An experimental study on the load carrying capacity of cold-formed steel studs and panels

A full-scale experimental study on the structural performance of load-bearing wall panels made of cold-formed steel frames and boards is presented. Six different types of C-channel stud, a total of 20 panels with one middle stud and 10 panels with two middle studs were tested under vertical compression until failure. For panels, the main variables considered are screw spacing (300 mm, 400 mm, or 600 mm) in the middle stud, board type (oriented strand board - OSB, cement particle board - CPB, or calcium silicate board - CSB), board number (no sheathing, one-side sheathing, or two-side sheathing), and loading type (1, 3, or 4-point loading). The measured load capacity of studs and panels agrees well with analytical prediction. Due to the restraint by rivet connections between stud and track, the effective length factor for the middle stud and the side stud in a frame (unsheathed panel) is reduced to 0.90 and 0.84, respectively. The load carrying capacity of a stud increases significantly whenever one- or two-side sheathing is used, although the latter is significantly more effective. It is also dependent upon the type of board used. Whereas panels with either OSB or CPB boards have nearly identical load carrying capacity, panels with CSB boards are considerably weaker. Screw spacing affects the load carrying capacity of a stud. When the screw spacing on the middle stud in panels with one-side sheathing is reduced from 600 mm to 300 mm, its load carrying capacity increases by 14.5 %, 20.6% and 94.2% for OSB, CPB and CSB, respectively.

Debonding and cracking energy release rate of the fiber/matrix interface

An investigation of fiber/matrix interfacial fracture energy is presented in this paper. Several existing theoretical expressions for the fracture energy of interfacial debonding are reviewed. For the single-fiber/matrix debonding and pull-out experimental model, a study is carried out on the effect of interfacial residual compressive stress and friction on interface cracking energy release rate.

Estudo da aderência de barras de aço coladas ao concreto com resina Epóxi.

Assim como em outras áreas do conhecimento a construção civil vem evoluindo ao longo dos anos. Grandes investimentos e elevadas taxas de demandas por novos projetos requerem uma maior velocidade na consolidação de obras. Neste cenário, ficam precários os estudos e pesquisas que avaliam a capacidade de novas tecnologias. Na área do concreto e estruturas de concreto armado, depara-se a associação de técnicas consolidadas à métodos inovadores. A utilização de polímeros como material de construção, como é o caso dos aditivos para concreto, dos tubos e conexões, das esquadrias e como adesivos, utilizados em ligações de aduelas de pontes, associados a fibras de vidro ou carbono para reforços estruturais e para fixação de armaduras ou conectores no caso de reparação de estruturas, oferecendo uma solidarização eficiente entre elementos estruturais. O presente trabalho visa avaliar uma pequena parcela de aplicação de materiais poliméricos, principalmente quanto a sua característica de aderência e colagem de barras de aço ao concreto. O desenvolvimento do estudo ocorreu sobre uma perspectiva de ensaios laboratoriais de arrancamento de barras coladas com resina epóxi em blocos de concreto, sendo estes resultados comparados com barras de aço concretadas em blocos de concreto. Desse modo o principal fator de comparação seria a tensão de aderência desenvolvida na área de contato da barra com o substrato. Alguns parâmetros foram inseridos para uma abordagem de maior amplitude, tais como variação do diâmetro da barra (φ = 10,0mm; φ = 12,5mm e φ = 16,0mm), do comprimento de ancoragem (múltiplos do diâmetro, sendo 5φ e 7,5φ) e da espessura da resina (1mm, 2mm e 3mm). De forma complementar procedeu-se ao ensaio de vigas bi-apoiadas submetidas à flexão visando representar o comportamento de uma recuperação/reforço estrutural aplicado em escala. Para avaliar o comportamento destas vigas, foram ensaiados dois espécimes, uma viga padrão concretada de uma única vez e outra submetida a um reparo estrutural, onde possuía a armadura inferior inserida posteriormente à concretagem inicial, colada com resina epóxi nas extremidades da viga.

