Experimental investigation of glued-laminated timber beams with Vectran-FRP reinforcement

The growing interest in sustainable buildings has inspired the improvement of timber structures in the construction market. As a raw material, wood may present natural defects that can cause changes in its mechanical properties, such as strength reduction, as well as brittle failure under tension, which limit the application of this material in construction. In recent decades, synthetic fibers with high tensile strength are available as construction material, and research to evaluate the efficiency of synthetic fibers and adhesive composites as a reinforcement for glued-laminated timber beams has been carried out. This paper deals with an experimental study applying bending tests to glue-laminated timber beams made of Pinus Elliottii, a low-strength wood class originated from reforestation, and strengthened with fiber reinforced polymers of Vectran fibers and epoxy adhesive. A numerical procedure based on the finite element method is also developed to compare with experimental results. Vectran is a synthetic thermoplastic fiber with high mechanical properties, however, its potential application as reinforcement material in structural pieces is still poorly explored. The results obtained in this work demonstrated that the application of Vectran-FRP reinforcement to glued-laminated timber beams provided both an increase of 19.48 to 34.95% in elastic regime stiffness and of 7 to 40% in ultimate load, when compared with unreinforced similar beams. Numerical analysis adequately confirmed the experimental results on elastic behavior, while in the non-elastic phase it revealed a considerable difference. A reduction in the rupture coefficient of variation regarding the reinforced beams was also verified. In addition, the application of fibers as structural reinforcement changed the timbefs failure mode from brittle in tension to ductile in compression. The results show that Vectran fibers are mechanically efficient as reinforcement, with perspectives of application in construction202CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQBrazilian National Council for Scientific and Technological Development (CNPq)National Council for Scientific and Technological Development (CNPq); University of Campinas (UNICAMP); School of Civil Engineering, Architecture and Urban Desig

Failure analysis of punching in reinforced concrete flat slabs with openings adjacent to the column

One of the main collapse modes of reinforced concrete flat slabs is the punching of the slab-column connection in which the load is applied in a reduced area. Such condition generates significant shear stresses in the slab region around the column. This failure mode should be avoided in order to provide conditions for the development of reinforcements yielding and bending collapse mechanisms prior to the occurrence of shear failure. Then, brittle failure and progressive collapse are prevented. In this study, 12 flat reinforced concrete slabs with dimensions 1800 mm x 1800 mm x 130 mm without shear reinforcement subjected to symmetrical loading were analysed experimentally. These slabs were divided into three groups according to the amount of openings adjacent to the column. The collapse load values and the failure modes were analysed. The results obtained experimentally were compared with results available in the literature, as well as with responses predicted from the normative instructions18233134

Response Surface Method strategies coupled with NLFEA for structural reliability analysis of prestressed bridges

The Response Surface Method (RSM) has become an essential tool to solve structural reliability problems due to its accuracy, efficacy, and facility for coupling with Nonlinear Finite Element Analysis (NLFEA). In this paper, some strategies to improve the RSM efficacy without compromising its accuracy are tested. Initially, each strategy is implemented to assess the safety level of a highly nonlinear explicit limit state function. The strategy with the best results is then identified and used to carry out a reliability analysis of a prestressed concrete bridge, considering the nonlinear material behavior through NLFEA simulation. The calculated value of is compared with the target value established in Eurocode for ULS. The results showed how RSM can be a practical methodology and how the improvements presented can reduce the computational cost of a traditional RSM giving a good alternative to simulation methods such as Monte Carlo.

5-Lypoxygenase Products Are Involved in Renal Tubulointerstitial Injury Induced by Albumin Overload in Proximal Tubules in Mice

The role of albumin overload in proximal tubules (PT) in the development of tubulointerstitial injury and, consequently, in the progression of renal disease has become more relevant in recent years. Despite the importance of leukotrienes (LTs) in renal disease, little is known about their role in tubulointerstitial injury. The aim of the present work was to investigate the possible role of LTs on tubulointerstitial injury induced by albumin overload. An animal model of tubulointerstitial injury challenged by bovine serum albumin was developed in SV129 mice (wild-type) and 5-lipoxygenase-deficient mice (5-LO(-/-)). The changes in glomerular morphology and nestin expression observed in wild-type mice subjected to kidney insult were also observed in 5-LO(-/-) mice. The levels of urinary protein observed in the 5-LO(-/-) mice subjected or not to kidney insult were lower than those observed in respective wild-type mice. Furthermore, the increase in lactate dehydrogenase activity, a marker of tubule damage, observed in wild-type mice subjected to kidney insult did not occur in 5-LO(-/-) mice. LTB4 and LTD4, 5-LO products, decreased the uptake of albumin in LLC-PK1 cells, a well-characterized porcine PT cell line. This effect correlated with activation of protein kinase C and inhibition of protein kinase B. The level of proinflammatory cytokines, tumor necrosis factor-α and interleukin (IL)-6, increased in mice subjected to kidney insult but this effect was not modified in 5-LO(-/-) mice. However, 5-LO(-/-) mice subjected to kidney insult presented lower macrophage infiltration and higher levels of IL-10 than wild-type mice. Our results reveal that LTs have an important role in tubulointerstitial disease induced by albumin overload