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Fire resistance of hollow load-bearing wall tile
268
U.S.
BUREAU OF STANDARDS NOTES.
[J. t:. I.
In the construction of the panels four sets of duplicates were made containing, respectively, hydrated lime, lime plus coarse impurity, lime plus medium impurity, and lime plus fine impurity. For convenience in reference, the 1923 report on the panels which have undergone change since then is given below, together with comments on their condition in December, 1928. H y d r a t e No. 5 plus iron carbonate. (1923) The hydrate itself shows a few pops and cracks. The additions of iron carbonate seem to have no effect. (I928) Decided map cracking has developed on the panels containing lime without impurity. Numerous cracks and pops have occurred on the panels containing coarse and medium impurity; some have occurred on the panels containing fine impurity. Hydrate No. 6 plus quicklime. (1923) The fine quicklime shows no noticeable effect; the medium shows a few additional pops, and the popping of the coarse particles is quite apparent. (I928) Numerous pops have developed on the panels containing fine quicklime. Hydrate No. Io plus lime burned during hydration. (I923) The coarse particles caused a few pops; with the medium size the pops are almost negligible; and the fine material caused no popping. (1928) Considerable cracking appears in the panels containing medium and fine burned lime. Hydrate No. I I plus tannic acid (fine). (I923) The surface is badly checked and discolored. (I928) Several large pops are noticeable. The results of this later inspection indicate that while in the majority of cases defects which develop in lime plaster are noticeable at the end of a year, certain impurities may cause defects which are only apparent after several years' aging. FIRE RESISTANCE OF HOLLOW LOAD-BEARING WALL TILE.
THE results of comprehensive tests to determine the fire resistance value of hollow clay wall tile conducted in cooperation with the Hollow Building Tile Association are
Feb., I92!i.]
U. S. BUREAU OF STANDARDS NOTES.
269
reported in the J a n u a r y n u m b e r of the Bureau of Standards Journal of Research. (Research Paper No. 37, 334 pages. Reprints obtainable from Superintendent of D o c u m e n t s at 75 cents per copy.) While hollow clay tile has been used in this country for about 5o years in floor arches, partitions and as protection for structural members, only during the past 2o years has it been extensively applied for load-bearing purposes in walls. T h e safe and economical use of this material as of other masonry materials, requires knowledge of its strength and fire resistance under conditions imposed by severe fires. Fire resistance of walls is rated mainly on ability to keep the temperatures of the side away from the fire to a point where they will not ignite combustible materials in contact with the wall. Ability to carry load t h r o u g h o u t the fire and to withstand the impact from hose streams are also necessary conditions. The a m o u n t of damage incurred and m e t h o d s of making repairs are also of interest. T h e work reported in the paper consists in the main of three series of fire tests of wall construction built of tile of representative designs and clay materials. The first tests were made on wall sections I foot wide and 6 feet high t h a t were subjected to fire on one side while under working load, the main object of the tests being to determine how the fire exposure affects the individual tile units. This was found to vary with the type of clay used, hardness of burning and design of the unit, from minor cracking of a few of the units in the specimen, to failure under load a little after 2 hours. T h e second group of tests was with wall specimens 4 feet wide and 4 feet high tested exposed to fire on one side, under load or restrained within the containing frames, and was made to study the effect of changes in design of the unit, and in the constitutents and preparation of the clay. Addition of ground b u r n t clay (grog) to the raw clay in a m o u n t s up to 2 per cent. was found to be without effect, b u t higher percentages increased the fire damage, apparently because of initial shrinkage cracks radiating from the grog particles. Additions of sawdust to the raw clay in a m o u n t s up to 15 per cent. by volume decreased the tendency to cracking when exposed to fire without seriously decreasing the VOL. 207, NO. I238--I 9
270
U.S.
BUREAU OF STANDARDS NOTES.
