Concrete highway bridges are important elements of our country's transportation infrastructure; however, only few studies that address their seismic behavior using data collected from instrumented structures are available in the literature. This gap of knowledge impairs full exploitation of structural health monitoring techniques for seismic damage assessment, and improvement of design recommendations. This research is particularly concerned with curved concrete box-girder highway bridges, whose seismic behavior is still widely unexplored due to lack of field monitoring data. By taking advantage of vibration records collected during six earthquake events at the West Street on Ramp, a curved concrete box-girder highway bridge located in Anaheim, California, this research aims at advancing knowledge about the seismic behavior of these bridges. Modal identification of the bridge during the earthquakes is conducted, and sensitivity analysis is carried out to reconcile the observed dynamic characteristics of the bridge with the behavior of its structural elements. Data collected from an instrumented large-scale bridge specimen during shaking table tests are also analyzed to gain insight about the response of the bridge bents during the earthquakes, and propose a strategy to model their seismic behavior. Information from modal identification and the shaking table tests analyses are instrumental in developing a nonlinear finite element model of the bridge, calibrated employing a multistage finite element model updating strategy. In order to evaluate the significance of using the structural-health-monitoring-informed structural model obtained, seismic performance assessment through incremental dynamic analysis is conducted, and results are compared with the predicted performance estimated with a conventional finite element model of the bridge. By advancing knowledge about the seismic behavior of concrete highway bridges, this research may ultimately contribute to improve structural health monitoring practices and design guidelines for this type of structures.

Abstract not available

Abstract not available

The objective of this study was to develop and validate practical modeling methods for investigating load paths and system behavior in a realistic, light-frame wood structure. The modeling methods were validated against full-scale tests on subassemblies and an L-shaped house. The model of the L-shaped house was then modified and used to investigate the effects of re-entrant corners, wall openings and gable-end retrofits on system behavior and load paths. Results from this study showed that the effects of adding re-entrant corners and wall openings on uplift load distributions were dependent on the orientation of the trusses with respect to the walls. Openings added to walls parallel to the trusses had the least effect on loads carried by the remaining walls in the building. Varying re-entrant corner dimensions of the L-shaped house under ASCE 7-05 (ASCE 2005) design wind loads caused increasing degrees of torsion throughout the house, depending on the relative location and stiffness of the in-plane walls (parallel to the applied wind loads) as well as the assumed direction of the wind loads. Balancing the stiffness of the walls on either side of the house with the largest re-entrant corner helped to decrease torsion in the structure somewhat. Finally, although previous full-scale tests on gable-end sections verified the effectiveness of the gable-end retrofit that was recently adopted into the 2010 Florida building code, questions remained about the effects of the retrofit on torsion in a full building. The current study found that adding the gable-end retrofits to the L-shaped house did not cause additional torsion. / Graduation date: 2013

The present thesis illustrates the application of the lower bound limit analysis in combination with finite elements and linear programming for obtaining the numerical solutions for various plane strain and axisymmetric stability problems in geomechanics. For the different plane strain problems dealt in the thesis, the existing formulation from the literature with suitable amendments, wherever required, was used. On the other hand for various axisymmetric problems, the available plane strain methodology was modified and a new formulation is proposed. In comparison to the plane strain analysis, the proposed axisymmetric formulation requires only three additional linear constraints to incorporate the presence of the hoop/circumferential stress (σθ). Several axisymmetric geotechnical stability problems are solved successfully to demonstrate the applicability of the proposed formulation. In the entire thesis, three noded triangular elements are used for carrying out the analysis. The nodal stresses are treated as basic unknowns and the stress discontinuities are employed along the interfaces of all the elements. To ensure that the finite element formulation leads to a linear programming problem, the Mohr-Coulomb yield surface is approximated by a polygon inscribed to the parent yield surface. For solving different problems, computer programs are developed in ‘MATLAB’. The variation of the bearing capacity factor Nγ with footing-soil interface roughness angle δ is obtained for different soil friction angles. The magnitude of Nγ is found to increase extensively with an increase in δ. With respect to variation in δ, the obtained values of Nγ were found to be generally smaller than the results available in literature. The effect of the footing width on the magnitude of Nγ has been examined for both smooth and rough strip footings. An iterative computational procedure is introduced to account for the dependency of φ on the mean normal stress ( σm). Two well defined φ- σm curves from literature, associated with two different relative densities, are being chosen for performing the computational analysis. The magnitude of Nγ is obtained for different footing widths, covering almost the entire range of model and field footing sizes. For a value of the footing width greater than approximately 0.2 m and 0.4 m, for a rough and smooth footing, respectively, the magnitude of Nγ varies almost linearly on a log-log scale. The bearing capacity factors Nc, Nq and Nγ are computed for a circular footing both with smooth and rough footing interface. The bearing capacity factors for a rough footing are found to be consistently greater than those with a smooth interface, especially with grater values of soil friction angle (φ). An encouraging comparison between the obtained results and those available from the literature is noted. Bearing capacity factor Nc for axially loaded piles in clays whose cohesion increases linearly with depth has been estimated numerically under undrained (φ = 0) condition. The variation of Nc with embedment ratio is obtained for several rates of the increase of soil cohesion with depth; a special case is also examined when the pile base was placed in the stiff clay stratum overlaid by a soft clay layer. It has been noticed that the magnitude of Nc reaches almost a constant value for embedment ratio approximately greater than unity. The bearing capacity factor Nγ has been computed for a rough conical footing placed over horizontal ground surface. The variation of Nγ with the cone apex (interior) angle (β), in a range of 30º - 180º, is obtained for different values of friction angle ( φ). For φ< 30º, the magnitude of Nγ is found to decrease continuously with an increase in β from 30º to 180º. On the other hand, for φ > 30º , the minimum magnitude of Nγ is found to occur generally between β = 120 and β = 150º. In all the cases, it has been noticed that the magnitude of Nγ becomes maximum for β = 30o. The vertical uplift resistance of circular plate anchors, embedded horizontally in a clayey stratum whose cohesion increases linearly with depth, has been obtained under undrained ( φ = 0) condition. The variation of the uplift factor (Fc) with changes in the embedment ratio (H/B) has been computed for several rates of the increase of soil cohesion with depth. It has been noted that in all the cases, the magnitude of Fc increases continuously with H/B up to a certain value of Hcr/B beyond which the uplift factor becomes essentially constant. The results obtained from the analysis are noted to compare quite well with those published in literature. From the investigation reported in this thesis, it is expected that the proposed axisymmetric formulation will be quite useful for solving various axisymmetric geotechnical stability problem in a rapid manner. The available plane strain formulation has also been found to yield quite satisfactory solutions even for a problem where the soil friction angle depends on the state of stress at a point.

