AMSYSCO Post Tension Blog

QUICKER CONSTRUCTION SCHEDULE

Another important element that has an environmental influence is the speed of the construction schedule.  Ideally, structures can be built faster with unbonded post-tensioning at no additional cost.   Accordingly, the impact of construction on the surrounding environment would be less.  The environment could be an urban jungle or the natural wildlife.

Living in downtown Chicago, I am accustomed to traffic jams due to construction projects.  The daily gridlock of automobiles and trucks create pollution and smog in the local vicinity.  AMSYSCO, Inc. worked on 340 E. Randolph Condominiums, a 62-story unbonded post-tensioned building that was built at a rate of one floor every 3 days.  (It became the first residential tower in the Mid-West America to achieve Silver LEED certification for its “green” design.)  The construction team shaved off more than two months from their schedule using a combination of post-tensioning, specialized forming and stronger concrete.  Ultimately, it reduced vehicular carbon emissions and the strain on local infrastructure.

Additionally, a quicker construction schedule will reduce the number of days with noisy construction (noise emission).  Residents and animal-wildlife in the surrounding ecosystem will benefit from the reduced human activity.  While there is the obvious political, social and economic pressure for constructing structures, we can attempt to protect the ecosystem and reduce the impact of the construction industry.

Post Tensioned Concrete and LEED (part 1)

Post Tensioned Concrete and LEED (part 2)

- Neel Khosa, AMSYSCO

Copyright © 2009 by AMSYSCO, Inc. All rights reserved.

Several years ago, I attended a symposium headed by Mr. Rick Fedrizzi, President of the U.S. Green Building Council (http://www.usgbc.org/), regarding the LEED green building program.  During the symposium, the environmental effects of construction, housing and coal powered plants were the topics of discussion.  I saw a definite value for reducing our carbon footprint during the construction and occupancy phases using the “less is more” philosophy.  In the past few years, I have noticed that more new construction projects have sought out a LEED certification.

While I don’t claim to be a LEED expert, I have done some basic research on the subject and how my industry, unbonded post-tensioned concrete, factors in.  I believe that unbonded post-tensioned concrete can help some mid-rise and high-rise office/residential buildings received a higher LEED rating.

BUILDING HEIGHT

The potential for a reduction in the building height (and floor-to-floor height) is one key benefit that Unbonded Post-Tensioning has over Structural Steel.  The Post-Tensioning Institute issued a technical bulletin which compares the savings in building height:  a typical 10-story structural steel building has a height of 125’ whereas a typical 10-story post-tensioning building has a height of only 108’.  The impact of the 13.6% reduction in vertical height is obvious – the quantities of all vertical elements will be reduced.

When compared to a Conventional Rebar slab, an Unbonded Post-Tensioning structure can function with thinner slabs and smaller columns.  The Post-Tensioning Institute issued a technical bulletin which showed a 16% reduction in concrete with a post-tensioned residential building (excludes foundation).  Also, the weight of the steel (post-tensioning tendon and rebar) inside the slabs/beams was 20% less in the post-tensioned structure versus a conventional rebar structure.  Finally, the vertical height was reduced by 2% in the post-tensioned building.

With a reduced building height due to unbonded post-tensioned concrete, there are potential savings for the following:

Construction

1. Piping for Mechanical, Electrical/ Telecom/Security, Plumbing, Fire Protection, etc.
2. Facades with Curtainwall, Precast, Masonry, etc.
3. Concrete Columns and Shear Walls
4. Elevators, Metal Stairs, Construction Hoists/Cranes
5. Reduced floor-to-floor height can reduce material for interior finishes (drywall, etc.)
6. Reduced freight, CO2, pollution, labor, manufacturing, etc.

Operational Life-Cycle Savings

1. The building will cast less of a shadow on the ground.  This can allow grade-level vegetation to receive more sunlight.  Therefore, landscaping costs and water usage for irrigation can be reduced.
2. There will be a reduction in the energy required to vertically transport liquids (water), gases, cooled air, people, etc.  Ultimately, this should reduce the energy bill for the owner(s).
3. Quicker evacuation times in case of emergencies for tenants on the upper levels.
4. Reduced floor-to-floor height and volume can reduce HVAC costs within units.

In future posts, I will talk about Building Weight, Quicker Construction and other LEED items.

Post Tensioned Concrete and LEED (part 2)

Post Tensioned Concrete and LEED (part 3)

- Neel Khosa, AMSYSCO Inc.

Copyright © 2009 by AMSYSCO, Inc. All rights reserved.