Browsing by Author "Guler, Soner"

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Axial Behavior of Frp-Wrapped Circular Ultra-High Performance Concrete Specimens
(Techno-press, 2014) Guler, Soner
Ultra-High Performance Concrete (UHPC) is an innovative new material that, in comparison to conventional concretes, has high compressive strength and excellent ductility properties achieved through the addition of randomly dispersed short fibers to the concrete mix. This study presents the results of an experimental investigation on the behavior of axially loaded UHPC short circular columns wrapped with Carbon-FRP (CFRP), Glass-FRP (GFRP), and Aramid-FRP (AFRP) sheets. Six plain and 36 different types of FRP-wrapped UHPC columns with a diameter of 100 mm and a length of 200 mm were tested under monotonic axial compression. To predict the ultimate strength of the FRP-wrapped UHPC columns, a simple confinement model is presented and compared with four selected confinement models from the literature that have been developed for low and normal strength concrete columns The results show that the FRP sheets can significantly enhance the ultimate strength and strain capacity of the UHPC columns. The average greatest increase in the ultimate strength and strain for the CFRP- and GFRP-wrapped UHPC columns was 48% and 128%, respectively, compared to that of their unconfined counterparts. All the selected confinement models overestimated the ultimate strength of the FRP-wrapped UHPC columns.
Evaluating Sustainable Colored Mortars Reinforced With Fly Ash: a Comprehensive Study on Physical and Mechanical Properties Under High-Temperature Exposure
(Mdpi, 2024) Akbulut, Zehra Funda; Guler, Soner; Osmanoglu, Faruk; Kivanc, Mehmet Riza; Khan, Mehran
This research primarily delves into a comprehensive investigation concerning the synergistic effects of fly ash (FA) with yellow pigment (YP) and red pigment (RP) in the workability, physical characteristics, and mechanical properties of colored mortars, both pre-and post-exposure to high temperatures. Within the experimental design, FA was employed as a 20% substitute for cement, while YP and RP were systematically incorporated into the cement mixtures at varying concentrations (1%, 3%, and 5% by weight). The specimens underwent controlled exposure to high temperatures, ranging from 300 degrees C to 800 degrees C. This study's outcomes unveiled that while the introduction of FA positively influenced mortar workability, including YP and RP adversely impacted spreading diameters (SD), resulting in a discernible reduction in overall workability. Despite these effects, FA emerged as a pivotal factor to enhancing the residual compressive strength (RCS) and residual flexural strength (RFS) of the colored mortars. For instance, after 90 days at 800 degrees C, the control concrete (R0) exhibited a notable 66.13% decrease in RCS, and the sample solely incorporating FA (R1) demonstrated a reduced reduction of 55.39%. Similarly, mortars with YP additives (R2-R4) and RP additives (R5-R7) showcased RCS reductions within the range of 53.32% to 55.12% and 54.51% to 56.04%, respectively.
Exploring the Flowability, Physical, and Mechanical Properties of Eco-Friendly Colored Cement Mortars With Metakaolin Under Sulfuric (H 2 So 4 ) and Nitric Acid (Hno 3 ) Attacks
(Elsevier, 2024) Akbulut, Zehra Funda; Guler, Soner; Osmanoglu, Faruk; Kivanc, Mehmet Riza; Ashour, Ashraf
This article aims to investigate the flowability, physical, mechanical, and durability properties of metakaolin (MK) -added colored cement mortars exposed to the effects of H 2 SO 4 sulfuric acid (SA) and HNO 3 nitric acid (NA). MK was used in 20 % replacement with cement, and yellow (YP) and red pigments (RP) were added to the mixtures at 1 % and 3 % of the cement by weight. According to the results, although MK reduced the workability and, therefore, the flow diameter (FD) of mortars, thanks to the void -filling feature of MK, filling the voids in the microstructure caused the samples ' apparent porosity (AP) and relative dynamic modulus of elasticity (RDME) to decrease. Additionally, MK significantly improved the residual compressive (RCS) and residual flexural strengths (RFS) of the samples thanks to the calcium -silicate -hydrate ( C - S - H) bonds it formed in the interior structure, owing to its high pozzolanic efficiency. Moreover, this improvement of MK is more remarkable in samples that remain subject to SA and NA attacks for more time. Furthermore, while YP reduces the workability of mortars and, therefore, the FD value due to its needle -tipped grain structure, RP increases the FD value of the mortars with its spherical grain structure. However, YP and RP contributed to reducing the AP of the samples and increasing RCS and RFS capacities at a meager rate by showing a micro -filling effect. In addition, there were significant increases in the total color changes ( Delta E) of YP and RP -added colored mortar samples, especially after longer SA and NA attacks.
