Residential Structure Investigations for Vibrations from Subsurface Drilling

CA investigated whether the alleged distress at 28 residences located in Peñitas, Texas was the result of drilling operations which occurred in the area between 2007 and 2011. The investigation included a detailed condition survey of each residence as well as an elevation survey of each residence’s slab-on-grade foundation. CA reviewed applicable industry standards and relevant published literature regarding ground vibrations and damage to existing structures. The investigation did not produce any evidence to support the conclusion that the alleged distress in the residences was the result of ground vibrations from the drilling operations. CA determined that the observed distress in the residences was most likely caused by one or a combination of the following: dimensional movement of the structure due to temperature and humidity cycles, drying shrinkage stresses, foundation movement, and/or deficient construction.

Retrofit of Reinforcement Concrete Cantilevered Seating Structure

CA investigated the structural adequacy of an as-built cast-in-place concrete cantilever seating structure in two levels of a sports venue’s grandstand. The cantilever section consisted of an almost 4-foot overhang. Sometime after placement, it was discovered that the cantilever’s tensile reinforcement was placed incorrectly. CA used ground penetrating radar scans to determine the actual reinforcement position, performed a structural analysis to determine the as-built capacity of the cantilever, and designed a retrofit to restore the capacity. CA performed a load test on the first section of repair to document the effectiveness of the retrofit solution. CA maintained a full-time field engineer to oversee and document the entirety of the grandstand repairs.

Evaluation and Repair of Concrete Slab Placed in Inclement Weather

Carrasquillo Associates investigated and characterized the surface distress occurring at an elevated post-tensioned concrete slab in a parking garage that is part of a high-rise building under construction in downtown Austin, Texas. CA’s investigation included an examination of the extent of distress or unsound concrete in an area within one level of the parking garage equal to approximately 10,000 square feet, where rain had affected the fresh concrete surface soon after it had been placed. CA conducted a site visit to the parking garage to perform a visual examination and condition survey, and to obtain core samples from the concrete deck. The cores were studied by a concrete petrographer, who determined the extent of rain damage within the depth of each core. CA utilized this determination in developing a repair plan for the affected concrete surface to restore its serviceability and long-term durability. This project provides an example of CA’s expertise in recognizing a structural or materials problem and its root cause, assessing how it will affect the structure, and offering a repair solution that efficiently and reliably restores the structure.

Convention Center CMU Wall Repair

Carrasquillo Associates designed repairs for a 50 ft. tall exterior concrete masonry unit (CMU) wall. During construction, it was discovered that the wall was constructed without the proper amount of reinforcement, essentially making it unreinforced. CA computed the loads acting on the wall from self-weight, cladding, and wind. Multiple wall sections were considered due to the varying cladding, geometry, and parapet details. Nearly the entirety of the wall was overstressed due to the wind load. CA’s repair involved adding a steel structural support to reduce the wall’s span and thus reduce flexural demands. This significantly reduced the overstressed areas such that localized areas could be strengthened with fiber reinforced polymer sheets. While developing the repair, CA collaborated with the Structural Engineer of Record to ensure that the added steel support would not overload the existing steel columns and braced frames.

Pavement Construction and Possible Overload Investigation

Several new structures for an oil-field equipment servicing company were constructed in 2012 in Houston, TX.  The structures were surrounded by three large reinforced concrete drive lanes utilized for delivery and pick-up of the large-size oil equipment parts.  Shortly after construction, the reinforced concrete pavement exhibited distress in form of spalled joints at dowel locations, pumping, and localized panel failures.  CA was retained to determine the cause(s) of the distress and provide repair recommendations.  CA’s field work included soil sampling and testing, non-destructive testing of the concrete pavement, including the use of ground penetrating radar, and relative elevation surveys to verify surface drainage patterns.  In addition to the field work, CA also performed an analysis of the pavement design to determine its structural adequacy as-designed considering the actual forklift and truck traffic.  CA’s investigation revealed numerous design deficiencies relating to the base material and pavement thickness considering the actual pavement loads. Certain construction deficiencies exacerbated the observed distress as well. CA provided a repair plan for the pavement.

