Mervyn Kowalsky

Recent damage following earthquakes in Alaska has exposed a potential issue regarding external abutment shear keys. The keys, referred to as ???hider walls??? are meant to serve as fuses that remain intact for smaller earthquakes, but break way in larger earthquakes thus limiting the force that can be transmitted to the abutments. In that manner, the abutments are ???capacity protected elements??? whose force input is limited by the shear key capacity. For the concept to work, the following three criteria must be met: (1) The demand on the shear keys for the seismic event for which they are expected to remain intact must be reliably predicted. (2) The capacity of the shear keys must be reliably predicted; (3) The shear keys should fail in a manner that is easy to repair following on an earthquake. Through a series of experiments on existing and proposed shear key designs, development of analysis methods for the prediction of shear key strength, and parametric studies on abutment shear key demand, this research will provide engineers with the tools needed to achieve designs that satisfy the intended performance objective.

This research will investigate the seismic behavior of a variety of bridge structures containing high strength reinforcement and other unique details. The research will primarily utilize shake table testing to investigate the dynamic behavior of bridge systems. The test units will be subjected to sequences of historical earthquake ground motions, and response measured through a variety of instrumentation systems. Computational modelling will also be conducted affirm or revise prior design recommendations

This proposal aims to develop a rapid seismic bridge assessment method that can be used for planning (via scenarios), and for post-earthquake assessment (inspection prioritization). Unlike existing methods which are largely probabilistic, and focused on high level assessment, the proposed methodology is sufficiently versatile that it can provide a range of information, spanning from deterministic bridge specific performance, to broader assessments of bridge vulnerability. The procedure relies upon the Direct Displacement-Based Design approach as the analysis engine, and has three components: (1) Bridge metadata; (2) Bridge limit state parameters; and (3) Seismic Hazard characterization. Given any 2 of the above, the third may be determined. While the approach will function with very course data (i.e. basic metadata such as span lengths, column diameter, and height; basic limit state parameters, such as limit state displacement; and course hazard definition (such as a 3 point code-based spectra), with more detailed information, the fidelity of the outcome increases significantly. The work described in this proposal will define limit state parameters for Alaska bridges and characterize the seismic hazard. The framework for the rapid assessment approach will also be developed and applied to a series of bridges. The final outcome will be detailed plans for development of a rapid assessment application which would be developed in a future phase of the research.

This proposal addresses the impact of bridge condition on behavior within the context of performance-based seismic design. Bridge engineers design structures assuming that their properties on day one remain constant throughout the life of the bridge. However, due to material degradation and lifetime transient loadings (including those from small earthquakes), the response of a structure to an extreme event such as an earthquake at some point in the future may be different from what the engineer calculates during the design phase. The research described in this proposal will assess the sensitivity of condition-dependent bridge response to inputs described below. There are five components to this research question. The interactions between these components are shown in Fig. 1 and described further to set the stage for the research that will be conducted in this multi-phase program.

This proposal addresses the impact of response spectra definitions on the design of multi-span bridges by conducting computational research to develop recommendations for hazard levels that are founded on non-linear bi-directional dynamic analysis. The research proposal also aims to develop simplifications to the direct displacement-based design approach for multi-span bridges that will facilitate implementation into bridge design practice. This will be accomplished by designing a series of bridge configurations to multiple hazard definitions. The resulting designs are then subjected to bi-directional non-linear dynamic analysis to assess the range of possible deformation demands that are then correlated to the assumptions made in selection of the seismic hazard for each design. By considering the instances that result in deformation demands exceeding the target for each hazard definitions across all rotation angles, it will be possible to select a seismic hazard definition that provides a known probability of exceedance for the design limit state. The data generated from the computational models will also facilitate simplifications to the direct displacement based design approach. The simplifications aim to reduce the effort to define the equivalent viscous damping, target displaced shape (and corresponding system displacement), and strength allocation to abutments vs. columns.

