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Zeitschriftendaten
Format
Zeitschrift
eISSN
1338-3973
ISSN
1210-3896
Erstveröffentlichung
23 May 2011
Erscheinungsweise
4 Hefte pro Jahr
Sprachen
Englisch

Suche

Volumen 27 (2019): Heft 3 (September 2019)

Zeitschriftendaten
Format
Zeitschrift
eISSN
1338-3973
ISSN
1210-3896
Erstveröffentlichung
23 May 2011
Erscheinungsweise
4 Hefte pro Jahr
Sprachen
Englisch

Suche

8 Artikel
access type Uneingeschränkter Zugang

On Steady Two-dimensional Free-surface Flows with Spatially-varied Discharges

Online veröffentlicht: 04 Oct 2019
Seitenbereich: 1 - 11

Zusammenfassung

Abstract

In an open-channel, the transition of a flow from a subcritical to a supercritical state may occur as a result of a lateral inflow or outflow that produces a streamwise discharge variation. Apparently, such a transition cannot be modeled accurately by a conventional hydrostatic pressure approach. In this study, a depth-averaged model that accounts for the effects of a spatially-varied discharge and a non-hydrostatic pressure distribution was developed and applied to simulate the transcritical flow in a lateral-spillway channel and the subcritical flow in a main channel fitted with side weirs. The model results for the axial free-surface profile and variation of discharge in the main channel were compared with the results of a shallow-flow model and experimental data, thereby resulting in a closer match to the measurements than the shallow-flow model. Overall, the investigation results confirmed the efficiency and validity of the non-hydrostatic depth-averaged model in simulating the mean flow characteristics of the subcritical and transcritical free-surface flows with spatially increasing or decreasing discharges, thus demonstrating its potential to be used as a numerical tool in engineering practice.

Schlüsselwörter

  • Hydraulicstructures
  • Side-weir overflow
  • Non-hydrostatic flow
  • Spatially-varied flow
  • Numerical model
  • Side-channel spillway
access type Uneingeschränkter Zugang

Seismic Response of Reactive Powder Concrete Columns Confined with FRP

Online veröffentlicht: 04 Oct 2019
Seitenbereich: 12 - 20

Zusammenfassung

Abstract

In this research, which is based on the finite element method, the behavior of reactive powder concrete (RPC) columns confined with fiber-reinforced polymer (FRP) under seismic excitation is investigated. The governing theory in the numerical simulation is based on the fiber finite element method. The adequacy of the fiber model in predicting the response of FRP-confined RPC columns is validated through comparisons with the available experimental results. To study the seismic behavior of FRP-confined RPC columns, the fiber model presented was subjected to different earthquakes. In this regard, four ground acceleration time histories with different peak accelerations were applied to investigate the response of FRP-confined RPC columns. The results show that reactive powder concrete columns confined with FRP exhibit an acceptable seismic performance. The investigation also confirms that RPC-confined columns show a high degree of ductility. Additionally, the load capacity (maximum lateral load) is increased, and the concrete’s compressive strength is increased.

Schlüsselwörter

  • Finite element method
  • reactive powder concrete column
  • seismic response
  • Compressive strength
  • Modelling
  • FRP
access type Uneingeschränkter Zugang

Requirements for Pavement Base Layers with Unbound Granular Material

Online veröffentlicht: 04 Oct 2019
Seitenbereich: 21 - 28

Zusammenfassung

Abstract

Pavement structures, layers, and parameters must meet the strict requirements of applicable standards and regulations. The thickness of layers and the choice of materials depend on the factors involved, i.e., the traffic load and climatic factors (changes in temperature, water, rain, snow); they are also dependent on the geological environment at the road construction site and the parameters and properties of the embankment (the subgrade of the pavement). In some cases, the capacity of the existing transport infrastructure is on the edge of sustainability. The increase in the traffic load and the use of lower-class roads by freight transport, together with insufficient maintenance, has resulted in a deterioration of road conditions, thereby causing many deficiencies and failures.

