metal building versus conventional steel framing

[archeng59]

What is anyone's experience with cost comparisons between a conventional steel framed structure versus metal building framing. Not pre-engineered metal building, but a custom building using metal building components. Conventional steel framed building is hot-rolled wide-flanged beams and columns, bar joist and metal deck roof, cold-formed stud walls. Custom metal building is one that does not utilize the metal wall and roof panels, but a different veneer system such as brick and a standing-seam roof with rigid insulation. I work with several architects who believe that as long as the structural framing is metal building components, the building costs must be significanly less. I contend that as long as the owner uses an off-the-shelf pre-engineered metal building with no modifications, that is the most economical. When either system is custom designed, there really is not a signifant difference in cost between a custom metal building and a conventional steel framed structure. Assuming the foundation is essentially the same regardless of framing system. I know there are alot of variables involved, but wondering if in general terms, am I off base here? Looking at the RS Means data, I believe I am correct.

 

[CTW]

You can't tell me that when owners are pushing for the cheapest product out there, that they don't know that they're getting a less durable building.

There are some owners who realize this and seek lowest cost over longterm performance, but I really think that most owners don't know what they're getting. What they hear is "our building meets code". That's true, but code minimum does not equal durability and serviceability.

 

[dik]

mtu1972... you aren't doing something to the building that will void the warranty? are you? Gotta be careful.

Dik

 

[JLNJ]

It's been my experience that owners and architects don't realize that PEMBs engineer right down to the nut. Generally speaking you get the absolute minimum factor of safety on every component.

We had a PEMB with modifications made (by others) to the columns, but the factor of safety was cut so close the modification ended up in a catastrophic failure (and lawsuit). My opinion is that almost any conventionally framed building would have easily survived the same modification.

It seems to me that PEMBs (and gas station canopies for that matter) suffer a disproportionate number of failures due to the fact that they cut it so close. Even designed to the same codes, the effective safety factor is less for a PEMB than a conventionally framed building, but the Codes were written around conventionally framed structures. Each PEMB component is skinnied down to the limit. Stability bracing is right on the edge. Deflections are run to the limit and are often based on a 10-year wind. Watch the Weather Channel and look for the crumpled Pre-Eng buildings and fly away gas station canopies.

 

[271828]

JLNJ, so if I understand you correctly, you're condemning MBMA companies because one designed and sold a product to an owner that was presumably exactly what the owner wanted and satisfied published codes, specs, and standards and then someone else came in and did one of the following:

1. Modified the structure and didn't run design calcs to make sure it was OK or

2. Modified the structure after incorrectly running design calcs, screwing up, and incorrectly determining that it was OK.

I don't follow your logic. I've worked on plenty of conventional bldg projects in which we modified the existing structure. It was MY responsibility as the new project EOR to make sure *I* wasn't going to cause a problem. You and several others in here seem to me like you're intimidated dealing with and competing with optimized designs, so you'd be happier if everybody else was too. In my experience, that kind of thinking doesn't lead to a very robust business model!

Not just to you, but to everyone else in here also:

If MBMA companies have it all wrong, then why don't you get together and start a competing trade organization? You could call it SMBMA (Strong Metal Bldg Manufacturers Association) or some other catchy name. Design your bldgs to tighter deflection and drift limits and avoid the use of slender elements. Heck, avoid the use of any element that requires more than Steel I to design, so that other folks won't come in later and struggle trying to figure out if they can safely modify it. Use only CMU, precast, brick, EIFS, etc. cladding and no cheap metal panels.

I think you guys should be able to sell the concept to owners, GCs, and architects. If you're just in here for a gripe and whine session, then forget the suggestion. Griping and whining is something that I think of being done by old gossips with nothing better to do, not highly educated professionals.

 

[mtu1972]

dik -

I'm not doing anything to the building. I specified the loads, including all specialized equipment, etc. and our designer provided interface on pipe chases, pipe racks, etc.

They were direct hired by the Contractor (who was really a Construction Manager) and we had several coordination meetings as to where and how we would do thickened floors, etc. if the building were convetionally framed.

