Post‐Fire Mechanical Properties of Steel S900MC

Abstract

This paper discusses mechanical properties after one heating and cooling cycle using experimental tests. The material tested was steel S900MC, which has the nominal yield strength of 900 N/mm2. The specimens were tested with being first heated up inside a furnace to a pre‐defined temperature, then cooled down to the room temperature. I n order to study the effects of cooling rates on mechanical properties, two different cooling methods were used: cooling inside furnace, and cooling in the air. The results indicated a clearly reduction of the strength when the steel was cooled from the temperature above 500 °C. The steel reduced 40% of its yield strength after cooled from 700°C, while only 20% remained when cooled from 900°C. The elastic modulus was regained to its original value after the steel was cooled from temperatures below 500°C, whereas about 80% was regained when the steel was cooled from 900°C. Cooling temperatures between 700°C and 900°C produced a large scatter among all the mechanical properties. The cooling rate did not affect the mechanical properteis when the maximum temperature remains below 700 °C before the cooling starts. However, when exposed to an elevated temperature above 700°C the effect is visible. The air‐cooled specimens had higher strength and lower ductility than furnace cooled specimens. The results of this study will help to evaluate the load‐bearing capacity and reusability of the steel members after fire‐exposure.

Impact of Firefighting Sprays on the Fire Performance of Structural Steel Members

“…The truss beams had local temperatures as high as 1100°C and the cooled down temperatures as low as 200°C, but the vertical displacement did not exceed the displacement limit criterion demonstrating an efficient load redistribution in the truss beam system. The material tests in [16] showed that, when the steel was cooled from 700°C to 900°C to room temperature, it had about 40% and 20% retention in strength, respectively. Therefore, the effect of the reduced strength on the structural response after cooling stage as well as the effects of different heating-cooling-heating cycles on the strength reserve needs further research.…”

“…One of the defensive actions that can be adopted is structural cooling where the aim is to cool the load bearing elements to prevent structure failure. But as sudden cooling of structural elements at high temperatures (> 600°C) can result in significant change in material properties and load bearing capacity [16,17], it is unclear how the structural cooling affects the safety of the building. In large openframe buildings (floor area > 500 m 2 ) with unprotected structural elements, both the fire and the fire intervention may contribute to the risk of structural failure.…”

Behavior of fin-plate connection of a composite beam subjected to different fire scenarios

“…To examine the behaviour of simple connections between composite beams and column in fire, two benchmark tests (CB-3 and CB-4) performed at Purdue University [17] were selected for creating FE models. The test setup and the specimen details are shown in Figure 1 and Figure 2.…”

“…The surface cooling or the gas cooling was intended to simulate the two cooling scenarios where either the structural member is cooled directly or the fire itself is cooled directly. A cooling rate of 40℃/min was selected as used in [17] for cooling the tensile coupon of S900 in air. The cyclic heating and cooling condition can occur in the travelling fire scenarios as reported in [5] or in applying the water sprays to the beam as reported in [6].…”