Jennifer Righman McConnell

Ultimate Capacity Destructive Testing and Finite-Element Analysis of Steel I-Girder Bridges

Current bridge design and rating techniques are based at the component level and thus cannot predict the ultimate capacity of bridges, which is a function of system-level interactions. While advances in computer technology have made it possible to conduct accurate system-level analyses, which can be used to design more efficient bridges and produce more accurate ratings of existing structures, the knowledge base surrounding system-level bridge behavior is still too small for these methods to be widely considered reliable. Thus, to advance system-level design and rating, a 1/5-scale slab-on-steel girder bridge was tested to ultimate capacity and then analytically modeled. The test demonstrated the significant reserve capacity of the steel girders, and the response of the specimen was governed by the degradation of the reinforced-concrete deck. To accurately capture the response of the specimen in an analytical model, the degradation of the deck and other key features of the specimen were modeled by using a...

Lower-leg Kinesio tape reduces rate of loading in participants with medial tibial stress syndrome

CONTEXT Medial tibial stress syndrome (MTSS) is an overuse injury occurring among the physically active. Linked to increased strain on the medial tendons of the ankle, studies emphasize controlling medial foot loading in the management of this condition. Kinesio taping (KT) has gained popularity for treating musculoskeletal pathologies; however, its effect on MTSS remains uninvestigated. This study aimed to determine if healthy participants and patients with current or previous history of MTSS differ in the rate of loading, and if KT affects plantar pressures in these participants. METHODS Twenty healthy participants and 20 participants with current or previous history of MTSS were recruited and walked across a plantar pressure mat prior to KT application, immediately after application, and after 24-h of continued use. Time-to-peak force was measured in 6 foot areas and compared across groups and conditions. RESULTS ANOVA revealed a significant interaction between group, condition, and foot area (F = 1.990, p = 0.033). MTSS participants presented with lower medial midfoot time-to-peak force before tape application (95%CI: 0.014-0.160%, p = 0.021) that significantly increased following tape application (p < 0.05). CONCLUSIONS These results suggest that KT decreases the rate of medial loading in MTSS patients. Future research might assess mechanisms by which this effect is achieved.

Development of a Novel Integrated Strengthening and Sensing Methodology for Steel Structures Using CNT-Based Composites

AbstractStrengthening of deteriorating structural members by fiber-reinforced polymers (FRPs) is an increasingly common and validated technique; however, concerns over means to evaluate the long-term durability of these retrofits exist. This paper explores a novel approach to overcome this concern through the use of a novel self-sensing composite material. Specifically, the objective of this paper is to provide a proof of concept for an integrated strengthening and sensing methodology for structural steel members achieved via infusing more-traditional composites with carbon nanotubes (CNTs). To assess the strengthening and sensing capabilities of the CNT-based composite, a set of unidirectional tensile tests were conducted. The experimental results show stiffness increases and strain reductions due to the application of the CNT-based sensing composites that were in close agreement with both analytical and finite-element models. The sensing aspect was also validated by a corresponding linear change in resi...

Field Testing of a Decommissioned Skewed Steel I–Girder Bridge: Analysis of System Effects

AbstractThis paper describes the field testing of a decommissioned, skewed, steel I–girder bridge and the resulting behavior that was observed. To more thoroughly evaluate the behavior observed in the field testing, where a load 17 times the design load was applied, a finite element model of this bridge was created, which illustrates the behavior of this structure at an even greater load and in greater detail than could be achieved in the field. The field and finite element analysis (FEA) results for this bridge were compared with expectations based on current bridge specifications. These results show that there is significant reserve capacity in this common bridge configuration, relative to both current bridge design and rating specifications and the maximum load that could physically be applied to the structure. This is attributed to transverse redistribution of force enabling the strength of this bridge to far exceed the strength of the limiting girder, which is termed the system effect in this work. C...

Moment-Rotation Response of Slender Steel I-Girders

While it is well known that slender girders have less ductility than their compact counterparts, this reduction has not been explicitly quantified. This results in limitations on the use of slender girders, and consequently, potential reductions in economy. These limitations are particularly significant in the AASHTO moment redistribution procedures, which exclude the use of girders that fail to satisfy certain compactness requirements. Thus, this paper reports the results of finite-element analysis (FEA) that has been validated by experimental testing of a series of I-girders with plate width-to-thickness ratios and unbraced lengths exceeding the limits for use of these provisions. From the FEA results and the complementary experimental results, the ductility of this class of girders is quantified in terms of moment-rotation response. Furthermore, a moment-rotation model that may be used to represent the ductility of any I-girder that satisfies AASHTO’s criteria for general I-girders is proposed.

