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The main aim of this study was to gain a deeper knowledge of flow behaviour and scour formation adjacent to bridge piers and offshore wind turbine foundations in shallow water using numerical modelling. Based on the literature, the capability of the previous models in the prediction of scour around the piers was attached to the pier shapes and its orientation angle to the flow. Hence, in this study, a coupled approach between a hydrodynamic and a morphodynamic model was implemented. The model was validated against eight different test cases for flow and sediment transport modelling. Overall, the results confirmed that the developed model has an acceptable capability in predicting local scour independent of the pier cross-section shapes. Furthermore, the model was applied to predict the flow field, bed shear stress and the development of local scour around a square-shaped pier with 45˚ (diamond) and 90˚ (square) orientation angle to the flow, a hexagon-shaped pier with 30˚ and 60˚ orientation angle to the flow and a group of two identical side-by-side circular cylinders with different spacing ratios G⁄D= 1, 2 and 3 under current flow and live-bed condition, where D represents the pile diameter and G is the distance between the piles. In the case of modelling a single pier, it was found that the maximum and minimum normalized quasi-equilibrium local scour depth occur for the square-shaped piers with 90^° and 45^° orientation angles to the flow, respectively. The normalized scour depth in quasi-equilibrium condition for the square pier was found to be almost twice (1.94) of that for the diamond pier. This ratio in the case of the hexagon-shaped pier for 60^° and 30^° orientation angles to the flow decreased to a value of 1.09. From these results, it was realized that an increase in the number of sides of the piers cross-section decrease the impact of the change in orientation angle to the flow in terms of normalized scour depth. It was also inferred that with an increase in the number of sides of the pier's cross-section the resultant normalized scour depth in equilibrium condition tend to get closer to that of the circular pier regardless of pier orientation angle to the flow. In the case of the local scour simulation around a group of two identical side-by-side piles, it was noticed that a deeper scour hole was observed in the area between the piles in all cases. However, due to the stronger turbulent structures and higher contraction of streamlines in the case of G⁄D=1, a deeper hole was observed adjacent to the piles in comparison to that of two other cases. The effect mitigated with an increase in spacing between the piles. The results showed that for G⁄D≥ 3 the pile group effect gradually vanishes, while it is assumed that the pile group effects are completely negligible for G⁄D≥ 5. An equation was fitted for the computed equilibrium scour depths for different spacing ratios which can be used for the prediction of the maximum scour depth adjacent to two side-by-side piles under steady current flow and live-bed condition for a specific range (G⁄D≥ 1).

Scouring around bridge piers is one of the major reasons for bridge failure. A total of 20 experiments of scour around tandem piers were conducted in an open channel, at a subcritical inflow velocity ( =0.67) by placing an equal or smaller diameter circular bridge pier downstream of an existing pier with relative diameters in the range 1.00 to 0.67, at varied normalized spacings in the range 4 to 9.33, and detailed measurements of the equilibrium scour beds were taken. Separate scour holes with distinct deposition between the piers was observed in the majority of cases. Highest reinforcement effects were observed for pier combinations with Dd/Du=0.90 and 0.80, resulting in larger scour hole dimensions at the upstream pier, compared to isolated condition. The spacing corresponding to the minimum scour hole dimensions at the downstream pier was observed in the range L/Du=4 to 9.33 for each pier combination and it decreased with the decrease in diameter of the downstream pier. Variations for the normalized equilibrium scour depth, lateral and longitudinal extents of the scour hole, scour surface area, and scour hole volume as a function of normalized spacing for different ratios of downstream and upstream pier diameters, are presented in the form of graphs and equations.

Employment of protective structures is vital for reducing the effect of the local scour created surrounding the bridge piers. One of the most effective protective structures used for controlling and reducing scour surrounding the bridge piers is the collars. Hence, research on the mechanism of scouring surrounding the combination of pier and collar as well as the effect of collar on reduction of scouring surrounding the pier is of great significance. In this study, the effect of various collar width-to-pier width ratios on reduction of scouring parameters surrounding the rectangular piers has been investigated experimentally in various 180-degree sharp bend positions. The experiments were conducted under clear water and threshold of sediment motion in the upstream straight path. Results indicated that collars with collar width-to-pier width ratios equal to 3 to 4 perform the best at reducing the maximum depth of scouring in front of the nose of piers. Increasing the width of collar surrounding the piers reduces the maximum depth of scouring. Increasing the length of pier reduces the efficiency and effectiveness of the collar in delaying the scour process at the pier nose as well as the amount of the maximum scour reduction. The highest amount of scour depth reduction occurred in the vicinity of the pier and the collar at the 90-degree section with the collar installed with a ratio of collar width to pier width equal to 4 surrounding the piers with a ratio of length to width equal to 2 and 3 by approximately 75 and 70%, respectively.

