1,720,979 research outputs found
Thermo-mechanical loading of GFRP reinforced thin concrete panels
Full text linkThe experimental investigation is focused on the thermo-mechanical behaviour of thin concrete panels reinforced with GFRP rebars. The considered thin panels (thickness of 4 cm) were exposed to increasing temperature and bending loading. These concrete elements are typical for low bearing function concrete layers in façade claddings. The influence of two aspects was studied: the concrete cover and the external surface of rebars. The heating condition was such that the temperature of the internal GFRP rebars reached about the transition temperature of the resins. This allowed to verify the variation of the deformability and the load carrying capacity of the panels with post-heating bending tests. As main
outcome, the imposed temperature did not generate evident degradation of the GFRP reinforcement and of its adhesion to the concrete, while a reduction of the initial global stiffness was measured
Static and fatigue bond behaviour of GFRP bars and concrete
No full textThe experimental investigation is intended to study the influence of some parameters on the quasi-static and the
fatigue behaviour of the bond between glass fibre reinforced plastic (GFRP) rebars and concrete. This is an
important aspect in FRP reinforced concrete structural elements and of relevant importance in thin reinforced
concrete panels extensively adopted as façade or pavements. The pull-out set-up with eccentrically positioned
GFRP ComBAR® bar was adopted to measure the effect of two parameters on the bond mechanical features:
thickness of the concrete cover and concrete mechanical properties. For cycling tests, another parameter, the
maximum load in the cycle, was introduced to estimate the fatigue life under different load levels. Quasi-static
tests showed that concrete compressive strength influence on bond properties is much more pronounced than that
of the concrete cover. Cyclic tests at highest load level revealed that higher concrete quality attained longer fatigue
life
Experimental investigation of the static and fatigue bond behaviour of GFRP bars and concrete
No full textThe experimental investigation deals with the quasi-static and fatigue behavior of the bond between GFRP (glass fibre reinforced polymer) rebars and concrete. Eccentric pull-out test set-up was adopted to measure the effect of concrete cover and concrete mechanical properties. For cycling tests, the ratio R of the maximum load in the cycle to the static strength was also varied to estimate the fatigue re-sistance under different load levels. GFRP rebars were considered of diameter 8 mm. Specimens were cast with two different concrete classes and bars were positioned according to two concrete covers. Cyclic loading was performed with two load levels. Quasi-static results show similar shear strength for the different concrete covers and the shear strength increases with the concrete mechanical proper-ties. Cyclic tests provide a fatigue life exceeding one million cycles for the minimum load level con-sidered while for the maximum the number of cycles to failure extremely increase considering the higher concrete quality
Thermo-mechanical response of concrete sandwich panels reinforced with glass fiber reinforced polymer bars
No full textThe thermo-mechanical behavior of sandwich panels was experimentally investigated. The panels featured two external concrete layers reinforced with glass fiber reinforced polymer rebars (GFRP) and an internal expanded polystyrene insulation layer. These are typical for low load bearing and thermally insulated panels in façade claddings. To assess the suitability of the internal GFRP reinforcement, the heating condition was such that rebars in one concrete layer were exposed to temperatures higher than the glass transition temperature of the resins. Such extreme condition allowed verifying the retention of the mechanical behavior, in terms of deformability and load-carrying capacity, with bending tests of unheated and heated panels. As main outcome, the elevated temperature produced significant modification of the insulation layer, considerable reduction of global stiffness and load-carrying capacity, while GFRP bars were not apparently modified
Concrete cover effect on the bond of GFRP bar and concrete under static loading
Full text linkPaper presents assessment of bond behaviour between GFRP bars and concrete, investigated through set of centric and eccentric pull-out specimens. Main parameters under investigation are 1) bar external surface, 2) concrete mechanical properties and 3) concrete cover. Corresponding tests with steel reinforcement are performed for comparison in some cases. DIC technique was used for recording and evaluating of strain field on frontal side of eccentric specimens. Consequently, cracking patterns and local bond behaviour are described in details. Increasing of concrete mechanical properties always enhanced bond strength and delayed cracking of concrete cover. Ribbed GFRP bars showed excellent bonding performance when combined with low concrete cover. Their low splitting tendency and specific rib geometry developed better bond behaviour in case of eccentric tests, which showed the possibility of a proper prediction of the bonding behaviour of structural components
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Zum Tragverhalten von Sandwichelementen aus Textilbeton mit schlaffer und vorgespannter Bewehrung
