EAH 422 ADVANCED WATER RESOURCES ENGINEERING

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1 EAH 422 ADVANCED WATER RESOURCES ENGINEERING Bridge Hydraulics Prof. Aminuddin Ab. Ghani

2 References

3 The Art And Science Of River Engineering

4 Bridge Failure Pier scour Pier scour Pier scour

5 Bridge Failure Abutment scour Abutment scour

6 Bridge Failure Destroyed by floating debris during Dec 2014 flood Sungai Nenggiri, Gua Musang

7 Bridge Failure Abutment scour during Dec 2014 flood Sungai Tanum, Kuala Lipis

8 Cross Drainage Structure built over the roads, railways and rivers Culverts shorter span < 6 m Bridges high level crossing structures which can be expensive for large rivers. It is therefore essential to protect them even from rare floods.

9 Sungai Muda

10 Sungai Muda Pier Group

11 Sungai Muda Pier Group

12 Sungai Muda Abutment

13 SHOUJIANG BRIDGE (Sichuan, China) The tallest piers were approximately ft (60 m) high, the approach spans were 98.4 ft (30 m) long, and the four main spans were ft (40 m) long

14 River Erne Bridge (Ireland, UK) Three span structure with a total length of 150m including a 70 m main span

15 In stream Sand Mining and Riverbed Degradation Sungai Jeniang

16 Hydraulic Issues in Bridge Design The presence of a bridge across a stream creates constricted flow through its openings because of (a) the reduction in the width of the stream due to piers and their associated end contractions and (b) the fluming of the stream itself (in the case of wide streams with flood plains) to reduce the costs of the structure

17 Velocity and streamlines at a bridge constriction In the bridge opening, approximately 90 percent of the flow is in the channel and 10 percent is in the floodplain area between the channel banks and abutments (setback area). Flow velocity is less than 1.7 m/s in the upstream channel and 0.37 m/s in the upstream floodplains. This compares with velocities in bridge opening as high as 2.7 m/s in the channel and 1.34 m/s in the setback areas. The higher velocities in the bridge opening generate much higher shear stresses and are much more erosive than the upstream flow velocities. In addition to the increased velocities, bridge structural elements (piers and abutments) locally obstruct flow and cause additional erosion at these locations.

18 Hydraulic Issues in Bridge Design Local scour around the piers and bridge abutments and possible bed erosion A considerable backwater effect of the bridge. The corresponding afflux (rise in upstream water level) depends on the type of flow (subcritical or supercritical). As most bridges are designed for subcritical flow conditions in order to minimize scour and choking problems, further discussions here are mainly confined to subcritical flow.

19 Hydraulic Issues in Bridge Design The establishment of afflux levels is extremely important for the design of upstream dykes and other protective works and also for the location of safe bridge deck levels (to avoid the flooding of the deck and any consequent structural damage). It is equally important to determine the minimum clear length of span (economic considerations) which will not cause undesirable afflux levels.

20 BACKWATER EFFECT (AFFLUX)

21 BACKWATER EFFECT (AFFLUX)

22 Afflux

23 Afflux

24 Afflux

25 Recommended ARI for Road Crossing Design (REAM, 2004)

26 Recommended Freeboard for Road Crossing Design (REAM, 2004)

27 Guidelines Department of Irrigation and Drainage, Malaysia (2009) All bridges and crossings shall be designed to allow for the design flow. The minimum freeboard (clearance) at the design flow level shall be 0.3 m. Where floating logs are expected, this minimum clearance shall be 1 m. There shall be no piers or (vertical wall of culverts) in the middle of the river cross section. For multiple box culverts, twin box culverts should be avoided and instead to use triple box culvert with the centre box in line with the mid flow section of the river or channel.

28 Guidelines Department of Irrigation and Drainage ( Banks stability analysis should be made. All bridges shall be studied for scour effects. Bridge soffit should be at least 1 meter higher than flood level (100 year ARI). Abutment walls shall be constructed at least 2 metres from the edge. Pile caps shall be constructed with a minimum depth of 1.5 meters below the ground level.

29 Guidelines Department of Irrigation and Drainage ( Design Requirement for Bridge

30 Guidelines Scottish Environment Protection Agency (SEPA), Scotland (2010) Pre cast Span Structure showing set back abutments and deep foundations An Example of Span Bridge

31 Guidelines National Roads Authority, Dublin, Ireland (2008) A well designed clear span bridge retaining the existing river channel with piers set back from the river bank

32 1. Backwater Level Short constrictions narrow bridge without approach fluming few piers bw relatively less important refer to Figure h K B 2 V 2 g S 0 L V1 2 g (10.8) K B = bridge loss coefficient (Table 10.2) = conveyance ratio = K b /K B = b/b V 2 = d/s velocity L = bridge length, see Fig S 0 = normal bedslope = contraction ratio = 1

33 Figure 10.10: Flow profile through bridge with contracted channel of relatively short length Table 10.2: Bridge loss coefficient, K B K B

34 1. BACKWATER LEVEL (bw) Long constrictions Large number of bridge piers; long approach embankment; Considerable backwater effects y = results of presence of piers & channel contractions Yarnell s (1934) equation, refer to Figure y y 3 KFr K 5 Fr (10.12) K = a function of pier shape (Table 10.3) Fr = Froude number = V / gy 3 3 valid if is large, i.e. subcritical flow with no choke for critical flow with choke effects (Fig ), limiting value Fr Fr 4 3

