Size effect on masonry subjected to out-of-plane loading

Size effect is a key aspect of masonry mechanics. This salient feature of quasi-brittle materials, which is mostly governed by the post-peak behavior of masonry and not by the randomness of the material strength, has been adopted in concrete codes but not in the new European code – Eurocode 6. In this paper, theoretical and experimental evidence of size effect in masonry subjected to flexure is presented, demonstrating the need of defining the flexural strength as a function of the width of the masonry wall

Contribution to design criteria for industrialized masonry vaults

Technical report 03-DEC/E-1

Caracterização do comportamento da ligação entre betões de distinta classe de resistência

Comunicação apresentada no Encontro Nacional Betão Estrutural 2004, Porto, Portugal, 17 - 19 Nov. 2004.O incremento do momento flector resistente que a técnica de reforço baseada na fixação de laminados de CFRP no betão de recobrimento de estruturas laminares de betão armado, por vezes, fica limitado pela extensão máxima de compressão aplicável ao betão. Nestes casos, a conjugação deste sistema de reforço com a aplicação de uma camada de compressão de betão reforçado com fibras de aço (BRFA) permite aumentar significativamente a resistência à flexão deste tipo de estruturas. Este trabalho é dedicado ao estudo da ligação entre camada de BRFA e o betão da estrutura a reforçar.Fundação para a Ciência e Tecnologia - SFRH/BD/11232/2002. “Companhia Geral de Cal e Cimento S.A. (SECIL)”. Sika S.A. “Central do Pego”. “Pedreiras Bezerras”. Bekaert NV. “Bettor MBT Portugal Produtos Químicos para Construção S.A.”

Efficient strengthening technique to increase the flexural resistance of existing RC slabs: NSM CFRP laminates and compressive thin bonded SFRC overlay

Technical report 09-DEC/E-0

Efficient strengthening technique to increase the flexural resistance of existing RC slabs

Composite materials are being used with notable effectiveness to increase and upgrade the flexural load carrying capacity of reinforced concrete (RC) members. Near-Surface Mounted (NSM) is one of the most promising strengthening techniques, based on the use of carbon fiber-reinforced polymer (CFRP) laminates. According to NSM, the laminates are fixed with epoxy based adhesive into slits opened into the concrete cover on the tension face of the elements to strength. Laboratory tests have shown that the NSM technique is an adequate strengthening strategy to increase the flexural resistance of RC slabs. However, in RC slabs of low concrete strength, the increase of the flexural resistance that NSM can provide is limited by the maximum allowable compressive strain in the compressed part of the slab, in order to avoid concrete crushing. This restriction reduces the effectiveness of the strengthening, thus limiting the use of the NSM technique. A new thin layer of concrete bonded to the existing concrete at the compressed region is suitable to overcome this limitation. Volumetric contraction due to shrinkage and thermal effects can induce uncontrolled cracking in the concrete of this thin layer. Adding steel fibers to concrete (Steel Fiber Reinforced Concrete - SFRC), the post cracking residual stress can be increased in order to prevent the formation of uncontrolled crack patterns. In the present work, the combined strengthening strategy, a SFRC overlay and NSM CFRP laminates, was applied to significantly increase the flexural resistance of existing RC slabs. Experimental results of four-point bending tests, carried out in unstrengthened and strengthened concrete slab strips, are presented and analyzed

CFRP group effect and interaction between stirrups and strips on the NSM-shear strengthening of RC beams

Available experimental research shows that the technique based on installing Carbon Fibre Reinforced Polymer (CFRP) strips into slits opened on the cover concrete of the beam’s lateral faces, designated as Near Surface Mounted (NSM), is very effective to increase the shear resistance of reinforced concrete (RC) beams. However, recent research has revealed that, in terms of NSM shear strengthening effectiveness, a detrimental effect can occur between existing steel stirrups and applied strips, as well as amongst the strips when the distance between strips, sf, is lower than a certain limit. In the present work, a test setup was developed and an experimental program was carried out to assess the influence of both sf and interaction between existing steel stirrups and strips on the shear strengthening of RC beams. The experimental program is described and the main results are presented and analyzed.(13-05-04-FDR-00031

Numerical modeling of single shell roofs

Relatório 03-DEC/E-2

Design of RC thin surface structures

Technical report 04-DEC/E-0

On bonding repairing steel fibre reinforced concrete to hardened concrete

In the last years an emerging repair and strengthening technique for concrete slabs has been used, consisting of applying a thin layer of steel fibre reinforced concrete (SFRC) onto the existent concrete slab. The performance of the structural system depends on the bonding behaviour between old and new concretes. Adhesives based on epoxy resins currently make this liaison. The prices of these adhesives are quite different depending, mainly, on the percentage of pure resin that they include. In the present paper, three commercial adhesive compounds of distinct prices and properties were selected to bond concrete base and repairing SFRC overlay. The bond behaviour was assessed from pull-off tests and the influence of the strength class of concrete base and repairing SFRC was analysed. Finally, the performance of the adhesives was evaluated, considering both the bond strength and their prices.Fundação para a Ciência e a Tecnologia (FCT) - PhD grant SFRH/BD/11232/2002

Sistema híbrido em materiais compósitos para reforço de lajes de betão armado

O desempenho em termos de aumento da resistência à flexão da técnica de reforço que combina laminados de CFRP à tracção com camada de compressão em betão reforçado com fibras de aço (BRFA), foi avaliado experimentalmente, efectuando-se ensaios em faixas de lajes maciças sem reforço (controlo), reforçadas apenas com laminados de CFRP, e duplamente reforçadas com laminados de CFRP e camada de BRFA. Os resultados obtidos permitem concluir que esta estratégia de reforço é eficaz, tanto para o estado limite de serviço (ELS) quanto para o estado limite último (ELU)