Browsing by Subject "Composite"
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Item Analytical and Experimental Assessment of an AASHTO I-girder Type I Prestressed with AFRP Tendons(2014-12-12) Cummings, Wesley DavidCorrosion induced deterioration is one of the main reason for repair and rehabilitation programs in conventional steel reinforced concrete bridge decks. Of all bridges in the United States, over 50 percent are constructed of conventional reinforced or prestressed concrete (NACE, 2013), where one in three bridges are considered structurally deficient or functionally obsolete due to corrosion of the steel reinforcement. According to NACE International (2013) the annual cost of corrosion-related maintenance for highway bridges in the U.S. is estimated at $13.6 billion. Over the past couple of decades, fiber reinforced polymer (FRP) bars have been noted by researchers and engineers as a corrosion-resistant alternative for either conventional reinforcing steel or prestressing strands. High strength-to-weight ratio, corrosion resistance, ease in placement of the bars and accelerated implementation due to light weight are the special characteristics that make these bars an appealing alternative. Up to this end, extensive research has been conducted on the structural performance of FRP reinforced concrete beams and slabs; however, less attention has been paid to FRP reinforced concrete bridge girders in composite action with the bridge deck. Accounting for the effect of composite action between the bridge girder and deck can significantly impact the structural performance of the girder including the load and deformation capacities as well as the failure mode. Therefore, separate tests of the FRP concrete beams and slabs may not be sufficient to study the structural behavior and to provide design guidelines for engineers. This thesis presents the experimental and analytical investigations on structural performance of a full-scale AASHTO I-girder Type I, reinforced and prestressed with aramid fiber reinforced polymer (AFRP) bars, where the bridge girder is composite with the deck. The major objectives of this research were to develop a reliable prestressing anchorage system, examine the constructability of the full-scale specimen, study the load and deformation capacities, determine whether or not the design criteria per AASHTO LRFD were met, and improve the performance of the specimen by adjusting the prestressing layout. The specimen was constructed at a prestressing plant in San Marcos, Texas and tested at the High Bay Structural and Material Testing Laboratory on the campus of Texas A&M University. The cross-section of the bridge girder was composed of self-consolidating concrete with a total of 24 prestressed and 8 non-prestressed AFRP bars. The bridge deck consisted of a 203 mm (8 in.) conventional steel reinforced concrete slab. A flexure test was conducted to determine the moment-curvature relationship, flexure load capacity, and failure mode. The test was conducted as a simply supported, four point bending test in order to create a region of constant moment at the center of the beam. Two shear tests were conducted to determine the shear capacity, failure mode, maximum strain in the web, and moment-curvature relationship. The shear tests were conducted as a simply supported, three point bending test with varying load placement. The results of these tests were compared to a similar study which investigated the structural performance of a conventional steel reinforced AASHTO I-girder Type I with topping deck (Trejo et al. 2008). The specimen was also analyzed analytically to determine the effect on performance of varying the prestressing ratio of the separate layers in the bottom flange of the girder. The goal of this analysis was to determine an optimal prestressing layout to improve the performance at the ultimate state, while still satisfying serviceability limits. The prestressing ratio of the layers were varied from 0 to 50 percent in 5 percent increments to study the moment and curvature at both the cracking and ultimate states, along with the available compressive stress due to prestressing at the bottom of the girder. The results of this research confirms that the experimental specimen showed adequate strength and deformation capacities, satisfying the AASHTO LRFD design criteria. Additionally, the experimental specimen showed significantly greater cracking when compared to the conventional steel reinforced specimen, which is an early warning of impending failure. It was also determined that reducing the prestressing ratio of the AFRP bars in the lower layers improves the ductility of the specimen. The moment capacity