Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection

Permanent URI for this collectionhttps://hdl.handle.net/11147/7148

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Author: search.filters.author.Demir, UgurSubject: search.filters.subject.Concrete

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  • Article
    Repair and Strengthening of Fire Damaged Concrete Cylinders Using FRP Confinement: Tests and Analytical Modelling
    (Elsevier Science inc, 2025) Demir, Ugur; Ilki, Alper
    This study examines the effects of fiber-reinforced polymer (FRP) repair and strengthening on the axial stress-strain behavior of concrete columns after exposure to realistic fires. A total of 30 plain concrete cylinders, each measuring 150 x 300 mm, were cast for this investigation. Of these, three specimens were kept as reference at ambient temperature, while the remaining were exposed to ISO-834 standard fire for durations of 30, 60 or 90 min, with nine specimens in each duration group. After natural cooling, the heated specimens were categorized into three groups: i) three were left unconfined, ii) three were repaired and strengthened using two layers of carbon FRP sheets, and iii) three were repaired and strengthened with four layers of carbon FRP sheets. This study employs realistic ISO 834 fire scenarios and investigates CFRP confinement with up to four layers, addressing high confinement demands beyond current literature. The results showed that transverse confinement provided by carbon FRP sheets significantly improved axial strength and deformability for all specimens, while it did not fully restore the axial stiffness achieved before fire exposure. The effectiveness of FRP confinement increased with longer fire exposure durations. Additionally, two analytical models proposed previously for predicting the axial strength and ultimate strain of FRP confined fire-damaged concrete were evaluated in terms of their accuracy. The accuracy of the predictions was reduced with an increase in exposure temperatures for both models. Therefore, a new model is proposed within the scope of study, which shows good agreement with the novel test results.
  • Article
    A Comprehensive Database and a New Model for the Axial Response of Heat-Damaged Concrete Before and After FRP Confinement
    (Springer, 2025) Akdag, Nefise; Demir, Ugur
    In this study, a total of 330 concrete specimens, compiled from existing experimental data, are systematically reviewed to assess their post-fire axial stress-strain behavior before and after circumferential confinement with fiber-reinforced polymers (FRPs). The selection criteria for the database are as follows: (i) studies had to be published in English, (ii) both lateral and axial ultimate strains must have been measured, (iii) the use of additional strengthening materials in combination with FRPs was excluded, (iv) only plain concrete specimens were considered, and (v) specimen dimensions and instrumentation details had to be explicitly reported. The dataset is structured to include heating/cooling and curing conditions, specimen properties, and FRP characteristics. Subsequently, the predictive accuracy of available models for post-fire axial strength and ultimate strain of concrete members, both before and after FRP confinement, is evaluated. The results based on the reviewed comprehensive database indicate that these models are inadequate in capturing the observed behavior in the experiments. As such, a new analytical model is developed based on the compiled dataset. The proposed model demonstrated reliable predictive performance in terms of post-fire axial response of concrete before and after FRP confinement while remaining user-friendly for practical engineering applications. This is done such that universal design guidelines on the behavior of heat-damaged concrete strengthened by FRP composites can be reliably formulated.