Flexão composta : análise comparativa REBAP vs. EC2

No contexto actual nacional, o dimensionamento de estruturas de betão armado tem sido maioritariamente efectuado em conformidade com a norma nacional, o Regulamento de Estruturas de Betão Armado e Pré Esforçado (REBAP). Com a aprovação, no passado recente, do Eurocódigo 2 (EC2) a nível europeu, antevê-se que em breve lhe seja atribuído o estatuto de norma nacional, através da publicação de um texto idêntico. Em termos gerais o EC2, quando comparado com o REBAP, apresenta diferenças consideráveis na forma e no conteúdo que se repercutem no dimensionamento das estruturas de betão armado. Perante este cenário torna se imperioso efectuar estudos comparativos entre as duas normas aos mais diferentes níveis. O caso particular do dimensionamento à flexão ao nível da secção transversal em elementos estruturais lineares, que tem por base a hipótese de Navier Bernoulli (secções planas antes e após a deformação), recorre a leis tensões extensões de cálculo dos materiais intervenientes: o betão e o aço. As propostas do REBAP e do EC2 para definir estas leis são ligeiramente diferentes. Em trabalhos anteriores demonstrou se que as diferenças obtidas no dimensionamento de secções rectangulares à flexão simples adoptando as duas regulamentações (REBAP e EC2) são marginais. No presente trabalho pretende se avaliar a mesma diferença, mas desta feita para o caso em que o elemento estrutural se encontra sujeito a flexão composta. Deste modo, o objectivo é o de analisar a influência das diferenças que existem entre o REBAP e o EC2 ao nível dos diagramas tensões extensões de cálculo para os materiais betão e aço, no dimensionamento de secções rectangulares à flexão composta. No presente trabalho descreve se o estudo comparativo efectuado, assim como as principais conclusões obtidas

3D behaviour of a 4 parameter isotropic nonlinear hardening plasticity model for concrete

In general, concrete is a highly nonlinear material with great dependence on the confining stresses, a type of behaviour also common in other granular and quasi-brittle materials. The CEB-FIP Model Code [1] recommends the use of a four-parameter failure criterion to estimate the strength of concrete under multiaxial states of stress. This failure criterion is also known as the Ottosen failure criterion, and it captures with high accuracy the behaviour of these materials, as demonstrated by several researchers, performing experimental test programs. The concrete strength estimation takes into account, with great precision, the effect of the increase in the confining stresses. In order to simulate the monotonic quasi-static multiaxial behaviour of concrete, one possible strategy is to introduce in this failure criterion a hardening parameter and the corresponding evolution law, under the isotropic behaviour framework. In the present work, the concrete compressive strength in the Ottosen failure criterion is assumed as the hardening parameter, and the CEB-FIP Model Code 90 law for the uniaxial nonlinear behaviour of concrete is used to derive the hardening law. In this case, the loading surface is not explicitly defined as a function of the hardening parameter, as in the other more common and simpler isotropic models. As a consequence, some difficulties may emerge, mainly of a numerical nature. In this context, the formulation of the model in a thermodynamically consistent framework is presented. The general behaviour of this model is accessed by the simulation of the monotonic multiaxial loading of concrete elements, and its numerical efficiency is discussed

Conference report : FRPRCS11-11th International Symposium on Fiber Reinforced Polymer for Reinforced Concrete Structures

The 11th International Symposium on Fiber Reinforced Polymer for Reinforced Concrete Structures (FRPRCS11), an event co-sponsored by IIFC, was held 26-28 June at the Vila Flor Cultural Centre of Guimarães City, in Portugal. Following peer review, 148 extended abstracts and full papers were accepted and published in the proceedings. Approximately 170 delegates representing 38 countries and 137 institutions were in attendance. The distribution of papers by theme is indicated in Table 1, where the tendency for a significant research effort on the “Reinforcement and strengthening performance of FRP systems” is clear, forming about one third of the accepted publications. The FRPRCS11 was composed of 20 sessions of 20 minutes presentations including about 5 minutes for discussion of each. The high technical/scientific level of the publications, and especially the enthusiastic and fruitful discussions which occurred during the presentations were highly remarked upon by the conference participants. Prof. Brahim Benmokrane and Prof. Stijn Matthys provided two stimulating keynote lecturers which provided extraordinary contribution to the motivation and enthusiasm of the delegates, and the scientific quality of FRPRCS11. The closing ceremony ended with the announcement of the chairman of the next FRPRCS conference, Prof. Zhishen Wu, who in 2015 will host FRPRCS12 in Nanjing, China

