International Concrete Abstracts Portal

Axial compression performance of concrete columns reinforced with GFRP bars and spiral, 2304 duplex stainless bars and spiral, and 316L stainless clad bars, in varying combinations is examined after exposure to accelerated corrosion. The hybrid columns were reinforced with a combination of metallic and GFRP reinforcement. After corrosion exposure the columns were tested under axial compression to failure. Columns with GFRP vertical bars and stainless steel spiral were less corrosion resistant and had smaller axial load capacity than hybrid columns with stainless clad or stainless steel vertical bars and GFRP spiral. Columns reinforced with stainless steel spiral achieving two to three times the maximum axial displacement of columns with GFRP spiral. Axial compression capacity of hybrid columns in both corroded and uncorroded conditions was modeled using concrete confinement models for metallic and GFRP reinforcement with good agreement.

The United States has over 600,000 bridges, nearly 40% of which are 50 years old or older. Additionally, over 46,000 bridge structures in the country were evaluated to be structurally deficient according to the National Bridge Inventory (NBI) 2019. The average age of America’s bridges keeps increasing and many of these bridges are approaching the end of their design life. Therefore, evaluating the existing condition and predicting the remaining service life of these bridges is of vital importance to agencies making the decisions to maintain, repair, or replace bridge structures based on their present and future expected conditions. Several models are available to predict the service life of new concrete structures. However, very few models are available to estimate the remaining service life of existing concrete structures. This paper presents a comparative study between two service life prediction models (Life-365 and NCHRP report 558). The service life prediction analysis was performed on bridge substructures (two abutments, namely North Abutment and South Abutment) subjected to corrosion-induced deterioration. Constructed in 1958, this bridge is located in Northern New Jersey and was 60 years old at the time this study was conducted. Review of the existing bridge documents, visual inspection, and concrete damage survey, field sampling and testing, and lab tests were performed to evaluate the existing condition of the structure and to obtain the parameters required for analysis. A good agreement between the analysis results of Life-365 and NCHRP report 558 models was obtained.

Traditionally, a time-varying mass system is viewed as the motion of moving bodies exiting or colliding with the system, such as rockets. A standing structure is not typically considered a time-varying mass system, but a silo during discharge of the infill is a subtle time-varying mass structure. Slender silos and silos with insufficiently stiffened supports are vulnerable to excessive vibration (silo quaking) and loud disruptive noises (silo honking) caused by the flow of the exiting masses. Using principles of mechanics and conservation of momentum, the equation of motion of such systems can be formulated to incorporate the discharge rate, material properties and the time-dependent characteristics of the system (mass, damping and stiffness). In this paper, the acceleration and mass flow of granular fill in a perspex tubing during discharge have been reproduced to simulate silo honking. By controlling the majority of influential factors, the replication of a small-scale silo design was possible with the repeatability of silo honking achieved in a controlled environment. A comparative study between discharge testing results of the sand fill with 0% (control), 5% and 10% moisture content shows that increasing the moisture content of the fill reduces the vibrational effect on the silo walls, and in turn reduces the magnitude of silo honking. Further, the effect of the sudden mass loss on a system of reinforced concrete columns depicting that of silo supports is investigated. The results show the exponential changes in the acceleration and velocity responses of the structure when subjected to a sudden mass loss. Finally, notes on how to consider the system of the forces in the silo structure based on the existing silo theory are provided.

Fireproofing deterioration is widespread in industrial facilities throughout the country. Spalling concrete has potential to damage equipment and harm personnel. Replacing concrete fireproofing like-in-kind, without consideration for proper anchorage or material durability, does not eliminate the hazard as spalls may potentially occur again over time. However, when properly designed and installed, concrete is a durable option for replacing deficient fireproofing in aggressive environments typically present in industrial processing units. This paper presents the results of a case study on a structure in a Midwest industrial complex. Extensive concrete fireproofing repairs were performed on the structure 12 years ago. Design requirements included normal weight concrete with polypropylene fibers which enhance durability by improving cracking resistance. During a fire, the fibers melt forming relief channels for moisture to escape, thus eliminating explosive spalling. Installation methods included welded wire reinforcement (WWR) with positive anchorage to structural steel. WWR was attached to post-installed adhesive anchors between column flanges where existing fireproofing was sound and difficult to remove. After 12 years in service, repairs exhibit no significant defects. This level of durability is attributed to the design and installation methods utilized. Concrete fireproofing is a durable option for fire protection, provided structures are designed to support its weight, its mixture design is properly proportioned, and it is adequately anchored and reinforced.

This paper presents a preliminary study on the durability of a bridge column under typical marine environments consisting of atmospheric, splash, and submerged conditions. To predict the migration of chlorides across the column, a simulation is conducted using a mathematical method, called cellular automata. Because chloride concentrations and the corrosion current density at the surface level of reinforcing steel can lead to the deterioration of a column over 100 years, they are of particular interest. The highest chloride concentrations are observed under the splash exposure, followed by the submerged and atmospheric conditions.