Week 7 Challenge
Aim: The aim of this project is to calculate the water currents forces on the substructure and apply the loads on the stadd model
Introduction: The bridge drawing is provided.
From the drawing it is clear that the abutments are protected from scour. The surroundings of the abutments are protected by proper water training works.
From the drawing it is given that the bed level of foundation and the top of the water level is only 2m , but the following calculations are made to find the scour depth and found that the scour depth is more (according to the valued assumed as per the formula requirement). Therefore the calculated depth which is more is considered in the design.
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The followig details are given
High flood level-none
River bed level-none
Height of pier subjected to water current-none
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PROCEDURE:
The following formula is used to calculate the velocity maximum
Then it is applied in the calculation of Pressure
Vmax = sqrt2xVmean = sqrt2x3=1.414x3=4.242
P = 52 k v2
= 52x0.66x4.242x4.242=617.57kN/m2
=617.57x3=1852.71kN/m(if its applied on beam element)
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SCOUR DEPTH CALCULATIONS
dsm-mean scour depth
Db- design discharge- Q=VA
Db=Q= VxA
V= 4.242m/s (From the above calculations)
A= (6m)x1(per meter width of water way)(average depth of water flow along the width is assumed as 6m)
A= 6m2
Db=4.242x6=25.42m3/s(per meter width of water way)
Considering the catchment to be between 3000-10000km2
therefore to be increased up to 30 - 20%
considering 20% increase in discharge
= 1.2X25.42=30.504
Ksf- silt factor for the bed material= (medium sand)-0.85-1.25
Here I am assuming the value as 1.0
dsm=1.34x(30.504/1)^1/3= 4.19 OR 4.2m
For piers from clause 703.1.1 of IRC 78
Max scour depth = 2Xdsm
= 2x4.2=8.4m
Therfore the depth of foundation is 8.4m from HFL
The total height of the pier = 8.4+5.36=13.76m =14m
The water pressure P has to applied for a height of 8.4m from the bottom.
P value calculated as 617.57kN/m2
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The following are the clauses provided in IRC - 6 as well as IRC - 78.
FROM IRC 78 SECTION VII FOUNDATION
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STADD MODEL.
Grillage model is applied'
The scour deth is calculated , which 2xdsm(mean scour depth)
The pier height is calculated as 14m.
The height of the abutment is provided in the drawing.
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SUPPORTS GIVEN TO THE PLATES
LOADING DIAGRAM
WATER PRESSURE APPLIED ALONG THE PLATES FOR A HEIGHT OF 8.5M
WITH MAXIMUM PRESSURE AT TOP
The hydrostatic loads are applied on the plates.
one of the split loads after applying are shown in the following image.
LOADING DIAGRAM
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RESULTS
BENDING MOMENT DIAGRAM OF THE WHOLE STRUCTURE
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Exaggerated view of Deflection pattern
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REACTIONS
PIER REACTIONS
ABUTMENT REACTIONS
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PLATE STRESSES
PIER STRESSES
LEFT ABUTMENT STRESSES
RIGHT ABUTMENT
Similarly other parametrs like Mx, My, SQX, SQy etc can be checked.
CONCLUTION: The behaviour of the hole structure is true to the model and the applied loads, The model is behaving appropriately according to the assumed supports.