Gotowa bibliografia na temat „PIER SPACING”

Compared to the scour around a single pier, the local scour process around tandem double piers is much more complicated. Based on laboratory experiments in a flume, we conducted the scour process around tandem double piers under an ice-covered flow condition. The results showed that when the pier spacing ratio L/D = 2 (where L = the pier spacing distance, and D = the pier diameter), the rear pier (the downstream one) will intensify the horseshoe vortex process behind the front pier, and the scour depth around the front pier will increase by about 10%. As the pier spacing ratio L/D increases, the scour depth around the front pier will gradually decrease. When the pier spacing ratio L/D = 5, sediment scoured around the front pier begins to deposit between these two piers. To initiate a deposition dune between piers, the pier spacing distance under an ice-covered condition is about 20% more than that under an open flow condition. The results also showed that the existence of the rear pier will lead to an increase in the length of the scour hole but a decrease in the depth of the scour hole around the front pier. The local scour around the front pier interacts with the local scour of the rear pier. The maximum scour depth of the scour hole around the rear pier increases first, then decreases and increases again afterward. When the pier spacing ratio L/D = 9, the scour depth around the rear pier is the least. With an increase in the pier spacing ratio, the influence of the local scour around the front pier on the local scour around the rear pier gradually decreases. When the pier spacing ratio L/D is more than 17, the scour around the front pier has hardly any influence on that around the rear pier. The scour depth around the rear pier is about 90% of that around the front pier.

Stable riprap size and optimized extension of the riprap layer around double and triple piers along the flow direction are studied experimentally. Results showed that the critical riprap failure area and stable riprap size around the first pier remain unchanged with increasing pier spacing. In addition, the largest stable riprap should always be placed in front of the first pier in comparison with the remaining downstream piers. However, by increasing the pier spacing, stable riprap size around the second and third pier increased and approached that around the first pier. A relationship was developed for designing stable riprap size in pier groups. Based on this relationship, different riprap sizes are suggested for different zones around the pier group. Experiments showed that the critical zone around the piers includes only a small area and the rest of the riprap extent area can be protected with smaller riprap stones.

Flow structure and channel bed deformation caused by double piers in a tandem arrangement under ice-covered flow conditions in a bent channel is more complicated than those around a single pier in a straight channel. Based on experiments in an S-shaped flume, the scouring phenomenon at double piers in a tandem arrangement under an ice cover has been conducted by varying pier spacing distance, bend apex cross section (BACS), and hydraulic parameters. Results show that, under identical hydraulic conditions, the variation trend of the scour depth in the vicinity of double piers in a tandem arrangement in a bent channel is similar to that in a straight channel. The deepest depth of scour holes at the upstream BACS is more than that at piers at the downstream BACS. At each BACS, the effect resulting from the interaction of double piers gradually decreases with the pier spacing distance. Different from the characteristics of local scour at double piers in a tandem arrangement in the straight flume, when the ratio of pier spacing distance to pier diameter (L/D) is more than 15, the horseshoe vortex generated by the front pier has negligible impact on the rear pier, and the maximum depth of scour hole at the rear pier scour hole is about 90% that of the front pier. Also, when L/D is higher than 15, the influence of the rear pier on the front one is negligible, and the scour hole depth at the front pier remains the same. However, this phenomenon occurs when the straight flume’s L/D is greater than 17.

Local scour at the piers is one of the main reasons of bridge foundation undermining. Earlier research studies focused mainly on the scour at a single bridge pier; nevertheless, modern designs of the bridges comprise wide-span and thus group of piers rather than a single pier are usually used to support the superstructure. The flow and scour pattern around group of piers is different from the case of a single pier due to the interaction effect. Reviewing the literature of local scour around bridge piers group revealed that the local scour around bridge piers group founded in cohesive soil bed was not investigated, and most of the scour studies were related to scour in cohesionless soils. The objective of the present study is to investigate the effect of the interaction between two in-line (tandem) circular bridge piers of variable spacings founded in cohesive soil on the local scour. A set of laboratory flume experiments were conducted under the clear-water scour condition to investigate this effect. This study is the first that investigates experimentally the scour around group of bridge piers in cohesive bed. It was found that the maximum scour depth at the upstream pier of the two in-line piers occurred at a spacing of two times the diameter of the pier, scour at the downstream pier was reduced due to a sheltering effect, the interference effect will be reduced for pier spacings larger than three times of the pier diameter. A recent pier scour equation was used to estimate the scour depths at the two in-line piers in cohesive soil and compare the estimated value with the measured scour depths in the laboratory. The comparison indicated that the proposed scour equation overestimates the scour depths at both the upstream and the downstream pier.

