By Alan Whitson
Slowly, green products are working their way into projects. New carpet is now made from old carpet. When that carpet must be replaced, the manufacturer will again recycle it into new carpet. Gypsum wallboard is being made from fly ash, a byproduct of electrical production, rather than gypsum from a quarry. Mercury is a highly toxic but essential component of fluorescent lamps; yet, one lamp manufacturer has invested millions of dollars in reducing the mercury in its lamps, while others simply looked for ways to pass government-mandated tests.
However, sustainability goes beyond using green products; it’s the whole process – from concept through operation – that makes a building sustainable. A common misconception about sustainability is that it costs too much. Not only is that wrong, but the sooner sustainability is integrated into the design and engineering process, the greater the opportunity for savings. The objective is to optimize the use of resources, reduce inefficiencies, and save both time and money.
Sustainability is really about adding value, whether it is shareholder value or the value of your building. You can literally turn green into gold.
Let’s illustrate by examining the Aladdin Hotel in Las Vegas. This 38-story, 2,600-room hotel was originally designed like most Las Vegas hotels to incorporate a concrete frame. However, when the bids were higher than expected, creative alternatives were needed.
SMI-Owen Steel Co., Columbia, SC, submitted a proposal for a staggered steel truss structural system that cost 10-percent less than the original concrete frame design. Besides saving over $4.5 million in hard construction cost, a major reduction in construction interest expense was possible since the hotel was completed four months sooner. However, the big money was in the ability to start the $2-million-a-day revenue from hotel and casino operations 120 days sooner – that’s almost a quarter of a billion dollars.
Developed by MIT in the late 1960s, the staggered-truss system is appropriate for use in such buildings as apartments, condominiums, dormitories, hotels, and nursing homes that are six stories or more in height. This innovative system has most of the advantages of flat-slab concrete construction at significantly lower cost. Neil Wexler, author of The AISC Design Guide for Staggered-Truss Buildings, says it’s the use of geometry that is the basis for the savings over concrete and traditional steel designs. Other benefits include minimum deflection and greater stiffness in the structure while reducing seismic loads and foundation costs.
The heart of the system is the story-high trusses that span the width of the building. The trusses are concealed inside demising walls with vierendeel openings in the trusses for corridors and door openings. This allows column-free areas up to 60 by 70 feet, while the column spacing for conventional post-and-beam steel construction is 25 feet to 30 feet; for a concrete structural system, it is 18 feet.
Structural elements align from floor to floor in typical post-and-beam construction. However, in a staggered-truss system, the trusses form a staggered pattern; hence, the name. To illustrate, the trusses on the second floor would extend across the building at column lines 1, 3, and 5; on the third floor the trusses would be at column lines 2, 4, and 6. The top chord of the second-floor trusses align with the bottom chord of the third-floor trusses. Precast concrete planks are used to create the floor deck, producing a semi-finished floor and ceiling in one operation, eliminating the wet trades and allowing all-weather construction.
Continue Article >> Part 2 - Less is More Green