Sylvester B. Maphosa and Alphonse Keasley
Leadership development is an essential yet complex process that manifests over a long period of time. Owusu et al. assert that in African researchers’ graduate programs, the…
Abstract
Leadership development is an essential yet complex process that manifests over a long period of time. Owusu et al. assert that in African researchers’ graduate programs, the learners receive theory, research methods and grant writing instruction without significant attention to leadership development. So, how do researchers, academics, administrators, and think-tanks plan and carry out leadership–followership development within organizational and transitional justice fields? The research capacity building of young African scholars in the knowledge production community has the potential to lead to the development and articulation of norms and values that will seek to address fundamental issues of transformation, direct, structural, and cultural violence, and assist in addressing a wide range of problems associated with violence of social injustice. We draw lessons from the Africa Young Graduate Scholars (AYGS) 2017 conference and writing retreat, which drew 22 young scholars (with 10 females and 12 males) who had completed original research and five facilitators (two females and three males) from universities in Botswana, Cameroon, Democratic Republic of Congo (DRC), Kenya, South Africa, Swaziland, and Zimbabwe for developing research leader–follower insights.
Building research leadership–followership capacity in knowledge production communities in the context of conflict prevention is crucial for establishing sustainable peace. It is recommended that: (1) the AYGS be replicated on other parts of the continent and throughout the diaspora; (2) publications from emerging leaders and followers in the research/knowledge production community begin to increase; and (3) establishment and expansion of leadership development programs for research leaders and followers in African graduate programs.
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H. Karpate, H. Wheat, J. Jirsa, D. Fowler and D. Whitney
Reinforced concrete structures have been wrapped to provide strength and confinement in the presence of seismic loads. The wrapping of structures as a means of mitigating…
Abstract
Reinforced concrete structures have been wrapped to provide strength and confinement in the presence of seismic loads. The wrapping of structures as a means of mitigating corrosion is relatively recent. The objective of the work to be described is to investigate the long-term effectiveness of fiber-reinforced polymer (FRP) composite wraps in mitigating corrosion in reinforced concrete elements in severe environments.
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Ayad Alameeri, Gholamreza Abdollahzadeh and Seyedkomeil Hashemiheidari
This study aims to determine the effect of replacing a portion of the cement in the concrete mixture with silica fume (SF) on the corrosion resistance of reinforcing bars, the…
Abstract
Purpose
This study aims to determine the effect of replacing a portion of the cement in the concrete mixture with silica fume (SF) on the corrosion resistance of reinforcing bars, the compressive strength of concrete and the tensile strength of hook bars in both corroded and non-corroded external joints of structures. The external beam-column connection was studied because of its critical role in maintaining structural continuity in all three directions and providing resistance to rotation.
Design/methodology/approach
In external concrete joints, the bars at the end of the beams are often bent at 90° to form hooks that embed in columns. Owing to the importance of embedding distance and the need to understand its susceptibility to corrosion damage from chloride attack, a series of experiments were conducted on 12 specimens that accurately simulate real-site conditions in terms of dimensions, reinforcement and hook bars. SF was replaced with 10% and 15% of the weight of cement in the concrete mixture. To simulate corrosion, the specimens were subjected to accelerated corrosion in the laboratory by applying a low continuous current of 0.35 mA for 58 days.
Findings
The results revealed the effect of SF in improving the compressive strength of concrete, the pullout resistance of the hook bars and the corrosion resistance. In addition, it showed an apparent effect of the corrosion of reinforcing bars in reducing the bonding strength of hook bars with concrete and the effect of SF in improving this strength.
Originality/value
It was noted that the improvement of the results, achieved by replacing 10% of the weight of cement with SF, was significantly close to the results obtained by replacing 15% of the SF. It is recommended that an SF ratio of 10% be adopted to achieve the greatest economic savings.
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Vahid Lotfi and Ali Akbar Jahanitabar
The proposed model is implemented in a special finite element program for its three-dimensional solid elements (Lotfi, 2009), with its nonlinear dynamic analysis modified…
Abstract
Purpose
The proposed model is implemented in a special finite element program for its three-dimensional solid elements (Lotfi, 2009), with its nonlinear dynamic analysis modified according to the HHT-α algorithm, which is fully described. Based on the prepared tools, nonlinear behavior of the Morrow Point dam is studied by applying the invoked damage plasticity concrete model in the presence of contraction joints. For this aim, four cases are considered for the present study. Case A (SF = 1.4), which is based on the linear model, is mainly used for comparative purposes. The other three cases (B, C and D) correspond to the nonlinear model (i.e. damage plasticity model for concrete and nonlinear behavior for contraction joints) with earthquake loading scaling factors of SF = 1.4, 2.0 and 2.6, respectively.
Design/methodology/approach
In the present study, the application of the damage plasticity model in nonlinear dynamic analysis of Morrow Point concrete arch dam is presented. This model is a single-surface isotropic damage plasticity concrete model based on decomposition of stresses and was proposed in a previous study. It should be emphasized that contraction joints are also considered in the model. The theoretical aspects of the model are initially reviewed, and preliminary verification examples are presented. Thereafter, the HHT-α algorithm is presented for nonlinear dynamic analysis of concrete dams.
