The Design and Construction of a Bridge to Span a River of Width 100 Metres - Report Example

BRIDGE DESIGN AND CONSTRUCTION By Student’s name Course code and name Professor’s name University name City, State Date of submission Contents 1.0Introduction 4 2.0Technical Aspects 6 2.1 Truss Bridge 6 2.1.1 I-girders 7 2.1.2 Connections 9 2.1.3 Piers 10 2.1.4 The Deck 11 2.2 Composite Beam Bridge 12 2.2.1 Piers 12 2.2.2 I-girders 13 2.2.3 Bridge Deck 14 2.2.4 Connection Flanges 14 2.2.4 Webs 15 3.0Economic Analysis 16 3.1 Cost of Materials 16 3.2 Maintenance Cost 17 4.0Environmental Impact Assessment 18 5.0Conclusion 19 6.0List of References 20 1.0 Introduction Bridge design and construction is increasingly becoming a wanting exercise in human life owing to the rate at which catastrophes take place. Therefore, there is need to avail high endurance infrastructure to facilitate manoeuvring from one area to the other as a means of easing congestion within the cities around the world. This document aims at designing 100 meter Access Bridge to connect Lower Darling Road to Wentworth-Pooncarie Road as an intermediary to reduce the traffic that is often encountered by the users. Figure 1: A map of Mildura area of New South Wales where 100m bridge is required to ease operations [Goo13]. According to Jagadeesh and Jayaram (2000), when designing and constructing a bridge, there are several details that should be put into consideration. The most important factors to consider include the expected traffic flow, nature of location and structural characteristics of the river topography. These characteristics are usually surveyed beforehand to ascertain the type of bridge and materials that shall be suitably applied to withstand physical factors such as weather conditions and possible catastrophes. This variation thus determines the complexity of data obtained with regard to geotechnical, hydraulic and structural attributes. 2.0 Technical Aspects The technical aspects that should be considered when coming up with this bridge range from the physical dimensions to the funds available for the sake of this project. These factors are well defined by different types of bridges that have so far been designed as per the standard conventions that govern this important discipline of structural engineering. In order to come up with the best choice, it is important to discuss some of these designs and their structural advantages. These may range from simple beam bridges or the complex truss or suspension bridges usually applied depending on the factors mentioned in the introductory section. 2.1 Truss Bridge Truss bridges are as a result of triangular fastening of beams as a means of load distribution amongst the members. These types of bridges contain of two principle sections mainly the upper and lower chords. The lower chord is designed to be longer than the upper and somewhat heavier than the former thereby resulting to a trapezoidal shape. According to Solomon (2008), these chords are joined by diagonal and vertical running ties throughout their length in a proportionate manner to the expected traffic. Their ends are also connected by piers which aid them in spanning the entire water body length. Additional piers for the case of the 100m bridge under design are thus not required since the structural integrity of these bridges is enough to nullify the rising need for extra bracing. Originally designed by Rider (1845), these bridges have are compact and strong due to the increased number of diagonal ties as much as the effectual resistance is desirable for durability. The structural components of these types of bridges are discussed below with the desired length in mind. Figure 2: Basic structural components of a girder bridge [Com77]. 2.1.1 I-girders The I-girders shall form the span of the bridge as the principal component highlighted in diagram 2 above. Made of structural steel, 4 girders shall run for the entire 100m while the rest of the upper girders shall span for only 96m to form the suggested trapezoidal shape. The multiple formations shall be utilized in order to increase the durability or the weight endurance of the entire structure. A section of these I-girders shall appear as shown in the diagram below: Figure 3: Positioning of girders along the bridge span. As shown above, the I-girders shall be spread along the span with a spacing of 6m on either sides of the bridge. These shall leave a spacing of 2m from either side making the effective length of the upper span with 96m. This shall amount to 16 girders on both sides of the bridge as shown in the figure below. Figure 4: A figure showing the distribution of I-girders. The 10 numbers span I-girders shall be placed parallel to each other with six at deck and 4 on the upper part. These shall run for 96 meters as shown in diagram 4 above. The vertical girders shall however be 6m in length. Since the standard I-girders come in length of 12 meters each, the required numbers shall be 82. Figure 5: A side view depiction of the truss bride. There shall be 32 diagonal I-girders along the span of the bridge; shown in diagram 5 above is the side view of the expected outcome. Each of the diagonal I-girders shall be braced at a 45° angle resulting from the 6x6m square of the box section. 