Experimental bond behaviour of GFRP and masonry bricks under impulsive loading

Fibre Reinforced Polymers have become a popular material for strengthening of masonry structures. The performance of this technique is strongly dependent on the bond between the FRP and the substrate. Understanding the strain rate effect on these materials and strengthening techniques is important for proper design and proper modelling of these systems under impacts or blast loads. This work aims to study the behaviour of the bond between GFRP and brick at different strain rates. A Drop Weight Impact Machine specially developed for pull-off tests (single shear tests) is used with different masses and different heights introducing different deformation rates. The strain rate effect on the failure mode, shear capacity and effective bond length is determined from the experimental results. Empirical relations of dynamic increase factors (DIF) for these materials and techniques are also presented.This work was performed under Project CH-SECURE (PTDC/EMC/120118/2010) funded by the Portuguese Foundation of Science and Technology – FCT. The authors acknowledge the support. The first author also acknowledges the support from his PhD FCT grant with the reference SFRH/BD/45436/2008

An overview of digital speech watermarking

Digital speech watermarking is a robust way to hide and thus secure data like audio and video from any intentional or unintentional manipulation through transmission. In terms of some signal characteristics including bandwidth, voice/non-voice and production model, digital speech signal is different from audio, music and other signals. Although, various review articles on image, audio and video watermarking are available, there are still few review papers on digital speech watermarking. Therefore this article presents an overview of digital speech watermarking including issues of robustness, capacity and imperceptibility. Other issues discussed are types of digital speech watermarking, application, models and masking methods. This article further highlights the related challenges in the real world, research opportunities and future works in this area, yet to be explored fully

Experimental Studies on Bond Performance of BFRP bars reinforced Coral Aggregate Concrete

As part of this study, has been developed a numerical method which allows to establish abacuses connecting the normal force with bending moment for a circular section and therefore to predict the rupture of this type of section. This may be for reinforced concrete (traditional steel) or concrete reinforced with steel fibers. The numerical simulation was performed in nonlinear elasticity up to exhaustion of the bearing capacity of the section. The rupture modes considered occur by plasticization of the steel or rupture of the concrete (under compressive stresses or tensile stresses). Regarding the fiber-reinforced concrete, the rupture occurs, usually, by tearing of the fibers. The behavior laws of the different materials (concrete and steel) correspond to the real behavior. The influence of several parameters was investigated, namely; diameter of the section, concrete strength, type of steel, percentage of reinforcement and contribution of concrete in tension between two successive cracks of bending. A comparison was made with the behavior of a section considering the conventional diagrams of materials; provided by the BAEL rules. A second comparative study was performed for fibers reinforced section

Effect of surface stress induced curvature on the eigenfrequencies of microcantilever plates

Ultrasensitive physical, chemical and biological sensors have emerged in the last decade based on the measurement of the eigenfrequencies of micro- and nanosized cantilever plates. Surface stress is omnipresent in these devices due to a variety of factors such as the fabrication process, temperature variations and analyte adsorption. How surface stress influences on the eigenfrequencies of cantilever plates has remained as an unsolved question in physics that has raised a long debate since first experiments in 1975. Recent theoretical models have shed light on the role of the net surface stress. Still, there exists a discrepancy between theory and some experimental reports, affecting to the capability for quantification of these sensors. In this Letter, we present a theoretical framework that demonstrates that the cantilever bending due to differential surface stress between opposite faces of the cantilever, a neglected effect in classical beam theory, plays a relevant role in the stiffness and eigenfrequencies of cantilevers. We develop a new theoretical framework that provides analytical equations that accurately describe the effect of surface stress on the first three vibration modes of cantilevers. Our findings provide the final piece of the puzzle for solving this long-standing problem in physics

Laboratory Tests and Numerical Simulations of CFRP Strengthened RC Pier Subjected to Barge Impact Load

Bridge piers are designed to withstand not only axial loads of superstructures and passingvehicles but also out-of-plane loads such as earthquake excitations and vessel impact loads.Vessel impact on bridge piers can lead to substantial damages or even collapse of bridgestructures. An increasing number of vessel collision accidents have been reported in the pastdecade. A lot of researches have been conducted for predicting barge impact loads and calculatingstructural responses. However, in practice it is not possible to design bridge structures toresist all levels of barge impact loads. Moreover, with an increasing tra±c volume and vesselpayload in some waterways, the bridge piers designed according to previous speci¯cations mightnot be su±cient to resist the current vessel impact loads. Therefore, strengthening existingbridge piers are sometimes necessary for protecting structures from barge impact. Carbon ¯berreinforced polymer (CFRP) has been widely used in strengthening reinforced concrete structuresunder impulsive loadings. It is an e®ective material which has been proven to be able toincrease the °exural strength of structures. In this study, CFRP composites are used tostrengthen reinforced concrete piers against barge impact loads. Pendulum impact tests areconducted on scaled pier models. Impact force and pier response with and without CFRPstrengthening are compared. The e®ectiveness of using CFRP strengthening the pier model isobserved. In addition, numerical models of the bridge piers are developed and calibrated withexperimental results. Parametric simulations of barge impacting on piers with or without CFRPstrengthening are carried out. The results show that compared with unstrengthened pier, CFRPcomposite strengthened bridge pier has a higher impact resistance capacity and hence enduresless structural damage under the same barge impact load. The e®ectiveness of CFRPstrengthening with di®erent CFRP thickness, CFRP strength and bond strength between thepier and the CFRP composite are also discussed