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Backcalculation of Residual Tensile Strength of Regular and High Performance Fiber Reinforced Concrete From Flexural Tests

Description

The tensile stress–strain response of a fiber reinforced concrete dominates the performance under many loading conditions and applications. To represent this property as an average equivalent response, a back-calculation process from flexural testing is employed. The procedure is performed by model fitting of the three-point and four-point bending load deflection…

The tensile stress–strain response of a fiber reinforced concrete dominates the performance under many loading conditions and applications. To represent this property as an average equivalent response, a back-calculation process from flexural testing is employed. The procedure is performed by model fitting of the three-point and four-point bending load deflection data on two types of macro synthetic polymeric fibers, one type of steel fiber and one type of Alkali Resistant (AR) glass fiber. A strain softening tensile model is used to simulate the behavior of different FRC types and obtain the experimental flexural response. The stress–strain model for each age, fiber type and dosage rate is simulated by means of the inverse analysis procedure, using closed-form moment–curvature relationship and load–deflection response of the piecewise-linear material. The method of approach is further applied to one external data set for High Performance Fiber Reinforced Concrete (HPFRC) with two different types of steel fibers and validated by tensile test results reported. Results of back-calculation of stress–strain responses by tri-linear tensile model for all mixtures are compared and correlated with the corresponding standard method parameters used for post crack behavior characterization and a regression analysis for comparative evaluation of test data is presented.
ContributorsMobasher, Barzin (Author) / Bakhshi, Mehdi (Author) / Barsby, Christopher (Author) / Ira A. Fulton Schools of Engineering (Contributor)
Created2014-11-15
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Counter-narratives of African American academic persistence: identity maps and funds of knowledge

Description
Over 150 years since the abolition of slavery, African Americans still lack equal access to education and other quality of life markers. However, a slow increase in African American students pursuing and obtaining higher education demonstrates the progress of African American academic success. Although still not at an equitable level,…

Over 150 years since the abolition of slavery, African Americans still lack equal access to education and other quality of life markers. However, a slow increase in African American students pursuing and obtaining higher education demonstrates the progress of African American academic success. Although still not at an equitable level, this progress, and the voices of success are often muted by the majoritarian narrative of African American student failure. This research focuses on African American student success and examines the specific socio-cultural characteristics and processes that shape the ways in which African American students develop their own counter-narratives to persist and gain access to higher education. This study utilizes narrative inquiry in the form of interviews, artifacts collection and student-drawn identity maps to understand the factors that influence the development of counter-narratives. The primary research questions included: What narratives did African American students tell themselves to help them persist in school, attain a high school diploma and pursue higher education? How did they develop their narratives? How did their narratives influence their educational experiences? Five African American students who attended an elite public university in the southwest United States participated in four to five interviews ranging from six to ten hours in total. Through the analysis of their stories, the importance of culture and context were clear. Specifically their social support systems including their parents, siblings, teachers and mentors, significantly influenced their identity development and human agency. The findings also point to a critical path forward: if society commits to supporting African American student success, then shine a light on stories of persistence and potential rather than shortcomings and failures.
ContributorsFreeman, Stacey Vicario (Author) / Kozleski, Elizabeth B. (Thesis advisor) / Fischman, Gustavo (Thesis advisor) / Artiles, Alfredo (Committee member) / Arizona State University (Publisher)
Created2016
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Tell it right: bidialectal practices in the secondary English classroom

Description
Due to the limits of Arizona's secondary education system, English teachers often have to teach Standard English without regard for students' dialects and home languages. This can contribute to a lack of academic success for students who speak nonstandard and stigmatized language varieties. During the discussions that appear in this…

Due to the limits of Arizona's secondary education system, English teachers often have to teach Standard English without regard for students' dialects and home languages. This can contribute to a lack of academic success for students who speak nonstandard and stigmatized language varieties. During the discussions that appear in this thesis, I examine pedagogical practices, particularly bidialectalism, that can be used to better teach these students. While these practices can apply to students of all languages and dialects, I focus on their effects on speakers of African American Vernacular English (AAVE). I also present some ways that educators can be better prepared to teach such students. I conclude with some practical applications, lessons, and activities that teachers in similar contexts can use and modify.
ContributorsGersten, Olivia (Author) / Adams, Karen (Thesis advisor) / Prior, Matthew (Thesis advisor) / Early, Jessica (Committee member) / Arizona State University (Publisher)
Created2014
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Using virtual testing for characterization of composite materials

Description
Composite materials are finally providing uses hitherto reserved for metals in structural systems applications – airframes and engine containment systems, wraps for repair and rehabilitation, and ballistic/blast mitigation systems. They have high strength-to-weight ratios, are durable and resistant to environmental effects, have high impact strength, and can be manufactured in…