2.1.2 Connections The flanges shall be designed to cater for the compressive and shear forces that are often encountered by the bridge. Each truss node shall incorporate splices on the members with minor connections across the lateral truss system. High tensile steel bolts shall be applied in conjunction welding for economic and speed purposes. The shrinkage index should however be put into consideration to avoid tension at the nodes Figure 6: Butt weld connections and gusset geometries in girder bridges avoid fatigue [Uni13]. The truss joints to be applied at the nodes of the trusses shall necessitate a change in cross-sectional area. The nodes are connected by use of bolted gusset plates which are as shown in the diagram below. Packing plates are also used for the purpose of strengthening the truss chords as shown in e. The high tensile bolts are used for this purpose in order to avoid wear that is observed in most materials that have been found to be ductile. Figure 7: Bolted connections for truss bridges [Uni13]. 2.1.3 Piers The piers to be applied on both sides of the bridge shall be as per the international conventions that require the use of squat piers for short bridges to the effect of the one under design. There shall be a support pier at the centre of the bridge in order to cushion excess shear stress that may accumulate during a busy day. This way the bridge design is meant to last for 100 consecutive years without any significant maintenance on the structural setup[Pil10]. Figure 8: An isometric elevation of the 10m pier to be applied as per conventions [Pil10]. 2.1.4 The Deck The deck shall consist of a deck plate that shall have an evenly distributed load to ensure a lane in each traffic direction. The pavement width shall be 12.0m leaving a pedestrian gap of 1.5m on each side as per the international conventions. A safety barrier of 0.5m shall also be put into consideration. The concrete thickness shall be 50mm throughout the span as a compulsory consideration. Figure 9: The suggested deck model [Uni13]. 2.2 Composite Beam Bridge A composite beam bridge utilizes girders and ladder decks to come up with a comprehensible structure. Therefore they incorporate concrete decks with the steel structure at advanced stages of design to instil the standard conventions. These have however forced these types of bridges to face difficult designs in areas such as connections and differing strengths from one portion of the span to the other. Other challenges that might be faced by engineers in coming up with these structure include the fact that the girders are curved, depths vary from one portion to the other for the piers and also that these types of bridges involve multiple piers. These parts are discussed below for clarity purposes. 2.2.1 Piers The piers of a composite beam bridge ensure that the structure seats well while supporting the entire weight of the traffic that plies the route. These piers consist of the headstock, cylindrical piles and the side wall. The headstock is meant for connection of the piles to the main I-girder beams that are meant for carrying the traffic weight. Due to the complexity of this bridge, the structural system is fastened by use of bolts that are spaced 30mm apart depending on the section to be joined. For the sake of this design, there shall be 4 headstocks spaced at 25m each along the bridge span. The cylindrical piles are used to support the main bridge frame since they are piled right to the topographic system of the soil. Therefore, various considerations should be put in place when carrying out such exercise. This bridge shall make use of 12 concrete piles driven right onto the river bed at a span of 25m. Lastly side walls shall be designed to allow for safety of the piers and a better general outlook of the bridge[Sta03]. Figure 10: A photograph showing a section of a modern composite beam bridge [Ste12]. 2.2.2 I-girders These are used to lay the bridge's deck. They usually run horizontally and across the bridge creating a good platform for load distribution. The I-girders chosen should however be sufficient to withstand the projected traffic weight at any given moment. Since they shall be required to be placed parallel to each other, there shall be a total of 42 I-girders with a standard length of 12m. This amount to five runs along the 100m span [Ste12]. 2.2.3 Bridge Deck The deck shall be made of concrete in an evenly distributed manner to carry the oncoming traffic weight. The standard dimensions of the bridge's deck shall be as described in the truss bridge system. Figure 11: A visual representation of a composite bridge deck [USD13]. 2.2.4 Connection Flanges These shall be utilized in connecting the frames that hold the bridge together. The bending strength is increased when such flanges are introduced mid-span of the bridge due to distributed lateral compression which reduces the ability of the structure to buckle. These flanges are also responsible of reduced cost of material although it is still high in comparison to truss bridges[Che07]. 