Dual story home located in Phoenix, AZ. Built-in 2004 with frame construction, tile roof and has post tension foundation. A homeowner called AZFS to inspect Horizontal Cracking along the east perimeter wall by the turn down concrete area of the foundation. The homeowner also had concerns in the home floors by the east wall where there is evidence of cracking.
During the initial visit, Trained and Certified Inspector Victor Rivera visited the site and evaluated the foundation was built post tension and the damage was only visible along the east wall. Evidence of damage to the post tension foundation was horizontal cracking 23ft of the turndown section. The exterior back patio slab also had horizontal cracking. While looking for signs of stress inside the home, it was noted that the interior tile along the east wall was also cracked from the living room traveling north towards the Kitchen Area.
After evaluating the initial signs of stress on the home, we explained the damage and the possible main causes for the foundation issues to the homeowner. After explaining how many factors go into diagnosing the problem correctly and how important it is to complete a further investigation, we recommended to the homeowner that we proceed with an in-depth engineered analysis and post tension study. For this next step, we would complete a foundation footprint, an exterior, and interior inspection, take pictures of the damages, including a manometer read and bring out a post tension specialist to evaluate the site damages. Once completed AZFS would determine the best plan for repair and give the home documentation and information to help the homeowner make the best-informed decision for their home.
Predetermination: An Engineered Analysis was completed consisting of a topographic map of the floor and a listing of damages and location of same. The topographical mapping (EA-Engineering Analysis) indicated that the slab was low along the east exterior wall (Living Room, Dining Room, and Kitchen) It also indicated that the east exterior wall along with the slab turndown had also settled in those areas. The remaining floor of the home was fairly consistent and level. Total elevation difference of the slab was .8 inches between high and low points.
In-Depth Analysis: The damages observed in the home and on the exterior were confined to the east side.
The damages consisted of the following:
The exterior turndown of the slab, as well as the slab, was badly deteriorated along the exterior of the east wall, particular in the center area. The concrete was cracked, rebar was exposed as well some of it rusted. The turndown had both longitudinal and vertical cracks. The wall was actually moving outward in that area. Some of the post-tensioned cables had come loose from the dead side plate and all of the plates were rusted. Other anchors and plates in the turndown were loose and rusted. The east wall with turndown had settled and there was moisture noted along and under the turndown. In the interior of the house running parallel to the east wall, about 16’’ from the wall, there was a 1/4’’ crack. The crack had penetrated the tile and the slab in that location.
In conjunction with the PT Specialist the following Repair Plan was derived:
1. Our overall plan was to de-tension and re-tension all of the cables. Prior to doing so, we needed to brace the east exterior wall and shore the second-floor framing that was pinned into and supported by the east exterior wall. We braced (kicked) the east exterior all to the outside and also placed shoring towers in the interior of the house along the east exterior wall. The purpose was to keep the wall from collapsing and/or moving out-ward when the cables in the slab were de-tensioned.
2. The next phase was to chip concrete in the turndown away from the cable ends to expose the cable ends and make it easier to attach to for de-tensioning and re-tensioning. To make it more accessible we also removed a 2’+ section of the slab along the east exterior wall in the interior of the house.
3. For another precaution, we also placed small hydraulic jacks under the turn down all along the east exterior wall as another safety precaution. It was wise to do so because of the jack at the NE corner of the east exit. wall became partially bent when the cables we de-tensioned. Without that jack in place at the location, there would have been severe damage at that wall corner. These types of jacks were also placed under the west exterior wall turndown, where the cable live ends were located, as an additional safety precaution.
4. The cables were all de-tensioned and replaced with new cables. The new cables were lat-er tensioned and the tension values checked by the Pt Specialist who was also the Special Inspector for the job. It is to be noted that all final inspection readings were acceptable to the engineering specifications. Any damaged or rusted plates, anchors, pins, bolts and ties that were associated with the cables were replaced and inspected. A final inspection was made of the cables, and anchor hardware.
5. Repairing the turndown and replacing the slab section that was removed along with the east exterior wall inside the house. This work took place after the cables were replaced and after re-tensioning. The turndown was repaired with new rebar installed where needed. Where required it was also patched and spalls were removed. The interior slab section was replaced with 400 psi concrete. A final inspection was made in these areas also. This completed the final inspection of the cables, anchors, and hardware.
6. As many as five (5) piers or piles will probably be installed under the turndown of the east exterior wall. It was felt that this may not be needed since the new cables and re-tensioning may keep the turndown from any more settling. However, the other thought was the fact that wall had settled and there was moisture under it and it should be supported. The cables would keep the slab stiff but not necessarily supported. Also, a post-manometer survey was accomplished after the cable work and there was another .3’’ drop in parts of the wall.
The cause of the problems and damages in a home with a PT slab may not readily be determined. The subsequent Repair Plan may also have to be revised one or more times during the course of the repairs.
For this situation, we fell that replacement of the cables was necessary for the longevity of the slab and to stop any further damage resulting from De-tensioned cables. Also, another conclusion was to slope the grade away from the east exterior wall. The client also removed a tree on the east side. The crack in the interior of the house, along the east exterior wall, was also removed when the concrete along the east exterior wall was removed and replaced.
It is recommended that piers be placed under the turndown of the slab on the east side which supports the east wall. The slab, turndown and exterior wall on the east side had settled and the soil may be unstable for an unknown depth. Installation of new cables would probably not entirely solve that problem. A post-manometer survey after the work had been concluded indicated a further settlement of .2’’ to .3’’ in that area.