15-10-2016, 02:58 PM
1459236720-Firebehaviourofsteelmemberspenetratingconcretewalls.docx (Size: 299.74 KB / Downloads: 8)
. Introduction
It is often desirable for structural steel members to pass through a fire wall or common wall rather than being curtailed on each side of the wall. In such cases, the penetrating member will often be fire protected for a certain length on each side of the wall so as to minimise the possibility of fire spread through heat conduction and excessive temperature rise of the member on the unexposed side of the wall. This latter aspect is necessary to ensure that lateral restraint will continue to be provided to the top of the wall by the member on the unexposed side of the wall, as illustrated in Fig.1. This lateral restraint is necessary to maintain the structural adequacy of the wall.
Such fire protection can be costly and it is not clear that it is necessary. The reasons for this is that although a steel member is heated intensely on one side of a wall, this heat will be readily conducted to the unexposed side where it will be lost by radiation and convection to the surroundings. Some heat will also be conducted into the concrete wall. These mechanisms are illustrated in Fig.2. Transient heat flow analysis can be used to demonstrate dramatic temperature drop across the width of the wall but such calculations need to be confirmed experimentally.
The ability of a penetrating member to act as an effective bracing member depends on the temperature of the member on the unexposed side of the wall: if the member is too hot, it will have insufficient stiffness to provide effective restraint. Similarly, high temperatures could lead to ignition of combustibles should these be in contact with the members on the unexposed side.
The tests [1] described in this paper were undertaken to better assess the above situation. The tests were conducted at the Centre for Environmental Safety and Risk Engineering of Victoria University of Technology.
2. Test set-up, test specimens and instrumentations
2.1 Test Set-up
The tests were conducted in a standard fire test furnace which internally measures 2.1 m width 1.8 m depth 2.1 m height. Fig.3 shows an overall view of the furnace with two test specimens mounted in the side walls of the furnace.
Test Specimens
A total of eight specimens were tested in a series of four tests, each test having two specimens, with one specimen placed in one wall of the furnace and the other in the opposite wall. Each test specimen contained two steel plates, one with dimensions of 2 mm thick x 100 mm wide x 1200 mm long and the other having dimensions of 20 mm thick x 100 mm wide x 1200 mm long. A concrete block of dimensions 365 mm x 385 mm x 120 mm (or 200 mm) thick was cast around the middle section of the length of the steel plates. The concrete block was considered to simulate a fire wall, and the plates chosen simulate the web or flange of a rolled section (in the case of the 20 mm plate) and a purlin penetrating the wall (in the case of the 2 mm plate).
Four specimens were cast in the horizontal position (i.e. with the steel plate vertical) so good compaction of the concrete was obtained. The concrete blocks for the other four specimens were cast with holes to allow grouting of the steel plates once they were located. For two of these specimens, the voids were grouted when the blocks were in the vertical position to simulate a situation that may occur on site. The other two specimens were grouted with the blocks in the horizontal position. Fig. 5 shows the dimensions of a typical specimen with the position of the steel plates and voids in relation to the concrete block.
Instrumentation
Type K mineral insulated thermocouples were used to measure furnace temperatures throughout the tests. The steel temperatures were measured using spot-welded thermocouples attached to the sides and edges of the steel plates. The thermocouple positions are shown in Fig. 7. The positions of furnace thermocouples are also shown in Fig. 7. Copper-disc thermocouples were also attached to the unexposed face of the concrete block to measure the temperatures of the concrete.