8.13. for the latter. The section of the outer girder is shown in Fig. of central girder = 925×12.0/4 = 2775 Kg. Live load moment on central girder = 1,87,000/3 x 1.11 = 69,190 Kgm. 8.4 will produce worst effect and will therefore, govern the design. BridgeLink is another free software in this bridge design software list for Windows. D.L. Attention Internet Explorer users: In order to download Mathcad files, right click on the link and choose "Save target as." The substructure is the foundation, transfers loads from the superstructure to the ground. 8.1. The average thickness of the overhang is 235 mm. Design a slab and girder bridge with 7.5 m. clear roadway having a span of 12.0 m. between centre line of bearings. Using 2 nos. Since θ and α values of both the decks are the same, the influence line for transverse moment coefficients as shown in Fig. The design of steel structures is covered in Section 6 of the AASHTO LRFD Bridge Design Specifications and only straight steel bridges are covered in the provisions as of this writing. The superstructure consists of several parts: The substructure is made of multiple parts as well: Two different girder bridges. shear on the outer girder = Distribution coefficient x average L.L. 8.10). ...Total D.L. = 20,830 Kgm. In the example, Class 70-R tracked vehicle will govern the design. A girder may be made of concrete or steel. i) At mid span, design moment = D.L.M. Class A wheel load as shown in Fig. The Bridge Design Manual shall be consulted for deck drain policy requirements. Let us assume that outer girders take 3/8th each and central girder ¼ th of the total load. 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 effective flange width shall be the least of the following: ii) Centre to centre distance of beam, i.e. 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. Material type, shape, and weight all affect how much weight a beam can hold. shear on central girder = 14,580 + 520 = 15,000 Kg. The Third Edition of the design specifications, to be published in 2004, will contain a complete set of new PGSuper is a computer program for the design, analysis, and load rating of precast, prestressed concrete girder bridges. of each part is assumed to act at its centre of gravity. This example illustrates the design of a two span cast-in-place post-tensioned concrete box girder bridge. If a shallow girder depth is selected, the girder spacing will be close to each other than bridges with deep girders. Prohibited Content 3. In order to build a beam bridge (also known as a girder bridge), all you need is a rigid horizontâ¦ They serve to help reduce the time required for preliminary bridge superstructure layout, girder plate sizing, and more. These designs allow bridges to span larger distances without requiring the depth of the beam to increase beyond what is practical. TOS 7. In this way with the help of supervision and available data & sources, we have designed this T -girder bridge. Permissible shear with shear reinforcement for M20 grade concrete = 0.07 x 20 = 1.40 MPa. Since the deck slab is monolithic with the cross-beams, it will be designed as a two-way slab supported on longitudinal girders and cross-beams with continuity on all sides. Shear resistance of 2 – 28 Φ bent up bars in double system = 2x2x615x200x 0.707 = 3,47,800 N, However, not more than 50 per cent of the shear shall be carried by bent up bars. 1.1 RC DECK OF RC GIRDER BRIDGES The design example comprises of 5.35m wide deck with 2-girder arrangement. Both must work together to create a strong, long-lasting bridge. Hence, shear to be resisted by bent up bars and stirrups is ½ x 4,56,700 = 2,28,350 N. each. Shear = 22,130 + 18,600 = 40,700 Kg. INITIAL DESIGN OF COMPOSITE GIRDER BRIDGES 3.1 Girder Spacing and Deck Slab Thickness. c) Udl due to self wt. After reading this article you will learn about the design of slab and girder bridges. [2][3][4][5] However, some authors define beam bridges slightly differently from girder bridges.[6]. Shear reinforcement at other sections of the girder shall be worked out on the same principles as outlined above. bars @ 150 mm (As = 375 mm 2). at the centre of the span. shear at the section = 15,100 – 6075 = 9025 Kg. 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. 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. Total D.L. The girders for this bridge are designed to meet â¦ interior girder Wearing Surface Load (DW) - Wearing surface = [0.025 x 40.0]/4 girders = 0.250 k/ft Note: Distributed equally to each girder B S D I Basic LRFD Design Live Load HL-93 - (Article 3.6.1.2.1) Design Truck: Þ or Design Tandem: Pair of 25.0 KIP axles spaced 4.0 FT apart superimposed on Design Lane Load As the Industrial Revolution came and went, new materials with improved physical properties were utilized; and wrought iron was replaced with steel due to steel's greater strength and larger application potential. Therefore, reaction of each support and as such the total L.L. DESIGN OF SEGMENTAL BRIDGES This article discusses the general design considerations, design sequence, conceptual and detailed design requirements, and analysis procedures of segmental prestressed concrete box girder bridges. in place of the slab thickness of 215 mm. Engineering, Designing, Highway, Bridges, Slab and Girder Bridges. The transverse moment coefficients may be obtained from the influence line curves (Fig. Less load on 2.5 m length i.e. where normal width of web of 300 is available and where the shear resistance of bent up bars is not effective). Define and design girder components in an interactive graphical calculation environment. ...Design shear on the cross-beam = D.L. They also dictate that the type of braces are to be web plates with â¦ = 3,22,900 N. Shear may also be calculated from the transverse moment on the cross girder found out previously assuming that UDL is acting on the cross-beam and the cross-beam is simply supported on the outer girders. 