structural drawings 4

[haynewp]

According to a recent publication by AISC, "When the engineer turns the structural drawings over to the fabricator the connections discussions start. These take a lot of time that could be greatly reduced if the engineer would indicate actual end reactions on the members." Has anyone been doing this? We usually leave connections up to fabricator,to develop full capacity of member at connection.

 

[Qshake]

My work is mainly with special structures and bridges, we rarely ever leave connection design up to the fabricator. Most of the time this is something that is driven by the owner, who, in most instances, is an engineer as well. For example we do most of our work for State DOTs, Army COE, Federal GSA etc. They simply want to know what they are getting and that all of the coordination issues are resolved before other parties begin work.

 

[austim]

In more than 30 years of practising in a design/construct contractors office and as a sole practitioner consultant, including work on large industrial buildings, heavy plant structures (coal washeries, major conveyors etc), mining structures, steel bridges of various sizes and major temporary work, I have NEVER seen connection design left to the fabricator.

 

[dik]

Unless the connections are wierd and wonderful, with the exception of splice details where moment and shear are required, I usually leave the connection to the fabricator just specify that connection must develop 50% or web shear or something of that ilk, min of 2 bolts, A325 Grade 1, etc... and then check to see if there's not something that's the exception...

 

[LPPE]

I agree with dik. For simple shear connections, I usually just show the end reactions on the drawings and let the fabricator do it, and include a note like dik said.

 

[phuduhudu]

It depends where you are working too. Here in Botswana we have inherited normal British practice which is to give no connection design information to the fabricator and let him design them. Unfortunately I don't think there are any fabricators here who employ structural engineers. What I tend to do is fully design the connections so there is no doubt. But what mostly happens is that the fabricator shows something on his shop drawing and this then gets checked by the engineer. It's kind of like designing connection by guesswork for the fabricator and then passing it to the engineer for approval. I agree with the AISC that connections should be thought through before they get to the fabricator. If you have a really good fabricator then I would discuss them with the fabricator to help with buildability but then that applies to the whole structure and not just the connections. Carl Bauer

http://www.bauerconsultbotswana.com

 

[dik]

Carl:
Not so much with steel, but with other materials where the project is located 'out of the way', perhaps like Botswana, even for simple projects, I tend to 'overdetail' because the control or skill isn't there... saves a pile of questions afterwards...

 

[JAE]

In the U.S. there is a variety of practices, depending on the type of clients and the general size of the project. Per austim and Qshake above, many projects like bridges and power plants necessitate the full detailing of each and every connection.

Some firms have taken upon themselves the task of connection design in all instances, probably out of concern for liability in the wake of the Hyatt Regency collapse, etc.

The firms I have been associated with have progressed from not showing anything to creating a full connection schedule. In cases of unique, odd, or skewed connections, we always detail and design it all. In the case of typical beam/column beam/beam connections we use a standard schedule through a spreadsheet and require our engineers to check each and every connection against the calculated capacity.

For standard connections, there isn't anything wrong with allowing the fabricator to design it, as long as you, the engineer of record, are satisfied with the process and result (checking their shops to spot check the more typical connections and fully verify the complex ones). After all....you are ultimately responsible for the connection...not the fabricator.

 

[suqlainUK]

The tendency in the UK for structural steelwork connections design is to leave them for the Fabricators. Member reaction forces are noted on the design drawings by the original designer who then "checks and reviews" the fabricators connection design and details before approving them for construction. The original designer remains in overall charge of the "design".
Having worked for a Fabrictor in the past, I found that they prefer to do the connections in-house so that they can utilise their "standard cleats and endplates", for faster fabrication in the automated modern workshops.
This split works well as the Consultant make a saving on his fee by not having to carry out this part of the design, and the fabricator is happy as he can design and detail the connection to suit his workshop. A win-win solution.

For structural concrete detailing however the recent tendency in the UK is to leave the reinforcement detailing to the contractor .....once again the Consultant passing on a labour intensive element of the design work onto the Contractor. In this case the reinforcement detailing is rarely checked in thorough detail.

 

[austim]

Is Australia on its own in having promulgated a set of standardized structural steel connections? We have been doing that for about twenty years or more.