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36 Table 10.3: Values of K as a function of pier shape Pier Shape K Remarks Semicircular nose and tail Lens-shaped nose and tail Twin-cylinder piers with connecting diaphragm Twin cylinder piers without diaphragm 90 0 triangular nose and tail Square nose and tail All values applicable for piers with length to breadth ratio equal to 4; conservative estimates of y have been found for larger ratios Lens-shaped nose is formed from 2 circular curves, each of radius to twice the pier width and each tangential to a pier face Figure 10.11: Flow profile with choke flow conditions

37 2. DISCHARGE COMPUTATIONS AT BRIDGE PIERS For subcritical and near critical flows (Nagler,1918), Fig Q K N b / g y h 2 g g V 2 1 V 2 (10.16) K N = Coefficient depending on channel contraction (Table 10.4) = Correction factor intended to reduce the depth y 3 to y 2 Default value = 0.3 = Correction for the velocity of approach (Fig b)

38 Figure 10.12: Discharge computations through obstruction Table 10.4: Values of K N and K A Type of pier Conveyance Ratio, K N K A K N K A K N K A K N K A K N K A Square nose and tails Semicircular nose and tails 90 0 triangular nose and tails Twin-circular piers with/without diaphragms Lens-shaped nose and tails

39 2. DISCHARGE COMPUTATIONS AT BRIDGE PIERS d Aubuisson s (1840) Formula, Fig a K A (10.17) = A function of channel contraction, shape and orientation of obstruction (Table 10.4) An approximate formula gh 2 1/ 2 q K b A y 2 V Chow (1983) Chart produced With values of and y 3, obtain the value of x enter x, values of F 3 and K in the chart to obtain the backwater h

40 3. SCOUR DEPTH UNDER THE BRIDGE Type of scour General scour Contraction scour Local scour

41 General Scour aggradations or degradations of the riverbed not related to the pressure of local obstacles Contraction Scour involves removal of material from bed and bank across most of the channel width Local Scour scour around obstacles in the path of the water flow

42 General Scour: Sediment Transport Contains all the latest research developments in hydrodynamics of sediment transport

43 Sediment Transport Equation for Malaysia Sinnakaudan, S. K., Ab. Ghani, A., Ahmad, M. S. S., & Zakaria, N.A.(2006). Multiple Linear Regression Model for Total Bed Material Load Prediction, Journal of Hydraulic Engineering, American Society of Civil Engineers, Vol. 132, No. 5, May, pp ISSN

44 Local Scour

45 Figure: The types of scour that can occur at a bridge Total Scour at Pier = General Scour + Contraction Scour + Local Scour

46 Physical model of the I 90 Bridge over Schoharie Creek, New York

47 Local Scour at Piers

48 Local Scour at Pier scour hole Acceleration of flow around the pier Formation of the vortices The horseshoe vortices removals material from the base

49 Types of Local Scour

50 COMMON PIER SHAPES

51 3. MAXIMUM SCOUR DEPTH AROUND BRIDGE PIERS

52 3. MAXIMUM SCOUR DEPTH AROUND BRIDGE PIERS

53 3. MAXIMUM SCOUR DEPTH AROUND BRIDGE PIERS 9. Khan, Azamathulla & Ab. Ghani (2012)

54 3. SCOUR PROTECTION WORKS AROUND PIERS AND ABUTMENTS Ripraps Many different types of countermeasures for local scour at bridge piers are introduced in the literature. Using riprap is one of the common countermeasures to control the pier and abutment scours. Ripraps around Pier Ripraps around Abutment

55 3. SCOUR PROTECTION WORKS AROUND BRIDGE PIERS Pier shape shape nose, cylinder Normal practice provide thick protective layers of stone or concrete apron around the piers Riprap protection (Bonasoundas, 1973) Riprap D = U U 2 D = thickness of riprap (m) U c = 6d 1/3 y 1/6 0 U= mean velocity (m/s) or for horizontal bed Uc= mean critical velocity U c = 4.29d 1/2 d = armour stone size (m) The riprap should be placed on a suitable inverted filter or a geotextile fabric (Figure 9.8)

56 3. SCOUR PROTECTION WORKS AROUND BRIDGE PIERS

57 3. SCOUR PROTECTION WORKS AROUND BRIDGE PIERS Collars The collars change the formation of the mechanisms and result in shifting the vortex away from the immediate vicinity of the pier or abutment.

58 Local Scour at Abutment Flow pattern around an abutment

59 Local Scour at Abutment Uniform Abutment (Without Foundation)

60 Local Scour at Abutment Compound vertical wall abutment

61 Local Scour at Abutment

62 Local Scour at Abutment Compound Abutment (With Foundation)

63 Local Scour at Abutment Uniform Abutment (Without Foundation)

64 Local Scour at Abutment Compound Abutment (With Foundation)

65 Local Scour at Abutment Estimating scour depth at a complex abutment: The effective length and Regression methods, can be used to predict the depth of scour at compound abutment:

66 Thank you Presented by Name Centre/Schools/Units etc