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.

173-182

Authors: Seda Yeşilmen

Engineered Cementitious composites (ECC) became widely popular in the last decade due to their superior mechanical and durability properties. Strength prediction of ECC remains an important subject since the variation of strength with age is more emphasized in these composites. In this study, mix design components and corresponding strengths of various ECC designs are obtained from the literature and ANN models were developed to predict compressive and flexural strength of ECCs. Error margins of both models were on the lower side of the reported error values in the available literature while using data with the highest variability and noise. As a result, both models claim considerable applicability in all ECC mixture types.

199-209

Authors: Rasheed Abdulwahab, Samson Olalekan Odeyemi, Habeeb Temitope Alao, Toyyib Adeyinka Salaudeen

Cement industry being source of emission of carbon dioxide (CO2) causing global warming; it is necessary to source for alternative binder in concrete. The problem of longer age strength attainment by pozzolanic blended concrete calls for introduction of treated pozzolans. This paper investigates the influence of co-addition Metakaolin (MK) and Treated Rice Husk Ash (TRHA) in the production of concrete. The kaolin was calcined at a temperature of 650C for 2 hours and thereafter, characterized. Furthermore, the rice husk (RH) was roasted to temperature of 700C and thereafter, treated with H2SO4. MK was replaced in varying percentages of 0%, 5%, and 10%. Thereafter, TRHA was added by weight of the cement in varying percentages of 1%, 2%, and 3% to the optimum MK replacement (5%). From the results, it was found that concrete with 5% MK and 2% TRHA had enhanced compressive strength as against the control. Hence, it can be inferred that 5% MK and 2% TRHA concrete could be used in the construction industry. The increase in the strength properties of the concrete could be as a result of additional binding tendency exhibited by MK and TRHA.

225-244

Authors: P N Ojha, Abhishek Singh, Brijesh Singh, Vikas Patel

In view of reducing the cost of concrete and to meet the demand of conventional raw materials used in concrete, various industrial and solid wastes are being studied for their utilization in concrete without affecting its fresh, hardened and durability properties. Ferrochrome slag is waste material obtained from manufacturing of high carbon ferrochromium alloy. Depending upon cooling process, two types of ferrochrome slag are produced i.e. air cooled by letting molten slag cooled down under normal temperature and water cooled ferrochrome slag by quenching molten slag. Presence of chromium in Cr+3 and Cr+6 state in ferrochrome slag is an area of concern towards its feasibility to be used as a constituent material in concrete. In this study, physical and chemical properties of both types of slags were evaluated to check the feasibility of replacing natural fine aggregates with water cooled ferrochrome slag and natural coarse aggregates with air cooled ferrochrome slag. In concrete mix designs, natural aggregates were replaced with ferrochrome slag at replacement levels of 30%, 60% and 100%. Mixes were prepared at two w/c ratios and were evaluated for different fresh, hardened and durability properties of concrete. It was concluded that 60% replacement of natural coarse aggregate with air cooled ferrochrome slag and 60% replacement of natural fine aggregate with water cooled ferrochrome slag in concrete is feasible.

259-272

Authors: Irmak Karaduman Er

In this work, the effects of Cd doping on the gas sensing properties of ZnO thin films were synthesized by SILAR method and studied gas sensing characteristics against NO, CO, ammonia, methanol and acetone, systematically. Whereas the operating temperature of NO gas was found 90 C, CO and acetone were 150 C and 170 C. The response was not observed in methanol and ammonia gases. Especially, it was observed that the response continued to increase as the temperature increased for methanol gas. In addition, the 5% Cd doped ZnO sensor exhibits the excellent selectivity for NO compared to other test gases as ∼12% at 0.01 ppm. NO gas sensing reactions are accelerated with Cd doping because Cd doping was created increasing oxygen vacancies surface chemisorbed oxygen species, and defects in the lattice.

281-295

Authors: Kadir Akcan, Eren Billur, H. İbrahim Saraç

As advanced high strength steels (AHSS) find more use in automotive industry to meet crashworthiness and light weighting targets, concurrently. AHSS typically have higher strength, but lower formability; often limiting a part’s dimensions and geometric complexity. Several studies have clearly shown that, in sheet metal forming, significant portion of the work done to overcome friction and to plastically deform a sheet is converted into heat. In this study, a thermomechanical finite element model has been developed to calculate the temperature rise in forming DP800 (AHSS). The model was validated with experiments from literature. A multi-cycle model is developed to find out possible problems due to tool heating. The process and material are selected to speed up the heating. Under different realistic press conditions, failures are observed after 20 to 80 hits.

