Vytautas Tamulenas

Deformation Analysis of RC Ties Externally Strengthened with FRP Sheets

The current study has two objectives: to validate the ability of the Atena finite-element software to estimate the deformations of reinforced concrete (RC) elements strengthened with fiber-reinforced polymer (FRP) sheets and to assess the effect of FRP-to-concrete bond strength on the results of numerical simulation. It is shown that the bond strength has to be selected according to the overall stiffness of the composite element. The numerical results found are corroborated experimentally by tensile tests of RC elements strengthened with basalt FRP sheets.

Mechanical Behavior of Steel Fiber-Reinforced Concrete Beams Bonded with External Carbon Fiber Sheets

This study investigates the mechanical behavior of steel fiber-reinforced concrete (SFRC) beams internally reinforced with steel bars and externally bonded with carbon fiber-reinforced polymer (CFRP) sheets fixed by adhesive and hybrid jointing techniques. In particular, attention is paid to the load resistance and failure modes of composite beams. The steel fibers were used to avoiding the rip-off failure of the concrete cover. The CFRP sheets were fixed to the concrete surface by epoxy adhesive as well as combined with various configurations of small-diameter steel pins for mechanical fastening to form a hybrid connection. Such hybrid jointing techniques were found to be particularly advantageous in avoiding brittle debonding failure, by promoting progressive failure within the hybrid joints. The use of CFRP sheets was also effective in suppressing the localization of the discrete cracks. The development of the crack pattern was monitored using the digital image correlation method. As revealed from the image analyses, with an appropriate layout of the steel pins, brittle failure of the concrete-carbon fiber interface could be effectively prevented. Inverse analysis of the moment-curvature diagrams was conducted, and it was found that a simplified tension-stiffening model with a constant residual stress level at 90% of the strength of the SFRC is adequate for numerically simulating the deformation behavior of beams up to the debonding of the CFRP sheets.

Experimental Investigation of the Capacity of Steel Fibers to Ensure the Structural Integrity of Reinforced Concrete Specimens Coated with CFRP Sheets

The capacity of steel fibers to ensure the structural integrity of reinforced concrete specimens coated with CFRP sheets was investigated. Test data for four ties and eight beams reinforced with steel or glass-FRP bars are presented. Experiments showed that the fibers significantly increased the cracking resistance and altered the failure character from the splitting of concrete to the debonding of the external sheets, which noticeably increased the load-carrying capacity of the strengthened specimens.

Steel Fibres: Effective Way to Prevent Failure of the Concrete Bonded with FRP Sheets

Although the efficiency of steel fibres for improving mechanical properties (cracking resistance and failure toughness) of the concrete has been broadly discussed in the literature, the number of studies dedicated to the fibre effect on structural behaviour of the externally bonded elements is limited. This experimental study investigates the influence of steel fibres on the failure character of concrete elements strengthened with external carbon fibre reinforced polymer sheets. The elements were subjected to different loading conditions. The test data of four ties and eight beams are presented. Different materials were used for the internal bar reinforcement: in addition to the conventional steel, high-grade steel and glass fibre reinforced polymer bars were also considered. The experimental results indicated that the fibres, by significantly increasing the cracking resistance, alter the failure character from splitting of the concrete to the bond loss of the external sheets and thus noticeably increase the load bearing capacity of the elements.

Experimental Investigation on Short- and Long-Term Deformations of Cracked Reinforced Concrete Ties

The current study reports the test results on deformations of cracked reinforced concrete (RC) ties. Four ties were tested under shortand long-term loading for 315 days. To perform the long-term tests, four testing rigs were constructed. The experimental results were compared with the Model Code 2010 predictions. It was revealed that the code overestimates the cracking load by 65-90%, and it is most likely due to the neglect of the shrinkage effect. It has been shown that 30-45% of the strain increment due to the long-term loading occurred during the first two-three days. The deformations of RC ties have practically stabilized after almost 300 days. The code quite accurately predicted the ultimate long-term strains. However, the prediction model was found to be too simplified to assess the increment of the long-term deformations. INTRODUCTION Structures are designed to satisfy both strength and serviceability requirements. In consequence of the extensive studies, the ultimate load behavior of reinforced concrete (RC) flexural members is well understood. Nevertheless, due to the use of refined ultimate state theories as well as higher strength materials, resulting in structures with longer spans and smaller depths, control of deformations is often the governing design criterion. Adequate modelling of cracking and, particularly, post-cracking behavior, as one of the major sources of physical nonlinearity, is the most important and difficult task of structural mechanics. Complex physical phenomena, such as concrete creep, shrinkage, and cracking greatly contribute to deformation increments: the long-term deformations might increase up to 3-4 times above the initial values (Gribniak et al. 2013). Most of the studies of the long-term deformations of RC members were dedicated to the investigation of bending members and only a few experimental programs were devoted to RC ties (Jaccoud 1987, Beeby and Scott 2005, Wu and Gilbert 2008, Vilanova et al. 2014). To fill this gap, the current study reports experimental results of four RC ties tested under short-term and under sustained load for a period of 315 days. The results gathered from the short-term experiments were compared to the deformations predicted by the Model Code 2010. CONCREEP 10 958