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Numerous bridges are destroyed worldwide every year mostly due to the role of hydraulic factors including scour being ignored when they are designed. Therefore, examination of the scour phenomenon around bridge piers in rivers and identification of the parameters affecting them gain a great level of significance. Particularly, if the bridge piers are installed at river bends, the complicated nature of the flow in bends adds to complications already existent in analysis of flow and scour patterns around such structures, which indicates the need for further study. Hence, the present study has utilized SSIIM numerical model to analyze the three-dimensional flow and scour patterns around perpendicular pier groups (two series of triad parallel piers) at different positions of a bended channel (at the 60-, 90-, and 120-degree angles). The simulated bended channel is a 1-m-wide channel with a central angle of 180 degrees and a relative curvature radius of 2. These data are first compared and confirmed with data collected by acoustic Doppler velocimetry under similar conditions for validation of the numerical data. The results obtained from this model indicated that changing the position of the bridge piers in the channel does not have a significant effect on the maximum scour value; however, the amount of the maximum sedimentation increases by 12% after relocating the piers from the 60- to the 90-degree angle, whereas relocating them from the 90- to the 120-degree position leads to a 42% reduction in the maximum sedimentation.

The flow being discharged from the culvert during flood events leads to significant alterations in the topographical features of the downstream bed. These modifications, manifested as scouring, have the potential to compromise the structural integrity of the culvert. It is therefore greatly important to investigate the factors affecting the extent and the form of scouring downstream. One effective approach to minimizing flow energy, thereby mitigating downstream scour, is the implementation of artificial roughness within the culvert structure. This study examined influences of a box culvert’s longitudinal gradient on the topographical variations of the bed downstream in relation to the artificial roughness. Moreover, the outcomes derived from various slope configurations were analyzed in conjunction with scenarios where the culvert was integrated with artificial roughness components and positioned horizontally with a zero slope. A key finding of this research was that the maximum slope examined had a more significant effect on diminishing the maximum scour depth downstream of culvert than the other slopes analyzed did. By inclining the culvert bed, the maximum sedimentation height in the downstream areas was enhanced in comparison to the horizontal culvert configuration. Furthermore, the configurations incorporating an artificial roughness with a height equivalent to 0.13 times the height of the culvert opening demonstrated a significantly advantageous impact toward mitigation of the maximum scour depth. The sedimentation volume and area downstream were observed to undergo reductions in instances where the longitudinal slope of the culvert was greater, in comparison to scenarios with other slopes.

Studying the potential of progressive collapse in structures is a new topic in the field of passive defense and has attracted the attention of many researchers, recently. This research investigates the behavior of steel structures with 3D sandwich infill panels after extensive damage. For this purpose, several moment resisting steel frames with different numbers of stories and span length to story height ratios are investigated. The steel frames have infill panels with 30, 50 and 100% of openings, and the initial widespread damage scenarios are consisted of removing 2 and 3 columns with their adjacent infill panels. The results show that the presence of the infill panel reduces the ductility of the structure by increasing the stiffness and prevents the extra rotation of the structural elements, significantly. On the other hand, infill panels can reduce the potential of progressive collapse by increasing the continuity and participating in transferring the extra load. According to the results, the frames without infill panels do not withstand the scenario of progressive collapse in extensive initial damage, however, infill panels help the 6 and 9-story studied structures survive regardless of their span length to story height ratios.

Engineers have dedicated considerable attention over the past ten years to studying the influences of dynamic loads caused by both intentional and unintentional events on infrastructures. As a result, determining how buried structures react to explosions and enhancing their security against blast loads have become crucial subjects in defensive engineering. To achieve this goal, constructing a protective barrier, which is known as a blast wall, in front of structures can be an effective measure. This research focused on examining the impact of a protective barrier on the response of a box-shaped tunnel located in Kobe, Japan, using a comprehensive numerical approach. The results revealed that incorporating a barrier with widths of either 1 m or 2 m resulted in a significant reduction in peak pressure. Specifically, the use of a 1 m wide barrier resulted in a 77% decrease, while a 2 m wide barrier achieved an even greater reduction of 84%. Additionally, it was observed that minimizing the distance between the barrier and the explosion point, as well as increasing the width of the barrier, resulted in reduced peak pressure throughout all sections of the tunnel.