Burnished Concrete Floor Finish Investigation

Carrasquillo Associates reviewed a 150,000 square foot interior slab-on-ground for a big box retailer in Cibolo, TX. The project specifications for the slab-on-ground finish incorporated strict aesthetic requirements.  Shortly after burnishing and cleaning the finished floor surface, the contractor was notified that the floor was unacceptable due to various aesthetic issues on the surface of the floor. CA extracted concrete core samples for petrographic examination of the concrete and finished surface. CA determined that the concrete floor was structurally adequate, but identified various deficiencies in the burnishing and/or cleaning operations which affected the initial hard trowel finish leaving a dull appearance and exposed aggregate at localized areas.

Repair of Slab-On-Grade Post-Tensioning

Carrasquillo Associates provided recommendations for the repair of a slab-on-grade after numerous post-tensioning tendons were cut during the installation of various plumbing trenches as part of an interior renovation project. As part of the repair process, CA documented the condition of the slab-on-grade by performing a crack map and elevation survey. These were performed both before and after the post-tensioning repairs to provide reassurance to the facility owner that the repairs had not negatively impacted the structure integrity of the slab-on-grade.  

Concrete Repairs under Severe Exposure at Wastewater Treatment Plant

The Govalle Tunnel is an approximately 8-mile long, 96-inch diameter, cast-in-place concrete tunnel at an average depth of 100 feet that conveys wastewater generated in central and southeast Austin, Texas to the South Austin Regional Wastewater Plant. Inspections performed by the City of Austin in 2002 identified rehabilitation needs for the tunnel system. Rehabilitation work included structural repair of large diameter and deep shafts and laterals using a cementitious repair material followed by the application of an epoxy protective system. The purpose of these repairs was to remediate the impacts of concrete deterioration due to exposure to sulfates and steel reinforcement corrosion and to protect from future deterioration. CA was retained by the City of Austin to determine the cause(s) and/or contributing factors resulting in the failure of the rehabilitation work using an approved repair mortar. Among the most relevant issues investigated were the quality of the substrate surface preparation, repair materials characteristics and properties, repair practices, and behavior, performance and curing requirements of the repair mortar at different temperatures.

Cementitious Underlayment Deficiencies in Hospital Operating Rooms

CA investigated the quality of a cementitious underlayment installed as part of the finish out of the 11th and 12th floors of an existing 33-story hospital building. The elevated concrete structural slabs of these floors were covered with a variable thickness cementitious underlayment material, with the intent to achieve an adequate floor surface that would later receive final floor finishes such as tile or carpet. The owner observed that this underlayment exhibited an inconsistent appearance, variable color, a dusty/powdery surface, and a poor bond with the finished flooring. CA evaluated the underlayment and assessed the expected performance of the floor, specifically its integrity and ability to resist wear due to long-term loading from wheeled medical equipment. CA’s investigation included a walk-through, visual condition assessment, core sampling, petrographic examination, and bond pull-off testing. CA’s analysis resulted in the removal and replacement of the underlayment to ensure a quality long-term floor system in the operating rooms and associated support rooms.

Post-Tensioned Slab Blowout

CA investigated a large post-tensioning blowout which occurred during construction of a complicated, unique portion of a 30-story residential tower. CA’s investigation was focused on reviewing the design and construction of the Project, specifically the post-tensioned slabs, as well as documenting and analyzing the conditions and circumstances associated with the post-tensioning blowout and subsequent repair. CA determined that the structural design did not consider the complexity of the blowout location. No direction was provided regarding the anchorage placement with regard to the curved slab edge and the close proximity of the distributed and banded tendons. CA performed a finite element analysis which showed that the blowout location experienced overlapping bursting stresses from distributed tendons and the banded tendons. This, combined with restraint and an upward post-tensioning force, resulted in a localized region of amplified tensile stresses. These amplified stresses made the section susceptible to a post-tensioning blowout failure during construction. The repair of the blowout area incorporated numerous modifications as compared to the original design, including the relocation of the distributed tendons away from the banded tendon anchorages. During the repair, the blowout did not re-occur, confirming that the cause and/or contributing factors related to the design had been eliminated and addressed.