VTechWorks Repository :: Browsing by Author "Hebdon, Matthew H."

Browsing by Author "Hebdon, Matthew H."

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Accelerated Corrosion Testing of ASTM A1010 Stainless Steel
Hebdon, Matthew H.; Groshek, Isaac (American Institute of Steel Construction, 2018-04-11)
ASTM A1010 (recently adopted as ASTM A709 Gr50CR) is a material which has advantageous corrosion properties. It is a low-grade stainless steel which forms a protective patina and has been marketed as an alternative to other bridge steels and corrosion protection methods due to its corrosion resistance in highly corrosive environments. However, the material is currently available in plate form only, and several of the applications in the United States were required to use alternative materials when constructing and connecting secondary members to the A1010 plate girders. This paper addresses the corrosion behavior of A1010 in several different details relating to recent applications in the US. An accelerated corrosion study was performed which simulated a highly corrosive environment typical of the environment justifying the use of A1010. The research investigated the resulting galvanic corrosion and its effect on the corrosion rate of A1010 plates, several different common bridge steels, and typical fastener materials. In addition, common surface preparation methods were evaluated for their aesthetic effect during patina formation.
Alternative Methods for Sealing Overlapping Steel Members with Narrow Gaps During Galvanizing
Sultan, Abdullah Emad (Virginia Tech, 2018-05-07)
Narrow gaps in overlapping structural steel surfaces are problematic when being hot-dip galvanized due to the potential for trapped cleaning solutions between the surfaces. A seal-weld is often used to prevent the cleaning solutions from penetrating this gap. However, these welds are not necessary used for strength, and add fabrication costs because of the additional weld. The purpose of this research is to provide alternatives, which fall under two major categories, to the seal-weld fabrication process. The first one was motivated by the steel fabrication industry and uses a commercial silicone caulk to seal the narrow gap instead of a seal-weld. The second was motivated by the galvanizing industry and increases the narrow gap to a minimum of 3/32 in. to allow free flowing of the liquids including viscous molten zinc. 45 specimens in six different overlapping configurations were tested. Three experimental tasks were performed as part of this research: two different types of silicone caulks were used to partially substitute the seal-weld to prevent fluid penetration; an accelerated corrosion test was performed to determine the long-term corrosion resistance of each configuration; and a coating layer evaluation was performed to investigate the bond of the metallurgical layer between the steel and the coating. Results indicate that silicone only partially prevented the penetration of the cleaning solutions into the gap but performed poorly when fully galvanized. Also, the accelerated corrosion and coating investigations indicated that the suggested caulks and the 3/32 in. gap were not as efficient as the seal-weld solution.
The Applicability of Additive Friction Stir Deposition for Bridge Repair
Asiatico, Patricia Magistrado (Virginia Tech, 2021-06-07)
The purpose of this research was to investigate the potential application of additive friction stir deposition (AFSD) to repair corroded steel bridge members. AFSD is an emerging solid-state additive manufacturing (AM) technology with many advantageous qualities such as low porosity, low residual stresses, flexibility in material, and a high build rate allowing for large-scale deposits. Two parameters were studied to understand the quality of AFSD on corroded steel: surface roughness and surface cleanliness. Three rounds of depositions were done: AerMet100, a high-strength corrosion-resistant steel, deposited onto AISI 1018 plates, with varying degrees of section loss, sectioned from a bridge taken out-of-service; AISI 1018 steel deposited onto an A572 Gr. 50 plate with 12 holes of varying diameters and depths drilled into the plate to simulate surface roughness; and AISI 1018 steel deposited onto an A572 Gr. 50 plate with mill scale, corrosion, and an industrial three-coat bridge paint system. The repair quality of each deposition was studied using scanning electron microscopy, microhardness testing, and three-point bending. Results from these tests indicated the following: AFSD can sufficiently mix dissimilar steels and result in a fine-grained microstructure; depositing onto a rough surface appeared to aid bonding between the two materials with little to no adverse effects on the repair quality; and finally, depending on the chosen deposition parameters, AFSD can mix foreign surface material into the matrix or mechanically remove the bulk of the foreign surface material appearing to clean the surface during the deposition.
