Contractor calls about construction loading
Contractor calls about construction loading
(OP)
"We just want to verify we can use a scissor lift on your slab"
How do you usually handle it when contractors call to make sure they can use a lift / forklift / other machine on your slab, either on grade or suspended?
We have basically said yes in an extremely roundabout, no liability way, assuming it seems reasonable, but I'm curious as to how others handle the calls.
How do you usually handle it when contractors call to make sure they can use a lift / forklift / other machine on your slab, either on grade or suspended?
We have basically said yes in an extremely roundabout, no liability way, assuming it seems reasonable, but I'm curious as to how others handle the calls.






RE: Contractor calls about construction loading
In most floors, the live load value is at least 40 psf if not higher, and with a parking garage live load requirement of 50 psf, this usually doesn't pose a concern relative to overall capacity. But does present a wheel load issue that should be check in terms of slab capacity and punching shear.
RE: Contractor calls about construction loading
This brings up another question though. When designing floor slabs, why aren't they designed for the point wheel loads from scissor lifts? I don't think I've seen a commercial construction job that didn't use a scissor lift on each floor.
RE: Contractor calls about construction loading
When checking construction loads such as scissor lifts, the point loads are usually not in addition to the full design live loads. I check the worst case point load in the midspan of each element without the full uniform live load (use 10 psf? or whatever you feel comfortable with)
RE: Contractor calls about construction loading
RE: Contractor calls about construction loading
RE: Contractor calls about construction loading
You are right that there's more time involved usually. Also, we as engineers should get paid for the value of the services we provide, not the time it takes to perform them.
RE: Contractor calls about construction loading
There seems to be an assumption that the contractor that calls you is shirking his duty and the ones that don't are hiring their own consultants to re-engineer your building for that specific load. You have to consider the distinct possibility that the one calling you is the conscientious one and that no wheel-load design gets done in the other cases. Of course, if they've built enough slabs of similar thickness with similar equipment on top, they probably have a fair idea that it'll work without actually designing anything.
RE: Contractor calls about construction loading
The contractor has the option of using the EOR or someone else to calculate those capacities but should expect to have to pay for that additional service.
RE: Contractor calls about construction loading
www.SlideRuleEra.net
RE: Contractor calls about construction loading
Fork lifts to transport construction material may impose more critical loading.
It is up to the contractor to decide whether they want to pay a nominal design fee or take a risk.
Per 2000 IBC, concentrated design live load for office floors is 2000#. Heavy manufacturing is 3000# and vehicular driveways subject to trucking is 8000#.
RE: Contractor calls about construction loading
We can't dictate means and methods and we shouldn't penalize our client for subjective construction loading (see Whyun's post regarding 2000# or 3000# etc) when in the final structure no such loading exists.
Regards,

Qshake
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.
RE: Contractor calls about construction loading
RE: Contractor calls about construction loading
Hospitals: 1000 lb
Libraries: 1000 lb
Light Manufacturing: 2000 lb
Heavy Manufacturing: 3000 lb
Offices: 2000 lb
Schools: 1000 lb
Retail: 1000 lb
Section 1607.4 says to assume the concentration occurs over a uniformly distributed area of 2.5 feet by 2.5 feet. There is a footnote under Table 1607.1 dealing with point loads in parking garages (distributed area of 4.5 by 4.5 inches).
A common slab we use is: 3 feet on center steel joists, 3-4" concrete on 1" metal deck (non-composite). This can handle a point load of 2000 lb live load distributed over 2.5 by 2.5 feet.
As for a scissor lift, I wouldn't assume it has a distributed area of 2.5 feet by 2.5 feet under each wheel. Also, the point load from one end of a scissor lift can easily exceed 1000 lb. Instead, I'd assume:
-it has a wheel bearing area of 3" by 1" (punching shear)
-the distributed area supporting each wheel is half the distance between wheels, or 18" width strip of slab, whichever is less when checking moment and shear in the slab.
A good guess when designing the slab is that a scissor lift will weigh between 2000-4000 lb. This slab can also handle the factored point load of (1/4 * 4000) distributed over an area of 18".
