August 11, 2010

Lightweight Steel Construction (Continued from p. 39 of the December 2008 issue of BD+C)

                  
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Reed Business Information is a Registered Provider with the American Institute of Architects Continuing Education Systems. Credit earned on completion of this program will be reported to CES Records for AIA members. Certificates of Completion for non-AIA members are available on request.
       This program is registered with the AIA/CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product. Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation. 

 

As far as overall cost and schedule considerations for metal systems, MBMA’s Praeger explains that one big advantage is being able to make accurate estimates of the major building systems up front. With a metal building package, he says, “Every piece is factory welded, pre-sized, and pre-drilled to an exact spec. Once on site, every one of the pieces bolts together, with little additional field cutting, drilling, welding, or fabrication required.”

As a result, says Praeger, metal building installation can take half to one-third the time of ordinary buildings. “This is truly a fast-track method of building construction where the building can be ordered while the rest of the construction project is being pulled together and phased properly,” he says.

Yet another advantage of metal-framed buildings is that they easily lend themselves to expansion, especially when future expansion is worked into the initial design. For example, “The end wall can be designed as if it were an interior frame, so lengthening the building is then not a significant structural modification,” explains Lee Shoemaker, PE, MBMA’s director of research and engineering. “Metal buildings can also be widened with ‘lean-to’ frame expansions,” he notes.

“Metal buildings are sometimes called upon to serve a new use or different application than they were originally designed for, and this can mean new loads to support or new codes to comply with,” says Shoemaker. “While this can be challenging for any construction type, metal buildings can be retrofitted in clever ways to increase the original design capacity. If another form of construction is touted for being able to adapt to new loadings without extensive retrofitting, it is likely that they [i.e., the load-bearing elements] were overdesigned to begin with.”

STEEL SYSTEMS GO FOR DECOR
Leveraging such benefits as eye-catching aesthetics, security, and light and air control, decorative steel systems offer a unique and long-lasting appeal.

For example, perforated steel panels were specified for new parking decks at Charlotte Douglas International Airport, and the installed products helped meet a number of practical and budgetary needs while also offering a compelling visual effect. The project team selected perforated panels with approximately 40% open area, so it serves as a translucent screen while also controlling natural light and air movement into the building. The panels also shielded from view certain equipment that the facility operator did not want visible. Another practical benefit: the material is lightweight, requiring limited structure to support the screen assembly.

Perforated metal screens also offer useful environmental benefits for sustainable buildings. For example, they can be used to reduce the need for artificial light or to cut light pollution. As at Charlotte Douglas International Airport, they also increase fresh air ventilation. This air-circulation capability was important in the design of a new YMCA facility in Houston, where perforated and corrugated fence panels were employed. According to project manager Greg Ryden, with Houston-based Brave Architecture, “We designed a rhythmic pattern that looks quite attractive while providing privacy and security and also allowing airflow.”
















    
Driven by the goal of creating a more visually animated finish, BHDP Architecture worked closely with the cladding manufacturer to develop a highly specular white colored metal panel to be used on a major retailer’s prototype department store. The process involved experimentation with various levels of metallic flake “floating” above the white background color, as well as multiple percentages of gloss top coating to reach the preferred effect. The color has been utilized successfully on several department store projects and currently is referenced by the name of the retailer. PHOTO: Courtesy of BHDP Architecture
       
The expansion of the 25,783-sf Blanca-Fort Garland Community Center (top, above) in Blanca, Colo., involved the use of a pre-engineered metal frame, standing seam metal roof, and insulated metal wall panels. Photo: Metal Building Manufacturers Association
           
The perforated metal screens used on the parking decks at Charlotte Douglas International Airport in North Carolina, address aesthetic concerns, but also help control light and air movement within the facility. Photos: Centria
        

Focusing more on the aesthetics of this basic punched-sheet material, G. Wesley Jones, AIA, NCARB, LEED AP, a principal with Ai Design Group, Charlotte, N.C., has used perforated metal panels for a number of his firm’s projects for the automotive racing industry. “We are using them on exterior applications as a decorative finish which can be applied after the building is dried,” says Jones. He says this works well on extremely fast-track projects such as the Zmax Dragway at Lowe’s Motor Speedway, in Charlotte. “These types of materials provide a high-quality, shop-fabricated finish which is semi-transparent, giving the building a sense of depth. We are also using these types of materials on the interior as decorative screen elements to reference the exterior design, such as on reception desk applications and as backlit perforated light screens.”

