c structuralforum shoemaker mar07

8/13/2019 C StructuralForum Shoemaker Mar07

1/3STRUCTURE magazine March 2007

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Structural Forum is intended to stimulate thoughtful dialogue and debate among structural engineers and other participants in thedesign and construction process. Any opinions expressed in Structural Forum are those of the author(s) and do not necessarily reflect theviews of NCSEA, CASE, SEI, C3Ink, or the STRUCTURE

magazine Editorial Board.

Metal building systems may not bepopular with some structural engineersbecause this construction alternativecompetes with traditional engineering op-portunities for conventionally designedand constructed facilities. Structural en-gineers who realize that the metal builingsegment of the low-rise construction mar-ket offers an opportunity, not a threat, willultimately benefit as metal building sys-tems continue to build solid market sharein every low-rise marketplace fromstrip centers to car dealerships to officecomplexes and call centers.

The Case for an Engineer of Recordfor a Metal Building SystemBy W. Lee Shoemaker, P.E., Ph.D.

What is a MetalBuilding System?

Many engineers (or design professionals)believe that a metal building is selectedfrom a catalog of standard designs, based

on the required size of the building. Un-fortunately, national ad campaigns bybrokers of metal building systems con-tribute to this misconception, and arenot representative of the common indus-try practice that involves a transactionbetween a metal building manufacturerand a builder.Most metal building manufacturers cus-

tom design a building after the order isplaced, based on the applicable buildingcode, loading conditions and serviceabil-ity requirements. Metal buildings are

governed by the same building codes andmaterial standards as other forms of con-struction. MBMA member companieshave registered professional engineerson staff who are highly skilled and ap-ply sound engineering principles towardthe optimal design of metal buildingsystems. In fact, MBMA members are re-quired to be certified, as discussed laterin this article, which includes a verythorough independent audit of theirengineering design practices. Advancedcomputer methods are used to help fa-

cilitate this design customization and op-timization. This is also why the industryis moving away from the outdated termi-nology, pre-engineered metal buildings,in lieu of the more accurate identificationof metal building systems.Metal building systems have evolved

over the years into assemblages of struc-tural elements that work together as avery efficient structural system. The ba-sic elements of the metal building system

are: primary rigid frames, secondarymembers composed of wall girts androof purlins, cladding, and bracing(Figure 1). Metal building system designmay seem trivial at first, but experienceshows that the complex interaction ofthese elements into a stable system is achallenging engineering task. MBMAmember companies have demonstratedthis expertise and are on the leading edgeof systems design.

Roles and Responsibilities What is the EOR Role?

When a project calls for a metal buildingsystem, design responsibilities are usuallydivided between the manufacturer and thedesign professional or EOR. Therefore, aclear understanding of their respectiveroles, as well as coordination and commu-nication are crucial for success.The manufacturer is responsible only

for the structural design of the metalbuilding system it sells to the builder.The manufacturer is not the designprofessional or the EOR for the con-struction project. The manufacturer is

not responsible for the design of anycomponents or materials not sold bythem. Nor are they responsible forthe interface and connection of othercomponents with the metal buildingsystem, unless such design responsibi-lity is specifically required by the orderdocuments.

...involvement of an EOR in a projectthat involves a metal building system.

Typical metal building framing, but witha clerestory.

Figure 1 Anatomy of a Metal Building Showing the primary framing, secondary framing,roof/wall cladding, and bracing.

continued on next page

It is not uncommon for a buildingowner to forego the services of an engi-neer of record (EOR) on a metal buildingproject. However, the Metal BuildingManufacturers Association (MBMA) en-courages the involvement of an EOR ina project that involves a metal buildingsystem. This article provides informationabout the metal building industry, iden-tifies some problem areas, and discusseswhy the involvement of an EOR is a keycomponent to a projects success.



It is the responsibility of the metal build-ing manufacturer to design a metal buildingsystem to conform to the specifications, in-cluding the design criteria and design loadsincorporated by the builder into the order doc-uments. The manufacturer is not responsiblefor making an independent determinationof any local codes or any other requirementsnot mandated within the order documents.When specified by the order documents, themanufacturer is responsible for supplyingadequate evidence of compliance with thespecifications, design criteria, design loads,and other specified information necessaryfor the EOR to incorporate the metal buildingsystem into the construction project.

turer typically reviews the order documents,while the EOR often evaluates the contractdocuments to ensure the specifications anddrawings have been properly interpreted.The owner may retain an EOR to create

the contract documents. The EOR may alsoreview the shop drawings prepared by the con-tractor (or subcontractor or manufacturer).In some cases, construction contracts requirethe contractor to provide delegated design

engineering to a licensed professional. Theengineering is based upon the manufacturersspecific component properties and may beperformed by the manufacturer or by anexperienced independent structural engineer.

...a proper specification ensures thebuilding performs satisfactorily and mee

the owners requirements.

The metal building system is just one ele-ment of the total construction project. Forexample, the metal building manufacturer

rarely provides site preparation, mechanical-work, electrical design, and certain buildingenvelope components/accessories. Similarly,he or she is not responsible for the founda-tions design. The EOR is typically responsiblefor these important elements of the project as

well as floor slabs, interior/exterior concretemasonry and/or tilt-up walls, and the con-nection of these walls to the metal buildingframing. With regard to the foundation de-sign, the manufacturer does prepare the anchor

bolt plans showing the location,diameter, and projection of the

bolts required to attach themetal building system to thefoundation.

