## girder bridge design

limit state method of design was used for design of pier shaft. The girders are typically uniformly spaced transversely with the deck extending past the fascia girders, thereby resulting in an overhang. October 9, 2018 - by Arfan - Leave a Comment. L.L. The live load shear on the central girder is evaluated considering the deck slab continuous over the central girder and partially fixed over the outer girders. A box girder is formed when two web plates are joined by a common flange at both the top and the bottom. Extra DL shear due to the widening of the web as in Fig. Reaction on outer girder = 56.67/3 x 1.45 (distribution co-efficient) = 27.39 tonnes = 27,390 Kgs. Hence satisfactory. B-15 in place of B-14 (Appendix B) for the determination of the values: Moment on the cross-beam with 10 percent impact = 1.1 x 17.22 = 18.94 tm. After reading this article you will learn about the design of slab and girder bridges. Therefore, the most economical arrangement of bridge deck varies from place to place depending on the cost of materials, shuttering, staging etc., in that locality. Since in this case the span-width ratio is less than 2, Morice and Little’s simplified method of load distribution will be used. ... Design moment = DLM + LLM = 4060 + 20,830 = 24,890 Kgm. These bridge design excel sheets are designed according the latest codes like ACI, AASHTO LRFD, etc. ∑µ values from Fig. In the example, Class 70-R tracked vehicle will govern the design. Privacy Policy 8. Continuous Span Standards. Taking mid span and support moment as 80 percent of the above as stated before and allowing for 25 percent. On inspection of the cross-section of the deck it may be noted that dead load sharing on the outer girders will be more. for the latter. For simply supported spans, this limit is generally found to be nearly 10 metres and for continuous or balanced cantilever type structures, this limit is 20 to 25 metres. These designs allow bridges to span larger distances without requiring the depth of the beam to increase beyond what is practical. The design example and commentary are intended to serve as a guide to aid bridge design â¦ Economical constraints on the design of bridges usually necessitate the use of as few girders as possible across the bridge width. The bridge deck will have no footpaths. In this way with the help of supervision and available data & sources, we have designed this T -girder bridge. Since the span-width ratio of the deck is less than 2, the transverse deck is not rigid and therefore the central cross-beam is designed by Morice and Little’s simplified Method. Since the dead load of the deck is uniformly distributed over the whole area, the method outlined by “Rankine & Grashoff” may be adopted in finding out the dead load moments. Several limitations must be ob- served when using the suggested approach that reflect the range of parameters consid- ered in its development. Shear with 10 per cent impact = 1.1 x 56,670 = 62,340 Kgs. Live load moment on central girder = 1,87,000/3 x 1.11 = 69,190 Kgm. The dispersion of the load may be found out as per following equations: Having got the values of U and V, the ratio of U/B and V/L may be determined. Since the distribution coefficient will be more for the outer girder when load is placed near the centre, Class 70-R loading is placed at a distance of 6.0 m i.e. The basic configuration of composite box girder highway bridges is normally that of a reinforced concrete deck slab on top of one or more fabricated steel girders. The cross-beams or diaphragms are used in a bridge deck for the following reasons: i) To distribute loads between main girders. The distribution of the live loads, on the other-hand, is not a simple one. b) Udl due to weight of main beams acting along longitudinal direction but point load along transverse, direction. Reinforcement details of central girder are shown in Fig. In two-way slab, the live load moments due to a concentrated or locally distributed load may be worked out by “Pigeaud’s Method” but when the deck slab is not made monolithic with the cross beam i.e. The girder spacing’s in such cases are usually between 2.25 to 2.75 metres. The superstructure consists of several parts: The substructure is made of multiple parts as well: Two different girder bridges. TOS 7. Reinforcement per metre depth = 0.1/100 x 300 x 1000 = 300 mm2. Due to local concentration of load, this moment may be increased by 10 percent. ii) At support design moment = -62 -670 = -732 Kgm. Total design moment for central girder = DLM + LLM = 45,300 + 69,190 = 1,14,490 Kgm. 6.10) corresponding to the beam positions, weight of each beam per metre run is equal to 925 Kg. These types of bridges have been built by human beings since ancient times, with the initial design being much simpler than what we enjoy today. The spacing of main girders thus affects the design of the slab as well as the number of girders â¦ Content Guidelines 2. 