Cambering In Steel Beams - Structural Engineers
Image courtesy of CAMBCO Inc.35Introduction to CamberingCambering is the process of creating an intentional slight curvature in a beamImage courtesy of CAMBCO Inc.3618
Introduction to Cambering Camber in a beam can be designed to compensate for either: A certain percentage of the dead load deflection The full dead load deflection The full dead load deflection as well as a percentage of the liveload deflection(Ricker 1989)Camber is usually designed to compensate for deflections causedby pre-composite dead loads37Advantages of Cambering Supporting beams will deflect under the load of concrete being placed This deflection can be exaggerated in a composite floor system where the fullstrength of the system is not achieved until the concrete has cured Cambered beams (top diagram above) should deflect to a straight line (bottomdiagram above), if load and deflection are predicted accurately and camberequals deflection This allows the floor slab to be flat while maintaining a consistentthickness(Larson and Huzzard 1990)3819
Advantages of Cambering If beams are not cambered (top diagram above) the deflection under the loadof the wet (plastic) concrete will result in a ponding effect in the concrete(bottom diagram above) To create a flat floor in this situation the concrete will need to be thicker at thecenter of the bay where the deflection is the greatest The volume of concrete used will typically be 10-15% more than if the floor is aconstant thickness(ASCE 2002)39Disadvantages of Cambering The use of cambered beams will, to a certain degree, be limited by otheraspects of the design for a structure Due to the complexity in detailing, fabrication, and fit-up associated withmoment connections (above left), camber should not be used in momentconnected beams Beams with simple framing connections (above right) may be camberedbecause the end rotational resistance of a simple connection is small incomparison to that of a moment connection4020
Disadvantages of Cambering1Specified Top OfSlab Elevation2 The processes used to create camber in beams as well as the actualdeflections under load of cambered beams are not exact Care needs to be taken in the specification and fabrication of camber to ensurethat a beam, once in place and under load, will perform within tolerances Levelness and consistent floor thickness can be a problem The diagrams above show two possible results of cambered beams notdeflecting as predicted under the load of the wet (plastic) concrete1. Stud heads are exposed2. Top of slab elevation out of tolerance(ASCE 2002)41Alternatives to Cambering21Alternative methods forachieving a level floor slabwithout using camberedbeams include:1.Pouring a slab ofvarying thickness overdeflecting beams2.Using over-sizedbeams to minimizedeflection3.Shore the beamsbefore placing theconcrete(Larson and Huzzard 1990)3ShoringConcrete At75% Strength4221
Shoring Shoring may be used in lieu of cambering The construction documents must specify the use of shoring There are several advantages to using shoring: Lighter floor beams may be used Cambers do not need to be designed or fabricated Less beam deflection allows for better control of the slab thickness Shoring can accommodate a contractor’s special loading requirements43When to Camber Girder Beams Filler Beams Members with uniform cross section Composite Floor Beams(Ricker 1989)4422
When Not to Camber Cantilevered Beams (above left) Braced Beams (above right) Crane Beams Spandrel Beams (above right) Moment Connected Beams(Ricker 1989)45When Not to Camber Beams with moment connections(above left) Beams under 20 feet in length(above right) Beams with non-symmetricalloading Beams with end plate connections(Ricker 1989)4623
Heat CamberingHeatedAreasBeamSupport Beams may be cambered by applying heat tosmall wedge-shaped areas at specificincrements along the beam (Ricker 1989) The beam is place upside down on supportsso the “bottom” flange can be heated The heated flange expands under the heatand contracts as it cools Camber is induced in the opposite side of thebeam as the heated flange cools Advancing this slide will begin an animationwhich shows the expansion and contractionthat occurs in a heat cambered beamTop Side of BeamWhen InstalledThe animation will repeat after several seconds47Installation of Heat Cambered Beams A heat cambered beam should be erected with the heat marks on the bottomside of the beam (see top diagram above) This places the beam in a camber up (or concave down) orientationHeat marks can be seen on the beams in the bottom picture above4824
Cold Cambering Cold cambering methods are more widely used and generally moreeconomical than heat cambering The beam is mounted in a frame and force from a ram(s) is used to bendthe beam to create camber(Ricker 1989)Image courtesy of CAMBCO Inc.49Creating CamberImage courtesy of CAMBCO Inc. Cambering is most commonly done at the fabricator’s shop after theconnections are fabricated (AISC 2000) The fabricator may mark cambered beams to ensure proper installation5025
