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Gainesville, FL, United States

Klammler H.,University of Graz | McVay M.,University of Florida | Horhota D.,State Materials Office
Journal of Geotechnical and Geoenvironmental Engineering

Load and resistance factor design (LRFD) is a method that aims at meeting specified target reliabilities (probabilities of failure) of engineered systems. The present work focuses on ultimate side friction resistance for axial loads on single cylindrical drilled shaft foundations in the presence of spatially variable rock/soil strength. Core sample data are assumed to provide reliable information about local strength in terms of mean, coefficient of variation and spatial correlation structure (variogram) at a site. The geostatistical principle of support up-scaling is applied to quantify the reduction in variability between local strength and the average ultimate shaft side friction resistance without having to recur to lengthy stochastic finite difference/element simulations. Site and shaft specific LRFD resistance factors (Φ values) are given based on the assumption of lognormal load and resistance distributions and existing formulas recommended by the Federal Highway Administration. Results are efficiently represented in dimensionless charts for a wide range of target reliabilities, shaft dimensions, and geostatistical parameters including nested variograms of different types with geometric and/or zonal anisotropies. Field data of local rock strength is used to demonstrate the method and to evaluate the sensitivity of obtained resistance factors to potentially uncertain variogram parameters. © 2010 ASCE. Source

Kim K.,University of Florida | Subgranon T.,University of Florida | Tia M.,University of Florida | Bergin M.,State Materials Office
Journal of Materials in Civil Engineering

Three full-size instrumented test slabs were constructed and tested by a heavy vehicle simulator (HVS) to evaluate the structural behaviors of internally cured concrete (ICC) for pavement use in Florida conditions. Three mix designs from a prior laboratory testing program were selected. The selected mixtures were a standard mixture with 0.40 water-cement (w/c) ratio, an ICC mixture with 0.40 w/c ratio, and an ICC mixture with 0.32 w/c ratio. Concrete samples were made and tested for their strength, elastic modulus, coefficient of thermal expansion (CTE), and shrinkage properties in the laboratory. A three-dimensional (3D) finite element (FE) model developed was calibrated by using a falling weight deflectometer (FWD) deflection basin as well as strain data under the HVS loading. From this study, it was found that ICC slabs appear to have better potential performance on the basis of the results of the critical stress analysis and the visual inspection of the test slabs. © 2016 American Society of Civil Engineers. Source

Klammler H.,Federal University of Bahia | McVay M.,University of Florida | Lai P.,05 Suwannee St. | Horhota D.,State Materials Office
Journal of Geotechnical and Geoenvironmental Engineering

Reliability-based design, such as LRFD, aims at meeting desired probability of failure levels for engineered structures. The present work attempts to contribute to this field by analyzing the influence of spatially variable soil/rock strength on the axial resistance uncertainty of single and multiple shafts in group layouts. This includes spatial variability over the individual shaft surfaces, effects of limited data, random measurement errors, and workmanship. A possible correlation between boring data inside or near the footprint of a foundation and the foundation itself is considered. In a geostatistical approach, spatial averaging (upscaling) and a degenerate case of ordinary kriging are applied to develop variance reduction charts and design equations for a series of foundation group layouts (single, double, triple, and quadruple). For the potential situation of an unknown horizontal correlation range at a site, the worst case scenarios are identified and demonstrated in an example problem. Resulting probabilities of failure are applied to the whole foundation (i.e., group) rather than single objects. It is found that a boring at the center of a group footprint can significantly reduce resistance prediction uncertainty, especially under the worst case scenario for unknown horizontal correlation range. In contrast, independent of the presence of a center boring or not, the uncertainty reduction through additional borings becomes small, once four or five borings are available. © 2013 American Society of Civil Engineers. Source

Paris J.M.,University of Florida | Roessler J.G.,University of Florida | Ferraro C.C.,University of Florida | DeFord H.D.,State Materials Office | Townsend T.G.,University of Florida
Journal of Cleaner Production

The amendment of concrete with waste products serves as an avenue to decrease the volume of wastes landfilled and to reduce the use of naturally mined materials, therefore, minimizing the footprint and impact that the construction industry has on the environment. This manuscript summarizes the current state of practice with regard to the use of waste products as supplementary cementitious materials (SCM) in portland cement concrete (PCC) and provides a summary of the comparatively sparse information on under-utilized waste materials such as: sugarcane bagasse ash, rice husk ash, waste wood biomass ash, and waste glass. The latter are all waste products that have the potential to be employed alongside traditional SCM, however much of the use to date has been done at the laboratory scale. This document will serve as a guide for the use of non-traditional waste SCM, to highlight areas likely requiring further refinement or research, and to indicate potential negative impacts from utilization of these products that might occur. The beneficial use of waste materials as SCM outside the United States has grown in recent years, mainly out of necessity; however, current research indicates that these materials typically provide a benefit when amending PCC and mortar. © 2016. Source

Lau K.,University of South Florida | Sagues A.A.,University of South Florida | Powers R.G.,State Materials Office

The extent of corrosion of epoxy-coated rebar (ECR) in marine bridges was found to be generally correlated with concrete chloride diffusivity, D App, with significant corrosion observed for bridges with D App values reaching up to ∼10 -7 cm 2/s but not for sound concrete locations in bridges with D App approaching the order of 10 -9 cm 2/s. However, significant ECR corrosion was observed in several preexisting cracked concrete locations of a low D App bridge after only ∼15 years of service. Wellmanifested, enhanced chloride and moisture penetration took place through the preexisting cracks of this bridge. The corrosion products in that case were solid and grew underneath the epoxy coating and had a composition consistent with that of chloride-substituted Akaganéite (β-FeO[OH]). Laboratory experiments showed that oxygen presence was not necessary for the formation of similar corrosion products, suggesting that corrosion damage could develop even with thin, moisture-filled cracks that would restrict oxygen flow to the corroding region. Other surveyed low D App bridges built with ECR showed also preferential chloride penetration at cracks, but no corrosion. An initial model formulation is introduced that may serve as a starting point for quantitative corrosion forecasting of possible damage in those other bridges. Exploratory projections indicate that, as expected, relatively isolated preexisting cracking should only create topical concrete damage with limited maintenance requirements. However, if the preexisting crack orientation with respect to the rebar were adverse and chloride transport were greatly enhanced (as it could be expected in relatively wide cracks), projected corrosion damage was more substantial. Source

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