Application of Ductile Yield Link in Glulam Moment Connections
Almousawi, Sayed Husain (Virginia Tech, 2018-08-17)
Wood beam-column connections have traditionally been designed as simple shear connections, ignoring their potential moment capacity. A major reason for not utilizing such moment connections is linked to the brittle limit states that wood components exhibit. The purpose of this research was to develop and test a ductile and high-strength wood moment frame connection. A design procedure for such a connection is presented herein. The proposed glulam beam-column connection utilizes an embedded steel knife plate with a reduced section that acts as a ductile yield link, thus limiting the moment that can be transferred through the connection. This configuration is intended to fail through yielding of the ductile link, thus preventing non-ductile failure mechanisms of wood from occurring. In addition, the connection provides more wood cover over the embedded steel plate, which potentially may increase the connection's fire rating as compared to typical connections. Two specimens, based on a baseline connection developed using the design procedure presented, were monotonically loaded until failure. Unlike the first specimen, the second was reinforced in the perpendicular-to-grain direction using self-tapping screws. Failure mechanisms were analyzed, and performance characteristics related to the connection's strength, stiffness, and ductility were evaluated. Results indicated that the reinforced specimen exhibited higher strength, stiffness, and ductility compared to the unreinforced specimen. The reinforced specimen showed improvements of 9.49% and 42.2% in yielding and ultimate moment, respectively, compared to the unreinforced specimen. Moreover, an improvement of 31.3% in ductility was obtained using perpendicular-to-grain reinforcement.
Blast Performance of Hollow Metal Steel Doors
Keene, Colton Levi (Virginia Tech, 2019-09-18)
Recent terrorist attacks and accidental explosions have prompted increased interest in the blast resistant design of high-risk facilities, including government offices, private sector buildings, transportation terminals, sporting venues, and military facilities. Current blast resistant design standards prioritize the protection of the primary structural system, such as walls, columns, and beams, to prevent a disproportionate collapse of the entire structure. Secondary structural systems and non-structural components, such as blast resistant doors, are typically outside the focus of standard building design. Components such as blast resistant doors are designed and manufactured by private sector entities, and their details are confidential and considered proprietary business information. For this reason, scientific research on blast resistant doors is sparse and most test results are unavailable for public consumption. Nevertheless, the performance of blast doors is crucial to the survival of building occupants as they are relied upon to contain blast pressures and remain operable after a blast event to allow ingress/egress. These important roles highlight the critical need for further research and development to enhance the level of protection provided by components that are often not considered in any detail by protective design practice. This thesis presents a combined experimental and analytical research program intended to support the development of blast resistant hollow metal doors. A total of 18 static beam-assembly tests were conducted, which consisted of the flexural four-point bending of door segments, to inform on the performance characteristics of full-sized blast resistant doors. Six tests were conducted to evaluate the effectiveness of three skin-core construction methodologies, which consisted of one epoxy and two weld attachment specifications, between door skins and their internal reinforcing structures. The remaining 12 tests were performed to evaluate the in-situ performance of hinge hardware typically installed on blast resistant door assemblies. The results of the skin-core construction tests demonstrated that closely spaced weld patterns would provide the best blast performance. The results of the hinge hardware tests demonstrated that hinges which provided a continuous load-path directly into the primary ii structural core elements of the door frame and door were ideal; furthermore, robust hinges with fully-welded or continuous knuckles were best suited for limiting undesirable deformations. A semi-empirical analytical methodology was developed to predict the global deformation response of full-sized hollow metal doors subjected to blast loading in the seated direction. The goal was to provide practicing engineers who are competent but non-expert users of high fidelity simulations with the flexibility to conduct in-house evaluation of the blast resistance of hollow metal doors without having to conduct live explosive or simulated blast tests. A finite element analysis was first performed to compute the door resistance function. Hollow metal door construction was idealized using a bulk material sandwiched between sheet metal skins and internally stiffened by stringers. The properties of the bulk material were calibrated such that the deformability of the idealized core reasonably approximated the global load-deformation behavior which occurs due to loss of composite action when welds fail. The resistance curves were then used in a singledegree-of-freedom dynamic analysis to predict the displacement response of the door subjected to blast loading. The proposed methodology was first validated against the static beam-assembly flexural tests. It was then extended to the case of a full-sized door subjected to shock tube blast testing using results published in the literature. The proposed methodology was found to reasonably approximate the out-of-plane load-deformation response of beam-assemblies and full-size doors, provided the bulk material properties of the idealized core are calibrated against experimental data. Finally, the new Virginia Tech Shock Tube Testing Facility was introduced. A description of the facility, including an overview of the shock tube's location, construction, main components, instrumentation, and key operating principles, were discussed. Operating guidelines and procedures were outlined to ensure safe, controlled, and repeated blast testing operations. A detailed calibration plan was proposed, and future work pertaining to the development of blast resistant hollow metal doors was presented.
