Showing 14 results for Bridge
S. Kouchakzadeh,
Volume 5, Issue 1 (4-2001)
Abstract
Bridge abutments are usually located in the floodplain zone of rivers where velocity and shear stress are not uniformly distributed. The influence of channel geometry and lateral momentum transfer in compound flow field on the scouring phenomenon has not been fully investigated and understood yet. The impact of lateral momentum transfer on the local scour at abutments terminating in the floodplain of a compound channel is presented in this paper.
It is shown that, by accounting for lateral momentum transfer at small floodplain/main channel depth ratios (λa/H<0.3), estimates of maximum local scour depth are increased by up to 30%. Therefore, ignoring the influence of the lateral momentum transfer, in such circumstances, might result in unrealistic estimation of the scour depth. To draw a more general conclusion, more data are required to assess the influence of different parameters affecting the phenomenon in compound flow conditions.
M. Heidarpour, H. Afzalimehr, M. Naderi Bani,
Volume 7, Issue 3 (10-2003)
Abstract
The use of slot through a pier is a new method proposed to control local scour at bridge piers. In this study, control of local scour at bridge pier is studied using 20 pier models under clear water conditions. The models consist of one circular pier without slot, three round-nosed piers without slot, and 16 piers with slot. Two slot lengths were chosen (yl=b and yl=2b, where y1 is the length of slot and b is the width (diameter) of the pier). Furthermore, they were located at two positions (near the bed and near the water surface).
The results showed that for a circular pier, the slots with the lengths of b and 2b, located near the water surface, had no influence on the equilibrium scour depth. It was also found that for all piers, maximum reduction in scour depth occurred for piers with a slot length yl=2b and close to the bed. Also, the efficacy of a slot for scour protection in the case of a round-nosed pier was more than a circular pier (with a diameter equal to the width of a round-nosed pier).
A. R. Masjedi, H. Kazemi, A. Moradi ,
Volume 15, Issue 57 (10-2011)
Abstract
In this research, the effect of installing position of bridge pier on scouring depth was studied in a bend laboratory flume, which is made of Plexiglas with 180 bend and a relative radius of Rc/B=4.7. Tests were conducted using one pier 6 cm in diameter under four discharge conditions with constant depth of 12 cm and clear-water conditions. Flume bed was fully paved by uniform sand. It was found that maximum scouring depth occurred in bend when bridge pier was installed in the position of 60 degrees. Also, in all situations increased scouring depth occurred by increasing discharge.
P. Shojaei, D. Farsadizadeh , A. Hoseinzadeh Dalir,
Volume 15, Issue 57 (10-2011)
Abstract
Submerged vanes are low aspect ratio flow-training structures mounted vertically on the river bed at an angle to the prevailing flow. The aim of application of vane is to generate a secondary circulation in the main flow, designed to modify the near-bed flow pattern and thus redistribute flow and sediment transport within the channel cross section. Collar is a flat sheet with low thickness fixed vertically on the pier at stream bed level or near it. Installation of a collar leads to protect the river bed against the direct impact of downflow produced at the upstream face of the pier and therefore reduces the scour depth. This research is a laboratory study that examines the effectiveness of submerged vanes and combination of submerged vanes and collar as a pier scour protection device. Experiments were conducted in an 8 m long and 0.8 m wide flume and a cylindrical pier used was 6 cm in diameter. Clear-water scour tests with u*/u*c = 0.9 were performed with a collar 3 times wider than the pier diameter at the stream bed level and submerged vanes 1.5 times longer than the pier diameter at the stream bed level (H=0). Different arrays of vanes with different angles to main flow direction were employed. The highest reduction in the depth of scour hole with four vanes and a collar showed 61% reduction in scour depth.
A. Masjedi, M. Sobhani,
Volume 19, Issue 74 (1-2016)
Abstract
Riprap is used to control scouring around the bridge abutment. In order to study the stability of riprap around two bridge abutments with two different shapes, experiments were conducted in a laboratory flume made of Plexiglass in 180 degree bend. In this research, several experiments were done by placing the two bridge abutments made of Plexiglas in a series of riprap. Experiments included two different types of riprap with different densities, four different diameters and constant rate of discharge under pure water condition. In each experiment, flow depth was measured in terms of moving threshold, then stability was calculated by using the data obtained. The results showed that in the same conditions chamfered wing-wall is greater than vertical-wall. So, chamfered wing-wall is, on average, 9 percent more stable than the vertical wall.
