. 5-6. 5. This Design Guide has been developed to educate the industry on the advantages, disadvantages, and potential problems associ- ated with specifying camber for steel floor or roof members in an effort to enable a practicing engineer to make informed deci- sions in evaluating the best solution with regard to camber for their specific project. . Camber design, especially for composite floor systems, is a complex steel design problem. Problems with steel headed stud anchors projecting above the slab surface for thin-slab systems have been reported when screeding to constant elevation. However, field surveys should be used to verify actual dead load defiections to determine whether changes need to be made when it comes to placing and screeding the concrete. The cambering process will yield the beam and possibly cause net section rupture at the holes. The introduction of composite design in the 1961 AISC Specification (AISC, 1961) made cambering much more common and increased the need for fabricators to camber more efficiently. 9921,000. . . In reality, some rotational restraint will exist. . . ASTM A6/A6M permits an out-of-straightness for wide-flange beams of 8in. Appendix Section C.4, Camber, states: Special camber requirements that are necessary to bring a loaded member into proper relationship with the work of other trades shall be set forth in the design documents. The new guide lists the key variables that can affect the dead load deflection of the beam and information to help designers make a judgment about their effect on the camber required for their specific project. . 3-10. Next there is a need to clearly convey what the expected performance of the structural system will be in order for the contractor to properly plan the work. Residual strains will vary depending on the camber required, the method of cambering, and the depth of section. Introduction and Basic Principles Design Guide 36: Design Considerations for Camber https://www.civilax.com/design-guide-36-design-considerations-for-camber/ AISC DESIGN GUIDE 36 / CAMBER / 47 037-048_DG36_EM.indd 47 8/26/20 2:48 PM 48 / CAMBER / AISC DESIGN GUIDE 36 037-048_DG36_EM.indd 48 8/26/20 2:48 PM Smarter. . When calculating the required strain to camber a beam, the typical elastic moment curvature equations do not apply in the inelastic region, and it is necessary to go to the strain curvature relationship shown in Figure2-2 (Bjorhovde, 2006). (a) Unsymmetrical about the x-x axis (b) Unsymmetrical about the y-y axis Fig. . Due to demand, the mills did adjust their limits to accommodate all of the composite beam sizes, but the process was still inefficient. . The curvature associated with camber is typically not expected to be visible once all the structural components are installed in the building. For members with designed or induced camber, this slight out-of-straightness can be ignored. 14 / CAMBER / AISC DESIGN GUIDE 36 011-020_DG36_Ch03.indd 14 8/26/20 2:47 PM it is often considered more art than science. . 18 / CAMBER / AISC DESIGN GUIDE 36 011-020_DG36_Ch03.indd 18 8/26/20 2:47 PM Table3-1. Long cantilever members, however, may be sloped and have a preset elevation specified for the free end. The variables that are expected to have the most impact on the beam performance are the connection restraint, variation in deck reaction based on span condition, fabrication tolerance, and possible span length reduction at column lines. If this thickness is not achieved, costly fireproofing may have to be added to the underside of the deck to achieve the required fire rating. 4-1. Heat cambering can also be used to correct any small camber change. The amount of permanent strain that will occur with heat is dependent on the temperature of the heated metal and the restraint that is applied. The fabrication tolerance effect should be considered when specifying the camber, but it does not affect the deflection calculation. Criste, E. (2009), Beam Cambering Methods and Costs, Structure Magazine, April. Both are the authors of AISC Design Guide 36: Design Considerations for Camber. Temperature (F) Modulus of Elasticity (ksi) Fig. If possible, the design should avoid holes in the center third of the top flange length for beams to be cambered. . The deflection at the column line may vary from 75 to 90% of the typical interior beam deflection, depending on the magnitude and presence of each of these variables. 5.3 CANTILEVER BEAMS Cantilever beams and the cantilever portion of continuous beams will be noncomposite and must be designed for the deflections of both dead and live loads. . 4.2 4.1.6 Material Properties Residual stresses have been shown not to be a problem in either loss of camber in shipment or in the ultimate strength capacity of the composite section. Design Guide 36 Welcome! 