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Forensic Structural Engineering: Fly Ash Silo Unit

The project involved a roof failure of a fly ash silo unit, which consisted of 12 inch thick cylindrical cast-in-place reinforced concrete walls and 7 inch minimum thickness cast-in-place concrete roof placed over metal decking and supported by steel beams. CA was hired to investigate the concrete cracking and spalling caused by the structural failure, design and provide guidelines and recommendations for the repair, and monitor the repairs to ensure that they were performed as per the product manufacturers’ guidelines and acceptable industry standards. CA’s investigation included, among others, site visits, non‐destructive testing services, photo documentation, detailed condition survey, and review of plans and drawings.  CA also designed and developed guidelines, recommendations, and specifications for the repair, and communicated with client and owner representatives. CA’s failure analysis included determining the limits of the distressed area of the silo roof and determining the areas of the silo roof that could be repaired and those that needed to be removed and replaced.

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Precast Concrete Investigation at a Water Filtration Plant

The construction of a water filtration plant consisted of a cast-in-place reinforced concrete foundation, perimeter walls, and partition walls dividing the structure into three separate underground tanks. The roof structure was comprised of 240 precast concrete hollow core planks supporting an insulated green roof. Approximately eight (8) years after construction, the roof planks began to exhibit severe deterioration at the longitudinal concrete expansion joints between planks. CA performed, among others, site visits to the water filtration plant and precast manufacturing facility, a review of construction documents including plans, drawings, and specifications, review of expert reports and material testing results, photographic documentation of the available roof planks from original construction, petrographic examination of sampled materials, and a structural analysis of the roof system and its individual components. CA’s investigation successfully determined the cause and factors contributing to the distress mechanism of the precast concrete planks.

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Condition Assessment of a Storm Water Detention Vessel

The project consisted of a storm water detention vessel with a precast concrete double-tee girder roof deck that also served as a parking lot for a local grocery store in Houston, Texas. CA was retained to perform a visual condition assessment to address concerns regarding the integrity of the structure and the condition of existing repairs. CA performed several site visits and achieved detailed photographic documentation of the structure. Special attention was given to areas exhibiting signs of distress and the quality of precast concrete double-tee girders. CA’s investigation identified areas of concern for further structural evaluation and repair.

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Evaluation of a Shopping Center Flooring System

An expansion to the second story of a commercial retail shopping center consisted of the addition of an elevated slab supported by several different types of framing systems, including a post-tensioned concrete beam and pan joist system, a composite flooring system consisting of metal decking and reinforced concrete, and a reinforced concrete slab and beam system. The flooring system of the second floor expansion contained limestone tile as the final floor finish, which exhibited signs of isolated distress in the form of random map cracking. CA performed, among other things, a detailed condition survey of the flooring system and its distress, a review of drawings and plans, an examination of the materials utilized in the flooring system, and a structural evaluation of the flooring system and its individual components. Testing conducted during the site investigations included bond pull-off tests, ground penetrating radar (GPR) mapping, concrete core sampling, and elevation surveys.  CA determined the cause of the distress exhibited by the tile flooring, provided recommendations for the repair and remediation of the flooring system, and developed guidelines to reduce the progression of the distress.

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Precast Concrete Welded Connections

A six (6) story parking garage for a residential building consisted of precast, pre-topped double-tee beams and pre-cast wall panels. A concern regarding life safety was expressed due to the observed distress consisting of spalling of the concrete beneath the welded connections along the flange of adjacent double-tee beams. In addition, concrete cracking in the vertical panels of the pre-cast walls was observed. CA’s investigation focused on determining the cause of the distress and included, but was not limited to, a detailed condition survey and visual inspections of over 1,600 welded connections and a review of the construction drawings and plans. CA determined the cause of the observed distress and developed recommendations for repair and rehabilitation of the concrete structure, including design of repair procedures, materials selection, and quality control/assurance procedures during and after implementation of the repairs.

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Power Plant Scrubber Mass Concrete Foundation

The project consisted of a cast-in-place reinforced mass concrete foundation at a power plant in Texas. The foundation was 94.5 ft. in diameter, nine (9) ft. thick, contained two (2) mats of reinforcing steel consisting of four (4) layers of large diameter (No. 11) bars, approximately 2,600 cubic yards of concrete, and was supported by 339 piles for the addition of a 525 ft. tall reinforced concrete chimney. The structural integrity and capacity of the foundation was questioned due to owner observed construction defects during concrete placement. CA’s investigation included, among others, review of structural concrete design calculations, a finite element structural analysis model to evaluate internal stresses, non-destructive testing of concrete, core sampling, assessment of the concrete production methods and logistics, and  numerous site visits to conduct field investigations and condition assessments totaling over 1,400 man-hours. CA’s extensive investigation uncovered the cause(s) of the distress and structural deficiencies.

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Structural Engineering Consulting: Expressway Concrete Bridge

The project involved converting a section of a concrete pavement highway in Puerto Rico with two lanes of traffic in each direction into an expressway concrete bridge requiring three lanes in each direction. CA’s structural engineering consulting services included evaluating the structural adequacy of the as-built cast-in-place concrete bridge foundations to resist the design loading conditions. CA performed a detailed structural analysis of the bridge foundations using both traditional beam theory and strut-and-tie modeling.  CA conducted an investigation that included, among other things, a review and interpretation of specifications, plans and construction drawings, concrete cylinder and core strength test reports, and applicable industry standards. Further, CA developed recommendations to improve the durability of the concrete foundation and to ensure the service life of the bridge structure in service.

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Moisture Induced Corrosion of Precast Double-Tee Roof

CA performed an initial investigation to determine the cause(s) of the observed distress in a roof of a parking garage structure consisting of precast double-tee girders in a hotel located in Laredo, Texas. CA performed an initial condition assessment and developed recommendations for a comprehensive investigation to determine a remediation procedure for the observed distress, which was indicative of distress caused by moisture intrusion. CA’s recommendations for a comprehensive investigation included determining the cause of the moisture intrusion, performing repairs to eliminate additional moisture intrusion, and assessing the extent of damage affecting the integrity of structural members with rebar corrosion and loss of concrete section.

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Litigation Support for a Regional Waterline Project

CA served as a structural engineer expert witness after performing an extensive forensic engineering investigation into determining the possible cause(s) for the premature failure of a 48 inch diameter precast concrete section of a pipeline extending about 28 miles. The pipeline was built to feed raw water from Lake Stillhouse Hollow to Lake Georgetown, Texas. The investigation conducted included a condition survey of failed sections of concrete pipe, the evaluation of construction related documents, quality control sampling and testing of the soil, backfill, and pipe materials, structural analysis of the pipe design, and evaluation of the construction means and methods, among others.

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Tunnel Construction and Design Consulting

This project, located in Austin, Texas, encompassed work associated with the design and evaluation of a flood control tunnel system and its associated components, including designing a system of storm drain interceptors, inlet and outlet structures, retaining walls, weirs, and vertical shafts. An evaluation of the tunnel alignment and design feasibility, providing alternatives to minimize the costs, was also included. The existing storm drains, which discharged into Waller Creek downstream of 12th Street, were analyzed for methods and costs of conveying their flow into the proposed diversion tunnel to reduce the flows into Waller Creek. As part of maintaining the quality in the tunnel and in Waller Creek during dry weather, a tunnel water recirculation system was required. Floodwater flows into the flood control tunnel via vertical drop shafts or channel side overflow weirs. A large diameter tunnel that connects the inlet structure and the outlet structure, lined with precast concrete liner panels or cast-in-place concrete, allows for easier maintenance access for tunnel de-watering and de-silting operations.