International Concrete Abstracts Portal

Accurate prediction of bond strength between steel reinforcement and concrete is essential for assessing structural safety and durability, particularly under reinforcement corrosion, where existing design codes such as ACI 408R-03 lack explicit modifiers. This study presents a physics-guided Bayesian framework that integrates dimensional analysis, probabilistic calibration, and uncertainty quantification to model bond strength while explicitly accounting for experimentally observed factors, including corrosion. Starting from a dimensionless power-law derived via Buckingham’s π-theorem, bond strength is expressed with globally interpretable exponents for embedment-to-diameter and cover-to-diameter ratios, while the scaling coefficient is adaptively modeled as a nonlinear function of experimental variables—including corrosion level, stirrup ratio, rebar type, and test method—through Random Fourier Features. Bayesian inference with Markov Chain Monte Carlo enables calibrated predictions with explicit decomposition of aleatoric and epistemic uncertainty, providing transparent insights into variability sources. Model performance and uncertainty behavior are examined through cross-validation and external validation. Beyond predictive performance, posterior analysis yields a concise, physics-consistent bond strength equation that explicitly incorporates corrosion effects and quantifies uncertainty, providing a practical and interpretable tool for reliability-based assessment of reinforced concrete structures.

The calculation of the nominal flexural strength of concrete members prestressed with hybrid (that is, a combination of bonded and unbonded [steel and/or carbon fiber-reinforced polymer (CFRP)]) tendons is dependent on determining the stress in the unbonded prestressed reinforcement. Current provisions in ACI CODE-318-25 are only applicable to members with either unbonded or bonded steel tendons. Additionally, while ACI 440.4R-04 is adopted for unbonded CFRP tendons, neither ACI provision addresses the use of hybrid tendons. This paper presents a closed-form analytical solution for the stress at ultimate derived based on the modified deformation-based approach (MDBA) that is applicable to beams prestressed with unbonded, hybrid (steel or FRP), external with deviators or internal tendons, with and without nonprestressed reinforcement. An assessment of its accuracy and applicability in calculating the nominal flexural strength is examined using a large database of 330 beams and slabs (prestressed with steel and/or CFRP tendons) compiled from test results by the authors as well as those available in the literature. Results predicted by the proposed approach exhibited excellent accuracy when compared to those predicted using ACI CODE-318 or ACI 440.4R stress equations. They also show that the approach is universally applicable to any combination of bonded and/or unbonded (steel and/or CFRP) tendons, span-depth ratio, and loading applications.

A slag-based zero-cement concrete (ZC) was newly developed as an alternative, eco-friendly material to portland cement concrete. To investigate the bond performance between ZC and steel reinforcing bars, lap-splice tests were conducted for ZC beams. Fourteen beams (two cementitious normal concrete [NC] beams and 12 ZC beams) were tested at the ages of 6 days (45 MPa [6.53 ksi]) and 28 days (60 MPa [8.7 ksi]). For steel reinforcement, Grade 600 MPa (87.0 ksi) reinforcing bars were used. The test parameters included the concrete type, concrete strength (that is, concrete age), reinforcing bar diameter, concrete cover thickness, ratio of actual to required lap-splice length, and use of stirrups. The test results showed that the performance of ZC beams was comparable to that of the counterpart NC beams in terms of moment-deflection relationship, damage mode, and reinforcing bar stress at the peak load. This result indicates that the bond performance of ZC was equivalent to that of NC with identical compressive strength. The bar development length specified in current design codes safely predicted the reinforcing bar stress of the ZC beams at failure; current design codes are applicable to the reinforcing bar development length design of ZC members.

An experimental study was conducted to compare the long-term performance of two partially prestressed concrete (PC) beams reinforced with either bonded carbon fiber-reinforced polymer (CFRP) tendons (CFRP-PC) or steel strands (steel-PC) under 1200-day sustained loading. The deflections increased rapidly during the first 200 days and then at a slower rate. The final-to-initial deflection ratio was 1.58 for the CFRP-PC beam and 1.45 for the steel-PC beam. The final-to-instantaneous maximum crack-width ratio was approximately 2.00 for both beams. Based on the age-adjusted effective modulus method (AEMM), a finite element analysis (FEA) program was developed and calibrated using the experimental results. Parametric simulations were subsequently performed on 14 beams. A modification of the suggested equation in ACI 440.1R-15 was proposed to predict the time-dependent deflection of PC beams, which exhibits an improved correlation with the experimental results as compared to the design standards.

Although grouted splice-sleeve connectors (GSSCs) are notably used in precast concrete structures, steel sleeves are heavy and have corrosion issues. The bond characteristics of GSSCs using cylindrical and tapered fiber-reinforced polymer (FRP) sleeves—lighter alternatives—were investigated in this study. A series of pullout tests for 144 specimens were conducted to evaluate the effects of FRP type, number of layers, shape, and length on the bond characteristics of GSSCs. The test results showed that for FRP GSSCs, tapered FRP sleeves effectively developed confinement compared with cylindrical FRP sleeves, leading to better bond strength and shorter development length. A design equation was proposed for estimating the tensile strength of FRP-based GSSCs, which predicted well the test results. The tapered FRP sleeves reduced the development length compared with cylindrical FRP sleeves, implying greater FRP GSSC efficiency in precast concrete structures, which provides engineers with valuable insights for efficient FRP splice-sleeve design in precast concrete structures.