structural design manual for improved inlets culverts
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structural design manual for improved inlets culvertsManual methods for structural analysis are included with a complete design procedure and example problems for both circular and box culverts. These manual methods are supplemented by computer programs which are contained in the Appendices. Example standard plans have been prepared for headwalls, wingwalls, side tapered, and slope tapered culverts for both single two cell inlets. Tables of example designs are provided for each standard plan to illustrate a range of design parameters. (FHWA) All Rights Reserved. Terms of Use and Privacy Statement. If you continue browsing the site, you agree to the use of cookies on this website. See our User Agreement and Privacy Policy.If you continue browsing the site, you agree to the use of cookies on this website. See our Privacy Policy and User Agreement for details.You can change your ad preferences anytime. In the process of scanning andconverting, some changes may have been made inadvertently. Thesemethods cover inlets to reinforced concrete pipe, reinforced concrete box sections andcorrugated metal pipe. They also apply to the design of culvert barrels, themselves, for each ofthe above type conduits.1.2 ScopeThe Manual is based on a review of the current state of the art for the design of culverts andinlet structures. This review included published technical literature, industry sources and statetransportation agencies. Existing practices were reviewed for accuracy, complexity, design timeand applicability to improved inlet design. Those methods that reflect current practice and bestaccount for the structural behavior of improved inlets are included in this Manual. Existingmethods were selected wherever possible. New methods were developed only where therewere gaps in existing design methods.http://sgd42.ru/userfiles/3m-mpro110-projector-manual.xml
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The principal design methods covered in this Manual are for the inlet itself; however, sinceheadwalls, wingwalls and aprons are also important to the proper hydraulic function of animproved inlet, design information is also included for these components.The Manual includes both hand and computer methods for analysis and design. The computerprograms were written for a large computer, but the hand methods are readily programmablefor hand-held calculators.Hand analysis and design methods are provided for: q One and two cell reinforced concrete box culverts q Reinforced concrete pipe culverts q Corrugated metal pipe culverts Typical plans, details and reinforcing arrangements of improved inlets are included inAppendix G. and typical designs are included in Appendix E. 1.3.1 Beveled Headwall A bevel can be characterized as a large chamfer that is used to decrease flow contraction at the inlet. A bevel is shown schematically in Figure 1-1, in conjunction with other features described below. A beveled headwall is a geometrical feature of the headwall and does not require unique structural design. Reinforced concrete pipe sections are generally precast, and can have a bevel formed at the time of manufacture, or in the case of pipe with bell and spigot joints, tests have shown that the bell will improve hydraulic capacity much the same as a bevel. Corrugated metal pipe can have bevels cast as a part of the reinforced concrete headwall. Typically, a bevel should be used at the face of all culvert entrances. A fall is used to increase the head atthe throat section. Structurally a fall apron represents a slab on grade, and shouldbe designed as such.1.3.3 Side Tapered InletA side-tapered inlet is a pipe or box section with an enlarged face area, withtransition to the culvert barrel accomplished by tapering the side wall (Figure 1-1). Abevel is generally provided at the top and sides of the face of a side tapered inlet,except as noted earlier.http://www.allsolarsystems.com.au/images/3m-mp8755-projector-manual.xml Because of these differing influences, the reinforcingdesign may be governed at the face, throat or some intermediate section. As aminimum, designs should be completed for the faces, throat, and middle sections.Typically, inlet structures are relatively short, and the most conservativecombination of these designs can be selected for the entire structure. For longerstructures where the use of two designs may be economical, either the face ormid-length design, whichever gives the greater requirement, may be used in theouter half of the structure. For simplicity, this shape will be calledelliptical in this Manual. Anyconsistent geometry that produces the desired face section may be used by thedesigner. The angle ?, is defined as the angle from the vertical, measured about thecenter of rotation of the radius