Spring
2005
Ahmed Asif Reza
There is
a worldwide concern on damage of bridge caused by local scour around bridge
pier. Structural failures of bridge induced by local scour usually occur in
extreme cases of flood flows interacting with pier or when considerable sediment
transport occurs. Experiences has shown all too often that scouring can
progressively undermine the structure. A through study has been conducted to
understand the state of art. So, to calculate the maximum locals scour depth at
bridge location of Ghior Khal in north central region three methods (FHWA,
Laursen’s and Breuser’s) for piers and two methods (Liu et al Method and
Simon & Sentruk’s) for abutments are selected in the present study. Local
scour at piers has been studied extensively in the laboratory. As a result of
the many laboratory studies, there are numerous pier scour equations. Scour
depth depends on various parameters (such as depth of flow, shape of pier, angle
of attack of flow, sediment size etc.). Different engineers have evaluated their
equations to predict scour depth using different parameters and field of
application. Thus to investigate the behavior of local scour against different
parameters a sensitivity analysis is being made in the present study for
circular pier. To
protect water structures such as bridges from failure it is very important for
the engineers to find out the most dominating parameters that are affecting the
maximum local scour depth. The obtained dominating parameter should be given
majority during design and construction of the structure. In the present study
it is found that the Laursen’s Method gives the highest scour depth, FHWA’s
Method gives the lowest scour depth and the Breusers Method gives the value in
between. From which the maximum scour depth is selected. It is also found that
velocity is of greater sensitive than pier width followed by flow depth and
angle of attack of flow is insignificant if the structure (Pier) is circular. |