Wyniki wyszukiwania - BazTech

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Theoretical and experimental in-service long-term deflection response of symmetrically and non-symmetrically reinforced concrete piles

Hernández-Montes E., Fernández-Ruiz M. A., Carbonell-Márquez J. F., Gil-Martín L. M.

Archives of Civil and Mechanical Engineering

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2017

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Vol. 17, no. 2

433--445

EN

Reinforced concrete piles employed in earth retaining systems are typically designed with symmetric reinforcement. The non-symmetric RC wall piles have recently been introduced by the authors, obtaining savings of up to 50% in weight in longitudinal reinforcing steel compared with the traditional solutions, leading to significant financial savings while also reducing associated environmental impacts. The structural behavior of this new RC member under long-term loading is studied, comparing it with its symmetrical counterpart. An experimental campaign has been carried out. Full scale specimens with circular cross sections symmetrically and asymmetrically reinforced were tested. Results have shown that asymmetrically RC pile developed a slightly higher deflection than its symmetrical counterpart. A new expression for the effective area of concrete in tension applicable to non-symmetrical piles is introduced. Moreover, a new stress–strain law for cracked concrete that accounts the tension stiffening effect for long-term loading is proposed. Finally, for non-symmetrical RC wall piles, the evolution of the parameter that takes into account the duration of loading in deformations is presented. Although more evidence is needed, it is shown that tension stiffening effect contribution could be overestimated by Eurocode 2 in the case of non-symmetrically or underestimated in case of symmetrically RC piles.

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Probability calibration of load duration modification factor for timber roofs in the Polish mountain zones

Domański T.

Archives of Civil Engineering

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2014

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Vol. 60, nr 2

195--208

EN

The resistance parameters of timber structures decrease with time. It depends on the type of load and timber classes. Strength reduction effects, referred to as creep-rupture effects, due to long term loading at high stress ratio levels are known for many materials. Timber materials are highly affected by this reduction in strength with duration of load. Characteristic values of load duration and load duration factors are calibrated by means of using probabilistic methods. Three damage accumulation models are considered, that is Gerhard [1] model, Barret, Foschi[2] and Foshi Yao [3] models. The reliability is estimated by means of using representative short- and long-term limit states. Time variant reliability aspects are taken into account using a simple representative limit state with time variant strength and simulation of whole life time load processes. The parameters in these models are fitted by the Maximum Likelihood Methods using the data relevant for Polish structural timber. Based on Polish snow data over 45 years from mountain zone in: Zakopane – Tatra, Świeradów – Karkonosze, Lesko – Bieszczady, the snow load process parameters have been estimated. The reliability is evaluated using representative short – and long –term limit states, load duration factor kmod is obtained using the probabilistic model.

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Badania zespolonych słupów stalowo-betonowych poddanych długotrwałym obciążeniom

Szmigiera E.

Przegląd Budowlany

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2011

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R. 82, nr 10

67-71

PL

Przedstawiono wyniki badań laboratoryjnych, przeprowadzonych na modelach zespolonych słupów stalowo-betonowych, poddanych działaniu obciążeń długotrwałych. Powstające od tych obciążeń odkształcenia nie są najważniejszym czynnikiem, uwzględnianym przy zniszczeniu konstrukcji zespolonych, jednakże mogą mieć istotny wpływ na użytkowalność i trwałość tych konstrukcji. Celem przedstawianych badań była próba ustalenia jakościowego wpływu pełzania betonu na pracę zespolonych słupów stalowo-betonowych wybranego typu, także w odniesieniu do słupów żelbetowych.

EN

The paper describes research on the long-term behaviour of steel-concrete composite columns. During investigation, fourteen models of columns were tested. The cross-sections of seven composite elements were consisted of partially encased steel I-shape HE120A. The elements were 1200 mm high. Additionally, the seven models were made of reinforced concrete with the same dimension of cross-section and height as composite models. At the beginning, six elements were loaded to the failure. Other models were investigated under long-term load and after a year were loaded to the failure. The paper also presents the results of those investigations. The bahaviour of composite models under long-term loading is analyzed in comparison with elements made of reinforced concrete.

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Investigation of timber-concrete composite beams under long term loading

Kanocz J., Bajzecerova V.

Zeszyty Naukowe Politechniki Rzeszowskiej. Budownictwo i Inżynieria Środowiska

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2009

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z. 52 [264]

71-78

EN

Experimental investigation of timber-concrete composite beams subjected to long term loading is presented. The first type of experimentally tested timber-concrete composite beams consisting from the vertically nailed timber planks with concrete deck on the top. Shear connection between the concrete layer and timber members by grooves in timber was realized, which guarantee the composite action of two layers. The second type of the composite beams consists from separated vertically oriented timber planks in certain distance covered by OSB sheet and from fiber reinforced concrete layer on the top. Shear transfer between the timber planks and upper layers by the pair of steel screws spaced along the timber beams was realized. Three by three from both types of beams to four point bending tests was exposed. Experimental results with existing theoretical models are compared.

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Non-linear physical relations for reinforced concrete elements under long-term loading

Balevicius R., Simbirkin V.

International Journal of Applied Mechanics and Engineering

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2005

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Vol. 10, no 1

5-20

EN

The paper presents a method for modelling material non-linearity for use in the analysis of load-carrying capacity and deformations of reinforced concrete beams, columns and membrane-bending plates subjected to long-term loads. Physical relationships expressing relations between internal forces and stresses, strains and stiffness are derived on the basis of the fracture and creep theories for concrete and using non-linear stress-strain diagrams modified for time effects. A specific implementation technique of a genetic algorithm is developed to find multiple solutions to non-smooth problems under consideration. The computation technique proposed is found to be effective in numerical examples, and an adequate accuracy of the analysis is verified by comparison with experimental data.

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Cell deformation in response to long-term hyperosmotic loading

Van Donkelaar C.C., Daniels M.A., Huyghe J.M.R.J.

Acta of Bioengineering and Biomechanics

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2003

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Vol. 5, nr 1

3-10

EN

Hypertrophic and elongated cells are found in differentiation zones of load-bearing tissues, where tissue hyperosmotic. In this paper we study if, in response to long-term hyperosmotic loading, cells are -affected with hypertrophy or elongation, and whether these responses are cell-specific. Surface adhesion and elongation of CHO-K1 and C2C12 cells were determined with CLSM, after 2 and 5 days of culture in 380 mOsmol medium. Results show that both cell types increase an adhesion area (p < 0.001 for CHO-K1 cells, p < 0.01 for C2Cl2 cells), independent of the method used to increase osmotic pressure. Despite the differences :dl types (CHO-K1 cells are smaller (p < 0.001) and their morphological changes are more pronounced). aspect ratio remains constant for all cell types and experimental conditions (p > 0.1). Conclusively, all cells hypertrophy, but do not elongate under hyperosmotic loading. Quantitatively, CHO-K1 cells respond more than C2C12 cells.