International Concrete Abstracts Portal

Slender reinforced concrete columns have been employed as components of telecommunication and internet infrastructure since the deployment of the system more than 30 years ago. The assessment of these structures must consider the time-dependent behavior of concrete. In this context, a numerical investigation is conducted to determine the critical buckling load and the stress distribution in sections subject to creep and shrinkage of concrete. The guidelines used are those from the American Concrete Institute. It is concluded that the maximum stress induced in the reinforcement is 1.14% of the steel yield stress. Therefore, no yielding of the reinforcement is registered to the examined case, which ensures safety against permanent deformation. During the elapsed time of 7500 days, the modulus of elasticity of concrete decreased by 53% and the critical buckling load by 40%. The results obtained can be applied to similar cases through the slenderness index and the reinforcement ratio.

New refined theoretical models for the study of concrete creep have been proposed, which jointly take into account the non-linear relationship between stresses and strains of concrete (non-linear creep) and the non-linear relationship between stresses and instantaneous strains of concrete (stress-strain curve). The fundamental theories of creep that needed to be refined were the elastic-creeping solid theory, elastic heredity theory, and aging theory. The relationship from Eurocode 2 (Sargin’s formula) was used as the analytical relationship for the stress-strain curve. Within the framework of the refined theory of concrete aging, the problem of determining the concrete creep coefficient in the study of compressed reinforced concrete columns was solved. The effect of the stress-strain curve on the formula for determining the concrete creep coefficient, which is used in American, European, and Russian standards to take into account the loading duration of reinforced concrete structures, has been revealed.

Controlling deflections in reinforced concrete (RC) flexural members under service loads is a serviceability requirement prescribed by design codes, such as ACI CODE-318. Serviceability requirements are challenged by productivity requirements, such as faster construction and longer span demands, among others. This paper summarizes a parametric analysis conducted to estimate long-term deflections of one-way RC slabs. The objective of this study is to assess the effect of geometrical, concrete, and construction parameters on the long-term deflections of one-way RC slabs. The effect of these parameters on immediate deflections is also analyzed. Results of this study show that increasing the slab thickness and the area of tension reinforcement proved to be the most effective strategies for reducing both immediate and long-term deflections of one-way RC slabs. Additionally, the results of the parametric study highlight the relative influence of each studied parameter in controlling deflections.

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.

This paper presents the results of creep rupture tests conducted ontwo different sizes of glass fiber-reinforced polymer (GFRP) bars from two different manufacturers under high alkaline conditions at room temperature (approximately 23 and 60°C [73.4 and 140°F]).Regular tensile tests were also conducted on the bars at the two temperatures to provide insight into the effects of high temperatureon their long-term performance. The results show that the larger bar performed slightly better at room temperature but significantly better at the elevated temperature. The larger-sized bars also lost less tensile strength at the elevated temperature. It was observed that temperature had a greater effect on the long-term performance of GFRP bars than alkalinity. The current design code limits on the allowable stresses were evaluated against the test results and found to be overly conservative.