Giorgio Proestos

In the design and analysis of reinforced concrete deep beams, such as bridge bent caps, the use of sectional design methods may result in unnecessarily conservative structures. The application of strut-and-tie procedures can result in more efficient structural designs that also better represent the load carrying mechanisms of the members. The research needing investigation, is to identify typical bridge bent caps for North Carolinian bridges and develop specific strut-and-tie design procedures for these members. The investigation will examine how the Department??????????????????s current design practices compare with the proposed procedures. The research also consists of conducting large-scale experiments of reinforced concrete deep beams monitored with full field of view digital image correlation (DIC) equipment.

Alaska is subjected to the highest seismic hazards within the US. As a consequence, their structural systems must be robust, redundant, and ductile such that interruptions to their service following an earthquake are minimal. Research over the last 20 years has led to improved design details that have been proven to work effectively by experimental, analytical, and field studies. However, much of Alaska is in a harsh environment with a comparatively short construction season. As a consequence, a premium is placed on rapid construction. Previous research has resulted in the development of an all-steel bridge system that can be easily constructed for temporary (or permanent) installations. That system has inspired the possibility of developing an alternative rapidly constructed bridge system for the more common bridge types deployed in Alaska ?????????????????? namely, Reinforced Concrete Filled Steel Tubes (RCFST) and Reinforced Concrete (RC) Column structures. These structural types are valued for their proven ductile performance. It is the goal of this research project to speed up the construction process, while retaining (or improving upon) their seismic behavior. To that end, this research aims to develop Accelerated Bridge Construction connections for RCFST and RC bridge systems that use ???????????????external socket?????????????????? or ???????????????external pocket?????????????????? connections. This is distinctly different from existing ???????????????socket?????????????????? or ???????????????pocket?????????????????? connections that are internal to the cap and can compromise seismic behavior. Lessons learned from the development of the steel bridge system (termed the ???????????????Grouted Shear Stud (GSS) Connection) will be valuable as the connections described in this proposal are developed. The research will consist of large scale experimental seismic tests on candidate connections coupled with advanced (and simple) computational models for their analysis and design. The end product will be a suite of connection types that are supported by experimental and analytical evidence that will lead to a simple design approach for their deployment in practice.

The NCDOT has previously funded FRP related research projects through NC State University. RP2014-09 consisted of material characterization of Glass FRP reinforcing bars and Carbon FRP prestressing strand (of the same type to be used in the Harkers Island Bridge replacement), and the design, construction and destructive testing of full-scale 45 ft. long hollow core slabs commonly used throughout North Carolina. The design was consistent with the then current ACI440 and AASHTO design guide documents. The test results demonstrated that the flexural and shear performance of the all FRP-reinforced cored slabs was ????????????????equivalent??????????????? to that of traditional steel-reinforced cored slabs designed to current NCDOT standards. More recently, RP2018-16 developed an innovative rapid repair solution suitable for common prestressed concrete bridge elements, including cored-slabs and C-channel beams. The system is comprised of a prestressed mechanically-fastened FRP plate that restores lost prestress force in deteriorated bridge beams such that inventory and operating load rating restrictions may be removed enabling the bridge to remain in service until replacement is scheduled. In April 2019 this repair system was implemented on Bridge No. 380080 in Franklin County, and a second application was installed on Bridge No. 810003 in Sampson County in November 2020. While there are applications of FRP materials and systems in the repair or strengthening of existing concrete bridges in North Carolina, the Harkers Island Bridge replacement will be the first to fully replace all internal reinforcing and prestressing steel with FRP alternatives in a new construction. The Harkers Island Bridge will be among the largest applications of FRP in a fully FRP-reinforced new concrete bridge in the United States. The experience and long-term performance data collected from this bridge will contribute to the validation and future editions of ASTM standards, material and construction specifications, and design codes including those from AASHTO and ACI. Ultimately, the outcomes of this research project will lead to improved NCDOT design and construction of durable bridge infrastructure resulting in reduced maintenance and repair, longer service life, and cost-savings.

