Post-fire serviceability and residual strength of composite post-tensioned concrete T-beams

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.

Fire spalling behavior of high-strength concrete: A critical review

“…Postcooling spalling can therefore be regarded as reasonable [85]. In another investigation, the sloughing-off spalling type of thermal-chemical spalling was seen in all test specimens at exceptionally high temperatures (700 °C and 800 °C) [91]. Samples showed signs of post-cooling thermal-chemical spalling in the form of a web of microscopic cracks after cooling.…”

“…-Due to internal cracking induced by differing thermal expansions of aggregate and strength loss caused by chemical transitions [89][90][91].…”

The Thermal Effects on the Self-Compacting Concrete Beams Exposed to the Fire

“…The onset of thermal stresses with the appearance of capillary cracks, and the expansion of the crack width [9] Figure 3, then cracks appear in other places far from the source of the fire. The advanced stages of the thermal effect begin with a temperature rise along the cross-section height, until the temperature of the reinforcing bars rises, creating a noticeable thermal gradient between the cover and the reinforcing bars, that leads to the breakup and separation of the cover, and damage to the surface of the concrete element.…”

“…Many researchers have studied the fire behavior of concrete elements, their studies included the evaluation and analysis method of reinforced concrete, by exposing a structure or member to experimental fire independently and then analyzing the results [9]. and there are several studies that have focused on the effects of fire on reinforced concrete members made of classical concrete (RC), and their behavior in this disaster [11].…”

Flexural Behavior (Load-Strain Curve) of Reinforced Concrete Beams Covered by Gypsum Layers and Exposed to Elevated Temperatures

“…Gypsum and plaster vacuoles are filled with water. Izzet and AL-Dulffy [1] studied the resistance of post-tensioned concrete beams when exposed to high temperatures, where they investigated the effect of residual bending strength when burning. It was used three types of temperature and two types of air cooling, the second with water, and the burning time is one hour.…”