315-330

Authors: Neritan Shkodrani, Huseyin Bilgin, Marjo Hysenlliu

On November 26,2019, an earthquake of magnitude 6.4 hit Durres city, Albania. After the earthquake, the inspection carried out by the authors in the region has provided relevant findings regarding the methods of construction, quality of the materials and the performance of structures. The dominant building types in the Albanian building stock comprise unreinforced masonry (URM) structures with load-bearing masonry walls. These units suffered the worst damage. Dynamic response of masonry is highly nonlinear, and generally shows high vulnerability to seismic loading. Moreover, many buildings of these type have undergone structural interventions like adding floors, or wall openings, especially in the first floors of the buildings, which are parallel to the main roads, because of great demand for shops and stores. This paper aims at making seismic performance assessment of the intervened buildings based on macro-element modeling approach. Due to its efficiency, this approach is becoming popular among the practitioners and field experts in this area and allows simulating the non-linear behavior of masonry buildings. This method is applied to two old masonry buildings from the Albanian construction practice that are representatives of mid-size residential buildings with and without interventions. It must be said that in Albania, masonry buildings have been built using templates all over the country, so both models with and without intervention are common. Capacity curves of the investigated buildings are derived to assess the most probable seismic response of the investigated housing construction in the region as well as to evaluate the seismic performance of the tested structures.

1-11

Authors: Hayri Baytan Ozmen

Earthquakes are natural events that turns into disasters in our country due to faults made in construction of structures. In order to prevent this, we need to determine solutions and act accordingly. The author wrote this paper to humbly share his knowledge and ideas on the subject with the public and his colleagues and encourage more discussions on the subjects. The mentioned points include views on the common public earthquake debates, main reason of damages being inadequacies in having healthy civil engineering services, the importance of informing and taking into consideration of the feelings of the suffered people, shortages of official damage assessment procedures, the necessity for unique building identifier and a fixed financial aid policy, suggestions on the civil engineering education, and how essential the proficient engineering concept is for robust construction of the structures.

35-49

Authors: Samson Olalekan Odeyemi, Omolola Titilayo Odeyemi, Adewale George Adeniyi, Zainab Tolu Giwa, Ademola Kamorudeen Salami, Adeyemi Adesina

Steel reinforcement corrosion emanating from ingress of chloride into concrete is the key reason for weakening of concrete structures globally. Infiltration of chloride into concrete happens by absorption and diffusion. On the other hand, reinforced concrete containing supplementary materials is more susceptible to corrosion exposure due to its high permeability. In this paper, two concentrations of sodium chloride (NaCl) were applied on concrete containing palm kernel shell as full replacement to granite. Concrete cube specimens of Grade 20 were cast into 150 mm by 150 mm by 150 mm moulds, and their workability were determined by compacting factor and slump tests. The hardened specimens were soaked in sodium chloride (NaCl) solution of 3% and 6% concentration. Spray, Absorption and Compressive strength tests were conducted at 7, 14, 21 and 28 days. Equations were generated by means of the data gotten from the laboratory tests to forecast the chloride penetration depth into the palm kernel shell concrete under the conditions considered in this work. The models generated revealed that absorption affected chloride ingress into the concrete significantly at 6% NaCl concentration. The models also reveal that the cover to reinforcements in Palm Kernel Shell Concrete subjected to chloride attack should be more than what is presently endorsed for reinforced concrete structures.

65-86

Authors: Ercan Işık, İbrahim Baran Karaşin

Structural dimensions and number of floors are some of the factors affecting the building behaviour under the earthquake effects. In this study, the structural footprint and the number of floors were selected as a variable. For this purpose, a steel structure model with fixed dimensions and properties of load-bearing system elements was selected. The structural footprint was selected as the first variable and then five different structure models were created. The structural footprint was changed by setting each axial clearance in both directions. Each axial clearance was increased by 0.5m in each structure model. Three different number of floors as to be 5, 6 and 7 floors were selected as the second variable. Eigenvalue and pushover analyses were performed for each model and each number of floors. As a result of the analyses, the target displacement values for period, frequency, cumulative participation mass ratio, base shear force, settlement, stiffness and degree of damage were acquired separately. As the structural footprint and number of the floors increase, while the period, settlement and the target displacement values increased, on the contrary, there was a decrease in participation mass ratio, base shear forces and stiffness values. In the study, cost comparisons of building construction were also made considering the change in the total structural area and the number of floors. The criterion of safety and economy was ignored due to increase both in the number of floors and the footprint. This study emphasizes the importance of avoiding the unnecessary structural dimensions via optimum design principles. As structural footprint area and number of floors increase, period values increase, stiffness and seismic capacity values decrease. As the number of floors and footprint area increases, the total building area increases, so the approximate building cost has also increased.

