There are more solutions to precast concrete connection difficulties than there are engineers solving the problem. These comments are not designed to discourage ingenuity in developing new designs, but to belabor the obvious factors that may be overlooked under the halo of enthusiasm. The first step in designing precast panels is to examine the governing building code. Keeping these code requirements in mind, it is obvious that the simplest connections to a building would be two load-bearing connections located as near the horizontal line through the center of gravity as possible, with tie-struts to prevent rotation due to horizontal forces perpendicular to the face of the building. If the height of the center of gravity above the support level is h and with width between the supports is a, for loads parallel to the face of the building the over turning force produces 2W times h. Next we must consider the condition of 2W acting horizontally at the center of gravity in the plane of the face of the building. Then vertical reactions then become .5W plus or minus 2Wh/a., which is a equals 4h, becomes .5W plus or minus .5W. Again, to provide relative movement between the panel and the building, the top connections may be simply bolts set in oversize holes with double nuts and washers, finger-tightened and tack-welded, to hold vertical alignment of the face of the panel. Economy of erection dictates that connections must be designed to allow the crane to set the panel in place with temporary anchorage permitting the crane to move on to the next piece. Alignment and permanent anchorage can be accomplished without the crane.