Supporting innovative and distinct designs, steel mesh is another attractive decorative steel choice can be a creative tool for trendsetting designers. For example, a mesh system designed for the Austin Convention Center in Texas helped create a striking, graceful façade blending a new cooling plant and parking garage with the main convention center buildings. The metal fabric was used to complement the facility’s brick walls. The rhythmic composition reduces the scale of the large brick façades and adds visual interest to the building, which spans a city block, according to blogger Shawn Zuver. At night, the building exudes a blue-green glow; during the day, the meshed metal fabric brings sunlight into the parking garage, while shading the sidewalks below.

Another project highlighting the visual possibilities of mesh is the World of Coca-Cola, Atlanta’s new museum for the famed soft drink. In this case, the company’s famous trademark was laser-etched onto the surface of a woven façade screen to enhance Coke’s corporate branding. At night, the corporate signature glows with a backlighting wash; during the day, the effect changes subtly with the movement of the sun. “Functionally, the mesh provides solar shading, light pollution reduction, and HVAC reduction,” notes Zuver.

Mesh and perforated panels also function well as exterior shading panels, admitting low-angle winter sun and morning and evening lighting while blocking higher angle and summer rays. For example, the new South Lake Building at the University of Washington was fitted with a woven mesh application that serves as an effective exterior shading system, dramatically reducing solar heat gain and cooling costs for the building. At the same time, the mesh lends a unique, modern aesthetic to the facility.

STEEL FINISHES OFFER PROTECTION
Although different types of steel finishes also provide aesthetic interest for building projects, their main function is the protection they provide. For instance, even though polyvinylidene fluoride (PVDF) resin offers a broad palette of colors, the space-age coating technology is better known for its durability, weather resistance, ultraviolet protection, thermal stability, formability, and protection against airborne pollutants, according to Glass Magazine’s Architect’s Guide to Glass. “PVDF paint coatings such as Kynar 500 and Hylar 5000, trade names for Teflon-related coatings that contain infrared pigments, are highly reflective and emissive, which help reduce the heat-island effect within urban areas,” says Praeger. (Heat-island effect causes urban areas to increase in temperature more than nearby vegetated areas.)

When compared to anodizing, a method of treating metals such as aluminum, PVDF lasts longer and offers better color consistency. On the other hand, anodizing is a harder coating; for that reason, it may be more appropriate for high-traffic areas. In addition, it lends a rich metallic appearance, tends to be less expensive, and cannot peel off, as the coating becomes part of the metal.

Yet even though anodizing is known to be superior in abrasion resistance, PVDF has captured a large portion of the commercial building market, according to the Architect’s Guide to Glass: “This is because for curtain wall and metal roofing, color consistency and color selection are more important than abrasion resistance.”

Another decision for designers, specifiers, and metal fabricators is how to protect steel materials and assemblies against rust. Here the main choice is a range of treated steel finishes, including Cor-ten, Galvalume, and galvanized steel. Galvalume coatings have become the industry standard for unpainted metal roof panels, according to MBMA technical staff member Jay Johnson. “The coating is an aluminum-zinc alloy and provides excellent corrosion protection by combining the barrier protection of an aluminum coating with the sacrificial protection of a zinc coating.” MBMA’s Praeger adds that Galvalume coating is highly reflective and has a very long life cycle cost feature. (Life cycle cost refers to the practice of determining the value of a building product over the facility’s operating period.)

The effect is a stable appearance that may appear mottled or rust-like, which develops over time. However, in order to ensure that the bolted and other connection points weather at the same rate as other galvanized materials, special welding techniques or materials may be required.

With regard to the organic coatings, one way to reduce air pollution is by utilizing a powder product, as opposed to a liquid, if possible. For long-term exterior architectural applications, solvent-borne coatings generally lose 70-80% of each gallon of paint to evaporation during the paint-curing process, according to the Architect’s Guide to Glass. These fumes make up a mix of hydrocarbons, known as volatile organic compounds (VOCs), by the U.S. Environmental Protection Agency. VOCs are essentially a “precursor to ozone formation similar to automobile exhaust.”

However, because some resins are more difficult to manufacture or apply as solvent-borne formulations, powder options are currently not available for those finishes. At the same time, with rising interest in sustainable building solutions and concerns about environmental regulations, organic coating manufacturers may eventually be forced into developing powder-coating technology or recommending the use of pollution-control equipment during finish applications.

MBMA’s Praeger sees environmental awareness as a growing trend. “The steel industry is beginning to work toward defining and measuring such architecture and engineering issues because we feel they will be important for environmental stewardship,” he says.

NOT THE SAME OLD ‘BUS BARNS’
While metal building systems have made great strides in environmentalism, performance, and durability, perhaps the most noticeable change has been its departure from what some observers call “the old bus barn look.” With new products and systems that provide a range of aesthetic options, metal systems are appearing in more and more building types and applications. In addition, they are often employed with other kinds of building materials, blending together or adding counterpoint to novel design compositions.