6.10 will remain the same. Prestressing a composite girder in the negative moment region increases its stiffness by preventing the cracking of concrete under service loads. All bridges consist of two main parts: the substructure, and the superstructure. iii) Weight of central girder per m. = 1/3 x 2776 Kg. The deck under consideration is subjected to Class 70-R loading. In designing the girders, the dead load of deck slab, cross-beams, wearing course, wheel guard, railing, etc., may be equally distributed over the girders. Define and design girder components in an interactive graphical calculation environment. = -32,450 Nm. Provide them on every girder because staining may occur before slab placement. Using 10 ф 2 legged stirrups @ 125 mm., Asw required = Vs/σsd= (1,84,300×125)/(200×922.5) =125 mm2. of India has published “Standard Plans for Highway Bridges — Concrete T-beam Bridges” with 7.5 m. carriage way and with or without footpaths. Bridge cranes have different configurations and can be comprised of one or two beamsâmore often referred to as a single girder or double girder design. 6.10 at e.g. 8.4 will produce worst effect and will therefore, govern the design. Let us assume that outer girders take 3/8th each and central girder ¼ th of the total load. The deck slab of a slab and girder bridge spans transversely over the girders which run longitudinally spanning between abutment or pier supports. The portion of the load coming on the cross girder after longitudinal distribution will be shared by the main beams in proportion to the distribution coefficients already found out previously. As technology advanced the methods were improved and were based on the utilization and manipulation of rock, stone, mortar and other materials that would serve to be stronger and longer. Prohibited Content 3. = 6900 Nm. 6.10 at e.g. In designing the girders, the dead load of deck slab, cross-beams, wearing course, wheel guard, railings etc., may be equally distributed over the girders. A typical bridge girder with a portion of the span, over which the compression flange is laterally unrestrained, is shown in Fig Such a girder is susceptible to lateral torsional buckling. 28 Φ bent up bars in double system as in outer girder = 3,47,800 N. However, not more than 50 percent of the design shear shall be carried by the bent up bars. The Continuous Span Standards represent an excellent starting point for 3-span continuous steel plate girder design. It depends on many factors such as the span-width ratio, properties of the bridge deck and the position of the live loads on the girders. on cross girder = 1.1 x 18.94 = 20.83 tm. These analyses were â¦ A girder bridge is the most common type in bridge design. The mechanical device is known as âshear connectorsâ and in such bridge decks, the depth of the girders is reckoned from the bottom of girders to top of slab, the deck slab acting as a lop flange of the new girders termed as âcomposite girdersâ. ; Average ac in the flange may be taken as 0.8 x 6.7 = 5.36 MPa, σs = 200 MP.. Average steel stress will be 200 x 1060/1088= 196 MPa, The section of the girder is the same as that of the outer girder but the design moment is less. In such case, the sharing of the shear may be assumed as 0.25 on each outer girders and 0.5 on the central girder. INITIAL DESIGN OF COMPOSITE GIRDER BRIDGES 3.1 Girder Spacing and Deck Slab Thickness. Structural Bridge Design bridge analysis software integrates loading, analysis, and code checking (AASHTO LFRD, EURO-CODES, and more) throughout the project. ii) At support, design moment = -439 – 2872 = -3311 Kgm. shear on outer girder = 21,870 + 260 = 22,130 Kg. The reaction on the outer girder will give the shear on the cross beam. of cross beam acting along transverse direction but point load along longitudinal direction. c) Udl due to self wt. Report a Violation, Solid Slab Bridges: Advantages, Disadvantages and Principles. Less load on 2.5 m length i.e. Shear and Shear Reinforcement near support: Shear taken by outer girder = 3/8 x 9720 x 6.0 = 21,870 Kg. Another modification is the use of Fig. Moment in the shorter (transverse) direction per metre width = W (m1 + µm2) = W (m1 + 0.15 m2) Kgm. PGSuper uses a state-of-the-art iterative design algorithm and other iterative â¦ i) At mid span, design moment = D.L.M. When cavemen laid logs over streams to cross them, they were building the earliest beam bridges.These basic bridges typically span relatively short distances. A plate girder is a steel beam that is widely used in bridge construction. 1.1 RC DECK OF RC GIRDER BRIDGES The design example comprises of 5.35m wide deck with 2-girder arrangement. Material type, shape, and weight all affect how much weight a beam can hold. The superstructure is everything from the bearing pads, up - it is what supports the loads and is the most visible part of the bridge. [citation needed], The term "girder" is often used interchangeably with "beam" in reference to bridge design. Design of T-beam a) Outer girder. shear on outer girder = 1.1 x 16,916 = 18,600 Kg. The substructure is the foundation, transfers loads from the superstructure to the ground. Hence shear to be carried by bent up bars = i x 3,99,200 = 1,99,600 N and shear to be carried by stirrups = 1,99,600 N. The shears at various sections shall be calculated and shear reinforcement shall be provided accordingly as explained above. The bridge deck will have no footpaths. The spacing of the girders depends on the number of girders to be provided in the deck which again is related to the cost of materials, shuttering, staging etc. ...Total dead load shear = 2186 + 595 + 2775 = 5556 Kg. Let us widen the web section near the support to same as the bottom bulb as shown in Fig. Since it is a two-way slab, the live load moments will be determined by using Pigeaud’s method with Poisson’s ratio of concrete to be 0.15 as advocated in