Beams: Shear splices Vs. Moment splices
Beams: Shear splices Vs. Moment splices
(OP)
Hi...I work in an office (difficult to get clear answers from people, so that's why I come to this website) where we have 3 different basic steel beam splice details:
1. Bolted/Bolted Moment Splice (flange plates bolted, web
clip angles bolted)
2. Welded/Bolted Moment Splice (bot flange plate bolted,
top flange has no plate-it's full pen welded so
as to create an even bearing surface, web clip angles
bolted)
3. Shear splice (web clip angles only-no flange attachment)
I have been told to keep MOMENT splices near pts of inflection/zero-moment areas...but then when would you ever use a SHEAR splice, which has little moment capacity? Thanks!....Biz
1. Bolted/Bolted Moment Splice (flange plates bolted, web
clip angles bolted)
2. Welded/Bolted Moment Splice (bot flange plate bolted,
top flange has no plate-it's full pen welded so
as to create an even bearing surface, web clip angles
bolted)
3. Shear splice (web clip angles only-no flange attachment)
I have been told to keep MOMENT splices near pts of inflection/zero-moment areas...but then when would you ever use a SHEAR splice, which has little moment capacity? Thanks!....Biz






RE: Beams: Shear splices Vs. Moment splices
For floors, where you have the requirement for alternating live loads, you can still use the non-moment shear splice. Again, you are forcing a pin into the structure and affecting the resulting moments.
By using moment splices on a floor you are adding to the rigidity of the continuous beam and perhaps reducing the beam size required....but this is offset by a larger cost of splice.
RE: Beams: Shear splices Vs. Moment splices
One word of caution, dont forget to take into account the deflection. There will always tend to be a very slight 'give' in the connection due to the bolt hole tolerance.
RE: Beams: Shear splices Vs. Moment splices
The additional connection cost is minimal and usually 'disappears' with a competitive bid. The economy in the reduced section size is, generally, far greater. This is partly because I have a personal quirk about only having 4 high strength bolts for an 18" deep beam if that's all that's required for shear. With the additional bolts that I would spec, I can 'make' the cost difference disappear <G>.
Also with any continuous construction in steel, elastic or plastic design, I use web stiffeners (even if not needed; another personal quirk).
The following for simple supported continuous beam design is somewhat simplified:
The alternate loading scenario virtually disappears with plastic design proportioning and the member is essentially proportioned for factored dead load and live load based on it's failure mechanism. The inflection point for total load is a start for the splice if required. On the total load moment diagram, the minimum loading moment diagram is superimposed. This is only to help determine where the splice should really be located and to provide a magnitude of the moment connection required. The splice point is 'juggled' to a location between the original point of contraflexure to equalize the original moment and the reduced load moment. The new moment diagram uses the reduced loading, but, keeps the original plastic design support moments. The splice is proportioned on the maximum of either the moment for the original loading or the moment for the reduced loading and maximum shear at the connection.
The Canadian code requires that plastic design connections connect for 25% of the moment capacity; this is usually fairly easy to attain with high strength bolts and often provides the required splice moment. In addition Class 1 sections must be utilized (less prone to local buckling). This may compel the designer to select a less cost effective section.
Deflection calculations are a bit of a nuisance; as a first guess for UDL loading I usually use 1/3 of the simple span deflection (1/3 * 0.00624ML^2/I; M in 'k, L in ft and I in in^4) for UDL.
An example using a 2 span continuous condition of say 24' and 30' and a factored UDL of 2klf. Combined length is 54' OK. The elastic moment would be approximately 2*27^2/9 = 180 'k, the max simple span moment 2*30^2/8 = 225 'k and the plastic design moment 2*30^2 * 0.0858 = 155'k. No splices for either elastic or plastic and stiff pl over support for both, just to illustrate the economy of the section required. (I haven't checked these for the actual section required and it may be that some of these converge based on sections available.)