SMARTeST Report on Design of Basic Flood Barrier Prepared for: Project Officer European Commission DRAFT May 2012
D… Flood Barrier Design
Prepared by
Name Cyprus Partner, under co-ordination of Antonis Toumazis,
Position Cyprus Partner
Signature
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List of content 1 Introduction ______4 2 The structure ______5 3 River and Rainwater Floods ______7 3.1 Problem Definition ______7 3.2 Hydrostatic Loading ______7 3.3 Wind Loading ______8 3.4 Wave Loading ______8 3.5 Debris Impact Loading ______9 3.6 Hydrodynamic Loading ______11 4 Coastal and Wave Overtopping Floods ______12 4.1 Problem Definition ______12 4.2 Broken wave ______12 5 Stress Analysis ______14 5.1 Load Path ______14 5.2 Secondary members ______14 6 Loading Combinations ______15 7 Design Tool ______16 7.1 Bending Moments, Shear Forces ______16 8 Examples ______17 8.1 River / rainwater flood case ______17 8.2 Coastal/ Wave Overtopping flood case ______20 9 Prototype Barrier ______25 9.1 Development stages ______25
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1 Introduction
During the case study for coastal flooding in Paphos Sea front area it was found that there are cases in which the requirements for flood barriers are very specific and most demanding. Potential clients and licensing authorities were raising genuine questions concerning the environment, the appearance, the traffic loading, the wave loading, the obstruction of utilities etc. There are numerous products in the market which are suitable for many applications. In cases like Paphos barrier manufacturers were prepared to listen to the project requirements and provide solutions. In order to improve the road-to-market for flood resilience technology a design tool was developed which enables consultants to design flood barriers specific to particular project requirements and derive the dimensions of the structural components. Consultants and Employers together will have the option to select non-structural components, deployment parts and water-tightness seals, depending on the flood resilience system adopted. Suppliers will be encouraged to produce innovative components, parts, seals. Contactors will be enabled to assemble and build the barriers using conventional contracts for firm designs.
Figure 1-1. Flood Barrier. During normal conditions (left), During flood conditions (right)
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2 The structure
The analysis model for the proposed barrier includes three (3) typical support conditions (figure 2-1):
Hbarrier Hbarrier Hbarrier
Hflood Hflood Hflood
Pin - Pin Cantilever Fixed- Pin Figure 2-1. Typical barrier support arrangements (a) Pin-pin (restraint in movement at base, reaction with some flexibility to move horizontally at top) (b) Cantilever (fixed support at base, free at top) (c) Fixed-pin (fixed support at base, reaction with some flexibility to move horizontally at top)
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It consists from the parts as shown below :
Figure 2-2. Barrier parts
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3 River and Rainwater Floods
3.1 Problem Definition
A typical barrier arrangement is shown in figure 3-1. The barrier is raised a distance Hbarrier above pavement level. The design flood level is a distance Hflood above pavement level. The loading acting on the mounted barrier is: 1. Hydrostatic and hydrodynamic loading
2. Short surface gravity waves with a wavelength L and wave height H s, approaching at an angle β to the barrier 3. Debris impact loading, the debris having a mass m and a velocity u, at an angle δ
4. Wind loading on the barrier surface above the flood level
u Barrier Hs, L Debris m
u m Hbarrier Hflood Debris ä â
Figure 3-1. Problem Definition Cross section (left), Plan (right)
3.2 Hydrostatic Loading
The hydrostatic loading has a triangular distribution, starting at the flood level and increasing to the maximum pressure at the toe of the barrier. (figure 3-2)
The maximum hydrostatic, P hydrost, pressure is equal to:
Phydrost = ρ g H flood (eqn 3-2.1)
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Hflood
P Hydrost Figure 3-2. Hydrostatic pressure Distribution
3.3 Wind Loading
The barrier surface above the still (flood) water level is exposed to the wind loading. The pressure acting on the exposed surface is equal to: 2 Pwind = 0.5 ρair Vwind (eqn 3-3.1)
PWind Hbarrier Hflood
Figure 3-3. Wind pressure Distribution
3.4 Wave Loading Short period gravity surface waves may be generated in the flooded area due to wind or other disturbances. The wave loading may be expressed as pressure distribution along the whole length of the wetted barrier height, i.e up to elevation η* above still (flood) water level.
