Choice of Aqueduct and Methodology Used for Its Design
BS 5400 part 2 cl 184.108.40.206.2
BS 5400 part 2
BS 5400 part 4 1990 table 3
The choice of aqueduct system. The two aqueducts of choice are the trough and the barrel type aqueduct. However, some of the specifications in their design are completely different and as such, require individual focus (Bos, 1976). The following design basically focuses on the barrel type aqueduct.
The three principal loadings are from:
· The self-weight
· The loading by the emergency vehicles
· Loading by the water(during operation of the canal
Beginning with the stresses that are induced on the slab(taking a trough aqueduct)
The self-weight properties of the slab and the trough
The stress that is induced by the concrete=
35 0.0980665= 3.4323275
The stress induced by the steel=
The concrete mix basically determines various parameters of the structural element and in this case, a C35 concrete mix is taken for the design purpose The density of water is
1000 and designing the elements per meter run the stress induced is
The size of the trough is given as 4.0m
The maximum depth that water is limited to flow is 1.8 meters. It is an important aspect of the design because of the thrust that the trough and slab are subjected to. The freeboard of the water of 0.5 meters prevents the water from causing considerable damage to the traffic and the footpath.
16mm S355 diameter bar is taken as the main reinforcing bar for our design purpose. The 16mm diameter is appropriate because it is the most viable among the three grades of steel. Though it does not possess the same characteristic strength as the S460 bars, it presents a comparatively cheaper option.
Taking the cover of the slab as 35 due to moderate exposure
Thereore,assuming a slab thickness of 230mm
Effective depth of the slab=230-35-8=187mm
And the effective span of the trough=the span effective depth
This results into a self-weight of (2500kg/m2 is the unit weight of reinforced concrete)
Designing the wing walls of the trough
The total height of the wingwall,which may be simply supported between the wuingwall and the pier=1.8+0.5+0.230=2.52 m
Furthermore, the wing wall may be described to span between the abutment and a pier that may be located midway through the total span that is 34 m. The pier will be located midway between the road and will separate the two traffic lanes
Taking a beam of 25 cm
The span is 34m
Taking a top abutment width of 15m,the width of the pier as 4m,the width of the bearing as 0.4m and the clear cover to the beam as 0.050m
Furthemore,taking the same diameter of reinforcement as the trough slab=16mm
Effective depth of the beams that span between the pier and the abutment
Furthermore, the effective span=34+0.4=34.4m
Design for the loads per meter run in the slabs spanning 34m
Various loads are present and pose some loading on the slab as well as the piers
Some of the loadings can be attributed to
· The dead weight of the construction materials such as concrete
· The imposed loads due to the traffic and the pedestrians
· The weight of the water which may be taken as a dead load
· The dead load that can be attributed to the side wall
All these loads are transferred to the pier which later on transmits them to the ground
However, the imposed loading due to traffic may provide the basic blueprint for the design purpose. The emergency loading provide the greatest stresses to the slab and the pier and as such, the design is very important
Considering that the width of the footpath/lane is 2.5mm,the aqueduct may be regarded to have only one notional lane
Considering a loaded length of 55m
=22.92 KN/m per notional lane
The knife edge load is 120 KN
Therefore for a meter width of the 34m wide span
Theefore,the maximum bending moment that can be witnessed in the deck slab is when the knife edge loading is at the middle span 10
The maximum bending moment= 1572.33kNm
The servicalibility limit state
Therefore, the moment that will be experienced on the bridge deck
Calculating the total loading that is experienced on the slab
The weight of the slab that holds the trough=0.230 2 2500=1150kg
Dead weight that is induced by the wing wall=2.52 =1575kg
The weight induced by the water=1.8 3600kg
Therefore the total weight that the pier has to hold=6325 kg
Based on the above calculations, and in addition to the bending moment due to thermal effects, the total bending moment can be deduced to ascertain the suitability of the depth of the slab
Bending moments due to thermal effects
h1,h2 and h3=0.3h
Hence positive temperature difference can be used to obtain moments induced when the temperature is very high
Temp 1=13.0,temp 2=3.0 and temp 3=2.0
Therefore, the force induced can be calculated as:
Coefficient of thermal expansion=
Thereore,the restrained stresses due to the temperature difference can be calculated as =0.354
Using the force and the stresses generated to determine the bending moments that may have adverse effects=
317KN moment area
Moment area=bd3/12= =1.01 mm4
Therefore the adequacy of the slab can be checked by combining all the moments from the differential loads
Bending moments due to the load effects wl /8
The moment required=Qbd
The depth that is required=
Therefore, the depth required to ensure the loading does not have any effect on the structure is 201mm and therefore our depth of 230 is satisfactory and safe.
The vetical deflection of the slab is a critical factor in its day to day operation and as such, the deflection check is required
20 for spans which are greater than 10m and therefore, the deflection = 5.88 which is less than 20, therefore the vertical deflection of the slab will be within the permissible limits during its functioning.