4-3. Whether the deck is a single span or multi-span will not affect the analysis or design of the composite beam for ultimate loads. . . Update Of Guide To Road Design Part 5: Drainage - General And Hydrology Considerations (Australian . . . 2, p. 14. . . Some of these variables, such as the actual restraint provided by the member end connections, are difficult to evaluate precisely. . for each 10 ft of length, except for certain sections ordered as columns that have special maximum limits. As can be seen in Figures4-1(b) and (c), the reaction to the supports will vary depending on the deck continuity. The double-press cambering machine shown in Figure3-2 applied at multiple locations will produce a similar curve. . 4.1 CAMBER DESIGN VARIABLES The design of the camber required to produce a level floor is an inexact process due to the many variables that affect the deflection of the beam. . . Because the exterior building faade system is attached to and/or supported by the spandrel members, the deflection characteristics of spandrel members can have significant impact on nonstructural components. The elastic strain or the amount of deformation that can be applied without causing permanent deformation of the material is shown in Figure3-10 as a function of temperature for a material that is fully restrained in one axis. . . He also currently serves on the AWS D1.1 Subcommittee D1Q on Steel. September 2020, Lawrence A. Kloiber, PE; Susan B. Burmeister, PE, Member: Free 38 LEVEL FLOOR CONSTRUCTION . . . . There are three primary methods of controlling the accuracy of the strike-off when placing concrete: The wet-screed guide uses a section of wet concrete that is struck-off to elevation. 18:118:23. This Design Guide follows the Institutes traffic class style by breaking traffic into six classes, I through VI. This resulted in a smoother curve and a reduction in the required strain. . Shoring was an economical option in the early days of composite construction. Using the 80% rule and rounding down in 4-in. 4-5. 4-7. Non-member: $50.00. The beam geometry may not be as simple as shown in Figure 3-1(a), but could have multiple slopes along the member length, as shown in Figure3-1(b). /article/Camber+Considerations/3785156/676603/article.html. 4.1.7 Span at Columns When floor beams at the gridline frame to the column flange, the member size does not typically change, but the reduction in effective span length can be significant. Do not camber spandrel members that support brittle faade materials. . . . . They may, however, contribute slightly to the deflection of the beam at full service loads. Goverdhan, A.V. AWS (2020), Structural Welding CodeSteel, AWS D1.1/D1.1M:2020, American Welding Society, Miami, Fla. Bjorhovde, R. (2006), Cold Bending of Wide-Flange Shapes for Construction, Engineering Journal, AISC, Vol. Residual stresses due to cold bending (10 R d 40) (Spoorenberg et al., 2011). . 7. While the new guide focuses primarily on camber for composite beams, it also discusses camber for non-composite members like girders, trusses, and joists, as well as roof framing and special conditions like ponding. Most beams have connection holes (except critical flange holes as discussed previously) made before cambering to accommodate the shop computer numerical control (CNC) material handling and hole-making equipment. For the purpose of inspection, camber shall be measured in the fabricators shop in the unstressed condition. The intersection of the plastic flow with the elastic strain is the point at which permanent deformation takes place. However, information in the Appendix is considered cautionary, not mandatory, so there is no obligation on the part of designers to follow it explicitly. . . . The design variables can cause the in-place beam deflection to vary from the design, and as a result, the finished top surface of the floor surface will also vary. 9, No. ACI 302.1R, Guide for Concrete Floor and Slab Construction (ACI, 2015), addresses the methods used for concrete strike-off. Do not camber crane beams or crane girders. . The term camber dates from the early 1600s . Strain softening has been cited in one paper (Lange and Grages, 2009) for its influence on the deflection behavior of composite beams. Steel deck is often sized based on a three-span condition, so the elevations may need to transition so the steel deck erector can properly place the steel deck. Thermally induced stresses in rolled shapes are caused by uneven cooling of the material after hot rolling. . . 24 / CAMBER / AISC DESIGN GUIDE 36 021-030_DG36_Ch04.indd 24 8/26/20 2:47 PM restraint, it is possible to approximate the restraint effect on the calculated simple beam deflection. Truss field assembled in supported conditionchecking camber. 