Ultimate Conditions Research Articles

Performance of RC beams strengthened with self-prestressed Fe-SMA bars exposed to freeze-thaw cycles and sustained load

Iron-Based Shape Memory Alloys (Fe-SMA) have been recently used by researchers as a strengthening material for Reinforced Concrete (RC) beams. This material is relatively inexpensive compared to the traditional Nickel Titanium SMA (NiTi-SMA), which makes it feasible for large-scale structural engineering applications. The Fe-SMA is mainly characterized by the Shape Memory Effect (SME) phenomenon, which allows the material to recover the induced deformations through heating. When the pre-strained Fe-SMA bar/strip is anchored on the tension side of an RC beam using the Near-Surface Mounted (NSM) strengthening technique and is then heated to the activation temperature, a tension force (prestressing force) develops in the material, which results in enhancing the flexural capacity of the RC beam at service and ultimate load conditions. This paper investigates the long-term performance of RC beams strengthened with NSM Fe-SMA bars and exposed to severe freeze–thaw cycles and sustained loading. The results revealed that the strengthened beam was superior in flexural performance compared to the un-strengthened beam, and there was minimal degradation compared to other beams tested at room temperature.

Flexural behaviour of precast segmental concrete beams internally prestressed with unbonded CFRP tendons under four-point loading

This study investigates the use of carbon fibre reinforced polymer (CFRP) tendons on precast segmental beams (PSBs) to tackle the corrosion problems which are likely to occur at joint locations of PSBs prestressed with steel tendons. Up to date, the use of CFRP tendons was extensively documented for monolithic beams while their application on PSBs has not been reported yet. Three precast segmental T-section beams including two beams with unbonded CFRP and one with steel tendons were built and tested under four-point loads in this study. The test results showed that CFRP tendons can be well used to replace the steel tendons on PSBs. The beams with CFRP tendons demonstrated both high strength and high ductility as compared to the beam with steel tendons. However, the stresses in the unbonded CFRP tendons at ultimate loading conditions of the tested beams were low, ranging from only about 66% to 72% of the nominal breaking tensile strength. The type of joints i.e. dry and epoxied, greatly affects the initial stiffness of the beams but has no effect on the opening of joints at ultimate loading stage. Moreover, a comprehensive examination on four existing code equations to predict the stress in the unbonded tendons showed that the four examined codes predicted well the stress at the ultimate loading condition of the unbonded steel tendons, however, they significantly under predicted those in the CFRP tendons. A modification in the strain reduction coefficient used by ACI 440.4R for predicting the stress increment in unbonded CFRP tendons of monolithic beams is therefore proposed for PSBs based on the experimental results.

Load-bearing capacity of flexural reinforced concrete members strengthened with fiber-reinforced polymer in fracture stage

The article examines the behavior of flexural reinforced concrete members, strengthened with fiber-reinforced polymers (FRP), under the ultimate loading conditions (in fracture stage). One of the m...

Fatigue properties of nano-reinforced bituminous mixtures: A viscoelastic continuum damage approach

The experimental investigation described in this paper focused on the effects of nanoclays on the fatigue behaviour of bituminous mixtures. Damage characteristics of a bituminous mixture produced by making use of a nano-reinforced binder were compared to those of a reference mixture obtained by employing the same neat bitumen used as a base in the preparation of the nanoclay–bitumen blend. Dynamic modulus tests and direct tension cyclic fatigue tests were carried out to determine the linear viscoelastic properties and the damage evolution characteristics of materials. Corresponding results were modelled by means of a viscoelastic continuum damage approach and by making use of a more empirical evaluation based on the classical Wöhler representation. It was found that the use of nanoclays produced a reinforcement of bituminous mixtures, the benefits of which were observed both in the progression of damage and in the occurrence of ultimate failure conditions.