The NCDOT is in the process of deconstructing the 56 year old Bonner Bridge. This deconstruction provides an opportunity to evaluate the aged girders of the bridge and to compare their performance to load rating calculations. Such a comparison will provide a better understanding of the accuracy and assumptions associated with prestressing losses and will allow for refinements to the load rating procedures. This project focuses on a complete performance evaluation of the Bonner Bridge girders including full-scale load testing of 9 of the 61 ft. by 45 in. deep AASHTO Type III girders. The load testing will be conducted in the Constructed Facilities Lab (CFL) located at North Carolina State University. The research will provide recommendations for updates to the NCDOT Structures Management??????????????????s Manual guidelines. These assessments will also include directly evaluating the current amount of stress (after losses) in the girder prestressing steel; the condition, strength and stiffness of the concrete materials; and the location and extent of damage and repair of the girders.

Bridge girder cross-sections continue to become regional in nature, with many state DOTs adopting their own unique sections at either the state or regional level. Typically, girders are developed without consideration of a formal ???????????????optimization?????????????????? of cross-section shape, or when any optimization was employed, the process of optimization and hence its outcome posed several limitations. For example, in many cases, the optimization focused on a single girder without considering any deck on it, whereas the lateral spacing of girders and thickness of the overhead deck are design variables which should be considered while optimizing the girder. Also, such optimization was often based on local search algorithms that do not guarantee global optimality, especially when the solution space is multi-dimensional and highly nonlinear. In most instances, optimization process only included ???????????????quantifiable?????????????????? factors like material cost, volume or weight, labor cost, and formwork cost, etc. But solutions that are mathematically optimal with respect to the quantified factors are not necessarily and readily acceptable when considering non-quantifiable factors and preferences pertaining to practical and field implementation issues. Hence, it is important to extend the optimization procedure to enable outcomes from a formal optimization to be integrated with important subjective considerations. The objective of this research is to develop and apply contemporary meta-heuristic global search procedures for optimizing pre-tensioned decked bulb-tee girders for systematically identifying new optimized cross-section shapes. It is envisioned that, for a specific girder span length and a number of lateral girders, several maximally different alternative cross-sections with competitive structural and cost performance will be first identified; this will be repeated for different combinations of girder spans and numbers of girders to analyze and develop structural and cost performance characteristics variation with girder span length. Then in consultation with AKDOT and precast manufacturers, the alternative optimized cross-section shapes will be screened and fine-tuned based on practical considerations to identify a small set of ???????????????best feasible?????????????????? cross-section shapes. The cross sections to be explored here will be compared for structural performance and material savings against existing ???????????????optimized?????????????????? sections as well as various legacy sections used by Alaska DOT (existing decked-bulb-tee section), and sections employed elsewhere around the US (i.e., AASHTO girders, PCI Bulb-Tees). Preliminary exploratory analysis will be conducted to study the effects of optimized cross-section shapes on extending the girder spans and reducing the number of spans, and therefore the approximate (empirically estimated) net life-cycle cost savings of the bridge system considering the number of piers, foundations, abutments, etc. We expect the outcomes of this project will potentially benefit the AKDOT in improving the ability to span longer distances, reducing overall bridge construction cost, and using resources more efficiently.

Recently, it has been shown that the premature deterioration of concrete overlays in waste transfer stations is a result of simultaneous exposure to leachate (organic acids) and mechanical abrasion by waste handling equipment. In our previous research, we developed a material design guide and specification that owners can use for design or bidding. There are however, important limitations to the developed guide in that it: (1) does not address repair strategies and repair material selection, (2) is limited to portland cement concrete, (3) does not cover the use of unconventional concretes such as iron aggregate and epoxy matrix, (4) applies to slabs with a minimum of 6-inch thickness and does not cover thin precast and prestressed overlays, and (5) does not include provisions for the use chemical or mineral admixtures that can increase the acid resistance of concrete. The industry is in need of low cost and effective repair strategies for existing concrete overlays. The goal of the proposed research is to develop a guideline for repair strategies and repair material selection that can be (1) used by owners and operators of waste transfer stations and (2) adopted and implemented by contractors without the need for specialized equipment and labor.