can also be improved depending on the prestressing layout. However, reducing the prestressing ratio of the bottom layers causes the cracking moment and available compressive stress at the bottom of the girder to diminish. In order to compensate for this loss, the non-prestressed bars in the web can be prestressed. The optimal prestressing layout features the bottom three layers of the specimen prestressed to 35, 40, and 45 percent of their ultimate capacity, and two of the three layers of middle bars prestressed to 50 percent of their ultimate capacity.Item Analytical Study on Adhesively Bonded Joints Using Peeling Test and Symmetric Composite Models Based on Bernoulli-Euler and Timoshenko Beam Theories for Elastic and Viscoelastic Materials(2012-02-14) Su, Ying-YuAdhesively bonded joints have been investigated for several decades. In most analytical studies, the Bernoulli-Euler beam theory is employed to describe the behaviour of adherends. In the current work, three analytical models are developed for adhesively bonded joints using the Timoshenko beam theory for elastic material and a Bernoulli-Euler beam model for viscoelastic materials. One model is for the peeling test of an adhesively bonded joint, which is described using a Timoshenko beam on an elastic foundation. The adherend is considered as a Timoshenko beam, while the adhesive is taken to be a linearly elastic foundation. Three cases are considered: (1) only the normal stress is acting (mode I); (2) only the transverse shear stress is present (mode II); and (3) the normal and shear stresses co-exist (mode III) in the adhesive. The governing equations are derived in terms of the displacement and rotational angle of the adherend in each case. Analytical solutions are obtained for the displacements, rotational angle, and stresses. Numerical results are presented to show the trends of the displacements and rotational angle changing with geometrical and loading conditions. In the second model, the peeling test of an adhesively bonded joint is represented using a viscoelastic Bernoulli-Euler beam on an elastic foundation. The adherend is considered as a viscoelastic Bernoulli-Euler beam, while the adhesive is taken to be a linearly elastic foundation. Two cases under different stress history are considered: (1) only the normal stress is acting (mode I); and (2) only the transverse shear stress is present (mode II). The governing equations are derived in terms of the displacements. Analytical solutions are obtained for the displacements. The numerical results show that the deflection increases as time and temperature increase. The third model is developed using a symmetric composite adhesively bonded joint. The constitutive and kinematic relations of the adherends are derived based on the Timoshenko beam theory, and the governing equations are obtained for the normal and shear stresses in the adhesive layer. The numerical results are presented to reveal the normal and shear stresses in the adhesive.Item Biodegradable natural fiber composites : fabrication and characterization of hemp fiber with PLA powder composites(2016-05) Dabhi, Anish Satish; Li, Wei, doctor of mechanical engineering; Chen, Jonathan YInterest in natural fiber composites has been increasing in recent years due to their environmental benefits, along with weight reduction and economic viability. The composites in some cases have proven to exceed glass fiber composites and are suitable substitutes for the same. Hemp-Polylactic acid (PLA) composites were fabricated using a novel method, wherein PLA powder is mixed with hemp fibers through a needle punching process. The composites were produced at three different fiber loading levels of 35%, 50% and 55% and showed differently finished top and bottom surfaces, the top being plastic and the bottom being fibrous. The mechanical, acoustic and thermal properties were characterized and it was found that 50% composites provided the best results. Overall, the composites performed in the range of previously documented non modified natural fiber composites, giving the fabrication process validity. The tensile and impact tests showed acceptable strengths and also demonstrated low shattering probability due to fiber entanglement. This was also seen from the high values of elongation at break. Dynamic mechanical analysis (DMA) showed the highest storage modulus for the 50% fiber loaded samples and an increased glass transition temperature compared to neat PLA. The samples showed low thermal conductivity values, comparable to asbestos, showing good thermal insulation properties. Acoustic absorption coefficients were measured using a two microphone impedance test at varying high