The required serviceability and operational performance of roads can be ensured by the choice of suitable quality materials and technological construction processes. Technologies that are environmentally acceptable and economically efficient should be preferred.

Schlüsselwörter

  • Pavementstructure
  • Unbound granular mixture
  • Laboratory tests
  • Modified Proctor Test
  • Immediate bearing index (IBI)
access type Uneingeschränkter Zugang

Numerical Investigation of the Behavior of Strip Footings under Large Eccentric Loads

Online veröffentlicht: 04 Oct 2019
Seitenbereich: 29 - 36

Zusammenfassung

Abstract

In this paper, numerical computations using the FLAC code are carried out to investigate of the behavior the bearing capacity of strip footings embedded in sandy soil and under large eccentric vertical load conditions. The study focuses on an evaluation of the non-dimensional reduction factor (RF), which is the ratio between the average bearing capacity of an eccentric footing and its bearing capacity when subjected to a central load. The results indicate a significant decrease in RF when the eccentricity increases and the curve of the decrease is parabolic, even in large eccentricity cases. Based on the numerical results obtained, a new formula of the RF is proposed, and the reasons for the discrepancy between the RF proposed by several authors are identified. The values provided by the proposed formula are in close agreement with some experimental results available in the literature.

Schlüsselwörter

  • Bearingcapacity
  • Reduction factor
  • Numerical modelling
  • Large eccentricity
access type Uneingeschränkter Zugang

Assessment of the Impact of Changes in Deforestation under the Effect of Severe Windstorms on Runoff Conditions in Small River Basins

Online veröffentlicht: 04 Oct 2019
Seitenbereich: 37 - 43

Zusammenfassung

Abstract

Forests represent the most natural means of retaining water in a basin. Assessing the impact of a forest on a hydrological cycle is a very current topic that hydrologists and water managers deal with. The differences between site conditions and a forest itself, together with various methods of exploring this issue, lead to inconsistent opinions on the extent of the ability of a forest cover to prevent or minimize surface runoff.

This article is therefore focused on an assessment of the impact of changes in the composition of a forest under the effect of severe windstorms on runoff conditions in the selected river basin. The most severe windstorms in the last 25 years and their impact on changes in forest cover in the selected area of the Ipoltica River basin have been assessed in this article. The most significant severe windstorm in terms of its impact on changes in the forest communities was Filip, which occurred in the year 2007. Therefore, the impact of changes in forest cover on the given territory was examined for the period after the year 2007. The WetSpa rainfall-runoff model was used to assess the changes.

Schlüsselwörter

  • land use change
  • Severe windstorm
  • WetSpa model
  • Rainfall-runoff modeling
access type Uneingeschränkter Zugang

Static and Dynamic Responses of a Reinforced Concrete Beam Strengthened with Steel and Polypropylene Fibers

Online veröffentlicht: 04 Oct 2019
Seitenbereich: 44 - 54

Zusammenfassung

Abstract

This paper describes an experimental investigation on mono steel and polypropylene (PP) fiber-reinforced concrete beams. The main aim of this present study is to evaluate undamaged and damaged reinforced concrete (RC) beams incorporated with mono fibers such as steel and PP fibers under free-free constraints. In this experimental work, a total of nine RC beams were cast and analyzed in order to study the dynamic behavior as well as the static load behavior of steel fiber-reinforced concrete (SFRCs) and polypropylene fiber-reinforced concrete (PPFRCs). Damage to the SFRC and PPFRC beams was obtained by cracking the concrete for one of the beams in each set under four-point bending tests with different percentage variations of the damage levels such as 50%, 70% and 90% of the maximum ultimate load. The fundamental natural frequency and damping values obtained through the dynamic tests for the SFRC and PPFRC beams were compared with a control RC beam at each level of damage that had been acquired through static tests. The static experimental test results emphasize that the SFRC beam has attained a higher ultimate load compared with the control RC beam.