Collars play an effective role in reducing scour by preventing direct collisions of the flow with the piers. Furthermore, because most rivers meander, this study considered various shapes of bridge piers with collars at various locations along a 180° sharp bend and compared the findings with those of similar cases with no collars installed. The findings show that the aerodynamic shape of the pier and the collar as well as the location of these structures have significant effects on the amount of scouring. The maximum and minimum scour depths which are 2.58 and 0.8 times the pier diameter, occurred in bridge piers with collars at jou.round piers installed at 60° and elliptical piers at 120°, respectively. Moreover, another finding of this study was that use of collars played a significant role in reducing scouring. The greatest effect of the collar was found on the elliptical pier located at the 120º angle with the reduction of the scour depth by 75% and the scour hole volume by 95%.

Local scour around bridge piers is one of the main causes of bridge failure all over the world. Experimental and hydraulic models were carried out to investigate two types of scour reduction methods around a single cylindrical pier, namely the pier's slots and collars. The efficiency of various types of pier slots and circular collars around the pier's base in reducing scour were studied. A new shape of a conical collar was developed by the authors and examined along with other shapes. The results revealed that collars, in general, have more influence in reducing scour depth than slots made in the front and rear of bridge piers. The sigma-slot acts better than other tested slots, with a reduction in the scour depths of 59.3% and 52.8% at the upstream and downstream of the pier, respectively. On the other hand, the conical collar appeared to be the most effective collar shape in reducing the scour around the bridge pier, with a 61.1% reduction in the scour depth downstream of the pier. A three-dimensional laser scanner was used to capture the bed topography at the end of each experiment and contour maps of the deformed bed were produced. A one-dimensional Hydrologic Engineering Center-River Analysis System model was developed with a single bridge pier to predict the scour depth around the pier in an attempt to introduce new values for the pier nose shape factor, , which describes the tested piers.

This paper proposes a rapid strengthening method for severely earthquake-damaged RC piers. In this strengthening method, high-strength steel bars (HSSB) HTRB600 were used as vertical and horizontal planting rebars anchored into pier footing and pier shaft, and ultra-high-strength concrete (UHPC) was used as grout material. Meanwhile, the UHPC was used to strengthen the damaged plastic hinge region to form the enlarged section to realize the mechanical integrity of the strengthening piers. Utilizing the early strength property of UHPC, the proposed rapid strengthening method can realize the rapid recovery of vertical bearing capacity of severely damaged RC piers, thus ensuring the rapid passage and emergency rescue of bridges after earthquakes. Four severely damaged RC piers under cyclic tests were strengthened and reloaded, and the seismic performance of strengthening and original RC piers was compared, including lateral bearing capacity, lateral stiffness, deformability and hysteretic dissipated energy. Research results show that, for RC piers with only bar buckling but no bar fracture in original specimen, the UHPC enlarged section over strengthens the damaged plastic hinge region, resulting in the plastic hinge of the strengthening piers being relocated to the upper part of enlarged strengthening section. The strengthening pier presents better seismic performance, including lateral bearing capacity, deformability and energy dissipation capacity than original piers. For RC piers with partial longitudinal reinforcement facture, two kinds of strengthening methods, with or without using horizontal planting rebars, were adopted. When using horizontal planting rebars, in spite of presenting asymmetric failure due to the asymmetric damage of original piers, the strengthening RC piers still present comparable seismic performance with original piers. However, the strengthening pier without using horizontal planting rebars presents more distinct pinching effect, lower deformability and hysteretic dissipated energy than original pier. Therefore, the horizontal planting rebars can enhance the force integrity between UHPC enlarged section and pier shaft, and then ensure the seismic performance of strengthening RC piers. Overall, the proposed rapid strengthening method with horizontal planting rebars can not only fulfill the post-earthquake rapid passage demand in short time for the severely earthquake-damaged RC piers, but also ensure the long-term service of strengthening bridge piers by restoring their seismic performance.

