Service of Science and Technology Yangon Technological University Department of Civil Engineering

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Service of Science and Technology Yangon Technological University Department of Civil Engineering Hydraulic Design of Bridge ( CE 5016 Design of Hydraulic Structures ) Daw Cho Associate Professor Department of Civil Engineering

Introduction ▪ The afflux (ascend in upstream water level) relies on upon the kind of stream (sub basic or supercritical). ▪ To limit scour and gagging issues, the stream is accepted as sub basic stream condition for the most scaffold outline. ▪ The foundation of afflux levels is critical for the outline of upstream dykes and other assurance works and furthermore for the area of safe extension deck levels. ▪ The admissible upstream stage level and downstream water level can be built up by back water calculation.

Back water levels Short compression ▪Bridge with just couple of wharfs might be generally less vital in back water issues. ▪The change in water level Δ h can be gotten by the vitality condition between areas 1 and 2.

Long Contraction ▪ Bridge has various extensive docks as well as long approach banks gets the water width. ▪ The backwater impact is extensive. ▪ Afflux is altogether made by the nearness of wharfs and channel compression. ▪ Momentum and congruity conditions between segments 1 and 3 result in

Yarnell's observational condition K is an element of the dock shape appeared in Table e.g. for half circle nose and tail, K=0.9 for square nose and tail , K=1.25 (for wharfs with length to expansiveness proportion = 4) This condition is legitimate just if σ is huge, i.e. the constriction can't set up basic stream conditions amongst wharfs and stifle the stream.

If the stream gets to be distinctly gagged by over the top constriction the afflux increments significantly.

The restricting estimations of σ (accepting uniform speed at segment 2)for basic stream at area 2 can be composed as 0.35 for square-edged docks 0.18 for adjusted closures (for wharf length width proportion =4 )

▪ Skewed scaffolds create more prominent affluxes. ▪ Yarnell found that ►10° skew extension gave no considerable changes ►20° skew delivered around 250% more afflux qualities. ▪ Martin-Vide and Piró prescribed for bakwater calculation of curve scaffolds that ►K=2.3m-0.345 where "m" is the proportion of the blocked and channel ranges for 0.324<m<0.65

(b) Discharge calculation For sub basic and close basic streams, ▪ Nagler proposed the condition ▪ ďAubuisson recommended the inexact recipe ▪ Chow exhibits the arrangement the plan outlines delivered by Kindsvater, Carter and Tracy.

(c) Scour profundity under the extension ▪ least stable width of an alluvial channel is W=4.75√Q ▪ If connect length< W , the typical scour profundity under the scaffold is ▪The greatest scour profundity is ►for single traverse extension with straight approach, over 25% of the ordinary scour ►for multispan structure with bended approach, over 100% of the typical scour ▪ If the narrowing is prevalent, the most extreme scour profundity is

(d) Scour around scaffold docks ▪ Several equation in view of test results have been proposed to foresee the "greatest" or "balance" scour profundity around scaffold wharfs. where

(e) Scour assurance works around scaffold docks ▪ To limit the scour and to avert undermining of the establishments, the defensive measures must be taken. ▪ Piers with base stomachs (flat rings) and different barrel sort docks have been found to limit the scour extensively. ▪ The ordinary practice for assurance of the establishment is to give thick layers of stone or solid smocks around the wharfs. ▪ A riprap security in the state of a longitudinal segment of an egg with its more extensive end confronting the stream is prescribed for a barrel shaped pier.▪

Example A street scaffold of seven equivalent traverse lengths crosses a 106m wide waterway. The wharfs are 2.5m thick, each with half circle noses and tails, and their length-expansiveness proportion is 4. The streamflow information are given as takes after: discharge=500cumecs; profundity of stream at downstream of the scaffold = 2.50m. Decide the afflux upstream of the scaffold. It has various vast docks. Hence back water calculation is made for long withdrawal.

K=0.9 (for half circle nose and tail) #########