Bonding Behaviors of GFRP/Steel Bonded Joints after Wet–Dry Cyclic and Hygrothermal Curing
Liu, Jie; Guo, Tong; Hebdon, Matthew H.; Liu, Zhongxiang; Wang, Libin (MDPI, 2020-08-05)
This paper presents the outcomes of a research program that tested and examined the behaviors of glass fiber-reinforced polymer (GFRP) bonded steel double-strap joints after being cured in a variety of harsh curing conditions. Nineteen specimens were manufactured, cured in an air environment (the reference specimen), treated with different wet–dry cyclic curing or hygrothermal pretreatment, and then tested under quasi-static loading. Based on the experimental studies, mixed failure modes, rather than the cohesive failure of the adhesive, were found in the harsh environmental cured specimens. Additionally, an approximately linear relationship of load–displacement curves was observed for all the GFRP/steel bonded specimens from which the tensile capacities and stiffness were discussed. By analyzing the strain development of the bonded specimens during quasi-static tensile testing, the fracture mechanism analysis focused on the threshold value of the strain curves for different cured specimens. Finally, based on the studies of interfacial fracture energy, G_f, the effects of harsh environmental curing were assessed. The results showed that the failure modes, joint tensile capacities, stiffness, and interfacial fracture energy G_f were highly dependent on the curing conditions, and a significant degradation of bonding performance could be introduced by the investigated harsh environments.
COCO-Bridge: Common Objects in Context Dataset and Benchmark for Structural Detail Detection of Bridges
Bianchi, Eric Loran (Virginia Tech, 2019-02-14)
Common Objects in Context for bridge inspection (COCO-Bridge) was introduced for use by unmanned aircraft systems (UAS) to assist in GPS denied environments, flight-planning, and detail identification and contextualization, but has far-reaching applications such as augmented reality (AR) and other artificial intelligence (AI) platforms. COCO-Bridge is an annotated dataset which can be trained using a convolutional neural network (CNN) to identify specific structural details. Many annotated datasets have been developed to detect regions of interest in images for a wide variety of applications and industries. While some annotated datasets of structural defects (primarily cracks) have been developed, most efforts are individualized and focus on a small niche of the industry. This effort initiated a benchmark dataset with a focus on structural details. This research investigated the required parameters for detail identification and evaluated performance enhancements on the annotation process. The image dataset consisted of four structural details which are commonly reviewed and rated during bridge inspections: bearings, cover plate terminations, gusset plate connections, and out of plane stiffeners. This initial version of COCO-Bridge includes a total of 774 images; 10% for evaluation and 90% for training. Several models were used with the dataset to evaluate model overfitting and performance enhancements from augmentation and number of iteration steps. Methods to economize the predictive capabilities of the model without the addition of unique data were investigated to reduce the required number of training images. Results from model tests indicated the following: additional images, mirrored along the vertical-axis, provided precision and accuracy enhancements; increasing computational step iterations improved predictive precision and accuracy, and the optimal confidence threshold for operation was 25%. Annotation recommendations and improvements were also discovered and documented as a result of the research.
Corrosion Behavior of ASTM A1010 Stainless Steel for Applications in Bridge Components
Groshek, Isaac Gerard (Virginia Tech, 2017-06-13)
The purpose of this research was the investigation of the corrosion behavior of a low chromium-content stainless steel, ASTM A1010, for use in steel bridge members. This stainless steel has been marketed as a potential replacement for conventional structural steels for bridges located in highly-corrosive environments, with the potential to provide life-cycle cost savings. Further investigation of the corrosion behavior of A1010 in corrosive environments was required for three bridge-specific applications: the galvanic corrosion of A1010 connected to plates and fasteners composed of dissimilar metals; the crevice corrosion of A1010 plates connected with other A1010 plates; and the effect of varying surface preparation techniques on the corrosion behavior of A1010. These behaviors were studied through the implementation of an accelerated cyclic corrosion test, the modified SAE J2334 Surface Vehicle Standard specification. Results from the accelerated corrosion test indicated the following: galvanic corrosion rates of A1010 with dissimilar metal plates may result in accelerated corrosion rates of the dissimilar metal plates beyond desirable levels; connections to many non-stainless fastener types show cause for concerns with galvanic corrosion, while B8 Class 2 austenitic stainless steel bolt assemblies exhibited superior performance; the relative corrosion-resistance of A1010 is decreased in detailing susceptible to crevice corrosion; and finally, numerous abrasive blasting procedures appear to be suitable for use with A1010.