To address concrete cracking in submerged box-shaped hollow thin-walled piers under static ice and hydrostatic pressure, this study proposes a composite strengthening method employing externally bonded steel plates coupled with concrete infill blocks. Based on mechanical theoretical derivation, the strengthened structure is simplified as a cooperative system comprising compression–truss and suspended-cable mechanisms. Key design parameters—including steel plate span, thickness, infill block height, and plate corner configuration—are optimized using a genetic algorithm. The optimization objective minimizes strengthening cost, subject to constraints of concrete crack resistance, steel plate strength, and deformation control, ultimately determining the numerically optimal composite strengthening solution. Validation through planar finite element models demonstrates that: (1) the proposed system effectively suppresses cracking in the original structure; (2) peak stresses in the steel plates remain below the yield strength of Q345 steel; and (3) the theoretical design is reasonable and effective, which can solve the cracking problem of the wading-tank hollow thin-walled pier under the action of surrounding load.

Previous investigations indicate that scour around bridge piers is one of the most important factors for the failure of waterway bridges. Hence, it is essential to determine the accurate scour depth around the bridge piers. Most of the previous studies were based on scour around a single pier; however, in practice, new bridges are usually wide and then piers comprise two circular piers aligned in the flow direction that together support the loading of the structure. In this study, the effect on maximum scour depth of the spacing between two piers aligned in the flow direction was investigated experimentally under clear water scour conditions. The results show that the maximum scour depth at upstream of the front pier occurs when the spacing between the two piers is 2.5 times the diameter of the pier. Two semi empirical equations have been developed to predict the maximum scour depth at upstream of both front and rear piers as a function of the spacing between the piers, in terms of a pier-spacing factor. If the new equations for the pier-spacing factor are used with some of the existing equations for scour at a single pier, the predicted scouring depths are in good agreement with observed results. The S/M equation exhibited the best performance among the various equations tested and was recommended for use in prediction of the equilibrium scour depth. The findings of this study can be used to facilitate the positioning of piers when scouring is a design concern.

This paper presents a study on extension of bridge pier cap beams reinforced with carbon fiber-reinforced polymer (CFRP) systems. Experimental tests and numerical modeling of quarter-scaled reinforced concrete hammerhead non-prismatic pier cap beams, extended on edges and reinforced with different CFRP systems, are presented. Five specimens were tested to evaluate the effect of various CFRP systems on ultimate strength, stifiness, and ductility. It was found that the failure mode changes as different CFRP systems are applied, which consequently impacted the ultimate strength and ductility of extended cap beams. A three-dimensional fnite element (FE) model was developed and presented in this paper. Failure mode and load-deffection response were successfully captured using the proposed FE model. Comparison and discussion of flexural capacities predicted using the FE model and current guideline were presented. Keywords: carbon fiber-reinforced polymer; fnite element modeling; flexural reinforcing; pier cap beam extension.

This study mainly investigates the impact of debris accumulation on scour depth and scour hole characteristics around bridge piers. Through controlled experiments with uniform sand bed material, the influence of various debris shapes (high wedge, low wedge, triangle yield, rectangular, triangle bow, and half-cylinder), upstream debris length, downstream debris extension, and debris thickness on scour depth and scour hole area and volume around the cylindrical pier were analyzed. The findings revealed that the shape and location of debris in the water column upstream of piers are key factors that determine the depth of scour, with high wedge shapes inducing the deepest scour and potentially the largest scour hole, particularly when positioned close to the pier and fully submerged. Scenarios in which triangle bow debris was submerged at full depth upstream of the pier closely resembled situations devoid of debris. Conversely, debris extension downstream of the pier was found to reduce local scour depth while concurrently enlarging the dimensions of the scour hole. The existing scour prediction equations tend to overestimate scour depth in scenarios involving debris, particularly when applying effective and equivalent pier width. This discrepancy arises because these equations were originally developed to predict scour depth around piers in the absence of debris. In response, a refined model for predicting scour induced by debris was proposed, integrating factors such as upstream debris length, downstream extension, obstruction percentage, and debris shape factor. This model demonstrated strong agreement with experimental data within the scope of this study and underwent further validation using additional experimental datasets from other research endeavors. In conclusion, this experimental study advances the comprehension of scour processes around cylindrical bridge piers, providing valuable insights into the role of debris characteristics and positioning.