Cast-in-place concrete, the next 'must have' for safety.

The recent disclosure of findings by the National Institute of Standards and Technology (NIST) regarding the September 11, 2001 collapse of the World Trade Center towers has borne out what the Concrete Alliance has been saying since 9/11--that cast-in-place reinforced concrete, due to its strength and lower thermal conductivity rating, is safer than any other building material.

Throughout its findings, NIST investigators clearly point out that the extreme heat caused by the ignited jet fuel and other factors, caused the steel frames of the buildings to buckle, contributing to the collapse of both towers.

According to NIST researchers, steel looses its strength and structural integrity quicker than high-strength concrete.

Damaged and dislodged fireproofing from the structural steel frames of the buildings also contributed to the collapse of the towers.

While spray-on fireproofing is an approved material for use in the construction of New York City high-rise buildings, the Concrete Alliance's inquiries to Underwriters Laboratories (UL) revealed that when UL conducted tests on spray-on fireproofing on steel to ascertain a fire rating for a manufacturer, water (in excess) was used to cool down the steel quickly.

In these tests, UL testers visually noted that spray-on fireproofing "falls off" the steel assemblies after the steel was hit with water to cool it down.

This would not happen if the steel were encased in concrete. However, the use of high-strength cast-in-place reinforced concrete frames for high-rise office towers, with concrete cores and wider egress stairs, provides a stronger, safer building that is terrorist resistant than other building materials, blast-resistant, soundproof and has the ability to reduce the feeling of motion caused by wind.

The primary emphasis has and continues to be that a cast-in-place reinforced concrete-framed high-rise office building provides a safer, stronger structure. For this reason, the Concrete Alliance has encouraged the use of the cast-in-place reinforced concrete for office buildings. After all, it is the material of choice for high-rise residential buildings, hotels, shopping centers, bridge roadway decks, dams and tunnels.

In other words, it protects where we live, vacation, shop as well as our water resources. The time has come for its extensive use as a framing system for our high-rise office buildings.

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. It would also provide more flexible space and significant energy savings over the lifetime of a structure.

The mass of a concrete structure makes it a significant thermal reservoir with the ability to store larger amounts of energy. In heating months, concrete walls and floors absorb interior heat during the day, and then radiates warmth back into the space at night. The same principle holds true for cooling. This thermal inertia allows concrete to maintain a relatively steady interior temperature.

Building owners using a cast-in-place reinforced concrete frame and a concrete core in the construction of a high-rise office tower results in additional savings. Because of the lower floor-to-floor heights, fewer electrical wiring ducts, piping and building skin is required. This saves the owner more money while providing more retable space, increased safety and greater structural integrity. In addition, insurance companies recognize the benefits of a cast-in-place reinforced concrete office building because the aforementioned benefits, i.e. increased safety and structural integrity, reduces 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.

When it comes to safety, especially for a high-rise office tower and its occupants, there is nothing like cast-in-place reinforced concrete. It's a shame it took a tragedy like 9/ 11 to point out the advantages of reinforced concrete over other building materials.