Response of reinforced concrete piles including soil–pile interaction effects

This paper discusses the importance of modeling soil–pile interaction in the response of reinforced concrete (RC) piles. A displacement-based, RC beam–column fiber model with distributed lateral deformable supports is presented first. The formulation is general and applies to both monotonic and cyclic loads. The proposed model is simple, computationally efficient and capable of representing the salient features of the soil–pile interaction, including dragging force and gap formation along the pile–soil interfaces as well as hysteretic responses of piles and surrounding soils. Two applications are presented to illustrate the model characteristics, to show the model capabilities, and to discuss the importance of modeling the pile–soil system. The first application deals with a single end-bearing pile embedded in a cohesionless soil. The proposed beam–column model is used to investigate the effects of different model parameters on the pile–soil response, including pile length, pile diameter, and pile and soil nonlinearities. The second application validates the accuracy of the proposed model with the experimental results of a cyclic test on a RC pile/shaft system where the influence of the pile–soil interaction is essential. Results from the correlation studies indicate that the proposed model can represent well both global and local responses of the pile–soil system. The effects of the interfacial characteristics between pile and soil on the system response are also studied.     

Correlation between beam on Winkler-Pasternak foundation and beam on elastic substrate medium with inclusion of microstructure and surface effects

A novel beam-elastic substrate element with inclusion of microstructure and surface energy effects is proposed in this paper. The modified couple stress theory is employed to account for the microstructure-dependent effect of the beam bulk material while Gurtin-Murdoch surface theory is used to capture the surface energy-dependent size effect. Interaction mechanism between the beam and the surrounding substrate medium is represented by the Winkler foundation model. The governing differential equilibrium and compatibility equations of the beam-elastic substrate system are consistently derived based on virtual displacement and virtual force principles, respectively. Both essential and natural boundary conditions of the system are also obtained. Two modified Tonti’s diagrams are presented to provide the big picture of both displacement-based and force-based formulations of the system. Due to similarity between the current problem and the one related to the beam on Winkler-Pasternak foundation, the so-called “natural” beam-Winkler-Pasternak foundation element coined by the authors is employed to perform two numerical simulations to study the characteristics and behaviors of a beam-substrate system with inclusion of microstructure and surface effects.     

Glass Fiber/Polyphthalamide Composites for 3D-Molded Interconnect Devices Application: Structure and Properties

The research work was to demonstrate the feasibility of a three-dimensional molded interconnect devices concept using the injection-molding technique and to investigate the effects of weld/meld line types on the structure and properties. Two different polymers based on polyphthalamide/glass fiber composites (PA6 T/X and PA10 T/X composites) were produced by injection molding at the different processing conditions. A mold was designed in such a way that a weld and meld line can be produced at different angles by changing an insert inside the mold. The mechanical properties such as stiffness, tensile strength, and flexural strength were determined in tensile and flexural tests, respectively. The adhesive strength and electrical resistance were studied with the pull-off process and four-point measurement, respectively, and are discussed. The dispersion of the glass fiber and types of meld/weld line were inspected using scanning electron microscopy. The results were in-line with the expectation of a reduction in mechanical properties in areas where weld/meld lines occurred. The results of tensile tests clearly showed that the weld and meld lines showed a considerable influence on mechanical properties. It was found that the tensile and flexural strength of polyphthalamide/glass fiber composites with weld line type decreased approximately 58 and 62%, respectively, compared to the composites without the weld line. On the other hand, the effects of injection time and mold temperature on the tensile strength were marginal.     

Performance evaluation of a 10 kWp PV power system prototype for isolated building in Thailand

This paper describes the design and testing of a 10 kW_p photovoltaic (PV) system and summarizes its performance results after the first 6 months of operation. This system functions as a stand-alone power system that is used to supply electricity for isolated buildings and is designed for integration with a micro-grid system (MGS), which is the future concept for a renewable energy-based power network system for Thailand. The system is comprised of the following components. An array with three different types of PV modules consisting amorphous thin film of 3672 W, polycrystalline solar cell of 3600 W and hybrid solar cell of 2880 W, making up a total peak power of 10.152 kW. In addition, there are three grid-connected inverters of 3.5 kW each, three bi-directional inverters of 3.5 kW each and an energy storage system of 100 kWh. After the first 6 months of system operation, it was found that all the components and the overall system had worked effectively. In total, the system had generated about 7852 kWh and the average electricity production per day was 43.6 kWh. The average efficiency of amorphous thin film panel, polycrystalline panel, hybrid solar cell panel and entire PV panel system was 6.26%, 10.48%, 13.78% and 8.82%, respectively. From the analysis of the daily energy production, daily energy consumption and energy storage, the results seem to indicate that there was some mismatching between energy supply and demand in the system. However, this can be overcome by integrating the system to a micro-grid network whereby the energy from the system can be diverted to other loads when there is a surplus and additional energy can be drawn from external sources and fed to the system when the internal supply is insufficient.     

Raw and chemically treated bio-waste filled (Limonia acidissima shell powder) vinyl ester composites: Physical,mechanical, moisture absorption properties,and microstructure analysis

The rapid growth of environmentally sustainable and eco-friendly materials tends to the utilization of biowastes as filler in polymer matrix composites. The particulate composite with improved wettability of fillers and advanced approach can evolve polymer composites that exhibit promising applications in packaging, automobile, marine, construction, and aerospace. In the present work, one of the biowaste fillers were synthesized from Limonia acidissima shells via a top-down approach (pulverizing) and the surfaces were chemically modified using sodium hydroxide (NaOH) before they were used as fillers in vinyl ester polymer composites by different weight percentage (0, 5, 10, 15, and 20 wt%). The prepared particulate composites were characterized by mechanical properties, moisture absorption behavior, and morphology. At different filler loading the tensile strength, tensile modulus, flexural strength, flexural modulus, impact strength, hardness, density, and moisture intake tests were performed. The results reveal that the properties increased for composites filled with alkaline treated fillers for the same filler loading and found to be higher at filler loading of 15 wt%. The morphological analysis confirms the better interfacial bonding between alkali-treated particles and matrix due to the removal of non-cellulose materials from the surface of the particles.     

