Research on Engineering Structures and Materials

331-346

Authors: Atike Ince Yardimci, Ahmet Sabri Ogutlu, Deniz Ogutlu

In this study, the influence of the oxidizers on the synthesis of carbon nanotubes by C2H4 decomposition over Fe catalyst has been investigated. CO2, O2, and H2O have been used as oxidizers, and to control catalyst particle formation and their sizes in the pretreatment stage. The same oxidizers have also been used in the growth stage to maintain the catalyst particle size, remove amorphous carbon formation to keep catalyst particle active. The results of scanning electron microscopy indicated that the average diameters of nanotubes decreased from 13.4±1.2 nm to 6.2±0.5 nm and extremely dense nanotubes were obtained when we added a small amount of CO2. Adding O2 extremely decreased the areal carbon nanotube density while widens the diameter distribution. H2O addition resulted in larger average diameters and made the growth strongly pretreatment dependent. Within the parameters tried for catalyst pretreatment and CNT growth processes, CO2 seemed the best choice for a weak oxidizing assistant. The strong dependency of the average diameter on pretreatment conditions indicated that pretreatment is a very important step in deciding the final diameters and their distribution.

361-373

Authors: Lütfiye Altay, Mehmet Sarikanat, Merve Sağlam, Tuğçe Uysalman, Yoldaş Seki

Polypropylene is one of the commodity thermoplastics that is widely used in many different applications such as automotive, building, electric-electronics, textile, and packaging industries due to its properties and favorable cost-benefit ratio. The incorporation of mineral fillers such as mica, talc, wollastonite, and calcium carbonate into thermoplastics is a common practice in the plastics industry in order to reduce the production costs of molded products and enhance processibility, mechanical, and thermal properties. Mineral filled polypropylene composites provides high mechanical stiffness, thermal stability, and good dimensional stability over a wide temperature range. The filler weight ratio, type, size, and dimension have significant effect on mechanical, thermal, physical, and rheological properties of composites. Four different mineral fillers (talc, mica, calcite, and feldspar) at weight fractions of 40% were compounded with polypropylene by using a twin-screw extruder. Test specimens were obtained by injection molding process. The effect of various filler types on rheological and mechanical properties of polypropylene was investigated in this study. It was found that talc and mica loadings at 40 wt. % into polypropylene increased the flexural strength of polypropylene. The rheological properties of samples were more affected by the talc than calcium carbonate.

393-411

Authors: Hikmat Daou, Wassim Raphael

Concrete is the most widely used material in the construction industry due to its strength, workability and durability. But under a sustained load, concrete is prone to creep causing excessive long-term deflection of structural members, cracks in tensile members, redistribution of stresses over time in composite structures, and loss of prestressing force in prestressed concrete elements. Therefore, structural engineers must accurately predict the concrete creep over the long-term. The concrete creep coefficient is an important entry in many calculations and analyses of reinforced concrete structures. Currently, many models such as the Eurocode 2 model have predicted the concrete creep coefficient. Based on a large database for creep tests, this study aims to improve the prediction of the Eurocode 2 creep coefficient model at long-term by implementing correction coefficients into the model. Since Bayesian-type inferences are suitable tools for revising and updating design codes, the correction coefficients are calculated based on Bayesian linear regression. Statistical indicators demonstrate the accuracy and effectiveness of the proposed improvement and modification.

431-444

Authors: Ali Bozer

Tuned Liquid Dampers (TLD) consist of a container that is generally partially filled with water. When the sloshing frequency of the water mass is tuned to the fundamental mode of the primary structure a significant amount of sloshing and wave breaking can be achieved which are the primary sources of energy dissipation. Although TLDs are easy to install, operate and maintain; it is generally challenging to model the nonlinear nature of sloshing water. Equivalent mechanical models provide a simplified solution in which sloshing liquid mass, liquid damping, and sloshing frequency are represented by an equivalent mass, damper, spring system. Equivalent mechanical model derivations are generally based on linear sloshing of water mass, which is possible when the water depth/tank length ratio is high and excitation amplitude is low. In this study, a well-known and widely accepted Housner equivalent mechanical model is used to model water sloshing. The water depth/tank length ratio is kept low to enhance the energy dissipation of TLD. The main objective of this study is to experimentally investigate the effectiveness of TLD and check the accuracy of Housner equivalent mechanical model under seismic excitations and low water depth/tank length ratio. Water depth is optimized by the Artificial Bee Colony algorithm which is a population-based optimization algorithm. Frequency sweep analysis and seismic excitations are employed to investigate TLD performance. It is shown that even TLD behavior is modeled by a simplified linear equivalent mechanical model, it is still effective in reducing structural response under large amplitude seismic excitations and low water level/tank length ratios. This is due to more energy dissipation with an increased amount of sloshing and wave breaking.

465-480

Authors: Cameron R. Rusnak, Craig C. Menzemer

Hand-holes are used in welded aluminum light poles which provide access to electrical wiring for both maintenance and installation. Light poles are usually slender and subjected to cyclic loading due to the response from wind. In the field, localized fatigue cracking around hand-holes has been observed but few studies have focused on the resistance of welded aluminum hand-holes. In this study, three-point bending fatigue tests were conducted on full-scale light poles samples. Specimens were constructed with a “flush” hand-hole utilizing reinforcement placed on the inside of the tube, with the handhole located 18 in from the base. Five of these poles, each containing two separate details were tested. Among the ten details that were tested, eight failed as a result of fatigue cracking and the resulting data is compared to current design S-N curves of the Aluminum Design Manual (ADM). A finite element model was created to help understand the local stresses around the hand-hole. this study, the estimation of shear force for blind shear ram type blowout preventer was investigated by using Finite Element Method (FEM). So, the effect of the blowout preventer working condition on shear force requirement for shear operation could be accurately approximated by simulating the entire process, and ram geometry could be optimized to reduce force and energy used to shear the tube by plastic deformation.