International Concrete Abstracts Portal

Precast concrete hollow-core floor units have been shown to sustain cracking to their unreinforced webs near the end support during earthquakes. Post-cracking shear strength is essential to maintain gravity loads following earthquakes. This paper presents the results of an experimental program that examined the post-cracking shear capacity of 12 full-scale hollow-core floor units. Variables included different support seating lengths, shear span-depth ratios, and loading protocols. Results showed that cracking in the unreinforced webs of hollow-core floor units can reduce shear capacity by at least 60% relative to uncracked strength. Additionally, reduced support seating length markedly decreased post-cracking shear strength: 30 mm (1.2 in.) seating provided no residual capacity, while 50 and 100 mm (2 and 4 in.) lengths retained approximately 50% and 100% of the calculated uncracked section capacity, respectively. The findings from this study provide a basis to quantify the residual capacity of web-cracked hollow-core floor units, which can be used in post-earthquake structural assessments.

Precast concrete (PC) moment-resisting frame systems with wide beam sections have been increasingly adopted in the construction industry due to their advantages in reducing the span length of PC slabs perpendicular to wide beam members and improving the constructability of precast construction. To further facilitate fast-built construction, this study introduces a novel PC wide beam-column connection system, where the solid panel zone is prefabricated and integrated into the PC column, allowing the upper floor to be quickly constructed without delay due to the curing time of cast-in-place concrete. Meanwhile, the current ACI 318-19 Code imposes strict allowable limits on the width of wide beams and complex reinforcement details as part of a seismic force-resisting system to effectively transfer forces into the joint, considering the shear lag effect. To address this, two full-scale PC wide beam-column test specimens were carefully designed, fabricated, and tested to explore the impact of large beam width and simplified reinforcement details beyond the code limit. The seismic performance was evaluated in terms of lateral strength, deformation capacity, stiffness degradation, failure mechanism, and energy dissipation. Based on the evaluation, the proposed PC wide beam-column connections demonstrated equivalent, or even better, seismic performance than the reinforced concrete control specimen. Additionally, it was found that the presence of corbels can mitigate the shear lag effect in PC wide beam-column connections, and that the current effective beam width limit imposed by ACI 318-19 is conservative for PC wide beam-column connections with corbels.

As modern industrial and residential buildings become larger and longer, the use of precast concrete (PC) has been essential in current practice. A PC lateral force-resisting system has inevitable discrete joints between precast components, which are considered one of its major concerns in structural integrity and emulative seismic performances comparable to monolithic connections. It can be overcome through code-compliant joint details and tight connection quality under capacity design philosophy, for which suitable emulative design methods also need to be adopted. This study aims to investigate various design options based on the so-called degree-of-coupling (DOC) in vertical wall-to-wall connections in lateral seismic design of an intermediate precast coupled shear wall system. To this end, a flexible and cost-effective lateral design method is proposed by addressing a simple but reasonable factor (G). To verify the proposed approach, an experimental campaign and robust analytical studies were conducted. Especially in the experimental program, several precast coupled shear walls with semi-emulative and fully emulative connection details in wall-to-wall vertical connections were tested under cyclic loading. On this basis, it appeared that an existing design process of precast coupled shear wall systems can be simplified, providing reasonable accuracy and design flexibility for engineers toward cost-effective intermediate precast shear wall systems.

Prestressed concrete enables slender, economical, and durable structures, with post-tensioned (PT) precast girders widely used in bridge construction. Accurate design requires precise prediction of prestress losses, among which friction losses, arising from duct curvature, wobble, and anchorage slip, are most significant. Existing codes employ simplified exponential models, yet notable discrepancies persist between predicted and actual field values. This study presents full-scale experimental testing on PT precast girders used in Egypt’s Light Railway Transit (LRT) Project. Prestressing forces were measured using strain gauges to evaluate friction losses along tendon profiles. Results revealed that measured losses consistently exceeded code-based predictions, highlighting the influence of stress level and nonlinear variation along the tendon; factors often ignored by current provisions. Regression analysis yielded refined exponential models with improved accuracy and strong agreement with observations. The proposed refinements enhance predictive reliability and provide a foundation for updating design codes toward safer, more realistic PT concrete structures.

Ultra-high-performance concrete (UHPC) often contains conductive steel fibers that interfere with conventional electrical durability tests, such as resistivity measurements, limiting their reliability for mixture qualification. This study proposed an accelerated chloride migration electrical (ACME) test to rapidly assess the durability of UHPC with steel fibers against chloride ingress. Four strength classes ranging from high-performance concrete to UHPC were made with three steel fiber contents (0, 1.5, and 2%) and cured under fog, steam, and precast regimens. ACME test results were compared against surface/bulk resistivity and long-term bulk diffusion measurements to assess their consistency and sensitivity to fiber content. Across mixtures ≥18 ksi, fiber inclusion had minimal influence on ACME penetration depth, and strong correlations were observed between ACME results and one-year diffusion coefficients. Based on these findings, a 7-day ACME limit for steam-cured samples is proposed as a rapid, fiber-independent acceptance criterion for qualifying the chloride penetration resistance of UHPC mixtures.