Chemical abundances and kinematics of barium stars

In this paper we present an homogeneous analysis of photospheric abundances based on high-resolution spectroscopy of a sample of 182 barium stars and candidates. We determined atmospheric parameters, spectroscopic distances, stellar masses, ages, luminosities and scale height, radial velocities, abundances of the Na, Al, $alpha$-elements, iron-peak elements, and s-process elements Y, Zr, La, Ce, and Nd. We employed the local-thermodynamic-equilibrium model atmospheres of Kurucz and the spectral analysis code {\sc moog}. We found that the metallicities, the temperatures and the surface gravities for barium stars can not be represented by a single gaussian distribution. The abundances of $alpha$-elements and iron peak elements are similar to those of field giants with the same metallicity. Sodium presents some degree of enrichment in more evolved stars that could be attributed to the NeNa cycle. As expected, the barium stars show overabundance of the elements created by the s-process. By measuring the mean heavy-element abundance pattern as given by the ratio [s/Fe], we found that the barium stars present several degrees of enrichment. We also obtained the [hs/ls] ratio by measuring the photospheric abundances of the Ba-peak and the Zr-peak elements. Our results indicated that the [s/Fe] and the [hs/ls] ratios are strongly anti-correlated with the metallicity. Our kinematical analysis showed that 90% of the barium stars belong to the thin disk population. Based on their luminosities, none of the barium stars are luminous enough to be an AGB star, nor to become self-enriched in the s-process elements. Finally, we determined that the barium stars also follow an age-metallicity relation.Comment: 30 pages, 26 figures, 18 tables, accepted for publication in MNRA

Performance assessment of overlay strengthened masonry under cyclic loading using the diagonal tensile test

Masonry elements with structural purposes can be found not only in historical heritage constructions, but also in residential buildings constructed during the last decades. With the aim of making these structures less vulnerable to seismic events, several strengthening techniques have been developed. One technique, recently considered of great potential, is based on the application of mortar and a FRP mesh embedded in that layer. The simple procedure of application and the use of relatively affordable materials seem to lead to economically competitive retrofitting solutions with great performance. In this paper the in-plane monotonic and cyclic characterization by means of diagonal tensile test of a high ductility strengthening system is presented. The discussion of results is mostly focussed on the analysis of the vulnerabilities of the masonry strengthening system, particularly regarding the behaviour of the interface between the overlay and the retrofitted substrate

Assessment of overlay masonry strengthening system under in-plane monotonic and cyclic loading using the diagonal tensile test

The development of novel strengthening techniques to address the seismic vulnerability of masonry elements is gradually leading to simpler, faster and more effective strengthening strategies. In particular, the use of fabric reinforced cementitious matrix systems is considered of great potential, given the increase of ductility achieved with simple and economic strengthening procedures. To assess the effectiveness of these strengthening systems, and considering that the seismic action is involved, one important component of the structural behaviour is the in-plane cyclic response. In this work is discussed the applicability of the diagonal tensile test for the assessment of the cyclic response of strengthened masonry. The results obtained allowed to assess the contribution of the strengthening system to the increase of the load carrying capacity of masonry elements, as well as to evaluate the damage evolution and the stiffness degradation mechanisms developing under cyclic loading.This research was carried in the framework of InoTec, Innovative material of ultra-high 16 ductility for the rehabilitation of the built patrimony, funded by COMPETE/QREN/FEDER 17 (NORTE-07-0202-FEDER-023024). InoTec project is promoted by CiviTest company 18 and University of Minho. S&P Clever Reinforcement Ibérica is gratefully acknowledged 19 for providing the materials used in the strengthening of the masonry specimens

Comparative susceptibility of southern and western corn rootworm adults and larvae to vATPase-A and Snf7 dsRNAs.

Corn rootworms (CRW) are the most important corn pests in the U.S. Corn Belt. Damage is caused by larval feeding on the plant roots. RNAi has been studied in CRW and has proven to be effective for the management of this insect with effects on both larval and adult stages. The objective of this study was to determine comparative susceptibility of adult and larva of Southern Corn Rootworm (SCR) and Western Corn Rootworm (WCR) to two different lethal RNAi target genes (vacuolar (v)-ATPase-A and Snf7). Adults and larvae were exposed to dsRNAs overlaid on artificial diet five times every other day. WCR larval susceptibility to vATPase-A was approximately 4-fold more tolerant than SCR, but were similar for Snf7 (2.6 ng/cm2 for both species). For adults, LC50s were generally higher for vATPase-A dsRNA relative to larvae with a 20-fold higher LC50 for WCR (SCR=33.3 ng/cm2; WCR=657.3 ng/cm2) relative to Snf7 dsRNAs (SCR=13.2 ng/cm2; WCR=60.2 ng/cm2). Gene silencing was also evaluated in adults and larvae exposed to the LC50 dsRNAs, and gene knockdown ranged from 48% up to 83% in adults fed for eight days in dsRNA, and from 55% to 89% in larvae fed for 24, 48 and 72 h, compared to control treatments. This is the first study to report LC50 values for dsRNA in WCR and SCR adults. The results indicate that both larvae and adults of both species were affected by vATPase-A and Snf7 dsRNAs suggesting that RNAi for the management of CRW should be considered for both stages