of the circular segment being considered. Thus, thepoint of reference for.This is shown in Figure1-1. Thus, for slopetapered inlets the face, bend and throat sections must be investigated to determinethe critical sections for design. As for side tapered inlets, additional sections shouldbe investigated in longer structures. Only box sections are normally used for slopetapered inlets, since the structure is generally cast-in-place. When it is cost effectiveto use a slope tapered inlet with a pipe culvert, a circular to square transition sectioncan be provided. (See Section 6.1). Equations for locating slope tapered culvertswithin embankments and for determining heights of fill at various sections arepresented in Appendix F. Design of these structures is discussed briefly in Chapter 6. Typical details areprovided in Appendix G.Go to Chapter 2 Theseare culvert weight, internal fluid weight, earth load and vehicle loads.2.http://www.drupalitalia.org/node/672331 Culvert WeightThe total weight of a reinforced concrete culvert per unit length, Wp, at a given section can be obtainedfrom tables in the American Concrete Pipe Association (ACPA) Pipe Design Handbook (2), or from thefollowing simplified equations for approximate total weight of structure in Ibs per ft. These equationsapply when Dj, Bj, h, r1, r2, u, v, HH, HV, TS, TT and TB are in inches, and the concrete unit weight is150 Ibs per cu. ft.Circular: Equation 2.1Elliptical Equation 2.2(Figure 1-2):Box Equation 2.3SectionsThe weight of corrugated metal structures is smalI relative to the earth load, and is generally neglectedin design.2.2 Fluid LoadsThe weight of fluid per unit length, Wf, inside a culvert filled with fluid can be calculated from thefollowing simplified equations for approximate total weight of water in Ibs per ft. These equations applywhen Dj, Bj, r1, r2, u and v are in inches, and the fluid unit weight is 62.5 Ibs per cu. ft. (This unit weightis slightly higher than the normal unit weight of clean water to account for any increases due todissolved matter.)Circular: Equation 2.4Elliptical: Equation 2.5Box Equation 2.6Sections Units are the same as for Equation 2.7a, Do is in inches. Equation 2.7bFe represents the ratio of the earth load on the culvert to the earth prism load, and may be determinedby the Marston-Spangler theory of earth loads on pipe (2, 3) or the approximations presented belowmay be used.Equations that may be used to locate culverts within embankments and determine the height of fillover design sections are presented in Appendix F. 2.3.1 Soil Structure Interaction Factor for Rigid Culverts When rigid conduits are installed with compacted sidefill they are subject to less load than when the sidefill is loosely installed. Other factors which affect the load on a conduit include trench width, if applicable, burial depth to span ratio and soil type.ACADEMYOCGC.COM/images/3m-9100-projector-manual.pdf Since inlet structures are generally short relative to the culvert barrel, and since they are typically under very low fill heights, it is recommended that conservative values be used for the soil structure interaction factor. Suggested values are 1.2 for sections installed with compacted sidefill, and 1.5 for sections installed with loose sidefill. Use of the above values is recommended for both reinforced concrete pipe and box sections. 2.3.2 Flexible Culverts For flexible metal culverts, AASHTO allows Fe to be taken equal to 1.0 for both trench and embankment installations; however, like box culverts, current research indicates that flexible metal culverts carry a load that is greater than the earth prism load. Estimates of the actual Fe are as high as 1.3 (6). The loads for such installations may also be determined by accepted methods based on tests, soil-structure interaction analyses (generally by finite element methods), or previous experience. However, these installation methods generally are used only for deep burial conditions and thus are not relevant to inlet designs.2.4 Construction LoadsInlet structures included in this manual will not normally be subjected to highway loads, but may beloaded by miscellaneous construction or maintenance equipment, such as bulldozers and mowingmachines. This is the equivalent of 2 ft.Any significant expected loads shouldbe specifically considered in design.2.5 Distribution of Earth Pressures on Culvert 2.5.1 Rigid Culverts Earth pressures are distributed around various rigid culvert types as shown in Figure 2-1. Equation 2.8 Equation 2.9a or approximately Equation 2.9b However, because of variations in installationconditions a more rational and conservative design is obtained by designing for maximumstress resultants produced by the range of a values between 0.25 and 0.50.Suggested pressure distributions for circular and elliptical rigid pipe are presented inFigures 2-1b