4.1.3 Welded Attachments Spandrel beams and similar members with field-welded attachments may lose some camber depending on the weld details. Cambco cambering machine with conveyor (Hydradyne, LLC Parker Fluid Products). 50 ksi = 0.953 The radius of curvature for a beam spanning 40ft with a 2-in. (1980), Vibratory Stress Relief: A Fundamental Study of Its Effectiveness, Journal of Engineering Materials and Technology, Vol. . . AISC Specification Section B3.4a defines a (a) Simple-span condition (b) Double-span condition (c) Triple-span condition Fig. . . What distinguishes a camber is its slight curve upward. The coupon code has been applied to your cart! . . . 'Sustainable Urban Drainage Systems', 2001: Best Practice . . (g) For a member that is fully assembled in the field in an unstressed condition, the same tolerances shall apply as if fully assembled in the shop. Scribd is the world's largest social reading and publishing site. . 26 4.3.1 Compounded Deflections . 23, No. 26 LOAD TO OFFSET . Practice in the industry is mixed, with some engineers preferring to require the concrete be screeded to provide a uniform plane surface and other engineers preferring to require the concrete be placed to a uniform slab thickness as shown in Figure4-2. AISC DESIGN GUIDE 36 / CAMBER / 15 011-020_DG36_Ch03.indd 15 8/26/20 2:47 PM The temperature of the heated metal and the rate at which the temperature rises are the most important factors in the heat straightening/cambering process and is one of the most difficult parameters to control. Appendices are included that discuss floor levelness and rules of thumb. For the purposes of this Design Guide, unless specifically identified as natural or mill camber, any time the authors refer to camber within the document, it will mean the specified camber imposed on the member by the design engineer through the steel fabrication process. The strip heat used on the flange shown in Figure3-13(b) should be located directly over the open end of the vee web heat and match the width of the vee where it intersects the flange. The differences in the top of steel elevations before any load is applied to the members may not be able to be accommodated by the metal deck, especially if the cambers are large or the deck design is dependent on multi-span deck installation. . However, if the designer desires a positive camber after loading, that alternative is left to the designers judgment. . . However, bottom flange bracing was required, and working around the shores often created onsite schedule problems. From Example2.1.1: R= 6,300in. . The design objective when cambering a horizontal framing member is to intentionally induce an upward curvature in the member such that when the member is subject to full loading, the members final deflected shape stays within a desired deflection criterion. The heat should be applied starting at the apex of the vee by slowly moving the torch in a circular pattern in each area until the thermal marking starts to melt. To complicate matters even further, we cannot simply assign a conservative value because there are potential issues associated with both over-specifying and under-specifying the amount of camber for a given beam size. . This not only effects the rate of strain, it also effects the restraint. A.3 LEVEL FLOOR CONSTRUCTION The traditional strict division of responsibilities where the structural engineer is responsible for design and the contractor is responsible for the means and methods of constructing the work can hinder the process of constructing a level floor. Since the introduction of the Cambco type machine shown in Figure 3-2, other manufacturers have developed similar pieces of cambering machinery utilizing the doubleram concept. . 12. . 1.3 PURPOSE AND BENEFITS OF CAMBER Camber is frequently associated with design of composite beams because it can provide so much benefit to those members. Steel. 1. The intent is to provide practical design information in an easily accessible manner. (2001) indicate peak residual stresses in both flanges will be in compression and on the heated flange may approach the yield level. . . . The elevation at the top of the column may vary from theoretical plan elevation due to fabrication and erection tolerances along with foundation settlement and the effect of column shortening. You can download midas Civil trial version and study with it:https://hubs.ly/H0FQ60F0midas Civil is an Integrated Solution System for Bridge & Civil Engineer. However, it might not be the best option for all structures. For fabricated trusses that are specified in the contract documents with