Beyond Autonomy:

What is studying in its difference from institutions? Benjamin took up the problem of studying with all the energy of his student dissatisfaction. In one of his early texts he investigates the “life of students” under the aspect of a historical concept in which history appears to be concentrated in a single focal point, like those traditionally found in the utopian images of the philosophers. He goes on to speak of elements of an ultimate condition that are deeply embedded in every present day. I would like to take these propositions as hints to the Benjaminian concept of study, and I want to show how Benjamin’s program to grasp student life metaphysically involves a fundamental connection between the practice of study and a discontinuous concept of time.

Stress-testing the ALFRED design - Part III: Safety margins evaluation

The advancement of the design of the Advanced Lead-cooled Fast Reactor European Demonstrator (ALFRED) beyond the conceptual phase, passes through the analysis of the impact of uncertainties, notably to what concerns safety-related conditions. Compliancy of plant safety to Design Extension Conditions is, according to IAEA and in line with the meaning itself of these beyond-design conditions, usually investigated by best estimates only. Due however to the demonstration nature of ALFRED, it was decided to assess the actual safety performances of this system even in ultimate conditions. To this regard, the emphasis was put on unprotected events like the UTOP (unprotected transient of over-power) and ULOOP (unprotected loss of offsite power, resulting from the combination of a loss of flow and loss of heat sink under unprotected conditions), pinpointed as the most challenging situations sought for the plant. The purpose of the present work, which has been divided in three parts, was then to assess the ultimate ALFRED safety margins against failure of the key core components and systems (Part III). To target this objective, the evaluation of uncertainties coming, on one hand, from nuclear data was performed at first, to retrieve their impact on the reactivity coefficients, thereby on the transient behavior driven by the latter (Part I); then, uncertainties from material properties, fabrication procedures, operation and measurement, and computational tools were propagated to assess their influence on the thermal-hydraulics of the system (Part II). In this work the efforts of Parts I and II are merged together and the effect of uncertainties on safety margins and salient parameters assessed. The retrieved uncertainties are propagated to the expected number of pins experiencing fuel melting during an UTOP and to the clad time-to-failure during an ULOOP. The former has been found to be quite affected by uncertainties, but still under limits not directly posing hazards to the people and the environment, even when extremely conservative assumptions are put forward; the latter shows a milder response to uncertainties, but always guaranteeing more than an order of magnitude of safety margin relative to WENRA recommendations.

Stress-testing the ALFRED design – Part I: Impact of nuclear data uncertainties on Design Extension Conditions transients

The advancement of the design of ALFRED beyond the conceptual phase, passes through the analysis of the impact of uncertainties, notably to what concerns safety-related conditions. Compliancy of plant safety to Design Extension Conditions is, according to IAEA and in line with the meaning itself of these beyond-design conditions, usually investigated by best estimates only. Due however to the demonstration nature of ALFRED, it was decided to assess the actual safety performances of this system even in ultimate conditions. To this regard, the emphasis was put on unprotected events like the UTOP (unprotected transient of over-power) and ULOOP (unprotected loss of offsite power, resulting from the combination of a loss of flow and loss of heat sink under unprotected conditions), pinpointed as the most challenging situations sought for the plant. The purpose of the present work, which has been divided in three parts, was then to assess the ultimate ALFRED safety margins against failure of the key core components and systems (Part III). To target this objective, the evaluation of uncertainties coming, on one hand, from nuclear data was performed at first, to retrieve their impact on the reactivity coefficients, thereby on the transient behavior driven by the latter (Part I); then, uncertainties from material properties, fabrication procedures, operation and computational tools were propagated to assess their influence on the thermal-hydraulics of the system (Part II). In this paper, presenting the first part of the work, the focus is on nuclear data. As such, a sensitivity/uncertainty analysis of the ALFRED core on key elementary reactivity effects, forming the basis for computing the feedback coefficients, has been performed. The sensitivity analysis allowed pointing out firstly the most relevant cross-sections for every response function. Uncertainty analysis allowed then establishing a possible range of confidence for the reactivity effects. The adjoint-based technique implemented in the TSUNAMI-3D module of the SCALE6 system was used. The confidence intervals identified for each reactivity effect have been combined then into confidence intervals for the feedback coefficients. Finally, the most conservative, yet physically sound (i.e., where correlations among coefficients, stemming from dependencies on common nuclear data, are taken into account), set of reactivity coefficients has been picked out from the confidence intervals, enabling transient calculations to propagate uncertainties into transient behavior. Using this off-nominal set, and comparing results with the reference ones, exploiting the system codes SIM-LFR and RELAP, a negligible effect of nuclear data uncertainties has been found for the ULOOP, while an increase of the maximum achieved power of around 6% has been computed for the UTOP. Overall, a modest contribution of nuclear data uncertainties for these transients has been found which, however, must be combined with the thermal-hydraulics one so to finally assess safety margins.