Schlüsselwörter

  • SFRC
  • PPFRC
  • Damage
  • FRF
  • Damping
  • Four-point test
  • Dynamic
  • Flexure
access type Uneingeschränkter Zugang

Optimization of Energy Generation based on Operations and Ecological Integrity Requirements

Online veröffentlicht: 04 Oct 2019
Seitenbereich: 55 - 62

Zusammenfassung

Abstract

The management of water resources for different purposes such as a domestic water supply and municipal, irrigation and hydropower generation requires optimization techniques for efficient reservoir operations. This study focused on the optimization of energy generation at Kainji hydropower station in Nigeria using operational and ecological integrity constraints. A linear optimization technique was used in optimizing the average total annual energy generation subject to operational and ecological integrity constraints. The model was solved using LINGO 17.0 software. The results revealed that the optimization approach would increase the total annual energy generation at the hydropower station by 1.84%. The outcome of this study can be adopted by the management of a hydropower station and other decision makers in Nigeria to improve the availability of electricity deployed to Nigeria’s national grid without compromising the ecological integrity of a reservoir.

Schlüsselwörter

  • Energygeneration
  • Optimization
  • Kainji reservoir
  • Ecological integrity onthly discharge
access type Uneingeschränkter Zugang

Formation of Gully Erosion in the Myjava Region

Online veröffentlicht: 04 Oct 2019
Seitenbereich: 63 - 72

Zusammenfassung

Abstract

The article deals with the problems of the occurrence and formation of gully erosion in the Myjava catchment. Gully erosion is a significant problem in that region of Slovakia. Together with this type of soil erosion, muddy floods, waste ground, economic losses in agriculture, and many other problems are involved. The main objectives of this article are an analysis of the occurrence of gully erosion in the Myjava region in different periods of time and identification of the most significant factors that have impacted the formation of the gully network. The appearance of gully erosion has been identified from historical maps and other historical documents preserved from the region. The factors analysed were mainly human activities that resulted in changes in land use and physical-geographic catchment characteristics such as the soil, the geology, and the morphology. Nowadays, we are seriously lagging behind in dealing with this issue compared to other European countries.

Schlüsselwörter

  • Myjava catchment
  • Gully erosion
  • Land use change
  • Historical maps
8 Artikel
access type Uneingeschränkter Zugang

On Steady Two-dimensional Free-surface Flows with Spatially-varied Discharges

Online veröffentlicht: 04 Oct 2019
Seitenbereich: 1 - 11

Zusammenfassung

Abstract

In an open-channel, the transition of a flow from a subcritical to a supercritical state may occur as a result of a lateral inflow or outflow that produces a streamwise discharge variation. Apparently, such a transition cannot be modeled accurately by a conventional hydrostatic pressure approach. In this study, a depth-averaged model that accounts for the effects of a spatially-varied discharge and a non-hydrostatic pressure distribution was developed and applied to simulate the transcritical flow in a lateral-spillway channel and the subcritical flow in a main channel fitted with side weirs. The model results for the axial free-surface profile and variation of discharge in the main channel were compared with the results of a shallow-flow model and experimental data, thereby resulting in a closer match to the measurements than the shallow-flow model. Overall, the investigation results confirmed the efficiency and validity of the non-hydrostatic depth-averaged model in simulating the mean flow characteristics of the subcritical and transcritical free-surface flows with spatially increasing or decreasing discharges, thus demonstrating its potential to be used as a numerical tool in engineering practice.