Alaska is subjected to the highest seismic hazards within the US. The state is also home to some of the most extreme climate in the country. Past studies have shown that low temperatures alter the behavior of reinforced concrete structures sufficiently that it must be considered in design to ensure the safety of the traveling public. Over the last several years, high strength steel reinforcement has become common in the market, with strengths as much as 50% higher than that typically deployed for seismic applications. It is well established that higher strength is not always desirable, especially if it results in a loss of energy dissipation capacity. Previous research has shown that high strength steel, even when meeting the requirements of appropriate ASTM designations, has reduced ability to deform compared to typical ???????????????seismic steel??????????????????. Through the use of material and structure level tests at low temperatures, as well as computational modelling, the impact of low temperatures on high strength steel is explored in this research project. The concern stems from the well established impact of reduced fracture toughness at low temperatures, and the recent observation that the stress concentrations at the base of reinforcing bar ribs impacts the strain capacity of the bars (and hence ductility of the reinforced concrete member). This research aims to determine if low temperatures further impacts the performance of columns reinforced with high strength steel.

Based upon a seismic analysis performed in 2013, the Anchorage Port Access bridge (Bridge number 0455) requires a seismic retrofit to safely accommodate the design earthquake. The bridge, shown in Figure 1, has several deficiencies including steel column-to-cap beam connections that were determined to perform poorly under seismic loading during the first phase of this study. The objective of this study is to develop retrofit recommendations through large scale testing, modelling, and analysis. During phase one of the work, a global computational model (using lumped plasticity frame elements) was developed to assess bridge deformation demands. As part of that work, hysteretic response of the components was represented through consideration of results of a local FEM model and experimental tests. Also included in that model was the impact of damping model choices, soil-structure interaction, and ground motion directionality. The local FEM model considered the details of the individual connections to assess stress concentrations, and was calibrated through the experimental tests. Lastly, the experiments that were conducted included half scale models of two representative bridge bents that were subjected to reversed cyclic loading. Details of each of these components of the first phase of work are described next.

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.

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.

This research consists of an analytical and experimental study aimed at understanding the non-linear behavior of bridge columns constructed from ASTM A706 Grade 80 reinforcing steel. Specifically, of particular interest are (1) Plastic hinge lengths (and spread of plasticity) as well as bond slip and development; (2) Reinforcing bar strain limit states such as onset of transverse reinforcement yield, onset of bar buckling, and tensile fracture; and (3) Hysteretic energy dissipation. To address these points we will develop a computational fiber-based model for analysis of columns, and conduct a series of sixteen large scale reversed cyclic tests on bridge columns. Direct comparisons with columns constructed from Grade 60 steel will be possible. This work follows upon a Phase 1 study at NC State for Caltrans that included 4 column tests. In addition to large scale tests, material level characterization will also be conducted as part of this work to assess the impacts of alloy composition on ductility.

The objective of this work is to develop an updated seismic hazard definition for use in the design of bridges nationwide. Previous efforts, including the work of NCHRP 12-106, have resulted in 1000-year return period uniform-hazard design spectra based on the USGS 2018 hazard model. A risk-targeted approach will be used to develop alternative nationwide design spectra, still based on the 2018 hazard model. This will be compared to the 1000-year motions. Based on direction from the T-3 chair, a web-based portal will be created and hosted by the USGS that will provide the selected design spectrum, in both acceleration and displacement formats, for a given latitude-longitude and site class pairing.

Bridge column repair has been studied for some time with several established techniques for repair for shear and confinement critical columns. Recent research at NC State has demonstrated the feasibility of repair of heavily damaged bridge columns, including those suffering buckling and fracture of reinforcement, through the use of ???????????????Plastic Hinge Relocation??????????????????. That research led to the development of a set of repair techniques using both conventional and advanced materials. The research described in this proposal aims to further advance the techniques that have been developed, while identifying others that may lead to a more efficient repair design. The specific objectives of the research described in this proposal are to: (1) Experimentally verify the behavioral mechanisms developed in the prior study; (2) Investigate options for simplifying the repair process through alternative connections between adjoining members; (3) Evaluate alternative forming options for the repair region; (4) Study the use of rebar couplers for fractured bars; and (5) Evaluate residual drift limits within the context of complete bridge structures. The above will be accomplished through large scale tests that will take advantage of columns already constructed and tests as part of a different research program. In addition, the residual drift computational study developed in Phase 1 will be further developed to evaluate its performance for more complex bridge systems. Recommendations will consist of additional repair technique alternatives that can be implemented into the design guide developed during Phase 1. It is worth noting also that although the focus of this project is on earthquake induced damage, the repair techniques developed will also be applicable to the repair of other forms of damage, including environmental deterioration such as steel reinforcement corrosion and ice flows.

