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Obliczanie strat siły sprężającej w elementach prefabrykowanych zespolonych z nadbetonem

Krzywoń Rafał

Inżynieria i Budownictwo

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2024

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R. 80, nr 3

141--145

PL

W artykule przedstawiono metodę wyznaczania strat siły sprężającej w strunobetonowej konstrukcji zespolonej. Przedstawione rozważania dotyczą w szczególności belek lub płyt, w których strunobetonowy prefabrykat jest zespalany z nadbetonem w fazie montażu. Wskutek zmiany geometrii po zespoleniu, a także różnych właściwości zespalanych betonów oraz zjawisk reologicznych modyfikacji muszą ulec wzory stosowane do obliczania opóźnionych strat siły sprężającej. Szczególne znaczenie ma skurcz nadbetonu, który wywołuje ugięcie i najczęściej wprowadza dodatkowe naprężenia rozciągające w obszarze cięgien sprężających. Zaproponowany tok obliczeń jest rozwinięciem założeń teoretycznych będących podstawą zasad określania strat siły sprężającej przedstawionych w Eurokodzie 2. Zasady te pozwalają uwzględnić wpływ historii obciążenia na przyrost odkształceń pełzania.

XX

The article presents the basics of the analysis of prestressing force losses due to common shrinkage and creep deformations of precast concrete, concrete topping and steel relaxation in a pre-tensioned concrete composite structure. The presented considerations apply to beams or slabs where the pre-tensioned unit is joined with the cast-in-place concrete topping. Due to the change in geometry, as well as various properties and rheological phenomena of the joined concretes, the formulas used to calculate time-dependent prestressing force losses must be modified. Of particular importance is the shrinkage of the concrete topping, which causes deflection and most often introduces additional tensile stresses in the area of the prestressing tendons. The proposed prediction method is an extension of the theoretical assumptions that are the basis for the principles of determining prestressing force losses presented in Eurocode 2. They allow to take into account the influence of load history on the increase in creep strains.

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Experiment of the monitoring prestress loss of prestressed concrete beams with damages under static loading

Wang Jinbo, Li Guodong, Lan Chunguang, Guo Nan

Archives of Civil Engineering

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2023

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Vol. 69, nr 1

437--451

EN

In this paper, based on the feasible method and sensors for the full-scale prestressed monitor, the novel optical fiber sensors and the traditional monitoring sensors will be set up into two prestressed concrete beams with the same geometrical dimensions, material properties, and construction conditions, etc. to investigate the working state of the novel sensors and obtain the evolution law of prestress loss of the prestressed feature component under the static load. The results show that the evolution law of prestress loss of the loaded beam under the condition of no damage state and initial crack is the same as the non-loaded one; however, the prestress loss increases with the increase of time under the situation with the limit crack. The total loss of the prestressed beam with the limit crack is 36.4% without damage. The prestress loss of the prestressed beam under the static load increase with the development of the crack (injury).

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Mosty sprężone: analiza strat sprężania

Stelmasik S.

Builder

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2018

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R.22, nr 8

64--68

EN

This paperwork is concentrated on the analysis of the loss of the compressing as well as temporary and rheological losses. Compared and contracted grounds of their occurrence and share in several losses in reference to final value. Studies were conducted based on taking certain assumptions – more or less pertinent, agreeable to the engineering art. In consequence obtained comparison of the losses and summary, how they impact on the final value of the forces which are taken to dimensioning structures by the designers.

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Pre-stress losses in FRP pre-stressed reinforced concrete – subject overview

Przygocka M., Kotynia R.

Archives of Civil Engineering

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2018

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Vol. 64, nr 4/II

257--268

EN

This paper discuss the issue of pre-stress losses which occur in the FRP prestressed concrete structures. The prestress losses consist of immediate losses just after pre-tensioning of the FRP composite and time-dependent losses. Prestress losses are affected by different factors as strength properties of used materials, ambient temperature, humidity, UV radiation, bond between the FRP material and RC specimen, type of anchorage and creep of prestressing system. Two types of tests can be found in the available literature: material samples subjected to sustained uniaxial tension which verify the relaxation of FRP tendons (Wang et al., Sasaki and Nishizaki, Shi et al and Oskouei and Taleie) and flexural tests of RC beams strengthened with pre-tensioned FRPs (Wang et al.). Authors considered different types of composites: carbon (Wang et al, Sasaki and Nishizaki, Oskouei and Taleie), aramid (Sasaki and Nishizaki, Oskouei and Taleie), glass (Sasaki and Nishizaki), vinyl (Sasaki and Nishizaki) and basalt (Shi et al.).

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Projektowanie konstrukcji sprężonych wg Eurokodu 2. Cz.4.

Derkowski Wit, Surma Mateusz

Builder

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2014

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R.18, nr 5

62--65

EN

It is established fact that the initial prestressing force applied to concrete member continuously decreases with a time. The proper determining of level of prestressing force at each loading stage - from the moment of transter of the force to the concrete, to the different stages at service load, up to the ultimate - is very important. The reduction of prestressing force may be divided into two groups: immediate loses and lime-dependent loses. The rules for the adoption of the initial force and description of the immediate losses of the prestressing force are given in the paper.