The pier scour process is normally intensified in the presence of an ice cover, which poses risks to the longevity and safety of bridges. In the present study, the impact of the densimetric Froude number, locations, and pier spacing of side-by-side piers on the local scour depth under ice-covered flow conditions were investigated based on clear water scour experiments in an S-shaped laboratory flume. The results demonstrated that the local scour at piers along the convex bank was more substantial than that along the concave bank when other factors stayed identical. The densimetric Froude number clearly has more impact on local scour at piers along the convex bank than that along the concave bank. Different from the mechanism of the pier scour in a straight channel, the scour depth around a pier along the convex bank in the S-shaped flume increases as the distance between two piers (or pier spacing) increases, while it decreases around the piers along the concave bank. Similar scour patterns were observed when the side-by-side piers were installed at different bend apex cross-sections. The maximum local scour depths at piers along the convex bank measured at different bend apex cross-sections were relatively unchanged when other influencing factors were held constant. However, the maximum scour depth around piers along the concave bank decreased as the bends increased toward downstream.

Bridge pier scouring is a significant problem in the safety estimation of bridges. This research is carried out to study the local scour around the piers of Al-Kufa bridge ,and to estimate the effect of the spacing between the piers on the depth of equilibrium scour . Dimensional analysis technique was used ,and from the collected data filed measurements ,an empirical formula was derived .I has been found that the predicated scour depth from the formula compares well with the observed values . It was found that no mutual influence on maximum scour depth occurs for spacing ratio in Al-Kufa bridge piers , and the scour depth in the middle pier is greater than the others . The study showed that the piers of Al-Kufa bridge is safe against scouring in the present time , However the scour around the piers should be main laned when the hydraulic conditions is change in the location of the bridge.

This study based on laboratory experiments for computing depth of local scour around abutment and bridge pier neighboring abutment considering the study of the effects of upstream flow conditions , pier and abutment sizes , median size of bed material and spacing between pier and abutment on the maximum scour depth and scour pattern around a pier and abutment. The study was conducted using a physical hydraulic model of pier and abutment operated under subcritical flow , clear-water condition and using uniform cohesionless sand as bed material . Three different size models of pier and abutment were used to show the effect of the size on the local scour and two different median size (d50) of sand were used in this study. Dimensional analysis techniques and statistical analysis were used to find new formulas with help of the experimental data . One of these formula was to compute the maximum scour depth at pier neighboring abutment and the other to find the maximum scour depth at abutment. There formula were derived to predict the maximum scour depth in terms of Froude number , diameter of pier and abutment , median size of sand , flow depth , flow velocity and spacing between pier and abutment.

Purpose: Due to an increase in a number of bridges being constructed, scour depth around bridge piers is gradually being recognized as one of the possible reasons for bridge failure. According to [1] about 53% of bridge failures in the US were caused due to floods and corresponding scour in the rivers. Lots of work has been carried out around the single pier but in the case of group piers, the work is very less. Hence, it becomes necessary to calculate the actual scour depth around the bridge piers considering the close location of bridges as well. Design/methodology/approach: Recognizing the need for research in this direction, an experimental study was planned and conducted in the Hydraulics Laboratory of Civil Engineering Department of National Institute of Technology Kurukshetra, India. Experiments were conducted in a standard recirculating tilting bed water flume 15 m long, 0.4 m wide, and 0.60 m deep. The orientation of more than one pier, namely Tandem pattern was employed for the work. Two pier models, 62 mm and 42 mm diameter were used for the experimental study. The mobile bed used in the experiments had an average mean size, d50 = 0.23 mm, 0.30 mm and 0.50 mm. Findings: The outcomes of the ANN function and M5 model analysis have been used to compare with experimental results. From the earlier studies, it was concluded that, when the clear spacing between the pier models was greater than 0D the scour depth around the piers increase with a rapid rate. However, in the case of modelling techniques, M5 models show higher predictive accuracy than ANN models. Research limitations/implications: It is a significant area of research. However, the present study has been a time and facility- constrained study. Therefore, there is a large scope to conduct further studies on the subject, Different pattern i.e. Side by Side; Staggered and Group of piers can be adopted for further investigations. Originality/value: Sufficient work has been done by number of researchers around the single bridge pier. But due to rapid urbanization a number of bridges constructed in close proximity to each other which affects the scour depth of each other. Modelling techniques used in hydraulic engineering are not always effective in practice. The present study discusses the effect of spacing on scouring around piers in a tandem arrangement using experimental as well as modelling techniques. To predict the scour depth of the Tandem arrangement 89 laboratory data sets have been used.