For most straight forward connections, we can simply go to our AISC (ie AUSTRALIAN ISC) connections reference, check the number of bolts needed to provide the required capacity, and fully specify the connection (cleat dimensions, bolt diameter and spacing, coping details, weld quality etc) by means of a simple reference to the AISC publication.

The range of connections covered includes welded or bolted splices or end connections and five different types of flexible end connections, plus purlin cleats and base plates.

This practice avoids the need to consider each fabricator's 'special cleats and end plates' since all fabricators are set up for the standard sizes, whether automated or not.

Thus I would suggest that we have a real win/win situation. The fabricators are not faced with too many idiosyncratic connection details, and the engineers have full control over one of the most vital aspects of their designs.

As for leaving reinforcement detailing to a contractor ('unchecked in thorough detail'), my stomach churns at the very thought. The UK lawyers must be rubbing their hand in glee.

 

[LPPE]

The American ISC ASD and LRFD have tables upon tables of connection capacities for different lengths and number of bolts, single shear, double shear, eccentric bolt loading, etc. We also specify that fabricators and erectors be AISC certified. So I don't see much of a problem letting the fabricator do the connection detail (unless it's an unusual connection). Besides, you get shop drawings to review, so you can check their connections then. Also, ask for a connection capacity chart with your shop drawings.

 

[srengr]

Anyone have a good detail for a non-driving prestressed pile splice?

 

[sc]

Just like to add to austims comment that we also allow time for the fabricator to want changes made as they may have different preferences for joint layouts. This is not really a major problem in most cases, as it protects the integrity of our designs by not allowing pin joints to become rigid joints at the fabricators whim.

 

[dlew]

Except for uncommom structures, I left the design of the connections to the steel fabricator.
I always show the design forces for the connections on the drawings, call for the fasteners to be used, and show typical details of the connections.
I check all the connections when the shop drawings are submitted.

AEF

 

[samdamon]

I do commercial, educational and industrial structural work. For simple shear connections, my office shows the gravity service-level reaction at the connection on the drawings, and has the fabricator do a design and detailing for each connection. My office then checks the connection designs during the shop drawing phase. And yes, we really do check it.

Fabricators tend to each have their own favored setup when it comes to shear connections. Some like to use just bolts, others like to weld on one side and bolt on the other, etc. Its impossible to forecast which preference they will have during the design phase. Its no sin to let them design and fabricate connections in a way they are set up for, but of course make sure the connections work.

For welded moment connections, I will also indicate the maximum service level bending moment on the plan, provide a typical detail showing one way to do the connection, then review what the fabricator does during shop drawings.

This approach seems to work ok in this neck of the woods. It allows some flexibility but the Engineer still is doing his job. It also seems to save some time; beats detailing every single connection on the Construction Docs, if you ask me.

However, as mentioned in other posts, if you have a special situation or building, unusual loads, etc, it makes sense to do final details and designs up front. That way there is no confusion or argument about what is required or needed.

 

[RiBeneke]

We were recently called by a fabricator to do some joint (connection) detailing for them on a chemical process building they were constructing.
We encountered a problem on many nodes where multiple bracings or bracings from multiple planes coincided at a node. The designer of the overall structure (the design was done in another country) had given only a maximum force for every member end through his range of load cases but without giving the individual load cases. When we came to design the joints, we were unable to obtain equilibrim of forces at nodes (out by up to 60% of the load) or to determine the critical load paths through the node.
If the structure designer leaves the joint design to someone else, the design information should be given in adequate engineering fashion.

 

Working as designer I always tried to put on the drawing actual loads for special cases. E.g. beam with the other one bearing near the end. Half of UDL will not always apply.
Now I work as Engineering Manager for fabricator. In many cases I decide to lower loads (short filler beams). Sometimes problem is in connection of deep beam into much smaller one. From engineering point of view everything is OK, but connection is difficult to make.
I agree, most fabricators have their own standards and it works very well. Provide all the details by EOR limits the fabricator choice and may be not economically sound.
Many fabricators use sophisticated detailing programs, able to make and check all AISC standard connections.
I agree, EOR should be a (leading) partner for fabricator in design of connections. Experianced Fabricators knows what they are doing.

 

[constructor10]

My approach is to provide a suggested detail and ask for equivalent strength if dealt with differently. I provide also end reactions if it is not necessary to design to full capacity.

I design concrete details fully.