Consulting-Specifying Engineer - August 2007 - (Page 34)

Lightning protection Inevitably, extra-tall buildings are occasionally struck by lightning. To protect life and property, it is important to provide a well-designed lightning protection system that complies with the local standards. Once again, the electrical engineer must cooperate closely with the architect and structural engineer. The lightning protection system will form a Faraday cage around the building. The architect and engineer must work together to ensure that the copper grid placed at roof level is adequately secured. The electrical engineer must work with the structural engineer to locate the down conductors that direct the lightning energy to the earth. Copper conductors within the structure can be used; however this added cost is unnecessary since the rebar that exists within the building columns already is also a good conductor and is commonly used for this purpose. equipment, but this solution is not practical for all types of equipment. Services will be supplied radially from each service room to the point of utilization. The routing of cables and conduits that exit these service rooms presents another challenge. The electrical and telecommunications rooms in the service cores may be located adjacent to an elevator shaft and riser shafts for air distribution or linen or garbage chutes. Service raceways may not penetrate such risers, so the electrical engineer may be faced with a limited exit window. Usually, these raceways will exit into a public area and must be routed above a ceiling. These constraints may limit the size of the raceway window to the extent that it cannot accommodate all required raceways, resulting in the need for additional service risers on each floor. Cabling limitations also may result in additional service risers. The length of power distribution conductors will be limited by overall voltage drop. HoriIn many cases, the electrical engineer will zontal telecommunication cables (category 5 and find that the electrical spaces provided in category 6) are limited to a the initial design are irregular, undersized maximum length of 295 ft. and impractical. to comply with acceptable standards. It is clear that the architect and electrical the design process, they usually result in engineer must work together closely so that unsatisfactory results and project delays. the electrical equipment can be accommoThe height of a structure is determined by dated and safely serviced without excessive the number of floors that the owner or developloss of usable space. This requires a signifier decides are necessary to make the building cant amount of cooperation and compromise financially successful, together with the floorfrom both parties. to-floor height of each floor. The greater the floor-to-floor height, the greater the cost of conStructural constraints struction. The architect’s challenge is to limit the It is common to embed electrical conduits floor-to-floor height while maintaining a pleasant into a concrete struc- environment and esthetically attractive appearture, which creates a ance. At the same time, the architect must work special challenge for with engineers to ensure that adequate space the structural engi- is provided for routing of services and that the neer, especially in integrity of the structure is maintained. high-rise construcUsually distributed through common tion. The electrical public areas above ceilings, the electrical engineer must consult and mechanical services must be carefully with the structural engineer to determine the maximum size and concentration of conduits that may be embedded in the slab. The type of slab construction and the thickness of slab will determine the extent to which the conduits can be accommodated. The complex structure of tall buildings usually includes levels with deep transfer beams. The electrical engineer must be familiar with the structural elements, as it is likely that they will cause interferences in routing of services. The structural engineer will usually accommodate limited, minor penetrations through structural elements; however, when these become numerous and large, careful coordination and planning will be required. The structural and electrical engineers must cooperate closely with respect to major vertical and horizontal structural penetrations. It is important that large penetrations and openings are identified early so that they can be designed into the structure. When these elements are identified late in 34 Consulting-Specifying Engineer • AUGUST, 2007

Table of Contents Feed for the Digital Edition of Consulting-Specifying Engineer - August 2007

Contents M/E Roundtable Giants 100 Pullout Poster Giants Stand Tall: CSE Giants 100 Report Electrical Design for Tall Buildings HVAC and Fire Safety for Elevator Systems How to Beat the Codes GAS Technology Supplement Recovering Waste Heat from Boilers New Applications for Tankless Water Heating Systmes Techniques Improve for Powder Coating MDF New Tools Available for Heat Treating Steel Direct Drive Engines

Consulting-Specifying Engineer - August 2007

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