Analysis and retrofitting design of a single-span R.C. bridge

This paper deals with the case history of a damaged one-span prestressed concrete bridge on a crucial artery near the city of Cagliari (Sardinia), along the sea-side. After being involved in a disastrous flood, attention has arisen on the worrying safety state of the deck, submitted to an intense daily traffic load. Evident signs of this severe condition were the deterioration of the beams concrete and the corrosion, the lack of tension and even the rupture of the prestressing cables. After performing a limited in situ test campaign, consisting of sclerometer, pull out and carbonation depth tests, a first evaluation of the safety of the structure was performed. After collecting the data of dynamic and static load tests as well, a comprehensive analysis have been carried out, also by means of a properly calibrated F.E. model. Finally the retrofitting design is presented, consisting of the reparation and thickening of the concrete cover, providing flexural and shear FRP external reinforcements and an external prestressing system, capable of restoring a satisfactory bearing capacity, according to the current national codes. The intervention has been calibrated by the former F.E. model with respect to transversal effects and influence of local and overall deformation of reinforced elements. © 2012 Taylor & Francis Group.

Monte Carlo simulation of the compatibility of graft copolymer compatibilized two incompatible homopolymer blends: Effect of graft structure

Compatibility of graft copolymer compatibilized two incompatible homopolymer A and B blends was simulated by using Monte Carlo method in a two-dimensional lattice model. The copolymers with various graft structures were introduced in order to study the effect of graft structure on the compatibility. Simulation results showed that incorporation of both A-g-B (A was backbone) and B-g-A (B was backbone) copolymers could much improve the compatibility of the blends. However, A-g-B copolymer was more effective to compatibilize the blend if homopolymer A formed dispersed phase. Furthermore, simulation results indicated that A-g-B copolymers tended to locate at the interface and anchor two immiscible components when the side chain is relatively long. However, most of A-g-B copolymers were likely to be dispersed into the dispersed homopolymer A phase domains if the side chains were relatively short. On the other hand, B-g-A copolymers tended to be dispersed into the matrix formed by homopolymer B. Moreover, it was found that more and more B-g-A copolymers were likely to form thin layers at the phase interface with decreasing the length of side chain.

Development of a technique to measure the residual strength of woodworm infested timber

This paper presents a study of the residual strength of Pinus sylvestris, which has been subject to attack by the furniture beetle (Anobium punctatum). It is relatively easy to stop the infestation, but difficult to assess the structural soundness of the remaining timber. Removal and replacement of affected structural elements is usually difficult and expensive, particularly in buildings of historic interest. Current on-site assessment procedures are limited. The main object of the study was to develop an on-site test of timber quality: a test which can be carried out on the surface and also at varying depths into the timber. It is based on a probe pull-out technique using a portable load-measuring device. Pull-out force values have been correlated with both strength and energy absorbed as measured by compression testing on laboratory samples of both sound and infested timber. These two relationships are significant and could be used to assess whether remedial work is needed. In addition, work on the use of artificial borings to simulate the natural worming of timber is presented and the findings discussed.

Bond and Interfacial Properties of Reinforcement in Self-Compacting Concrete

This paper reports a study carried out to assess the impact of the use of self-compacting concrete (SCC) on bond and interfacial properties around steel reinforcement in practical concrete element. The pull-out tests were carried out to determine bond strength between reinforcing steel bar and concrete, and the depth-sensing nano-indentation technique was used to evaluate the elastic modulus and micro-strength of the interracial transition zone (ITZ) around steel reinforcement. The bond and interracial properties around deformed steel bars in different SCC mixes with strength grades of 35 MPa and 60 MPa (C35, C60) were examined together with those in conventional vibrated reference concrete with the same strength grades. The results showed that the maximum bond strength decreased when the diameter of the steel bar increased from 12 to 20 mm. The normalised bond strengths of the SCC mixes were found to be about 10-40% higher than those of the reference mixes for both bar diameters (12 and 20 mm). The study of the interfacial properties revealed that the elastic modulus and the micro-strength of the ITZ were lower on the bottom side of a horizontal steel bar than on the top side, particularly for the vibrated reference concrete. The difference of ITZ properties between top and bottom side of the horizontal steel bar appeared to be less pronounced for the SCC mixes than for the corresponding reference mixes.

Finite Element Analysis of Drilling of Carbon Fibre Reinforced Composites

Despite the increased applications of the composite materials in aerospace due to their exceptional physical and mechanical properties, the machining of composites remains a challenge. Fibre reinforced laminated composites are prone to different damages during machining process such as delamination, fibre pull-out, microcracks, thermal damages. Optimization of the drilling process parameters can reduces the probability of these damages. In the current research, a 3D finite element (FE) model is developed of the process of drilling in the carbon fibre reinforced composite (CFC). The FE model is used to investigate the effects of cutting speed and feed rate on thrust force, torque and delamination in the drilling of carbon fiber reinforced laminated composite. A mesoscale FE model taking into account of the different oriented plies and interfaces has been proposed to predict different damage modes in the plies and delamination. For validation purposes, experimental drilling tests have been performed and compared to the results of the finite element analysis. Using Matlab a digital image analysis code has been developed to assess the delamination factor produced in CFC as a result of drilling. © Springer Science+Business Media B.V. 2011.