Improved mechanical and thermal properties of spent coffee bean particulate reinforced poly(propylene carbonate) composites

Using biodegradable polypropylene carbonate (PPC) as the polymer matrix and 5 to 25?wt% content of spent coffee bean powder (SCBP) as filler, completely biodegradable composite films of PPC/SCBP were prepared. These composite films were characterized by polarized optical microscopy (POM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis, differential scanning calorimetry (DSC), and tensile tests. The POM images indicated the uniform distribution of the SCBP in the composites. The FTIR spectra indicated that the PPC structure was retained by the composite films. The XRD analysis found that the composite films had lower crystallinity than the PPC due to the presence of amorphous hemicellulose containing SCBP. A significant enhancement in thermal stability of the filler reinforced composite was noticed which was more than 30% of the PPC matrix due to the presence of polyphenols in SCBP. A maximum increase of 35% of tensile strength was observed with the addition of 20?wt% SCBP filled composite films. These biodegradable composite films with higher thermal stability and tensile strength can be considered for packaging applications.     

Poly (butylene terephthalate)/silica nanocomposites prepared from cyclic butylene terephthalate

Poly (butylene terephthalate) (PBT)/silica nanocomposites were compounded from cyclic butylene terephthalate (CBT) resin with very low melt viscosity via high-speed stirring and subsequent in situ polymerization. The effect of silica nanoparticles on the properties of CBT and its polymer composites has been studied. It was shown that the well-dispersed silica nanoparticles, even in small content (1–2 wt.%), result in the dramatic extension of the polymerization process of CBT resin. The flexural properties of polymerized PBT nanocomposites, including modulus, yield strength and failure strain, was improved significantly with the incorporation of silica nanoparticles.     

Failure Mode Analyses of Reinforced Concrete Beams Strengthened in Flexure with Externally Bonded Fiber-Reinforced Polymers

As existing structures age or are required to meet the changing demands on our civil infrastructure, poststrengthening and retrofitting are inevitable. A relatively recent technique to strengthen reinforced concrete (RC) beams in flexure uses fiber-reinforced polymer (FRP) strips or sheets glued to the tension side of the beam. A number of researchers have reported that the failure mode of an FRP-strengthened RC beam can change from the desired ductile mode of an underreinforced beam to a brittle one. This paper analyzes the effects of this strengthening technique on the response and failure modes of a reference RC beam. A nonlinear RC beam element model with bond-slip between the concrete and the FRP plate is used to study how the failure mechanism of simply supported strengthened RC beams is affected by the following parameters: plate length, plate width, plate stiffness, and loading type. The beam geometry is kept constant. The parametric studies confirm the experimentally observed results according to which the most commonly observed failure modes due to loss of composite actions are affected by the plate geometric and material properties. In addition, distributed loads (difficult to apply in an experimental test) may not be as sensitive to plate debonding in the region of maximum bending moment as are beams subjected to point loads.     

Size effects in two-dimensional layered materials modeled by couple stress elasticity

In the present study, the effect of material microstructure on the mechanical response of a two-dimensional elastic layer perfectly bonded to a substrate is examined under surface loadings. In the current model, the substrate is treated as an elastic half plane as opposed to a rigid base, and this enables its applications in practical cases when the modulus of the layer (e.g., the coating material) and substrate (e.g., the coated surface) are comparable. The material microstructure is modeled using the generalized continuum theory of couple stress elasticity. The boundary value problems are formulated in terms of the displacement field and solved in an analytical manner via the Fourier transform and stiffness matrix method. The results demonstrate the capability of the present continuum theory to efficiently model the size-dependency of the response of the material when the external and internal length scales are comparable. Furthermore, the results indicated that the material mismatch and substrate stiffness play a crucial role in the predicted elastic field. Specifically, the study also addresses significant discrepancy of the response for the case of a layer resting on a rigid substrate.     

Effects of Indium Content on Microstructural,Mechanical Properties and Melting Temperature of SAC305 Solder Alloys

The present study investigated the effects of indium (In) addition on the microstructure, mechanical properties, and melting temperature of SAC305 solder alloys. The indium formed IMC phases of Ag₃(Sn,In) and Cu₆(Sn,In)₅ in the Sn-rich matrix that increased the ultimate tensile strength (UTS) and the hardness while the ductility (% EL) decreased for all In containing solder alloys. The UTS and hardness values increased from 29.21 to 33.84 MPa and from 13.91 to 17.33 HV. Principally, the In-containing solder alloys had higher UTS and hardness than the In-free solder alloy due to the strengthening effect of solid solution and secondary phase dispersion. The eutectic melting point decreased from 223.0°C for the SAC305 solder alloy to 219.5°C for the SAC305 alloy with 2.0 wt% In. The addition of In had little effect on the solidus temperatures. In contrast, the liquidus temperature decreased with increasing In content. The optimum concentration of 2.0 wt % In improved the microstructure, UTS, hardness, and eutectic temperature of the SAC305 solder alloys.