University of Macau / Faculty of Science and Technology / Department of Civil and Environmental Engineering

University of Macau / Faculty of Science and Technology / Department of Civil and Environmental Engineering

University of Macau / Faculty of Science and Technology / Department of Civil and Environmental Engineering

An automated method in damage state assessment of reinforced concrete columns for the purpose of establishing a rapid and quantitative post-earthquake safety and structural evaluation procedure is proposed. Several techniques from the fields of computer vision and image processing are employed in order to develop a set of methods capable of automatically detecting spalled regions on the surface of reinforced concrete columns as well as the properties of cracks and spalled regions on these surfaces. The resulting properties of the observed visible damage on the reinforced concrete column surfaces are then utilized to automatically estimate the existing condition and safety of the column. The damage state is quantified according to the maximum drift capacity of the column. The methods proposed in this research were implemented in a Microsoft Visual Studio .NET environment, and tested on real images of damaged columns. The test results indicated that the methods could automatically detect spalled regions and retrieve the properties of spalling and cracks on reinforced concrete column surfaces in images or video frames, and further, that this retrieved information could be accurately translate to a meaningful assessment of the column's existing damage state in the form of the maximum drift capacity.

Condition assessment and safety verification of existing bridges and decisions as to whether bridge posting is required are addressed through analysis, load testing, or a combination of methods. Bridge rating through structural analysis is by far the most common procedure for rating existing bridges. The American Association of State Highway and Transportation Officials (AASHTO) Manual for Bridge Evaluation (MBE), First Edition permits bridge capacity ratings to be determined through allowable stress rating (ASR), load factor rating (LFR) or load and resistance factor rating (LRFR); the latter method is keyed to the AASHTO LRFD Bridge Design Specifications, which is reliability-based and has been required for the design of new bridges built with federal findings since October, 2007. A survey of current bridge rating practices in the United States has revealed that these three methods may lead to different ratings and posting limits for the same bridge, a situation that carries serious implications with regard to the safety of the public and the economic well-being of communities that may be affected by bridge postings or closures. To address this issue, a research program has been conducted with the overall objective of providing recommendations for improving the process by which the condition of existing bridge structures is assessed. This research required a coordinated program of load testing and finite element analysis of selected bridges in the State of Georgia to gain perspectives on the behavior of older bridges under various load conditions. Structural system reliability assessments of these bridges were conducted and bridge fragilities were developed for purposes of comparison with component reliability benchmarks for new bridges. A reliability-based bridge rating framework was developed, along with a series of recommended improvements to the current bridge rating methods, which facilitate the incorporation of various in situ conditions of existing bridges into the bridge rating process at both component and system levels. This framework permits bridge ratings to be conducted at three levels of increasing complexity to achieve the performance objectives, expressed in the terms of reliability, that are embedded in the LRFR option of the AASHTO Manual of Bridge Evaluation. This research was sponsored by the Georgia Department of Transportation, and has led to a set of Recommended Guidelines for Condition Assessment and Evaluation of Existing Bridges in Georgia.