Engineering
Signs of Distress:
Cracks in concrete
If you were to break a pencil in slow motion; the first thing that would happen is that a crack would develop at the bottom of the pencil where you were applying pressure This initial crack would be the sign of impending failure. Similarly, some cracks that develop in concrete are pre-cursors to failure. It is important to evaluate cracks in concrete to be sure that they are not compromising the integrity of the structure.
Of course, it is well known that concrete will crack due to temperature and thermal induced stress. These cracks typically do not threaten the integrity of the parking garage structure. Consequently it is important to distinguish between the two.
Rusting of steel decking
Steel decking may provide structural integrity to a concrete slab structure or may simply have been used as a form for the wet concrete mix. It is important to make this determination and evaluate the extent of the corrosion. If the steel deck is corroding, there is a strong possibility that the reinforcing bars or wire in the concrete is also corroding. This reinforcing is everything he load carrying capacity of the concrete. When it fails, so does the deck (See Below).
Concrete decks are relatively thin supporting members that span from beam to beam. It is the embedded steel reinforcing bar or wire mesh of the work in supporting the applied loads. This steel is located within the concrete section and is not visible during routine visible inspection. Since plain concrete is a semi-permeable material, it is not uncommon for water and worse, road salt to reach the steel. This of course leads to the deterioration of the steel through oxidation or rusting. The loss of steel is directly correlated to the weakening of the concrete deck (see figure 1). Making matters worse, as a result of the expansive pressure of growing rust, the concrete surrounding the steel spalls and delaminates.
If the concrete deck is damaged, it is important to observe the condition of the reinforcing steel to make sure it is still in good condition. If the reinforcing bars or wire is damaged to any extent, structural restoration must be accomplished.
Ultimate failure of the deck can occur by the weight or impact force caused by a vehicle driving over the deck. This could cause part or a large section of the concrete slab to collapse creating a potential for injury or a fatality.
The Engineering process of evaluating and restoring a parking garage is as follows:
Evaluation Phase – Identifying the damage
Initial Site Visit Evaluation Survey to identify deck damage and deterioration Perform probes and tests Provide Engineering Report
Design Phase – Designing the repairs
Determine repair required Draft construction drawings Develop construction specifications and bid documents Coordinate Bid process and select contractor
Construction Phase – Correcting the damage
Observe contractor’s work and verify adherence to construction documents
