Ultra high performance fiber reinforced concrete for strengthening and protecting bridge deck slabs

An original concept is presented for the durable rehabilitation of concrete bridge deck slabs. The main idea is to add a layer of Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) with or without steel reinforcing bars over the concrete slab to create a composite section. The layer of UHPFRC strengthens the structural element for high traffic loads. Experimental studies on composite beams and slabs were carried out to study their behavior under various types of loading and identify the failure modes and the contribution of the UHPFRC layer to the resistance. Analytical models were then developed to calculate the resistance of composite beams. The concept has been validated by field applications demonstrating that the technology of UHPFRC is mature for cast in-situ

Impact of repairs on embodied carbon dioxide expenditure for a reinforced-concrete quay

Studies on structural repair using life-cycle analysis are still lacking the environmental impact of repair actions. This research work shows that the choice of the best repair option for reinforced-concrete structures is a function of long-term environmental impact, considering the longevity of maintenance intervention and embodied carbon dioxide expenditure. The purpose of this work was to assess the lifetime of a quay superstructure exposed to an aggressive marine microenvironment by using a probabilistic performance-based approach and then to select the best repair option for its reinforced-concrete structures. The comparison is made for reinforced-concrete service life using three different concrete types and two different corrosion inhibitors. Longevity and embodied carbon dioxide were predicted for the expected number of repair actions per 100 years. It is shown that concretes may have a higher impact at the outset, although they result in a much lower impact across the service life of the structure

Mechanical behavior of concrete prisms reinforced with steel and GFRP bar systems

Being immune to corrosion, and having a tensile strength up to three times higher than structural steel, glass fiber reinforced polymer (GFRP) bars are suitable for reinforcing concrete structures exposed to aggressive environmental conditions. However, a relatively low elasticity modulus of GFRP bars (in respect to the steel) favors the occurrence of relatively large deformability of cracked reinforced concrete. Lack of ductility and degradation of properties under high temperature can be also identified as debilities of GFRP bars over steel ones. Combining GFRP and steel bars can be a suitable solution to overcoming these concerns. Nevertheless, the application of such hybrid reinforcement systems requires reliable material models. The influence of the relative area of GFRP and steel bars on the tensile capacity of cracked concrete (generally known as tension-stiffening effect), was never investigated from the experimental point of view, mainly crossing results from different tools on the assessment of the cracking process. This paper experimentally investigates deformations and cracking behavior of concrete prisms reinforced with steel bars and GFRP bars in different combinations. The test results of 11 elements are reported. A tensile stress-strain diagram is conceptually proposed for modelling the tension-stiffening effect in elements with such hybrid combination of the reinforcement. The cracking process in terms of crack width and crack spacing is analyzed considering the hybrid reinforcement particularities and a preliminary approach is proposed for the prediction of the crack width for this type of reinforced concrete elementsResearch Council of Lithuania (Research Project S-MIP-17-62). The second author also 590 wish to acknowledge the support provided by FCT through the PTDC/ECM591 EST/1882/2014 projec

Assessment of different methods for characterization and simulation of post-cracking behavior of self-compacting steel fiber reinforced concrete

The post-cracking tensile properties of steel fiber reinforced concrete (SFRC) is one of the most important aspects that should be considered in design of SFRC structural members. The parameters that describe the post-cracking behavior of SFRC in tension are often derived using indirect methods combined with inverse analysis techniques applied to the results obtained from three- or four-point prism bending tests or from determinate round panel tests. However, there is still some uncertainty regarding the most reliable methodology for evaluating the post-cracking behavior of SFRC. In the present study a steel fiber reinforced self-compacting concrete (SFRSCC) was developed and its post-cracking behavior was investigated through an extensive experimental program composed of small determinate round panel and prism bending tests. Based on the results obtained from this experimental program, the constitutive tensile laws of the developed SFRSCC were obtained indirectly using two numerical approaches, as well as three available analytical approaches based on standards for estimating the stress versus crack width relationship (). The predictive performance of both the numerical and analytical approaches employed for estimating the relationship of the SFRSCC was assessed. The numerical simulations have provided a good prediction of the post-cracking behavior of the concrete. All the analytical formulations also demonstrated an acceptable accuracy for design purposes. Anyhow, among all the employed approaches, the one that considers the results of small determinate round panel tests (rather than that of prism bending tests) has predicted more accurately the constitutive tensile laws of the SFRSCCFEDER funds through the Operational Programme for Competitiveness and Internationalization - COMPETE and by national funds through FCT (Portuguese Foundation for Science and Technology) within the scope of the project InOlicTower, POCI-01-0145-FEDER520 016905 (PTDC/ECM-EST/2635/2014)

Closed-form expressions for predicting moment redistribution in reinforced concrete beams with application to conventional concrete and ultrahigh performance fiber reinforced concrete

Publication Date : 2020-03-27The redistribution of moment within a statically indeterminate reinforced concrete beam at the ultimate limit state occurs through variations in the flexural rigidities and through the formation of hinges. The phenomena of moment redistribution (MR) is used to increase the efficiency of reinforced concrete design by allowing moments to be transferred away from critical cross sections thereby resulting in lower design moments. To allow for this effect in design, two main approaches are adopted. The first is to perform an elastic analysis and then to adjust the resulting distribution of moment using a codified MR factor. The second is to apply a plastic analysis allowing for the formation of hinges, and to calculate the rotational requirements at the hinges from first principles. This paper uses fundamental plastic analyses to derive closed‐form expressions for the hinge rotational requirements for full MR (that required to achieve the theoretical maximum applied load within the beam based on the moment capacity of sections within the beam). These closed‐form solutions are then used to quantify the maximum load on a beam when the rotational capacities at a hinge are less than the rotational requirements for full MR (partial MR). Closed‐form solutions are then used to derive MR factors which do not require semimechanical calibration.Alexander B. Sturm, Phillip Visintin, Deric J. Oehler