Yongcheng Ji

Evaluation of Prestressed Concrete Bridges under Light Rail Loading

This paper presents the evaluation of prestressed concrete bridges carrying light rail loading, which is significantly unexplored relative to bridges subjected to conventional heavy-haul and highspeed trains. Four bridges in Denver, CO, are selected to investigate static and dynamic responses, including flexural behavior, passenger occupancy, statistical properties, live load distributions, natural frequencies, and user comfort. Three-dimensional finite element models are developed to complement in-place findings. The measured train loadings are statistically stable along with Gaussian distributions and increase by 10.8% when their average operating speed rises from 32.9 to 49.0 mph (53 to 78 kmh). Passenger loading that is stochastic in nature also increases the train loading by 23.3%, on average. Existing design approaches for live load distributions deviate from those attained from the field, which is particularly noticeable for interior girders. Deflection control criteria used in practice are not applicable either. In accordance with the deflection and frequency of the bridges, the user comfort of light rail systems (pedestrians and passengers) is assessed. Statistical properties are acquired and characterized, which are valuable when developing design guidelines.

Characteristics and Chloride Permeability of Internally Cured Concrete

This paper presents an experimental study on the physical characteristics of internally cured concrete using organic and inorganic materials, including chloride-related responses. The curing agents saturated before mixing the concrete are microporous lightweight aggregate (LWA), crushed returned concrete aggregate (CCA), and superabsorbent polymer (SAP). The inorganic agents (LWA and CCA) replace the concrete’s fine aggregate by 25 to 75% in mass, while the organic agent (SAP) is added to the concrete mixture by 0.2 to 0.6% of the cement mass. A variety of test schemes are employed—namely, compression strength, resonant frequency, drying shrinkage, chloride permeability, and digital microscopy. Selected specimens are preloaded to examine the performance of the internally cured concrete subjected to service loading. The compressive strength of the concrete decreases as the amount of the curing agents increases. The strength decrease rate of the LWAand SAP-mixed concrete is more rapid than that of the CCA-mixed concrete. In terms of resonant frequency, the LWA-mixed concrete is more susceptible relative to its CCA and SAP counterparts because of the LWA’s microporous structure. The concrete mixed with LWA reveals dynamic to static elastic modulus ratios higher than the concrete with the other agents. Although all concrete mixtures’ drying shrinkage is influenced by the agents’ quantity, the inclusion of SAP results in more shrinkage. Electric charges passed through the internally cured concrete are higher than those of the control concrete, which represent the degree of chloride permeability. The occurrence of cracks in the concrete caused by preloading accelerates the mobility of chloride ions; nonetheless, the addition of SAP alleviates the implications of the mechanical damage.

Effects of Sulfuric Acid on Durability Characteristics of CFRP Composite Sheets

AbstractThis paper presents the chemical, physical, and mechanical characteristics of carbon fiber–reinforced polymer (CFRP) composite sheets subjected to sulfuric acid (H2SO4). Test coupons are su...

Various FRP-Bracing Configurations for Multistory Buildings under Seismic Loading: Conceptual Modeling and Comparative Assessment

AbstractThis paper presents the behavior of multistory buildings with fiber-reinforced polymer (FRP) brace members for new construction and for retrofit applications, including a comparative assessment against conventional steel brace systems. The El Centro earthquake load with a magnitude of 7.1 is employed to examine the performance of three brace types (hollow structural steel sections, and pultruded carbon FRP (CFRP) and glass FRP (GFRP) tubes for new buildings; and CFRP-confined and aramid FRP (AFRP)-confined concrete elements for existing buildings: seismic strengthening with FRP wrapping) and three shapes frequently used in practice (single-bay X-brace, super X-brace, and chevron brace). Nonlinear pushover and time-history models are developed to predict the seismic response of the retrofitted buildings with an emphasis on base shear force, ductility, mode shapes and frequencies, and strain energy. The brace materials and confinement schemes of the buildings control the effectiveness of the seismic...