97-120

Authors: Tanay Karademir

One of the most important properties of a fabric (geotextile) and also one of the focus areas of the current research study is its tensile strength, and thus, mechanical properties (modulus, resilience, strength, toughness). To this end, the mechanical properties of the geotextiles must properly be evaluated at the “macro-scale” as well as at the “micro-scale” as they are fibrous synthetic materials including polymeric fibers as well as significant volume of void space. As being a polymer, the mechanical behavior of the geotextile micro-fibers is highly dependent on the ambient conditions including particularly the temperature. In light of this, the tensile behavior of geotextile single micro-fibers was characterized by performing micro-mechanical tensile tests at “micro-scale” level at different cold temperature conditions using Dynamic Thermo-Mechanical Analyzer (DMA) to measure the developed “micro-scale” tensile stress – strain behavior of geotextile micro-fibers. The results examined from the influence of micro-mechanical properties of polymeric fibers on the observed temperature dependent stress-strain curve were used to determine the modulus of elasticity (E), modulus of resilience (UR), ultimate tensile strength (τmax), amount of plastic strain (εp), toughness (UT), rupture strength (τR) for the polypropylene (PP) micro-fiber of needle-punched nonwoven (NPNW) geotextile and the variation in those important mechanical properties with a change in ambient temperature conditions. The experimental results show that the mechanical properties of the PP fibers do not remain constant within the common range of cold temperatures (-10 °C – 21 °C) found in typical civil engineering applications such that the temperature change was found to be an important factor affecting the PP fiber micro-mechanical properties such as modulus, strength, toughness and plastic elongation. Therefore, the test results provide an index of behavior at “micro-scale” level for the polymeric geotextile single fibers at cold temperature conditions.

135-156

Authors: Güliz Akyüz, Aykut Elmas, Müberra Andaç, Ömer Andaç

Metal Organic Frameworks (MOFs) have found wide applications as a drug carrier in nanotherapeutics because of adjustable pore-sizes, controllable structural properties, large surface area and high pore volume. In this work, nanosized Mg@BTC is synthesized by electrochemical method and used as a new drug carrier for ibuprofen. The ibuprofen (IB) is loaded to the Mg@BTC 1:1 ratio with the amount of %99.8. The release of ibuprofen from nanocarrier has been observed experimentally for long term. After 100.5 hours, the release ratio yields 36 %. The ibuprofen has been tested at 40 ± 0.5 °C. System showed a rapid release after 100 hours, the release ratio yields 72.29 %. The release profile of IB loaded Mg@BTC is tested by using model depended mathematical models to get observation and prediction of the release. Zero Order Model, First Order Model, Higuchi Model, Peppas Model and Hixon Model functions are fitted to the release profiles. Watson’s U Squared Method is used to test the fit strength of the models. Observation from the release profiles, it is seemed Peppas Model yields the best results. Also, thermodynamic analysis has been studied.

293-313

Authors: Ahmet Meram, Betül Sözen

This paper investigates the manufacturing variants influential on the strength of 3D printed products. In contrast to the traditional manufacturing methods which produce the final product via removing materials from parts, in 3D printing technology the products are provided with adding layer by layer directly from a digital file. 3D printing technology due to overcoming the many difficulties and limitations of conventional fabrication approaches is a rapidly progressing technology which takes attention in many industries such as aerospace, automotive, medical and building industries. This paper aims to research the variants affecting the mechanical properties of components produced by 3D printing technologies. To reach this aim a comprehensive review was conducted to determine the various process and geometric parameters in 3D printing technologies. The conducted literature survey results indicate that besides the filament material, the nozzle speed and diameter, layer thickness, filament diameter, printing raster angle, printing pattern, temperature and infill density are parameters which influence the final product quality and mechanical properties in term of ultimate tensile strength, yield stress and elasticity modulus. It is concluded that 3D printing filament materials strength has direct affect on the strength of final product. By providing the adequate thermal behavior of the system, the cohesion between layers can be improved. Extrusion speed affects surface roughness and quality of the produced components. Nozzle diameter has a significant influence on interlayer cohesion. The honeycomb pattern due to facilitating the load transfer between layers provides higher mechanical strength. Findings of this study will guide the researchers and manufacturers to select appropriate printing parameters to produce component with optimum mechanical properties.

