Analysis of water hammer in a penstock in the case of valve closure. Part 3: Pressure losses concentrated upstream

Dans cette troisième contribution, en utilisant toujours la même approche analytique basée sur la construction graphique de Bergeron que dans les deux premières parties, nous analysons le phénomène du coup de bélier induit par la fermeture lente d’une vanne en considérant les pertes de charges concentrées en amont de la conduite forcée, juste à la sortie du réservoir. Les équations analytiques gouvernant la propagation des ondes élastiques en charge sont ainsi développées. Le même exemple pratique étudié lors de nos deux premières contributions est ici analysé et les résultats, des débits et des pressions au niveau de la vanne et du réservoir à différents instants, sont comparés à ceux obtenus, en considérant respectivement les pertes de charges négligeables puis concentrées en aval de la conduite, juste à l’entrée de la vanne de sectionnement.In this third contribution, still using the same analytical approach based on Bergeron's graphical construction as in the first two parts, we analyze the water hammer phenomenon induced by the slow closing of a valve by considering pressure losses concentrated upstream of the penstock, just at the outlet of the reservoir. The analytical equations governing the propagation of the elastic waves in charge are thus developed. The same practical example studied during our first two contributions is analyzed here and the results, flow rates and pressures at the level of the valve and the tank at different times, are compared with those obtained, by considering respectively the negligible pressure drops then concentrated downstream of the pipe, just at the inlet of the shut-off valve

Analysis, Behavior, Strengthening and repairing of Reinforced Concrete Corbels: Comprehensive Review

In this review, an extensive survey on the theoretical models and approaches that were proposed in literature to study the behavior of RC corbels has been presented. Such approaches included the shear friction approach, strut and tie model, finite element and Neural networks. Moreover, the review has been extended to consider the studies conducted experimentally by researchers and scholars to investigate the response of the RC corbels. Furthermore, various proposals that were suggested regarding strengthening and repairing of RC corbels have been discussed. Different materials have been used to improve the performance of RC corbels, such as steel fibers, FRP composites, NSM steel bars, NSM CFRP bars and composite sections have been considered. The most important findings reported in the relevant literature have been summarized. In addition, several recommendations to extend the studies concerning the RC corbel to improve the knowledge about the behavior of this significant structural member have been presented

Influence of ground motion duration on seismic fragility of base isolated NPP structures

This study investigates the influence of earthquake duration on seismic fragility of base isolated nuclear power plant (NPP) structures. Two groups of ground motions are employed in performing time history analyses, in which short duration (SD) and long duration (LD) characteristics are considered. The advanced power reactor 1400 (APR1400) NPP structures are used for developing finite element model, which is constructed using lumped-mass stick elements. A series of 486 lead rubber bearings (LRBs) are installed under the base mat of the NPP structures to reduce the seismic damage. Seismic responses of the base isolated NPP are quantified in terms of lateral displacements and hysteretic energy distributions of LRBs. Seismic fragility curves for damage states, which are defined based on the deformation of LRB, are developed. The results reveal that the average lateral displacements of LRBs under SD and LD motions are very similar. For PGA larger than 0.4g, the mean deformation of LRB for LD motions is higher than that for SD motions. The probability of damage of base isolated NPP structures under LD motions is reduced approximately 15% compared to that asubjected to SD earthquakes. This finding emphasizes that it is crucial to use both SD and LD ground motions in seismic evaluations of base isolated NPP structure

The effect of the solar wall heating on the flow structure within the cross-ventilation of isolated building

In this paper a comprehensive study is conducted on the heat transfer between building and the atmosphere within a cross ventilation situation, this situation is characterized by a transverse flow between the two parallel windows of an isolated building.  The study is divided into two parts, in the first part, the effect of the walls, solar heating during the day (windward between sunrise and noon, the roof at the moon and leeward between noon and sunset) on the air temperature distribution and air velocity inside and outside an isolated building is studied when a numerical simulation is conducted in an atmospheric micro scale. For the second part, the study is focused on the effect of temperature change of the building floor, by an external heating source such as a recessed serpentine, on cooling or heating the air but in this case only inside the building by numerical simulation. The numerical results are validated using experimental measurements (velocity profiles and turbulent kinetic energy) of Y. Tominaga realized at Niigata Institute of Technology in Japan, these measurements provide a very useful database for validation of numerical models of computational fluid dynamics (CFD). Compared to those wind tunnel experimental measurements, the numerical results of the cross-ventilation show a good agreement. The detailed results analysis shows that the differential heating of all building surfaces can greatly influence the capacity of the flow to transport and exchange heat

Assessment of Influence of Reinforcement Detailing on Blast Resistance of Reinforced Concrete Beam-column Connections

This study investigates the influence of blast loading on Reinforced Concrete (RC) beam-column connections, which are critical components for maintaining the structural integrity of buildings during extreme events like explosions. The impact of varying blast loads, detonation distance, and reinforcement detailing on the extent of damage in the RC frame and connections is analyzed using ABAQUS/CAE Finite Element Method (FEM) software. Joint rotation is used as a damage indicator to assess the damage level in the structure. The study evaluates the effect of reinforcement detailing on the blast damage resistance of the RC frame and connections and proposes recommendations for reducing damage in the connections through the effective placement of steel reinforcement. The effectiveness of different configurations of reinforcing steel bars is also analyzed, and the presence of shear and diagonal reinforcements is found to reduce joint damage by 3-4 times. This study highlights the significance of reinforcement detailing and recommends its careful consideration in the design of blast-resistant structures