Schlüsselwörter

  • Hydraulicstructures
  • Side-weir overflow
  • Non-hydrostatic flow
  • Spatially-varied flow
  • Numerical model
  • Side-channel spillway
access type Uneingeschränkter Zugang

Seismic Response of Reactive Powder Concrete Columns Confined with FRP

Online veröffentlicht: 04 Oct 2019
Seitenbereich: 12 - 20

Zusammenfassung

Abstract

In this research, which is based on the finite element method, the behavior of reactive powder concrete (RPC) columns confined with fiber-reinforced polymer (FRP) under seismic excitation is investigated. The governing theory in the numerical simulation is based on the fiber finite element method. The adequacy of the fiber model in predicting the response of FRP-confined RPC columns is validated through comparisons with the available experimental results. To study the seismic behavior of FRP-confined RPC columns, the fiber model presented was subjected to different earthquakes. In this regard, four ground acceleration time histories with different peak accelerations were applied to investigate the response of FRP-confined RPC columns. The results show that reactive powder concrete columns confined with FRP exhibit an acceptable seismic performance. The investigation also confirms that RPC-confined columns show a high degree of ductility. Additionally, the load capacity (maximum lateral load) is increased, and the concrete’s compressive strength is increased.

Schlüsselwörter

  • Finite element method
  • reactive powder concrete column
  • seismic response
  • Compressive strength
  • Modelling
  • FRP
access type Uneingeschränkter Zugang

Requirements for Pavement Base Layers with Unbound Granular Material

Online veröffentlicht: 04 Oct 2019
Seitenbereich: 21 - 28

Zusammenfassung

Abstract

Pavement structures, layers, and parameters must meet the strict requirements of applicable standards and regulations. The thickness of layers and the choice of materials depend on the factors involved, i.e., the traffic load and climatic factors (changes in temperature, water, rain, snow); they are also dependent on the geological environment at the road construction site and the parameters and properties of the embankment (the subgrade of the pavement). In some cases, the capacity of the existing transport infrastructure is on the edge of sustainability. The increase in the traffic load and the use of lower-class roads by freight transport, together with insufficient maintenance, has resulted in a deterioration of road conditions, thereby causing many deficiencies and failures.

The required serviceability and operational performance of roads can be ensured by the choice of suitable quality materials and technological construction processes. Technologies that are environmentally acceptable and economically efficient should be preferred.

Schlüsselwörter

  • Pavementstructure
  • Unbound granular mixture
  • Laboratory tests
  • Modified Proctor Test
  • Immediate bearing index (IBI)
access type Uneingeschränkter Zugang

Numerical Investigation of the Behavior of Strip Footings under Large Eccentric Loads

Online veröffentlicht: 04 Oct 2019
Seitenbereich: 29 - 36

Zusammenfassung

Abstract

In this paper, numerical computations using the FLAC code are carried out to investigate of the behavior the bearing capacity of strip footings embedded in sandy soil and under large eccentric vertical load conditions. The study focuses on an evaluation of the non-dimensional reduction factor (RF), which is the ratio between the average bearing capacity of an eccentric footing and its bearing capacity when subjected to a central load. The results indicate a significant decrease in RF when the eccentricity increases and the curve of the decrease is parabolic, even in large eccentricity cases. Based on the numerical results obtained, a new formula of the RF is proposed, and the reasons for the discrepancy between the RF proposed by several authors are identified. The values provided by the proposed formula are in close agreement with some experimental results available in the literature.

Schlüsselwörter

  • Bearingcapacity
  • Reduction factor
  • Numerical modelling
  • Large eccentricity
access type Uneingeschränkter Zugang

Assessment of the Impact of Changes in Deforestation under the Effect of Severe Windstorms on Runoff Conditions in Small River Basins

Online veröffentlicht: 04 Oct 2019
Seitenbereich: 37 - 43

Zusammenfassung

Abstract

Forests represent the most natural means of retaining water in a basin. Assessing the impact of a forest on a hydrological cycle is a very current topic that hydrologists and water managers deal with. The differences between site conditions and a forest itself, together with various methods of exploring this issue, lead to inconsistent opinions on the extent of the ability of a forest cover to prevent or minimize surface runoff.