Precast double tees with thin stems are a widely used and highly successful floor member in parking structures and other buildings. Frequently, the end supports are dapped such that the bottom of the double tee is level with the bottom of the inverted tee or ledger beam on which it is supported. The dapped connection detail is especially important at crossovers between spans in parking structures because the overall structural depth and floor-to-floor height need not be increased where the double tee is supported by an inverted tee beam. Double tees with dapped ends are typically 24??????????????? to 30??????????????? deep and often carry parking loads, however, much deeper tees (48???????????????) are becoming more common due to the heavier loads and longer spans needed in data centers and other specialty structures.

In recent years, flooding at nuclear power plants (NPP) has increased emphasis on using high fidelity simulations to evaluate the vulnerability of nuclear plants. One of the key limitations in the use of high fidelity simulations is related to a lack of verification and validation (V&V) of such simulations. One outcome of incomplete and insufficient V&V relates to a large degree of uncertainty in the simulation results which in turn leads to conservative assumptions by the decision makers. Past experience has shown that such conservative assumptions in the context of safety assessment for other external hazards such as seismic have resulted in highly overdesigned NPP systems and excessively high costs. Therefore, it is quite important that various uncertainties in this process are appropriately identified and included through formal uncertainty quantification (UQ). A robust framework for verification and validation is needed to not only include uncertainties but also to formalize the confidence in predictions of system level validation that are based on component level data using Bayesian Network. In addition, the framework has to identify the basic events that are critical in the perspective of overall validation. This process helps in allocating the resources efficiently thereby reducing the effort to conduct high fidelity simulations and large-scale experiments.

Reinforced concrete deep beams are members that have a relatively small shear span with respect to their depth. When the shear span to depth ratio (a/d) of such members becomes less than about 2.5, the members are governed by shear deformations and plane sections do not remain plane. Reinforced concrete transfer girders, bridge pier caps, and corbels are all examples of deep beams. These members are often heavily stressed and contain large quantities of reinforcement. The proposal is to conduct six large scale tests to investigate the performance of high strength T-headed reinforcing bars for use as shear reinforcement in shear critical deep beams. The large-scale experiments will be heavily instrumented with three-dimensional LED Optotrak targets as well as large field of view three-dimensional digital image correlation systems. In addition to experimental investigations, the research will be complimented with analytical evaluation of deep beams. These analytical methods will be used to predict the effect of using high strength T-headed reinforcing bars on material stresses, failure mechanisms, crack widths, crack slips and global member response.

In recent years, flooding at nuclear power plants (NPP) has increased emphasis on using high fidelity simulations to evaluate the vulnerability of nuclear plants. One of the key limitations in the use of high fidelity simulations is related to a lack of verification and validation (V&V) of such simulations. One outcome of incomplete and insufficient V&V relates to a large degree of uncertainty in the simulation results which in turn leads to conservative assumptions by the decision makers. Past experience has shown that such conservative assumptions in the context of safety assessment for other external hazards such as seismic have resulted in highly overdesigned NPP systems and excessively high costs. Therefore, it is quite important that various uncertainties in this process are appropriately identified and included through formal uncertainty quantification (UQ). A robust framework for verification and validation is needed to not only include uncertainties but also to formalize the confidence in predictions of system level validation that are based on component level data using Bayesian Network. In addition, the framework has to identify the basic events that are critical in the perspective of overall validation. This process helps in allocating the resources efficiently thereby reducing the effort to conduct high fidelity simulations and large-scale experiments.