16mm diameter S355
Description on the choice of aqueduct and the methodology
There are some basic factors that separate the two types of aqueducts stated in this report: the trough aqueduct and the barrel type. The aqueducts serve the function of transporting water different terrains but they have different design shapes and basically a varied functioning base (Chanson, 1999). To begin with, the trough type aqueduct has on many occasions been flumed and as such, the upstream and downstream sides of the aqueduct do not lose as much energy as in other types (Chow, 1983). Moreover, this flume is basically about 75% of the bed width and therefore maintains the head loss to limited values (Coleman, et al., 2003).
One of the major factors that has to be considered in the design of this type of aqueduct is the water thrust that the walls as well as the slab are subjected to (Indian standards, 2003). Therefore, it is particularly useful when designing aqueducts that the design considers varied amounts of water. Some of the areas that may use this type of aqueduct involve; areas subject to flooding, areas that have varied water demand patterns among others. Moreover, the project might be economical on the aspect that the roadway can be designed above the trough.
The design of the trough type of aqueduct begins with determining the amount of loads to be transported over the roadway (Dey & Barbhuiya, 2005). The aqueduct is designed under the roadway and as such, the structural integrity of the concrete and the roadway surface has to be checked to ensure that there is no aspect of failure. Another advantage of the aqueduct is the fact that there is the minimization of the costs on structures such as weirs that are used to ensure the water level remains within some specified limits. Furthermore, the water remains within the trough and as a matter of fact, there is a reduction in the exposure to the environment ( Chang , 1980)
However economical, viable and effective the aqueduct may be, there are some disadvantages associated with it.
The first disadvantage is the fact that there is increased concrete use because of the roadway alignment over the waterfowl (Coleman, et al., 2003).In this, the designer has to ensure that the concrete is sufficient enough to hold the roadway over the canal (Hager, 1999). If the concrete is not sufficiently strong and durable, the roadway may cave in and cause unreversable damage, both to the community and the engineers’ reputation. Moreover, the reinforced concrete has to ensure that the bars are at sufficient depths that limit the susceptibility to corrosion (Indian standards, 2003). Since the water surface is always in contact with the concrete surface, there should be a design consideration on the aspect of cover and the number of bars that are going to be used. As a matter of fact, some types of aqueducts are restricted to specific water types because of the susceptibility to corrosion from different types of water ( Nandana & Chiranjeevi, 1983).
Loadings and Self-Weight Properties
The barrel type aqueduct is more versatile because of the different forms it can be designed into. The aqueduct can be designed as either rectangular, circular etc. Furthermore, it can be divided into various cells that basically transport the water (Punmia & Pande , 2009).Presently, most designers prefer reinforced concrete because of the durability and the strength of the combination of steel and concrete.However,the previous designers opted for masonry and as such, the earlier version aqueducts were nor as strong and as durable as the current (Zarrati, n.d.). More about the aqueduct is that it is more inclined towards the downstream side as compared with the other type of aqueducts. The inclinations may vary between 3H: 1V or 4 H: 1V (Hamill, 1999).Furthermore, the design requirements may entail that the aqueduct have sufficient water velocity so as to have sufficient energy for self-cleaning (US Army Coastal Engineering Research Center, 1984). The velocities may vary between 6m/s to 8m/s for the reinforced concrete aqueducts and masonry aqueducts respectively ( Chitale , 2002).
The major advantage of this type of aqueduct may be its economic perspective. The design of such an aqueduct is not as expensive as other types because of the simplicity. In this, the aqueduct can be mold into different shapes and forms and can basically fit into any type of terrain or land surface. By doing so, the designer ensures that all problems that may be associated with canal and water movement are put to a minimal. Aspects such as the land area required, space required etc. is considered on the most economic methodology. Another important aspect off this type of aqueduct is the fact that it is not used by heavy vehicles that would subject it to HB loading and enormous tensile stresses and moments (Siow-Yong, 1997). As per the design case above, the vehicles that move over the aqueduct are mainly for service purposes. Therefore, they subject the pathway to lesser stresses and moments. Therefore, the design of this type of aqueduct is very economical because of the reinforcements and the concrete used in the design.
The interaction between the water surface and the concrete is put to a minimal, in comparison to the trough type, because only three faces are in direct contact with the water. By reducing the number of faces that may be in contact with the water, there is the economy associated with the number of reinforcements used and the cover provided by the concrete to the reinforcements ( Standard, 2000). As a matter of fact, the reinforcements used in this type of aqueduct are not as many as in the trough type aqueduct.
As with the limitations and the disadvantages of the aqueduct, the main issue is the freeboard surface maintenance, especially during floods. As in comparison with the trough type aqueduct where the water is safely contained between the road surface and the trough slab, in this case the water flows over an open surface and if there is no proper measures taken to ensure that the water remains in the canal way, there might be the exposure of the less protected concrete surface to the effects of water. Exposure might consequently lead to corrosion of the reinforcement and as such, a likelihood for a catastrophe. Another major disadvantage is the exposure of the water to environmental factors. A barrel type aqueduct transports the water over an open surface and as such, there is the exposure to environmental factors. The exposure might be harmful in cases where the water transported is for consumption purposes and as such, a proper framework that will ensure the transportation of water is all in line with the safety and health requirements needs to be put in place (Board, 1992). Water transported for uses other than consumption need not to be closely monitored.