2010. Shear with 10 per cent impact = 1.1 x 56,670 = 62,340 Kgs. = 11,22,000 Nm. 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. The substructure is the foundation, transfers loads from the superstructure to the ground. The deck slab has to distribute wheel loads to the main girders and also to transfer some load from more highly loaded girders to adjacent ones. This document consists of a comprehensive steel girder bridge design example, with instructional commentary based on the AASHTO LRFD Bridge Design Specifications (Second Edition, 1998, including interims for 1999 through 2002). It has been observed that three beams deck is generally found economical than two, four or five beams deck having a carriageway for two lanes. Many shorter bridges, especially in rural areas where they may be exposed to water overtopping and corrosion, utilize concrete box girder . 28 Φ HYSD bars (As = 7380 mm2). With a stirrup spacing of 175 mm, ...If 10 Φ 4 legged stirrups are used, Asw provided = 4 x 78 = 312 mm 2. Both deck and girder concrete shall be of 28 days crushing cylinder strength fâc = 25 â¦ The top is a, National Institute of Industrial Technology, "Bridge Engineering: A Global Perspective", List of medieval stone bridges in Germany, https://en.wikipedia.org/w/index.php?title=Girder_bridge&oldid=948746270, Articles with unsourced statements from November 2018, Creative Commons Attribution-ShareAlike License, This page was last edited on 2 April 2020, at 20:27. A spacing of about 4.5 m. to 6.0 m. is generally found satisfactory. Steel Girder Design Mathcad® Sheets . The deck under consideration is subjected to Class 70-R loading. In a beam or girder bridge, the beams themselves are the primary support for the deck, and are responsible for transferring the load down to the foundation. This exceeds the permissible limit of shear stress of 1.40 MP, with shear reinforcement. a) Udl due to deck slab and wearing course: To find out the transverse moment due to load of item (a) above, the equivalent deck of width 7.35 m. may be divided into a number of equal parts’ say 4 equal pans each of 1.84 m. width and the effect of each load on the transverse deck acting at the e.g. The distribution of the live loads, on the other-hand, is not a simple one. Shear at a distance of 2.5 m. (i.e. Load per metre of deck excepting wt. The box is typically rectangular or trapezoidal in cross-section. 6.10 at beam position are as below: The cross beams may be divided into 4 equal parts the wt. A box girder is formed when two web plates are joined by a common flange at both the top and the bottom. In truss and arch-style bridges, the girders are still the main support for the deck, but the load is transferred through the truss or arch to the foundation. = 6900 Nm. The AREMA Manual limits the spacing of knee braces to 12 feet maximum. All bridges consist of two main parts: the substructure, and the superstructure. The spacing of main girders thus affects the design of the slab as well as the number of girders â¦ The superstructure design includes the following elements: deck design, prestressed girder design, and bearing pad design. 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. However, with the inclusion of a truss or arch the bridge is no longer a true girder bridge. i) At mid span, design moment = 31 + 670 = 701 Kgm. If no gap between the deck slab and the cross beams is maintained, the slab panel becomes a two-way slab continuous in both the direction. of cross beam acting along transverse direction but point load along longitudinal direction. 8.9. σc = 6.7 MP. Continuous Span Standards. When cavemen laid logs over streams to cross them, they were building the earliest beam bridges.These basic bridges typically span relatively short distances. Sometimes in long bridges, it is necessary to keep provision for carrying pipes (gas, oil or water), cables etc., through the bridge deck for which space under the footway may be utilised as shown in Fig. 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. In the example, simple thumb of rules are used to start the AASHTO-LRFD design for prestressed precast girders. The study considered several bridge configurations for which detailed finite element analyses were conducted. Total design moment for central girder = DLM + LLM = 45,300 + 69,190 = 1,14,490 Kgm. m.s. T Beam Girder Bridge Design. The bridge decks have three number T-beams of varying depths depending upon spans. 22.5.3 Precast single span bridge girder (bridge design model) Two traffic bridge design models having one 45 m single span were analysed (see Almansour and Lounis, 2008).They consist of precast/prestressed girders and a cast-in-place â¦ Structural Bridge Design bridge analysis software integrates loading, analysis, and code checking (AASHTO LFRD, EURO-CODES, and more) throughout the project. All bridges consist of two main parts: the substructure, and the superstructure. limit state method of design was used for design of pier shaft. The reaction on the outer girder will give the shear on the cross beam. Hence this stress in within the permissible limit with shear reinforcement. //]]>. of T-bcam as worked out before = 6944 Kg. The oldest types of bridges are the beam, arch and swing bridges, and they are still built today. Since the shear stress exceeds the permissible limit of 0.34 MP, without shear reinforcement, the same is necessary. Rough sketch of bridge design: When the engineer is sure that a design idea has emerged in his mind, he should pick up a pencil and a scale and by the help of sketching, learned at school, he should start from sketching the probable road direction, beam depth(For beam bridge) the piers, the abutments and the bottom â¦ Reinforcement for central girder, As = 11,22,000 x103/ 196×1060 = 5400 mm2, Provide 12 Nos. As per Clause 304.7 of IRC: 21-1987, permissible shear stresses for M20 concrete, i) Without shear reinforcement = 0.34 MPa, ii) With shear reinforcement = 0.07 x 20 = 1.40 MPa.