Natural Mill Camber Natural mill camber, which is a slight camber present in a beam when it isreceived from the mill, will exist in most beams If the natural mill camber is at least 75% of the specified camber, nofurther cambering by the fabricator is required If camber is not specified, the beams will be fabricated and erected withany natural mill camber oriented up (or concave down)(AISC 2000)51Cambered Beams on Structural PlansCambered beams should be clearly marked on the structural plans (AISC 2000)5226
Cambered Beams on Structural Plans The structural plan above shows which beams are cambered The amount of camber is indicated for each cambered beam c 3/4” indicates that the beams are cambered 3/4” at the center c 1 ¼” indicates that the girders are cambered 1 ¼” at the center53Installation of Cambered Beams The installation of cambered beams is similar to that of other structuralsteel members No additional tooling, equipment, or hardware should be required5427
Quality Control Per the AISC Code of Standard Practice “camber shall be measured in theFabricator’s shop in the unstressed condition.” (above left) The amount of camber specified on the shop drawing (above right) is forthe beam center line in an unstressed or unloaded conditionTolerances for camber are specified in the AISC Code of Standard Practice: Members 50 feet or less in length minus 0” and plus 1/2” Members over 50 feet the plus tolerance is increased by 1/8” for every 10feet over 50 feet(AISC 2000)55Quality Control It is possible for all or part of the induced camber to come out of a beam duringshipment to a jobsite This is acceptable under the AISC Code of Standard Practice (2000), but thefabricator’s quality control procedure should provide verification that thespecified camber was measured in the shop5628
Cost of Cambering Cambered beams require additional fabrication resources which will makethem cost more than non-cambered beams The additional cambering cost should be compared with Cost of additional concrete due to “ponding” Cost of using shored construction Cost of using a heavier section that does not need to be camberedImage courtesy of CAMBCO Inc.57Cost Savings from Cambering The cost to camber beams may be less than the alternatives A cost comparison can reveal the savings associated with the use of camberedbeams Larson and Huzzard (1990), in their study of cambered beams anduncambered beams found a cost savings of approximately 4% A 30’ x 30’ bay size was used Filler beams were spaced at 10’ o.c.5829
Impacts on the ScheduleImage courtesy ofCAMBCO Inc. There will be an increase in fabrication duration for structural steel to accountfor time required to create camber in beams The amount of time required to create camber is dependent on a fabricator’sinternal scheduling and fabrication methods59Impacts on the ScheduleDelivery, shakeout, and erection durations should not be impacted by the use ofcambered beams6030
beams include: 1. Pouring a slab of varying thickness over deflecting beams 2. Using over-sized beams to minimize deflection 3. Shore the beams before placing the concrete (Larson and Huzzard 1990) Alternatives to Cambering 1 2 3 Shoring Concrete At 75% Strength
1501.13 Rolled Beams with Cover Plates 1502. Heat Cambering of Rolled Beams and Welded Plate Girders 1502.1 General 1502.2 Heat Cambering of Rolled Beams -1502.3 Heat Cambering of Welded Plate Girders 1502.4 Support of Members for Heat Cambering 1503. Heat Straightening D
Residual Performance of Structural Steel Beams after Plastic Deformation and Strain Aging . trimming, protrusions, cambering, etc., may be unsuitable for reuse. However, scientific basis is needed to . steel that strain aging can result in a favorable
Over the last 20 years many changes have occurred in the steel construction industry. Years ago, the steel mills provided most of the cambering while today the Fabricator typically does the cambering in his shop. In the past, the Fabricator had to straighten the steel before fabrication to re
Prestressed beams were separated by box beams and I-beams to evaluate their performance individually. Figure 2-3 shows that box beams reach poor condition at 35 years. Figure 2-4 shows that prestressed I-beams reach poor condition at 52 years. Figure 2-6 displays both deterioration curves within the same plot. Notice how the box
prestressed steel beams can present both structural and economic advantages when compared with non-prestressed (traditional) beams. . cambering it upward with a concrete slab, and jacking the beam downward again. Method 3: Apply tens
Table 2.11: Panel grades* for box beams and I-beams Selection BEAM WEB SERVICE CLASS PLYWOOD BS EN 636 PARTICLEBOARD BS EN 312 OSB BS EN 300 MDF BS EN 622-5 FIBREBOARD BS EN 622-3,4 CBPB BS EN 634 Box beams and I-beams 1,2 636-2 P5 OSB/3 - HB.HLA2 - *The table provides the minimum grade of panel that satisfies the particular set of requirements .
Castellated beams spanning 25 meters and featuring important camber 3.2. Customization of castellated beams 3.2.1. Curving or cambering Where required to accommodate architectural or serviceability issues (i.e. to meet requirements of unique roof
Am I My Brother's Keeper? On Personal Identity and Responsibility Simon Beck Abstract The psychological continuity theory of personal identity has recently been accused of not meeting what is claimed to be a fundamental requirement on theories of identity - to explain personal moral responsibility. Although they often have much to say about responsibility, the charge is that they cannot say .