Comparative relevant aspects regarding lightweight concrete containing polystyrene beads

Generally, the main of this experimental work is to found new resources in materials of constructions, especially with the interdiction of the exploitation of some sea sand careers. Thus, advanced constructors use light products, which is going to represent a primordial advantage in the reduction of the seismic risks, because the seismic strength represents a fraction of the total mass of the construction.Moreover, the use of lightweight materials and concrete gives a prime advantage in Algeria regarding the earthquake so try to lighten the slabs as much as possible. Lightweight aggregate concrete is characterized by a combination of cement and low-hardness aggregate. These aggregates have the characteristics of high porosity; they can absorb a large proportion of water from fresh concrete, which reflects the water demand of lightweight aggregate. The latter is also seriously affected by the surface structure and shape of the aggregates used. Based on fly ash aggregate and polystyrene concrete, this paper studies the preparation of lightweight concrete with different amounts of polystyrene concrete instead of fly ash sand. The results show that the cement quality and aggregate density affect the workability and lightweight of concrete

Study of the performance of passive cooling strategies in buildings under arid weather conditions

In Algeria, the building sector accounts for approximately 43% of total primary consumption and accounts for more than one-third of energy-related greenhouse gas emissions. It should be a primary focus for reducing energy consumption and greenhouse gases (GHG) emissions. The new buildings, particularly in the hot and arid southern regions, are completely unsuitable for the climate. The use of inefficient building materials results in high energy consumption. The goal of this project is to investigate passive cooling solutions in order to reduce discomfort and the use of air conditioning systems inside buildings. A two-pronged approach combined chart-based bioclimatic analysis with building performance simulation. The impact of some passive cooling strategies on typical buildings constructed with conventional and local materials was investigated. The study found that when a building uses passive cooling strategies, total cooling needs can be reduced by up to 27% with conventional materials and up to 40% with local materials. In addition, average daily operating temperatures in local buildings can be reduced by up to 2.5 °C and about 1.5 °C in conventional buildings

Using optimization algorithms to detect damages on free-free beam based on dynamic results

This article describes a Modal Analysis method for detecting damage in free-free beams using natural frequency data. The method involves updating a numerical model of the beam with experimental or reference natural frequencies to determine the damage location and damage index. The accuracy of the method was verified through simulations and experiments on beams with both single and double damage zones. The results demonstrate that the method is effective in detecting the damage location for single damage zone and double damage zones with the same or different damage index. However, when the two damage zones are close together, the method that updates the model through PSO optimization algorithm using the reference frequency data may produce inaccurate results. Furthermore, when using experimental frequency data for damage beams, the results indicate that the method has a damage location error of approximately 3.5% along the entire beam length, which is considered acceptable in practical applications. The natural frequency-based damage detection method described in this article offers a useful tool for the assessment of damage in free-free beams and can be effectively combined with visual inspection techniques

Appropriate sample size and effects of microscopic parameters on the shear strength and strain localisation of 2D cohesive-frictional granular assemblies

Granular materials are made up of smaller particles, manifestation of microstructure results in a macroscopic response of granular material. Understanding the overall mechanical behaviour from microscopic parameters is one of the main challenges in many engineering fields including civil engineering. When modelling this kind of material by Discrete Element Model (DEM) using idealized circular grains, the effects of appropriate sample size and microscopic parameter changes have been a crucial subject. Previous research has primarily relied on the case of purely frictional granular materials. In this paper, we use DEM to investigate the appropriate sample size and the relationship between microscopic parameters and the macroscopic responses of cohesive-frictional granular assemblies by performing a series of biaxial tests. Our findings indicate that a minimum number of particles is required to balance between mechanical behaviour and computing time. In addition, through extensive parametric studies, the paper explores the impact of factors such as interparticle bonds, intergranular friction coefficients, and initial void index on the overall shear behaviour of granular assemblies. Also, the result reveals a strong correlation between shear band formation and the break field of cohesive contact (static variable) and the translations and rotations of grains (kinematic variable)

Study on the performance of natural fiber reinforced concrete of different strength with DIP technique and T- Test Analysis

This work focuses on the effect of natural plant fiber as reinforcement on the strength properties of concrete of different grade strength (M30-M50). Fibers of different length were added to the concrete mix at the rate 3% of the binder content. Three different lengths of fibers (10-30 mm) at fixed volume fraction were added to M30, M40 and M50 grades of concrete. The fresh and mechanical property of twelve different fiber reinforced concrete mixes was investigated.  The effect of fibers on the pre cracking, post cracking behaviour of the concrete specimen was investigated using digital image processing technique and video measuring system images.  Using the developed linear regression plot, empirical equations were formulated to establish relation between the compressive strength and other mechanical properties of concrete. From the study it can be concluded that the caryota fiber with rich cellulose content contributes to arrest the cracks at the initial stage of loading and prevents major crack plane in the post peak region. Fibers mainly contribute to increase the tensile property of concrete. The effect of fibers is more prominent in M30 mix concrete when compared to M40 and M50 concrete mixes