International Concrete Abstracts Portal

With a well-thought-out packing theory for sand, fine aggregates, cement, a water-cement ratio lower than 0.2, and steel fibers, ultra-high-performance concrete (UHPC) achieves remarkable mechanical properties. Despite UHPC’s superior mechanical properties compared to conventional concrete, its use remains limited, especially in structural applications, due to factors such as high cost, lack of design standards and guidelines, and inadequate correlation between material properties and structural behavior. By compiling and synthesizing the behavior of 70 structural- or full-scale axial UHPC columns, this research provides a new set of generalized design and detailing guidelines for axial UHPC columns. The study first uses the assembled database to assess and revisit the current ACI 318 axial strength design factors for applicability for UHPC. Next, the behavior trends are carefully analyzed to provide detailed recommendations for proper transverse reinforcement (ρt volume), spacing-to-longitudinal reinforcing bar diameter ratio (s/db, where s represents the centerline-to-centerline spacing between transverse reinforcement), and UHPC steel fiber ratio for best use of confinement.

Reinforced concrete (RC) structure design codes stipulate various design limits to prevent the brittle failure of members as well as ensure serviceability. In the structural design of RC walls, the maximum shear strength is limited to prevent sudden shear failure due to concrete crushing before the yielding of shear reinforcement due to over-reinforcement. Despite the increase in wall shear strength provided by a compression strut, the maximum shear strength limit for walls in the ACI 318-19 code is the same as the maximum torsional strength. Consequently, the shear strength of large-sized walls with high-strength concrete is limited to an excessively low level. The ACI 318-19, Eurocode 2, CSA-19, and JSCE-17 standards provide similar equations for estimating wall strength, but their maximum shear strength limits for walls are all different. In this study, experimental tests were conducted on nine RC wall specimens to evaluate the maximum shear strength. The main variables of the specimens were the shear reinforcement ratio, compressive strength of concrete, and the failure mode. The experimental results showed that the maximum load was reached after the yielding of shear reinforcement even when the shear reinforcement ratio was 1.5 times higher than the maximum shear reinforcement ratio specified in the ACI 318-19 code. In addition, the measured shear crack width of all specimens at the service load level was less than 0.42 mm (0.017 in.). The shear strength limits for walls in the current codes were compared using 109 experimental results failing in shear before flexural yielding or shear friction failure, assembled from the literature. The comparison indicated that the ACI 318-19 code limit underestimates the maximum shear strength of walls, and it particularly underestimates the maximum shear strength of walls with high-strength concrete or barbell-shaped cross-sections. Additionally, this study proposes an equation for estimating the maximum shear strength limit of walls based on the truss model. The proposed equation predicted the maximum shear strength of RC walls with reasonable accuracy.

Performance-based seismic standards establish acceptance criteria to determine whether structural members can adequately withstand seismic deformation demands. These criteria primarily consist of member deformation limits, such as plastic rotation. There is however a shift towards strain-based limits, as strains can provide more reliable estimates of material damage, and strength degradation, and can better account for variations in member boundary conditions like axial load. The process of estimating local material strains in concrete members remains challenging, mainly due to the paucity of physical models and test data at the strain level. To address this challenge, a framework based on fiber-section elements and mechanics-based behavioral models is proposed. This framework allows for strain demand estimates based on member-level deformations. Particularly the framework provides strain demands on longitudinal bars and concrete within the plastic hinge regions of frame members, while accounting for differences in steel properties as grade increases.

Ground-glass pozzolan has recently been considered a supplementary cementitious material by Canadian (CSA A3000) and American (ASTM C1866/C1866M) standards, but limited studies have been done on ground-glass use on-site. So, in this study, several sidewalk projects were performed by the SAQ Industrial Chair at the University of Sherbrooke from 2014 to 2017 on fields with different proportions of ground glass (that is, 10, 15, and 20%) in different conditions considered in such a cold climatic region. Sidewalks are a nonstructural plain concrete element that are among the most exposed to chloride and freezing and thawing in saturated conditions of municipal infrastructures. Coring campaigns were carried out on these concretes after several years of exposure (between 5 and 8 years). The results of core samples extracted from the sites were compared to the laboratory-cured samples taken during the casting. These laboratory concrete mixtures were tested for fresh, hardened (compressive strength), and durability (freezing and thawing, scaling resistance, chloride-ion penetrability, electrical resistivity, and drying shrinkage) properties (up to 1 year). The results show that ground-glass concrete performs very well at all cement replacements in all manners in terms of long-term performance. Besides that, using ground-glass pozzolan in field projects also decreases the carbon footprint and environmental and glass disposal problems.

The existing design standards of fiber-reinforced polymer bar-reinforced concrete (FRP-RC) beams provide a conservative shear capacity and fail to accurately reflect the effects of various factors. In this study, a comprehensive analysis was conducted on 174 sets of shear capacity data for FRP-RC beams with stirrups. Gray correlation analysis was utilized to investigate the correlations between the longitudinal reinforcement ratio, stirrup spacing, shear span-to-depth ratio, and shear capacity of FRP-RC beams with stirrups. The results show that stirrup spacing and shear span-to-depth ratio significantly influence the shear capacity of FRP-RC beams with stirrups, and thus must be considered in shear design. Based on the results of the gray correlation analysis, recommendations were proposed for modifying the shear contribution of concrete and stirrup in the calculation formula of shear capacity for FRP-RC beams with stirrups in five design standards. The accuracy of modified formulas was verified with the experimental data, which showed significant improvement in the shear capacity prediction in terms of mean value, coefficient of variation, and safety factor. By incorporating a database comprising 23 FRP-RC beams with stirrups, the revised formula was comprehensively validated for its sufficient applicability in shear design of three types of FRP-RC beams with stirrups.