BFI Investigation of Cracking Post Tensioned Concrete Parking Structure
The following are excerpts from a BFI Building Forensics International investigation report of a concrete post tensioned parking structure.
The focus of the investigation had to do with the presence of cracking in elevated post tensioned slabs, this report can be divided into three parts, including: (1) Cracking of elevated slabs and shear walls; (2) Loading of the elevated slabs with stored and moving materials; and, (3) Conditions of the work like the presence of moisture and its consequence, including various kinds of stains and coatings.
For each elevated level, field notes for the deck were divided into the North and South portions, generally observing each deck’s cold joints as the dividing line for making records of features examined. After the observations made on the way to the Amenity Deck, BFI elected to count the number of cracks, measure cracks widths, report the widest of them on a deck to deck (half-deck) basis, and note whether there was evidence of prior repair.
While on the lowest three or four levels, there was a significant amount of construction activity in process. This included completion of the parking structure with ongoing installation of painting, fire sprinklers signage, lighting, ventilation, electrical power and controls, and plumbing to name a few. Thus there was quite a bit of traffic associated with these activities. Additionally, there was traffic and moving loads associated with delivering materials from the street to within the structure for use in the adjoining residential structure. When the first tour was complete to the Amenity Deck, many areas were noted where stored construction materials, tools and equipment were present, often enclosed within a lockable cage or fence.
All diagonal cracking was parallel and trended upwards from south to north, but had a consistent change of direction to horizontal as they approached the end of the wall. Described differently, when viewed from the parking deck, the cracks were oriented from bottom right to the upper left, becoming horizontal nearer the left end of the wall. Where these cracks were observed, the cracks could be observed from both the parking side of the shear wall and the stairwell side as enclosed by it. Measurement of crack width was not attempted as there was conspicuous evidence of several passes of sacking and patching which would render such measurements of doubtful benefit.
recurring diagonal pattern present intermittently from the base of the structure to the top. The determination of the need for any epoxy repair to this wall should be made by others consulted for that purpose. Alternatively, should you authorize BFI to consider it more fully, BFI would be pleased to do so. Evidence of sacking and patching is also present to conceal blemishes and cracks, and reestablish drainage gradients in many areas of the structure, and in the opinion of the undersigned, more sacking and patching may remain to be done if required by the Owner or its representative.
ted slabs is more than typical for the most heavily used lower decks and typical to trivial for those that are used less and which have experienced less loading whether by gross weight or frequency, or both. The most heavily used and cracked decks also display cracks which are wider than the others.
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