Masonry Magazine August 1982 Page. 28
FRAME SHORTENING
continued from page 9
its floors at the theoretical elevations called for in the drawings.
Engineers have long known of this condition and have taken it into consideration in their detailing. Sometimes, however, craftsmen in the prefabricated curtain wall industry, including prefabricators of natural stone panels, have not given this sufficient consideration. On many highrise projects designed to be clad with stone, the panels have arrived at the jobsite equipped with connections that do not line up to the corresponding concrete slabs-because of the shortening that has taken place. Or they have been installed and popped out sometime later as the frame shortened. This is true for all types of curtain wall materials.
The way to avoid this is simple: understand that all non-structural elements of a building, including the curtain wall, must be able to act independently of the structural frame. Then the materials can be designed and installed accordingly.
In the case of stone curtain walls, the detailer and fabricator must allow for some future movement at the point where each prefabricated panel is connected to the concrete slab, and establish proper joint dimensions between the panels. This is true for both stone panels supported on concrete panels, and for those supported on steel frames. This principle should be no great mystery to curtain wall fabricators because they must also take into account the effects of thermal changes, which tend to make the panels expand after they are installed.
Pre-construction Surveys Urged
Curtain wall fabricators should perform a pre-construction survey. This appraisal will enable them to modify the theoretical joints between panels so as to compensate for the elastic shortening of the frame which has already occurred and permit connection of the panels to the structural frame. Fabricators must make certain that there is sufficient joint left to accommodate long-term shortening of the frame and thermal expansion of the metal.
With brickwork, horizontal compression joints are specified which, if properly constructed, will accommodate thermal expansion of the masonry wall and shortening of the structural frame.
This relatively simple problem is causing some major headaches, costing millions of dollars and only helping lawyers and claims consultants who are busy handling its disputes. The building industry at large should realize what is happening, and why it's happening. With this basic knowledge future mistakes, miscalculations, and misunderstandings can be avoided.
Fig. 3-Whenever mechanical engineers and contractors design and install vertical pipes, they must make allowances for frame shortening and take care to prevent the pipes from adhering to the concrete slabs.
An Observation by PCA
Although initially it was assumed that creep and shrinkage shortening of the concrete walls and columns were the primary causes of distress in the cladding, it was found that a number of factors contributed to the expansion of the cladding which magnified the problem, such as:
* expansion of the cladding due to hot exterior temperature and direct sun radiation; and
* expansion of masonry due to moisture absorption, particularly in inadequately fired clay masonry.
Where no special details were considered in the design, vertical piping has occasionally exhibited distress where hot liquids have elongated the pipes.-Portland Cement Association
Insurance Insights...
$2,000,000 Verdicts?
The $2,000,000 personal injury verdict may become commonplace, according to Trial Lawyers Quarterly. Since the first $1,000,000 verdict was returned in 1963, there have been 318 more seven-figure decisions in the appellate court. In 1970 a brain-damaged child could expect average compensation of $400,000. Today, amputee victims receive up to $800,000, while paraplegics and quadraplegics can expect as much as $1.9 million.
If this prediction sounds extreme, consider the case of nine-year-old Margaret Noble of Ronkonkoma, N.Y., who suffered brain damage and was rendered blind and partially paralyzed after remaining under anesthesia and left unattended for 20 minutes following an operation. The court approved a settlement of $6.7 million with her surgeon and anesthesiologist-$500,000 up front plus annual payments for the rest of her life.
The trend seems inevitable. Yes, it's probably time to review the limits of liability on ALL your insurance-both property AND casualty. Commercial Insurance Service, Inc. Newsletter, Charleston, W.Va.
30 MASONRY-JULY/AUGUST, 1982