The wave induced pressure distribution may be derived using Goda (1974) equations.
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p1=Pressure at crest of barrier p2=Pressure at flood level p3=Pressure at bottom support
= ĕĔĥĥĜĘĥ ͯ ęğĢĢė for dz > else = (eqn 3-4.1) ͤͦ ʠ1 Ǝ Vdz ʡ ͤͥ ͂--$ - Ǝ ͂!'** ͤͦ 0 p1= ͦ (eqn 3-4.2) 0.5 ʚ1 ƍ ͗ͣͧ ʛʚ ͥ ƍ ͦ ͗ͣͧ ʛ 2 ͛ ͂ . p3=α3 p1 (eqn 3-4.3)
dz (eqn 3-4.4) Ɣ 0.75 ʚ1 ƍ ͗ͣͧ ʛ͂ . xŗāęğĢĢė = ą ͦ (eqn 3-4.5) ͥ 0,6 ƍ 0,5 ʞ ʟ .$)#ʚͨ_ ęğĢĢė / ʛ (eqn 3-4.6) ͦ Ɣ 0 ͥ (eqn 3-4.7) ͕ͧ Ɣ vŗāęğĢĢė *.#ƴ ą Ƹ Where
is the maximum wave height in front of the barrier = 1.8 H s (where H s is the significant ͂ . wave height)
P * 2 η
P1 Hbarrier Hflood
P3
Figure 3-4. Wave induced pressure loading
3.5 Debris Impact Loading An accidental load that may be the critical one is debris impact loading.
3.5.1 Hard impact
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The force induced in case of hard impact by a mass m hitting the barrier with a velocity u at an angle δ is given by equation 3-5.1. (Annex C of Eurocode 1part 7 (EN 1991-1-7:2003).
1/2 Fdebris =u·cos δ·(m·k) (eqn 3-5.1) Where k is the equivalent elastic rigidity of debris k= E·A / L (eqn 3-5.2) m is the mass of debris m= ρ·A·L The shape of the force due to impact can be assumed as rectangular pulse of duration ∆Τ = (m/k) 1/2 thus F ·∆Τ = m·v.
3.5.2 Soft impact In case where the structure is assumed elastic and the colliding object rigid, the above formulae still apply, with k being the stiffness of the structure. If the structure is designed to absorb the impact energy by plastic deformations then it must be ensured that its ductility is sufficient to absorb the total kinetic energy 2 ½ m v r of the colliding object.
3.5.3 Rigid-plastic response In the limit case of rigid-plastic response of the structure, the above requirement is satisfied if 2 ½·m·vr ≤ F 0·y0 Where
F0 is the plastic strength of the structure y0 is its defomation capacity
3.5.4 Impact force by FEMA Another equation recommended by FEMA Technical Bulletin 3-93, Non-Residential Floodproofing – Requirement and Certification for Buildings Located in Special Flood Hazard Areas in accordance with the National Flood Insurance Program is equation 2-4.3.
Fi= W V / (gt) (eqn 3-5.3)
Where Fi is the impact force W is the weight of the object (1000 pounds but can be reduced to 500 pounds for areas subject to minor debris flow potential. V is the velocity of the object g is the acceleration of gravity t is the duration of impact. t= 1 second in this equation
Both equations are equivalent. The impact force increases with the debris mass and the debris velocity. The more flexible the barrier, the longer the duration of impact, the smaller the impact force (for the same debris mass and velocity).
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Equation 3-5.1 allows the user to optimise the barrier rigidity/ stiffness and thus reduce the impact force. The more the flexibility the less the rigidity, the less the force but the larger the displacements.
3.6 Hydrodynamic Loading This is the force exerted on vertical surfaces exposed to moving floodwaters.
It has a triangular distribution starting with maximum value at the top of the flood and decreasing to zero at the toe of the barrier.
