Masonry Magazine October 2006 Page. 17
V
WITHIN THE LAST FEW YEARS, THE GROWING CELLULAR PHONE INDUSTRY HAS UNDERTAKEN THE TASK OF ADDING THOUSANDS OF NEW ANTENNAS TO IMPROVE THE QUALITY OF ITS SERVICE. Since they have the need to locate antennas at regular intervals throughout large urban settings, some of the networks have contracted with owners of existing properties to attach them to the tallest structures in the area. Many of these locations happen to feature tall masonry chimneys.
The usual type of antenna for cellular networks consists of an array of vertical metal tubes attached to structural steel support frames, and there is often a significant amount of weight and wind resistance associated with their installation. Of course, when such conditions pose a risk to the safety of the structure, local authorities call upon structural engineers and chimney inspection firms to assess the likelihood of damage and/or collapse of these chimneys.
Design History Versus Present Day Conditions
PRIOR TO THE WIDESPREAD USE of natural gas and oil-fired boilers, most industrial and institutional chimneys were designed to convey coal-fired boiler exhaust gases. These gases were generally quite hot (400 degrees F, or higher) and they contained large percentages of noxious sulphuric and nitric oxide gases. Because coal was inexpensive and coal-fired boilers were not particularly efficient, the chimneys were called upon to exhaust very large quantities of gas at relatively tall heights so as to keep the surrounding air clear of ground-level atmospheric contamination. The resultant chimney had to then meet the following criteria:
* The cross-sectional area of the chimney had to be large enough to handle a heavy volume of flue gas.
* The structure had to be able to withstand high heat conditions without transmitting heat through any of its walls that were in contact with adjacent building components.
The Voice of the Mason Contractor
October 2006
Masonry
15
2006.
06 Jupiterimages Corporation