camber, the variation in camber at each specified camber point shall be equal to or less than plus or minus 1 800 of the distance to that point from the nearest point of support. The loss of camber due to vibration should not occur with cambered beams based on a study of effectiveness of vibratory stress relief (Dawson and Moffat, 1980). . Additionally, there was some question about the accuracy of the camber based on statements in earlier editions of the AISC Manual of Steel Construction (AISC, 1989) about possible camber loss in shipment. Beam camber is commonly used with both methods to optimize the beam size while still conforming to the project-specific deflection requirements. . From a serviceability perspective, another concern was that when the shores were removed, some deflection still occurred and significant cracking tended to occur over the supporting girders. . 32 5.3 CANTILEVER BEAMS . The plastically strained area was localized at the load point, which required imposing larger strains than would have been required for a continuously curved member to achieve the required camber. . Cambering has always been recognized as the more economical material option over upsizing the beams and adding more concrete to compensate for deflection. 5 2.1 2.2 2.3 CHAPTER 5 CAMBER FOR SPECIAL CONDITIONS . AISC DESIGN GUIDE 36 / CAMBER / 29 021-030_DG36_Ch04.indd 29 8/26/20 2:48 PM (a) Partial framing plan (b) Section at load bearing wall (c) Section at mid-span column Fig. . . There is a difference between level and levelness. Typical stress and strain diagrams for steel members. SEAoC (2008), Considerations for Steel Framed Floors, Structural Engineers Association of Colorado, RMSCA Steel Liaison Committee Report, September. . . For double-pitched top chord profiles with steeper pitch ratesthat is, greater than 2in./ftor for an arched top chord profile, it may be desired to specify no camber where there is a need to match elevation with adjacent framing or a wall due to pitch rate or profile. There was no research or data provided to verify this. The result is that most members fabricated with camber will have more camber than was specified. . For fabricated trusses that are specified in the contract documents without indication of camber, the foregoing requirements shall be applied at each panel point of the truss with a zero camber ordinate. 2-4. 410414. . Organization : AISC. Typical framing bay. To account for this unknown contribution of connection restraint on the beam deflection, designers typically specify camber amounts based on engineering judgment that are less than the calculated simple-span deflection from the fully applied dead load. The dimensions shown in Figure2-4 are as follows: R= c2 sin ( 2) (2-5) The vertical rise, y, for the straight tangent leg is: y= 3 ( ) L tan 2 8 (2-6) 1 Because tan ( 4) tan ( 2 ), the vertical offset within 2 the curved beam segment, b, is: b= c c 1 tan = tan 2 4 2 2 2 (2-7) The total camber, c, is equal to the sum of y + b: c = y + b = 3 c 1 L tan + tan 8 2 2 2 2 (2-8) Example2.1.1Geometric Evaluation of Camber Radius of Curvature Given: Determine the specific radius of curvature for a W2144 beam spanning 40ft with a specified camber of 2in. Faade support attached to spandrel members. Special care should be taken to ensure that the entire assembly is stable when the beam starts to move as heat is applied. . The strip heat at the top should also be marked in segments. PDF - Complete Book (41.02 MB) PDF - This Chapter (6.06 MB) View with Adobe Reader on a variety of devices These issues are discussed in greater detail in AppendixA, SectionA.2. . . Gagging is similar to cambering where a shape is loaded to yield by a large hydraulic ram centered between two supports. 4.3 s > s Fig. . . . Example of cambered beam geometry. Spandrel beams with supplemental steel framing to support the faade need to be carefully coordinated with the architectural faade details and the faade system joint limitations. Non-member: $60.00. . This is a result of both the machine setup and the most efficient method of achieving the design camber. While theoretically two adjacent beams could vary in camber by 2in. Most steel decks, however, are installed in a multi-span condition. . The yield stress also decreases at a significant rate at temperatures above 800F as shown in Figure3-9. Variation of the modulus of elasticity vs. temperature (Roeder, 1986). 