The determination of hydrodynamic force is based on the expected velocity of the floodwaters with depths to the floodproofing design level and the shape of structure.(EN 1991-1-7:2005)
2 Fwa =0.5 k ρwa h b u (eqn 3-6.1) Where k is the shape factor (1.44 for rectangular horizontal cross section ,0.70 for circular horizontal cross section) h is the water depth b is the width of the object
ρwa is the density of water u is the mean velocity of water
Figure 3-5. Pressure and force due to currents
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4 Coastal and Wave Overtopping Floods
4.1 Problem Definition
A typical barrier along the sea front is shown in figure 4-1. In such cases the design wave conditions are depth limited. The waves that overtop the sea front and impinge on the barrier are usually broken waves.
The barrier is raised a distance H barrier above pavement level. The wave crest level, or the flood level, is at distance H flood above pavement level.
FLOOD LEVEL
Hbarrier Hflood
NORMAL WATER LEVEL
d
Figure 4-1. Vertical Cross-section – Coastal/ Wave overtopping Flood Barrier
The loading acting on the mounted barrier is:
1. Broken wave loading
2. Wind loading on the barrier surface above the flood level(as descripted in previous session)
4.2 Broken wave The broken wave pressure loading is given by equation 4-2.1 (Blackmore and Hewson (1984)).
2 Pbroken wave=λ ρ Τp Cb (eqn 4-2.1) Where
λ is the aeration coefficient
ρ is the density of sea water
Tp is the wave spectra peak period
Cb is the velocity of the breaker at the barrier
Cb in its simplest form may be approximated by linear wave theory for shallow water
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1/2 Cb=(gd) Where d=water depth
Suggested values for λ are given in table 4-1.
Bed Slope
Foreshore conditions 1:5 to 1:10 1:30 to 1:50 1:100
Smooth bed, sand 1.5 0.9 0.7
Rough, Rocky 0.5 0.3 0.24
Very Rough, emergent rocks 0.13 0.18 0.14
Table 4-1, Aeration Coefficients, λ, for broken waves (Blackmore and Hewson (1984))
PBroken Wave Hbarrier Hflood
Figure 4-2. Broken Wave induced pressure loading
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5 Stress Analysis
5.1 Load Path
Main Member Rigidity=F/ δx Secondary Members
H barrier H flood ∆z
Y1 Vertical Section Elevation Figure 5-1. Barrier Vertical cross section (left), elevation (right) The pressure loading is transferred through plates/ membranes to horizontal (secondary) members (figure 5-1). The end reactions of the secondary members consist the loading to the vertical (main) members. The vertical members transmit the load to the foundations/ supports.
5.2 Secondary members The software tool initially computes the pressure loading for each loading type on the horizontal/ secondary members, assuming simply supported connections in-between panels.
It then computes the stresses along the members and support reactions at the two ends.
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6 Loading Combinations
The member stresses derived from the individual loadings are combined together in order to obtain the design stresses.
There is no provision in the Eurocodes for the imposed loads, the corresponding load factors and the loading combinations.
The user has the freedom and the privilege to assess the particular conditions and define the magnitude of the design parameters and the load factors to be applied.
In the case of river/ rainwater flood barrier, a critical parameter is the debris impact load. This loading is associated with flood-borne debris being transported by flowing flood water and hitting the flood barrier.
FEMA (Federal Emergency Management Agency) of the USA, recommends that the mass of debris is 1000 pounds (454kg) and may be reduced to 500 pounds (227kg). The debris velocity depends on the flow velocity and is of the order of 8 feet/second (2.44m/s).
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7 Design Tool
7.1 Bending Moments, Shear Forces
The design tool developed computes and plots the bending moments and the shear forces for each load case and for the loading combinations specified.
It then computes the usage factor.