Influence of adhesive stiffness on the post-cracking behaviour of CFRP-reinforced structural glass beams

Reinforcement strategies have been developed to prevent catastrophic failures of glass structures after cracking. In this context, the composite action between glass and reinforcement plays a crucial role in the post-cracking performance of glass composite systems. Hence, this paper presents an experimental and numerical investigation on glass-CFRP composite beams manufactured using three different adhesives, with high, intermediate and low stiffness. The experimental programme comprised (i) mechanical characterization tests, (ii) tensile tests on double-lap joints and (iii) flexural tests on composite beams. Moreover, numerical simulations were carried out aiming at providing reliable numerical tools for the design of glass structural elements. Bending tests have shown that it is possible to obtain ductile failure modes in glass elements reinforced with CFRP laminates, sometimes attaining or surpassing the cracking load during the post-cracking phase, depending on the type of adhesive. On the other hand, glass-CFRP composite beams manufactured with stiff, moderate and flexible adhesives were well simulated (i) neglecting the physical existence of the adhesive layer, (ii) assuming the linear elastic behaviour of the adhesive, and (iii) modelling the bond behaviour of the adhesive joint, respectively.This work is financed by the national funds through Fundação para a Ciência e a Tecnologia, IP (FCT), under the grant agreement [SFRH/BD/122428/2016] attributed to the 1st author. This work was partly financed by FCT/MCTES through national funds (PIDDAC) under the R&D Unit Institute for Sustainability and Innovation in Structural Engineering (ISISE), under reference UIDB/04029/2020

Feasibility of mechanical post-tensioning of annealed glass beams by activating externally bonded Fe-SMA reinforcement

The structural concept of post-tensioned glass systems has been investigated to minimize the unpredictable response of structural glass in tension. The Fe-SMAs have been successfully explored for strengthening existing structures due to their advantages in comparison with the conventional reinforcement materials. In particular, the recently developed Fe-17Mn-5Si-10Cr-4Ni-1VC (mass-%) alloy seems sustainable and shows promising properties for the construction industry. This study investigates the feasibility of post-tensioning glass beams by activating externally bonded Fe-SMA strips. The investigation is mainly focussed on (i) the activation process of Fe-SMA strips, with temperatures ranging between 120 °C and 160 °C, and (ii) the advantages of this reinforcement for post-tensioning of glass structural elements, in terms of applicability and structural response. Flexural tests show that it is possible to obtain ductile failure modes when glass beams are reinforced with passive or activated Fe-SMA strips. Activation of Fe-SMA strips resulted in an increase of up to 30 % of the cracking load.The first author wishes to acknowledge the grant SFRH/BD/122428/2016 provided by Fundação para a Ciência e a Tecnologia, IP (FCT), financed by European Social Fund and by national funds through the FCT/MCTES. This work was partly financed by FCT / MCTES through national funds (PIDDAC) under the R&D Unit Institute for Sustainability and Innovation in Structural Engineering (ISISE), under reference UIDB/04029/2020

Comportamento de painéis de alvenaria reforçados com FRCM sujeitos a ações no plano: Estudo da interface

O presente trabalho dedica-se à caracterização do comportamento de modelos de alvenaria reforçada com FRCM (fiber reinforced cementitious matrix) quando sujeitos a ações que atuam no plano da parede. O sistema de reforço, composto por uma camada de argamassa cimentícia reforçada com uma malha de CFRP (carbon fiber reinforced polymer), foi aplicado a modelos de alvenaria de tijolo furado. Considerando a importância da interface entre a camada de reforço e o substrato para a eficiência do sistema de reforço, procedeu-se à caracterização do comportamento mecânico da interface por intermédio de ensaios de corte direto, com os quais foi possível definir as superfícies de cedência e de rotura da interface. Os resultados obtidos permitiram a quantificação dos parâmetros que caracterizam a interface entre o material cerâmico e uma argamassa do tipo PFRM (polypropylene fibre reinforced mortar) quando sujeita a cargas de corte combinadas com cargas normais à interface. Através de expressões analíticas e do critério de rotura de Mohr-Coloumb foi analisada a adequação de um critério baseado numa aproximação linear, aos dados obtidos experimentalmente.Projeto InoTec - Material inovador de ultra-alta ductilidade para a reabilitação do património construído, financiado pelo COMPETE / QREN / FEDER (NORTE-07-0202-FEDER-02302