International Concrete Abstracts Portal

This paper presents the implications of creep-fatigue interactions for the long-term behavior of bulb-tee bridge girders prestressed with either steel strands or carbon fiber-reinforced polymer (CFRP) tendons. A large amount of weigh-in-motion data incorporating 194 million vehicles are classified to realistically represent live loads. Computational simulations are conducted as per the engagement of discrete autonomous entities in line with time- dependent material models. In general, the properties of CFRP tendons vary insignificantly over 100 years; however, the stress range of CFRP responds to fatigue cycles. Regarding prestress losses, the conventional method with initial material properties renders conservative predictions relative to refined approaches considering time-varying properties. The creep and fatigue effects alter the post-yield and post-cracking responses of steel- and CFRP-prestressed girders, respectively. From deformational capability standpoints, steel-prestressed girders are more vulnerable to fatigue in comparison with CFRP-prestressed ones. It is recommended that the fatigue truck and the compression limit of published specifications be updated to accommodate the ramifications of contemporary traffic loadings. Although the operational reliability of both girder types is satisfactory, CFRP-prestressed girders outperform their steel counterparts in terms of fatigue safety. Technical findings are integrated to propose design recommendations.

Remodeling aging structures is common to enhance their structural, economic, and functional performance. However, the exceeding of bearing capacity of existing piles caused by increased upper loads due to vertical expansion frequently hinders their revitalization. In this paper, a methodology is proposed to control the demand-tocapacity ratio of existing piles without retrofitting the foundation, which is often accompanied by technical limitations and safety issues. A total of 12 tests were performed on four full-scale specimens, with tendon shape, wall thickness, boundary condition, and construction sequence as variables. Factors affecting load-transfer performance were identified based on test results. The target load transfer pattern implemented in accordance with the tendon shape was confirmed. To verify the validity of the method, tests using tendon shape and wall thickness as variables were compared with results from finite element analysis.

North American technical committees are currently devoting enormous efforts to incorporating the design of concrete columns reinforced with fiber-reinforced polymer (FRP) bars in the upcoming edition of FRP-reinforced concrete (RC) structures design codes. This paper attempts to develop reliability-based design provisions for slender FRP-RC columns. Firstly, effective flexural stiffness equations of slender FRP-RC columns in the available technical literature were reviewed, and their model errors were evaluated based on a large experimental database of 160 slender columns. Subsequently, an analytical procedure based on Monte Carlo simulations was developed to perform a rigorous reliability analysis of slender FRP-RC columns. On this basis, sensitivity analyses were performed to examine the influence of various design parameters on the reliability index. The stiffness reduction factors were then calibrated to achieve a predetermined target reliability index. Finally, the stiffness reduction factors for slender FRP-RC columns were proposed in a convenient form for design procedures, depending on the effective flexural stiffness equation used.

Modulus of elasticity (MOE) is one of the main factors that affect the deformation characteristics and serviceability of concrete in the hardened state. The use of recycled concrete aggregate (RCA) in concrete production can lead to a significant reduction in the MOE. An artificial neural network (ANN) was employed to quantify the effect of coarse RCA on the concrete’s MOE. A database summarizing over 480 data series obtained from 52 technical publications was developed and analyzed using ANN. Concrete mixture proportions and aggregate properties were considered input parameters. The rate of reduction in 28-day MOE was considered the output parameter. An additional data set of 43 concrete mixtures obtained from laboratory investigation of concrete with well-known properties was used to validate the established model. Several combinations of input parameters and ANN architectures were considered in the analysis. Results indicated that the performance of the system was acceptable, with a coefficient of correlation ranging from 0.71 to 0.95 for the training, validation, and testing of the model with a mean square error limited to 0.008. The developed model was incorporated for a case study on a typical concrete used for rigid pavement construction. Contour graphs were developed to showcase the effect of up to 100% coarse RCA replacement on the variations in the MOE of concrete made with 0.40 water-cementitious materials ratio (w/cm) and 323 kg/m3 (545 lb/yd3) of a binary cement, designated for rigid pavement construction. The results indicated that depending on the RCA quality, a reduction of 10 to 30% in the MOE of pavement concrete made with 50% RCA can be expected. However, the reduction in the MOE will be limited to 10% when RCA with water absorption limited to 2.5% and an oven-dry specific gravity of over 2500 kg/m3 (156 lb/ft3) is used.

This paper presents the flexural characteristics of highway bridge girders prestressed with fiber-reinforced polymer (FRP) tendons. Of interest are the technical challenges identified by ACI Subcommittee 440-I (FRP-Prestressed Concrete): long-term multipliers, deformability, and minimum reinforcement. Aramid and carbon FRP (AFRP and CFRP, respectively) composites are used to prestress concrete girders. Based on analytical models, new design expressions are proposed for the aforementioned items, followed by an assessment using laboratory test data and full-scale benchmark bridges. The long-term multipliers calibrated per reliability theory are mostly different from the empirical multipliers adopted in ACI 440.4R-04. The girders prestressed with AFRP/CFRP sufficiently deform in flexure, even though their moment-curvature responses are not comparable with those of steel-prestressed girders. The new deformability index specifies design requirements for AFRP/CFRP-prestressed members with either compression-controlled or tensioned-controlled sections. The importance of a potential change in FRP modulus during the service life of prestressed concrete girders is examined. A factored ultimate-tocracking moment ratio of ϕMn/Mcr = 1.2 is suggested for girders prestressed with AFRP/CFRP, which aligns with the articles of existing design manuals and specifications dedicated to prestressed concrete.