Efficient Prestressed Concrete-Steel Composite Girder for Medium-Span Bridges

In this dissertation, a new Prestressed Concrete-Steel Composite (PCSC) girder system is introduced. The PCSC girder is composed of a lightweight W-shape steel section with shear studs on its top and bottom flanges to achieve composite action with the pretensioned concrete bottom flange and the cast-in-place concrete deck. The PCSC girder is lightweight, economical, durable and easy to fabricate. To prove its feasibility and potential, this study is to investigate design and fabrication issues associated with the PCSC girder. A service design procedure is proposed using Age-adjusted Elasticity Modulus Method (AEMM) to evaluate the time-dependent stresses and strains in the PCSC girder due to creep and shrinkage effects of concrete and relaxation of strands. The strength design method, as a rational approach replacing the current working stress method, is proposed for the design of PCSC girders at prestress release, to assist engineers to accomplish economic design and production of PCSC girders. Finite Element Analysis (FEA) of PCSC girders at prestress release is performed to understand stress distributions and the transfer of the prestressing force from the strands to the composite section and investigate the influence of stud distribution on the stresses in the concrete bottom flange. A PCSC girder specimen was successfully fabricated and instrumented in the structural lab following the proposed fabrication procedure. Design using AEMM and FEA were validated against the strain profiles at different sections, concrete surface strains and camber at mid-span. Flexural and shear tests were conducted to evaluate the flexural and shear capacities of the fabricated specimen. The crack moment, ultimate moment and ultimate shear obtained in tests satisfy the demand of bridge girders and well predicted using design calculations. Adviser: George Morcou

Investigation of the Impact of Dual-Lane Axle Spacing on Lateral Load Distribution

The spacing of adjacent wheel lines of dual-lane loads induces different lateral live load distributions on bridges, which cannot be determined using the current American Association of State Highway and Transportation Officials (AASHTO) Load and Resistance Factor Design (LRFD) or Load Factor Design (LFD) equations for vehicles with standard axle configurations. Current Iowa law requires dual-lane loads to meet a five-foot requirement, the adequacy of which needs to be verified. To improve the state policy and AASHTO code specifications, it is necessary to understand the actual effects of wheel-line spacing on lateral load distribution. The main objective of this research was to investigate the impact of the wheel-line spacing of dual-lane loads on the lateral load distribution on bridges. To achieve this objective, a numerical evaluation using two-dimensional linear elastic finite element (FE) models was performed. For simulation purposes, 20 prestressed-concrete bridges, 20 steel bridges, and 20 slab bridges were randomly sampled from the Iowa bridge database. Based on the FE results, the load distribution factors (LDFs) of the concrete and steel bridges and the equivalent lengths of the slab bridges were derived. To investigate the variations of LDFs, a total of 22 types of single-axle four-wheel-line dual-lane loads were taken into account with configurations consisting of combinations of various interior and exterior wheel-line spacing. The corresponding moment and shear LDFs and equivalent widths were also derived using the AASHTO equations and the adequacy of the Iowa DOT five-foot requirement was evaluated. Finally, the axle weight limits per lane for different dual-lane load types were further calculated and recommended to complement the current Iowa Department of Transportation (DOT) policy and AASHTO code specifications

Investigation of the Effect of Speed on the Dynamic Impact Factor for Bridges with Different Entrance Conditions

The dynamic interaction of vehicles and bridges results in live loads being induced into bridges that are greater than the vehicle’s static weight. To limit this dynamic effect, the Iowa Department of Transportation (DOT) currently requires that permitted trucks slow to five miles per hour and span the roadway centerline when crossing bridges. However, this practice has other negative consequences such as the potential for crashes, impracticality for bridges with high traffic volumes, and higher fuel consumption. The main objective of this work was to provide information and guidance on the allowable speeds for permitted vehicles and loads on bridges. A field test program was implemented on five bridges (i.e., two steel girder bridges, two pre-stressed concrete girder bridges, and one concrete slab bridge) to investigate the dynamic response of bridges due to vehicle loadings. The important factors taken into account during the field tests included vehicle speed, entrance conditions, vehicle characteristics (i.e., empty dump truck, full dump truck, and semi-truck), and bridge geometric characteristics (i.e., long span and short span). Three entrance conditions were used: As-is and also Level 1 and Level 2, which simulated rough entrance conditions with a fabricated ramp placed 10 feet from the joint between the bridge end and approach slab and directly next to the joint, respectively. The researchers analyzed and utilized the field data to derive the dynamic impact factors (DIFs) for all gauges installed on each bridge under the different loading scenarios