Composite materials are finally providing uses hitherto reserved for metals in structural systems applications – airframes and engine containment systems, wraps for repair and rehabilitation, and ballistic/blast mitigation systems. They have high strength-to-weight ratios, are durable and resistant to environmental effects, have high impact strength, and can be manufactured in a variety of shapes. Generalized constitutive models are being developed to accurately model composite systems so they can be used in implicit and explicit finite element analysis. These models require extensive characterization of the composite material as input. The particular constitutive model of interest for this research is a three-dimensional orthotropic elasto-plastic composite material model that requires a total of 12 experimental stress-strain curves, yield stresses, and Young’s Modulus and Poisson’s ratio in the material directions as input. Sometimes it is not possible to carry out reliable experimental tests needed to characterize the composite material. One solution is using virtual testing to fill the gaps in available experimental data. A Virtual Testing Software System (VTSS) has been developed to address the need for a less restrictive method to characterize a three-dimensional orthotropic composite material. The system takes in the material properties of the constituents and completes all 12 of the necessary characterization tests using finite element (FE) models. Verification and validation test cases demonstrate the capabilities of the VTSS.
ContributorsHarrington, Joseph (Author) / Rajan, Subramaniam D. (Thesis advisor) / Neithalath, Narayanan (Committee member) / Mobasher, Barzin (Committee member) / Arizona State University (Publisher)
Created2015
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Analytical load-deflection equations for beam and 2-D panel with a bilinear moment-curvature model

Description
A simplified bilinear moment-curvature model are derived based on the moment-curvature response generated from a parameterized stress-strain response of strain softening and or strain-hardening material by Dr. Barzin Mobasher and Dr. Chote Soranakom. Closed form solutions are developed for deflection calculations of determinate beams subjected to usual loading patterns at…

A simplified bilinear moment-curvature model are derived based on the moment-curvature response generated from a parameterized stress-strain response of strain softening and or strain-hardening material by Dr. Barzin Mobasher and Dr. Chote Soranakom. Closed form solutions are developed for deflection calculations of determinate beams subjected to usual loading patterns at any load stage. The solutions are based on a bilinear moment curvature response characterized by the flexural crack initiation and ultimate capacity based on a deflection hardening behavior. Closed form equations for deflection calculation are presented for simply supported beams under three point bending, four point bending, uniform load, concentrated moment at the middle, pure bending, and for cantilever beam under a point load at the end, a point load with an arbitrary distance from the fixed end, and uniform load. These expressions are derived for pre-cracked and post cracked regions. A parametric study is conducted to examine the effects of moment and curvature at the ultimate stage to moment and curvature at the first crack ratios on the deflection. The effectiveness of the simplified closed form solution is demonstrated by comparing the analytical load deflection response and the experimental results for three point and four point bending. The simplified bilinear moment-curvature model is modified by imposing the deflection softening behavior so that it can be widely implemented in the analysis of 2-D panels. The derivations of elastic solutions and yield line approach of 2-D panels are presented. Effectiveness of the proposed moment-curvature model with various types of panels is verified by comparing the simulated data with the experimental data of panel test.
ContributorsWang, Xinmeng (Author) / Mobasher, Barzin (Thesis advisor) / Rajan, Subramaniam D. (Committee member) / Neithalath, Narayanan (Committee member) / Arizona State University (Publisher)
Created2015
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Mechanical Characterization of the Tensile Properties of Glass Fiber and Its Reinforced Polymer (GFRP) Composite Under Varying Strain Rates and Temperatures

Description

Unidirectional glass fiber reinforced polymer (GFRP) is tested at four initial strain rates (25, 50, 100 and 200 s-1) and six temperatures (−25, 0, 25, 50, 75 and 100 °C) on a servo-hydraulic high-rate testing system to investigate any possible effects on their mechanical properties and failure patterns. Meanwhile, for…

Unidirectional glass fiber reinforced polymer (GFRP) is tested at four initial strain rates (25, 50, 100 and 200 s-1) and six temperatures (−25, 0, 25, 50, 75 and 100 °C) on a servo-hydraulic high-rate testing system to investigate any possible effects on their mechanical properties and failure patterns. Meanwhile, for the sake of illuminating strain rate and temperature effect mechanisms, glass yarn samples were complementally tested at four different strain rates (40, 80, 120 and 160 s-1) and varying temperatures (25, 50, 75 and 100 °C) utilizing an Instron drop-weight impact system. In addition, quasi-static properties of GFRP and glass yarn are supplemented as references. The stress–strain responses at varying strain rates and elevated temperatures are discussed. A Weibull statistics model is used to quantify the degree of variability in tensile strength and to obtain Weibull parameters for engineering applications.
ContributorsOu, Yunfu (Author) / Zhu, Deju (Author) / Zhang, Huaian (Author) / Huang, Liang (Author) / Yao, Yiming (Author) / Li, Gaosheng (Author) / Mobasher, Barzin (Author) / Ira A. Fulton Schools of Engineering (Contributor)
Created2016-05-19