I think my future plan will be to tell the contractor that it's a means and methods, and that he can hire us or another engineer to check whether he can use a scissor lift on our slab. However, I'll also be able to sleep at night when I dont' get any call on it, and I'm sure the contractor hasn't thought to check before he lifts the scissor lift up there, which is almost always.
Thanks for all the helpful responses.
RE: Contractor calls about construction loading
I've got a couple of articles on slab design that take into account wheel loads for fork lifts and such.
"Slab Thickness Design for Industrial Concrete Floors on Grade" by Robert G. Packard. It was in PCA's Concrete Information
"Concrete Floor Slabs ON Grade Subjected To Heavy Loads" Departments Of The Army And The Air Force Technical Manual
Army TM 5-809-12
Air Force AFM 88-3, Chap. 15
The copy I have is from August 1987. I'm sure there's a newer version out there.
Good luck.
RE: Contractor calls about construction loading
Get the publication by Nucor "Designing with Vulcraft" 2nd ed. They have an example calc of concentrated loads for suspended slabs. And there is a plethora of design aids out there for wheels on slabs on grade. Go conservative on your assumptions and "suggestions" (never "recommendations") so if he overloads it and something does happen then there's no chance you're going to court.
RE: Contractor calls about construction loading
"Also, we as engineers should get paid for the value of the services we provide, not the time it takes to perform them."
That paradigm shift nearly knocked over my building.
RE: Contractor calls about construction loading
If it's not properly designed, it'll fall over and cost millions. Therefore your work is worth millions. Good luck charging the customer for that.
I've seen previous comments on basing charging on a percentage of project cost due to liability, rather than just an hourly basis, and assumed that was what was intended.
RE: Contractor calls about construction loading
However, giving away services (answering construction related, means and methods questions) only further erodes the value that an engineer brings to a project.
Typically your contract is with an owner or contractor. Your scope of work should be clear as to who is responsible for construction engineering. If it is not in the contract, additional fee should forth coming. The other thing to consider is your insurance carrier. Does it cover means and methods?
RE: Contractor calls about construction loading
RE: Contractor calls about construction loading
After you do a few of these calcs, it does not take all that long to do another one once the contracotr provides the maximum wheel load. I can do most of these in 15 to 20 minutes.
The hour (or less) you spend on this will be more than paid back in a better working relation with your contractor. I find, for the most part, if you treat the contractor with repect and help him/her out when you can, they tend to help you out when they can, say, when your mistakes come to light. (And we all make mistakes on every job we do. ) A good working relation with your contractor can significantly reduce the amount of time you spend on a project in the construction phase. It also has the additional bonus of reducing your stress level significantlyy.
In addition, on a fair percentage of projects we do these days, the contractors are on board before we are. Either through deign build or through existing relationships with the owners. We get a fair portion of our workload through contractor recommendations. They appreciate the help on the little things, like this, that we do for them, and so return the favor by recommending us for projects. Don't develop a reputation as a difficult engineer to work with. This will come back to haunt you in a lot of ways over the years.
RE: Contractor calls about construction loading
There is a time and place to be hardnosed to the contractor. This is not typically one of those instances.
RE: Contractor calls about construction loading
I have checked the calculations of good respected engineers with 30 or more years of experience and I always find mistakes (even though they are sometimes small ones). If you build up a good relationship with a contractor, they will tell you if something does not look right, if you build up a confrontational relationship then they wont tell you.
I agree that we should not give away free advice, but surely there has been an allowance in the design fee for construction queries.
RE: Contractor calls about construction loading
Don't forget the saying: "No good deed goes unpunished".
You might build a good buddy relationship with the contractor by offering him "free" services in helping him out with construction loading issues, but if something goes wrong, that good-buddy relationship will not exist.
I agree with building a good working relationship with contractors. I treat them with the utmost respect and they know that I respect them for what they do.
But that doesn't mean charging them for legitimate engineering services is being hardnosed.
It takes time to verify any sort of construction loading and I would suggest the contractor is being hardnosed, or disingenuous, to suggest that you shouldn't get paid for it.