Determination of Lateral Resistance of Deck Tie Fasteners in Smooth Top Bridge Girders
Vasudevan, Vishali Mylapore (Virginia Tech, 2018-05-24)
The purpose of this research was to investigate and create preliminary design aids for the determination of lateral resistance capacity and spacing requirements of deck tie fasteners in curved railroad bridges with smooth top girders. In railroad bridge design, required lateral resistance dictates the spacing of deck tie fasteners. Currently, no provisions exist to aid in the calculation of lateral resistance for systems that include bridge ties, fasteners, and girders which experience centrifugal or lateral forces. Thus, design practices specific to each railroad vary, producing inconsistent fastener spacing in existing railroad bridges. This project identified and quantified three factors contributing to lateral resistance through experimental testing: resistance due to friction at the tie-girder interface; resistance from the fastener; and resistance from dapped ties bearing against the girder flange. Three fastener types were studied in this research: Square body hook bolts, Lewis Forged hook bolts, and Quikset Anchors. Results indicated that frictional resistance is a product of the train wheel load and the friction coefficient. Fastener resistance was determined to be a function of fastener type and lateral track displacement. Finally, dap resistance was found to be a function of the area of the shear plane in a dapped tie. A preliminary equation for calculating the total lateral resistance capacity was developed utilizing superposition of all three resistance contributions. Lateral demand loads were compared with reported lateral capacity to create a preliminary design aid to determine fastener spacing.
Determining typical buyer sensitivity for solar installation cost - Energy savings benefit
Miller, S. E.; Rapp, R. R.; Hebdon, Matthew H. (American Solar Energy Society, 2012-12-31)
A survey was conducted at the U.S. Department of Energy Solar Decathlon 2011 in Washington, DC to determine why American consumers have not yet adopted solar electric technology in their homes. With over 700 respondents, the data showed the three most prevalent concerns include: cost of installation and maintenance, geography, and knowledge about the technology. The survey also sought to find what customers accepted as a payback period if a solar electric home would cost them 20 percent extra. Purdue University's entry in the 2011 competition, the INhome, promoted the practicality of solar living by presenting an efficient, affordable, and conventional home. With a second place finish in the decathlon, Team Purdue's design showed consumers the reality that solar living is achievable today. The following analysis of the survey data obtained at the decathlon compares American residential consumer concerns and desires regarding solar electric power with Team Purdue's INhome.
