Tarek Omar

Effect of triaxial specimen size on engineering design and analysis

BackgroundTriaxial tests are often used to determine the behavior and strength characteristics of soils. Specimen size can have a significant impact on the measured shear strength. Accordingly, the selected parameters affect the related geotechnical engineering analysis and design.MethodsWe tested three different specimen sizes of loose Ottawa sand in triaxial compression tests. The measured shear strength and friction angle are used to explain some of the observed scale effects in engineering design and analysis. Critical state parameter and shear strength from the laboratory tests are employed to assess the static and seismic slope stability of an embankment dam, to calibrate a critical state soil constitutive model, to study the soil behavior under shallow foundations, and to evaluate liquefaction triggering and failure of retaining structures.ResultsWe show that all of these analyses can be significantly affected by the choice of the specimen size used to determine shear strength parameters.ConclusionWhile using small size samples for determining shear strength parameters might result in un-conservative design, a large sample size is consequently a more accurate representation of soil strength conditions and field deformations.

Performance of NDT Techniques in Appraising Condition of Reinforced Concrete Bridge Decks

AbstractThe colossal backlog of deteriorated concrete bridge decks draws attention to the importance of nondestructive testing (NDT) technologies as potential bridge condition assessment tools. The...

Integrated Condition Rating Model for Reinforced Concrete Bridge Decks

AbstractMost commonly used bridge condition rating systems utilize data emanating from visual inspection reports, inevitably associated with considerable uncertainty. This could possibly lead to un...

Influence of Specimen Size in Engineering Practice

A combined laboratory experimental and numerical analysis is presented to investigate the influence of specimen size and scale effect on engineering analysis and design. Laboratory triaxial compression and direct shear tests show that the size of the specimen has a significant influence on the stress-strain behavior of sands with larger specimens mobilizing smaller shear strengths. Shear strengths measured in laboratory direct shear tests are incorporated in a FEM and slope stability analyses to evaluate and compare the shear stress distribution and deformational behavior of a slope case study. The numerical analyses are conducted using ABAQUS and mohr-coulomb failure criteria. The performance of the slope under load application due to staged highway embankment construction is also evaluated. The analyses results show that the shear stresses and performance of slope and highway embankment are influenced considerably by the size of the triaxial specimens. This would have significant implications on engineering design and the choice of a representative sample size. In order to apply the shear strengths in design, it is suggested to employ larger specimen sizes to achieve the critical state strengths of the soil and better representation of field deformations.

Rational Condition Assessment of RC Bridge Decks Subjected to Corrosion-Induced Delamination

AbstractPrecise evaluation of the condition of RC bridge decks, particularly for corrosion-induced delaminations, is decisive for ensuring bridge performance and safety. Although infrared thermogra...

Automated Data Collection for Progress Tracking Purposes: A Review of Related Techniques

The automated data collection of civil infrastructure projects, whether under construction, newly put into service, or in operation has been receiving increased attention by researchers and practitioners. Such real-time progress tracking is essential for the active monitoring of production during the construction phase of a project and for the built assets during their service lives. Automatic progress tracking can result in timely detection of potential time delays and construction discrepancies and directly supports project control decision-making. This paper outlines recent research efforts in this field and technological developments that aim to facilitate project management toward achieving project objectives. 3D imaging, geo-spatial, enhanced IT, and augmented reality technologies have recently achieved significant advances in this field. These technologies are discussed and compared herein in terms of their strengths and limitations to identify various trends concerning their applicability in data acquisition for construction projects and to formulate recommendations for their suitability in different projects. Prospects for improvement and challenges that can be expected in future research and development are considered. It is hoped that this discussion will assist construction stakeholders in choosing appropriate data collection tools, and motivate further research and development to assist in delivering projects on time and within budget.

Clustering-Based Threshold Model for Condition Assessment of Concrete Bridge Decks Using Infrared Thermography

Bridge decks are deteriorating at an alarming rate due to corrosion of the reinforcing steel, requiring billions of dollars to repair and replace them. Nowadays, infrared thermography (IRT) diagnostics represent a mature high-technology field that combines achievements in the understanding of heat conduction, material science, and computer data processing. The high interest in the IRT inspection technique is related to its universal character, high testing productivity and in-service safety. However, the analysis of IRT data to evaluate the condition of concrete bridge decks is still rather qualitative, thus preventing the progressive competition of IRT with other inspection techniques. The goal of this research is to understand the relationship between IRT and deck deterioration, and develop a model to determine delamination quantities in concrete bridge decks using a relatively low cost microbolometer infrared camera. Infrared testing was conducted in-situ on a full-scale bridge deck. The thermal IR images were enhanced and stitched using specially developed Matlab codes to create a mosaicked thermogram of the entire bridge deck. Image analysis based on the K-means clustering technique was utilized to segment the mosaic and identify objective thresholds. Hence, a condition map classifying different categories of delamination severity was created and also validated through the results of other techniques obtained on the same bridge. The findings from this study demonstrate that IRT can provide transportation agencies both quantitative and qualitative indications of subsurface delamination defects, thus assisting efficient maintenance and repair decision-making, and focusing limited funding on the most deserving bridge decks.