This research will aim to investigate a series of steel column to cap connections historically employed for bridge design that are felt to be deficient with regards to seismic performance. Computational models for the global bridge system and local connections will be developed, along with large scale seismic testing of bridge components. The goal of the research is to assess the behavior of such connections and eventually propose retrofit techniques as needed.

TBD

This is a proposal for a two-year project for the Alaska Department of Transportation and Public Facilities (AKDOT&PF), for the development and implementation of non-destructive testing techniques to determine the length of piles supporting bridge substructures. Fifty two bridges in AKDOT&PF??????????????????s inventory have undocumented foundation characteristics (U-bridges); the most common unknown variable is pile length. This complicates evaluation of substructure vulnerability to scour, which is a mandatory evaluation at all bridges, per the Federal Highway Administration (FHWA).

This research proposal studies the behavior of a common bridge system employed in Alaska that utilizes decked bulb-tee girders connected by a diamond shaped longitudinal grouted keyway joint with intermittent steel shear connectors. While the behavior of the joint under gravity loads is well established, the performance under transverse seismic excitation is largely unknown. Through the use of full scale subassembly tests and non-linear modelling, recommendations on (1) Connection limit states; (2) Improvements to the connection (if needed); and (3) Lateral Modeling approaches will be proposed

This research proposal addresses the design and behavior of a new, recently developed connection for steel bridge substructures. This new connection, termed the grouted shear stud connection (GSS), was shown to be an effective and improved design over current practice of directly welding hollow circular steel pipe piles to steel cap beams. In previous studies, the new connection performed well, in both quasi-static and dynamic tests at ambient (indoor) laboratory temperatures. Because this new connection relies upon the integrity of grout, a cementitious material prone to degradation from severe environmental conditions typical in Alaska, the durability of this material and the connection as a whole must be assessed. This proposed project focuses on the durability of the GSS by optimizing the grout properties through material testing, and subsequent tests of weathered and unweathered full-scale connection specimens when subjected to temperatures as low as -40????????? C. The outcome of this research will be a set of design recommendations to maximize the durability and hence the long term performance of the grouted shear stud connection. While developed for new bridge construction, the GSS connection is readily adapted to retrofit applications in existing steel bridge substructures with deficient pipe column to cap beam connections. The results of this study may therefore be of value in the eventual structural upgrade of Bridge No. 455, the Anchorage Port Access.