Measuring specific parameters in pretensioned concrete members using a single testing technique

Pretensioned concrete members are designed and manufactured by using at least two materials: concrete and prestressing reinforcement. Also, two main stages must be considered: prestress transfer and member loading. Hence, the behavior of these members depends strongly on the reinforcement-to-concrete bond performance and prestress losses. In this paper, a testing technique to measure the specific parameters related with the involved phenomena is presented. The testing technique is based on the analysis of series of specimens varying in embedment length to simulate several cross sections at only one end of a pretensioned concrete member. Each specimen is characterized by means of the sequential release of the prestress transfer (detensioning) and the pull-out (loading) operation. The test provides data on prestressing force, transmission length (initial and long-term), anchorage length (without and with slip), reinforcement slips, bond stresses, longitudinal concrete strains, concrete modulus of elasticity, and prestress losses (instantaneous and time-dependent).

Influence of embedded length on strength of BFRP rods bonded parallel to the grain in low grade timber by pullout-bending tests

Bonded-in rod connections in timber possess many desirable attributes in terms of efficiency, manufacture, performance, aesthetics and cost. In recent years research has been conducted on such connections using fibre reinforced polymers (FRPs) as an alternative to steel. This research programme investigates the pull-out capacity of Basalt FRP rods bonded-in in low grade Irish Sitka Spruce. Embedded length is thought to be the most influential variable contributing to pull- out capacity of bonded-in rods after rod diameter. Previous work has established an optimum embedded length of 15 times the hole diameter. However, this work only considered the effects of axial stress on the bond using a pull-compression testing system which may have given an artificially high pull out capacity as bending effects were neglected. A hinge system was utilised that allows the effects of bending force to be taken in to consideration along with axial forces in a pull-out test. This paper describes an experimental programme where such pull-bending tests were carried out on samples constructed of 12mm diameter BFRP bars with a 2mm glueline thickness and embedded lengths between 80mm and 280mm bonded-in to low-grade timber with an epoxy resin. Nine repetitions of each were tested. A clear increase in pull-out strength was found with increasing embedded length.

Characterisation of the cyclic behaviour of reinforced concrete elements with plain bars

Sismos recentes comprovam a elevada vulnerabilidade dos edifícios existentes de betão armado. A resposta das estruturas aos sismos é fortemente condicionada pelas características da aderência aço-betão, que exibe degradação das propriedades iniciais quando sujeitas a carregamentos cíclicos e alternados. Este fenómeno é ainda mais gravoso para elementos com armadura lisa, predominantes na maioria das estruturas construídas até à década de 70 nos países do sul da Europa. A prática corrente de conceção, dimensionamento e pormenorização das estruturas antigas leva a que tenham características de comportamento e níveis de segurança associados não compatíveis com as exigências atuais. Os estudos realizados sobre o comportamento cíclico de elementos estruturais de betão armado com armadura lisa são ainda insuficientes para a completa caracterização deste tipo de elementos. Esta tese visou a caraterização da relação tensão de aderência versus escorregamento para elementos estruturais com armadura lisa e o estudo da resposta cíclica de pilares e nós viga-pilar de betão armado com armadura lisa. Foram realizados dez séries de ensaios de arrancamento (nove monotónicos e um cíclico) em provetes com varões lisos. Os resultados destes ensaios permitiram propor novas expressões empíricas para a estimativa dos parâmetros usados num modelo disponível na literatura para representação da relação tensão de aderência versus escorregamento. É ainda proposto um novo modelo monotónico para a relação tensão de aderência versus escorregamento que representa melhor a resposta após a resistência máxima de aderência. Uma campanha de ensaios unidirecionais em pilares e nós viga-pilar foi também realizada com o objetivo principal de caracterizar o comportamento cíclico deste tipo de elementos. No total foram realizados oito ensaios em pilares, sete ensaios em nós viga-pilar interiores e seis ensaios em nós viga-pilar exteriores representativos de estruturas antigas de betão armado com armadura lisa. Os resultados experimentais permitiram avaliar a influência do escorregamento e estudar o mecanismo de corte em nós e a evolução dos danos para elementos com armadura lisa. Com base nos resultados experimentais foi proposta uma adaptação na expressão do Eurocódigo 8-3 para o cálculo da capacidade última de rotação de elementos com armadura lisa. Foi também desenvolvido um estudo paramétrico, com diferentes estratégias de modelação não linear, para a simulação da resposta de pilares considerando o escorregamento da armadura lisa. Por último, foi proposto um novo modelo simplificado trilinear para o aço que contempla o efeito do escorregamento da armadura lisa.