and 2-1c.https://snabavto.com/wp-content/plugins/formcraft/file-upload/server/content/files/1626bf220ca36d---canon-xl1-repair-manual.pdf These distributions consist of a radially applied earth pressure overa specified load angle, ?1, at the top of the pipe, and a radially applied bedding pressureover a specified bedding angle, ?2, at the bottom of the pipe. This pressure distribution isbased on the work of Olander (7). Olander proposed that the load and bedding anglesalways add up to 360 degrees; however, this results in increased lateral pressure on the In view of this, the load angle should be limited to a maximum of 240 degrees. This limitation should apply even in cases where the bedding and load angles do not add up to 360 degrees, as is shown in Figure 2-1b. The same system for distribution of earth pressure can also be used for elliptical pipe, as shown in Figure 2-1c The earth pressure is always applied normal to the curved segments that make up the elliptical section, that is, radial to the center of curvature of the particular segment. 2.5.2 Flexible Culverts The distribution of earth pressure on a flexible metal culvert tends to be a fairly uniform radial pressure, since the pipe readily deforms under load, and can mobilize earth pressures at the sides to help resist vertical loads. No pressure distribution is shown here, however, since metal culvert design is done by semi-empirical methods and typically a specific pressure distribution need not be assumed by the designer.Go to Chapter 3 The structural analysisand design of culverts can be completed very efficiently by computer. Computer programs are presented inChapter 5 for analysis and design of reinforced concrete single cell box culverts, and circular and ellipticalpipe culverts. The method discussed below are appropriate for hand analysis, or are readily programmablefor a hand-held calculator.None of the computer or hand analysis methods presented in this manual account for effects of variation inwall stiffness caused by cracking. This is consistent with current general reinforced concrete designpractice.AYBAR-GALLERY.COM/userfiles/files/986-owners-manual-pdf The reduction in stiffness produced by cracking becomes more significant when soil-structureinteraction is considered, using finite element models of the pipe-soil system. Models that account for suchchanges in stiffness have developed and correlated with test results, but currently these are only beingused for research on the behavior of buried conduits.3.1 Reinforced Concrete Box SectionsThe first step in box section design is to select trail wall haunch dimensions. After these dimensions areestimated, the section can then be analyzed as a rigid frame, and moment distribution is often used for thispurpose. A simplified moment distribution was developed by AREA (8) for box culverts under railroads.Modifications of these equations are reproduced in Table 3-1 and Table 3-2 for one and two cell boxculverts respectively. This analysis is based on the following assumptions.Standard haunches have horizontal and vertical dimensions equal to the top slab thickness.Any one of these cases can bedropped by setting the appropriate unit weight (soil, concrete or fluid) to zero when computing the designpressures pv and ps.The equations provide moments, shears and thrusts at design sections. These coefficients should only be used when the sidefill is compactedduring installation. Compacting the sidefill allows the development of the beneficial lateral pressuresassumed in the analysis. Coefficients for two bedding conditions areprovided, corresponding to traditional Class B and Class C bedding conditions (2). These coefficients alsoshould only be used for pipe installed with compacted sidefill.These coefficients represent a Figure 3-6 providescoefficients for water load analysis of circular pipe. The coefficients in Figure 3-5 and Figure 3-6 can alsobe used to approximate the moments, thrusts and shears in elliptical pipe of equal span for these two lesscritical types of load.3.https://www.medicalart.com.tr/wp-content/plugins/formcraft/file-upload/server/content/files/1626bf22b6b29b---canon-xl1-service-manual-download.pdf3 Flexible Pipe SectionsFlexible pipe culverts are typically designed by semi-empirical methods which have been in use for manyyears. Design by these methods does not include a structural analysis per se, since the analysis isgenerally implicit in the design equations. These modifications are usually proprietary,and designers should consult with the manufacturers before completing detailed designs.Go to Chapter 4 For reinforced concrete inlets, the designer typically selects a trial wall thickness and then sizes the reinforcing tomeet the design requirements. For precast structures the trial wall thickness is normally limited to standard wall thicknessesestablished in