Spur dike is one of the river training structures. This work presented a numerical simulation of flow field and three-dimensional velocity around a T-shaped spur dike located in bend using SSIIM model. The main objective of this work is to investigate the three-dimensional velocities and streamlines at transverse and longitudinal sections and plan views around the T-shaped spur dike in different submergence ratios (0, 5%, 15%, 25% and 50%). It is concluded that by increasing the submergence ratio from 5% to 50%, the maximum of scour is reduced; the maximum of longitudinal velocity increases by 7.7% and occurs at the water surface in spur dike axis. Near the bed, the maximum of vertical velocity occurs at the end of spur wing. By analyzing the streamlines at transverse sections, the followings were deduced for different submergence ratios: different dimensions and different positions of vortices around the spur dike.

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%.

High flow velocity near the free surface in rivers is due to the presence of shear stress near the bed and its absence on the free surface. This phenomenon results in unsteadiness of the vertical velocity profile. Moreover, secondary flows in river bends cause velocity variations, accordingly leading to changes in shear stress near the bed. The present study evaluates and analyzes the effect of streamlines variations, maximum velocity distribution, and secondary flow strength on bed shear stress distribution along a 180 degree sharp bend built in the Hydraulic Laboratory of Persian Gulf University. Results suggest of the occurrence of maximum secondary flow strength at the second half of the bend. The evaluation of bed shear stress distribution using the TKE, modified TKE, and Reynolds methods at turbulent boundary layer demonstrated that the maximum shear stress occurred from the entrance of the bend to the bend apex area near the inner wall. Moreover, comparison of the Reynolds shear stress method at distances of 5 and 15% of the flow depth from the bed indicated that the maximum shear stress occurring at the lower layer moved from the 40 degree cross section to 60 degree cross section at the upper layer.

Analysis of bridge failures due to scouring has been extensively studied by different researchers in recent years and as a result various methods of controlling local scour cavity have been given. Since most of the research in this field has been done on straight paths and also the complexity of the flow pattern in bends, studying the scouring pattern around the bridge piers located in the bends has become a necessity. Therefore, one of the main objectives of this study is to investigate the scouring around the circular piers which are protected by collars at the river bends. The performance of the collar significantly depends on its level around the pier, which has been studied in this study. The results showed that the optimal performance of this structure, in positions 60°, 90° and 120° at the level of 0.2 pier width under the bed with 3 mm thickness (0.06 of pier width) by approximately 68, 63 and 70% of the maximum pier scour depth was reduced compared with collarless pier, respectively. By analyzing the results of this research, it was observed that the optimum level range of collar around the pier at various bend angles is the initial bed level up to 0.4 times the pier width at the bottom of the incipient level of the bed. Moreover, getting closer to the plate placement level toward the initial bed elevation enhances the collar’s function in decreasing scouring.

In this paper, the effect of collar width ratio on the flow pattern around an oblong pier in a 180-degree channel bend was experimentally studied. This channel has a rectangular cross section. It is 1 m in width and 0.7 m in height. The upstream and downstream paths are respectively 6.5 and 5 m long. The ratio of the bend's central curvature radius to the channel width is 2; hence, it qualifies as a sharp bend. Experiments were carried out under clear water approach flow conditions. The results showed that the presence of collars around an oblong pier creates vortices in the opposite direction of the longitudinal flow, causes the distortion and disturbance of the streamlines toward the pier downstream, and decreases downflow strength in front of the pier nose. Furthermore, doubling the collar width results in 0.93 and 0.68 times the vorticity and the power of the secondary flow on the pier upstream, respectively. It also reduced the maximum values of the Reynolds stresses perpendicular to the y-plane in x direction and perpendicular to the z-plane in y direction by respectively 45 and 60%, and increased the Reynolds stress perpendicular to the z-plane in x direction by 25%.

To understand the scouring mechanism around bridges, it is crucial to comprehend the flow pattern in their vicinity. The positioning of the piers along meandering rivers complicates the flow pattern and exacerbates scouring. Therefore, by employing hydraulic structures like submerged vanes to modify the flow pattern around the piers, scouring and further damage can be mitigated. This research investigated the streamlines around one pier and two transverse piers due to the installation of vanes with 25% submergence in a sharp 180° flume channel with a rectangular cross-section. The findings showed that the streamlines in the plan section at the pier locations, from the bed to about 50% of the flow depth at the inlet of the bend, directed towards the inner wall; then, from this level to the water level, the streamlines shifted towards the outer wall. In the plan sections, the maximum positive tangential velocity rose with distance from the bed surface. In the scour hole, radial velocities were negative, while tangential and vertical velocities were positive, resulting in the formation of clockwise vortices in these regions.