Rotation Requirements for Moment Redistribution in Steel Bridge I-Girders

One of the key assumptions in inelastic design is that members have adequate ductility to allow moments to redistribute. However, while AASHTO specifications contain moment redistribution provisions for steel I-girders, the amount of ductility that is adequate for this specific design situation has not been studied in detail. As a result, the scope of these specifications is limited to beam types known to have significant ductility, which restricts the use of these procedures and causes negative economic consequences. The goal of this work is to determine ductility requirements specifically applicable to AASHTO moment redistribution procedures that are valid for all I-girders. This is accomplished through an analytical procedure, detailed herein. The results of this work are empirical equations predicting the amount of rotation required as a function of the intended level of moment redistribution as well as the material properties and span configuration of the girder. With these requirements known, there is a basis for reducing the overly conservative nature of the existing AASHTO moment redistribution specifications.

Novel self-sensing carbon nanotube-based composites for rehabilitation of structural steel members

Fatigue and fracture are among the most critical forms of damage in metal structures. Fatigue damage can initiate from microscopic defects (e.g., surface scratches, voids in welds, and internal defects) and initiate a crack. Under cyclic loading, these cracks can grow and reach a critical level to trigger fracture of the member which leads to compromised structural integrity and, in some cases, catastrophic failure of the entire structure. In our research, we are investigating a solution using carbon nanotube-based sensing composites, which have the potential to simultaneously rehabilitate and monitor fatigue-cracked structural members. These composites consist of a fiber-reinforced polymer (FRP) layer and a carbon nanotube-based sensing layer, which are integrated to form a novel structural self-sensing material. The sensing layer is composed of a non-woven aramid fabric that is coated with carbon nanotubes (CNT) to form an electrically conductive network that is extremely sensitive to detecting deformat...

Full-Scale Destructive Bridge Test Allows Prediction of Ultimate Capacity

Contemporary bridge design is generally based on designing individual members for the maximum force effect that each member may experience. This approach ignores the system-level interactions of these individual members, which may greatly increase the ultimate strength of the complete structure. In an attempt to understand better the load redistribution mechanisms that lead to this increase in ultimate strength, the destructive testing of a skewed steel I-girder bridge was planned and executed. However, because of the enormous system-level reserve capacity of the structure, the structure generally responded elastically, despite being loaded with the equivalent of 17 HS-20 design vehicles. Thus, a validated finite element analysis (FEA) approach was used to predict the ultimate capacity of this structure and to analyze the force redistribution as the bridges elastic limit was exceeded. The FEA results predicted that the equivalent of 41 HS-20 vehicles was needed to plastify fully the four girders of the subject bridge and show the significant amount of yielding that occurs in the cross-frames when the ultimate capacity of the girders is achieved.

EVALUATION OF MISSING COLUMN ANALYSES IN PROGRESSIVE COLLAPSE DESIGN CODES

Progressive collapse specifications prescribe alternate load path analysis as a means for ensuring adequate structural integrity and load redistribution capability. This approach is generally viewed as “threat-independent” in that it assumes the removal of individual columns, but does not consider the initiating event leading to the failure of these members. However, for reasons described herein, it is of interest to determine the blast loading that corresponds to column failure, which is an underlying threat implicitly assumed by these provisions. This is carried out through dynamic finite element modeling using the commercial software LS-DYNA. The modeling methods are validated using experimental results available in archival literature and sensitivity studies are performed to assess meshing requirements. As a result, the charge size and standoff distance producing failure of an individual member is determined.

Design of Cellular Composite Sandwich Panels for Maximum Blast Resistance Via Energy Absorption

This paper presents a design methodology for optimizing the energy absorption under blast loads of cellular composite sandwich panels. A combination of dynamic finite element analysis (FEA) and simplified analytical modeling techniques are used. The analytical modeling calculates both the loading effects and structural response resulting from user-input charge sizes and standoff distances and offers the advantage of expediting iterative design processes. The FEA and the analytical model results are compared and contrasted then used to compare the energy response of various cellular composite sandwich panels under blast loads, where various core shapes and dimensions are the focus. As a result, it is concluded that the optimum shape consists of vertically-oriented webs while the optimum dimensions can be generally described as those which cause the most inelasticity without failure of the webs. These dimensions are also specifically quantified for select situations. This guidance is employed, along with the analytical method developed by the authors and considerations of the influences of material properties, to suggest a general design procedure that is a simple yet sufficiently accurate method for design. The suggested design approach is also demonstrated through a design example.