Hominin skeletal part abundances and claims of deliberate disposal of corpses in the Middle Pleistocene

Humans are set apart from other organisms by the realization of their own mortality. Thus, determining the prehistoric emergence of this capacity is of significant interest to understanding the uniqueness of the human animal. Tracing that capacity chronologically is possible through archaeological investigations that focus on physical markers that reflect "mortality salience." Among these markers is the deliberate and culturally mediated disposal of corpses. Some Neandertal bone assemblages are among the earliest reasonable claims for the deliberate disposal of hominins, but even these are vigorously debated. More dramatic assertions center on the Middle Pleistocene sites of Sima de los Huesos (SH, Spain) and the Dinaledi Chamber (DC, South Africa), where the remains of multiple hominin individuals were found in deep caves, and under reported taphonomic circumstances that seem to discount the possibility that nonhominin actors and processes contributed to their formation. These claims, with significant implications for charting the evolution of the "human condition," deserve scrutiny. We test these assertions through machine-learning analyses of hominin skeletal part representation in the SH and DC assemblages. Our results indicate that nonanthropogenic agents and abiotic processes cannot yet be ruled out as significant contributors to the ultimate condition of both collections. This finding does not falsify hypotheses of deliberate disposal for the SH and DC corpses, but does indicate that the data also support partially or completely nonanthropogenic formational histories.

Effect of Load Cycling, FRP Jackets, and Lap-Splicing of Longitudinal Bars on the Effective Stiffness and Ultimate Deformation of Flexure-Controlled RC Members

AbstractPractical models for the deformations of flexure-controlled reinforced concrete (RC) members at flexural yielding and at ultimate conditions and for their secant-to-yield-point stiffness we...

Confinement Behavior of Spun Pile using Low Amount of Spiral Reinforcement – an Experimental Study

In this paper, further analysis from the result of spun pile test under reverse flexural load and combined with two levels constant axial load, 40 tons (0.08fc’Ag) and 80 tons (0.16fc’Ag), is presented. The analysis is related to the confinement behavior of the concrete section of pile using the low amount of spiral reinforcement. It is shown that the strain readings from the spiral reinforcement indicate a subtle contribution in terms of confinement mechanism of the hollow section of a pile. In addition, it is evident that spiral reinforcement seems to be compressed when the concrete section resists compression strain due to flexural load. The crushing of concrete at ultimate condition could also not be resisted by spiral reinforcement by any means.

Ultimate boundedness sufficient conditions for nonlinear systems using TS fuzzy modelling

Using Takagi–Sugeno (TS) fuzzy modelling, sufficient conditions to ensure ultimate boundedness of solutions of nonlinear switched systems are given. The sufficient conditions are given in terms of properties of invariant sets and of an auxiliary system formed by a convex combination of the switching subsystems. By exploring the results of this paper, estimates of the attractor and domain of attraction can be found even when (i) the derivative of an auxiliary function V, which plays the same role of a Lyapunov function, attains positive values in some sets and (ii) the solutions of each subsystem of the switched system are not necessarily ultimately bounded. The sufficient conditions are formulated as a problem of checking the feasibility of linear matrix inequalities (LMIs). Indeed, these LMIs provide a systematic procedure that can help to find auxiliary scalar Lyapunov-like functions for a class of switched nonlinear systems. A numerical example illustrates the effectiveness of the proposed approach in estimating attractors of nonlinear dynamic switched systems.

