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Recent documents in Publicationsen-usWed, 17 May 2017 02:05:20 PDT3600Prestress Loss Distributions along Simply Supported Pretensioned Concrete Beams
http://opensiuc.lib.siu.edu/cee_pubs/5
http://opensiuc.lib.siu.edu/cee_pubs/5Mon, 15 May 2017 08:32:29 PDT
ABSTRACT: The prestressing forces in prestressed tendons undergo a process of reduction over a period of time. A common assumption is that prestress loss is constantly distributed throughout the span of a simply supported pretensioned concrete beam. The purpose of this work is to investigate the accuracy of this assumption. The types of prestressed concrete beams investigated in this work include the following three typical types of tendon profile: (I) straight strands, (II) single-point depressed, and (III) two-point depressed. The major findings derived from this work are: (1) The total prestress loss is not constantly distributed throughout the span of a simply supported pretensioned concrete beam with any of the three types of tendon profiles, (2) The variation of prestress loss along the span of a pretensioned beam caused by elastic shortening of concrete or creep of concrete is much more significant than that caused by shrinkage of concrete or relaxation of tendons, and (3) The type of tendon profile in a simply supported pretensioned concrete beam has significant effects on the pattern of prestress loss distribution along the beam.
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Jen-kan Kent HsiaoPOST-TENSIONED BOX GIRDER BRIDGE An Analysis Approach using Equivalent Loads
http://opensiuc.lib.siu.edu/cee_pubs/4
http://opensiuc.lib.siu.edu/cee_pubs/4Tue, 07 Jun 2016 08:21:47 PDT
Continuous-span, cast-in-place box girders have been popular in modern bridge construction. Secondary moments due to prestressing in continuous-span, post-tensioned girders, however, have significantly complicated the structural analysis and design of the girders. The equivalent load method is a commonly used method in the analysis of continuous-span, post-tensioned concrete girders since the method reduces the analysis of a prestressed structure to that of a nonprestressed structure in which the consideration of secondary moments is not required. The basic concept of the equivalent load method is that the effects of prestressing are replaced by equivalent loads produced by the prestressed tendon along the span of the structure. The approximate equivalent load method significantly simplifies the procedure for the computation of equivalent loads for post-tensioned concrete girders with parabolic tendons and therefore has commonly been used by structural engineers. In this paper, three examples of simply-supported, posttensioned concrete girders with various combinations of locations of the centroid of tendons (c.g.s.) and the centroid of concrete (c.g.c.) are demonstrated to verify the accuracy of the approximate equivalent load method. Finally, an example of the analysis of a bridge composed of a continuous-span, post-tensioned concrete box girder superstructure and a concrete pier is also demonstrated using the approximate equivalent load method. Inconstant cross sections (inconstant c.g.c, lines) near the pier of the bridge are considered in this example.
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Jen-kan Kent Hsiao et al.Evaluation of InSpectra UV Analyzer for Measuring Conventional Water and Wastewater Parameters
http://opensiuc.lib.siu.edu/cee_pubs/1
http://opensiuc.lib.siu.edu/cee_pubs/1Mon, 10 Aug 2009 12:06:34 PDT
A relatively new analytical instrument for the measurement of BOD5, COD, TSS, TOC, nitrates and surfactants has been developed commercially. It is based on the use of ultraviolet spectrophotometry and a deterministic approach to analyze the sample’s spectrum by comparing it with a series of historical reference spectra. Using standard methods for the measurement of BOD5, TSS and TOC as true values, the use of this instrument was evaluated. The samples tested were obtained from both wastewater and water treatment facilities. Results indicate that the BOD5 measurement performed best. There was no correlation found for TSS or TOC.
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Lizette R. Chevalier et al.Feasibility of Calcium Peroxide as an Oxygen Releasing Compound in Treatment Walls
http://opensiuc.lib.siu.edu/cee_pubs/3
http://opensiuc.lib.siu.edu/cee_pubs/3Mon, 10 Aug 2009 09:53:26 PDT
This research investigates the use of a proprietary formulation of powdered calcium peroxide (PermeOx Plus®) as an oxygen releasing compound in a treatment wall. Laboratory scale column studies evaluated the release of oxygen and the permeability effects resulting from a treatment wall mixture of the calcium peroxide and a representative aquifer sand (40-mesh Unimin sand). The mixtures evaluated ranged from 0.1 to 1.0 percent by weight. Influent water was prepared at an average dissolved oxygen concentration of 3.1 mg/L and pumped into the treatment wall soil at a constant rate of 0.17 cm^{3}/sec (0.53 ft^{3}/day) to simulate ground water dissolved oxygen and flow conditions. The average changes in relative permeability for mixtures of 0.1%, 0.5% and 1.0% calcium peroxide by weight were 65.6%, 66.1% and 77.1%, respectively. The peak dissolved oxygen levels in the same mixtures were 5.9, 7.40, and 10.7 mg/L, respectively.
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Lizette R. Chevalier et al.Use of Optimization to Develop a Correlation Model for Predicting Residual NAPL Saturation
http://opensiuc.lib.siu.edu/cee_pubs/2
http://opensiuc.lib.siu.edu/cee_pubs/2Mon, 10 Aug 2009 09:38:50 PDT
Predicting the residual saturation of a trapped non-aqueous phase liquid contaminant is critical to estimating the region of contamination, the design of remediation strategies, and risk assessment. Models were developed to predict residual NAPL saturation utilizing optimization and non-linear error functions, consequently allowing for a broader mathematical approach to model development. The input parameters evaluated represent soil and fluid properties: the uniformity coefficient (C_{u}), the coefficient of gradation (C_{c}), the capillary number (Nc), the bond number (Nb) and the total trapping number (Nt). Overall, the model that performed best was based on a second-order equation with the independent variables C_{u} and Nt_{1} using the sum of the squares of the errors. The nonlinear error function based on a derivative of Marquardt’s Percent Standard Deviation performed best for three other cases.
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Lizette R. Chevalier