“Advanced design and construction techniques invite unique façades of glass, stone, brick, metal, concrete, or wood,” says MBMA’s Johnson. “Likewise, the interiors of metal building buildings can be finished to meet a variety of needs.” He adds that the increased flexibility and the growing popularity of decorative steel systems are helping drive innovation in both manufactured product and detailing and installation creativity. “The metal building system designer has the ability to integrate complex building footprints, hips, and valleys in the roof system, cantilevers, and overhangs,” he adds. “The designer has many options.”

Perhaps that’s why MBMA’s Fischer and other industry observers point out the adaptability and increasing applicability of steel building systems. Whether it’s healthcare, education, or recreational facilities, structural steel continues to be a preferred option thanks to its durability, speed of construction, attractive appearance, energy efficiency, and cost-effectiveness.

“Structural steel is widely used in all types of building construction, as is evidenced by the market share for most building types exceeding 50%—more than twice the share of concrete,” says John Cross, the AISC director of marketing. “These project types include stores, restaurants, warehouses, offices, manufacturing facilities, process industrial facilities, schools, hospitals, government facilities, arenas, stadiums, hotels, and dormitories.”

Cross offers this summary of structural steel design trends and benefits for various building applications:
Multistory residential. In addition to traditional steel framing design for this building type, four other innovative approaches are gaining popularity. One of these is the staggered truss framing system, which uses floor-to-ceiling trusses the width of the structure set in an alternating arrangement from floor to floor. Precast plank is used as a deck system, with the plank sitting on the bottom chord of one truss and the top chord of the next truss. The result is a structure with 60-foot-wide bays, the width of the structure with no columns extending through the interior of the structure. This allows for flexible room layouts, rapid construction, and wide-open interior spaces.

The girder-slab system is also being used more frequently for apartment and condominium construction. Girder-slab also utilizes precast plank, but in combination with a specially fabricated D-beam that allows the plank to rest on the bottom rather than on the top flange of the beam. The entire system is grouted together and results in an economical system that can be constructed relatively quickly. By using standard systems, this system lends itself to typical 8-foot, 8-inch floor-to-floor heights.

The third type of system in this category utilizes shop-machined interlocking connections to reduce erection time for multistory residential and other types of projects. These systems, such as Conxtech (www.conxtech.com), are sometimes called “full-scale Erector sets” by building experts. They include structural steel moment frames and space frames of hollow structural section (HSS) columns and wide-flange beams, and a range of gravity and moment connectors that can work with proprietary roof systems, corrugated metal decking, panelized exterior walls, and even full-stair systems with built-in railings.

Another trend, says AISC’s Cross, is the significant increase in the coordination of architectural layouts with the steel framing systems. This results in an in-wall beam configuration that allows a minimization of floor-to-floor heights.

Parking structures. For decks and other facilities with structured parking, concrete is a commonly employed choice. Yet a steel framing system may allow a better return on investment under certain conditions. An initial construction cost savings of 10- 20% over concrete has been observed, according to AISC. In addition, a steel structure can provide more parking spaces than a concrete structure in the same building footprint because steel columns require 80% less floor space than equivalent concrete columns. Also, because of the smaller member sizes, steel framing simplifies erection in locations with restricted delivery or construction access and allows construction in cold weather conditions. Finally, a steel framing system can be erected in a period of weeks rather than months, which enables earlier occupancy.

Yet another benefit is reduced maintenance costs, according to some parking facility experts. Exposed beams, girders, and columns permit direct inspection, evaluation, accessibility of the frame, and ease of maintenance of the structural surfaces.

Reduced costs for restoration may be another benefit. Studies conducted by parking consultants have indicated that over a 50-year building life, the cost to maintain a precast concrete deck-and-frame system will be between $0.50 and $0.80 per square foot, while the cost to maintain a post-tensioned deck on a steel frame will be between $0.30 and $0.50 per square foot, a savings of about 40%.

To achieve even better long-term durability, some Building Teams coat the structural steel frames with a high performance multicoat paint system using a zinc-rich primer. When properly applied over a prepared surface, a three-coat paint system can provide more than 30 years of corrosion protection. Some parking structure owners have chosen to protect their structures by using galvanized steel; this involves cleaning the steel in an acid bath, then dipping it in a hot zinc bath, yielding protection from corrosion in excess of 40 years.

Additional benefits of steel-framed parking structures include greater design flexibility that comes with the well-controlled drainage systems and pipe locations in steel structures. Embedded conduits, ceiling-mounted light fixtures, and signage placement can be simplified for a tight, efficient parking structure with clean architectural lines. In fact, electrical conduit and other ceiling-mounted fixtures can be run through holes drilled in the steel beams, rather than having to be bent under and around concrete columns.