Study of bond behaviour between FRP reinforcement and concrete

El uso de barras de materiales compuestos (FRP) se propone como una alternativa efectiva para las tradicionales estructuras de hormigón armadas con acero que sufren corrosión en ambientes agresivos. La aceptación de estos materiales en el mundo de la construcción está condicionada a la compresión de su comportamiento estructural. Este trabajo estudia el comportamiento adherente entre barras de FRP y hormigón mediante dos programas experimentales. El primero incluye la caracterización de la adherencia entre barras de FRP y hormigón mediante ensayos de pull-out y el segundo estudia el proceso de fisuración de tirantes de hormigón reforzados con barras de GFRP mediante ensayo a tracción directa. El trabajo se concluye con el desarrollo de un modelo numérico para la simulación del comportamiento de elementos de hormigón reforzado bajo cargas de tracción. La flexibilidad del modelo lo convierte en una herramienta flexible para la realización de un estudio paramétrico sobre las variables que influyen en el proceso de fisuración.

Farmer experience of pluralistic agricultural extension, Malawi

Purpose: Malawi’s current extension policy supports pluralism and advocates responsiveness to farmer demand. We investigate whether smallholder farmers’ experience supports the assumption that access to multiple service providers leads to extension and advisory services that respond to the needs of farmers. Design/methodology/approach: Within a case study approach, two villages were purposively selected for in-depth qualitative analysis of available services and farmers’ experiences. Focus group discussions were held separately with male and female farmers in each village, followed by semi-structured interviews with 12 key informants selected through snowball sampling. Transcripts were analysed by themes and summaries of themes were made from cross case analysis. Findings: Farmers appreciate having access to a variety of sources of technical advice and enterprise specific technology. However, most service providers continue to dominate and dictate what they will offer. Market access remains a challenge, as providers still emphasize pushing a particular technology to increase farm productivity rather than addressing farmers’ expressed needs. Although farmers work in groups, providers do not seek to strengthen these to enable active interaction and to link them to input and produce markets. This limits farmers’ capacity to continue with innovations after service providers pull out. Poor coordination between providers limits exploitation of potential synergies amongst actors. Practical implications: Services providers can adapt their approach to engage farmers in discussion of their needs and work collaboratively to address them. At a system level, institutions that have a coordination function can play a more dynamic role in brokering interaction between providers and farmers to ensure coverage and responsiveness. Originality/value: The study provides a new farmer perspective on the implementation of extension reforms.

Human carrying capacity and human health

The silence around overpopulation prevents the global health community from making the necessary link between the planner's limited ability to support its people and health and development crises. The author describes how popular thinking on population control has been shaped over the last 200 years and how out failure to address the population explosion may be one cause of recent epidemics and social unrest.

Gifted education, professional development and the contemporary landscape of teachers' work : challenges and choices

This paper examines the perspectives of primary school teachers, administrators and personnel working in eastern suburban Melbourne as they consider the rationale for, and the purposes of, gifted education within the broader landscape of teachers' work. The data for this presentation are drawn from a single case qualitative case study where semi-structured interviews were held four years after the school participated in the Bright Futures gifted professional development. The school proudly proclaims a tradition of scholarship and excellence within a friendly, caring, cooperative and democratic ethos. Teachers welcomed the opportunity to express their thoughts, sentiments and opinions on curriculum, assessment and reporting practices, their attitudes to the aims of gifted education, the selection of children for pull-out programs, and their views to school management and to parents in relation tho these matters. Using a Foucoultian framework, I analyse how teachers juggle many goals within the complex reality of daily classroom teaching, and how they are wedged between the power of formal school rhetoric and educational policy working to improve learning outcomes for all students. This, in turn, has significant repercussions for addressing the needs of gifted students and generates considerable ambivalence about the implementation of gifted programs. I propose that such responses are important elements in the contemporary landscape of teacher's work