Evaluating Shear links for Use in Seismic Structural Fuses
Farzampour, Alireza (Virginia Tech, 2019-01-28)
Advances in structural systems that resist extreme loading such as earthquake forces are important in their ability to reduce damages, improve performance, increase resilience, and improve the reliability of structures. Buckling resistant shear panels can be used to form new structural systems, which have been shown in preliminary analysis to have improved hysteretic behavior including increased stiffness and energy dissipating ability. Both of these characteristics lead to reduced drifts during earthquakes, which in turn leads to a reduction of drift related structural and nonstructural damage. Shear links are being used for seismic energy dissipation in some structures. A promising type of fuse implemented in structures for seismic energy dissipation, and seismic load resistance consists of a steel plate with cutouts leaving various shaped shear links. During a severe earthquake, inelastic deformation and damage would be concentrated in the shear links that are part of replaceable structural fuses, while the other elements of the building remain in the elastic state. In this study, by identifying the issues associated with general fuses previously used in structures, the behavior of the links is investigated and procedures to improve the behavior of the links are explained. In this study, a promising type of hysteretic damper used for seismic energy dissipation of a steel plate with cutouts leaving butterfly-shaped links subjected to shear deformations. These links have been proposed more recently to better align bending capacity with the shape of the moment diagram by using a linearly varying width between larger ends and a smaller middle section. Butterfly-shaped links have been shown in previous tests to be capable of substantial ductility and energy dissipation, but can also be prone to lateral torsional buckling. The mathematical investigations are conducted to predict, explain and analyze the butterfly-shaped shear links behavior for use in seismic structural fuses. The ductile and brittle limit states identified based on the previous studies, are mathematically explained and prediction equations are proposed accordingly. Design methodologies are subsequently conceptualized for structural shear links to address shear yielding, flexural yielding and buckling limit states for a typical link subjected to shear loading to promote ductile deformation modes. The buckling resistant design of the links is described with the aid of differential equations governing the links' buckling behavior. The differential equations solution procedures are developed for a useful range of link geometries and the statistical analysis is conducted to propose an equation for critical buckling moment. Computational studies on the fuses are conducted with finite element analysis software. The computational modeling methodology is initially verified with laboratory tests. Two parametric computational studies were completed on butterfly-shaped links to study the effect of varying geometries on the shear yielding and flexural yielding limit states as well as the buckling behavior of the different butterfly-shaped link geometries. It is shown that the proposed critical moment for brittle limit state has 98% accuracy, while the prediction equations for ductile limit states have more than 97% accuracy as well. Strategies for controlling lateral torsional buckling in butterfly links are recommended and are validated through comparison with finite element models. The backbone behavior of the seismic butterfly-shaped link is formulized and compared with computational models. In the second parametric study, the geometrical properties effects on a set of output parameters are investigated for a 112 computational models considering initial imperfection, and it is indicated that the narrower mid-width would reach to their limit states in lower displacement as compared to wider mid-width ones. The work culminates in a system-level validation of the proposed structural fuses with the design and analysis of shear link structural fuses for application in three buildings with different seismic force resisting systems. Six options for shear link geometry are designed for each building application using the design methodologies and predictive equations developed in this work and as guided by the results of the parametric studies. Subsequently, the results obtained for each group is compared to the conventional systems. The effect of implementation of the seismic links in multi-story structures is investigated by analyzing two prototype structures, with butterfly-shaped links and simple conventional beam. The results of the nonlinear response history analysis are summarized for 44 ground motions under Maximum Considered Event (MCE) and Design Basic Earthquake (DBE) ground motion hazard levels. It is shown that implementation of the butterfly-shaped links will lead to higher dissipated energy compared to conventional Eccentrically Braced Frame (EBF) systems. It is concluded that implementation of the seismic shear links significantly improves the energy dissipation capability of the systems compared to conventional systems, while the stiffness and strength are close in these two systems.
Evaluating the Fracture Potential of Steel Moment Connections with Defects and Repairs
Stevens, Ryan T. (Virginia Tech, 2020)
Steel moment frames are a popular seismic-force resisting system, but it is believed that they are susceptible to early fracture if there is a stress concentration in the plastic hinge region, also known as the protected zone. If a defect is present in this area, it may be repaired by grinding and/or welding, but little research has investigated how the repairs affect the performance of full-scale moment connections subjected to inelastic rotations. Thus, the goals of this research were to establish the performance of full-scale moment connections with repairs and defects, then develop a method for predicting fracture of the full-scale specimens using more economical cyclic bend tests. To do this, six full-scale reduced beam section (RBS) connections were tested having arrays of repairs or defects applied to the flanges. The repairs were 0.125 in. deep notches ground to a smooth taper and 0.25 in. deep notches ground to a smooth taper, welded, and ground smooth. The defects were sharp 0.25 in. and 0.375 in. notches. In addition, 54 bend tests were conducted on beam flange and bar stock coupons having the same repairs and defects, power actuated fasteners, puddle welds, and no artifacts. Finally, Coffin-Manson low-cycle fatigue relationships were calibrated using results from the cyclic bend tests with each artifact (repair, defect, or attachment method) and used in conjunction with estimates of full-scale plastic strain amplitudes to predict fracture of full-scale specimens. All four of the full-scale moment connections with repairs satisfied special moment frame qualification criteria (SMF). One full-scale specimen with sharp 0.25 in. notches satisfied SMF qualification criteria, but the flexural resistance dropped rapidly after the qualification cycle. On the other hand, the specimen with sharp 0.375 in. notches did not satisfy SMF qualification criteria due to ductile fractures propagating from the notches. The proposed method for predicting fracture of full-scale connections was validated using the six current and six previous full-scale RBS specimens. This method underpredicted fracture for eleven of the twelve specimens. The ratio of the actual to predicted cumulative story drift at fracture had a mean of 1.13 and a standard deviation of 0.19.