M. Zare , T. Honar1,
Volume 19, Issue 74 (1-2016)
Abstract
The most important cause of concern about the stability of bridge foundation is the occurrence of scour around bridge piers. Therefore, different methods have been proposed to prevent or reduce scouring around bridge piers. The use of groynes is one of the modern methods to control and reduce local scour. In the present study, the effect of a solid groyne on reduction of the scour depth around a cylindrical bridge pier, located in the bend of a laboratory flume is assessed. Experiments were conducted for groyne model angled at 50˚, 90˚ and 120˚ to the downstream channel sidewall with three flow rates of 47, 49 and 51 liters per second in a sediment free condition. Results showed that in at ratios of velocity to critical velocity and all groyne angles, in comparison with no groyne, the scour depth was reduced. At all ratios of velocity to critical velocity, the best operation was related to normal groyne and the average operation of repelling groyne was better than attracting groyne. The operation of normal groyne decreased and attracting groyne function improved as the flow rate increased. Also, the normal groyne (ratio of velocity to critical velocity equal to 0.87) had the best effect on reducing the scour depth (by about 71.4 percent).
Mr A. Nouri Imamzadehei, Manouchehr Heidarpour, M. R. Nouri Imamzadehei, B. Ghorbani,
Volume 21, Issue 2 (8-2017)
Abstract
Flood currents are considered threatening factors by creating local scour along bridge piers. One method for decreasing local scour is to strengthen the bed against imposed tensions. Among methods which can directly be appropriate in decreasing and controlling local scour of bridge piers is to employ geotextile around bridge piers. In the present study, the effect of geotextile layer in decreasing local scour of cylindrical single-pier was investigated with the purpose of proposing the best effective method of covering bridge pier. So, layers with circular and oval shapes were put around the pier, in proportion with pier diameter, and the performance of each was compared with the unprotected pier. Test results showed that with installing the oval geotextile layer, final scour depth around the pier reached to 1.25D. Also, comparing geotextile and collar with 2D diameter, the delay of scour process around geotextile was 40 times higher than the collar, but the collar decreased the ultimate scour depth further than geotextile.
M. Naserian, A. Masjedi,
Volume 21, Issue 4 (2-2018)
Abstract
River bend due to particular pattern, called 'Vortex Flow,' has greater erosion than straight path. Occurrence of scour around bridge abutment on curved paths is one of the main reasons for destruction of bridges. Riprap is one of the methods to control the scouring around the bridge abutment. The purpose of this study was to assess stability of the riprap around the bridge abutment at 180 degree river bend. In order to study stability of riprap around the bridge abutment, experiments were done in a laboratory flume made of Plexiglas under 180 degree bend, 2.8 m in central radius, 0.6 m in width and R/B=4.67. In this research, several experiments were done by placing a bridge abutment with vertical winged wall made of Plexiglas surrounded by a series of riprap. Experiments were done by three different types of riprap with different density 1.7, 2.1 and 2.42, four different diameters 4.76, 9.52, 12.7 and 19.1 mm and four rates of discharge under pure water condition. In each experiment, flow depth was measured in terms of moving threshold and failure threshold and then the formulas were calculated by using data obtained. The results showed that the relative diameter of riprap increased with increasing Froude number in terms of moving threshold and failure threshold. Finally, the suitable formula to estimate diameter of riprap around the bridge abutment at 180 degree bend were presented in terms of moving threshold and failure threshold.
H. Ghafari, M. A. Zomorodian,
Volume 23, Issue 4 (12-2019)
Abstract
One of the main reasons for bridge failure is the local scour around the pier. Pier groups are popular in the structural designs due to economical and geotechnical reasons. The mechanism of scouring at the pier groups is more complicated than the single one. In this study, the scour around group piers in the sandy soil and a mixture of sand and clay in some relative compaction equal to 90% and the optimum moisture was studied. The arrangement of the group piers was 1pier * 3pier and 3pier * 1pier along and transverse of the flow direction, respectively, at the interval space of D, 2D and 2.5D intervals. The effect of the Bentonite clay content was investigated. Finally, by using Kaolinite clay, the effect of the clay mineral was studied. The results showed that the scouring depth was different not only in cohesive and non- cohesive soils, but also according to the type of the clay mineral. The use of 10% bentonite clay mixed with sand reduced scour more than 90%, as compared to the sandy soil. On the other hand, using 15% of kaolin in the similar conditions reduced scour depth by only a 34%, in comparison to the sandy soil.
R. Daneshfaraz, M. Sattariyan Karajabad, B. Alinejad, M. Majedi Asl,
Volume 24, Issue 4 (2-2021)
Abstract
The scour around the bridge piers is one of the main causes of bridge failure and the extraction of aggregates may aggravate this phenomenon. The present study comprehensively investigated the scour around the groups of bridge piers in the presence of aggregate extraction pits, using different discharges. The bridge piers roughened by gravel had been compared with the simple bridge piers; so, the results showed that the roughening caused the reduction of the scour depth. Scour depth change rate led to an increase in the equilibrium time. The results also showed that the reduction of the scour depth at the downstream groups of piers was more than that in the upstream. For the lowest discharge, the aggregate extraction pits had a considerable effect on the scour depth difference for the groups of piers in the downstream and upstream. On the other hand, the effects were decreased when the rate of discharge was increased. The experimental results obtained by the rough surface models showed that as the discharge was increased, the local scour was increased too; at the same time, the bed profile was posed at the low level. Generally, the scour depth of the groups of piers in the downstream of the extraction pit was more than that in the upstream. The results of the current research, therefore, demonstrated that the surface of the bridge pier roughened by gravel reduced the scour depth.