The sliding formwork, combining high efficiency and low cost, is a kind of advanced technology in the construction of sluice pier of hydropower projects. Number of jacks and elevating shelf spacing are two important parameters in the structure design of sliding formwork, the mathematical model of the relationship between manufacture costs and jack number, spacing between the elevating shelf was established using polynomial least square method, the best value of jack number and spacing between the elevating shelf were calculated by using the simulated annealing algorithm, thereby optimized the design parameters of sliding formwork structure, whilst expatiated the technology of installing, debugging, sliding and disassembly of sliding formwork, put forward the feasible methods for solving the problems that often appeared in the construction of sliding formwork, summed up the merits of sliding formwork, analyzed the technology and economical benefit of sliding formwork

Scour is caused by the erosive action of flow of water, which erodes and takes away sediments from the river bed, as well as from the area of bridge piers and abutments. This process of scour is well-known for its complicated behaviour, and this process becomes more complex for the group of piers. As per the literature available, scour is a major contributor for the collapse of the bridge structures. Hence it becomes essential for the researches to predict the scour depth accurately. To fulfill this necessity, the deep understanding of the flow-field around the piers and factors affecting the scour depth is important. Numerous studies are available in the literature on the flow-field and local scour, but majority of them are focused only on single pier. However, multiple piers are more common in the bridge designing due to economical and geotechnical considerations. Engineers across the world are predominately considering single pier characterization for the group of piers, although all bridge structures are laid on the group of piers. The design considerations developed for a single pier mostly ignores the most significant group effects for multiple piers such as: pier sheltering, pier spacing and mutual interference effect. It is demonstrated by the fact that inadequate research and development for the multiple piers have been observed. Therefore, it is utmost important to investigate the factors affecting the multiple piers and develop an equation by considering all the variables for accurate prediction of scour depth. The primary aim of this research is to investigate the effect of the pier spacing (Ps) between the piers and temporal scour development on scour depth and propose a new equation for scour depth estimation. In order to meet the objectives of this research, detailed experimental study has been conducted for, single pier, two piers, and three piers. In total, 232 experiments have been carried out for various pier spacing and pier arrangements on uniformly graded sediment in the Hydraulic Engineering Laboratory of Delhi Technological University, Delhi, India. Pier arrangements studied in this research are: single pier, two piers in tandem arrangement, two piers in side-by-side arrangement, two piers at an angle of 15 and 30 degrees to the direction of flow, three piers in tandem arrangement, three piers in side-by-side arrangement and three piers in staggered viii arrangement. The instantaneous 3-D velocity measurement is conducted by utilizing SonTek 16-MHz Micro-ADV (Acoustic Doppler Velocimeter) has been used. For profoundly understanding and continuous monitoring of scour evolution SeaTek Ultrasonic ranging system have been used. The Experimental observations for the temporal scour evolutions and scour hole development pattern for all the pier arrangements under various pier spacing has been presented in the graphical and pictorial form. The findings of this research shed light on the factors that causes scour: pier spacing, flow depth, Froude number, and scour development pattern. These are all important variables, which needs to consider in order to accurately predict the maximum scour depth. Results shows that, the flow-field around the group of piers is much more complex than single pier and pier spacing plays a major role in the scour depth estimation. The results also exemplify that non-dimensional scour depth increases with the increase in the Froude number and velocity of flow. The effect of pier spacing shows that the scour depth increases as the pier spacing increases at a certain Ps range, then it decreases. Furthermore, two semi empirical equations has been proposed for the tandem and side-by-side arrangements by using GEP, and the comparison of the proposed GEP equation with the well-known equation and experimental results shows that the GEP is better prediction tool for scour depth. Lastly, to evaluate the influence of various parameters on the scour depth sensitivity analysis has been conducted, and concluded that pier spacing plays an important role in scour estimation. The findings of this study can be further used for the evaluation of the research data.

<p>It is difficult to understand the mechanical performance of large-span and super-width steel box girder during the incremental launching construction, and it varies with the number of temporary piers. Combined with the engineering example of Qilu Yellow River Bridge in Jinan, this paper conducts research on the layout of temporary piers. Firstly, stress envelope of main girder and maximum support reaction forces under different layout schemes are analyzed with the frame model. Then, the local plate-shell model is used to obtain stress distribution of main plates and local stability of main girder segment under the most unfavorable loading conditions. The results show that local mechanical performance of steel box girder plays a crucial role in ensuring its safety during the incremental launching construction. Besides, rational spacing between temporary piers is 70m for Qilu Yellow River Bridge.</p>