Should the Designer Consider the Construction Process 2

[DRC1]

AggieYank asked in "Contractor Calls About Construction Loading" what responsibility does the Structural engineer have to check the suitibilty of the structure for the contractors equipment. The subsequent discussion has brought me to ask the following question: How much should the engineer consider the construction practice in his design, and what should he communicate to the contractors about the construction loads and sequence to the bidders and contractors.
My take is that although the designer can not consider exactly how the structure will be built, some consideration of the construction process and communication of those thoughts will go a long way in achieving more constructable projects that will go more smoothly and more profitably for everyone. What does everyone else think?

 

[dik]

Over time, it becomes second nature to think about how a contractor will build something... becomes a matter of detailing for constructability.

Dik

 

[Qshake]

I've worked for several clients where the finished engineered product is value engineered by the contractor wherein the client pays for us to review the contractors design and construction. That is the only way I would consider the contractors point of view unless the project were DB. When the client pays for an engineering review and it's in the scope I have no problems with it.

Regards,
Qshake

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[RARWOOD]

Some one has to build the structure, that you design. As Dik mentioned with experience an engineer develops an understanding of how a contractor will construct the building.

Means and methods are not something an EOR should specify, however an engineer should have a basic understanding of how buildings are constructed. A designer looks really foolish if his or her design is not buildable.

I dealt with a project where once the beams and columns were in place it was not physically possible to place the roof rafters. In this case a modification in the design solved the problem.

There was a way that the building could be built. It would have required placing the rafters providing temporary support for them, sliding the 70' long supporting beam in horizontally under the rafters. Holding the beam in place while placing the support columns for the beam. This would have required at least two cranes, probably three and a large number of man hours to complete.

The argument,that when the contractor submitted a bid on the job, he was agreeing that the building could be built: only goes so far. In a case like the one I described above a large contractor will refuse to construct the building until design changes are made. Smaller contractors might walk away from the job, figuring that the loss incurred would be less then the loss if he or she actually tried to complete the project with no changes.

 

[COEngineeer]

I call contractors all the time asking on how they are going to build certain things. Then I put it on paper. Many times though our client is the owner/archictect not the contractor so we have no idea who will build it.

 

[haynewp]

The bottom line is that if you design in ways which cannot be constructed, it will eventually get back to your clients and make you look bad.

I have given guidance on the drawings the stages by which something is to be constructed if it is critical for the design to actually work. But 99% of the time I do not give instructions and leave it to the contractor, unless I notice when something may not be buildable by ordinary methods or if the ordinay methods adversely affect the capacity of my design. There is also something called staged construction analysis that might be of interest to you.

 

[mitchelon]

Isn’t one of our responsibilities to design for economy and also for constructability? Are you going to tell your client “by the way, I’m not sure if you can build this and didn’t even verify if there is a more economical way.” Of course you have to consider how it is going to be built – you don’t have to specify it on the drawings, unless is critical like haynewp mentioned. In concrete construction, for example, labor and formwork are more expensive than the actual concrete. So, don’t design a slab with drop panels that cannot be easily or economically formed with actual lumber sizes or pre-fabricated forms just to save 0.5” in concrete.

 

[whyun]

I agree with the other posts that the engineers should be aware of standard construction processes and reflect them in the details. Occassional extraordinary cases requiring special sequencing may warrant additional notes for the contractor's benefit which they may use or they may use alternate methods of their own.

The bottom line is: documents must be buildable.

 

[Loui1]

Depends. The owner will be pissed if you make a heavy building just to make it easy on the contractor, but will be happy if you design something that gets built on schedule. You gotta balance the two, and I guess that just comes with experience of knowing what things are commonplace.

 

[csd72]

You should design a structure that 'CAN' be built in an efficient and safe manner.

You should not specify 'HOW' it is to be built as the contractor usually has far more knowledge and experience at this than the designer.

Calling up a specific construction method may in fact cost the client more money as the contractor may have put in a better tender if they were allowed to do it their way.

The exception to this rule is when the project involves demolition or underpinning. In these cases I always call up where shoring is required even if I dont call up a capacity.

 

[henri2]

This is most certainly an interesting thread.

The posts I have read in this thread, buttress the widely held view that, the pratice of strucural engineering, depends amongst other things on: the region/area one is located, insurance and litigation concerns, client, nature of project,.....

 

[valleyboy]

In the UK, designers are legaly bound to design structures which are safe to construct by the requirements of the CDM Regulations.

VB

 

[nutte]

As this pertains to the original discussion, the consensus that building designs should be "constructable" is of course true, and that resonsibility falls onto the engineer. Specific methods that will be used, and how these might impact the structure (such as a scissor lift supported by a floor slab) are still beyond the scope of the engineer's work.

 

[Qshake]

I've been in the structural industry for many years and I've not seen a structure so different from the norm that it can't be built. I have, on the other hand, seen contractors bid and win contracts that they don't have the equipment to build.

And,yes, I've worked on structures that require staging and construction related analysis. What we do for such structures is to have available to us an inventory of erection equipment and use probalistic methods to determine the load for the structural element that is under construction in that phase. Typically in these structures the construction loads and vertical loads, wind loads on the structure are very large. Yet, in most if not all of those types of structures the contractor will revise the structure based on his equipment and submit calculations to EOR for review. And that is usually part of our scope for the construction phase.

For Design/build we evaluate specific contractor methods also.

Otherwise we don't design for contractor equipment, we use the applicable codes.

Regards,
Qshake

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[haynewp]

I haven't seen an entire building that couldn't be built but I have seen details generated by people directly out of school or else didn't know what they were doing that couldn't be built. It actually happened to me when I first started out on a concrete project, my boss wasn't happy.

 

[dik]

I had one project, a freestanding curved stair that the contractor didn't want to remove the formwork because he didn't think it would stand up...

Dik

 

[JAE]

DRC1 -
Your original question - I believe that an engineer has a responsibility, but more importantly, an opportunity, to perform great engineering when they do consider somewhat the contractor's means and methods of construction....for exemplary projects.

For the vast majority of construction, though, the systems are usually tried and true and the construction equipment and methods aren't really that big of an issue.

I'd say its a good talent to have, as an engineer, to know when the construction equipment, means, methods, whatever, can become serious issues on a unique project.

 

[DRC1]

Thanks for everyone's interest. I feel that this issues is ne of the hallmarks that seperate good designs from bad. I thik I agree with everyone in general. My question now is is there a systematic way to acheive this? I don't believe the designs in general should specify a method of construction. For example, when we design a structure, we have no idea how the stucture will be loaded. We dont know where the file cabinets will be or the bookcases. We have floor loads that account for that so we are comfortable there is sufficent capacity. Sooo... would it make sense to have a design guide that a.) provided a check list of some basic constructibilty details and b) provided a means to state what the capacity of certian structural elements are during construction?
This may be similar to the British spec Valleyboy was refering to. If you have a link, could you please post it?

 

[JAE]

I don't think a design guide would be very useful - first, it would have to be constantly updated with new equipment, procedures, etc.

Second, I think that when you start up a unique, difficult project, where you know there will be constructibility issues beyond the normal framed building, then it makes sense to start talking to contractors or other experts to work through the initial design concepts. Some of those guys are simply walking talking constructibility guide books.

 

[Qshake]

For each material there are reams of sound details that have evolved with years of input (as you are suggesting DCR1) from both designers and contractors.

You can find such by going to ACI, AISC, TMS, etc and searching for details or design details. Most of the publications for these societies actively support these documents where possible for constructability.

They may not be in a single document but you'll find them.

Regards,
Qshake

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