Hybrid Fiber Reinforced Concrete-Filled Square Stub Columns Under Axial Compression
(Elsevier Sci Ltd, 2019) Guler, Soner; Yavuz, Demet; Aydin, Muhammet
The main aim of this study is to compare the axial load, ductility, and toughness capacities of square concrete-filled carbon steel (CFCST), stainless steel (CFSST) and aluminum tube (CFAT) columns filled with plain concrete, single (steel) and hybrid (steel + synthetic) fiber-reinforced concrete under axial compression. To this end, the enhancement in axial load, ductility and toughness capacities of steel and hybrid fiber-reinforced CFCST, CFSST, and CFAT columns were obtained with regard to fiber volume ratio (0.5 and 1.5%), compressive strength of concrete (30 and 70 MPa) and the steel tube thickness (2, 3 and 4 mm). A total of 99 hollow, steel and hybrid fiber-reinforced CFCST, CFSST, and CFAT columns were tested under axial compression. The results showed that although the use of steel and synthetic fibers in single and hybrid form is very limited for enhancement of the axial load capacities of CFAT, CFCST and CFSST columns, the enhancement in ductility and post-peak toughness capacities are notable especially for CFCST and CFSST columns. However, the effects of steel and synthetic fibers on post-cracking behavior of the CFAT columns are not significant due to early rupture of AL tubes that cause highly brittle behavior after first peak load. In addition to this, the use of steel and synthetic fibers in hybrid form is slightly better at improving the ductility and toughness capacities of most of the CFAT, CFCST and CFSST columns than the use of steel fibers in single form.
Review of Current Design Guidelines for Circular Frp-Wrapped Plain Concrete Cylinders
(Asce-amer Soc Civil Engineers, 2016) Guler, Soner; Ashour, Ashraf
With the widespread use of fiber-reinforced polymer (FRP) composites in the construction sector as a strengthening technique, the development of design guidelines for the field application of externally bonded FRP systems is ongoing in Europe, Japan, Canada, and the United States. The main goal of this study is to evaluate the current seven international design guidelines and four other design models for the prediction of confined concrete compressive strength of FRP-wrapped plain concrete cylinders against the experimental results of a large database of 812 specimens reported in the literature. The results clearly show that the reliability of predictions of confined concrete compressive strength of FRP-wrapped plain concrete cylinders by the design guidelines significantly varies for different ranges of unconfined concrete compressive strength. For example, the gain in confined concrete compressive strength of FRP-wrapped low- and medium-strength concrete cylinders is larger than that of high- and ultrahigh-strength concrete cylinders. Furthermore, a simplified model for the prediction of design/characteristic-confined concrete compressive strength is developed based on the design-assisted-by-testing approach. The developed simplified model accounts for the variation in confinement effectiveness for different ranges of unconfined concrete strengths.
Strength Prediction Models for Steel, Synthetic, and Hybrid Fiber Reinforced Concretes
(Ernst & Sohn, 2019) Guler, Soner; Yavuz, Demet; Korkut, Fuat; Ashour, Ashraf
This paper proposes new strength models to predict compressive, splitting tensile and flexural strengths of steel, synthetic and hybrid fiber reinforced concretes. The strength models depending on fiber reinforcing index, concrete compressive strength, and fiber volume fraction have been developed by multiple regression analyses of the experimental results obtained from a comprehensive experimental program. Twenty-five concrete batches, one control and 24 fiber reinforced concrete with target compressive strength of 40MPa were produced. Steel and synthetic fibers, namely hooked-end steel (HF) and polyamide (PA) synthetic fibers of total volume of 0.25, 0.5, and 0.75% were added in single and hybrid forms to concrete mixes. Moreover, the predictions of the proposed strength models have been compared with the existing strength models in the literature. The test results clearly showed that the predictions of the proposed strength models are more accurate than the existing strength models for compressive, splitting tensile and flexural strengths of all the fiber types. Although the existing strength models may be applicable to the prediction of compressive strength of steel, synthetic, hybrid fiber reinforced concrete (FRC), they may not be safely used for splitting tensile and flexural strength of steel, synthetic and hybrid FRC.