An experimental study was herein presented focusing the effect of different type, shape and volume fraction of fibers on the hardened properties of concrete including compressive, splitting tensile and flexural strengths at 7 and 28 curing days. A control concrete mixture with no fiber was prepared and six fiber reinforced concrete mixtures were designed by using two different types of fibers which were steel fibers with different shapes (short straight and hooked end) and polypropylene fiber with the volume fraction of 0.4% and 0.8%. The load-deflection curves and toughness of the specimens were analyzed based on ASTM C1609. The results showed that the utilization of short straight steel fibers with 0.8% volume fraction was most efficient at improving the compressive strength while the use of 0.8% long hooked end steel fibers provided better splitting tensile and flexural strengths. Besides, the long hooked end steel fibers with the volume fraction of 0.8% contributed to an excellent deflection hardening behavior resulting in higher load deflection capacity and toughness at peak load, L/600 and L/150. On the other hand, with incorporation of polypropylene fiber, all strength values were decreased regardless of the volume fraction and curing days.

This study proposes a field-calibrated, NDT-integrated BIM modeling framework to improve the reliability of post-earthquake assessment for reinforced concrete (RC) buildings. The approach combines destructive and nondestructive testing (NDT) data—including core drilling, Schmidt hammer, ultrasonic pulse velocity (UPV), and Windsor probe—through a site-specific WinSonReb regression model. The calibrated material properties (average compressive strength ≈ 18.6 MPa, CoV > 20%) were embedded into a Building Information Modeling (BIM) environment, producing an as-is, NDT-calibrated BIM model representing a Level-2 static digital twin of the structure. Nonlinear static pushover analyses performed in accordance with TBDY-2018 and ASCE 41-17 showed that the calibrated model exhibits a fundamental period of 0.85 s—approximately 18% longer than the uncalibrated BIM model. This elongation increased displacement demand and caused a shift in performance classification: while the uncalibrated model indicated Life Safety (LS), the calibrated model predicted behavior approaching Collapse Prevention (CP) in the Y direction. Furthermore, calibration reversed the predicted damage hierarchy, from ductile beam hinging to brittle column- and wall-controlled failure near elevator openings, consistent with post-event observations from the 2023 Kahramanmaraş earthquakes. These results demonstrate that integrating field-calibrated NDT data into BIM-based seismic models fundamentally alters both strength estimation and failure-mechanism prediction, reducing epistemic uncertainty and providing a more conservative basis for retrofit prioritization. Although demonstrated on a single case study, the proposed workflow offers a realistic and scalable pathway for NDT-supported seismic performance assessment of existing RC buildings.

In engineering materials, defects, such as cracks, may occur during production and/or owing to various reasons. One of the aims of fracture mechanics is to determine the fracture toughness-based residual strength of structural members with cracks. A quasi-brittle material, such as concrete or rock, may include certain defects, such as voids and cracks, even before being exposed to loads. Experimental analyses on concrete members indicated that specimens’ nominal strength values decreased as their sizes increased while specimen geometry remained the same. In fracture mechanics, this condition is defined as the ‘size effect’ in both concrete and reinforced concrete units. In the literature, numerous theoretical and experimental studies have been conducted on beams, while compact split-tension specimens, particularly notched ones, are limited. In this study, six series of notched beams with three different sizes and notched square prismatic specimens with four different sizes were tested. According to the test results, the peak loads were analysed by using the fundamental theorem of the modified size effect law. In conclusion, two formulae were proposed to predict the flexural strength and the splitting strength of quasi-brittle bodies with cracks.

This study proposes a holistic workflow to investigate the impact of systematic bias and uncertainty in Non-Destructive Testing (NDT)-based strength estimations on structural performance decisions for earthquake-damaged buildings. Element-level material properties were obtained using a field-calibrated multivariate WINSONREB model (combining Windsor Probe, UPV, and Schmidt hammer tests) and subsequently integrated into a Building Information Modeling (BIM) platform to develop an as-is digital representation of the structure. Quantitative analyses revealed that the proposed model systematically overestimates concrete strength by an average of +5 MPa, particularly in low-strength zones, and that the model's standard error (±5.7 MPa) is sufficient to shift the building's performance classification between Collapse Prevention (CP) and Life Safety (LS) levels under the Turkish Building Earthquake Code (TBEC). These findings highlight the critical importance of adopting a probabilistic framework for interpreting NDT data, as opposed to deterministic assumptions, to adequately capture uncertainty propagation in engineering decision-making.