Thanks for the warning about the warranty though - because invariably we will be called in for rebuild upgrades.


271828 -

I realize that this will become all the more prevalent as the years progress. Let's face it, the buildings Metal Building groups did in the late 70's into the 90's were usually simple rectangular boxes. But they now have dedicated staffs, state of the art computer modeling abilities, and the where-with-all to realize that there was a huge untapped market out there.


Still one thing really bugs me, and that is putting a grid line at the face of the girt.

GJC

 

[271828]

"Still one thing really bugs me, and that is putting a grid line at the face of the girt."

NO argument there!

 

[dik]

Best get your loading in place now... make sure that the purlins can support 500 lb loads at any three points and that the building frame can accommodate 2000 or 3000 lb loads at anywhere as well as 1000 lb lateral loads at any location along the vertical leg of the freame, etc. Modify above loads to suit. I'll repost my pre-eng building notes below:

METAL BUILDING SYSTEM (PRE-ENGINEERED METAL BUILDING)

DESIGN STANDARDS FOR THE METAL BUILDING SYSTEM ARE TO MEET THE REQUIREMENTS OF PART 4 OF THE MANITOBA BUILDING CODE AND CSA S16 AND CSA S136

ALL STRUCTURAL STEEL COMPONENTS, INCLUDING ANCHOR RODS SHALL BE CERTIFIED AS WELDABLE

PREFABRICATED METAL BUILDING SYSTEM SUPPLIER SHALL SUPPLY ALL ANCHOR RODS, NUTS AND WASHERS TO SECURE THE BUILDING TO THE FOUNDATION. ANCHOR RODS ARE TO BE DESIGNED FOR ALL HOR AND VERT LOADS

DESIGN OF THE BUILDING FRAME AND ALL COL MEMBERS SHALL ASSUME THAT ALL FRAME AND COL BPS ARE SUPPORTED ON 1" OF GROUT. ANCHOR RODS SHALL HAVE A MIN 3" PROJECTION ABOVE THE BP AND SHALL HAVE A MIN EMBEDMENT LENGTH AND CONFIGURATION TO RESIST ALL SHEAR AND UPLIFT FORCES

FABRICATION SHALL BE IN ACCORDANCE WITH CSA S16 AND CSA S136, AS APPLICABLE. WELDING SHALL BE PERFORMED IN ACCORDANCE WITH CSA W59 AND CSA S136. MANUFACTURER TO BE APPROVED BY THE CANADIAN WELDING BUREAU, IN ACCORDANCE WITH CSA W47.1 FOR DIVISION 1 OR DIVISION 2

THE BUILDING SHALL CARRY A 25 YEAR ROOF WARRANTY AND A 15 YEAR SIDING WARRANTY AGAINST DEFECTS IN MATERIALS AND SHALL CARRY A 5 YEAR WARRANTY AGAINST DEFECTS IN WORKMANSHIP

MIN ROOF SLOPE SHALL BE 1/2:12

THE BUILDING SHALL BE DESIGNED FOR THE FOLLOWING LOADS IN ADDITION TO THE LOADS STIPULATED IN NOTES FOR DESIGN LOADS:
ROOF PURLINS: DEAD LOAD = 5 PSF UDL
LIVE LOAD = 5 PSF UDL AND POINT LOAD OF 250 LBS SUSPENDED FROM ANY LOCATION
BUILDING FRAME: DEAD LOAD = 1000 LBS SUSPENDED FROM ANY LOCATION
LIVE LOAD = 2000 LBS SUSPENDED FROM ANY LOCATION

PURLIN BRACES ARE TO BE PROVIDED IN ACCORDANCE WITH CSA S136, CLAUSE 8. IN PARTICULAR, FOR A STANDING SEAM ROOF SUPPORTED ON MOVABLE CLIPS, BRACES PROVIDING LATERAL SUPPORT TO BOTH TOP AND BOT PURLIN FLANGE ARE TO BE PROVIDED. THE NUMBER OF ROWS SHALL BE DETERMINED BY ANALYSIS BUT IN NO CASE TO BE LESS THAN 1 FOR SPANS UP TO 23 FT. OR LESS THAN 2 FOR SPANS GREATER THAN 23 FT

