Civil Engineering

Permanent URI for this collectionhttps://hdl.handle.net/10679/312

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    Bio-derived rheology modifying agents for cement-based materials
    (Springer, 2020) Azima, M.; Bundur, Zeynep Başaran; Civil Engineering; BUNDUR, Zeynep Başaran
    In recent few years, significant development has been made in concrete technology to accommodate the requirements of high-performance concrete. Rheology Modifying Agents (RMAs) (such as superplasticizers) and Viscosity Modifying Agents (VMAs) have been developed as two alternative admixtures to obtain the required workability. However, these admixtures not only increased the environmental impacts of concrete production but also increased the unit cost of concrete. Following these concerns, several studies have been focusing on exploring more sustainable approaches in concrete production such as the use of bio-based admixtures in concrete production. Throughout the literature, bio-based polysaccharides (cellulose, chitosan, etc.) were found to be highly effective as VMAs. Long chain molecules of these polysaccharides stick to the water molecules, decrease their relative motion and forms a gel, so increase the yield stress and plastic viscosity. This behaviour reduces the bleeding and segregation, which results in robust highly workable concrete. The interest in this study was motivated by the vital demand to introduce a greener and more sustainable VMA to improve the rheological properties of cement paste. To this end, bacterial cells proposed as VMAs for cement-based materials. The bacterial cells were directly incorporated into the mix of water without any additional intervention. The rheological measurements were implemented to evaluate the influence of cells on apparent viscosity and yield strength. In addition, the use of superplasticizers and fly ash on the performance of biological VMA were also investigated. Our results showed that the apparent viscosity and yield stress of the cement-paste mix were increased with the addition of the microorganisms. Moreover, bacterial cells were found to be compatible with the use of both fly ash and superplasticizers.
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    Conference ObjectPublicationMetadata only
    A comparison study between 1D and 2D site response analyses based on observed earthquake acceleration records
    (Springer, 2023) Shamekhi, Shima; Ansal, Mustafa Atilla; Kurtuluş, Aslı; Civil Engineering; ANSAL, Mustafa Atilla; KURTULUŞ, Asli; Shamekhi, Shima
    The objective of the present work is to evaluate the necessity of 2D site response analysis based on the comparison among the peak ground and spectral accelerations recorded by Istanbul Rapid Response Network and Istanbul vertical array stations during the Mw = 6.5 24/5/2014 Gökçeada and Mw = 5.9 19/5/2011 Kütahya earthquakes with the calculated accelerations by 1D and 2D site response analyses. The shear wave velocity profiles determined based on in-situ geophysical and geotechnical measurements and laboratory tests within the Istanbul Microzonation Project are revaluated adopting a revision scheme to obtain the best fits between the recorded and calculated spectral accelerations by 1D site response analysis. These modified shear wave velocity profiles are later used for 1D and 2D site response analyses performed in North–South and East–West directions to model peak ground and spectral accelerations on the ground surface. Finally, by modelling different distances around boreholes the influence of variation of the soil profile in horizontal direction is investigated by 2D analyses.
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    Designing redundant cable-driven parallel robots for additive manufacturing using end-effector compliance index
    (IEEE, 2023) Kara, Burhan; Qureshi, Muhammad Sarmad; Bundur, Zeynep Başaran; Bebek, Özkan; Civil Engineering; Mechanical Engineering; BUNDUR, Zeynep Başaran; BEBEK, Özkan; Kara, Burhan; Qureshi, Muhammad Sarmad
    This paper presents a methodology for optimizing cable anchor points for cable-driven parallel robots (CDPRs) for specific additive manufacturing tasks. Much of a CDPR's workspace is generally not used for printing tasks. The unused workspace of the CDPR can be sacrificed to gain greater control to fulfill the printing task. In this paper, the CDPR is designed for a specific task to achieve the best printing results. To find the optimum robot size, the stiffness of the end-effector and mean cable tension are analyzed. The end-effector compliance index (ECI) is proposed to assess the stiffness of the end-effector within the workspace. The ECI uses cable directions to determine the compliance of a given robot pose. From simulation results, a relation to get optimum CDPR frame size is achieved for both suspended and constrained type CDPRs. The proposed method can be used to design low-cost cable-driven robots for additive manufacturing.
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    Conference ObjectPublicationOpen Access
    Site response from Istanbul vertical arrays and strong motion network
    (Earthquake Engineering Research Institute ( EERI ), 2014) Ansal, Mustafa Atilla; Kurtuluş, Aslı; Tonuk, G.; Civil Engineering; ANSAL, Mustafa Atilla; KURTULUŞ, Asli
    In the framework of Istanbul Microzonation Project for the European side, the investigated region was divided by a grid system of 250m×250m and site investigations were performed for each cell based on borings and in-situ seismic wave velocity measurements for defining representative soil profiles with shear wave velocity values extending down to the engineering bedrock. Geological and geotechnical laboratory and field testing data with measured seismicwave velocities enabled to determine the engineering properties of the soil and rock layers encountered in all the cells. There have been limited number of earthquakes within 100km range of Istanbul with local magnitude in the range of ML=4-5 and few more distant and more stronger earthquakes that were recorded by the existing three vertical arrays as well as by the Istanbul Rapid Response Network (IRRN) strong motion stations. Even though the maximum PGA were similar, the observed spectral response were different indicating the importance of the distance and source magnitude concerning the frequency content and predominant soil period ranges. Even though the level of ground shaking intensity is relatively low, efforts were made to evaluate the variation of the recorded accelerations with depth in vertical arrays located at Ataköy, Zeytinburnu and Fatih. Attempts were also made to model the recorded acceleration time histories at the triggered IRRN stations using the acceleration records obtained at the bedrock level from the vertical array stations in the case of the recent 19.5.2011 Mw=5.7 Kütahya earthquake that took place approximately 185km away.
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    Conference ObjectPublicationOpen Access
    Two-part bio-based self-healing repair agent for cement-based mortar
    (International Center for Numerical Methods in Engineering, 2020) Tezer, Mustafa Mert; Bundur, Zeynep Başaran; Civil Engineering; BUNDUR, Zeynep Başaran; Tezer, Mustafa Mert
    Factors affecting durability of concrete structures are generally associated with each other. Due to its brittle nature, concrete can crack under stress and these cracks are one of the main reasons for a decrease in service life in concrete structures. Therefore, it is crucial to detect and recover microcracks, then to repair them as they were developed to wider cracks. Recent research in the field of concrete materials suggested that it might be possible to develop a smart cement-based material that is capable of remediate cracks by triggering biogenic calcium carbonate (CaCO3) precipitaton. This paper summarizes a study undertaken to investigate the self-healing efficiency of Sporosarcina pasteurii (S. pasteurii) cells immobilized on both diatomaceous earth and pumice, to remediate flexural cracks on mortar in early ages (28 days after mixing). To obtain a two-phase bio additive, half of the minerals were saturated with a nutrient medium consisting of urea, corn-steep liqueur(CSL) and calcium acetate and the cells with immobilized to the other half without nutrients. Screening of the healing process was done with ultrasonic pulse velocity (UPV) testing and stereomicroscopy. With this approach, the cracks on mortar surface were sealed and the water absorption capacity of the so-called self-healed mortar decreased compared to its counterpart cracked mortar samples.