RE: Contractor calls about construction loading
With the above being said, if a mistake by me comes to light and the contractor is able to fix it in an efficient, low cost manner I appreciate it. In the same way that if a construction mistake happens, I will work with the contractor to design an efficient, low cost solution. Construction mistakes and design mistakes are separate from means and methods of the contractor and should not be confused as the same.
RE: Contractor calls about construction loading
JAE is right about potentially paying the price after being a good Samaritan. Not just in the construction industry either.
RE: Contractor calls about construction loading
'Designing with Metal Deck' By Vulcrat has good examples and explanation of how to check this. Once you have done it, and understand the methodolgy, it does not take very long to do it again for different deck and wheel loads.
If I can do this to help a contractor out, it goes a long way to establishing a good working relationship with the contractor.
This good working relationship saves ME considerable time and stress during the construction phase. Thus paying for itself mutliple, mutliple times over. If you want to make a profit on your construction phase services ( assuming you contracted for a lump sum fee), working with your contractor (within reason of course) goes a very long ways towards acheiving ths goal. If you are desirious of losing money on your construction phase services, fight your contractor every step of the way. See what happens.
It has not been my expereince at all that trust between engineers and contractors is an old fashion idea. Quite the contrary. Maybe I have just been fortunate to work with good contractors and subs, but it is a very rare occasion when things aren't worked out in a team-like fashion on our projects. Maybe others have different expereinces. I am just relating my expperience over the last 15 years.
RE: Contractor calls about construction loading
Ask a contractor to add to his scope and see if he is willing to do it for free.
RE: Contractor calls about construction loading
RE: Contractor calls about construction loading
While I'm all for being generally helpful and furthering relationships, we're not here to make friends, we're here to make money. I'm sure that no contractor would show up at my house to do a few hours worth of work, such as pouring a patio or driveway, for free, especially just to help our relationship. I see no reason to open myself up to more liability plus the losing the time that gets donated to the "contractor needs a new boat" fund.
I believe also that not everyone can be lumped into the same boat. If you have a client who has been good to you for 10 years, yes, help him or her out. If it's a new client, someone you don't know well or trust much, you really need to cya first, help second.
RE: Contractor calls about construction loading
RE: Contractor calls about construction loading
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Contractor calls about construction loading
RE: Contractor calls about construction loading
I am saying that the means and methods of constructing a building are typically the contractor's responsibility and if you, as the EOR, dive in to "help" the contractor with free means and methods services, this doesn't magically make you a "team player" or represent the only means to build a good working relationship on a project.
And you are definitely....absolutely....exposing yourself to a higher level of liability - anything that goes wrong with the structure that is in any way remotely associated with the scissor lift will be, to some degree...your fault. I've been practicing engineering in multiple states for over 27 years and I've seen so many times when this has happened to engineers. One crack in the floor and its "Hey - the SE told us we could put this unit on the floor and look what happened."
This doesn't mean you shouldn't do it. I'm only agreeing with what SperlingPE said above: "Legitimate services should not be given away"
I am all for "establishing a good working relationship with the contractor". I do this ALL the time and I agree with you lkjh345, that it's a great idea.
But we engineers are professionals who provide services that have value and it is NOT unreasonable to simply charge an appropriate fee for that effort as it validates that we are SERIOUS about what we do and SERIOUS about the question they pose to us about some dumb scissor lift.
And despite what I said above, sometimes it does take a significant amount of time to properly check a floor for a scissor lift which will be driven all over the place...there could me multiple spans and conditions which should be checked....for a complex floor system, it could take up to one or two days to do it right.
RE: Contractor calls about construction loading
RE: Contractor calls about construction loading
The structural engineer's job is to design a building that in its final state will meet the owner's and the building code's requirements. In its finished state, an office building will not have a scissor lift in the break room by the coffee maker, so the floor shouldn't be designed for it.
It is the contractor's job to build the building. How he gets there is his responsibility, the "means and methods" of construction. If he needs to shore floors before they're complete, brace columns before the framing is all tied in, it's his job to figure that out.
