Girder Beam Sizes
Charise Farag
As with any design problem there are many solutions. Each project will have a unique set of loading and serviceability (deflection and vibration) parameters. The design information and example have been prepared accurately and consistently with current structural design practice for multiple load cases. The information presented in this publication has been prepared in accordance with recognized engineering principles and is for general information only. While it is believed to be accurate, this information should not be used or relied upon without competent professional examination and verification of its accuracy, suitability, and applicability by a licensed professional engineer or architect.
Many specific parameters and limitations go into the design of any structural member. Loads imposed by earthquake, wind, snow, rain, construction methods, etc., vary across the country. Live loads are generally specified in the applicable building codes. Dead loads are much more variable and require special attention in their computation. Specific requirements for strength, serviceability, lateral stability of individual elements, and the lateral resistance of the overall building all contribute to the design of a safe and efficient building. The information presented in the following tables is intended for use in establishing preliminary floor and roof framing member depths only, without regard to earthquake loading or contributing to lateral resistance of the building.
Beam spans in these tables range from 15-feet to 45-feet, in 5-foot increments. Girder spans also range from 15 feet to 45 feet in 5-foot increments for each of the beam spans noted. Therefore, beam/girder depths tabulated cover 28 different bay sizes for each of three load cases. Dead loads address the self-weight of the floor/roof framing system. Different topping-slab thicknesses, concrete densities, and beam spacings options have been presented to address varying preferences around the country to address required floor/roof fire rating requirements as well as local availability of concrete aggregate.
You were right to call out the missing brackets. May just be the angle, but looks like those posts are warped and twisted already. How were they attached at the bottom?
Also from here it looks like those bottom plates are not treated?
To any that may still be following this a year later it has been resolved. After threats of lawsuits and an engineers evaluation it was found that both the posts and fasteners were a defect. The issue was fixed by sistering up treated 2x8s and 2x6s for the full length of the posts as well as overlapping any boards possible 2 feet above the post and onto the girder beams. All were fastened with treated appropriate 3 inch nails one of which I was able to confirm because it was a misfire banana out of the side of a board.
Finally after engineering reports and threats of litigation the builder did the right thing. Thanks to all for the help on this one.
In many cases, the load strength can be restored with steel straps or by sistering of the structural member. It really depends on the size/location of the notch and the obstruction placed within the framing member.
A 1/4" thick flitch plate same size in depth of the girder or beam is installed on one side or two sides depending on the stregth required to make the repair. 5/8" 307 bolts are used to bolt through the plates and beam in an alternate pattern and the jack is removed.
Size of notch and span affected determines the length of the flitch plate.
What I was talking about is something like the pictures below where the beams are overspanned, and broke in the middle due to a hole drilled for a light.
I also have a string to show the deflection, if you look close. The beam is also over spanned, framed in the wrong direction and broken at the light.
This is what I done to fix it.
The Type AF girder clamp is used to achieve a fast steelwork fixing connection where high load capacities are present in either tensile, frictional or combined load directions. It has a recessed top to hold the bolt head captive while the nut and washer are tightened down using only one tool, alternatively use a Type AFW washer to convert the recess to a flat top. The skirt on the underside of the clamp abuts the edge of the beam flange and prevents the clamp rotating during installation. Manufactured from SG iron with a hot dip galvanised finish to provide high performance and anti-corrosion protection.
The clamp is available in two tail lengths, Short or Medium, and can be used with Lindapter packing pieces to increase the clamping range. Choose the correct combination of tail length and packing pieces to suit a specific flange thickness. Download datasheet for selection table.
These plates ensure the clamps and bolts are located in the correct position relative to the supporting steelwork. Location plates are simple fabricated items designed to sit between the two sections to be clamped together to ensure the bolts are fixed at the correct centres. End plates are simple fabricated items that are pre-welded to support frames, bracket or sections, allowing connection to the supporting structure with standard Lindapter clamps. Download datasheet for further information.
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Steel girders and beams make up the primary support system of buildings, bridges, ships, and other large structures. Both are fabricated to transfer weight-bearing force into support columns and down into the foundation, but is there a difference between a girder and a beam, or are these two names for the same thing?
Both beams and girders need to be precisely manufactured to support the weight of a structure. This includes exact measurements for the flanges and webs. Structural steel fabricators rely on state-of-the-art, CNC plasma-cutting technology like BeamCut to ensure their work is spot on.
The following sections, except those specified as modified, shall be preferred because of their familiarity to local precast plants. These sections have been entered into the beam section libraries of in-house design software. The top flange height and overall height may be increased if required but any deviation from the standard sections shown shall be discussed with Structural Project Manager or Structural Liaison Engineer. The use of the modified girders shall be discussed with Structural Project Manager or Structural Liaison Engineer.
These charts only contain data on designs with a concrete compressive strength equal to 8.0ksi, this is due to a lack of sufficient data for designs using a concrete compressive strength of 6.0ksi or 7.0ksi.
No limits are set for other types of prestressed girders however the Structural Project Manager or Structural Liaison Engineer shall be consulted prior to the design of any unusually long prestressed girder.
Non-Integral end bents with skews greater than 40 degrees shall always have girder ends coped. Skews less than 40 degrees shall have girder ends coped on case by case basis. It is preferable to not cope across the web.
Check clearance from fill face of integral end bents to bottom flanges of NU girders. Maintain 3-inch minimum clearance. Coping may be permitted with approval of the Structural Project Manager or Structural Liaison Engineer.
Girders shall be first designed assuming that the contractor will vary the joint filler supporting the panels on the girder flange. This assumption will maintain the minimum slab/panel combination thickness of 8 1/2 inches, and will eliminate the possibility of increased load due to varying slab thickness.
The girder and bearing designs should be checked for the constant joint filler option and constant joint filler load. However, camber, haunching and beam seat elevations shown on the plans should be based on the variable joint filler option.
The prestressing force may be assumed to vary linearly from zero at the point where bonding commences to a maximum at the transfer length. The transfer length may be taken as 60 times the strand diameter.
Harped strands, although they add to the shear strength of the girder, are primarily used to keep the girder stresses (both top and bottom) within allowable limits while developing the full capacity of the girder at midspan.
Harped strands should be held down at points of 0.4 of the distance from each end of the girder. Distances along girder to hold-down devices and between hold-down devices should be reported on the plans to the nearest inch. Per Sec 1029, precaster may position hold-down devices +/- 6 in. longitudinally from position shown on the plans.
The jacking force applied to prestress strands produces an excessive vertical uplift in short spans on tall girders resulting in failure of harped strand hold-downs. The allowable limits for hold-downs are as follows:
If necessary lower harped strand end location to meet criteria or use straight strands only. Investigate the possibility of using all straight strands when strength check of a hold-down device exceeds allowable.
Using all straight strands for girder lengths less than 70 feet shall be investigated for Type 6, 7 and 8 girders and all NU girders in order to reduce risk of strand or hold-down breakage, increase safety by reducing risk of injury during fabrication and reduce cost.