Modern seismic design practices for bridge structures involve the use of capacity design principles that locate plastic hinges in columns, while protecting against other modes of failure or locations of damage. For large earthquakes, the formation of plastic hinges in columns can lead to buckling and rupture of longitudinal steel. Traditionally, once buckling occurs, bridge columns are demolished and rebuilt because the cost to replace portions of columns can be prohibitive. Replacement is deemed necessary since the inelastic strain capacity of reinforcing bars is severely diminished once buckling occurs, rendering the structure vulnerable to collapse in future earthquakes. Bridge column repair has been studied for some time with several established techniques for repair for shear and confinement critical columns. To the knowledge of the PIs, there is little data available on repair of columns that are otherwise designed to modern standards. Similarly, there is little data available on developing an understanding of when repair is truly needed, and when repair is truly no longer feasible. A recent pilot study conducted at NCSU demonstrated the feasibility of a repair technique which employed the relocation of the plastic hinge to a previously undamaged location within the column. This was successfully employed for columns that sustained buckled reinforcing bars, and showed promise for columns with fractured bars. In this proposal, the pilot study is expanded by developing a suite of repair techniques aimed at achieving plastic hinge relocation in damaged columns. Techniques may include the use of fiber reinforced polymers, high strength steel, reinforced concrete and structural steel. The focus will be on the concept of ???????????????hinge relocation for repair?????????????????? and will consider variables such as the need for rapid deployment following an event, environmental conditions at the time of repair, and expertise of potential repair workers in Alaska. The research will utilize columns that will be built and damaged as part of another AKDOT research project, thus maximizing resources. Recommendations will consist of analysis and design guidelines, as a function of damage level (i.e. strain limits), for repair design of reinforced concrete (RC) bridge column to footing connections. The recommendations will also be applicable to some RC column to cap connections, although specific tests on that configuration are not part of this phase of work.. In addition, analytical studies will be conducted on other bridge column connection types (e.g., reinforced concrete filled steel pipes to pile cap beams) such that the direction for future experimental work on those connections may proceed.

This research conducts an analytical and experimental study aimed at understanding the non-linear seismic behavior of bridge columns constructed from ASTM A706 Grade 80 reinforcing steel. Specifically, of particular interest are (1) Plastic hinge lengths (and spread of plasticity) as well as bond slip and development; (2) Reinforcing bar strain limit states such as onset of transverse reinforcement yield, onset of bar buckling, and tensile fracture; and (3) Hysteretic energy dissipation. To address these points the team will develop a computational fiber-based model for analysis of columns, and conduct a series of four large scale reversed cyclic tests on bridge columns. Direct comparisons with columns constructed from Grade 60 steel will be possible.

Ongoing research at NCSU funded by AKDOT and AUTC has investigated the impact of loading history on the definition of strain limit states, as well as the relationship between strain and displacement. The 2009 AASHTO Seismic provisions are a displacement-based document and as a consequence, accurate estimates of displacement at key performance limit states are essential. This research project is the next logical step in the study on load history where the impact of a 2-dimensional load path is investigated. The research will also include a component of study related load path effects on the stability of ductile wall piers. Presented in this proposal is background information regarding the prior study in load history conducted at NCSU, followed by a discussion of the critical issues identified in the literature regarding multi-directional loading and a proposed task-by-task approach to the research program.

A research project on reinforced concrete filled pipe piles concluding in May of 2013 had the following objectives: (1) Develop recommendations for strain limits for use in seismic design at key design limit states as a function of diameter/thickness (D/t) ratio and material properties, (2) Develop an equation (via computation) for the plastic hinge length of ?below ground hinges?, (3) Quantify the impact of reinforcing steel on performance and confirm that strain compatibility can be used for prediction of the force-displacement response. These three objectives have been studied through the use of large scale experimental testing, and the analysis of pile members. In addition, work in the project provided recommendations for equations to estimate equivalent viscous damping, which are required for implementation in a direct displacement-based design approach. This proposal builds upon the work previously conducted through the following tasks: (1) Large scale testing of reinforced concrete filled pipe piles in soil; and (2) FEA and fiber-based SSI analysis. The specific goals of this proposed research project are to examine the impact that soil stiffness has on: (1) Pipe pile strain limit states; (2) Plastic hinge length and integration of curvature for deformations; (3) Proposed analysis methods, and (4) Damping

Caltrans has expressed a desire to utilize ASTM A706 Grade 80 reinforcing steel for design of capacity protected members, as well as for members expected to form plastic hinges in bridges. As a consequence, the complete stress-strain curve of the material must be characterized such that it may be used in moment-curvature analysis and section design. There is little information available in the literature on material tests of A706 Grade 80 steel, thus necessitating a comprehensive evaluation across many bar diameters, mills, and heats to get a statistically defendable stress-strain curve of the material. The goal of this research project is to determine the stress-strain curve for A706 Grade 80 steel. In order to achieve this goal, the work is divided into three tasks: (1) Review of existing data; (2) Physical testing of materials; and (3) Recommendations on stress-strain curve.

