International Concrete Abstracts Portal

To evaluate the calculation accuracy of traditional yield displacement models and to describe the probabilistic characteristics of yield displacement, a probabilistic model for yield displacement of reinforced concrete (RC) columns with flexural failure was developed based on the Bayesian theory and the Markov Chain Monte Carlo (MCMC) method. The analytical expression for the yield displacement of RC columns was established by applying the plane-section assumption and cross-section analysis first. Then, the probabilistic model for yield displacement of RC columns with flexural failure was developed by replacing the empirical coefficients in the analytical expression with probabilistic coefficients. Moreover, the posterior information of the probabilistic coefficients was determined based on the prior information from experimental data and the MCMC method. Finally, the calculation accuracy of deterministic models for yield displacement was evaluated based on the experimental data, probability density functions, and confidence intervals. Analysis results demonstrate that the proposed probabilistic model provides an alternative approach to evaluate the calculation accuracy of deterministic models for yield displacement of RC columns with flexural failure. Priestley's model, JTD's model, and Cui's model tend to underestimate the yield displacement of RC columns, while Fardis's model and Billah's model often overestimate the yield displacement of RC columns.

During past earthquakes, failures of beam–column joints have commonly been observed on the exteriors of buildings. However, only one side of these joints can be retrofitted because of the presence of beams on the other three sides. Therefore, this study aims to test four exterior beam–column joints with transverse beams, leaving the rear side as the only viable location for placing fiber-reinforced polymer (FRP) laminate. All four test specimens are designed with insufficient joint shear strength, as determined by ACI 318 equations, while satisfying the criteria for a strong-column–weak-beam mechanism and sufficient development length for bar anchorage. A total of two un-retrofitted specimens, with and without joint hoops, are constructed as controls. Subsequently, two similar specimens are retrofitted by applying an FRP laminate on the rear side. The results show that sufficient FRP laminate can enhance the seismic performance of joints in terms of deformability, energy dissipation, and failure delay.

The reduction in the shear capacity using recycled coarse aggregate made from crushed concrete is evaluated in terms of tensile cracking and fracture surface characteristics. An experimental investigation is presented into the fracture and flexure-shear behaviors of recycled aggregate concrete (RAC). Replacing natural aggregate in concrete proportioned for 30 MPa compressive strength with recycled coarse aggregate results in lower compressive and tensile strengths. The tensile fracture surface characteristics vary between RAC and natural aggregate concrete (NAC). While the surface area created in the tensile fracture of RAC is larger than that of NAC, the fracture surface profile in RAC has a smaller roughness than that of NAC. In the flexure-shear response of reinforced concrete beams, the dilatancy determined from the slip and crack opening displacements measured across the shear crack is smaller in RAC than NAC. The failure in the reinforced beam is due to the frictional stress transfer loss across the primary shear crack. There is a larger decrease in the shear capacity with the use of RAC than indicated by the reduction in compressive strength. The reduced shear capacity of reinforced RAC is due to the combined influences of reduced tensile strength and crack surface roughness. The design provisions require calibration for crack surface roughness when using RAC in structural applications.

Prompt-gamma activation analysis (PGAA) is an elemental analysis method based on radiative neutron capture that has a high sensitivity to chlorine (Cl). To evaluate the feasibility of replacing the conventional wet chemistry method, ASTM C1152, with PGAA, four mixtures of concrete were prepared with Cl added, ranging from a 0.004 to 0.067% mass fraction of Cl in concrete. The PGAA method detected levels of 100 μg/g Cl in concrete. While both the PGAA and C1152 methods gave results systematically below the nominal values of added Cl, the PGAA data showed excellent correlation (R2 of 0.999) with the C1152 results measured on the same samples. Given that PGAA can measure Cl in concrete as well as C1152 and is faster and less labor-intensive, it can be a candidate for development as a standard method for an alternative to the latter.

Supplementary cementitious materials (SCMs) have been used to replace portland cement and are used in conjunction with advanced mixture design approaches in reinforced concrete for the purpose of creating low-carbon concrete (LCC). In this research, functionally graded concrete (FGC) was used with LCC to provide strength and serviceability for reinforced concrete one-way slab strips by placing a higher-strength/stiffness concrete in the flexural compression region and LCC in all other locations. The behavior of FGC slab strips with varied connection types, placement methods, reinforcement ratios, and ages were compared to uniform specimens with different types of LCC and conventional concrete. Behavior was evaluated through load deflection, cracking, and strains during four-point bending, which were measured using distributed sensing, including distributed fiber-optic sensing and digital image correlation. Limited differences in behavior existed among specimens with the same reinforcement ratios. However, some FGC specimens had higher stiffness and ultimate capacity. Implications of FGC, including cracking behavior at the interface, are also discussed.