Numerical Investigation of Masonry Strengthened with Composites.

In this work, two main fiber strengthening systems typically applied in masonry structures have been investigated: composites made of basalt and hemp fibers, coupled with inorganic matrix. Starting from the experimental results on composites, the out-of-plane behavior of the strengthened masonry was assessed according to several numerical analyses. In a first step, the ultimate behavior was assessed in terms of P (axial load)-M (bending moment) domain (i.e., failure surface), changing several mechanical parameters. In order to assess the ductility capacity of the strengthened masonry elements, the P-M domain was estimated starting from the bending moment-curvature diagrams. Key information about the impact of several mechanical parameters on both the capacity and the ductility was considered. Furthermore, the numerical analyses allow the assessment of the efficiency of the strengthening system, changing the main mechanical properties. Basalt fibers had lower efficiency when applied to weak masonry. In this case, the elastic properties of the masonry did not influence the structural behavior under a no tension assumption for the masonry. Conversely, their impact became non-negligible, especially for higher values of the compressive strength of the masonry. The stress-strain curve used to model the composite impacted the flexural strength. Natural fibers provided similar outcomes, but a first difference regards the higher mechanical compatibility of the strengthening system with the substrate. In this case, the ultimate condition is due to the failure mode of the composite. The stress-strain curves used to model the strengthening system are crucial in the ductility estimation of the strengthened masonry. However, the behavior of the composite strongly influences the curvature ductility in the case of higher compressive strength for masonry. The numerical results discussed in this paper provide the base to develop normalized capacity models able to provide important information on the out-of-plane behavior of masonry elements strengthened with inorganic matrix and several kinds of fibers, both synthetic and natural.

Development of the Main Wing Structure of a High Altitude Long Endurance UAV

To enhance the flight endurance of a HALE UAV, the main wing of the UAV should have a high aspect ratio and low structural weight. Since a main wing constructed with the thin walled and slender components needed for low structural weight can suffer catastrophic failure during flight, it is important to develop a light-weight airframe without sacrificing structural integrity. In this paper, the design of the main wing of the HALE UAV was conducted using spars which were composed of a carbon–epoxy cylindrical tube and bulkheads to achieve both the weight reduction and structural integrity. The spars were sized using numerical analysis considering non-linear deformation under bending moment. Static strength testing of the wing was conducted under the most critical load condition. Then, the experimental results obtained for the wing were compared to the analytical result from the non-linear finite-element analysis. It was found that the developed main wing reduced its structural weight without any failure under the ultimate load condition of the static strength testing.

Stress-testing the ALFRED design - Part II: Quantification of uncertainties on the fuel assembly temperature field