ServiceabilityAn EOR can provide the own-er with essential advice on theserviceability requirements for aproject, especially with regard tothe buildings functional perfor-mance requirements under ser-vice loads, including lateral drift,

MBMA highly recommends that the endcustomer hire an EOR to be responsible for

specifying the design criteria for the metalbuilding system. These design criteria, to beused by the builder and manufacturer, shouldinclude the geometric requirements, all ap-plicable codes and/or design loads, site andconstruction conditions that affect designcriteria, and serviceability criteria. As with anybuilding, clear and accurate specificationsensure the builders/manufacturers bidding onthe project understand and interpret the re-quirements in a similar and accurate manner.Just as importantly, a proper specification en-sures the building performs satisfactorily and

meets the owners requirements.In the sale of most metal building systems,

there are at least two independent writtenagreements the building order documentsand the contract documents. The order docu-ments are normally required to process theorder for the metal building system, while thecontract documents (including the drawingsand specifications) define the material andwork to be provided by the contractor forthe total construction project. The manufac-

continued on page

Depending on the application and architecturaltreatments, a metal building system can look nodifferent than other construction.

deflection, and vibration. This is a critical nin the projects specification phase, as servability decisions address an owners needs preferences that may not be spelled out in building code.Metal building systems, clad in flexi

metal siding and roofing, can tolerate sable amounts of movement. Howemasonry, concrete and other more bri

wall materials are increasingly being inc

porated into metal building systems becaof owner or architectural preferences. Tis especially true for many retail and intutional applications.Since drift limits are not covered in

building codes, it is important they are proply specified, depending on the flexibility of

wall materials. MBMA recommends usthe American Institute of Steel Construct(AISC) Design Guide No. 3, ServiceabiDesign Considerations for Low-Rise Build(recently revised and renamed, ServiceabiDesign Considerations for Steel Buildings).

The owner does not always understandthe need for an engineer of record...

An EOR is in a better position to evaluatethe owners needs and recommendappropriate serviceability limits...

For longer spans, bar joists are used instead of cold-formed purlins.

While it is important to specify approprdrift limits, giving consideration to the defltion tolerances of any brittle wall elementshould also be understood that limits thatoverly restrictive influence the cost of a buing. An EOR is in a better position to evaluthe owners needs and recommend appropr

serviceability limits, such as given in reference cited above, that do not leadunnecessary building costs.

Inspection ServicesOne of the most common problems t

can occur with metal building systemsquality control during the erection procFlange braces that are left out may not shup until a major snowstorm. The mbuilding manufacturer is not responsible inspection of a construction project unless is incorporated into the order docume

Typically, a manufacturer is limited becauslogistical constraints as well as not having expertise in inspection services. Furthermoa manufacturer is not in the best positioninspect the work of the builder who is manufacturers customer.Ideally, an end customer should uti

the inspection services of the EOR for project to provide this important functiThe EOR can ensure that the projectconstructed according to the manufacturerection drawings.



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Certification ofthe Manufacturer

An EOR should also be aware of the rig-orous certification program that is availableto metal building manufacturers throughAISC. This can be an advantageous additionto the specification of a metal building sys-tem by requiring that the manufacturer beAISC-MB certified. Manufacturer certifica-

tion should be included in the specification,because it ensures the building is being provid-ed by a manufacturer that has demonstrateda high level of competency in all aspectsof engineering design and fabrication.In fact, the metal building industry is the

only industry that has a certification programincorporating design engineering. The pro-gram also examines policies and proceduresat each of the manufacturers facilities, andverifies the application of those policies andprocedures within randomly selected projects.Inspection and evaluation teams from an in-

dependent engineering auditing firm annu-ally observe and evaluate the manufacturerin almost every aspect of professional designand manufacturing.Therefore, an EOR working on a metal

building project with a certified manufac-

turer can have a higher level of confidencethat they are working with a thoroughlyqualified company. A current list of certi-fied manufacturers is available on the AISC

website (www.aisc.org).

SummaryMetal building systems are widely used in

all types of building applications. The owner

does not always understand the need for anengineer of record and his/her role in a proj-ect. MBMA highly recommends that the endcustomer hire an EOR to be responsible forspecifying the design criteria for the metalbuilding system, designing the building com-

ponents not supplied by the metal buildmanufacturer and their interface with the mal building, and providing inspection servas needed or required by the building codeMBMA is trying to be more proactive

working with the engineering communto educate EORs about the metal buildindustry and to find ways to improve the ordination and understanding of the shadesign responsibility in metal building pr

ects. It is hoped that this article will helpthis important effort.

More information is available inthe newly updated Metal BuildingSystems Manual, as well as other

publications on the MBMAwebsite (www.mbma.com).

W. Lee Shoemaker is the Director of Researcand Engineering for the Metal Building

Manufacturers Association, Cleveland, OH

He serves on the ASCE 7 Committee, theAISC Steel Specification Committee andthe AISI Cold-Formed Steel SpecificationCommittee. He can be reached via e-mail [email protected].

A metal building system with a steep roofand masonry wall cladding.

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