2.2.4 Webs These are connectors meant for joining each and every existing girder to make a unit. These girders have been profoundly used due to their ability to instil structural strength without tampering with the strength of the material. This thus utilizes the existing material while ensuring that the strength is not tampered with in the long run. These fames shall run across each of the bridge sections in a spacing of 6m making it 32 frames on the whole span. These webs shall appear as shown in the diagram below. Figure 12: Composite box girder showing two webs [Uni13]. 3.0 Economic Analysis An economic analysis was carried out on the best option of bridge which in this case was identified as composite beam bridge. Material availability as a paramount factor for this kind of project was also considered for the sake of project deliverables. The bill of quantities for composite beam bridge was thus defined as show in the table below. According to Brook (2004), bill of quantities form a very important part of project documents since they contain vital data on initial project costing. 3.1 Cost of Materials The cost implication of the composite beam bridge which is the selected choice owing to the above technical analysis is show below. Material Particulars Quantity Unit Cost Total Cost Mild steel beams Depth (w) = 198mm Flange (d) = 99mm Flange (t) = 7.0mm Web (t) = 4.5mm Flange depth = 184mm 42 Lengths $760.00/m $ 31,920.00 Concrete Blocks 1 (Headstock) Width (w) = 1,500mm Height (h) = 2,000mm Length (l) = 12,000mm 4 Pieces $ 47,000/piece $ 188,000.00 Concrete piles Height (h) = 10,000mm Diameter (d) = 1,000mm 8 Pieces $ 47,000/piece $ 376,000.00 Concrete Blocks 2 (Side wall) Width (w) = 750mm Height (h) = 1,000mm Length (l) = 12,000mm 8 Pieces $ 10,000/piece $ 80,000.00 Concrete Blocks 3 (Deck) Width (w) = 12,000mm Height (h) = 300mm Length (l) = 100,000mm 100m $ 420/m $ 42,000.00 Concrete Blocks 4 (Road) Width (w) = 8,000mm Height (h) = 150mm Length (l) = 100,000mm 100m $ 350/m $ 35,000.00 Concrete Blocks 5 (Barrier) Width (w) = 250mm Height (h) = 1,000mm Length (l) = 100,000mm 200m $ 100/m $ 20,000.00 Labour and miscellaneous Costs _ _ _ $ 227,080.00 Grand Sum $ 1,000,000.00 3.2 Maintenance Cost The maintenance costs for this bridge is dependent on the type of materials used for this particular project. This is usually higher than the net present value of the project material usage. An aggregate value of 3% of the total amount utilized on the project is projected for this kind of maintenance totalling to $ 30,000.00 per year thereof. 4.0 Environmental Impact Assessment Construction of structures amounts to wanton environmental disruption especially when the contractor is not provided with proper guidelines. The degradation of nature as seen in most cases depends on the type of structure under construction within the area of allocation. This in turn affects land vegetation and marine life in the areas outlying construction of the bridge. As part of environmental impact assessment exercise, Department of Transport and Main Roads (2012) outlines that land, water and aesthetics should be well taken care of and documented by these ventures. Land in particular is affected as plants and animals that live nearby are forced to migrate elsewhere due to intrusion. The plants should be transplanted or imported to other areas in cases where they are portable for future return. On the other side this idea might also cause mayhem in cases whereby the area is affected by various plant or animal diseases which may be transferred to another location. Creating a safe passage for humans may also lead to low oxygen levels in water due to the piling exercise. This results to mass deaths of marine animals and plants which is a highly disputed environmental activity. On the other side, shock caused during this processes might affect the production patterns of fish and animals living within this catchment - this may also cause migration from River Darling to its tributaries which have been found to be seasonal by nature. The aesthetics of this area may also be affected due to the centre piers which are piled deep into water. Humans and resulting bridge activities may not be so welcome in the area due to low aesthetics. These factors do not however stop the project from carrying on owing to the numerous benefits attached to it. 5.0 Conclusion The report is carefully drafted to meet its initial objectives of designing a 100m bridge for construction. It is established at an early stage that composite beam bridges are more economical and environmental friendly as compared to the rest of the counterparts which were listed for consideration in the introduction part. This is particularly owed to the low cost of materials unlike truss bridges which utilize pure mild steel materials. Further it is also indicated that the composite beam bridge is the best choice for this sort of span. 6.0 List of References Goo13: , (Google Maps, 2013), Com77: , (Comp & Donald, 1977), Uni13: , (University of Ljubljana, 2012), Pil10: , (Pilar & Davaine, 2010), Pil10: , (Pilar & Davaine, 2010), Sta03: , (State of Connecticut Department of Transportation, 2003), Ste12: , (Steelconstruction.info, 2012), USD13: , (U.S Department of Transportation, 2013), Che07: , (Chen & Han, 2007), Read More