The advancement of the design of the Advanced Lead-cooled Fast Reactor European Demonstrator (ALFRED) beyond the conceptual phase, passes through the analysis of the impact of uncertainties, notably to what concerns safety-related conditions. Compliancy of plant safety to Design Extension Conditions is, according to IAEA and in line with the meaning itself of these beyond-design conditions, usually investigated by best estimates only. Due however to the demonstration nature of ALFRED, it was decided to assess the actual safety performances of this system even in ultimate conditions. To this regard, the emphasis was put on unprotected events like the UTOP (unprotected transient of over-power) and ULOOP (unprotected loss of offsite power, resulting from the combination of a loss of flow and loss of heat sink under unprotected conditions), pinpointed as the most challenging situations sought for the plant. The purpose of the present work, which has been divided in three parts, was then to assess the ultimate ALFRED safety margins against failure of the key core components and systems (Part III). To target this objective, the evaluation of uncertainties coming, on one hand, from nuclear data was performed at first, to retrieve their impact on the reactivity coefficients, thereby on the transient behavior driven by the latter (Part I); then, uncertainties from material properties, fabrication procedures, operation and computational tools were propagated to assess their influence on the thermal-hydraulics of the system (Part II). In this work the focus is on the latter uncertainties. The adopted methodology is presented at first, namely the semi-statistical vertical approach – characterized by an optimal degree of conservatism among the classical approaches – targeting a 3σ confidence interval. Then, the identification and propagation of each effect are shown, by means of the heat equations, so to retrieve the actual uncertainties on the parameters of interest (the temperatures themselves). Finally, a hot spot analysis to quantify the uncertainty-distorted temperature field is elaborated and presented. The performed analysis has revealed the great impact of fabrication tolerances for the coolant, film and clad temperature rises, particularly affecting safety margins during an ULOOP, while models and material properties uncertainties seem to dominate for the gap and fuel rises, which concur notably in challenging the respect of the fuel melting limit in an UTOP.

Preloading Effect on Strengthening Efficiency of RC Beams Strengthened with Non- and Pretensioned NSM Strips

The near surface mounted (NSM) technique has been shown to be one of the most promising methods for upgrading reinforced concrete (RC) structures. Many tests carried out on RC members strengthened in flexure with NSM fiber-reinforced polymer (FRP) systems have demonstrated greater strengthening efficiency than the use of externally-bonded (EB) FRP laminates. Strengthening with simultaneous pretensioning of the FRP results in improvements in the serviceability limit state (SLS) conditions, including the increased cracking moment and decreased deflections. The objective of the reported experimental program, which consisted of two series of RC beams strengthened in flexure with NSM CFRP strips, was to investigate the influence of a number of parameters on the strengthening efficiency. The test program focused on an analysis of the effects of preloading on the strengthening efficiency which has been investigated very rarely despite being one of the most important parameters to be taken into account in strengthening design. Two preloading levels were considered: the beam self-weight only, which corresponded to stresses on the internal longitudinal reinforcement of 25% and 14% of the yield stress (depending on a steel reinforcement ratio), and the self-weight with the additional superimposed load, corresponding to 60% of the yield strength of the unstrengthened beam and a deflection equal to the allowable deflection at the SLS. The influence of the longitudinal steel reinforcement ratio was also considered in this study. To reflect the variability seen in existing structures, test specimens were varied by using different steel bar diameters. Finally, the impact of the composite reinforcement ratio and the number of pretensioned FRP strips was considered. Specimens were divided into two series based on their strengthening configuration: series “A” were strengthened with one pretensioned and two non-pretensioned carbon FRP (CFRP) strips, while series “B” were strengthened with two pretensioned strips. Experimental tests illustrated promising results at ultimate and serviceability limit state conditions. A significant gain of the load bearing capacity, in the range between 56% and 135% compared to the unstrengthened beams, was obtained. Tensile rupture of the NSM CFRP strips was achieved, confirming full utilization of the material.

The level of organizational culture as a constant challenge for company management – an empirical research in the Czech Republic and Poland

Due to the pressure of global competition, shortened product-life cycles and the increasing opportunity to imitate product designs or their elements, companies continuously focus on innovations as one of their main agenda in order to maintain their global or national competitiveness. Besides, these innovations are considered as an ultimate source of productivity improvement, the growth in sales volume, and the capability of a company in question to stay competitive on the global market (Liao, Hu, Chen, & Lin, 2015). Companies perceive the need to continuously adapt, develop, and innovate as an economic necessity that results from global market pressures. The enhancement of product design and quality, accessorial technological services, their accessibility and reliability are no longer only seen as a benefit but rather an ultimate condition for the sustainability of company competitiveness.

