What Is a Truss Bridge - Assignment Example

Explain how your design would.. Introduction What is a truss bridge? This is an ancient form modern bridge. If you want to know the nineteenth and early twentieth century engineers, it is so easy to understand the truss bridges shown here which have simple designs that could be easily analyzed . Owing to its efficient use of materials, a truss bridge is economical to construct. According to physical science, where there is a great law of motion exists,, the nature of a truss allows for the analysis of the structure using a few assumptions and the application of Newton's laws of motion. In order to analyze, trusses are considered to be pin jointed where the elongated parts come. The truss members will only act in tension or compression that is the assumption. In the bridge illustrated, preventing it from buckling the central vertical member stabilizes the upper compression member. If these vertical parts are removed, the top member is sufficiently strong and stiff. If the outer vertical parts are removed, but with additional strength added to other members in compensation, the lower member is sufficiently strong and stiff. There is a lot of and large variety of truss bridge types is made due to the ability to distribute the forces in various ways. Truss What is truss? It is a simple skeletal structure and the individual members of a simple truss are only subject to tension and compression forces and not bending forces in design theory. Thus all beams in a truss bridge are straight for the most part. The simple fact is that many small beams that together can support a large amount of weight and span great distances which is the base. The fabrication, design, and erection are relatively simple by all means.. Based on the design used, Trusses are classified as various types. The common trusses are the Pratt truss, Howe truss, Warren truss etc.. For both simple and continuous trusses, the Warren truss is perhaps the most common truss. No vertical members are used For smaller spans, providing extra strength and for longer spans vertical members are added . Except for the very end ones, all slant down and in toward the center of the span the Pratt truss is identified by its diagonal members. In a more economic design, this allows for thinner diagonal members resulting. Mach inability of bridge- The ease of machining depends upon (i) the design of tools, (ii) method of lubrication, and (iii) the microstructure and properties of the metal. — Mach inability is an important property of a metal used in manufacturing operations. It may be measured as the quantity of chips that can be removed in a given time, as the weight of chips per hour. Since the behavior of tool is important also, one may choose to determine mach inability in terms of useful life of the tool used or in terms of energy absorbed in machining one kg of chips. Taylor' measured the cutting qualities of a tool by measuring the fastest speed of turning that permitted the tool to hold its edge for 20 minutes. If surface finish appears to be of prime importance, one may like to determine mach inability in terms of surface finish of the work piece. One may, thus, conclude that mach inability involves several properties of a material, each of varying importance. Hence, mach inability of a metal may be considered very good if the greatest amount of material can be removed in the shortest time for each grind of a given tool, while obtaining satisfactory surface finish, with the ultimate objective being low overall cost. Good mach inability is associated with: the removal of material with moderate forces the formation of rather small chips medium degree of tool abrasion good surface finish. All machinable metals are compared to a basic standard, and the comparison yields a percentage of rating which indicates the ease of cutting each metal. The standard metal used for the 100% mach inability rating is steel, coded by the American Iron and Steel Institute (AISI) Index as B 1112 steel. It is free machining steel. When compared to this steel, different metals have their mach inability rating as follows: Metals Mach inability Rating (%>) Aluminium 300-2000 Ni-steels 40-50 C-steels 40-60 Cast Iron 50-80 Thermal expansion When thermal energy is added to a material, a change in its dimensions occurs. For example, if a 10 cm long rod of mild steel is heated (and it is free to expand) it increases in length. This phenomenon is thermal expansion and the property of a material responsible for this is known as coefficient of thermal expansion. The coefficient of (linear) thermal expansion is the amount of expansion in a unit length of a solid material as a result of a temperature rise of 1°. — Coefficient of thermal expansion, a = 1 di I ' Dt ...(in)(vi) Copper, nickel, aluminum and austenitic alloys retain their much of tensile ductility and resistance to shock at low temperatures in spite of the increase in strength, (v/i) F.C.C. metals and alloys retain their ductility substantially unimpaired up to - 24°C. (viii) A tendency for B.C.C. metals (e.g., steels) to (become sensitive to multi axial stresses under shock load conditions and this is manifested by the sharp decline in the value of the absorbed energy in the notch impact test thereby indicating that the materials) behave in a brittle manner, at lower temperatures. THERMAL PROPERTIES By thermal property is meant the response of a material to the application of heat. As a solid absorbs energy in the form of heat its temperature rises and its dimensions increase. The energy may be transported to cooler regions of the specimen if temperature gradients exist and ultimately, the specimen may melt. Thermal shock resistance of the truss bridge Thermal shock defines the conditions of a body when it is subjected to sudden and severe changes in temperature caused either by a change in external environment or by internal heat generation. The ability of a body to withstand such temperature changes without failure is called thermal shock resistance. A ductile material will withstand severe thermal shock much better than brittle materials of comparable strength and thermal properties. In ductile materials any excessive thermal stress developed can be dissipated as the result of plastic deformation whereas, in brittle materials, the stress at a point of stress concentration is usually the governing stress tending toward failure. Thus, in ductile materials, even