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Innovators of Post-tensioned, Reinforced Concrete, Tilt-up Wall and Steel Frame Software

Saturday, March 13, 2010

Structural Engineering's Part in Sustainable/Green/LEED Design

Sustainable Design / Green Building / LEED are terms that are becoming a large part, & will become a much larger part, of our profession.  But what do these terms really mean?  What makes a Sustainable Design or a Green Building or a LEED certified project? And how does this affect Structural Engineering?

But first, why should we care?

On average, each American uses their weight in natural resources (food, fuel & materials) on every day.  If every person in the world were to live at our standard (which they are ALL trying to do), we would need 5 planet earths to sustain it.  In the mean time, at our present rate of consumption, we have increased the level of greenhouse gases to the extent that the polar ice caps are melting, we are experiencing violent storms like never before, we have wiped out half of our forests and have already faced the largest extinction of organisms and species since the dinosaurs.

To simply maintain what we have, we ALL need to be taking significant pro-active steps to reduce the impact that we have on our environment.  For us in the Building Design Professions, that means designing Sustainably.

For the sake of the conversation, let’s just use the word GREEN.  The ultimate GREEN building would be one that:

1.     Used very little energy to operate (i.e. My father built his house in 1952 with concrete block “thermal mass” exterior walls, white rock roof, with an attic fan connected to a thermostat to cool the house and a highly efficient regionally controlled radiant heating system).  In modern terms, this could be as simple as installing solar collectors on the roof;

2.     Used very little energy and natural resources to build;

3.     Used waste materials (i.e. flyash) and/or recycled (or recyclable) building materials that preferably came from local indigenous building materials (the cost to the environment in pollution to transport building materials from distant places is antithetical to GREEN).  If you are in the Pacific Northwest, building out of wood makes GREEN sense – it is local, renewable AND in many ways feeds the local lumber economy;

4.     Created little pollution in it’s construction and long term operation (this applies not just to the building, but also to the actual building materials. Manufacturing building materials creates pollution itself – although sometimes for the better good, i.e. the manufacture of the waste product sawdust into lumber, and sometimes not);

5.     Created little or no damage to the local environment (i.e. I remember reading an environmental impact report for a full valley that had been bulldozed to bare earth, that the construction of new housing in this valley would have no negative impact on the indigenous plant and animal life – Heck NO – the bulldozers killed them all already – there were none left to impact);

6.     Utilized the surrounding environment to reduce use of energy in construction and long term use (i.e. My father built his house under the shade of 4 mature walnut shade trees);

7.     Is designed in a way that the Building itself does not create pollution or negatively impact the environment (i.e. new large building projects are in many places that are now required to capture and pre-treat rain water on the site, prior to discharging the water to the Storm Sewer);

8.    Is designed in a manner that the waste products from construction (and demolition) are reduced and/or properly recycled; and

9.    Is designed in a manner that does not negatively impact the surrounding existing buildings or environment.

What a mouthful!!   Is all that possible?  Most likely not – but that is not the point of GREEN design.

Every action has a reaction – that Newton taught us. 

On a reality tv show, they build a shelter with indigenous palm throngs and cut bamboo and ultimately leave a mess that they set fire to at the end of the season – NOT VERY GREEN. 

In cutting lumber, milling lumber, shipping and installing lumber, energy is used and damage to the environment occurs.

It is pretty much a no- brainer to realize that an 80 story building, which requires a 60 foot deep hole in the ground & pilings extending another 40 feet into the ground (forever dedicating this site to this building) and massive amounts of building materials to construct (to the point that it is more expensive to demolish than to build) is on it’s face not GREEN.  In fact, on this basis, pretty much every modern building that we construct is not GREEN – in this Ultimate sense.

But then we can’t all just crawl into our thatch huts.

The whole point of GREEN design is to make intelligent decisions that reduce the impact of Architecture on the environment (in a positive manner) while at the same time increase the efficiency, useability and, in addition, the life span of such buildings.

Within the GREEN community, within Architecture & Mechanical/Electrical/Plumbing Engineering,  what is Sustainable Design is in many cases codified.  Plumbing systems that reduce the use of water, Electrical Systems that reduce the use of energy, Architectural building designs that provide shading, use low e glass, etc.

But for Structural Engineering, there is little specific to point to.  The use of Fly Ash (the waste product of burning coal) in concrete mixes is usually the first thing mentioned, and then the conversation often turns silent.

The Structural Engineer’s job in GREEN design is to:
A.     As much as possible, utilize renewable building materials in their designs;
B.     Recommend and design innovative new or already existing building materials and/or construction methods that meet the goals mentioned above;
C.     Sharpen the pencil and design efficiently.

In recent years, in virtually every building material, there have been great advances in new methods of building. 

Masonry - the use of structural brick instead of concrete block allows you to use less material in construction and cause less damage to the environment in manufacture.

Wood – economizing in material (i.e. using 2x6 studs at 24” o.c. instead of 2x4 studs at 16”) or utilizing new engineered materials (i.e. new glulam beams which have lvl’s as the outer ply’s) or designing with LRFD are just examples of ways to improve the building performance or reduce the use of resources.

Light Gauge Metal Framing – when used as bearing walls in multistory buildings, where concrete or conventional steel frame would otherwise be required, significant reductions of the use of steel are realized, since the partitions do double duty as the structural system.

Steel Frame – the use of tapered beams or girders, reducing the section of the steel to what is actually required, has been a proven method over the years for reducing the weight of the structure and improve building performance.  POSTEN Engineering Systems sells a great program “TaperSTEEL” for this Efficient Tapered Steel design.

Concrete – Post-tensioned Concrete has all but replaced conventionally reinforced concrete structures due to the significant savings of concrete and steel.  But designing with most post-tension programs is inherently inefficient.  These programs use a trial and error method to lead you after a lot of work to a “code compliant” design.  You may never get to an efficient design.  But even an inefficient post-tension design is better than a conventionally reinforced concrete design. 

On the other hand, POSTEN Multistory by POSTEN Engineering Systems Automatically designs (not just a code compliant design) a Highly Efficient Design.  Going further, POSTEN Engineering Systems, with it’s proprietary stress balancing algorithms, will Automatically design the most efficient design possible, and then tell you how much steel was saved in the process.  In addition, POSTEN Multistory will Automatically determine the thinnest section of concrete possible and Automatically design an Efficient design for that thinnest section.  Going for that Ultimate GREEN design, POSTEN Multistory is the only program in the world that will design a Multistory Post-tensioned Concrete Moment Frame Structure.

The opportunities for GREEN building structural design are endless. All it takes is a different Holistic approach to design and a willingness to do it.

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