During the first two days of the meetings, instructors Kowalsky, Priestley, Calvi, and Goodnight will present the displacement-based design approaches as it is applied to bridge structures. The procedure, which has undergone continual development since 1993, led to a textbook on the topic in 2007. Since that time, refinement have continued to be developed. During the 2 days of the seminar, the procedure will presented, with the end outcome being the tools needed to apply the DDBD approach to the design of highway bridges, typical of those seen in the state of Alaska. Topics covered include seismic demands, equivalent damping, moment curvature analysis, member response, design for SDOF systems, special design cases, impacts of P-D effects, limit state displacements, soil structure interaction, design verification tools, longitudinal bridge design, transverse bridge design, curved bridges, design of column plastic hinges, overstrength, shear design, bridge isolation systems, cable stay bridges, and wharves. Example problems will be posed to attendees at the end of the first day for overnight solution and presentation of results the following morning. The final two days of the meetings will deal with design implementation of past research conducted at NCSU for AKDOT. This will include sessions on the new grouted shear stud connection for bridge substructures, the impact of load history on bar buckling, new proposed plastic hinge length equations, and behavior of concrete filled pipe piles. In addition, an interactive discussion in planned for the final day on current and future research projects. In all cases, these projects have already found implementation into AKDOT practice, and the objective of these sessions will be to present the outcomes, and allow for question/answer/interaction on proposed design recommendations

There are two related problems addressed in this research: (1) Currently, structural engineers utilize concrete and steel strain limit states that have minimal experimental or theoretical basis. While the strain limits that are typically utilized attempt to account for cyclic loading, there is no current basis for their selection. Furthermore, the strain limits typically proposed do not consider the effects of temperature. Lastly, while strain limits that occur early in the non-linear range are well established (i.e. serviceability limit state), the strain limits which define maximum structural capacity are less well defined. Most well detailed modern reinforced concrete sections fail by buckling of reinforcement ? a limit state which is still ill-understood. (2) In design, engineers relate strains to displacement via monotonic section analysis, however, earthquakes impose cyclic loading on structural systems. As a result, strain limits that are currently utilized can be correlated to different displacement limits depending on the load history the structure is subjected to. As a result, there is a pressing need to (1) Propose strain limit states that account for low temperature effects and regional seismic load histories, and (2) Develop an approach to allow AKDOT engineers to easily relate proposed strain limits to target displacements for design.

The use of concrete filled steel tubes in bridge construction is common in the state of Alaska, as well as in other states and regions of the country. One reason for their use is that construction is simplified because the steel tubes serve the dual function of the foundation, i.e., piles below the ground surface, and the above-ground columns for the cap beam. The majority of past research has dealt with concrete filled steel tubes at very small scale and without internal reinforcement. In Alaska, the preferred system utilizes longitudinal reinforcement in addition to the steel tube itself. While available research has shown that the performance of concrete filled steel tubes is satisfactory, a number of important questions remain unanswered for the particular application commonly used in Alaska. The problems that will be addressed in this research project include the impact of reinforcing steel on the behavior of the pile-column, the accuracy of analysis methods for prediction of force-deformation response of the pile-column system, the impact of the ratio of tube diameter to tube thickness (D/t ratio) on the performance of the pile-column at multiple limit states, and the plastic hinge length for the below-ground hinge developed in the pile-column. These problem areas will be examined through a series of 10 large-scale tests on concrete filled pile-columns, and from the development of a finite element model capable of capturing all of the anticipated modes of failure, including local buckling of the steel tube. Two of these tests will be conducted in the environmental chamber at NC State, in an attempt to capture the effects of low temperatures (-40C) on structural behavior and performance. The research will result in design expressions relating D/t to strains at various limit states, design expressions for plastic hinge lengths for concrete filled pipes with internal reinforcing steel, and modifications to moment-curvature analysis tools, if required, to predict the force-deformation response to cyclic loading. The research findings will be summarized in a concise design manual appropriate for AKDOT use.

