Influence of bond stress-slip relationship on bond strength prediction

The study of the bond stress-slip relationship of FRP (fibre reinforced polymer) adhered to concrete has been a key point to understand the bond behaviour of externally bonded reinforcement (EBR) and near surface mounted (NSM) systems. Researchers have made an effort to determine bond-slip relationships through experimental and analytical/numerical methods, although they have not obtained univocal results. The area under the bond stress-slip relationship, representing the fracture energy, is one of the main parameters to make bond strength predictions. The fracture energy may be divided in two parts: elastic and softening contribution. These parts act both in a different way in predicting the failure load and the effective transfer length. In this paper the influence of the shape of the bond stress-slip relationship on the prediction of the bond strength and transfer length is investigated. Hereby, a comparison is made between the bilinear bond stress-slip relationship (linear elastic ascending branch-linear softening branch) and the elastic-exponential bond stress-slip relationship (linear elastic ascending branch-exponential softening branch)

Fire endurance and residual strength of insulated concrete beams strengthened with near surface mounted reinforcement

The comparatively weak performance of fiber-reinforced polymer (FRP) strengthened members under fire exposure is a primary factor hindering the application of FRP strengthening in buildings in which fire risk is not negligible. As part of a larger ongoing study investigating the behavior of FRP strengthening systems under fire exposure, an investigation was set up to examine and document the performance of six full-scale near-surface mounted (NSM) FRP-reinforced concrete beams exposed to 1h of fire. All the specimens were preloaded to the service load of the strengthened member. Tests results indicated that, if appropriately insulated, the NSM FRP-strengthened beams can achieve a satisfactory fire endurance of 1h as per fire resistance test specifications. Moreover, this paper also presents a study on the residual performance of fire-tested beams. Results of this study suggest that if the insulation system is able to maintain the adhesive temperature at relatively low value ( for the beam configuration in this test program), the FRP concrete bond degradation under fire is limited, and the FRP-strengthened beam can retain a large part (up to 92% in this test program) of its original strength

Fire tests on RC beams strengthened with NSM

The use of Near Surface Mounted (NSM) FRP for strengthening and rehabilitation of reinforced concrete structures has been the subject of various research projects in recent years. FRP strengthening systems are known to perform weak at elevated temperatures. This can be attributed to the relatively poor performance of both adhesive and FRP matrix polymers at temperatures in the range of their glass transition temperatures. Hence, there is a need for thermal protection of such elements. An investigation on the fire endurance of NSM FRP concrete beams under standard fire conditions was undertaken. Six reinforced concrete beam were strengthened in flexure with NSM bars and insulated with different insulation system. Temperatures and deflections were measured during fire testing. Test results indicated that insulated NSM FRP strengthened beams can achieve a fire endurance of at least two hours

Automatic security assessment for next generation wireless mobile networks

Abstract. Wireless networks are more and more popular in our life, but their increasing pervasiveness and widespread coverage raises serious security concerns. Mobile client devices potentially migrate, usually passing through very light access control policies, between numerous and heterogeneous wireless environments, bringing with them software vulnerabilities as well as possibly malicious code. To cope with these new security threats the paper proposes a new active third party authentication, authorization and security assessment strategy in which, once a device enters a new Wi-Fi environment, it is subjected to analysis by the infrastructure, and if it is found to be dangerously insecure, it is immediately taken out from the network and denied further access until its vulnerabilities have been fixed. The security assessment module, that is the fundamental component of the aforementioned strategy, takes advantage from a reliable knowledge base containing semantically-rich information about the mobile node under examination, dynamically provided by network mapping and configuration assessment facilities. It implements a fully automatic security analysis framework, based on AHP, which has been conceived to be flexible and customizable, to provide automated support for real-time execution of complex security/risk evaluation tasks which depends on the results obtained from different kind of analysis tools and methodologies. Encouraging results have been achieved utilizing a proof-of-concept model based on current technology and standard open-source networking tools

Distributed Temporal Link Prediction Algorithm Based on Label Propagation

Link prediction has steadily become an important research topic in the area of complex networks. However, the current link prediction algorithms typically neglect the evolution process and they tend to exhibit low accuracy and scalability when applied to large-scale networks. In this article, we propose a novel distributed temporal link prediction algorithm based on label propagation (DTLPLP), governed by the dynamical properties of the interactions between nodes. In particular, nodes are associated with labels, which include details of their sources, and the corresponding similarity value. When such labels are propagated across neighbouring nodes, they are updated based on the weights of the incident links, and the values from same source nodes are aggregated to evaluate the scores of links in the predicted network. Furthermore, DTLPLP has been designed to be distributed and parallelised, and thus suitable for large-scale network analysis. As part of the validation process, we have designed a prototype system developed in Pregel, which is a distributed network analysis framework. Experiments are conducted on the Enron e-mails and the General Relativity and Quantum Cosmology Scientific Collaboration networks. The experimental results show that compared to the most of link prediction algorithms, DTLPLP offers enhanced accuracy, stability and scalability

Energy-oriented denial of service attacks: an emerging menace for large cloud infrastructures

This work analyzes a new and very subtle kind of security threat that can affect large-scale cloud-based IT service infrastructures, by exploiting the computational resources of their component data center to waste as much energy as possible. The consequence of these threats ranges from increased costs in the energy bill, to penalization for exceeding the agreed quantity of greenhouse gases (GHG) emissions, up to complete denial of service caused by electrical outages due to power budget exhaustion. We analyzed different types of such attacks with their potential impacts on the energy consumption, modeled their behavior and quantified how current energy-proportional technologies may provide attackers with great opportunities for raising the target facility emissions and costs. These efforts resulted in a simple model with some parametric reference values that can be used to estimate the impact of such attacks also in presence of very large infrastructures containing thousands or millions of servers.Peer ReviewedPostprint (author's final draft