Abstract
In this study, the response of ten composite post-tensioned concrete beams topped by a reinforced concrete deck with adequate reinforcing shear connectors is investigated. Depending on the concrete compressive strength of the deck slab (20, 30, and 40 MPa), beams are grouped into three categories. Seven of these beams are exposed to a fire attack of 700 and 800 °C temperature simultaneously with or without the presence of a uniformly distributed sustained static loading. After cooling back to ambient temperature, these composite beams are loaded up to failure, using a force control module, by monotonic static loading in a four-point-bending setup with two symmetrical concentrated loads applied in the middle third of the effective span. The objectives of this study include investigating the behavior of the composite prestressed concrete beams under and after the exposure to a direct fire flame, as well as finding their residual load-carrying capacity. Tests demonstrate significant deteriorations caused by exposure to high temperatures associated with the increase of the member’s camber. The increase of the midspan camber after heating exposure reached approximately 200%. On the other hand, the 1-h steady-state exposure of test specimens to temperatures of 700 and 800 °C led to reduce the load-carrying capacity of the heat-deteriorated beams up to 45% and 54%, respectively.
Highlights
Introduction and research significanceReinforced concrete is considered as the most versatile construction material used in structural engineering applications
The increase of the midspan camber after heating exposure to 700 °C reached 200, 209.1, and 227.3% in specimens with a top flange of 20, 30, and 40 MPa design compressive concrete strength, respectively. Whereas this increase after heating exposure of 700 °C and 800 °C in the presence of the superimposed loading attained (181.8 and 190.9%) and (190.9 and 200%) in beams with a concrete flange of 30 and 40 MPa, respectively. This evidence attributes to the increased deteriorations that occur in the concrete of the top flange with higher compressive strengths that are caused by the increase in density and the decrease in porosity that affects the thermal conductivity of the concrete
By right, unlike the concrete in compression flange, the longitudinal steel reinforcement in the tension zone is considered a key parameter that determines the length of the exploitation period of the composite post-tensioned concrete members subjected to fire exposure and to static loading
Summary
Introduction and research significanceReinforced concrete is considered as the most versatile construction material used in structural engineering applications. Composite post-tensioned concrete T-beams have been widely implemented in civil and industrial concrete structures, where their fire resistance is highly dependent on their configuration, the constituent of materials used in their fabrication, the type, and intensity of the applied load, and the characteristics of the fire itself. These composite systems consist of two components of different initial stress statement, different concrete strengths, and different ages. The two components were connected together by shear connectors to enable performing under the applied load as one unit
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