The research program described in this proposal is a follow up to a previously conducted project in which a structural system in common use in Alaska was evaluated. Of primary interest in the prior project, and in this proposed phase two project, is the welded connection between the circular pipe piles and the double HP cap beam, a system commonly used as the supporting bents for Alaska bridges and marine structures. Phase one was essentially an investigation into the assessment of current design practice, and a proof of concept to identify improved connection design approaches. The results of phase one indicated that the current practice of fillet welding the cap beam to the pile is inadequate. Additional tests on alternative weld details proved that welding alone is not likely to produce the necessary ductility and energy absorbing capacities required for satisfactory designs in Alaska. The final test in phase one, in which a plastic hinge-relocating concept was investigated, proved successful. In this concept, a round steel column capital was utilized, in which the top portion welded to the cap beam is thicker than the bottom thinner portion welded to the pile. This turned down column capital was successful in reducing the inelastic demands of the cap beam weld, and forced the inelastic action to occur in the pile itself. The research proposed in phase two includes the optimization of the column capital design to improve displacement capacity and ductility and an investigation of additional connection designs proposed by AKDOT engineers (kerf, pocket, and truss-type connections). A set of nine full scale tests will be conducted, in conjunction with both finite element and frame analyses. The research team will work closely with AKDOT engineers, as they have in current and past projects, to design the tests to achieve the most meaningful results. Since the number of full scale tests is limited, it is important to learn as much as possible from each. The design of subsequent tests takes into consideration all results from previous tests. The research will result in a series of design recommendations consistent with the various levels of seismicity found within the State of Alaska. The primary benefit of this project will be the improved design and performance of steel bridges and marine structures containing similar connections.Alaska DOT engineers will be provided with guidelines to ensure that Alaska?s bridges and marine structures remain safe in major earthquakes.

NCDOT Research Problem Statement 2403 addresses the need for basic data and analysis on the relationship between estimated axle load distributions provided by truck operators, actual axle load distributions, and the impacts of overweight ?super heavy? commercial vehicles on North Carolina bridges and highways. Trucks such as Goldhofer vehicles carry one million pound loads and may be 10 or 20 feet wide and 91 or more feet long. They may have as many as 16 lines of axles with each line having 8 to 16 tires to distribute the heavy loads to stay within NC axle load limits; otherwise overweight permits will not be issued. The State Bridge Management Unit in collaboration with the Oversize/Overweight Permit Unit and the NC Highway Patrol seek axle load verification data to substantiate the estimates provided by commercial operators.

This research project investigates the impact of seismic loading history on the design of reinforced concrete bridge columns typical of those used in the State of Alaska. Currently, structural engineers use concrete and steel strain limit states in seismic design which have minimal experimental or theoretical basis. While the strain limits that are typically used attempt to account for cyclic loading which earthquakes impose, there is insufficient basis for their selection. Furthermore, these strain limits are often converted, through monotonic section analysis, to displacement limits for design purposes. But again, the cyclic nature of earthquake loading can significantly alter the relationship between strain and displacement. An understanding of this relationship between strain and displacement, as a function of loading history, is essential for reliable seismic design. The overall objective of this project is to propose strain limit states that account for regional seismic loading histories in Alaska, and to relate these proposed strain limits to displacement limits. The goals of this project will be met through a combination of analytical and experimental studies. A key requirement of the experimental work is the ability to measure large strains (up to 12%). NCSU has an optical measurement system previously purchased for this purpose which has been shown to be reliable for such measurement of strains in reinforcing steel. The seismic loading histories to which the test specimens will be subjected will be determined from a dataset developed by researchers at the University of Alaska-Anchorage. Results from both frame-type and fiber-based analyses using the ground motions from the dataset will guide the initial selection of specimen design variables. A total of nine tests on essentially full scale circular bridge columns will be performed. The details of the specimens will be determined based the results obtained from the current project, from the analytical results, and from each of the previous tests in this proposed phase two project. Given the limited number of tests, it is important to learn as much as possible from each test before designing and conducting additional tests. This approach has worked successfully in current and previous projects sponsored by the Alaska DOT. These nine test units will be subjected to load histories with varying characteristics, but typical of those experienced in Alaska. The results of this research project will be presented as proposed tensile and compressive strain limits and corresponding displacement limits. The primary benefit of this project will be a better understanding of how seismic load history influences the performance of reinforced concrete bridges in Alaska. Alaska DOT engineers will be provided with tools to refine bridge designs optimized for regional seismicity, ensuring that bridges in Alaska remain safe in major earthquakes and serviceable in smaller earthquakes.

