FRP strengthening of RC walls with openings

Strengthening reinforced concrete (RC) walls with openings using fibre reinforced polymers (FRP) has been proved experimentally to be a viable rehabilitation method. However, very few theoretical investigations are reported. In this paper two methods of analysis are presented. Since openings vary in size, the analysis of a strengthened wall can be divided into frame idealization method for large openings, and combined disk and frame analysis for smaller openings. The first method provides an easy to use tool in practical engineering, where the latter describes the principles of a ductile strengthening method, relying on dislocation of yield lines and creation of a new yield mechanism. The frame idealization method can be considered as a safe guideline for real strengthening projects based on commonly used principles. The principles in the latter are new and promising, and need experimental verification before use in strengthening projects.Strengthening reinforced concrete (RC) walls with openings using fibre reinforced polymers (FRP) has been experimentally proven to be a viable rehabilitation method. However, very few theoretical investigations are reported. In this paper two methods of analysis are presented. Since openings vary in size, the analysis of a strengthened wall can be divided into frame idealization method for large openings, and combined disk and frame analysis for smaller openings. The first method provides an easy to use tool in practical engineering, where the latter describes the principles of a ductile strengthening method, relying on dislocation of yield lines and creation of a new yield mechanism. The frame idealization method can be considered as a safe guideline for real strengthening projects based on commonly used principles. The principles in the latter are new and promising, but need experimental verification before use in strengthening projects.Godkänd; 2009; 20091214 (gabsas

Freeze-thaw damage evaluation and model creation for concrete exposed to freeze–thaw cycles at early-age

Concrete subjected to freeze–thaw cycles action at early-age will suffer serious physical damage, resulting in degradation of the concrete’s performance. The subsequent curing conditions after early-age freeze–thaw cycles (E-FTCs) are critical to the development of the properties of frost-damaged concrete. Four test environments were set up for this study, based on different numbers of E-FTCs and subsequent curing conditions. The later-age resistance to freeze–thaw of concrete exposed to E-FTCs was evaluated by analysing the influence of precuring times and curing conditions. Results show that the earlier the FTCs occur, the worse the later-age freeze–thaw resistance is. In particular, for the frost-damaged concrete with a pre-curing time of 18 h, its freeze–thaw resistance is significantlypublishedVersio

Evaluation of Mechanical Properties of existing reinforced concrete bridges.

When performing numerical evaluations on concrete bridges, the Fracture Energy (GF) plays a very important role, and this Fracture Energy value is calculated using empirical formulas derived from compressive strength tests. In order to perform such experiments, methods for obtaining the fracture energy have been carried out on concrete belonging to a 55-year-old bridge located in the city of Kalix, northern Sweden. For this purpose, cylindrical concrete samples were taken from the bridge and other bridges and tested in uniaxial tensile tests. In this Thesis, different methods for determining the Fracture Energy of concrete will be discussed, and recommendations for evaluative procedures will be given. Firstly, a literature review will be carried out, in which the different methods for obtaining the Fracture Energy experimentally will be studied in depth. In addition, these methods will be compared with each other to check for possible discrepancies, and the different factors that affect the Fracture Energy results will be discussed. Secondly, the methodology of the experiments will be explained in more detail.Thirdly, all the experimental work that has been carried out in the laboratory will be discussed, i.e., all the work performed, both the preparation prior to the tests and the tests themselves, will be described. Fourthly, the results obtained from the experiments will be put on paper and analyzed in order to check how reliable they are and whether they meet the established expectations. Finally, a conclusion will be made about all the work done, both outside and inside the laboratory, and the study carried out on the Fracture Energy in concrete bridges will be evaluated.<br /

A Review of Bio-Oil Production through Microwave-Assisted Pyrolysis

The issue of sustainability is a growing concern and has led to many environmentally friendly chemical productions through a great intensification of the use of biomass conversion processes. Thermal conversion of biomass is one of the most attractive tools currently used, and pyrolytic treatments represent the most flexible approach to biomass conversion. In this scenario, microwave-assisted pyrolysis could be a solid choice for the production of multi-chemical mixtures known as bio-oils. Bio-oils could represent a promising new source of high-value species ranging from bioactive chemicals to green solvents. In this review, we have summarized the most recent developments regarding bio-oil production through microwave-induced pyrolytic degradation of biomasses

Mechanical and durability properties of concrete subjected to early-age freeze–thaw cycles