a very severe thermal shock may not result in fracture, but it can cause distortion or excessive deformation. However, low ductility and notch sensitivity will enhance thermal crack formation. - Thermal fatigue also may occur in systems subjected to cycles of many sudden changes of temperature. Repeated cycles of rapid heating or drastic cooling tend to reduce the capacity of the will be either larger or smaller in diameter as compared to the solvent atom. For example, steel contains iron as solvent and carbon as solute atoms, having large difference in their diameters. Since, solvent and solute atoms have different sizes, when solute is added to solvent, distortion in lattice takes place. If the solute atom is larger than the solvent atoms, compressive strain fields are set up, and if it is smaller, tensile fields. In both the cases, the stress field of a moving dislocation interacts with the stress field of the solute atom, thereby increasing the stress required to move the dislocation through the crystal. This impedes dislocation motion. The more the difference between atomic sizes of solvent and solute atoms, the higher is the stress field around solute atoms. This provides more resistance to the motion of dislocations and hence increases the tensile strength and hardness of the material. If the amount of solute or the number of solute atoms is more, greater will be the local distortion in the lattice and hence more will be the resistance to the moving dislocations. This will increase the hardness and strength of the material. When it comes the details of site Where justified by the scale and importance of the project, or the complexity of the ground conditions, these investigation methods may be supplemented by regional geological studies and geophysical tests. This determines the selection of the optimum foundation system for the proposed structure. ArchSD (2003). General Specification for Building. (2003 edition). Architectural Services Department, Hong Kong, 521 p. EXCAVATIONS Open Cuts Trenching Braced Excavations Rock Excavation Groundwater Control Excavation Stabilization, Monitoring, and Safety COMPACTION, EARTHWORK, AND HYDRAULIC FILLS Embankment Cross-Section Design Compaction Requirements and Procedures Embankment Compaction Control Borrow Excavation Hydraulic and Underwater Fills ANALYSIS OF WALLS AND RETAINING STRUCTURES Computation of Wall Pressures Rigid Retaining Walls Design of Flexible Walls Cofferdams SHALLOW FOUNDATIONS Bearing Capacity Spread Footing Design Considerations Mat and Continuous Beam Foundations Foundations on Engineered Fill Foundations on Expansive Soils Foundation Waterproofing Uplift Resistance DEEP FOUNDATIONS Foundation Types and Design Criteria Bearing Capacity and Settlement Pile Installation and Load Tests Distribution of Loads on Pile Groups Deep Foundations on Rock Lateral Load Capacity Concrete is a building and structural material obtained by mixing cement a mineral aggregate and water in suitable proportions so that the result is a plastic and workable mass that can be molded into any desired shape. Mixes with cement, sand, gravel or crushed stone volume proportions of 1:1.5:3, 1:2; 4 and 1:3:5have been widely used. Asphalt Concrete It is competitive with cement concrete for use in construction of high ways, road beds and other surfaces. It is made by mixing a suitably graded hot aggregate produced from crushed rock with asphalt cement. One must take into account the effect of the shadows of surrounding buildings and also the thermal comfort of the space if it is going to be an enclosed bridge. The climatic conditions of the place should also be considered while designing the bridge. During the day there is glare and photo-chromatic glass can be used to remove that. If the bridge gets the shadows of other surrounding buildings, then also photo-chromic glass that has the ability to darken under the varying sun conditions of the location is appropriate. If we use elechtrochromic system with a polarizing filter, the bridge can get a regulated interior lighting, ArchSD (2003). General Specification for Building. (2003 edition). Architectural Services Because the bridge needs to be lighted for twenty-four hours, proper lighting should be provided by simple incandescent lamps which need higher maintenance as well as a higher energy. Fluorescent strip lamps have a reduced operating cost, but look more artificial. Depending on the aesthetic needs, this choice can be made. Conclusion Truss bridge is an ancient form modern bridge. Owing to its efficient use of materials, a truss bridge is economical to construct. In order to analyze, trusses are considered to be pin jointed where the elongated parts come. The truss members will only act in tension or compression that is the assumption. It is a simple skeletal structure and the individual members of a simple truss are only subject to tension and compression forces and not bending forces in design theory. In truss bridges no vertical members are used for smaller spans, providing extra strength and for longer spans vertical members are added. The ease of machining depends upon: (i) the design of tools, (ii) method of lubrication, and (iii) the microstructure and properties of the metal. RFEERENCES 1. ArchSD (2003). General Specification for Building. (2003 edition). Architectural Services Department, Hong Kong, 521 p. 2. ArchSD (2003). General Specification for Building. (2003 edition). Architectural Services 3. 2005 NYSDOT Traffic Data Report: AADT Values for Select Toll Facilities". https://www.nysdot.gov/portal/page/portal/divisions/engineering/technical-services/hds-respository/appendixctdr.pdf. 4. Caro, Robert (1974). The Power Broker. Vintage. ISBN 0-394-72024-5. 5. Safire, William (2008-07-13). "On Language: Dead End". New York Times. http://www.nytimes.com/2008/07/13/magazine/13wwln-safire-t.html 6. "Triborough Bridge may be renamed for Robert F. Kennedy". Daily News. 2008-01-08. http://www.nydailynews.com/news/2008/01/08/2008-01-08_triborough_bridge_may_be_renamed_for_rob.html. 7. Metropolitan Transportation Authority (2008-11-21). Triborough Bridge Renamed Robert F. Kennedy Bridge. Press release. http://www.mta.info/mta/news/releases/?en=081121-BT1. Retrieved on 2008-12-04. 8. Chan, Sewell (2008-11-19). "The Triborough Is Officially the R.F.K. Bridge". New York Times. http://cityroom.blogs.nytimes.com/2008/11/19/triborough-bridge-is-renamed-for-rfk/. Retrieved on 2008-12-04. Read More