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

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Service of Science and Innovation Yangon Mechanical College Branch of Structural Building. Water powered Outline of Scaffold ( CE 5016 Configuration of Pressure driven Structures ) Daw Cho Partner Teacher Bureau of Structural Designing. Presentation.

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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

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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.

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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.

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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

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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.

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

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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 )

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▪ 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

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(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.

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(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

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(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

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(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.▪

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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.

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