107115. . . Camber can be designed or inputted (as an absolute value or as a value relative to the span length). The designer will have to specify the camber that is expected to remain in the girder as each floor is placed and adjust concrete elevations as necessary. In this scenario, it is reasonable to select beam camber that offsets the combined structure self-weight plus 100% of the expected superimposed dead load. . Both approaches are used throughout the industry and are structurally acceptable. Welded plate girders can be cambered by cutting the web plate to the specified camber curve and then fitting the flanges to the web. His example of sharing his knowledge in that paper and numerous others that followed set an example of professional responsibility that should inspire all of us. . 2. . . max = 8 ( number of feet of total length 10 ) (3-1) There are a few things to note when discussing natural camber. Show required camber for each member on the framing plans or in the model. The SJI Code of Standard Practice for CJ-Series Composite Steel Joists (SJI, 2016), Section 2.6(b), states the following: It is standard practice that the CJ-Series joists are furnished with sufficient camber for 100 percent of the non-composite dead load (joist, bridging, deck, and concrete slab). . . The key to this is to re-straighten the surface with a bull float or the use of a riding trowel with float dishes. . flange thickness to 1 in. . 27 4.3.2 Floor Plan Framing Considerations . Usually several heats will be required to achieve the design camber, and these can be grouped in the center at 2- or 3-ft spaces, depending on the depth of the member and size of the vee. Use of minimum-size stitch welds that are not closely spaced will limit the negative heat effects that could reduce, or relax, the imposed camber. Stamping Design Guidelines Jonathan Zhang 4 2. . . Document Number : 836. . Given a specific set of conditions, closer tolerances can be held, e.g . tan + tan 8 2 2 2 2 Solving for / 2: / 2 = 0.546 And the radius of curvature, R, is: c2 sin 2 120 in. While it is believed to be accurate, this information should not be used or relied upon for any specific application without competent professional examination and verification of its accuracy, suitability and applicability by a licensed engineer or architect. Holt, R.E. . Do not camber members with spans less than 25ft. Beams less than 25ft may require special procedures due to machine limitations. . . Once the vegetation finish has been determined the structural and design considerations and green roof components can be proposed. Measurements were taken using a string line and foot rule to the nearest zin. The variations in residual stress depend on mill rolling stresses and the camber and cambering process. . 4-4. The advancement in analysis software has simplified the calculation of deflection; however, in most cases there will still be assumptions on connection stiffness, support restraint, and actual loads so that the deflection will be a design approximation. The contractor needs to know what the anticipated deflection will be and how his proposed method of placement might affect the levelness specified. . For thicker slabs, there is sufficient length between the minimum and maximum stud length permitted by the AISC Specification that a length can be specified that will allow extra tolerance for concrete cover. . Recommended Torch Tips for Various Thicknesses of Material (Avent and Mukai, 1998) Steel Thickness, in. Depending on the travel of the ram, the beam was strained into the plastic region until the required permanent set was achieved. Fabricated Standard Camber (SJI, 2015) Top Chord Length Approximate Camber, in. Steel, when heated, tries to expand uniformly in all directions. 102, April. . . The beam was positioned horizontally and loaded by the ram so that a plastic hinge formed at the load point. Consider the beam deflections resulting from three different hypothetical slab systems where calculated deflections vary from 1in. It is important when designing cambered trusses with HSS chords and direct-welded HSS web members as shown in Figure 5-6 that gapped type joints are specified. The American Institute of Steel Construction bears no responsibility for such material other than to refer to it and incorporate it by reference at the time of the initial publication of this edition. Design Considerations for Camber Lawrence A. Kloibe, American Institute of Steel Construction www.aisc.org One East Wacker Drive Suite 700 Chicago, IL 60601 312.670.2400 . . End connection slope. A survey of design office practices by the guides authors indicated that many firms use a rule-of-thumb design that specifies a design camber of approximately 80% of the simple-span deflection. Additional restraint may be provided by positioning the member to use the weight of the member along with added load from weights or jacking with special loadlimiting jacks. . Another summary of heat straightening is Synthesis Study: Heat Treatment and Its Effects on Rehabilitating Steel Bridges in Indiana (Lackowski and Varma, 2007). Provided the magnitude of the outof-straightness is within the tolerance limits established by ASTM A6/A6M, these natural cambers, both positive and negative, are acceptable and can be neglected in the beam design and fabrication processes. . The AISC Code of Standard Practice Section 6 identifies permissible tolerances applicable to induced cambers of 0in. . The camber study discussed in Section 2.3 (Larson and Huzzard, 2003) indicated that beams that were cambered to AISC Code of Standard Practice allowable tolerances at the mill arrived at the fabrication shop with an average of xin. . 