Feasibility Study on Highly Slender Circular Concrete Filled Tubes Under Axial Compression
Mysore Paramesh, Pragati (Virginia Tech, 2017-02-14)
Circular Concrete Filled Tubes are gaining importance in the construction industry due to their advantages insofar as economy and structural efficiency. Due to the recent developments in concrete and steel technology, the usage of high strength materials in these concrete filled tubes is increasing. The governing American specification (AISC 360-16) classifies these composite members as compact, non-compact and slender sections. The allowed section slenderness (ratio of diameter to thickness ratio) in each classification is related to the material properties (ratio of Young's modulus to yield strength ratio). AISC 360-16 is applicable for steels up to 75 ksi and concretes up to 10 ksi. These limits are lower than current available materials and restricts the usage of highly slender sections. As the strength of these tubes is dependent on local buckling, tests on many combinations of high strength steel and concrete are needed to extend these material limits. This preliminary research work focuses on understanding the local buckling behavior of highly slender sections and the effect of concrete infill and its confinement. The research began by compiling a database that highlighted a gap on tests with highly slender sections and high strength materials. To address this issue, a pilot set of experimental tests were conducted on short circular concrete filled members. An analytical evaluation of these experimental results are performed using 3D finite element analysis models. The critical buckling load is determined using J2 deformation theory, which proves to give a good estimate when compared with the experimental results. The main objective of the work is to determine if a simplified test like the one used in this work could be used for the large experimental study that will be necessary to expend the material limits in AISC 360-16. The limited data developed in this study indicates that the test can provide satisfactory results with a few improvements and refinements.
Finite Element Modeling of Steel Corrosion in Concrete Structures
Farhadi, Mehrnoush (Virginia Tech, 2018-09-14)
Concrete is a popular construction material for bridges, due to its high durability and energy efficiency. An important concern for concrete bridges is the possible occurrence of chloride- induced corrosion in prestressing strands and reinforcing bars, which may substantially impact the service life of such structures. Chloride- induced corrosion is a complicated electrochemical process which is affected by heat transfer, moisture flow and transport of chemical species through the concrete pore network. Reliable and robust analytical tools are required to allow multi-physics simulations of steel corrosion. This study has developed a nonlinear finite element analysis program, called VT-MultiPhys, to enable multi-physics simulations, including analyses of chloride-induced corrosion. The program includes constitutive laws, element formulations and global solution schemes to allow the analysis of steady-state (static) and time-dependent (dynamic) problems, involving multiple, coupled processes such as mechanical deformation, heat transfer, mass flow and chemical reactions combined with advective/diffusive transport of the various species. Special analysis schemes, based on the streamline-upwind Petrov-Galerkin (SUPG) method, have also been implemented to address the spatial instabilities which characterize analyses of advection-dominated transport. The finite element modeling scheme, constitutive laws and boundary conditions for analysis of chloride-induced corrosion are described in detail. The constitutive laws can be combined with inelastic material models to capture the damage (e.g., cracking) due to chloride-induced corrosion. A set of verification analyses is presented, to demonstrate the capabilities of VT-MultiPhys to conduct different types of simulations and reproduce the closed-form analytical solutions of simple cases. Validation analyses for heat conduction, moisture flow and chloride transport, using data from experimental tests in the literature, are also presented.