Numerical Analysis of Concrete-Filled Circular Steel Tubes

Concrete-filled steel tubes have been widely used in building and bridge construction. In this paper, the flexural behaviour of concrete-filled steel tubes is investigated using finite-element analysis and theoretical sectional analysis. The numerical results from both analytical methods are validated against published experimental test results. It is shown that both methods are capable of predicting the elastic and the ultimate moment capacities of concrete-filled steel tubes. Due to its computational efficiency, theoretical sectional analysis is more suitable for the design of concrete-filled steel tubes than finite-element analysis

Study of Deformation-Compensated Modeling for Flexible Material Path Processing Based on Fuzzy Neural Network and Fuzzy Clustering

In this paper, the Flexible Material Path Processing (FMPP) deformation compensation modeling method based on T-S fuzzy neural network is proposed. This method combined with T S fuzzy reasoning and fuzzy neural network.Firstly, fuzzy clustering is introduced to extract fuzzy membership functions and the fitness of fuzzy rules of T S fuzzy neural network antecedent from historical processing data; secondly, through back-propagation iteration to calculate connection weights of the network. Processing experiments shows that T S fuzzy neural network modeling in this paper is superior to typical T S model，the angle error and straightness error processing by NTS FNN is decreased than these of STS FNN

Field Monitoring of Curved Girder Bridges with Integral Abutments

Nationally, there are questions regarding the design, fabrication, and erection of horizontally curved steel girder bridges due to unpredicted girder displacements, fit-up, and locked-in stresses. One reason for the concerns is that up to one-quarter of steel girder bridges are being designed with horizontal curvature. There is also an urgent need to reduce bridge maintenance costs by eliminating or reducing deck joints, which can be achieved by expanding the use of integral abutments to include curved girder bridges. However, the behavior of horizontally curved bridges with integral abutments during thermal loading is not well known nor understood. The purpose of this study was to investigate the behavior of horizontal curved bridges with integral abutment (IAB) and semi-integral abutment bridges (SIAB) with a specific interest in the response to changing temperatures. The long-term objective of this effort is to establish guidelines for the use of integral abutments with curved girder bridges. The primary objective of this work was to monitor and evaluate the behavior of six in-service, horizontally curved, steel-girder bridges with integral and semi-integral abutments. In addition, the influence of bridge curvature, skew and pier bearing (expansion and fixed) were also part of the study. Two monitoring systems were designed and applied to a set of four horizontally curved bridges and two straight bridges at the northeast corner of Des Moines, Iowa—one system for measuring strains and movement under long term thermal changes and one system for measuring the behavior under short term, controlled live loading. A finite element model was developed and validated against the measured strains. The model was then used to investigate the sensitivity of design calculations to curvature, skew and pier joint conditions. The general conclusions were as follows: (1) There were no measurable differences in the behavior of the horizontally curved bridges and straight bridges studied in this work under thermal effects. For preliminary member sizing of curved bridges, thermal stresses and movements in a straight bridge of the same length are a reasonable first approximation. (2) Thermal strains in integral abutment and semi-integral abutment bridges were not noticeably different. The choice between IAB and SIAB should be based on life – cycle costs (e.g., construction and maintenance). (3) An expansion bearing pier reduces the thermal stresses in the girders of the straight bridge but does not appear to reduce the stresses in the girders of the curved bridge. (4) An analysis of the bridges predicted a substantial total stress (sum of the vertical bending stress, the lateral bending stress, and the axial stress) up to 3 ksi due to temperature effects. (5) For the one curved integral abutment bridge studied at length, the stresses in the girders significantly vary with changes in skew and curvature. With a 10⁰ skew and 0.06 radians arc span length to radius ratio, the curved and skew integral abutment bridges can be designed as a straight bridge if an error in estimation of the stresses of 10% is acceptable