ALL STRUCTURAL STEEL SHALL BE PRIME PAINTED. IF A PAINT TOP COAT IS REQUIRED, PRIMER SHALL BE COMPATIBLE WITH THE TOP COAT

ALL ROOF PURLINS AND WALL GIRTS TO HAVE A ??? COATING CONFORMING TO ???. COLOUR SHALL BE SELECTED BY THE CLIENT FROM THE MANUFACTURER'S LIST OF STANDARD PROVEN COLOURS

ALL ROOF PURLINS AND WALL GIRTS TO HAVE BE HDG WITH A COATING CONFORMING TO Z275

ALL ROOF CLADDING SHALL HAVE A COATING CONFORMING TO CSSBI [SERIES 5000 | SERIES 10000 | BARRIER | METALLIC/ELITE SERIES]. COLOUR SHALL BE SELECTED BY THE CLIENT FROM THE MANUFACTURER'S LIST OF STANDARD PROVEN COLOURS

ALL WALL CLADDING SHALL HAVE A COATING CONFORMING TO CSSBI [SERIES 5000 | SERIES 10000 | BARRIER | METALLIC/ELITE SERIES]. COLOUR SHALL BE SELECTED BY THE CLIENT FROM THE MANUFACTURER'S LIST OF STANDARD PROVEN COLOURS

ALL LINER PANELLING SHALL HAVE A ??? COATING CONFORMING TO ???. COLOUR SHALL BE SELECTED BY THE CLIENT FROM THE MANUFACTURER'S LIST OF STANDARD PROVEN COLOURS

ALL LINER PANELLING SHALL HAVE A GALVALUME COATING CONFORMING TO ZF075

COLOUR OF TRIM, RAKE, EAVESTROUGHING AND DOWNSPOUTS SHALL BE SELECTED BY THE CLIENT FROM THE MANUFACTURER'S LIST OF STANDARD PROVEN COLOURS

THE BUILDING SHALL BE INSULATED AND THE PREFABRICATED METAL BUILDING SUPPLIER SHALL SUPPLY ALL NECESSARY THERMAL BLOCKS. INSULATION SHALL BE PROVIDED BY ???

DEFLECTION OF WALL AND ROOF CLADDING SHALL BE IN ACCORDANCE WITH THE REQUIREMENTS OF CSA S136-94

DEFLECTION OF WALL GIRTS AND ROOF PURLINS SHALL BE IN ACCORDANCE WITH THE REQUIREMENTS OF CSA S16. IN ANY EVENT, LIVE LOAD DEFLECTION SHALL NOT EXCEED L/240. THE METAL BUILDING SYSTEM SUPPLIER SHALL PROVIDE FOR SUPPORT OF ANCILLARY STRUCTURAL ELEMENTS WHERE NOTED ON THE DWGS. THE METAL BUILDING SUPPLIER SHALL PROVIDE FOR REDUCED DEFLECTION LIMITATIONS AS REQUIRED FOR ATTACHMENT TO OTHER BUILDING COMPONENTS

SHOP AND ERECTION DWGS OF THE METAL BUILDING SYSTEM, BEARING THE SEAL OF A PROFESSIONAL ENGINEER REGISTERED IN MANITOBA, ARE TO BE SUBMITTED TO THE [CONSULTANT | ENGINEER] FOR REVIEW PRIOR TO THE PLACEMENT OF FOUNDATIONS. SHOP DWGS ARE TO PROVIDE LOCATION OF GRID LINES, AB CLUSTERS, AND SIZES. ANCHOR ROD AND BASE PLATE DESIGN SHALL ASSUME THAT BASE PLATES ARE SUPPORTED ON 1" GROUT

