The listing of Problems-Preventive Measures- Remarks at the end of this article is a compilation of the most frequently encountered situations related to structure, some thoughts on preventing or at least minimizing their occurrence, and the reasons most often cited for not complying with the suggested preventive measures. This discussion presumes theat the structural design has been accomplished utilizing all available advanced technology for high rise buildings and that faulty design is not the reason for the distress. (1) Shrinkage cracks in structural slabs and walls occur primarily when large areas are cast continuous and/or abrupt change is required in plan geometry. They are also aggravated by casting concrete with high water/cement ratio or using wire heating. A preventive measure would be to cast concrete in manageable size areas with construction joints at predetermined lines of possible shrinkage cracks. Use a checkerboard casting pattern if possible. Use low slump concrete and assure that no water is added to the concrete at the job site. (2) Cracking and/or honeycombing is found at the bottom of concrete slabs. Inattention to construction overloads on the slab and lack of or incorrect shoring are the most usual causes of cracking or honey-combing. In many cases, however, it is caused by placing greater than one-half inch conduit below the bottom reinforcing. This requires epoxy cement for adequate repair. (3) Temperature movements of exterior concrete frame or concrete walls create cracks in partitions and slabs of buildings greater than 25 to 30 stories in height. Preventive measures include partition joints to allow for building movements, designing the structures to allow rotation in the slabs, and insulation of the structure against temperature variations.