[J. F. I.
normal strength of the tile. Fine grinding and greater a m o u n t of pugging of the raw clay increased the strength of the tile and consequently its load-carrying ability when exposed to fire. Of modifications in the design of the unit, one with double outside shells improved the fire resistance for all b u t very dense tile in confining the cracking mainly to an outer thin shell. Increased shell thickness was also found to decrease the fire effects~ as also fillets of up to ~ inch radius at the junctions of shells and webs. T h e final series consisted of I67 fire endurance tests and four fire and water tests of typical wall constructions, 7I of which were made with walls between Io and I I feet high and 8 to I6 feet wide. T h e thickness ranged from 8 to I6 inches, and plaster, stucco, or brick facing was applied on a n u m b e r of the walls. The walls were subjected to constant applied loads of 7o to I2O lbs./in. ~ during the fire test, were restrained within the containing frames, or were tested unrestrained, the latter condition being representative of walls in low buildings or the upper story walls of higher buildings. T h e results are summarized as fire resistance periods, which are determined by the time the walls sustained load under fire exposure and prevented the average temperature rise on the unexposed side from exceeding I39 ° C. (25o ° F.), or the m a x i m u m rise at any point where t e m p e r a t u r e measurements are takeia from exceeding I8o.6 ° C. (325 ° F.). Freedom from cracks or openings large enough to transmit flame or ignite combustible materials is also required both in fire endurance tests and fire and water tests. T h e final grouping of test results is in three classes, determined by the design of the tile. Fire resistance periods are given for 8, I2, and I6 inch walls in each class, the values varying with the thickness and design from I to I I hours for unplastered walls and from 4 to 15 hours for walls plastered on both sides. Periods are also given for wails assumed to have combustible members projecting into t h e m 4 inches from the unexposed side, this being determined by the time required for temperatures high enough to ignite wood to obtain at the given d e p t h in the wall. Fire resistance periods for this condition ranged from one hour with 8-inch unplastered walls to Io hours with I6-inch plastered walls built of tile of the designs giving the highest results.
Feb., ~Oz!~.l
lj. S. BUREAU OF STANDARDS NOTES,
27I
G y p s u m and portland cement plasters applied on one or both sides of the wall constructions not only increased their fire resistance periods b u t t h a t on the side exposed to fire also appreciably decreased the fire effects on individual units and the construction generally. \Vhere applied on split furring tile, plaster was found to prevent all fire damage to the loadbearing tile in fire tests lasting as long as six hours.
U.S.
BUREAU OF STANDARDS NOTES.
[J. t:. I.
In the construction of the panels four sets of duplicates were made containing, respectively, hydrated lime, lime plus coarse impurity, lime plus medium impurity, and lime plus fine impurity. For convenience in reference, the 1923 report on the panels which have undergone change since then is given below, together with comments on their condition in December, 1928. H y d r a t e No. 5 plus iron carbonate. (1923) The hydrate itself shows a few pops and cracks. The additions of iron carbonate seem to have no effect. (I928) Decided map cracking has developed on the panels containing lime without impurity. Numerous cracks and pops have occurred on the panels containing coarse and medium impurity; some have occurred on the panels containing fine impurity. Hydrate No. 6 plus quicklime. (1923) The fine quicklime shows no noticeable effect; the medium shows a few additional pops, and the popping of the coarse particles is quite apparent. (I928) Numerous pops have developed on the panels containing fine quicklime. Hydrate No. Io plus lime burned during hydration. (I923) The coarse particles caused a few pops; with the medium size the pops are almost negligible; and the fine material caused no popping. (1928) Considerable cracking appears in the panels containing medium and fine burned lime. Hydrate No. I I plus tannic acid (fine). (I923) The surface is badly checked and discolored. (I928) Several large pops are noticeable. The results of this later inspection indicate that while in the majority of cases defects which develop in lime plaster are noticeable at the end of a year, certain impurities may cause defects which are only apparent after several years' aging. FIRE RESISTANCE OF HOLLOW LOAD-BEARING WALL TILE.
THE results of comprehensive tests to determine the fire resistance value of hollow clay wall tile conducted in cooperation with the Hollow Building Tile Association are
Feb., I92!i.]