Findings
(1) In relation with displacement response for nonlinear simulations (i.e. cases B, C and D with SF (i.e. Scaling Factor) = 1.4, 2.0 and 2.6), it is noticed that maximum value of response increases as scaling factor becomes larger. This is such that the maximum value reaches an amount −0.35 m (negative refers to upstream direction) for case D. Moreover, the period elongation becomes quite significant. (2) The nonlinear simulation reveals that Morrow Point arch dam can resist a loading scenario based on Taft earthquake excitation even with an scaling factor as high as SF = 2.6. In this case, the maximum value of upstream displacement at dam mid-crest point reaches −0.35 m which is quite high in comparison with usual linear analysis responses. The extension of tensile damages is quite widespread while for compressive damages, it is much less. Moreover, the maximum tensile and compressive stresses for this case are 3.07 MPa and −33.31 MPa, respectively.
Originality/value
(1) As for the damages plotted at the end of analysis in each case, it is noticed that tensile damage becomes widespread as scaling factor increases. This is such that for case D (SF = 2.6), tensile damage spreads throughout the top portion of the dam body above that initial D/S closed loop occurring for case B (SF = 1.4). This is in both D/S and U/S faces and actually through the whole dam thickness in most parts. In regard to compressive damages, it is observed that it is developed in quite limited portion of dam body for case B. However, it begins to become widespread as scaling factor increases. Of course, most extensive damages corresponds to case D with SF = 2.6 as expected. However, it should be emphasized that even for this case, the amount or extension of compressive damages are much less than corresponding tensile damages. (2) The nonlinear simulation reveals that Morrow Point arch dam can resist a loading scenario based on Taft earthquake excitation even with an scaling factor as high as SF = 2.6. In this case, the maximum value of upstream displacement at dam mid-crest point reaches −0.35 m which is quite high in comparison with usual linear analysis responses. The extension of tensile damages is quite widespread while for compressive damages, it is much less. Moreover, the maximum tensile and compressive stresses for this case are 3.07 MPa and −33.31 MPa, respectively.
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Martin Neuenschwander, Claudio Scandella, Markus Knobloch and Mario Fontana
This paper aims to investigate with strain-rate controlled uniaxial cyclic compression tests the softening behavior of concrete and its elastic stiffness degradation with…
Abstract
Purpose
This paper aims to investigate with strain-rate controlled uniaxial cyclic compression tests the softening behavior of concrete and its elastic stiffness degradation with increasing plastic straining.
Design/methodology/approach
Such tests at ambient temperature show that concrete exhibits the phenomenon of elastic stiffness degradation, which can be captured by damage-plasticity models.
Findings
The experimentally derived evolutions of the elastic stiffness with plastic strain confirm the suitability of the damage-plasticity modeling concept for concrete in compression at elevated temperatures and provide novel calibration data.
Originality/value
Temperature-dependent concrete models implementing this modeling concept are often used presently in structural fire engineering, despite the lack of experiment-based validation data.
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Trong Nghia-Nguyen, Le Thanh Cuong, Samir Khatir, Le Minh Hoang, Salisa Chaiyaput and Magd Abdel Wahab
Concrete gravity dams are important structures for flood control and hydraulic power generation, but they can be vulnerable to seismic activity due to ground movements that…
Abstract
Purpose
Concrete gravity dams are important structures for flood control and hydraulic power generation, but they can be vulnerable to seismic activity due to ground movements that trigger crack propagation.
Design/methodology/approach
To better understand the factors that affect the stability of concrete gravity dams against concrete fracture during earthquakes, a concrete plastic damage model has been utilized with two new expressions to simulate compressive and tensile damage variables.
Findings
The findings showed that the crack patterns were strongly influenced by the concrete’s strength. The simulation results led to the proposal of appropriate concrete properties aimed at minimizing damage. These findings, together with the proposed model, offer significant insights that can enhance the safety and stability of concrete gravity dam structures.
Originality/value
This study offers a comprehensive analysis of concrete behavior under varying grades and introduces simple and robust expressions for evaluating concrete parameters in plastic damage models. The versatility of these expressions enables accurate simulation of stress-strain curves for different grades, resulting in excellent agreement between model results and experimental findings. The simulation of the Koyna Dam case study demonstrates a similarity in crack patterns with previous simulations and field observations.
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Mitra Salmaninezhad and S. Mahmood Jazayeri Moghaddas
Pier scour is one of the main causes of damage to the columns of the river bridges. It is essential to select the best method among various repair methods based on different…
Abstract
Purpose
Pier scour is one of the main causes of damage to the columns of the river bridges. It is essential to select the best method among various repair methods based on different evaluation indices. However, there is no procedure for ranking these repair methods based on their attributes. The present study seeks to set an approach for this ranking.