material specifications such as ASTM C76, C655 and C789 (AASHTO M170, M242 and M259). Forcorrugated metal structures, the designer typically selects a standard wall thickness and corrugation type that provide therequired ring compression and seam strength, and the required stiffness to resist buckling and installation loads.The design approach suggested herein is to treat inlet structures, that have varying cross sections, as a series of slices thatbehave as typical culvert sections. Representative slices along the length of the inlet are selected for design. The face andthroat sections and one or more additional slices are usually included. For corrugated metalstructures, the structure requirements are usually based on the maximum condition. This approach is illustrated in theexample problems in Appendix D. Special considerations required for slope tapered inlets (Figure 1-3) are discussed inSection 4.1.6.4.1 Reinforced Concrete DesignThe method for the design of reinforced concrete pipe and box sections presented below was recently adopted by theAmerican Concrete Pipe Association and has been recommended by the AASHTO Rigid Culvert Liaison Committee foradoption by the AASHTO Bridge Committee.https://www.northamericatalk.com/wp-content/plugins/formcraft/file-upload/server/content/files/1626bf2397abaf---canon-xl1-service-manual.pdf This design method provides a set of equations for sizing the maincircumferential reinforcing in a buried reinforced concrete culvert. For additional criteria, such as temperature reinforcing inmonolithic structures, the designer should refer to the appropriate sections of AASHTO (4).Typically, the design process involves a determination of reinforcement area for strength and crack control at variousgoverning locations in a slice and checks for shear strength and certain reinforcement limits.The number and location of sections at which designers must size and reinforce and check shear strength will vary with theshape of the cross section and the reinforcing scheme used. Figure 4-1. shows typical reinforcing schemes for precast andcast-in-place one cell box sections. The design sections for these schemes are shown in Figure 4-2. For flexural design of Shear design is by two methods;one is relatively simple, and requires checking locations 3, 6, 10 and 13 which are located at a distance dvd from the tip ofhaunches.Typical reinforcing schemes and design locations for two cell box sections areshown in Figure 4-3.A typical reinforcing layout and typical design sections for pipe are shown in Figure 4-4. Pipes have three flexure designlocations and two shear design locations. Figure 4-4 is also applicable to elliptical sections. In this design approach, the structure is proportioned to satisfy the following limits ofstructural behavior: q Minimum ultimate strength equal to strength required for expected service loading times a load factor q Control of crack width at expected service load to maintain suitable protection of reinforcement from corrosion, and in some cases, to limit infiltration or exfiltration of fluids.avtomix.com/upload/files/986-manual.pdfIn addition, provisions are incorporated to account for a reduction of ultimate strength and service loadperformance that may result from variations in dimensions and nominal strength properties within manufacturingtolerances allowed in standard product specifications, or design codes.Moments, thrusts and shears at critical points in the pipe or box section, caused by the design loads andpressure distribution, are determined by elastic analysis. In this analysis, the section stiffness is usually assumedconstant, but it may be varied with stress level, loosed on experimentally determined stiffness of crocked sectionsat the crown, invert and springlines in computer analysis methods. Also, the suggested load factors are intended to beused in conjunction with the strength reduction factors given below.The 1981 AASHTO Bridge Specifications (4) specify use of a minimum load factor of 1.3 for all loads, multipliedby.If hot rolled reinforcing is used in a precast structure, or if any unusual conditions exist, a strength reduction factor of 0.9, instead of 1.0, should be used in flexural calculations.4.1.2 Design of Reinforcement for Flexurol StrengthDesign for flexural strength is required at sections of maximum moment, as shown in Figure 4-2, Figure 4-3 andFigure 4-4.