Browsing by Subject "Damage"

Now showing 1 - 5 of 5
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    Effects of Implements of Husbandry (Farm Equipment) on Pavement Performance
    (Minnesota Department of Transportation Research Services Section, 2012-04) Lim, Jason; Azary, Andrea; Khazanovich, Lev; Wang, Shiyun; Kim, Sunghwan; Ceylan, Halil; Gopalakrishnan, Kasthurirangan
    The effects of farm equipment on the structural behavior of flexible and rigid pavements were investigated in this study. The project quantified the difference in pavement behavior caused by heavy farm equipment as compared to a typical 5-axle, 80 kip semi-truck. This research was conducted on full scale pavement test sections designed and constructed at the Minnesota Road Research facility (MnROAD). The testing was conducted in the spring and fall seasons to capture responses when the pavement is at its weakest state and when agricultural vehicles operate at a higher frequency, respectively. The flexible pavement sections were heavily instrumented with strain gauges and earth pressure cells to measure essential pavement responses under heavy agricultural vehicles, whereas the rigid pavement sections were instrumented with strain gauges and linear variable differential transducers (LVDTs). The full scale testing data collected in this study were used to validate and calibrate analytical models used to predict relative damage to pavements. The developed procedure uses various inputs (including axle weight, tire footprint, pavement structure, material characteristics, and climatic information) to determine the critical pavement responses (strains and deflections). An analysis was performed to determine the damage caused by various types of vehicles to the roadway when there is a need to move large amounts agricultural product.
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    Nondestructive Evaluation Advancements for Damage Detection in Concrete
    (2016-06) Freeseman, Katelyn
    While concrete is the most widely used civil engineering material, damage detection and progression in concrete structures have still proven to be difficult to address, especially when only one-sided access is available. New technological advances in nondestructive testing technology have created the opportunity to better utilize ultrasonic waves to aid in this damage detection process. However, interpretation of the signal data is a challenging task which often requires subjective assessments. This thesis addresses these limitations via the utilization of ultrasonic array technology for nondestructive damage detection purposes. The ultrasonic shear velocity array system used for this research is particularly advantageous because it can obtain measurements on virtually any concrete specimen, from columns and beams to concrete pavements, and provides a wealth of data from a single measurement. Novel signal interpretation methods were developed for several important concrete applications. Detection of load-induced damage in laboratory beams and a full-scale reinforced concrete column, as well as standard life-cycle damage in concrete pavements caused by freeze thaw or alkali-silica reaction degradation were considered. These investigations culminated in the development of successful and efficient quantitative damage detection methods. Finally, the development and refinement of a simulation program allowed for verification of the experimental investigation and a greater understanding of signal results.
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    Performance of Full-Scale Reinforced Concrete Columns Subjected to Extreme Earthquake Loading
    (2015-12) Nojavan, Alireza
    Seven full-scale reinforced concrete (RC) columns were tested at the Multi-Axial Subassemblage Testing (MAST) Laboratory of the University of Minnesota to investigate their performance under extreme seismic events that would produce near-collapse conditions. One of the goals of the tests was to investigate any potential differences in performance with column size, thus, the test specimens were larger than nearly all of the columns tested previously. In order to investigate the adequacy of current provisions, the specimens were designed according to seismic provisions of ACI 318-11 and featured two different cross sections (36×28 in. and 28×28 in.). Another goal of the program was to investigate the influence of loading history, thus the column specimens were subjected to several large displacement loading protocols, including monotonic and uniaxial and biaxial cyclic loading protocols. The last overall goal of the program was to investigate the post-peak behavior of the specimens at near-collapse conditions, hence loading on the specimens continued beyond the stopping criteria in previous tests until the specimens exhibited severe strength loss and stiffness degradation. Results from these tests were combined with the available dataset of RC column tests to study the effects of cross-sectional size on parameters representing seismic performance of columns including moment capacity, effective stiffness, drift capacity, displacement ductility, and reinforcing bar buckling. It was revealed that unlike the other parameters, specimens featuring larger cross-sectional depths are more prone to in-plane bar buckling, a failure mechanism that has never been reported during previous tests of RC columns. Unlike outward buckling of bars, in-plane bar buckling is not generally controlled by confining reinforcement; rather it is the concrete surrounding the bars that restrain them from in-plane buckling. To better understand this phenomenon, finite element (FE) models of isolated bars as well as a three-dimensional (3D) FE model of the lower portion of the tested specimens were analyzed. A parametric study indicates that concrete compressive strength, bar size and overall cross-sectional size of the columns can affect bar buckling while the effects of longitudinal bar and tie spacing are minor. The evolution of damage during application of the various loading protocols was quantified using several cumulative and noncumulative damage index models. In addition, observed visual damage to the specimens was used to assess calculated damage indices based on different models. Calculated and measured damage quantities were considered in combination with the lateral force-deformation cyclic envelope, strength loss, stiffness reduction, and hysteretic energy dissipation of the specimens to study the effects of applied loading protocols on the performance of tested column specimens.
