Why 50%UDL vs. Posted Reactions?
This image below is a marked up plan from the connection engineer on a project that has 50% UDL in the structural specifications from the Engineer of Record (EOR). This is often what happens instead of the EOR posting the end reactions on the design drawings from their structural analysis. The problem is that often times 50% UDL or Max Shear which often governs on shorter beams is often overkill to what is actually loaded on the members.
Cost to the Fabricator, Detailer, and Connection Engineer
What ends up happening is the connection engineer, contracted by the steel fabricator, will over design and often create more unique parts and connections which significantly increases the cost of steel fabrication. Then there are cases where a feasible connection can't be designed, and it causes the connection engineer to mark up plans and submit an RFI like above asking to verify smaller capacities. The detailer then needs to look at these plans and the connection schedules to make sure they adhere to all of these conditions. This slows detailing down and increases detailing costs in having to coordinate some beams being based on UDL and others are based on these marked up plans. The connection engineer then spends more time during shop drawing review having to check the detailer followed this. Worst case, the EOR takes 2 weeks to answer this RFI and comes back disagreeing with the connection engineer and the detailer has to go back into his model and shop drawings and change things.
Cost and Impact to the Engineer of Record (EOR)
EOR's may be saving hours at the early stages of a project by not noting the end reactions on the design plans, but it just comes back to them later on in the project when they have to answer RFI's like this and tie it back to the shop drawing review process.
It also increases RISK on the job when information isn't just easily posted in one consistent way and location for the detailer to follow. The detailer could miss something and apply the wrong connection. This is rare since both the connection engineer and detailer spend extra resources on "checking" to make sure this doesn't happen and everything is caught.
Cost and Impact to the Owner
The Structural Engineer (EOR) is often judged by the building Owner on the weight of the structure he provides since this often is the unit of measure in cost from the contractor to the owner. "What's the price per ton?" The thing is the connection detailing and fabrication can impact the costs in just as big of a way. If connections are oversized it may cause costly extra doubler plates and welding which drives up the cost in the shop. It also might mean bigger gusset plates that reduce the room for MEP routing. So in the end the Owner is paying a higher total installed cost of the building when the reactions aren't posted and the structure isn't thoroughly designed with connections also in mind.
What's the Win-Win Solution?
So what are some options that will help everyone be more cost effective on the project?
When Using 2D Drawings
A couple of win-win solutions here that will benefit everyone is that on beams with larger reactions, post those on the design drawings and then have a min kip reaction note for most of the other smaller beams. This allows you to be cost effective in making the design plans while also being clear the true reactions on larger more complicated beams and braces.
When Using 3D BIM
If you transfer the design model from say Autodesk Revit or from your Structural Analysis package can you ensure the reactions are exported so the detailing system can automatically use these and be taking advantage of by the connection engineer. This doesn't cost the EOR extra time annotating 2D plans and elevations, but helps convey more accurate information than 50% UDL.
It would be great for Structural Engineers to share their thoughts on the benefits of specifying 50%UDL vs. posting the reactions on the drawings and anyone else's suggestions on how we can make this process better.
Detailing Manager
4 年Calculate loads distributed on short beams Using loading charts/load diagrams in structural drawings. As EOR also calculates Loads using this load diagrams....
Structural Engineer (Senior Associate) at Dunbar
6 年or better yet...design them yourself like we do at DMWPV.
Energy | EPC | Project Management | Oil & Gas | Green Ammonia | Green Hydrogen | BIM | Digital Twin | Power To X
6 年Having worked on 3 project where the detailing and connection design was off loaded to Steel fabricator I can totally understand the pain behind this. And to be honest we had a very good steel fabricator which whom we sat down initially and decided during that meeting the blanket load values rather than UDL for all smaller beams. We provided connection force sets for all major connections and blanket values for all minor stuff, but whenever we used to report force value we ourselves used to run a design check to make sure that we are not getting any doublers or excessive weld sizes etc. Like in case shear tabs if used to give batch results, just cause envelope with full axial and shear would lead to huge sizes. Similarly I guess more than the fabricator, it is the responsibility of the EOR to consider the fabricator as part of his team and actually own the final connection design atleast in spirit if not legally. All boils down to proper communication and collaboration. We got several RFi’s but used to make sure that all are relied within two days.
Principal - Structural and Building Remediation
6 年This is a carry-over from the old days, and has no place in current practices by the EOR. Between RAM and other analysis programs is is easy to get all the reactions on the drawings.?