and low frequencies. The coefficients showed high acoustic absorption even at moderate frequency levels, owing to the dampening effect of the hemp fibers.Item Coextrusion : a feasible method to manufacture negative stiffness inclusions(2013-08) Hook, Daniel Taylor; Kovar, DesiderioThis work demonstrates the effectiveness of coextrusion as a method to manufacture negative stiffness inclusions for use in vibrational damping applications. The theory and mechanics of negative stiffness and coextrusion are introduced and the process of creating and extruding a feed rod with negative stiffness architecture explained. Coextrusion is shown to be a viable method to create negative stiffness inclusionsItem Fabrication of amorphous metal matrix composites by severe plastic deformation(Texas A&M University, 2006-10-30) Mathaudhu, Suveen NigelBulk metallic glasses (BMGs) have displayed impressive mechanical properties, but the use and dimensions of material have been limited due to critical cooling rate requirements and low ductility. The application of severe plastic deformation by equal channel angular extrusion (ECAE) for consolidation of bulk amorphous metals (BAM) and amorphous metal matrix composites (AMMC) is investigated in this dissertation. The objectives of this research are a) to better understand processing parameters which promote bonding between particles and b) to determine by what mechanisms the plasticity is enhanced in bulk amorphous metal matrix composites consolidated by ECAE. To accomplish the objectives BAM and AMMCs were produced via ECAE consolidation of Vitreloy 106a (Zr58.5Nb2.8Cu15.6Ni12.8Al10.3-wt%), ARLloy #1 (Hf71.3Cu16.2Ni7.6Ti2.2Al2.6 -wt%), and both of these amorphous alloys blended with crystalline phases of W, Cu and Ni. Novel instrumented extrusions and a host of postprocessing material characterizations were used to evaluate processing conditions and material properties. The results show that ECAE consolidation at temperatures within the supercooled liquid region gives near fully dense (>99%) and well bonded millimeter scale BAM and AMMCs. The mechanical properties of the ECAE processed BMG are comparable to cast material: ????f = 1640 MPa, ????f = 2.3%, E = 80 GPa for consolidated Vitreloy 106a as compared to ????f = 1800 MPa, ????f = 2.5%, E = 85 GPa for cast Vitreloy 106, and ????f = 1660 MPa, ????f = 2.0%, E = 97 GPa for ARLloy #1 as compared to ????f = 2150 MPa, ????f < 2.5%, E = 102 GPa for Hf52Cu17.9Ni14.6Ti5Al10. The mechanical properties of AMMCs are substandard compared to those obtained from melt-infiltrated composites due to non-ideal particle bonding conditions such as surface oxides and crystalline phase morphology and chemistry. It is demonstrated that the addition of a dispersed crystalline phase to an amorphous matrix by ECAE powder consolidation increases the plasticity of the amorphous matrix by providing locations for generation and/or arrest of adiabatic shear bands. The ability of ECAE to consolidated BAM and AMMCs with improved plasticity opens the possibility of overcoming the size and plasticity limitations of the monolithic bulk metallic glasses.Item Fatigue behavior of post-installed shear connectors used to strengthen continuous non-composite steel bridge girders(2016-08) Ghiami Azad, Amir Reza; Engelhardt, Michael D.; Williamson, Eric B., 1968-; Helwig, Todd A; Jirsa, James O; Taleff, Eric MMany older bridges in Texas are constructed with floor systems consisting of a concrete slab over steel girders. A potentially economical means of strengthening these floor systems is to connect the existing concrete slab and steel girders using post-installed shear connectors to change the behavior of the beam from non-composite to partially-composite. Since fatigue is one of the main concerns in designing bridges, investigating the fatigue properties of these post-installed shear connectors becomes crucial. Results from direct-shear testing show that post-installed shear connectors have a better fatigue life compared to conventional welded shear studs. However, based on currently available data from direct-shear tests, fatigue life of post-installed shear connectors is still inadequate for economical retrofit in some cases. Furthermore, it is unclear if direct-shear tests provide an appropriate means of evaluating fatigue performance. The objective of this dissertation is to develop new and more accurate approaches for evaluating the fatigue characteristics of post-installed shear connectors. This objective is addressed through large-scale beam fatigue tests and computational studies. The focus of the work is on evaluating fatigue life of shear connectors based on both slip and stress demands.