3-9. Each of these items has been discussed in greater detail in the preceding sections, providing some additional insight as to why these rules of thumb exist and when they may not be applicable. . There can be another problem with thin slabs when the steel headed studs project above the top of the finished floor. When the beam is oriented with the web vertical, any out-of-straightness should be an upward, or positive, deviation from a straight line. . When the constant elevation method for concrete placing is specified, it is important as noted in ACI 302.1R that beams are fully deflected before the concrete in the area is screeded. 2-1. R= = 525 ft (2-5) Example2.1.2Determine the Maximum Strain Factor for the Beam in Example2.1.1 Given: Determine the maximum strain factor for the cambered beam given in Example2.1.1. . 6 Example 2.1.2 Determine the Maximum Strain Factor for the Beam in Example 2.1.1 . . (This is the deflection caused by the dead load weight of the wet concrete on the tributary area.) Typically, it was necessary to move the beam and use multiple load points to achieve the required camber curve while keeping strain levels well below strain hardening. The coupon code has been applied to your cart! Designers should be cognizant of these tolerances when specifying cambers, especially when selecting slab thickness and finishing requirements for concrete floor systems. . . . . 5-2. Levelness implies a tolerance to a plane surface that may or may not be level. The early uses of heat cambering or bending primarily involved straightening members during the fabrication process. . . While the goal when screeding to a uniform elevation is for the floor beam to be close to level once the precomposite dead load is imposed, the expectation is that there will be some net negative deflection that is compensated for when the concrete is placed level. Special levelness requirements will increase the cost of the structure, and if they are not required for serviceability, they do not increase the value to the owner. These types of members usually require costly heat cambering. Joist bearings act as pinned/pinned-end Fig. Fig. Fortunately, by examining the different variables and understanding the role each plays in influencing the beam deflections, it is possible to select a camber value for a beam design that will result in an acceptable final product. Recommended maximum and minimum cambers for various beam depths and spans were given for beams cold cambered by gagging at the mill as shown in Figure2-5. . All Rights Reserved. . Bauschinger effect (Lange and Grages, 2009). Mechanical/cold cambering in the fabrication shop is typically a trial-and-error process where the machine operator uses judgment to advance the ram or rams a trial distance and then releases the pressure and checks the permanent set. Lange, J. and Grages, H. (2009), Influence of the Bauschinger Effect on the Deflection Behavior of Cambered Steel and Steel Concrete Composite Beams, Structural Engineering International, Vol. The temperature can vary significantly across a member as the heat is applied. Design Guide 36: Design Considerations for Camber pdf Download File Size 7.16 MB Authors Lawrence A. Kloiber, Susan B. Burmeister Year 2020 Edition 1 Number of Pages 58 Publisher AISC ISBN 9789999999995 Samples Description Design Considerations for Camber is a comprehensive new document on the art and science of camber. over the specified camber. The strip heat on the flange progresses from the center out, but can be done either in a transverse back and forth pattern or a circular longitudinal pattern moving from the centerline out. Figure 5-1 illustrates two different, yet common, drainage configurations. This is called the Bauschinger effect; at larger loads deformation increases. . Most members are typically manufactured with less natural camber than this maximum limitation. Floor plan framing considerations. . . What is more important is that in this study, the members received by the fabricator had cambers that averaged more than xin.