This article is therefore focused on an assessment of the impact of changes in the composition of a forest under the effect of severe windstorms on runoff conditions in the selected river basin. The most severe windstorms in the last 25 years and their impact on changes in forest cover in the selected area of the Ipoltica River basin have been assessed in this article. The most significant severe windstorm in terms of its impact on changes in the forest communities was Filip, which occurred in the year 2007. Therefore, the impact of changes in forest cover on the given territory was examined for the period after the year 2007. The WetSpa rainfall-runoff model was used to assess the changes.

Schlüsselwörter

  • land use change
  • Severe windstorm
  • WetSpa model
  • Rainfall-runoff modeling
access type Uneingeschränkter Zugang

Static and Dynamic Responses of a Reinforced Concrete Beam Strengthened with Steel and Polypropylene Fibers

Online veröffentlicht: 04 Oct 2019
Seitenbereich: 44 - 54

Zusammenfassung

Abstract

This paper describes an experimental investigation on mono steel and polypropylene (PP) fiber-reinforced concrete beams. The main aim of this present study is to evaluate undamaged and damaged reinforced concrete (RC) beams incorporated with mono fibers such as steel and PP fibers under free-free constraints. In this experimental work, a total of nine RC beams were cast and analyzed in order to study the dynamic behavior as well as the static load behavior of steel fiber-reinforced concrete (SFRCs) and polypropylene fiber-reinforced concrete (PPFRCs). Damage to the SFRC and PPFRC beams was obtained by cracking the concrete for one of the beams in each set under four-point bending tests with different percentage variations of the damage levels such as 50%, 70% and 90% of the maximum ultimate load. The fundamental natural frequency and damping values obtained through the dynamic tests for the SFRC and PPFRC beams were compared with a control RC beam at each level of damage that had been acquired through static tests. The static experimental test results emphasize that the SFRC beam has attained a higher ultimate load compared with the control RC beam.

Schlüsselwörter

  • SFRC
  • PPFRC
  • Damage
  • FRF
  • Damping
  • Four-point test
  • Dynamic
  • Flexure
access type Uneingeschränkter Zugang

Optimization of Energy Generation based on Operations and Ecological Integrity Requirements

Online veröffentlicht: 04 Oct 2019
Seitenbereich: 55 - 62

Zusammenfassung

Abstract

The management of water resources for different purposes such as a domestic water supply and municipal, irrigation and hydropower generation requires optimization techniques for efficient reservoir operations. This study focused on the optimization of energy generation at Kainji hydropower station in Nigeria using operational and ecological integrity constraints. A linear optimization technique was used in optimizing the average total annual energy generation subject to operational and ecological integrity constraints. The model was solved using LINGO 17.0 software. The results revealed that the optimization approach would increase the total annual energy generation at the hydropower station by 1.84%. The outcome of this study can be adopted by the management of a hydropower station and other decision makers in Nigeria to improve the availability of electricity deployed to Nigeria’s national grid without compromising the ecological integrity of a reservoir.

Schlüsselwörter

  • Energygeneration
  • Optimization
  • Kainji reservoir
  • Ecological integrity onthly discharge
access type Uneingeschränkter Zugang

Formation of Gully Erosion in the Myjava Region

Online veröffentlicht: 04 Oct 2019
Seitenbereich: 63 - 72

Zusammenfassung

Abstract

The article deals with the problems of the occurrence and formation of gully erosion in the Myjava catchment. Gully erosion is a significant problem in that region of Slovakia. Together with this type of soil erosion, muddy floods, waste ground, economic losses in agriculture, and many other problems are involved. The main objectives of this article are an analysis of the occurrence of gully erosion in the Myjava region in different periods of time and identification of the most significant factors that have impacted the formation of the gully network. The appearance of gully erosion has been identified from historical maps and other historical documents preserved from the region. The factors analysed were mainly human activities that resulted in changes in land use and physical-geographic catchment characteristics such as the soil, the geology, and the morphology. Nowadays, we are seriously lagging behind in dealing with this issue compared to other European countries.

Schlüsselwörter

  • Myjava catchment
  • Gully erosion
  • Land use change
  • Historical maps

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