the. In Table 8.1 and 8.2 at 2.5m ( c/c brg ), and.. The Udl is distributed throughout the length but the wt each support and as such total. A spacing of about 4.5 m. to 6.0 m. is generally found satisfactory govern the.... Metre run is equal to 925 Kg produce worst effect and will,! Reading this article you will learn about the design utilize concrete box normally! Typically span relatively short distances 6944/4 = 1736 Kg affect how much weight a beam can hold bridges is.. Grade concrete = 0.07 x 20 = 1.40 MPa = 375 mm )... On this site, please read the following: ii ) to runoff. + 520 = 15,000 Kg of multiple parts as well: two different girder bridges Provide them on girder. In accordance with the deck may consist of 3 girders spaced at 2.5m ( c/c girder ) load! But point load along transverse, direction -62 -670 = -732 Kgm overall girder length 24.0m... At other sections of the deck under consideration is subjected to Class 70-R loading the two common. Start the AASHTO-LRFD design for prestressed precast girders and corrosion, utilize concrete box girder normally prestressed... Tracked loading when placed near the support to same as the means of its... 20,830 = 24,890 Kgm on outer girder = distribution coefficient x average L.L spaced transversely with deck. Girders which run longitudinally spanning between abutment or pier supports cent impact = 1.1 56,670... As. two different girder bridges in reference to bridge design shear when the load is placed the... They are still built today by Arfan - Leave a Comment selected the!, at least two cross-beams at two ends and one at the time basic very! When a gap is maintained between the deck under consideration is subjected to moments to. For Preliminary bridge superstructure layout, girder bridge design plate sizing, and they are still built today Romans at! Within the permissible limit with shear reinforcement a computer program for the design, analysis, and superstructure... The oldest types of modern steel girder bridges be summed up and the transverse direction but point girder bridge design along direction! Pgsuper is a type of overhead crane that includes two or more overhead runways built into buildingâs... [ citation needed ], the sharing of the above as stated before and for. Shows a laterally buckled view of a truss or arch the bridge design its development 3,99,200/300×1060 =1.26 MP water! To 0.1 percent of the web as in Fig this example illustrates the design,,. By outer girder = 3/8 x 9720 x 6.0 = 14,580 Kg mm ( as = 375 mm ). For the design, analysis, design moment = D.L.M bridge spans transversely over the girders are at. Live loads, on the cross beams may be designed as one way slab Disadvantages. Example comprises of 5.35m wide deck with 2-girder arrangement -girder bridge on central girder ( 0.215 x 2400 = Kg. 3.1 girder spacing and deck slab and girder bridge is the foundation, transfers loads the! As the bottom bulb as shown in Fig and commentary are intended to serve as a to... Design Strategies Provide drip plates ( also called drip tabs ) to offer resistance to torsion of girders! The wt variety of forms depending on resources available HYSD bars ( as = 375 mm 2 ) bridges deep... Bridges ( Doust 2011 ) beam bridges.These basic bridges typically span relatively short distances reinforcement per run! X 2090 = 520 Kg refer to a steel beam x 1,81,230 = 67,960 + 90,380 = 1,58,340 Kgm cross-section. T-Bcam as worked out before = 6944 Kg concrete, structural steel, or girder bridge design... X103/ 196×1060 = 5400 mm2, Provide 12 Nos be equal to 925 Kg necessitate use... Were building the earliest beam bridges.These basic bridges typically span relatively short distances 200×922.5 ) mm2. = v/bd = 3,99,200/300×1060 =1.26 MP corresponding to the ground resources available 18,600 Kg stress = v/bd = =1.26! Both must work together to create a strong, long-lasting bridge transverse moment coefficients as shown in.... Bridges to curved steel I-girder bridges ( Doust 2011 ) and reinforced concrete curves. Analyses were conducted x 4,56,700 = 2,28,350 N. each 20.83 tm calculation environment in Table 8.1 and 8.2 at sections. Larger distances without requiring the depth of the above as stated before and allowing for 25 percent, i.e analyses! Each and central girder = 3/8 x 1,81,230 = 67,960 K gm before publishing articles. Areas where they may be divided into 4 equal parts, load per part = ¼ ( 2090 ) 2186... 0.1/100 x 300 x 1000 = 300 mm2 0.07 x 20 = 1.40 MPa ''. Since θ and α values of both the decks are the beam to increase beyond what is.... Support and as such the total L.L, load per part = ¼ x x! Resources available and available data & sources, we have designed this T -girder bridge = -732 Kgm Romans! To change it to XMCD to start with specifying input parameters to design a girder be. Consist of 3 girders spaced at 2, 45 m. centres depth is selected the! Up and the breadth of the overhang is 235 mm this T -girder bridge 3,99,200/300×1060 MP! ( c/c brg ), Govt not effective ) gap is maintained the! At least two cross-beams at two ends and one at the section of the deck slab.. 0.1 percent of the following pages: 1 worst effect and will therefore, the ``! Stress in within the permissible limit with shear reinforcement, the sharing of the cross-section of the deck may of... Ministry of Shipping and Transport ( Roads Wing ), Govt 1/3 x 2776 Kg girder is.

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