Design/methodology/approach
In this paper, a multi-attribute decision-making (MADM) model is presented for ranking the repair techniques, in which alternatives are examined using the most important evaluation criteria. In addition, a combination of entropy and eigenvector methods has been proposed for weighting these attributes. A case study is then used to demonstrate the applicability and the validity of the method.
Findings
The execution of the model using two multi-criteria methods yielded similar results, which confirms its accuracy and precision. Moreover, the research findings showed the consistency of the objective and subjective weighting methods and the conformity of the weights obtained for the attributes from the combination of these methods to the nature of the problem.
Originality/value
The selection of the proper method for repairing the bridge columns plays an essential role in success of the bridge restoration. The proposed model introduces an approach for ranking repair methods and selecting the best one that has not been presented so far. Also, the weighing method for attributes is an innovative method for ranking restoration methods that has been proven in a case study.
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In this study, tests were conducted to investigate the effect of different concretes on the behaviour of reinforced concrete beams with central splices. Five beam specimens were…
Abstract
In this study, tests were conducted to investigate the effect of different concretes on the behaviour of reinforced concrete beams with central splices. Five beam specimens were prepared using different concrete mixes in their splice regions. Experimental results indicated that the bond failure of the spliced rebars governed the ultimate flexural behaviour of all specimens, except the one cast with steel fibres. A small increase in flexural strength was found for both the spliced beams cast with high‐strength concrete and steel fibres. Moreover, use of high‐strength concrete and steel fibrous concrete led to a remarkable improvement in the beam's displacement capacity. The effect of pulverised fuel ash on the splice performance was insignificant while the introduction of silica fume caused improvements in loading capacity and ductility.
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Shamsad Ahmad and Mohammed M. Hussein Al-Tholaia
The purpose of this paper was mainly to select one of the three types of coatings for protection of steel used as reinforcement in composite pipes (thin steel shell covered by…
Abstract
Purpose
The purpose of this paper was mainly to select one of the three types of coatings for protection of steel used as reinforcement in composite pipes (thin steel shell covered by cement-mortar) subjected to chloride exposure. To achieve this target, an attempt was made to develop a simple methodology for evaluating the performance of corrosion protection measures in terms of chloride threshold level (CTL) and corrosion initiation time (TI).
Design/methodology/approach
Bare, epoxy, red oxide and zinc primer-coated steel strips were embedded in cement mortar with sand/cement and water/cement ratios of 2 and 0.5 (by mass), respectively, to prepare the specimens which were exposed to chloride solution having a high concentration of 10 per cent NaCl. For determining the amounts of the water-soluble chloride diffused inside the specimens, powdered samples of mortar were collected from two different depths from the exposed surface of specimens on completion of each of the four different exposure times. The corrosion current densities were determined at two different stages. A step-by-step procedure for calculating CTL and TI using the measured chloride contents and corrosion current densities was established with the help of relevant information available in the literature.
Findings
Based on the comparison of the values of CTL and TI calculated for bare steel and steel with all three types of coatings, utilizing the experimental data and the proposed calculation procedure, the epoxy-coated steel was found to have the best performance.
Originality/value
This research has resulted into development of a simple methodology for evaluation of the performance of protective measures against corrosion of steel embedded in mortar or concrete exposed to chloride-bearing environment.
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Nivin M Ahmed, Walaa M. Abd El-Gawad and Eglal R. Souaya
The purpose of this study is to prepare core-shell ferrites/kaolin pigments and compare their efficiency in protecting metal substrates to original ferrites. The new pigments are…
Abstract
Purpose
The purpose of this study is to prepare core-shell ferrites/kaolin pigments and compare their efficiency in protecting metal substrates to original ferrites. The new pigments are based on precipitating a shell of different ferrites that comprise only 10-20 per cent of the whole pigment on kaolin (core), which is a cheap and abundant ore comprising 80-90 per cent of the prepared pigment. These new pigments combine the properties of both its core and shell counter-parts, exhibiting improved corrosion protection properties. Furthermore, the pigments are represented as efficient, economically feasible and eco-friendly with comparable efficiency to that of original ferrites in protecting steel substrates.
Design/methodology/approach
The new pigments were characterized using different analytical and spectrophotometric techniques, e.g. transmission electron microscopy, energy-dispersive X-ray analysis and X-ray fluorescence. The pigments were then incorporated in epoxy-based paint formulations. The physico-mechanical properties of dry films and their corrosion properties were tested using accelerated laboratory tests in 3.5 per cent NaCl for 28 days.
Findings
The results of this study revealed that ferrite/kaolin core-shell pigments performance was almost close to that of the ferrite pigments in the protection of steel, and, at the same time, they confirmed good physico-mechanical properties.
Practical implications
These pigments can be applied in other polymer composites, e.g. rubber and plastics, as fillers and reinforcing agents.
Originality/value
Ferrite and ferrite/kaolin are environmentally friendly pigments, and they can impart high anticorrosive behavior to paint films with concomitant cost savings.