Forces acting on well foundation


List of forces to be considered while designing a well foundation are as follows:

  1. Dead loads: it includes weight of superstructure (pier/abutment) + self weight of well.
  2. Live loads: the design live loads incase of railway bridges are extracted from I dial Railway bridge rule and codes. For road bridges, the live loads may be specified via standard specifications and code of practice for road bridges.
  3. Impact loads: the impact loads is the result of live load and shall be considered only during the design of a pier cap and the bridge seat on the abutment. However, for other components of the well this effect shall be neglected.
  4. Wind loads: the wind loads shall be seen only on the exposed area in elevation and hence acts laterally on the bridge.
  5. Water pressure: the water pressure due to water current is acted on the portions of substructure that lies between the water level and the maximum scour level. In case of piers lying parallel to the direction of water, the intensity of water shall be determined by, P = kV2 Where, p = intensity of pressure (KN/m2), k = constant that depend upon the shape of well. Maximu 8m — 0.788 for square ended piers, Minimum — 0.237 for piers having cut and ease/clam water, V- –Velocity of current/water flow (m/s), An assumption is made that V2 is maximum at free surface of water and zero at the deepest scour level. The velocity at surface is assumed to be ?2 times the average velocity.
  6. Longitudinal forces: longitudinal forces results from tractive and braking forces. The longitudinal forces depend on the type of vehicles and bearing. These forces get transferred/transmitted into the substructure via fixed bearings and friction in movable bearings.
  7. Centrifugal force
  8. Buoyant forces: the buoyancy tends to decrease the effective weight of well. For masonry/concrete steining 15-20% buoyancy is assumed to account for the porousness.
  9. Earth pressure: The Rainkines’s theory and Coulombs theory is utilized to calculate the earth pressure.
  10. Temperature stresses: the longitudinal forces are resulted because of the temperature changes. The movements caused by temperature changes are partly restrained in the girder bridges due to friction at the moveable end.
  11. Seismic forces: seismic forces are vital when the wells are constructed in seismic zones. The seismic forces act on every members of the superstructure. These forces is principally determined as, ?W, where w= weight of component and ?=seismic coefficient which depends upon the type of seismic zone and its value shall extracted from code. Usually taken between 0.01-0.08.  This seismic force is characterized to cat through the C.G. of the component. These may act in any direction but generally assumed to act in one direction at a time.

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