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Volume 15 (1966)
- Issue 2 Pages 23-
- Issue 1 Pages 1-
Volume 15, Issue 2
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Paper
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Hikaru SAITO1966 Volume 15 Issue 2 Pages 23-30
Published: 1966
Released on J-STAGE: August 21, 2013
JOURNAL FREE ACCESSThe paper presents the results of the theoretical analysis of explosive spalling mechanism of precast-and prestressed concrete members in fire.
The explosive spalling is not caused by the steam pressure of the heated water within concrete voids but caused by thermal stress of concrete near the surface.
As the distribution of temperature in concrete near the surface is not linear, thermal stress occurred.
The explosive spalling dose not occur until thermal stress becomes greater than compressive strength of concrete.
According to above opinion, it is possible to explain clearly every phenomenon of explosive spalling prestressed concrete in fire.
Explosive spalling of prestressed concrete member can be avoided by adding fire proof covering to the member surface or applying some kinds of aggregates, which have a small coefficient of thermal expansion at high temperature, to its concrete.View full abstractDownload PDF (558K) -
Tosiro KINBARA, Hiroshi ENDO, Setsuko SEGA1966 Volume 15 Issue 2 Pages 31-37
Published: 1966
Released on J-STAGE: August 21, 2013
JOURNAL FREE ACCESSFollowing the previous study using sheets of paper, the downward smouldering propagation through rod-shaped materials held vertically in a chamber of given temperature was studied both experimentally and theoretically.
The material used were incense-sticks (senko) or cardboards. When a piece of an incense stick is pulverized and squeezed out from a glass tube after being kneaded with water, the rod-shaped paste, when dried, turns into a stick of any radius according to the tube. Rod-shaped samples were also made with paper. A sheet of moistened cardboard was tightly rolled into a circular or rectangular rod and then was bound with a thin thread. It was dried for some days in a furnace before being used.
The material of the rod turns a brownish color before burning and from this it is revealed that the isotherms near the front of smouldering is a plane perpendicular to the rod. As in the case of paper, we derived the following formulae considering the heat balance in the layer near the front.
υ2=8k/c2ρ2(q/(Ti-Ta)-h)(1/r+Δ/r2) for a circular rod,
υ2=8k/c2ρ2(q/(Ti-Ta)-h)(1/b+1/d+4Δ/bd) for a rectangular rod,
where υ = propagation velocity, c = specific heat, ρ = density, Ti = ignition temperature, Ta = ambient temperature, q = a chemical constant depending upon the material and Δ = thickness of the stagnant layer around the rod.
Experimental results showed very good agreement with these formulae and the values of Δ, q, h are all reasonable as shown in the following table.
circular rod rectangular rod
incense stick card board card board
Δ(mm) 2 2 1
q(cal/cm2·s) 0.11 0.13 0.13
h(cal/cm2·deg·s) 1.5×10-4 2.2×10-4 2.2×10-4View full abstractDownload PDF (579K) -
Sizuo YOKOI1966 Volume 15 Issue 2 Pages 38-51
Published: 1966
Released on J-STAGE: August 21, 2013
JOURNAL FREE ACCESSIf the fire spreads from one floor to upstairs in a building, both floors will be enveloped in the flame. Suppose that the space of both floors are communicated with stairs opening. The author has had a question whether, in this case, one common neutral layer appears to both floors or neutral layers appear in each floor respectively. After the big fire broke out in Tōkyū Kaikan in Tokyo, 10th April 1965, the author inspected the state after the fire. This fire broke out in the 7th floor and soon it spread to the 8th floor. Judging from the track of the smoke, attached on the wall of the building, the author found out that neutral layers existed in both floors respectively.
After that, the author attempted to calculate the positions of the neutral layers with a brief model building expressed in Fig. 1 and Fig. 2. This building has a window in each floor. and both floors are communicated with a stair case, whose horizontal opening area is S.
The results of calculation gave the following conclusions :
(1) The positions of the neutral layers depend on the position and size of the window, the room temperature, the ratio of the area of the horizontal opening of the stair to that of the floor.
(2) As the value of this ratio increases, the position of the upstairs’ neutral layer drops down and that of the downstairs’ rises. If this value of ratio exceeds a certain value, the neutral layer does not exist in upper floor but it looks as if it existed in the lower floor.
(3) As the value of this ratio approaches 1, this virtual neutral layer nearly coincides with the neutral layer of the lower floor. In this case, it looks that a common neutral layer exists to both floors.View full abstractDownload PDF (1202K)
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