Flexural Behavior of Cold-Formed and Hot-Rolled Steel Sheet Piling Subjected to Simulated Soil Pressure
Ritthiruth, Pawin (Virginia Tech, 2021-01-11)
Hot-rolled sheet piling has long-been believed to have a better flexural performance than cold-formed sheet piling based on a test conducted by Hartman Engineering twenty years ago. However, cold-formed steel can have similar strength to the hot-rolled steel This experimental program studied the flexural behavior of hot-rolled and cold-formed steel sheet pilings. This program quantified the influence of transverse stresses from soil pressures on the longitudinal flexural strength. Four cross-sections with two pairs of equivalent sectional modulus were investigated. Sheet-piling specimens were subjected to simulated soil pressure from an air bladder loaded transversely to their longitudinal axis. The span lengths were varied, while the loading area remains unchanged to examine the effect of different transverse stresses. Lateral bracings were provided at discrete locations to establish a sheet piling wall behavior and allow the development of transverse stresses. Load-pressure, load-deflection, load-strain, and moment-deflection responses were plotted to demonstrate the behavior of each specimen. The moment-deflection curves were then normalized to the corresponding yield stress from tensile coupon tests to make a meaningful comparison. The results indicate that transverse stresses influence the flexural capacity of the sheet pilings. The longer span length has less amount of transverse strains, resulting in a higher moment capacity. The hot-rolled sheet pilings have better flexural performance also because of less transverse strains.
Fracture Resilience and Redundancy of Built-up Steel Girders
Hebdon, Matthew H.; Connor, Robert J. (American Institute of Steel Construction, 2016-04-15)
Internal member redundancy provides built-up steel girders with the ability to resist total member failure in the event an individual component fails. Anecdotal evidence of in- service performance has historically shown this to be the case in many bridges. However, due to the lack of experimental data, these members are currently required to be inspected as fracture-critical when deemed non-redundant. The full-scale experimental and analytical research program described in this paper provides needed information on parameters that affect the ability of built-up members to arrest a fracture, as well as describing the length of the remaining fatigue life. The results from this study have been used to develop recommended assessment procedures for built- up flexural members when a component has failed. Proposed evaluation guidelines will permit bridges with built-up steel girders where sufficient capacity exists, and the fracture critical designation can be removed, to be inspected using a rational in-service interval and level of detail. Considering the large number of riveted fracture critical bridges in the inventory, both highway and railroad bridge owners will benefit from this research since it allows for implementation of a more rational inspection strategy without compromising safety and reliability. The strategy provides a more integrated approach to inspection that accounts for the probability of detection capabilities, fatigue life, and fracture resilience. Further, new members utilizing high-strength bolted built-up members have the potential to be used without the penalty of being classified as fracture critical in terms of inspection
Investigation of the Time-Dependent Longitudinal Flexural Behavior of the Varina-Enon Bridge
Lindley, Seth Michael (Virginia Tech, 2019-08-05)
Post-tensioned concrete is a building technology which provides a compressive force to concrete via steel tendons. This combination of steel and concrete allows for the construction of lighter and stiffer structures. Post-tensioned concrete is widely utilized throughout the United States highway system and bridge construction. Over time, the force in the prestressing strands is reduced by delayed strains in the concrete. The accurate estimation of this prestress loss is vital for making good decisions about the remaining capacity of a structure and the infrastructure system at large. The Varina-Enon Bridge is a post-tensioned concrete box-girder bridge in Richmond Virginia. Cracks in the bridge prompted an investigation into the magnitude of prestress loss experienced by the structure. To estimate prestress loss, a computer model of the structure was created. In addition, data from sensors previously installed on the bridge were used to back calculate prestress loss. It was found that the estimation of losses from the field closely matched those estimated at the construction of the bridge. Additionally, more updated loss models estimated similar, or slightly smaller values for prestress loss.
Load Testing Deteriorated Spans of the Hampton Roads Bridge-Tunnel for Load Rating Recommendations
Reilly, James Joseph (Virginia Tech, 2017-01-12)
The Hampton Roads Bridge-Tunnel is one of the oldest prestressed concrete structures in the United States. The 3.5 mile long twin structure includes the world's first underwater tunnel between two man-made islands. Throughout its 60 years in service, the harsh environment along the Virginia coast has taken its toll on the main load carrying girders. Concrete spalling has exposed prestressing strands within the girders allowing corrosion to spread. Some of the more damaged girders have prestressing strands that have completely severed due to the extensive corrosion. The deterioration has caused select girders to fail the necessary load ratings. The structure acts as an evacuation route for the coast and is a main link for the local Norfolk Naval Base and surrounding industry. Because of these constraints, load posting is not a viable option. Live load testing of five spans was performed to investigate the behavior of the damaged spans. Innovative techniques were used during the load test including a wireless system to measure strains. Two different deflection systems were implemented on the spans, which were located about one mile offshore. The deflection data was later compared head to head. From the load test results, live load distribution factors were developed for both damaged and undamaged girders. The data was also used by the local Department of Transportation to validate computer models in an effort to help pass the load rating. Overall, this research was at the forefront of the residual strength of prestressed concrete girders and the testing of in-service bridges.