E. Yarmohammadi, S. Shabanlou, A. Rajabi,
Volume 25, Issue 1 (5-2021)
Abstract
Optimization of artificial intelligence (AI) models is a significant issue because it enhances the performance and flexibility of the numerical models. In this study, scour depth around bridge abutments with different shapes was estimated by means of ANFIS and ANFIS-Genetic Algorithm. In other words, the membership functions of the ANFIS model were optimized using the genetic algorithm, finding that the performance of ANFIS model was increased. Firstly, effective input parameters on the scour depth around bridge abutments were defined. Then, by using the input parameters, eleven ANFIS and ANFIS-GA models were produced. Next, the superior ANFIS and ANFIS-GA models were introduced by analyzing the numerical results. For example, the correlation coefficient and scatter index for ANFIS model were calculated to be 0.979 and 0.070; for ANFIS-GA, these were 0.986 and 0.056, respectively. In addition, the average discrepancy ratio (DRave) for ANFIS and ANFIS-GA models was 0.984 and 0.988, respectively. Also, it was shown that the ANFIS-GA models had more accuracy, as compared to the ANFIS models. Moreover, a sensitivity analysis showed that Froude number (Fr) and ratio of flow depth to radius of scour hole (h/L) were the most influential input parameters for simulating the scour depth around bridge abutments.
. M. Karimaei Tabarestani,
Volume 25, Issue 1 (5-2021)
Abstract
One of the most common and practical methods in controlling the local scour around bridge pier is to place a protective riprap layer. Due to various uncertainties in the design of this countermeasure method, in the present study, the reliability analysis method was applied for the design of a riprap size around a real bridge pier as a case study. Therefore, four different methods including First Order Second Moment, First Order Reliability Method, Spread Sheet and Monte Carlo Simulation Technique were used to quantify the uncertainties and design of riprap size. The results showed that the probability of riprap size failure, which was calculated by the empirical equation and the use of the mean value of effective parameters in the case study, was very high, nearly 34%. In the following, the relationship between safety factor and the reliability index at the site of this case study was determined. Finally, in order to achieve more realistic results, the hydraulic correlation coefficient between depth and flow velocity parameters and its effect on the probability of the riprap failure were studied. It was shown that the correlation coefficient between these two hydraulic parameters was very high and more than 90%, and its maximum effect on the probability of the riprap failure was less than 10%.
H. Kazemizadeh, M. Saneie, H. Haji Kandi,
Volume 25, Issue 2 (9-2021)
Abstract
To prevent demolishing bridge piles due to developing the scour hole under the foundation of these piles some solution has been proposed in the literature. One of the important approaches could be installing different geometric of roughness at the downstream and upstream piles sections. This causes the downward flows which are performing the main role in developing scour holes to be marginally decreased. The present study explores the effect of geometric roughness and also, continuity and un-continuity of roughness length on maximum scour holes around bridge pile. Results indicate that due to increasing the length of roughness the developed scour holes were formed by less scour hole depths. Furthermore, continuity of roughness increases the scour hole depths; however, un-continuity causes the height of scour holes to be developed by fewer values. Also, the comparison shows that the length of installed roughness in maximum value is decreasing the scour hole depth constitute 34 percent. Based on the non-linear regression technique an equation has been proposed to predict the maximum scour hole due to different conditions. Comparison between experimental and proposed values shows that the accuracy of the proposed equation has an acceptable error which has been calculated less than 11 percent.
S.a.r Esmaili, A. Mosaedi,
Volume 26, Issue 1 (5-2022)
Abstract
In recent decades, population growth, urban sprawl, urban environmental changes, and related issues are one of the significant issues in proper planning to manage the urban environment. One of the issues in urban development is the occurrence of floods and flooding due to heavy rains. In this research, flood modeling was studied in Mashhad Zarkash watercourses. The amount of rainfall for the return period of 10, 25, 50, 100, and 200 years were extracted by CumFreq software using the maximum 24-hour rainfall statistics of three rain gauge stations closer to the Zarkesh, Jagharq, Sar-e-Asyab, and Torqabeh watercourses basins during the statistical years 1364 to 1390. The peak discharge was calculated using the US Soil Protection Organization (SCS) rainfall-runoff method. Zarkesh watercourse is located on the outskirts of Mashhad. River and flood flow modeling was performed using Arc GIS, HEC-GEORAS, and HEC-RAS software in two conditions including structure (bridge) and no structure. Due to urban marginalization, urban development and land use change have greatly expanded in this region. The results of flood simulation showed that flood levels with a return period of 50 years increased by 50000 m2 equal to 22% in the presence of a structure compared to the state without a structure. The results of this research show that the construction of bridges on the river, the roughness coefficient by land use change, and the number of curves due to land permeability changes are effective in the flood zone.