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    Strength and Stability of Prestressed Concrete Through-Girder Pedestrian Bridges Subjected to Vehicular Impact
    (Minnesota Department of Transportation, Research Services Section, 2007-01) Baran, Eray; Schultz, Arturo; French, Catherine
    Two issues regarding the prestressed concrete through-girder pedestrian bridge system are investigated. The first issue concerns the ductility of prestressed concrete girders in these bridges because the section that is typically used may be considered to be over-reinforced according to AASHTO LRFD Bridge Specifications. Response of the section, including neutral axis location, strand stress at ultimate capacity, and moment capacity, predicted by AASHTO Standard and AASHTO LRFD Specifications are compared with the sectional response determined from nonlinear strain compatibility analyses. Modifications are proposed to the AASHTO LRFD procedure to rectify the errors in predicting sectional response. The second issue that was investigated concerns the strength and stability of prestressed concrete through-girder pedestrian bridges when subjected to impact by over-height vehicles. Three-dimensional finite element models of entire bridges and subassemblages were used to evaluate the strength, stiffness, and ductility characteristics of the bridge system and connection details. Accurate representation of the bridge details in the finite element models were assured by utilizing experimentally determined load-deformation characteristics for the connections. Results showed that significant improvements in the lateral load-deflection behavior of the bridge system could be obtained by implementing alternate connection schemes, and that concrete side-walls should be provided at girder ends.
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    Surface instability as damage evolution in rock.
    (2011-12) Kao, Chu-Shu
    A surface instability apparatus (SIA) was used to reproduce spalling in a laboratory setting, and damage in the rock was monitored by acoustic emission (AE) and digital image correlation (DIC) techniques. Lateral displacement served as the feedback signal to control the post-peak response with a closed-loop, servo-hydraulic load frame. Two types of clustering analysis, spatial clustering through the fractal dimension and hierarchical clustering through a dendrogram construction, were performed to analyze AE locations. Results showed an increasing FD as the damage level developed. The fractal dimension was close to 2.0 at lower load ratios, representing a planar distribution of samples. Then FD increased to a value of 2.4 to 2.5 in the post-peak stage, meaning a more scattered distribution in space. The hierarchical clustering was applied to low signal to noise ratio events provided "super AE" locations, a group of events with similar wave signals. These locations matched the crack trajectories. DIC was used to investigate incremental displacement fields during surface spalling. Real-time images were successfully captured under high stress levels through modification of the device. Displacement fields computed by DIC were through the comparison of two digital sub-images (subsets) with a unique white-light speckle pattern, and strain fields can be estimated from the displacement information. A continuum damage mechanics model was used to describe the damage progression in surface instability test. The continuity parameter serves as a state variable representing the evolution of damage, which is linked to the inelastic total lateral strain computed from the displacement fields using DIC. The critical value of inelastic total lateral strain was selected at the moment of spalling being captured by the digital imaging system. For the two Berea sandstone and one Serena sandstone specimens, consistent values were observed. This observation implies that the critical inelastic lateral strain may provide an indicative metric for determining the moment of surface instability.