Furthermore, as more jurisdictions adopt building codes requiring structural design and detailing for earthquake loads, the ductility, durability, and reliability of structural steel framing provides both engineering advantages and peace of mind for both owners and occupants.

In terms of green building, steel parking facilities have a reduced foundation footprint, resulting from steel’s lighter structure. To accommodate future growth, a steel-framed structure can expand vertically through the splicing of existing columns. The ability to penetrate, weld, bolt, and reinforce structural steel in the field makes even unanticipated changes and retrofits practical.

During the construction phase, shop fabrication of steel framing eliminates weather as a factor in scheduling, while also minimizing quality-control issues. 

Office buildings. Perhaps the chief advantage of utilizing structural steel for office building construction is cost. Steel is easily integrated with other building systems, facilitates reduction in floor-to-floor heights and mechanical equipment requirements, and can lower both construction and ongoing operational costs. In situations where offices are developed through adaptive reuse, many older structural steel buildings can be economically rejuvenated. Other benefits include:
Enhanced scheduling. By using the latest interoperable design-to-fabrication software systems, Building Teams can benefit from improved communications and often reduced project schedules. The technology, when applied to steel systems, can reduce the lead time required to get design approvals and fabricated steel to the job site.
Greater flexibility. Universal structural systems can be economically integrated with all types of cladding and floor systems to achieve desired architectural and structural requirements. Wide-open, column-free areas maximize usable office space and offer tenants the freedom to maximize productivity through flexible office planning. Economical post-construction structural modifications are also possible with steel framing, helping owners to attract and retain tenants.
Favorable initial and life cycle costs. Steel’s low-cost construction and operational costs, together with the flexibility to meet changing tenant needs and to upgrade the appearance of the building, can lower owner break-even points and maximize profit over the life of the property.

Healthcare. The health sector demands buildings that are flexible and adaptable in use, and which can be constructed rapidly to meet tight program requirements. A number of construction systems have been developed to ensure that Building Teams have a range of options for healthcare projects, which require speed of construction, flexibility, and adaptability for future requirements. They must also meet seismic requirements, overall quality needs, and budgetary constraints.

With regard to technical needs specific to healthcare, using steel can assist in minimizing disruption to ongoing hospital operations and ensuring relatively clean construction operations. Steel systems can be detailed to improve vibration and acoustic performance, as well as to integrate building services as needed through web penetrations. Moreover, the thermal insulation and environmental sensitivity of many steel cladding systems make them suitable for use in the healthcare industry, where these factors are in high demand. For seismic upgrades, new innovations such as steel plate shear walls have also been effectively utilized in many recent healthcare projects.

Schools and universities. In classroom and laboratory buildings, steel maintains a market share in excess of 70%, according to the AISC. Educational facilities often require long-span roof systems and large bay sizes for which structural steel, combined with steel joists, is ideally suited. At the university level, a strong trend is developing to select structural steel framing systems for dormitory applications with the girder-slab system.

Stadiums and arenas. Long-span roof trusses are the ideal solution for roofed stadium and arena structures, many of which (including some with retractable roofs) have been constructed in recent years. The ability to utilize 3D modeling, such as building information modeling, or BIM, as well as steel design-to-fabrication systems, has enhanced the integration of structural design and detailing for the compressed project schedules for stadiums in Chicago, New York, and Washington, D.C.

Industrial buildings. Here, the trend is toward more open and flexible interiors, similar to warehouse and distribution facilities. Structural steel combines the strength to efficiently handle large industrial loads with the long spans necessary to minimize column grids within manufacturing zones. Low-rise buildings now dominate the U.S. industrial building market. These structures are either fully framed in structural steel—with perimeter steel framing—or they utilize tilt-up concrete panels as load-bearing walls on the exterior with steel framing and column systems in the interior. 

Retail. Here, too, open floor plates are driving design solutions, and so traditional steel framing dominates the retail marketplace, with owners recognizing the benefits of large clear spaces for merchandising and operational efficiency. Retail owner-operators have many demands, which steel construction can meet: fewer interior obstructions and exterior limitations; greater ease of expansion, operational changes, reinforcement, and changes in usage; and less hassle with architectural changes, resale opportunities, and construction scheduling and budgeting. Some owners also appreciate the savings in foundation costs, the efficient use of fire protection, and long-term durability that steel affords.

About the authors

C.C. Sullivan is a communications consultant and author specializing in architecture and construction. Barbara Horwitz-Bennett is a writer and contributor to construction industry publications.












































































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This BD+C continuing education program qualifies for 1 AIA HSW learning unit.

Reed Business Information is a Registered Provider with the American Institute of Architects Continuing Education Systems. Credit earned on completion of this program will be reported to CES Records for AIA members. Certificates of Completion for non-AIA members are available on request.
       This program is registered with the AIA/CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product. Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.


         
 

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