(a) Reinforcement for Flexural Strength, As Equation 4.4 Equation 4.5 d may be approximated as Equation 4.6 Experience within the precast concrete pipe industry has shown that such variations are significant. If Equation 4.13 yields values of Frp less than 1.0, a value of 1.0 may still be used if a review of test results shows that the failure mode was diagonal tension, and not radial tension. If a limiting value of less than 1.0 is specified for Fcr, the probability of an 0.01 inch crack is reduced. No data is available to correlate values of Fcr with specific crack widths other Thus, Method 2 should also be checked.Method 2: Method 2 is based on research sponsored by the American Concrete Pipe Association (9), and ismore complex than Method 1, but it reflects the behavior of reinforced concrete sections under combined shear,thrust and moment with greater accuracy than Method 1, or the current provisions in the reinforced concretedesign section of the AASHTO Bridge Specification.Determine Vu at the critical shear strength location in the pipe or box.Experiencewithin the precast concrete pipe industry has shown that such variations are significant.The recommended design procedure for precastinlets is to analyze the section and design the reinforcing based on earth loads applied normal to the section, asshown in Figure 4-7a; however, since it is usually easier to build cast-in-place inlets with the main sidewallreinforcing (ASl) vertical, the reinforcing spacing and area must be adjusted to provide the necessary area. Thisis accomplished, as shown in Figure 4-7b, by using the transverse spacing assumed for the analysis as thehorizontal spacing, and by modifying the area of sidewall outside reinforcing by Equation 4.35 These stress resultants are relatively small and sufficientflexural resistance is usually developed if the minimum flexural reinforcing is provided in the longitudinal direction,as shown in Figure 4-7b. This approachresults in more economical structures for large spans.The concept of special features also applies to side tapered corrugated metal inlets; however, it is not practical to providespecial features for small inlets, and thus a special condition exists. The recommended approach for these structures is thateither special features must be provided, or the handling and buckling criteria must be met by the corrugated metal sectionalone. This is not specifically allowed by the AASHTO Bridge Specification, but is within the design philosophy of the code. Use of the computer methods allows theengineer to make a more complete evaluation of various culvert configurations for a giveninstallation.5.1 Box SectionsThe design program for buried reinforced concrete box sections provides a comprehensive structuralanalysis and design method that may be used to design any single cell rectangular box section withor without haunches. For tapered inlet design, the program may be used to design cross sections atvarious locations along the longitudinal axis that the designer may then assemble into a singledesign. This section gives a general description of the program. Specific informationneeded to use the program is given in Appendix B. A program listing is provided in Appendix H. 5.1.1 Input Variables The following parameters are input variables in the program: q Culvert geometry - span, rise, wall thicknesses, and haunch dimensions.The only parameters that must be specified are the span, rise, and depth of fill. If no values are input for the remaining parameters, then the computer will use standard default values. Default values are listed in Appendix B (Table B-1) for all the input parameters. The twofoot surcharge load (Section 2.4) is added to the height of fill, and is therefore consideredas a permanent dead load.Earth pressures are assumed distributed uniformly across the width of the section andvary linearly with depth. Soil reactions are assumed to be uniformly distributed across thebase of the culvert.5.1.3 Structural AnalysisTo determine the design moments, thrusts, and shears, the program employs thestiffness matrix method of analysis. Box culverts are idealized as 4 member frames ofunit width. For a given frame, member stiffness matrices are assembled into a globalstiffness matrix; a joint load matrix is assembled, and conventional methods of matrixanalysis are employed.This method is presented in Chapter 4. For agiven trial wall thickness and haunch arrangements the design procedure consists ofdetermining the required steel reinforcement based on flexural strength and checkinglimits based on crack control, concrete compressive strength, and diagonal tensionstrength. If the limits are exceeded, the designer may choose to increase the amount ofsteel reinforcement, add stirrups for diagonal tension, or change the wall thicknesses andhaunch geometry as required to provide a satisfactory design. Five steel areasdesignated as AS1, AS2, AS3, AS4 and AS8 in Figure 4-1 are sized based on themaximum governing moment at each section. The area AS1 is the maximum of the steelareas required to resist moments at locations 5, 11 and 12 in Figure 4-2. Areas AS2,AS3, AS4 and AS8 are designed to resist moments at locations 1, 15, 8 and 4,respectively. The steel areas determined for flexural strength requirements are thenchecked for crack control. The program