No full textThe combination of high-strength concrete with non-corrosive reinforcement made of carbon fibre reinforced plastic (CFRP) or alkali-resistant (AR) glass creates a high-performance composite material which is characterised by high load-bearing capacity and durability. The use of this composite material in sandwich construction enables the manufacturing of lightweight and slender precast elements for building envelopes with excellent physical properties. The characteristics of the insulation core and its bond properties with the two facings made of textile-reinforced concrete are decisive for the performance of such sandwich elements. In this thesis, the development of two sandwich elements is described, which are designed for use as wall and roof elements, respectively. For the long-span roof elements, a two-component polyurethane (PU) is used as stiff core with high bond strength. To reduce cracking and deflection of the roof elements, the facings are prestressed with CFRP tendons. Due to limited dimensions and thus lower stresses, a soft insulation material and a non-corrosive reinforcement without prestressing are used for the wall elements. In order to analyse the load-bearing and deformation behaviour of the two element types, small-sized test specimens are initially examined. In the next step, the bond properties of the reinforcement materials are determined with pull-out tests and tests on transfer length, while the load-bearing behaviour of the composite material is characterised by tensile tests and four-point bending tests. Tests on small-sized sandwich elements under tensile, compression and shear loads provide information on the sandwich effect and the decisive failure mechanisms. Generally, the sandwich core consists either of a textile connecting device, a foamed PU insulation or a combination of both components. Based on the results, models for describing the load-bearing and deformation behaviour of the small-sized sandwich elements are developed, serving as input values for the calculation approach of the large-sized elements. Finally, large-sized bending tests are conducted to determine the performance of the developed sandwich elements. Based on the sandwich theory of STAMM and WITTE, an analytical model is developed to calculate the load-bearing and deformation behaviour of the large-sized specimens. Spring models with graded spring characteristics are used to implement the textile connecting devices and the foamed PU core as well as their successive failure in the calculation approach. The calculated ultimate loads, deformations and failure mechanisms are in good agreement with the test results of the large-sized sandwich elements
A novel approach for the production and design of load-carrying sandwich panels with reinforced concrete facings
No full textThe demands on contemporary buildings make new construction methods and materials essential. Sandwich elements with high-performance concrete and additional specialized characteristics could fulfill the requirements of sustainable building envelopes with esthetic appeal. The rapidly expanding usage of sandwich elements in the building industry requires more attention with respect to continuous production techniques. The aim of the theoretical and experimental investigations presented in this thesis is to engage with some of the aspects in the production and design of load-carrying sandwich panels with reinforced concrete facings. The main emphasis is placed on the realization of a reliable interface between the core and concrete wythes and providing a suitable analytical model for design purposes. The first part of this thesis is devoted to optimizing the manufacturing efficiency of concrete sandwich elements in the building industry. In close collaboration with industrial partners (The Chemical Company BASF and Rudolph Baustoffwerk GmbH), a new production method has been developed to convert raw PU materials into a finished insulation layer through foaming the PU mixture in pack between two concrete wythes. The bond quality and the load-bearing behavior of the sandwich sections have been investigated by tensile and shear tests. The experimental investigations have proven that specimens with foamed PU obtained 40% higher bond strengths than those produced with standard slabstock foams. Moreover, the repeatability of the bond quality achieved through this new method must be emphasized. The second part of the thesis addresses requirements on buildings of low and medium heights, including structural and architectural considerations. Based on these considerations and the preliminary design of sandwich elements, different cross-sectional geometries were planned for experimental investigations. Furthermore, some solutions for the connection detailing and the load transfer between the panels are provided. In the third part of this thesis, a series of sandwich panels (2:6 m x 1:5 m) were produced. The elements demonstrate that the foaming process is applicable even for large-sized elements, and that a homogeneous bond quality is obtainable. Each panel was cut into five equal segments along the longer dimension in order to perform tests under combined axial and flexural loads. The PU properties showed a negligible scatter of less than 10% compared to small-sized tensile and shear tests. Finally, in the last part of this thesis, an analytical model based on the theory of Stamm and Witte was derived to predict the load-bearing behavior of sandwich panels under combined axial and flexural loading. The model provides a calculation method to determine the ultimate load and considers the cracking of concrete facings. The model was calibrated with results from shear tests. The analytical results are in very good agreement with the aforementioned panel test results. Based on this model, a design approach is presented at the end of this thesis
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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