Design of an aqueduct
The design of an aqueduct entails the design of a bridge system. However, the main difference between an aqueduct and a bridge is the fact that an aqueduct is mainly used for the transport of water from one side of a terrain to the other (Yawar , et al., 2016). Therefore, the aspect of the thrust of the water is the main factor that limits the design of an aqueduct in relation to a bridge system. However, the main elements that are designed in a bridge system are also designed in the aqueduct system.
The abutment serves the purpose of anchoring the bridge to the soil s and as such, the design of the abutment will involve the various properties of sand such as the internal angle of friction, the pore water pressure etc (Kollipara , et al., 2016). All these properties that are used in the design of an abutment are further used in the design of foundations. To ensure that the abutment is stable and strong enough to hold the bridge, there need to be proper site investigations to establish a proper site for the erection of this structure, Stable soils and bedrocks provide a necessary foundation for its erection.
During the erection of a bridge, there is a roadmap that marks the progress and the various accomplishments. All this is bound to change within the near future with the development of technology and the advancement of knowledge in the different branches of civil engineering. As per the above design of the aqueduct, the initial step would be to build the foundation. Foundations are the most vital structures of any bridge system because of the need for stability. Therefore, one requirement of this stage is the detailed and extensive research on the soil properties. As with the foundation of the aqueduct designed above, the presence of a rock foundation just 1m below the ground provides a much needed platform for the erection of the structure. This bedrock ensures that the aqueduct has the capability to hold and transport the design amount of water. However, the foundation has to be in line with the technical requirements as well as the methodology employed for the construction (Ranga Raju, 1993). The aesthetics basically describe the importance of various design consideration before the actual construction.
The load that acts on a bridge structure is the most important consideration on bridge design. Various bridge systems are designed for various purposes and as such, the design has to be specific to the load requirements of the structure. An aqueduct is designed for the movement of water over different terrains which can either be natural or manmade. As with the design of the above aqueduct, the terrain is manmade. During the construction process, the factors that should be considered express extreme situations and limit the possibility of failure of the structure. A simple error can lead to the loss of humongous amounts of money. Therefore, during the erection process, one of the most significant factors is to identify the necessary pressure losses in the aqueduct.
The head loss in any conveyance system presents a major problem for the movement of water downstream. The head loss is basically described by the manning’s formula and the variables that determine this head loss include the roughness coefficient, the slope etc. All these should be checked prior to the actual construction in order to ensure that the structure will efficiently convey the water from one side of the road to the other. The temperature effects of a bridge system are some of the times under looked yet they pose significant threat, particularly because of the bending effects caused. Therefore, the coefficient of thermal expansion of both the concrete and the reinforcement need to be properly looked into to ensure that there is no room for error when the temperatures change.
Another important factor Is the young’s modulus of elasticity which basically describes the properties of the reinforced concrete when subjected to varying degrees of temperature.Therefore,during erection,the designers and the construction workers need to ensure that there is no possibility of structural failure during the operation of the work.However,an aqueduct can balance the external temperature with the temperature of the water and as such, the designers need to ensure that all the temperature factors are taken into consideration. Temperature effects during construction as well as the effects during the operation of the aqueduct.
One basis of the design of an aqueduct is the type of water that is conveyyed.There are varying degrees of water acidity and alkalinity and as such, the designer has to ensure that there is sufficient protection to all the structural members such as slabs and beam in direct contact with the water. However, as in the design case above, the water is fresh and as such, the corrosion effects are very limited. Nevertheless, the design should ensure that the system has the necessary gradient and energy for the movement of water from one side of the road to the next. The 6m/s and 8m/s flow may be adequate for many types and sizes of aqueducts (Linsley & Frazini, 1979).
Bending Moments Due to Thermal Effects
The last factor is the bearing systems. Bearing systems provide a cushion between the slab and the pier and as such, prevent excessive shocks from destroying the pier. This is a necessary tool because of the variable loads that a bridge structure may be subjected to. However, this should be in accordance to the design specifications.
Bridge construction and manufacture
Preferably, the bridge construction should be on site. In this, the members should be on site as per the engineer’s specification.Construcion of the deck and the canal should be as per the site conditions and the site investigation..
As with a deck design, the cross section will be upon the specifications stated. The M6 toll bridge was a work of nature and was designed as per the site conditions. Stipulations as per the drawings. The typical bridge is composed of the deck, asphalt layer, beams, abutment, and the piers across the motorway but in the design of an aqueduct, certain modifications need to be done to all these members. Because, the design focuses on a barrel type aqueduct, the individual members will need to be laid on site. The formwork will play a major role in ensuring that the slab, beam, deck, piers and the canal are per the specifications stated. Therefore, the actual work will be as per the site conditions with the workability of the concrete as well as the methods of compaction and curing determining the structural conformity of the individual members.
Plan of the aqueduct
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