Early-age frost damage to concrete used in winter construction or in cold environments negatively affects the development of the hydration process and the performance of the concrete, thereby reducing the service life of the building structure. Experimental research was carried out to investigate the compressive strength,resistance to chloride penetration and resistance to freeze–thaw of concrete specimens subjected to earlyage freeze–thaw cycles (E-FTCs). The effects that different pre-curing times of concrete and mineral admixtures have on the properties of early-age frostaffected concrete were also analyzed. Results show that the earlier the freeze–thaw cycles (FTCs), the poorer the later-age performance. Later-age water-curing cannot completely restore the damage that E-FTCs do to concrete. In the same conditions used in this study, the effects of E-FTCs on later-age mechanical and durability properties of ordinary Portland cement concrete (OPC)are small. The incorporation of fly ash significantly reduces the resistance to freeze–thaw of concrete during early-age and later-age. The presence of silica fumes has an adverse effect on the later-age resistance to freeze–thaw. In general, the recovery percentage of later-age durability indexes of concrete subjected to E-FTCs is lower than that of compressive strength. For concrete subjected to E-FTCs, it is more important to ensure the recovery of later-age durability.publishedVersio

Experimental and numerical assessment of the effectiveness of FRP-based strengthening configurations for dapped-end RC beams

This paper presents experimental and numerical assessments of the effectiveness of strengthening dapped-end reinforced concrete beams using externally bonded carbon fiber reinforced polymers (CFRPs). The research was prompted by a real application, in which the dapped-ends of several precast/prestressed concrete beams developed diagonal cracks due to errors during assembly. Hence, the dapped-ends were strengthened on-site using CFRP plates to limit further crack opening. In the empirical phase of the study, four similar specimens were tested: one unstrengthened reference specimen, two strengthened with high-strength CFRP plates, and one with high-modulus CFRP sheets. The specimens strengthened with plates had slightly higher load carrying capacity than the reference element, but failed by debonding, while the specimens strengthened with sheets showed no increase of capacity and failed by the fibers rupturing. Nonlinear finite element analysis of the specimens under the test conditions indicated that: (a) debonding is more likely to occur at the inner end of dapped-ends and (b) the capacity could have been increased by up to 20% if the plates had been mechanically anchored.The research work was partially supported by research Grant type A No. 27688/2005, awarded by the National University Research Council, Romania. The authors would also like to thank SIKA Romania Corporation for offering the composite systems used in the experimental tests

Assessment of the strengthening effectiveness of EBR and NSM techniques for beams’ dapped-end by FEM analysis

This document presents the work related to the assessment of the effectiveness of strengthening reinforced concrete (RC) dapped-end beams using carbon fiber reinforced polymers (CFRP). Several non-linear finite element analyses were performed using different strengthening configurations, from the simplest solutions to the more complex ones in which different application schemes were overlapped. The work is focused on evaluating the strengthening systems, considering the ultimate capacities they can lead to and the failure modes involved. There were modeled 17 different strengthening configurations. While some of them provided a marginal increase in the ultimate load that can be applied, several of them provided significant load bearing capacity increase. The observed failure modes ranged from a sudden failure of the whole strengthening system up to the desired progressive failure of the individual components of each strengthening system

Influence of large-scale asperities on the stability of concrete dams

For concrete dams founded on rock, there are only a few options in the common analysis methods to account for large‐scale asperities. However, previous research alludes that they have a significant impact on the behaviour of interfaces under shear. This study investigates the behaviour of concrete dam scale models with varying interface geometries, under a realistic set of eccentric loads. The outcome of the scale model tests shows that not only the capacity of the scale models was significantly impacted by the asperities, but also the type of failure in the scale models.Influence of large-scale asperities on the stability of concrete damspublishedVersio

Are available models reliable for predicting the FRP contribution to the shear resistance of RC beams

In this paper the trustworthiness of the existing theory for predicting the FRP contribution to the shear resistance of reinforced concrete beams is discussed. The most well-known shear models for EBR (External Bonded Reinforcement) are presented, commented on and compared with an extensive experimental database. The database contains the results from more than 200 tests performed in different research institutions across the world. The results of the comparison are not very promising and the use of the additional principle in the actual shear design equations should be questioned. The large scatter between the predicted values of different models and experimental results is of real concern bearing in mind that some of the models are used in present design codes

Round robin testing initiative for fiber reinforced polymer (FRP) reinforcement

An international Round Robin Testing (RRT) programme on FRP reinforcement was conducted within the framework of the Marie Curie Research Training Network, ENCORE, and with the support of Task Group 9.3 of the International Federation for Structural Concrete (fib). Eleven laboratories and six manufacturers and suppliers participated in this exercise. As part of this extensive experimental endeavour, one or more of the following tests were performed by the participating laboratories: 1) tensile tests on FRP bars and strips; 2) tensile tests on FRP laminates; 3) double bond shear tests on FRP laminates (Externally Bonded Reinforcement, EBR) and FRP bars/strip (Near Surface Mounted reinforcement, NSM). This paper will discusses the results of the RRT initiative, among which the experimental results of bond tests on concrete specimens strengthened with EBR and NSM FRP