U. S. BUREAU OF STANDARDS NOTES.
269
reported in the J a n u a r y n u m b e r of the Bureau of Standards Journal of Research. (Research Paper No. 37, 334 pages. Reprints obtainable from Superintendent of D o c u m e n t s at 75 cents per copy.) While hollow clay tile has been used in this country for about 5o years in floor arches, partitions and as protection for structural members, only during the past 2o years has it been extensively applied for load-bearing purposes in walls. T h e safe and economical use of this material as of other masonry materials, requires knowledge of its strength and fire resistance under conditions imposed by severe fires. Fire resistance of walls is rated mainly on ability to keep the temperatures of the side away from the fire to a point where they will not ignite combustible materials in contact with the wall. Ability to carry load t h r o u g h o u t the fire and to withstand the impact from hose streams are also necessary conditions. The a m o u n t of damage incurred and m e t h o d s of making repairs are also of interest. T h e work reported in the paper consists in the main of three series of fire tests of wall construction built of tile of representative designs and clay materials. The first tests were made on wall sections I foot wide and 6 feet high t h a t were subjected to fire on one side while under working load, the main object of the tests being to determine how the fire exposure affects the individual tile units. This was found to vary with the type of clay used, hardness of burning and design of the unit, from minor cracking of a few of the units in the specimen, to failure under load a little after 2 hours. T h e second group of tests was with wall specimens 4 feet wide and 4 feet high tested exposed to fire on one side, under load or restrained within the containing frames, and was made to study the effect of changes in design of the unit, and in the constitutents and preparation of the clay. Addition of ground b u r n t clay (grog) to the raw clay in a m o u n t s up to 2 per cent. was found to be without effect, b u t higher percentages increased the fire damage, apparently because of initial shrinkage cracks radiating from the grog particles. Additions of sawdust to the raw clay in a m o u n t s up to 15 per cent. by volume decreased the tendency to cracking when exposed to fire without seriously decreasing the VOL. 207, NO. I238--I 9
270
U.S.
BUREAU OF STANDARDS NOTES.
[J. F. I.
normal strength of the tile. Fine grinding and greater a m o u n t of pugging of the raw clay increased the strength of the tile and consequently its load-carrying ability when exposed to fire. Of modifications in the design of the unit, one with double outside shells improved the fire resistance for all b u t very dense tile in confining the cracking mainly to an outer thin shell. Increased shell thickness was also found to decrease the fire effects~ as also fillets of up to ~ inch radius at the junctions of shells and webs. T h e final series consisted of I67 fire endurance tests and four fire and water tests of typical wall constructions, 7I of which were made with walls between Io and I I feet high and 8 to I6 feet wide. T h e thickness ranged from 8 to I6 inches, and plaster, stucco, or brick facing was applied on a n u m b e r of the walls. The walls were subjected to constant applied loads of 7o to I2O lbs./in. ~ during the fire test, were restrained within the containing frames, or were tested unrestrained, the latter condition being representative of walls in low buildings or the upper story walls of higher buildings. T h e results are summarized as fire resistance periods, which are determined by the time the walls sustained load under fire exposure and prevented the average temperature rise on the unexposed side from exceeding I39 ° C. (25o ° F.), or the m a x i m u m rise at any point where t e m p e r a t u r e measurements are takeia from exceeding I8o.6 ° C. (325 ° F.). Freedom from cracks or openings large enough to transmit flame or ignite combustible materials is also required both in fire endurance tests and fire and water tests. T h e final grouping of test results is in three classes, determined by the design of the tile. Fire resistance periods are given for 8, I2, and I6 inch walls in each class, the values varying with the thickness and design from I to I I hours for unplastered walls and from 4 to 15 hours for walls plastered on both sides. Periods are also given for wails assumed to have combustible members projecting into t h e m 4 inches from the unexposed side, this being determined by the time required for temperatures high enough to ignite wood to obtain at the given d e p t h in the wall. Fire resistance periods for this condition ranged from one hour with 8-inch unplastered walls to Io hours with I6-inch plastered walls built of tile of the designs giving the highest results.
Feb., ~Oz!~.l
lj. S. BUREAU OF STANDARDS NOTES,
27I
G y p s u m and portland cement plasters applied on one or both sides of the wall constructions not only increased their fire resistance periods b u t t h a t on the side exposed to fire also appreciably decreased the fire effects on individual units and the construction generally. \Vhere applied on split furring tile, plaster was found to prevent all fire damage to the loadbearing tile in fire tests lasting as long as six hours.