Methods for Evaluation of the Remaining Strength in Steel Bridge Beams with Section Losses due to Corrosion Damage
Javier, Eulogio Mendoza (Virginia Tech, 2021-06-02)
This research is intended to better understand the structural behavior of steel bridge beams that have experienced section loss near the bearings. This type of deterioration is common in rural bridges with leaking expansion joints, which exposes the superstructure to corrosive road deicing solutions. Seventeen beams from 4 decommissioned structures throughout Virginia were tested to induce web shear failure near the bearing locations and measured for load, vertical displacement, and web strain behavior. The strain was measured using a digital image correlation (DIC) system to create a digital strain field at equal loading and beam displacement intervals during testing. The data recorded during these large-scale tests was compared to several existing methods for calculating the shear capacity of the damaged beams. Finally, the most appropriate method of these approaches was identified based on accuracy, conservatism, and ease of implementation for load rating. When using load rating methods to determine a steel beam's capacity, this study also recommends that the effective area of the web used in determining the percentage of remaining thickness should consist of the bottom 3 inches of the web and should extend the length of the bearing plus one beam height excluding any areas without any noticeable section losses.
Multiscale Modeling of Fatigue and Fracture in Polycrystalline Metals, 3D Printed Metals, and Bio-inspired Materials
Ghodratighalati, Mohamad (Virginia Tech, 2020-03-16)
The goal of this research is developing a computational framework to study mechanical fatigue and fracture at different length scales for a broad range of materials. The developed multiscale framework is utilized to study the details of fracture and fatigue for the rolling contact in rails, additively manufactured alloys, and bio-inspired hierarchical materials. Rolling contact fatigue (RCF) is a major source of failure and a dominant cause of maintenance and replacements in many railways around the world. The highly-localized stress in a relatively small contact area at the wheel-rail interface promotes micro-crack initiation and propagation near the surface of the rail. 2D and 3D microstructural-based computational frameworks are developed for studying the rolling contact fatigue in rail materials. The method can predict RCF life and simulate crack initiation sites under various conditions. The results obtained from studying RCF behavior in different conditions will help better maintenance of the railways and increase the safety of trains. The developed framework is employed to study the fracture and fatigue behavior in 3D printed metallic alloys fabricated by selective laser melting (SLM) method. SLM method as a part of metal additive manufacturing (AM) technologies is revolutionizing the manufacturing sector and is being utilized across a diverse array of industries, including biomedical, automotive, aerospace, energy, consumer goods, and many others. Since experiments on 3D printed alloys are considerably time-consuming and expensive, computational analysis is a proper alternative to reduce cost and time. In this research, a computational framework is developed to study fracture and fatigue in different scales in 3D printed alloys fabricated by the SLM method. Our method for studying the fatigue at the microstructural level of 3D printed alloys is pioneering with no similar work being available in the literature. Our studies can be used as a first step toward establishing comprehensive numerical frameworks to investigate fracture and fatigue behavior of 3D metallic devices with complex geometries, fabricated by 3D printing. Composite materials are fabricated by combining the attractive mechanical properties of materials into one system. A combination of materials with different mechanical properties, size, geometry, and order of different phases can lead to fabricating a new material with a wide range of properties. A fundamental problem in engineering is how to find the design that exhibits the best combination of these properties. Biological composites like bone, nacre, and teeth attracted much attention among the researchers. These materials are constructed from simple building blocks and show an uncommon combination of high strength and toughness. By inspiring from simple building blocks in bio-inspired materials, we have simulated fracture behavior of a pre-designed composite material consisting of soft and stiff building blocks. The results show a better performance of bio-inspired composites compared to their building blocks. Furthermore, an optimization methodology is implemented into the designing the bio-inspired composites for the first time, which enables us to perform the bio-inspired material design with the target of finding the most efficient geometries that can resist defects in their structure. This study can be used as an effective reference for creating damage-tolerant structures with improved mechanical behavior.

Browsing by Author "Hebdon, Matthew H."

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