327-350

Authors: Aykut Elmas, Güliz Akyüz, Ayhan Bergal, Müberra Andaç, Ömer Andaç

Mathematical models of the drug release have been used in the drug delivery (DD) field for more than 50 years by the scientists in the drug development process. These models not only help scientists to learn the dynamics of the drugs release, but also help them to save money and time by helping to design more effective experiments. There is no model in the literature that covers all drug release scenarios. Also, some system-specific models have complex mathematical equations and these models are not suitable for general use. Zero Order Model, First Order Model, Higuchi Model, Peppas Model and Hixon Crowell Model are used in 85% of drug release studies in total. The popularity of these models comes from their simplicity, easy mathematical expressions and implementation. In this review, mathematical derivations of these five models are shown in detail. The points to be considered during the derivation and the problems that may be encountered are carefully explained along with their solutions. In addition, the application of the models to drug release data and the points to be considered were obtained by writing from the scratch without using any ready software while obtaining the fit function. In this way, many problems are better understood, and their solutions are explained. Finally, the obtained fit functions are interpreted.

363-374

Authors: Canan Kandilli, Mert Uzel

Photovoltaic thermal systems (PVT) produces both electricity and thermal energy by the same module. However, solar energy exhibits non-continuous character, and causes some problems for obtaining stabile energy due to its unsteady regime. Thermal energy storage systems could be employed as a solution the mentioned problems. There are no studies in the literature regarding evaluation of the annual performance of PVT systems integrated with natural zeolites. It is the motivation behind of the present study. Natural zeolites could be utilized for thermal storage and management with PVT systems. In this study, it is aimed to performed annual performance of the PVT system integrated with natural zeolite as a thermal storage material to manage the excessive heat on PV. Average overall energy efficiency values were found as 0.56; 0.54; 0.49; 0.49; 0.48; 0.46; 0.45; 0.46; 0.50; 0.53; 0.54 and 0.56 from January to December, respectively. Annual total overall energy produced by the PVT system integrated with natural zeolite was found as 1294.88 kWh/year per module. Annual saving per module is reached as 117.83 € per module. With the acceptance of the system cost of 942.8 €, simple payback period is approximately 8 years. This payback time, which is found on a single module, will surely decrease at higher installed powers.

385-409

Authors: Abdullah Fettahoglu, Mehmet Cemal Genes

Deformation of most pavements is practically inelastic. Thus, the exact calculation of pavement deformation often requires use of a damage evaluation law to characterize the stress-strain relationship mathematically. Asphalt, polymer, and reinforced concrete are all examples of such pavements. However, concrete pavements without reinforcement are generally assumed to behave linear elastic. Concrete pavements without reinforcement are used sometimes as permanent pavements with dowels such as airport apron pavement, but sometimes they are used as temporary pavements during the mobilization or initial phases of new construction projects as well. When used as permanent pavements, their design is performed similar to rigid pavements, which has international acceptance by highway engineers, or by finite element analysis. When used as temporary works during the mobilization phase, or when a road is urgently required on a construction site, their design is often problematic, because advanced highway design or finite element analysis might be momently unavailable. A rapid, conservative, and reliable hand calculation method for temporary concrete pavements without reinforcement is therefore required. In this study, design charts are provided to allow hand calculations of temporary concrete pavements. In addition, a numerical example is solved to illustrate the use of derived charts. The effects of certain parameters on the stress behavior of concrete pavements are also investigated.

425-437

Authors: Marjo Hysenlliu, Altin Bidaj, Huseyin Bilgin

Recent earthquakes occurred in many parts of the world have shown that unreinforced masonry [URM] buildings constructed according to older codes may constitute an important source of risk. It is known that the mechanical response of the masonry structures depends on several factors including the compressive and shear strength of its constituents, bricks shape as well as the volumetric ratio between the wall texture and components. In this study, the effects of the material choices of a particular type of masonry buildings were studied. The typology chosen in this study represents a typified masonry building of the current Albanian building stock; these buildings were mostly built between 1977-78 and thus were designed without considering the seismic requirements proposed in today’s modern codes. This template building has been constructed in different regions of the country with the same architectural and structural configuration in two versions; red clay bricks and silicate bricks. The aim of this study is to investigate the influence of these two different materials on the seismic response of the selected masonry building. The evaluation is based on the use of nonlinear static analyses, performed by using TREMURI software. In order to estimate the reliable seismic response for this typology, extensive research in terms of historical information, structural characterization and the definition of the inherent material parameters has been executed. Upon the evaluation of the obtained results, in contrast to the type of buildings constructed by clay masonry, calcium silicate one showed a stiffer and slightly stronger response. However, at similar values of in-plane, lateral drift they exhibited more brittle response yielding unforeseen damage during seismic excitations.