Ultimate strength and strain models proposed for CFRP confined concrete cylinders

The use of external carbon-fiber-reinforced polymer (CFRP) laminates is one of the most effective techniques existing for the confinement of circular concrete specimens. Currently, several researches have been made to develop models for predicting the ultimate conditions of this type of confinement. As most of the major existing models were developed based on limited experimental database. This paper presents the development of new confinement ultimate conditions, strength and strain models, for concrete cylinders confined with CFRP composites based on a statistical analysis of a large existing experimental database of 310 cylindrical concrete specimens wrapped with CFRP. The database is used to evaluate the performance of the proposed and major existing strength and strain models. Based on the two different statistical indices, the coefficient of determination (R2) and the Root Mean Square Error (RMSE), the two proposed confinement ultimate conditions presents a good performance compared to the major existing models except the models of Lam and Teng (2003) and Youssef et al. (2007) which have relatively similar performance to the proposed models.

Production of Bio-Oil from Agriculture Waste

Biomass energy which includes producing energy fuel from plant is considered a promising source of renewable energy. This research aims to develop a new method to liquefy two types of agriculture waste and compare between their produced bio-oils in terms of ultimate production conditions, compositions and applications.Firstly, One gram of two different types of agriculture wastes include Corn sticks (CS) and Palm leaves (PL) were liquefied by autoclaving at 2.5 atm pressure and 220°C temperature. The liquefaction process had been performed in the range of 10 to 80 ml ethanol/g treated solid, and retention time ranges between 10 to 120 min., the produced bio-oil were extracted and separated into three fractions: volatile, light and heavy.The results show that, the maximum amount (0.04 g/g) of volatile bio-oil can be produced from CS at 40 ml ethanol/g treated solid and 30 min retention time. However maximum amount of light bio-oil (g/g) was obtained from CS at 30 ml ethanol/1 g treated solid and 60 min retention time. For heavy bio-oil, maximum amount (0.25 g/g) was derived from CS when the ratio between ethanol (ml): treated solid (g) is 30:1 and the retention time is 60 min.Experimental data had been analysed using matlab software to get the modules which give the relations between bio-oil produced, ethanol to solid ratio and retention time in order to get the ultimate conditions of the process. GC-MS and FTIR analysis has been done to identify the bio-oils compositions. The results show that produced bio-oil from CS is highly contained carbon atom from C20-C38 in addition it contains high percentage of C6-C9 atoms. Therefore, the bio-oil from CS can be used as bio-fuel. However, the produced bio-oil from PL is mainly unsaturated acids which has carbon atom from C10-C18. Thus, it has pharmaceutical applications.

Physiological and biochemical basis of fruit development and ripening-a review

Fruits and vegetables are the natural source of vitamins, minerals and nutrients that play an important role in the human diet. Despite of tremendous increase in production and productivity, their per-capita availability for world population is a great challenge ahead due to constant postharvest losses occurring in perishable horticultural produce. These postharvest losses especially in terms of quality and nutritional composition could be controlled to a greater extent with better knowledge regarding their postharvest physiology. The ultimate physiological condition of the fresh produce determines their fitness for end use, including storability and acceptability for primary or secondary processing. Hence, it is indispensable to understand the physiological responses of perishable commodities to the storage conditions in direct relation to the intended end use. Physical, physiological and biochemical changes occurring during fruit ripening seem to modify their internal quality in terms of firmness, colour, starch content, organic acids and flavouring compounds. Thus, the knowledge on physiological profile of perishable fruits and vegetables could act as a powerful tool for their optimized commercial utilization.

Increasing the reliability of the soil slopes design using evolutionary modelling

An issue has been discussed on determining the best value of quadrangular trench slopes, grade considering the provision of reliability for soil steady position in minimizing the quantity of the necessary earthworks. The calculation algorithm has been described including the determination of stability coefficient for a soil slope being in the ultimate rock equilibrium condition. The task is completed via the method of circular-cylindrical revolving surfaces using the genetic algorithm.