International Concrete Abstracts Portal

ACI 318 permits the use of mechanical couplers for Grade 60 (420 MPa) bars in hinge regions, but not for higher-grade bars. This restriction was introduced due to limited testing of mechanical couplers under inelastic strain demands and is hindering the use of higher-grade bars in seismic regions. Eleven mechanical couplers splicing Grade 80 (550 MPa) bars through varying connection details were tested in a uniaxial testing machine to evaluate their performance compared to bare bars under reversed cyclic inelastic strain demands, akin to those experienced in hinge regions of special seismic systems. The low-cycle fatigue life of coupled subassemblies is compared to those of the bare bars tested under the same loading protocol. Results indicate that some coupled bars can have equivalent fatigue life to the bare bars, while others can have substantially reduced fatigue life. A qualification test is proposed to qualify mechanical splices for use in seismic hinge regions of special concrete systems.

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 the CFRP tendons insignificantly vary 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 the steel- and CFRP-prestressed girders, respectively. From deformational capability standpoints, the steel-prestressed girders are more vulnerable to fatigue in comparison with the 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, the CFRP-prestressed girders outperform their steel counterparts in terms of fatigue safety. Technical findings are integrated to propose design recommendations.

A comprehensive laboratory testing program, field-testing program, numerical analysis, and life-cycle cost analysis were conducted to evaluate the beneficial effects of incorporating shrinkage-reducing admixture (SRA), polymeric microfibers (PMFs), and optimized aggregate gradation (OAG) into internally cured concrete (ICC) mixtures for rigid pavement applications. Results from the laboratory program indicate that all the ICC mixtures outperformed the standard concrete (SC) mixture. All the ICC mixtures showed a decrease in drying shrinkage compared to the SC mixture. Based on the laboratory program, three ICC mixtures and one SC mixture were selected for the full-scale test and subjected to a heavy vehicle simulator for accelerated fatigue testing. Extensive testing and analysis have shown that ICC mixtures incorporating SRA, PMFs, and OAG can be beneficially used in pavement applications to achieve increased pavement life.

Superloads, defined as vehicles with a gross vehicle weight of over 890 kN, are believed to overload jointed plain concrete pavements (JPCPs) and have the potential to cause significantly more fatigue damage than typical truck traffic. It is anticipated that the fatigue damage is greater when the superload is applied later in the life of the JPCP. In this study, the stress pulses generated by superloads on JPCPs were characterized using finite element modeling and related to fatigue damage through the fatigue testing of concrete beams. Concrete beams subjected to loading profiles that simulate those of a superload were observed to accumulate fatigue damage at an accelerated rate when applied after 70% of the fatigue life of the concrete was consumed. Moreover, through the collection of fatigue life and beam response data, the effects of stress ratio, stress range, flexural strength, and damage state at the time of loading on the fatigue damage imposed by a superload movement were elucidated.

In this study, the flexural fatigue performance of reinforced concrete (RC) beams strengthened with a fiber-reinforced polymer (FRP) grid-reinforced engineered cementitious composite (ECC) matrix was experimentally investigated. An FRP grid-reinforced ECC matrix (FGREM) composite strengthening layer was applied by reinstating the original concrete layer to a predetermined depth. The load level, FRP grid type, and strengthening amount were considered as test variables. The ultimate fatigue failure of the strengthened beams was found to be governed by the fracture of tensile steel bars. However, premature end debonding could be triggered in specimens subject to excessive strengthening. Furthermore, the fatigue life of the strengthened beams was distinctively improved owing to the relieved tensile stress range of the steel reinforcements. By relieving the damage accumulation of the constituent materials, this strengthening system can effectively ameliorate cracking, which is of great significance to the degeneration of stiffness and the development of deflections.