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8 Examples
8.1 River / rainwater flood case A flood barrier design is shown in the following example (table 8-1).
1 INPUT DATA
1,1 Barrier Data
Barrier height Hbarrier = 1,00 m
Spacing between main members Y1= 1,00 m Spacing between secondary members Δz= 0,10 m Barrier rigidity K=F/δx 90.000 N/m Type of barrier elastic
1.2 Water Data 3 Water Density ρw= 1.000 kg/m
1.3 LOADING DATA 1.3.1 Hydrostatic
Flood elevation above bottom support Hflood = 0,90 m
1.3.2 Wind Air density ρ= 1,25 kg/m 3 Wind velocity v= 36,00 m/s
1.3.3 Wave
Design Wave height Hdesign = 0,10 m Wavelength L= 19,20 m Incident wave angle β= 0 degrees
1.3.4 Debris flow velocity v= 2,0 m/s incident angle δ= 0 deg mass of debris m= 500 kg
Debris width dw= 0,5 m 2 Debris modulus of elasticity Edeb = 20000000 N/m 3 Debris density ρdeb = 700 kg/m 2 Debris colliding area Adeb = 0,25 m
deformation capacity of structure y0= 0,02 m duration of impact (for use in fema) t= 1 s type of debris rigid
1.3.5 Current
incident angle of flow αwa = 45 deg
velocity of flow= vwa = 2 m/s shape coefficient k= 1,44
1.3.6 Acceleration of gravity g= 9,81 m/s 2 Table 8-1. Input Data for river/ rainwater flood barrier design
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The pressure distribution, in N/m, along the vertical on the barrier is shown in figure 8-1.
Hydrostatic Debris Wave Wind Current
1,2
1,0
0,8
0,6
0,4
0,2
0,0 0 5000 10000 15000 20000 25000 30000
Figure 8-1. Pressure distribution (N/m)
The next step is to define the loading combinations and the partial safety factors. Table 8-2 presents the selections made in this example. It is noted that in loading combination 3, there is no debris impact but there is an excessive partial load factor for the hydrostatic load.
Partial Safety Factor combination hydrostatic wind wave debris Current 1 1,5 1,5 1,4 1,5 1,4 2 1,0 1,0 1,0 1,0 1,0 3 10,0 1,5 1,4 0,0 1,4 Table 8-2. Input Data for river/ rainwater flood barrier design
The derived loading distribution after applying the loading combinations is shown in figure 8- 2. It is noted that in this case the barrier is a soft system, with high elasticity and reduced debris impact.
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Figure 8-2. Pressure distribution (N/m) for the loading combinations
The structural members are then analysed. The horizontal/ secondary members are analysed as simply supported beams.
Combination 1.0 Combination 2.0 Combination 1.0 Combination 2.0 Combination 3.0 Combination 3.0 0 6000 -200 0.00 0.20 0.40 0.60 0.80 1.00 4000 -400 2000 -600 0 -800 -2000 0.00 0.20 0.40 0.60 0.80 1.00 1.20 -1000 -4000 -1200 -6000
Figure 8-3. Bending Moment and Shear Force Diagrams for Secondary beam at base of barrier
The design tool computes the moment utilisation factor for the section properties input by the user, as shown in table 8-3.
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Section Modulus Proposed, Z 12 cm3
Characterestic Strength in Tension Proposed, f yd 500.00 N/mm2
Moment Utilisation Factor 0.74 OK
Table 8-3. Computed moment utilisation factor for the input member properties
The bending moment and shear force diagrams for each loading combination are then derived for the main/ vertical members. Figure 8-4 presents the diagrams for the case of a barrier with pin support at both ends.
Combination 1 Combination 2 Combination 1 Combination 2 Combination 3 Thousands Combination 3 Thousands 0.00 0.00 -4 -3 -2 -1 0 1 -20 -10 0 10 20 -0.20 -0.20
-0.40 -0.40
-0.60 -0.60
-0.80 -0.80
-1.00 -1.00
-1.20 -1.20
Moment→Nm Shear→N
Figure 8-4. Bending Moment and Shear Force Diagrams for Main Members for Pin-Pin barrier
Section Modulus Proposed, Z 10 cm3
Characterestic Strength in Tension Proposed, f yd 500 N/mm2
Moment Utilisation Factor 0.74 OK
Table 8-4. Computed moment utilisation factor for the input member properties
The design tool computes the moment utilisation factor for the section properties input by the user, as shown in table 8-4.
8.2 Coastal/ Wave Overtopping flood case
The flood level is 0.9 m.