Deformation-compensated modeling of flexible material processing based on T-S fuzzy neural network and fuzzy clustering

According to the factors that influence flexible material processing (FMP), the deformation compensation modeling method based on T-S fuzzy neural network is proposed. This method combines T-S fuzzy reasoning with a fuzzy neural network. Firstly, fuzzy clustering is introduced to extract fuzzy membership functions and the fitness of fuzzy rules of T-S fuzzy neural network antecedent from the past processing data. Secondly, with the steepest descent method, back-propagation iteration is used to calculate the connection weights of the network. The processing of experiments shows that T-S fuzzy neural network modeling is superior to typical T-S model. The angle error and the straightness error processed by NTS-FNN is 40.4 %, 28.8 % lower than those of STS-FNN. The minimum processing time processed by NTS-FNN is lower by 46.1 % than that of STS-FNN

The Organic Amendment Improve the Yield and Quality of Vegetable

Using biotechnology, we can change agricultural wastes into high‐quality organic fertilizers, which leads us in the direction of the development in modern agriculture and act as substitute to the chemical fertilizers. In this chapter, five types of technologies of organic amendment are elaborated. Each method can be selected based on the specific circumstance. The effects of the technology in the production are introduced and the principles of the technologies are explained in a simple manner

Actividad antioxidante, fenoles totales y flavonoides totales en extractos de tallos de Jasminum nervosum Lour

Guangxi traditional Chinese Medical University Universidad de Medicina Tradicional China de Guangxi This study evaluated the antioxidant activities of the extracts of Jasminum nervosum Lour. stems along with the effects of different extract solvents on total phenolics (TP), total flavonoids (TF), and antioxidant potential. The antioxidant activity of the extracts was assessed using the following methods: DPPH, ABTS+ both free radicals scavenging assays, and reducing assays. TP and TF were detected by spectrophotometric and HPLC methods. In former methods, the highest amount of TP content was ethy lacetate extract (EAE), expressed as gallic acid equivalents. The greatest TF content was in the n-butanol extract (BE), expressed as lutin equivalents. No significant difference was observed in the TP/TF content between these two extracts. The antioxidant activity and TP/TF content of three extracts seemed to follow the same trend. This implied that there is a good correlation between antioxidant activities and TP/TF content. But in HPLC methods, EAE contained the highest content of lutin and gallic acid, which decreased in the same order of EAE > BE > PE, the rank order of TP/TF content of EAE and BE were different according to antioxidant ability. The overall results showed that the EAE and BE were richer in phenolics and flavonoids than petroleum ether extract (PE), and may represent a good source of antioxidants.Este estudio evaluó las actividades antioxidantes de extractos de tallos de Jasminum nervosum Lour., y el efecto de diferentes disolventes de extracción en los fenoles totales (TP) y flavonoides totales (TF), y su potencial antioxidante. La actividad antioxidante de los extractos fue evaluada usando los siguientes métodos: DPPH, ABTS+ y ensayos reductores. TP y TF fueron detectados por métodos espectroscópicos y por HPLC. Con el primer método, el contenido más alto de TP se obtuvo en el extracto con acetato de etilo (EAE), expresado como equivalentes de ácido gálico. Por su parte, el mayor contenido de TF se obtuvo en el extracto con n-butanol (BE), expresado como equivalentes de luteína. No se observaron diferencias significativas en la relación TP/TF entre los dos extractos. La actividad antioxidante y la relación TP/TF de los tres extractos parecen seguir el mismo comportamiento. Esto implica que hay una buena correlación entre las actividades antioxidantes y la relación TP/TF. Con el método de HPLC, el extracto EAE contenía los más altos contenidos de luteína y ácido gálico, que decrecieron en el mismo orden de EAE > BE > PE, el orden de la relación TP/TF de EAE y BE fueron diferentes de acuerdo a su capacidad antioxidante. En conjunto, los resultados muestran que los extractos de EAE y de BE fueron más ricos en compuestos fenólicos y flavonoides que el extracto de éter (PE), y pueden representar una buena fuente de antioxidantes