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When the water flow in river is deflected by obstructions like bridge piers, scouring would occur arising from the formation of vortexes. The mechanism of formation of vortices is as follows: the flow hits the bridge piers and tends to move downwards. When the flow reaches the seabed, it would move in a direction opposite to its original flow direction before hitting the bridge piers.
The presence of bridge piers across a stream causes constricted flow in the openings because of the decrease of width of stream owing to the presence of the piers. Moreover, it creates the following problems from hydraulic point of view:
(i) Local scouring at the piers and bed erosion may take place. To avoid the damage to the foundation of piers, some protective layers of stone or concrete apron could be provided around the piers.
In uniaxial compression test of concrete, upon reaching the ultimate load failure of concrete occurs where major cracks line up in the vertical direction and the concrete cube would be split up. The development of vertical cracks involves the expansion of concrete in lateral directions. In case the concrete is confined in lateral directions, it was observed that the formation of vertical cracks would be hindered as indicated in past experiments. As a result, the concrete strength is increased with also a rise in failure strain.
Accidental collision of heavy vehicles such as tractor-trailer with bridge piers is not uncommon around the world. The consequence of such collision is catastrophic which may involve the collapse of bridges and loss of human lives. As such, suitable provisions are made to protect bridge piers against these accidental collisions.
Waterproofing materials like membranes are applied on top of bridge deck surface because:
(i) Vehicular traffic (e.g. tanker) may carry dangerous chemicals and the leakage of such chemicals in the absence of waterproofing materials may endanger the life of bridges. The chemicals easily penetrate and cause the deterioration of concrete bridge decks.
After years of servicing, some overlays may be applied on the top surface of bridges. Overlays on concrete bridge decks achieve the following purposes:
(i) It aims to provide a smooth riding surface. Hence, it may be applied during the maintenance operation to hide the uneven and spalling deck surface and offers a smoother surface for road users.
If the depth of a box girder bridge exceeds 1/6 or 1/5 of the bridge width, then it is recommended to be designed as a single cell box girder bridge. However, if the bridge depth is smaller than 1/6 of the bridge width, then a twin-cell or multiple cell is a better choice as suggested by Jorg Schlaich & Hartmut Scheef (1982).
Diaphragms are adopted in concrete box girder bridges to transfer oads from bridge decks to bearings. Since the depth of diaphragms normally exceeds the width by two times, they are usually designed as deep beams. However, diaphragms may not be necessary in case bridge bearings are placed directly under the webs because loads in bridge decks can be directly transferred to the bearings based on Jorg Schlaich & Hartmut Scheef (1982). This arrangement suffers from the drawback that changing of bearings during future maintenance operation is more difficult.
Diaphragm is a member that resists lateral forces and transfers loads to support. Some of the diaphragms are post-tensioned and some contain normal reinforcement. It is needed for lateral stability during erection and for resisting and transferring earthquake loads. Based on past research, diaphragms are ineffective in controlling deflections and reducing member stresses. Moreover, it is commonly accepted that diaphragms aided in the overall distribution of live loads in bridges.