As weird as this sounds to some, this has been standard practice for a long time. After all, there is more than one way to get a building built. If the engineer did want to check these things during the design phase, how would he know which methods the contractor is going to use? By leaving this up to the contractor, he has the flexibility to proceed with construction as he sees fit.
RE: Contractor calls about construction loading
One exception I see is a design-build situation where contractor hires the EOR to do both.
RE: Contractor calls about construction loading
Regards,

Qshake
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.
RE: Contractor calls about construction loading
As an addendum to nutte's comments. There are many ways in which to build a given type of building, and the choice of which depend on factors like timescale, cost, health and safety, and availability of labor/equipment.
Most of these are beyond the scope of structural engineering and those that are not are not usually known at the time of design.
There are also a lot of personal preferences of individual builders.
You can be guaranteed that if you did design all the temporary works for a building project, then the contractor would call up asking to do it a different way.
Bridges are a different case altogether, and it is usually the construction method that dictates the design (part of the reason why design and build is more common for bridges).
RE: Contractor calls about construction loading
Design build in the transportation/infrastructure is relatively new due largely to the fact that nearly all states were locked into the idea that the owner should have complete oversight of the engineering and construction but that construction should not be involved with engineers or vice versa due to conflict of interest and that is possible the engineer would not be acting in the best interest of his contractual client. Since DOT's are funded by State and Federal funds it actually takes an act of congress to allow D/B to exist in any one state. At this time, the majority of states do not have D/B provisions. Of those that do, Florida is probably the most active in this area.
In the bridge industry we stay out of contractors means and methods. In some cases this comes close to lunacy. For example, segmental bridges. Bridge Designers can design them and produce plans for them. But construction methods for segmental bridges is highly proprietary and in most cases, the winning contractor will redesign the bridge for his equipment thereby forcing the EOR to review the contractor's work. In this scenario, the DOT pays for the design twice.....crazy!
Regards,

Qshake
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.
RE: Contractor calls about construction loading
RE: Contractor calls about construction loading
As some of you have figured out and some of you have not, We are all building the same structure for the same client, the owner. I am not suggesting that upon completion of the design you gratuiosly take on all the design functions for the contractors. But knowing that equipment wil be needed, you could give guidelines to what can be put on the slab after say 7 days vs 28 days. Other construction considerations can be incorperated in the design and guidelines set in the contract documents. This would not be free but would be billed to the owner as part of the design. What would the owner get out of it? by having these details, contractors could more accurately plan their work resulting in better bids. There would be less time lost worring about details such as lifts, becuase invariably some of these questions come up at the last minute and it is a fire drill in order to keep the project moving. Thus by eliminating these questions the job flows smoother.
I know I may have been baiting a bit, but it never fails to amaze me that we believe that the design and construction of any structure is two seperate and isolated functions. Guys we are different instuments in the same band.
RE: Contractor calls about construction loading
So looking a bit more at this situation it is not that we are ignorant of the construction loading or that we maliciously refuse to be of help, it is a matter that was decided by the court of law many decades ago and is certianly being upheld on occasion to this very day.
In my opinion, the contractors have a lot more responsibility for being in their current position with respect to construction loading than you're presently giving them.
Regards,

Qshake
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.
RE: Contractor calls about construction loading
RE: Contractor calls about construction loading
I see your point of view, but think you're making a mountain out of a molehill for something like a scissor lift. If you go conservative and document correctly, doing this yourself will save yourself money and liability issues in the long run.
I'm not the contractor's favorite guy out on the jobsite, but he repects my decisions and recommends me to others. Asking for an extra on something like this will give you the reputation of a nickle and dimer. Typically, thats not a good image to portray to the construction community unless you're really that good and people are begging to work with you.
Proper judgement must be used. If they plan on placing a crane up on an elevated slab, then yea, you probably have a point in asking for money or telling the contractor to go ask someone else, but not for something fairly straightforward as the original post describes.
RE: Contractor calls about construction loading
RE: Contractor calls about construction loading
RE: Contractor calls about construction loading
You could also consider pallet loading, temporary shoring for deep concrete beams / walls, etc.