then checks shear by both Methods 1 and 2(Section 4.1.4) at the locations shown in Figure 4-2. The more conservative criteria isused as the limiting shear capacity.For the reinforcing scheme for precast box sections (Figure 4-1a), the theoretical cutofflengths, for AS1 in the top and the bottom slab are calculated from the assumption ofuniformly distributed load across the width of the section. The point where the negativemoment envelope is zero is computed from the minimum midspan moment. Input for a particular box culvert may range from a minimum of 3 cards to amaximum of 16 cards depending on the amount of optional input data required by thedesigner. The type of data to be supplied on each card is specified in Appendix B. Aprogram with minimum data would require only a title card, data card 1 specifying thespan, rise and depth of fill, and data card 15 indicating the end of the input data.The amount of output can be controlled by the user, as described in Appendix B. Theminimum amount of output that will be printed is an echo print of the input data and a onepage summary of the design. An example design summary sheet is included in AppendixB. Additional available output includes maps of major input arrays, displacements, endforces, moments, thrusts and shears at critical sections, and shear and flexure designtables. Information needed to use the program is presented in Appendix C. 5.2.1 Input Variables and Dimensional Limitations The following parameters are input variables in the program: q Pipe Geometry diameter for circular pipe, or radius 1, radius 2, horizontal offset, and vertical offset for elliptical pipe, and wall thickness (see Figure 1-2) q Loading Data depth of fill over crown of pipe, density of fill, bedding angle, load angle, soil structure interaction factor, depth of internal fluid and fluid density q Material Properties reinforcing tensile yield strength, concrete compressive strength and concrete density q Design Data load factors, concrete cover over inner and outer reinforcement, wire diameters, wire spacing, reinforcing type, layers of reinforcing, capacity reduction factor, crack control factor, shear process factor and radial tension process factor The pipe geometry and height of fill are the only required input parameters. Default values are assumed for any optional data not specified by the user. Appendix C (Table C-1) lists all the input parameters and their associated default values.The two foot surcharge load suggested in Section 2.4 should be added to the height of fill input into the program. The pipe ismodeled as a 36 member plane frame with boundary supports at the crown and invert.Each member spans 5 degrees and is located at middepth of the pipe wall. For eachmember of the frame, a member stiffness matrix is formed, and then transformed into aglobal coordinate system. The loads on the pipe are calculated as pressures appliednormal and tangential to each of the 36 members. These pressures are converted intonodal pressures that act radially and tangentially to the pipe. Loads of each joint areassembled into a joint load matrix, and a solution is obtained by a recursion algorithmfrom which member end forces are obtained at each joint. Analysis is completedseparately for each load condition. If necessary, the reinforcement areas are increased to meet these otherrequirements. The design procedure is the same as used for box sections (See Chapter4).Reinforcing is designed at three locations; inside crown, inside invert and outsidespringline (See Figure 4-4).When the applied shear exceeds the shear strength,stirrups are designed by outputting a stirrup design factor (Sdf). This is then used todetermine stirrup area by the following equation: Equation 5.1This allows the designer to select a desirable stirrup spacing and to vary fv dependingupon the developable strength of the stirrup type used. For an elliptical pipe, the number of data cards required may range from 5 cardsto 14 cards. For circular pipe design, one less card is required. The type of data to bespecified on each card and format is described in Appendix C. The first card for everydesign is a problem identification card which may be used to describe the structure being Data cards 1 through 3 are required cards that specify the pipe geometry and height of fill. Data cards 4 through 12 specify the loading data, material strengths, and design criteria to be used. A data card over 12 indicates that the end of the data stream has been reached. For elliptical pipe, a design with a minimum amount of data would require a title card, data cards 1 through 3 specifying the culvert geometry and height of fill, and a data card with code greater than 12, indicating the end of the data stream. For circular pipe, data card 2 is not required. The amount of output can be controlled by the user, as described in Appendix C.