197-206

Authors: Melik Ziya Yakut, Sinem Esen

In this study; based on energy-efficient design parameters, the effects of building design parameters on the energy consumption of the building were examined. Accordingly, a reference building has been created as an example of application in the hot-humid climate zone. In the process of modelling the building, BIM (Building Information Modelling) software Autodesk Revit was used. The model has been transferred to Green Building Studio (GBS) for energy performance analysis and evaluation of design alternatives. The parameters evaluated in terms of energy consumption of the building were selected from among the design alternatives produced by GBS, based on energy-efficient design parameters. As a result of the energy performance analysis of the reference building via GBS, the building's annual electricity consumption is 35,137 kWh and the annual fuel consumption is 93,729 MJ. Based on the evaluation of selected design parameters as a result of reference building energy performance analysis; HVAC systems have been found to have the most impact on energy consumption (rates of changes; 36.83% in annual electricity consumption, 90.27% in annual fuel consumption). HVAC systems, selected to be highly efficient and suitable for climate type, have the potential to save significant energy in the amount of energy consumption throughout the life cycle. In addition to this, as of the early design phase, the energy efficient design of the building is of great importance in terms of a holistic evaluation and maximum energy efficiency.

229-240

Authors: Hayri Baytan Ozmen, Mehmet Inel, Yunus Demirtas

Soft story irregularity is one of the main reasons of the building damage during past earthquakes and has been mentioned in almost all reconnaissance reports. Soft story due to increased story height is a recognized subject but soft story may also arise due to abrupt changes in amount of infill walls between stories, which are usually not considered as a part of load bearing system. This study investigates soft story behavior due to increased story height, lack of load bearing infill walls at ground story and existence of both cases using nonlinear static and dynamic response history analyses. Mid-rise reinforced concrete buildings are considered due to their high portion in existing building stock. Displacement capacities at Immediate Occupancy, Life Safety and Collapse Prevention performance levels and story drift demands of the regular and soft story models are determined. Soft story behavior due to change in story height and/or infill amount is evaluated in view of displacement capacities, drift demands and structural behavior. It is observed that, soft story due to infill walls may be as damaging as soft story due to increased story height.

257-269

Authors: Fatoş Koç, Selay Sert Çok, Nilay Gizli

In this study, silica aerogels were produced by two-step sol-gel method to investigate the effect of pH on the physical, chemical and textural structure of aerogels. Tetraethyl orthosilicate (TEOS) used as a silica source. (3-aminopropyl) triethoxysilane (APTES) acted as a silica co-precursor. The quantity of sol precursors kept constant through the experiments and the pH of hydrolysis and condensation reactions were varied. As a result of the experimental studies, the optimum pH values to achieve monolithic aerogel were obtained when the pH of hydrolysis is 3 and the pH of condensation is 10. Physical, chemical and morphological characteristics of the samples were examined by performing FTIR and SEM and density analyses. Results showed that the sample SG-pH3/7 had also well-defined porous structure with homogenous pore distribution, a stable lightweight and monolithic form.

283-292

Authors: Ekrem Altuncu, Recep Akyüz

Automobile brake disc are subjected to cyclic thermal, mechanical and corrosive effects. In general, gray cast iron grades are preferred as disc brake materials. Lamellar cast iron disc brakes have a limited lifetime and are replaced periodically during the maintenance-service process. With the growing interest in the number of Battery Electric Vehicles (BEV), there is a need for disc brake with longer service life on discs. Therefore, in the automotive sector, in line with increasing competition and user demands, there is an interest in new coating types and materials with corrosion free properties, a longer service life and high brake performance. Wear and corrosion resistant plasma spray coatings are the key to increasing the service life and braking performance of cast iron discs. In this study, the discs (GG20) are coated with Alumina- Titania based ceramic material by atmospheric plasma spray method. The ceramic coated disc brakes were installed on the road driving test vehicle and disc brake thickness reduction were measured periodically according to wear test plan throughout 20.000 km. The test results show that the ceramic coating provides 18 times more wear resistance compared to uncoated disc brake. In addition, coated disc brakes exhibited superior performance in corrosion tests. As a result of the investigations carried out on disc brakes, it is understood that plasma spray ceramic coatings can be used alternatively in brake disc systems.