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INPUT DATA
Barrier Data
Barrier height Hbarrier = 1,00 m
Spacing between main members Y1= 1,00 m Spacing between secodary members Δz= 0,10 m Barrier rigidity K=F/δx 90.000 N/m
Water Data 3 Water Density ρw= 1.000 kg/m Normal water level d= 1,00 m
LOADING DATA Wind Air density ρ= 1,25 kg/m 3 Wind velocity v= 36,00 m/s
Wave
Wave crest above barrier support Hflood = 0,90 m
Wave spectral peak period Tp= 5,20 s aeration coefficient λ= 0,24
g= 9,81 m/s 2 Acceleration of gravity Table 8-5. Input Data for coastal/wave overtopping flood barrier design
The pressure distribution, in N/m, along the vertical on the barrier is shown in figure 8-4.
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Figure 8-5. Pressure distribution (N/m)
The next step is to define the loading combinations and the partial safety factors. Table 8-6 presents the selections made in this example.
Partial Safety Factor combination wave wind 1 1,4 1,5 2 1,0 1,0 3 1,0 0,0 Table 8-6. Input Data for coastal/wave overtopping flood barrier design
The derived loading distribution after applying the loading combinations is shown in figure 8- 6.
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combination 1 combination 2 combination 3
1.2 1.0 0.8 0.6 0.4
Barrierheight → m 0.2 0.0 0 2000 4000 6000 8000 10000 12000 14000 16000 18000 D.L. → N/m
Figure 8-6. Pressure distribution (N/m) for the loading combinations
The structural members are then analysed. The horizontal/ secondary members are analysed as simply supported beams.
Figure 8-7. . Bending Moment and Shear Force Diagrams for Secondary beam at base of barrier The design tool computes the moment utilisation factor for the section properties input by the user, as shown in table 8-7.
Section Modulus Proposed, Z 0,6 cm3
Characterestic Strength in Tension Proposed, f yd 500,00 N/mm2
Moment Utilisation Factor 0,88 OK
Table 8-7. Computed moment utilisation factor for the input member properties The bending moment and shear force diagrams for each loading combination are then derived for the main/ vertical members. Figure 8-8 presents the diagrams for the case of a barrier with pin support at both ends.
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Combination 1 Combination 2 Combination 3 Combination 1 Combination 2 Combination 3 Thousands Thousands 0,00 0,00 -1,5 -1 -0,5 0 0,5 -5 0 5 -0,50 -0,50
-1,00 -1,00 Barrier heightBarrier →m Barrier heightBarrier →m -1,50 -1,50
Moment→Nm Shear→N
Figure 8-8. Bending Moment and Shear Force Diagrams for Main Members for Pin-Pin barrier
Section Modulus Proposed, Z 3 cm 3 2 Characterestic Strength in Tension Proposed, f yd 500 N/mm
Moment Utilisation Factor 0,80 OK
Table 8-8. Computed moment utilisation factor for the input member properties
The design tool computes the moment utilisation factor for the section properties input by the user, as shown in table 8-8.
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9 Prototype Barrier
9.1 Development stages In order to enable the road to market, a basic barrier was developed which can be adapted to particular applications. In order to enable the user to select the finished floor material of the barrier and not to interfere with buried utility services, the barrier is horizontal when idle opening in such a way that the wetted surface is different from the finished floor material. (fig. 9-1)
Figure 9-1. The basic barrier design – Wetted surface different from exposed face when idle
The barrier has the option of having a wave return curvature, reducing wave overtopping due to waves. The traffic load when closed is transferred directly to the foundation, since the wetted face is resting on the up-stand foundation. The barrier wall consists of a series of overlapping “doors”. Special seals are placed in-between the door overlaps and at the contact surface between the barrier and the immovable base. Each barrier “door” has two braces at each end. In order to keep adjacent and overlapping “doors” tightly in contact, one bracing is pulling towards the flood zone and the adjacent bracing is resisting the pulling force. The brace taking the flood load is in pre-tension and the adjacent brace is in compression. The various stages of the prototype development are illustrated in figure 9-2 to 9-6.
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Figure 9-2. Initial Concept Ideas – Small Scale Model
Figure 9-3. Small Scale Model – Office Work
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Figure 9-4. Prototype at workshop (SEMESCO)
Figure 9-5. Prototype at Outdoor Testing Grounds (SEMESCO)- Leakage test
Figure 9-6. Prototype at SMARTeST Conference and Exhibition, Athens, Sept. 2012