THE CONTRACTOR SHALL SUBMIT SHOP DWGS PRIOR TO FABRICATION FOR THE [CONSULTANT | ENGINEER]'S REVIEW. UNLESS NOTED OTHERWISE, SUBMIT SHOP DWGS AS FOLLOWS:
1 SET OF DWGS ON REPRODUCIBLE VELLUM
1 SET OF DWGS IN DIGITAL FORMAT
2 SETS OF PRINTS MADE FROM THE REPRODUCIBLE VELLUM

A SHOP DWG SHOWING THE ANCHOR SETTING LOCATIONS FOR THE BUILDING MUST BE PROVIDED. THIS DWG SHALL SHOW:
ANCHOR ROD LOCATIONS, TYPE, DIA, PROJECTION AND LENGTH, MAX AND MIN REACTIONS BASED ON THE LOAD COMBINATIONS STIPULATED IN THE MANITOBA BUILDING CODE SHALL BE PROVIDED FOR ALL SUPPORTS (A TABULAR FORM SHOWING LOADING REACTIONS FOR VARIOUS LOAD CASES IN NOT ACCEPTABLE)

COORD X-BRACING ELEMENTS WITH ARCH TO PREVENT CONFLICT WITH OPENINGS

THE BUILDING SHALL BE COMPLIANT WITH THE REQUIREMENTS OF ASHRAE 90.1

THE BUILDING SHALL BE COMPLIANT WITH THE REQUIREMENTS OF THE CURRENT NATIONAL ENGERGY CODE

THE BUILDING SHALL BE COMPLIANT WITH THE REQUIREMENTS OF FM GLOBAL FOR AN I-60 RATING

THE BUILDING SHALL BE COMPLIANT WITH THE REQUIREMENTS OF FM GLOBAL FOR AN I-90 RATING

THE METAL BUILDING SYSTEM MANUFACTURER SHALL SUBMIT THE CSSBI CERTIFICATE OF DESIGN AND MANUFACTURING CONFORMANCE TO THE [CONSULTANT | ENGINEER] PRIOR TO SHIPMENT OF THE PREFABRICATED BUILDING TO SITE

Bend and mutilate as necessary...

Dik

 

[JLNJ]

271828

My post does not "condemn" the MBMA or claim that they have it "all wrong". MBs are sold mostly based on cost. Those MBMA companies have done a great job with that business model- there's no doubt about it. However, lowest cost comes with its drawbacks and penalties and many owners and architects don't understand those penalties.

 

[271828]

JLNJ, I agree with your last post. MB systems definitely have limitations and get used incorrectly at times. Some owners might get fooled or led down the wrong path. In my limited experience with owners I've known personally, they knew what they were getting and were happy to save a few tens of thousands of bucks that they could pour into something more productive than bigger columns and more durable cladding, LOL. I'd assume that most folks with enough drive to buy a bldg for a business are smart enough to know what they're getting, but maybe I'm wrong.

What I was referring to was:

"We had a PEMB with modifications made (by others) to the columns, but the factor of safety was cut so close the modification ended up in a catastrophic failure (and lawsuit). My opinion is that almost any conventionally framed building would have easily survived the same modification. "

I'm not a mind reader, but this seems to be an attempt at putting blame on a MB company where I'd argue that the EOR who agreed to the modifications is more directly at fault.

Put it this way: Say I design a concrete flat slab for 60 psf LL and I optimize it down to the last rebar and cutoff length. The punching shear ratio is 1.000 and long term deflections are right at whatever we'd say is the max reasonable limit. Now some owner wants to use it for a heavy storage area with much large LL. The new EOR approves it for some bizarre reason and it has some kind of problem. It's not my fault for optimizing it to the nut, as one guy put it. It's the new EOR's fault for either not checking it or not knowing how to check it--neither of which is the first EOR's fault

 

[rowingengineer]

was there an EOR involved? I would say not and this is where the problems come about, with modifications. The public expect to be able to make some minor modifications without having to go to the next level ie getting an EOR on board.

The problem is so big with this type of structures in my area, that the local steel association has decided to put out a minimum standards book, because engineers where cutting it too fine. Relying on cladding without doing fatigue analysis/testing for shear loading ect.


Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that them like it

 

[271828]

What minor modification could be made to a MB column that would cause catastrophic failure? I can think of only one that an unsuspecting owner might *reasonably* consider harmless, but would be dangerous, but it's a long shot.

 

[dik]

I've encountered many PEMB's that have been modified by the owner without realising that they were reducing the strength of them. One I'm helping a junior engineer with right now has a series of 3 overhead cranes that have been added in the past without engineering and they wanted to add another 2...

Many owners don't appreciate the level of 'fineness' in the design of these things and think it's like banging a nail in the wall to hang a picture.

Dik

 

[spats]

Metal buildings do not necessarily have a higher rate of failure than conventional buildings because they are designed skinny or because they are abused by modification. They primarily fail under high wind loads, such as a hurricane. When the exterior skin is breached, and significant wind loads get INSIDE the building... that's when all hell breaks loose. In other words, the building envelope is primarily the culprit.

 

[271828]

I don't see how this has anything to do with the bldg type. Is it not possible that an engineer would design a conventional bldg with optimized crane runway beams? That's all it would take to cause problems if a larger crane was added. It wouldn't matter if the rest of the bldg was made of heavy reinforced concrete.

I know if I was hired to design a bldg with a 10 ton crane with whatever wheelbase, etc., I'd design a good beam for that situation. It's not my fault if the guy comes in with another 10 ton crane or replaces his crane with a 50 ton one.

 

[JLNJ]

271828

The jury on final word on the cause of the failure is still out. Our firm was involved just on the very periphery and I'm not sure of the final ruling or if there has been one yet. The leading indicators show that it was a column or "knee" compression flange failure due to inadequate lateral bracing. There are other complicating issues as well which involve some modifications over time and bit higher load than might have been originally anticipated.

My contention is NOT that the PEMB manuf designed things improperly, but rather by its very nature a PEMB often has a lesser safety factor. Most of the time we don't know just how close we come to using up all that reserve strength - and sometimes we find out quite suddenly. The 1.6 safety factor was developed in a time before MBs really got their foothold. Maybe the 1.6 doesn't provide the same reserve strength from framing system to framing system. In the case I cited, several circumstaces chewed into the reserve capacity/safety factor, eventually causing failure.

 

[audeuce02]

JLNJ, since it was a failure of the compression flange, had a flange brace or girt been removed, or the elevation changed. The most common cause for failures in PEMB is flange braces either being removed or not installed as indicated.

Do we design our buildings right on the edge? You better believe it. But we provide exactly what is in the Contract Documents. The entire discussion about deflections/servicability is a little skewed. While MBMA does publish servicability guidelines, they are identical to what is published in AISC Design Guide 3.

On a daily basis I deal with buildings that have changed ownership and the current occupant needs to support an RTU, exhaust hood, mezzanine, etc. We do expect to get paid for this analysis and specifying of any re-enforcing scheme, but I think that anyone expects to be paid for services outside the scope of the original Contract. Many times it does take significant field work to install the re-enforcement and if that is the case I warn the customer that it may not be feasible to attempt the modification.

It seems a little like a witch hunt here. Multiple structural failures, comparing PEMB to a gas station canopy, and having a structural failure that the most likely cause is due to modification without approval or analysis from the PEMB supplier? Is there an axe to grind with the PEMB Industry, because as mentioned above these are no longer off the shelf buildings. Each building is designed per Code and the Contract Documents.

 

[hokie66]

Welcome to Eng-Tips, audeuce02. 271828 needs all the help he can get.

 

[rowingengineer]

What minor modification could be made to a MB column that would cause catastrophic failure? I reviewed a building were the someone had put a window in the wall sheeting (in this case bracing), the window was for a toilet (1 sqaure foot). The building fell down in the next puff of wind.

"Each building is designed per Code and the Contract Documents" would you like to bet your house on that.


Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that them like it

 

[rowingengineer]

I missed the "column" (the most important part)part when i red the sentence, sorry.

Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that them like it

 

[271828]

"271828 needs all the help he can get."

LOL, I thought I was doing pretty well for 1 against 5!