–. PCI has developed Preliminary Design Charts in accordance with the AASHTO. shear on outer girder = 1.1 x 16,916 = 18,600 Kg. A design example followed by a load rating analysis illustrates the engineering computations performed by PGSuper. These analyses were â¦ shear due to cross-beam on central girder = ½ x ½ x 2090 = 520 Kg. shear = 5556 + 27,390 = 32,946 Kg. The girders are spaced at 2.5m (c/c girder). Copyright 10. Fig shows a laterally buckled view of a portion of the span. 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. Reinforcement details of central girder are shown in Fig. D.L. 8.2a. of deck slab and wearing course spread throughout the length and the breadth of the deck. Important details of these bridges are given in Table 8.1 and 8.2. Class 70-R tracked vehicle will produce maximum shear when the load is placed on the deck as shown in Fig. ; 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. Hence satisfactory. (vide dead load calculation for the design of girder) = 925 Kg. A synopsis of the method is given here. ¼ x 9700 x 2.5 = 6075 Kg. as calculated before. ∑µ values from Fig. shear will be 35.0 tonnes = 35,000 Kg. Content Guidelines 2. Longer spans, more traffic, or wider spacing of the beams will all directly result in a deeper beam. 6.10) corresponding to the beam positions, weight of each beam per metre run is equal to 925 Kg. A girder bridge is a bridge that uses girders as the means of supporting its deck. Reaction on outer girder = 56.67/3 x 1.45 (distribution co-efficient) = 27.39 tonnes = 27,390 Kgs. shear = 1.45 x 35,000/3 = 16,916 Kg. [CDATA[ + L.L.M. = 220 + 2872 = 3092 Kgm. Shear and Shear Reinforcement near support: Shear taken by outer girder = 3/8 x 9720 x 6.0 = 21,870 Kg. The closed cell which is formed has a much greater torsional stiffness and strength than an open section and this is the main reason why box girder configuration is usually adopted in long span bridges. Loading â Single lane of Class 70-R or two lanes of Class A: of each part may be summed up and the transverse moment may be obtained from equation 8.3 assuming u = c = a. Hence, the section is safe in compression. How simple? Shear resistance of 2 Nos. of each part = ¼ (2090) = 520 Kg. In this publication, attention is concentrated upon medium-span highway bridges - those with the longest span in the range 45 m to 100 m. Dead load shear due to weight of cross beam on outer girder = 1/4 of total shear = ¼ x ½ x 2090 = 260 Kg. You need to start with specifying input parameters to design a specific bridge structure. PGSuper uses a state-of-the-art iterative design algorithm and other iterative â¦ of cross-beam = i x 2.45 x 0.81 x 0.25 x 2400 = 595 Kg. Now the transverse deck is subjected to moments due to the following dead loads: a) Udl due to wt. Effective flange width shall be the least of the following: The distribution of dead load of slab, wearing course etc. With 10 per cent impact, L.L. T. Stengel, P. Schießl, in Eco-efficient Construction and Building Materials, 2014. It has been advocated that due to continuity, the mid-span moments may be reduced by 20 percent and the same moment may be taken as the support (negative) moment also. Consider what the diverted water will stainâfor example, do not Moment in the shorter (transverse) direction per metre width = W (m1 + µm2) = W (m1 + 0.15 m2) Kgm. Disclaimer 9. The bridge has spans of â¦ Knee Brace for Through-Girder Bridge Through girders should be laterally braced with gusset plates or knee braces with solid webs connected to the stiffeners as shown in . The span of the girders is 23.35m(c/c brg), and the overall girder length is 24.0m. ...Total dead load shear = 2186 + 595 + 2775 = 5556 Kg. Deck design follows the NMDOT standard deck slab detail in Chapter 4 of the NMDOT Bridge Procedures and Design Guide, hereinafter referred to as Design Guide. Privacy Policy 8. 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. on the inner side. However, there are three number cross-girder for effective spans up to 16.5 m. and four number cross-girder for effective spans of 18.75 to 24.75 m. The design is based on M20 grade concrete and S 415 grade steel. The Continuous Span Standards represent an excellent starting point for 3-span continuous steel plate girder design. Since in this case the span-width ratio is less than 2, Morice and Little’s simplified method of load distribution will be used. Class 70-R tracked loading when placed near the support will produce maximum effect (Fig. where W is the total load. 25 Φ HYSD bars bent up bars, shear resistance = 2 x 490 x 200 x 0.707 = 1,38,600 N. Balance shear of 1,84,300 N is to be resisted by stirrups. 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. Closer beam spacing means lesser thickness of deck slab and consequently savings in concrete and steel in deck slab but since the number of beams is more in that case, this increases the quantity of concrete, shuttering and reinforcement for girders and for longer spans where bearings are required, the number of bearings. 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. //