Past performance of spirally welded pipe piles has been questionable, however, advantages related to quick delivery and cost make their use attractive. As a result, the project described in this proposal has been developed to identify the required information needed by structural engineers to make a proper judgment on the use of these piles in coastal applications subjected to storm surge and wave action. Spirally welded pipe piles are manufactured in a manner that may result in various categories of welded joints (examples of three are shown in Fig. 1), any of which at or near the plastic hinge zone of a pile may impact its performance. The location of the plastic hinge zone in the ground will depend on the stiffness of the soil and pile diameter. The three scenarios of weld categories shown in Fig, 1 represent the simplest, which is spiral only (Fig. 1a) to most complex, which includes a spiral, skelp and splice weld (Fig. 1c) . This project will conduct experiments to determine the load-displacement responses under a load history that would mimic the effects of surge loading as well as to determine failure mechanisms for these three welds located at the plastic hinge of the pile.

The research described here aims to assess the influence of low temperatures on the ductility of reinforced concrete structures in seismically active regions such as those found in Alaska. The final goal of the research project is to develop recommendations for: (1) Temperature dependent ductility factors for Alaska DOT bridge structures, and (2) Temperature dependent overstrength factors for Alaska DOT bridge structures. This will be accomplished through a series of 10 large scale tests (see Table 1), and analysis of typical Alaska DOT structures accounting for the effects of temperature on strength and ductility. Recommendations will be provided for both current force-based design utilized by Alaska DOT as well as for displacement-based design. These recommendations will be provided in a final report and will also be presented to Alaska DOT engineers at a workshop at the conclusion of the research program.

The research described in the original proposal aims to investigate the use of polymer fiber and waveguide sensors for the performance-based assessment and health monitoring of civil infrastructure systems. Although the sensors to be developed as part of the proposal can be utilized to measure strains under a variety of load conditions and structural materials, this research program will focus on application of the sensors to concrete and steel structures subjected to dynamic load conditions, such as those imposed due to earthquakes loads

The objective of the research described in this proposal is to utilize a non-contact method of assessment that involves the recording and analysis of sound waves that are generated by the structure during the ?extreme event?. The goals of the research described in this proposal are: (1) Development of a Sound Acquisition System (SAQS) suitable for the recording of sound waves generated during the large scale testing of concrete bridges and buildings. (2) Application of the SAQS to a series of large scale tests underway at the NCSU Constructed Facilities laboratory over the next 12 months. (3) Correlate audible sound waves to events observed during testing, with a specific focus on identifying events that initiate failure of structural components in the test. (4) Utilize data from these pilot studies to prepare a proposal for the upcoming NSF solicitation on Sensors for Security of Infrastructure Systems

The research described in this proposal aims to expand upon work currently underway for Pile-Bent bridge structures to all sub structure systems employed by NCDOT including spread footings and columns supported on drilled shaft foundations. The research task encompass identifying issues specific to drilled shaft bent design and selection of a series of sample structures for design. The outcome of the proposed work will (1) Provide a better understanding of the actual performance of NCDOT sub-structure systems (depth to fixity; connection performance, effective length factors), (2) Provide a rational basis for identification of key performance limit states (drift and strength limits), (3) Provide a new analysis and design platform based on Florida Pier and NCPIER that has been verified by comparisons with FEA programs and section analysis tools, (4) Provide design examples comparing LFD and LRFD, and lastly, (5) Facilitate implementation of LRFD criteria for bridge sub-structures.