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Advantages and Disadvantages of steel structures over reinforced concrete structures???

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What are the advantages and disadvantages of steel structures of reinforced concrete structures???

asked Jul 23, 2012 in Civil Engineering by Naveen222  
edited Aug 16, 2012 by Haseeb Jamal

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Safety

Concrete: Concrete is safer. The building’s core (where elevators, stairs, and power systems are located) will be encased in 2-foot-thick concrete for protection in the event of a fire or terrorist attack. Cast-in-place reinforced concrete offers outstanding resistance to explosion and/or impact. Moreover, it can endure very high temperatures from fire for a long time without loss of structural integrity.

Concrete requires no additional fireproofing treatments to meet stringent fire codes, and performs well during both natural and manmade disasters. Because of concrete’s inherent heaviness, mass, and strength, buildings constructed with cast-in-place reinforced concrete can resist winds of more than 200 miles per hour and perform well even under the impact of flying debris. Concrete can exhibit increased ductility - a must in areas prone to seismic activity. However, according to the Skokie, IL-based Portland Cement Association (PCA), the performance of any building during an earthquake is largely a function of design rather than the material used in construction.

Steel: Experts acknowledge that steel can soften and melt with exposure to extremely high temperatures. However, with the addition of passive fire protection, such as spray-on fireproofing, buildings built of structural steel can sustain greater temperatures and, therefore, provide additional safety.


COST

Concrete: It’s true: Prices of construction materials have spiked. However, the cost of ready-mix concrete remains relatively stable, and even the increase in steel has had a minimal effect on reinforced concrete building projects. Concrete prices remain very steady despite the fluctuating and substantial increases in other building material prices.

While cast-in-place concrete construction can be pricier on the front end, the return on investment achieved can lessen the cost differential. Insurance companies recognize the benefits of a cast-in-place reinforced concrete office building because the aforementioned benefits - increased safety and structural integrity - reduce liability on their part. Insurance companies also report that owners and developers of a Class-A, cast-in-place reinforced concrete-framed office tower with a concrete core and wider egress stairs will save nearly 25 percent annually on the cost of property insurance.

Steel: The big news in development is the price of steel. And while structural steel has experienced a 50-percent increase over mill prices since November 2003, experts like Cross stress that structural steel represents less than 20 percent of all the steel used in building construction. If you look at the overall impact on project costs, in the past year we’ve seen project costs go up by about 10 percent as a result of increases in all types of construction materials. The increase in cost of the structural framing system represents less than 2 percent of the 10-percent increase in project costs.


MATERIAL AVAILABILITY

Concrete: As recently as the fall of 2004, many states were reporting a shortage of cement, the primary binding ingredient used in concrete. Other factors contributing to the shortage are shipping rates and the limited availability of transport ships. With imported cement supplementing domestic supplies, skyrocketing shipping rates and limited freight transport have resulted in higher costs and unreliable supply.

Despite tight supplies of cement in some regions of the United States, the impacts have been greatest on smaller companies, builders, or contractors. Developers are using concrete frame buildings in every building sector, and count on concrete for stable pricing and availability regionally.

Steel: Steel availability has been the subject of more than a few conversations lately, with the blame placed on the ever-expanding construction activity in Asian countries like China. However, experts from the steel industry are eager to dispel the myth that there simply isn’t enough steel to go around. Over the past year, there’s been a lot of misperception out there in terms of availability of material. “There is no shortage. The United States’ structural steel industry has the capacity to produce 6 million tons of structural steel per year. In 2004, our usage was about 4 million tons of wide-flange structural product, which means there is certainly adequate capacity to meet any growth in the foreseeable future. Structural steel is readily available.”


CONSTRUCTION SCHEDULING

Concrete: The old adage “time is money” was never more true than when talking about construction schedules. Buildings with concrete can almost always be built faster. When compared to structural steel, sometimes twice as fast. It is not uncommon for cast-in-place reinforced concrete buildings to rise one floor every other day. Developers can finish jobs faster, earn a profit, recoup capital, and move on to the next project.

Steel: While concrete’s 2-day cycle may seem to give it an unarguable advantage, steel provides many construction benefits of its own. We believe that they result in an accelerated schedule. We also believe that quality is enhanced because of off-site fabrication, and that the productivity opportunities that exist in construction can be best addressed in off-site fabrication with a reduction of actual on-site time and on-site construction.


DESIGN POSSIBILITIES

Concrete: Concrete buildings are taking many different shapes. In addition to the unique aesthetics achieved with concrete construction, these buildings offer some very real space advantages. Public and private developers should also realize that using cast-in-place reinforced concrete to frame a high-rise office building would yield more rentable space because of lower floor-to-floor heights. With proper engineering, concrete building can also offer uninterrupted floorplates.

Steel: Steel has the highest strength-to-weight ratio of any construction material. And with new construction methods, steel buildings remain a popular choice for office and multifamily developers. Use of girder slab, staggered truss, and castellated beam construction enables lower floor-to-floor heights than typically expected in structural steel buildings. Steel can accomplish extremely long spans in structures [and] very open-bay footprints without intermediate columns. It’s a very flexible material in terms of different ways to address design requirements.

answered Aug 16, 2012 by Haseeb Jamal  

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