as a function of the initial slip, the final slip, and the fatigue bond life. These models were capable of capturing the experimental behaviour reported in the literature. Slip-life models for unwrapped and FRP wrapped beam specimens were developed using non linear regression analysis.
Harajli et al. (2004) static bond stress-slip law was modified in order to model the bond stress-slip behaviour for the unwrapped and FRP wrapped beam specimen under monotonic and cyclic loading. The proposed cyclic bond stress-slip behaviour followed the monotonic bond stress-slip envelope and satisfactorily modeled the experimental behaviour.
From the principles of statics of bond and using the derived cyclic bond stress-slip envelope, an equation to calculate the required development length of steel reinforcement was derived. The proposed equation is dependent on the material and the geometrical properties of a structural member. The derived equation was able to satisfactory predict the fatigue bond life.Applied Science, Faculty ofEngineering, School of (Okanagan)Graduat
Preventive Measures of Alkali–Silica Reaction in Concrete Buildings: Use of Hybrid Waste Coal Ash and Steel Wire Cut Fibers
No full textThe main cause of premature deterioration in concrete buildings is linked with the alkali–silica reaction (ASR) owing to the use of reactive aggregates and severe exposure conditions. This research aimed to explore the mitigation of ASR in concrete buildings using waste coal ash (CA) and steel fibers cut from long wire. CA and SF were acquired from a local market. The studied dosages of CA were 10%, 20%, 30% and 40% by cement weight and steel fibers were added at 0.5% and 1% of the total volume of the mixture. Specimens were cast and immersed in a 1N NaOH solution at 80 °C for 90 days as per ASTM C1260 guidelines. The compressive and flexural strengths of the control mixture without CA and the mixture with 10% of CA had a comparable behavior. A decrease in the compressive and flexural strengths was observed for higher dosages of CA (30% and 40%). Specimens incorporating 30% of CA showed a compressive strength of 24 MPa at 56 days compared to that of 33 MPa for the identical control specimen without CA. This strength decrease was due to the porous nature of the used CA and was compensated for by the incorporation of steel fibers. Specimens with 1% of steel fibers exhibited higher strength properties compared to those with 0.5% of steel fibers for all the tested dosages of CA. The control specimens without CA and steel fibers showed expansions higher than 0.10% and 0.20% at 14 and 28 days, respectively, demonstrating their reactive behavior. The hybrid incorporation of CA and steel fibers decreased the ASR expansion. The mortar bar specimen incorporating 10% of CA and 1% of steel fibers showed an expansion of 0.168% at 28 days compared to that of 0.321% for the control specimen without CA and steel fibers. A decrease in the compressive and flexural strengths was observed for the specimen placed in ASR exposure conditions compared to identical specimens placed in normal water. However, specimens incorporating CA and steel fibers showed relatively fewer effects under the ASR exposure conditions. The control specimens without CA and steel fibers also showed micro-cracking due to ASR exposure, as observed through scanning electron microscopy. This study will assist practitioners to construct a sustainable building using locally available waste materials with the additional advantage of mitigating the ASR-related damages
Approximating fixed points of multivalued ρ-nonexpansive mappings in modular function spaces
No full textThe existence of fixed points of single-valued mappings in modular function spaces
has been studied by many authors. The approximation of fixed points in such spaces
via convergence of an iterative process for single-valued mappings has also been
attempted very recently by Dehaish and Kozlowski (Fixed Point Theory Appl.
2012:118, 2012). In this paper, we initiate the study of approximating fixed points by
the convergence of a Mann iterative process applied on multivalued ρ-nonexpansive
mappings in modular function spaces. Our results also generalize the corresponding
results of (Dehaish and Kozlowski in Fixed Point Theory Appl. 2012:118, 2012) to the
case of multivalued mappings.http://www.fixedpointtheoryandapplications.com/hb201
Strong and △-convergence of some iterative schemes in CAT(0) spaces
No full textAbstractIn this paper, we get some results on strong and △-convergence in CAT(0) spaces for an iterative scheme which is both faster than and independent of the Ishikawa scheme. We also obtain some results for two mappings using the Ishikawa-type iteration scheme. The motivation of the present work comes from that of Dhompongsa and Panyanak (2008) [3]
Common fixed point results for a banach operator pair in cat(0) spaces with applications
No full textModeling the Effect of Repeated Loading on the Behaviour of CFRP Confined Bond of Corroded Reinforcement
No full textMechanical Behavior of Ultrahigh-Performance Concrete Tunnel Lining Segments
No full textUltrahigh-performance concrete (UHPC) is a novel material demonstrating superior mechanical, durability and sustainability performance. However, its implementation in massive structures is hampered by its high initial cost and the lack of stakeholders’ confidence, especially in developing countries. Therefore, the present study explores, for the first time, a novel application of UHPC, incorporating hybrid steel fibers in precast tunnel lining segments. Reduced scale curved tunnel lining segments were cast using UHPC incorporating hybrid 8 mm and 16 mm steel fibers at dosages of 1%, 2% and 3% by mixture volume. Flexural and thrust load tests were conducted to investigate the mechanical behavior of UHPC tunnel lining segments thus produced. It was observed that the flow of UHPC mixtures decreased due to steel fibers addition, yet steel fibers increased the mechanical and durability properties. Flexural tests on lining segments showed that both the strain hardening (multiple cracking) and strain softening (post-peak behavior) phases were enhanced due to hybrid addition of steel fibers in comparison with the control segments without fibers. Specimens incorporating 3% of hybrid steel fibers achieved 57% increase in ultimate load carrying capacity and exhibited multiple cracking patterns compared to that of identical UHPC segments with 1% fibers. Moreover, segments without fibers incurred excessive cracking and spalling of concrete at the base under the thrust load test. However, more stable behavior was observed for segments incorporating steel fibers under the thrust load, indicating its capability to resist typical thrust loads during tunnel lining field installation. This study highlights the potential use of UHPC with hybrid steel fibers for improved structural behavior. Moreover, the use of UHPC allows producing structural members with reduced cross-sectional dimensions, leading to reduced overall structural weight and increased clear space
Common fixed points of two multivalued nonexpansive maps in Kohlenbach hyperbolic spaces
No full textIn this paper, we introduce an iteration scheme for two multivalued maps in Kohlenbach hyperbolic spaces. This extends the single-valued iteration process due to Agarwal et al. (J. Nonlinear Convex Anal. 8(1):61-79, 2007). Using this new algorithm, we approximate common fixed points of two multivalued mappings through △-convergence and strong convergence under some weaker conditions. A necessary and sufficient condition is given for strong convergence.http://link.springer.com/journal/11784hj201
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