Designing for every temporary construction load would limit the contractor to the means and methods you've decided upon, which would almost definitely be more expensive and less efficient than what the contractor may choose, based on his expertise and experience in his field, not to mention what is available to him. Only if you're working alongside the contractor in a design/build atmosphere would this be a good idea. It's my guess that even in design build, temporary construction loads are designed for as the project gets close to that point, and not upfront in the design process.
The alternative would be to design your building for the worst case possible scissor lift, forklift, pallet loading, etc, to not limit the means and methods of the contractor, but you'd end up with a building that costs 50% more than it should.
RE: Contractor calls about construction loading
1. Means and methods are typically not part of the EOR's contract. Insurance carriers will scrutinize any work done that is not contractually required.
2. The amount of time it takes to do a loading check is irrelevant. It is still giving away engineering services. Respect the engineer enough to pay for legitimate work. Respect a contractor enough to pay for legitimate work.
Working with a contractor to solve problems that arise during construction (design ommisions / contractor mistakes) are most certainly a part of any job.
RE: Contractor calls about construction loading
I agree that it's giving out a free service, no doubt about it. Though, unless some unified organization bands us structural engineers together so we all do it and it becomes commonplace, then I "could" make a stink about it to the contractor. But as we all know, that isnt the case and I have to worry about the next project. Therefore, that is why I push my pride to the side and take 5 minutes, go conservative, and give the contractor an answer. If it doesnt work by conservative methods, then I tell him it wont work and they almost always have no problems about it.
Do you charge for analyzing baseplate slotting too? What misplaced auger cast pile groups? The list goes on.
RE: Contractor calls about construction loading
RE: Contractor calls about construction loading
The construction started up and things initially went well, but very soon after we started getting all sorts of calls from the contractor. The superintendent just wasn't very good. Anchor bolts were bent, some were in the wrong place. Footings were placed in offset locations. There were perhaps six to 10 problems that we had to fix.
In all of these situations we responded for the best interests of the Owner, our client. We sketched up fixes, visited the site, took photos, explained to the on-site super what was required in the plans. Basically we went the extra two miles.
After about a month of this we started complaining to the superintendent and to his project representative/manager that this was getting out of hand.
Next day we get a message from our president that the contractor was coming over to our office to discuss how we weren't behaving in a "team" manner. The president of the construction company, his VP, his PM, and some of the superintendents all showed up. We sat down in our conference room and the president of the construction company began complaining that we weren't responding fast enough to their RFI's and other requests.
Needless to say, we were quite P.O.'d. After the guy finished, I responded that I appreciated team effort, but fixing four to five field mistakes, all free of charge, to me - represented a very high level of Team effort.
Our architect PM also responded that in his experience he found that whenever there was a mistake or field error by the contractor then - boy - we should all be a team and pitch in to make it right. But if there was any sort of error on the A/E plans then the contractor immediately charged extra for the cost. This wasn't very team oriented at all.
The president of the construction company hadn't heard that there were numerous field errors that we had fixed for them without charge. We could tell that this was all new to him. He glanced over at his people and got up, said, "sorry to have bothered you - you are right" and left...his people following with, I could swear, tails between their legs.
This seems to happen a lot with poor quality contractors - there is a disconnect between the construction company leaders and the field personnel such that we A/E's sometimes get painted with an unfair brush by the field folks. And this leads to a lack of team attitude on everyone's part.
This isn't directly associated with this thread, but does go to show that simply offering the contractor free engineering help doesn't always make it to the top of the contractor organization, and as a result can eliminate any good will that you intend by offering free services.
RE: Contractor calls about construction loading
Regards,

Qshake
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.
RE: Contractor calls about construction loading
I’m with JAE and those who have said that means and methods are the responsibility of the contractors. Liability is the word here. I would agree to review the calculations of their construction ENGINEER, but even then, I would not approve the use of the fork lift. I would either review or disapprove.
RE: Contractor calls about construction loading
Even when dealing with good and reputable contractors, consulting engineers still have to put the guards up these days. Haven't seen much favors being exchanged between companies lately.