Concrete or steel?

THE DESIGN of the new World Trade Center in New York includes safety measures such as a 24-inch-thick concrete wall enclosure for its building core, where the elevators, stairs and power system are placed for protection from fire or terrorist attack. Photo from boston.com

Choosing A construction material for a building is a dilemma for any designer. The right decision can have a positive or negative impact on the success of a project in terms of cost, schedule and overall quality.  The construction industry accounts for half of all resources used worldwide, which calls for building designers to use caution in the choice of material.

This is particularly the case when choosing the material for the structural system of a building—literally the spine that keeps the building standing.

Today there are two dominant building construction materials—steel and concrete. They make a good combination in construction. Concrete provides a solid support for the weight of the building and steel can hold taller structures up.

The question is which material is the best for construction—steel or concrete?

Time savings with steel

Using time element as the starting point, steel-frame construction helps reduce construction time with on-site erection of the steel frame. This means less overhead costs during project construction. For high-rise buildings the time gain can be considerable.

With the advancements in building information modeling, integrating the design and fabrication of steel has resulted in an accelerated process.

Although steel-frame construction is faster, the procurement, fabrication and delivery of steel may take 6 to 10 months lead time.

Steel members can be assembled in factories providing better quality control whereas pouring of on-site concrete is subject to labor-intensive systems that may affect quality.

Structural steel frames can provide longer spans, thus offering column-free spaces and flexibility in space planning.

Steel may be recycled in its original or near-original state while concrete can be reused mostly in a downgraded form such as filling material.

More steel is recycled each year than all other materials combined, including aluminum, paper and glass. Steel is the only material that can be recycled over and over without ever losing its quality.

The key to sustainability in steel construction lies in its design. It should be readily dismantled.  Bolted connections are preferable to welded connections.

Concrete is safer

The design of the new World Trade Center in New York includes safety measures such as a 24-inch-thick concrete wall enclosure for its building core, where the elevators, stairs and power system are placed for protection from fire or terrorist attack.

Today’s buildings in Asia are also adopting similar measures for protection from seismic forces and terrorist attack.

These developments confirm what the concrete industry is saying: concrete is safer.

Reinforced concrete is resistant to explosion and impact.  It resists high temperature from fire for a long time without loss of structural integrity.

For concrete, the design possibilities are almost limitless. It can take on many unique shapes and forms.

Aside from their varied design possibilities, concrete construction gives more rentable space because of lower floor-to-floor heights. Steel framing details typically involve decking that rests on joists, joists on beams, then beams on girders.  This can mean a very thick floor.  Concrete requires only 8 inches where utilities can run.

In the end, it’s the building’s function and requirements that will determine whether to choose concrete or steel.

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