BRICK WALLS

Wanganui Chronicle, Volume 74, Issue 229, 28 September 1931, Page 10

BRICK WALLS

LATERAL PRESSURES AN “EARTHQUAKE” TEST REMARKABLE RESISTANCE. WELLINGTON, Sept. 25. Brick, as a material for building homes and public edifices, has come in for a good deal of criticism since the Napier earthquake, for the reason that a large proportion of the buildings iu that district were of brick, and many of them collapsed, but it is the carefully considered opinion of architects who have studied the subject that brick is as dependable a building material as any other if the work is faithfully done. This opinion was strenghtened in the minds of many architects, engineers, and inspectors who witnessed a remarkable test carried out yesterday afternoon at the Amalgamated Brick and Pipe Company’s (Ltd.) works at Miramar. There were present members of the engineering staffs of the Wellington. Harbour Board, Bailway Department, Public Works Department, City Council, prominent architects and structural engineers, as well as Dr. Adams, the Government Seismologist, and many prominent builders. Nature of Test. The test was of the lateral strength of brick walls. A nine-inch brick panel, ten feet high and twelve feet wide, had been built inside a concrete frame. The bricks were the ordinary double frogged double pressed bricks made by the company, bonded by three-to-one cement mortar, without reinforcement of any kind. The frame surrounding them was reinforced with 5-8 inch steel rods. The test carried out was the application of steady horizontal pressure to the centre of the panel> by means of a hundred-ton hydraulic jack, on which pressure was superimposed a heavy blow. The wall stood a total pressure of 15 tons. This is equivalent a uniform pressure of 560 pounds on every square foot of the brick panel. If this wall had been used as a floor it would stand before fracture a uniform pressure of 470 pounds on every square foot of surface, and would be suitable for aw office floor with a factor of safety of four, states Mr. Peter Holgate, M.N.Z. Soc. C.E.M.I. C.E., Struct. E. (London), who conducted the experiments. These were carried out with the idea of simulating the action of an earthquake on a reinforced concrete or steel-framed building with brick panels. Methods Used. The whole of the pressure was applied by a plate measuring eighteen inches by six inches, against which the head of the jack pushed. A strong wooden box filled with pig iron, working on a four-foot lever, was raised by a screw to engage with a trigger, and when this was tripped a system of levers added a blow of several tons to the steady pressure of the hydraulic jack. On a former test, it was found that the unsupported wall leaned away from the pressure, and that accurate readings of the deflection of the wall in response to tho pressure were therefore not obtainable. On this occasion strong anglo-steel clamped the mechanism to the back of the surrounding reinforced concrete frame, and with its head “in chancery” the wall had to tell the truth. Gradually Increased Pressures. The test took some time, because it was desired to obtain data over a series of experimental pressures. At a combined pressure of 2.75 tous, the deflection was only .07in, at 3.39 tons .10in, and at 6 tons 0.1 Siu. When tho steady pressure of tho jack was raised to 6 tons, and the tripped box of gradually added pig iron delivered a blow in addition of four tons, making a total of eleven tons of horizontal pressure, of which nearly half was suddenly applied, the deflection was .3in. With a seven-ton pressure and a five-ton blow, the deflection increased to ,4in. So far the wall, despite tho repeated application of these heavy pressures to the limited space of the 18in by 6in plate, shojved no cracks or signs of cracking and it was not until successive pressures of 13, 14, and 15 tons, consisting of a blow remaining constant at five tons, and a hydraulic pressure increas-

ing to make up the totals mentioned, that the first crack, a hairline, showed at the back of the wall. Effects Begin to Show. After 16 tons had been applied, measurements of the face of the wall, by means of strained wires, showed that it had given only one-sixteenth of an inch inwards at the centre, and showed only an eighth of an inch deflection at the top. Its own weight naturally held the lower portion firm, keyed in as it was by the more solid lower concrete frame. The top of the wall, which had been built into the frame, and not keyed in, gradually began to draw away from the upper part of the frame, this accounting for the discrepancy of a sixteenth of an inch in the deflections of the two portions. It was not until a steady pressure of 13 tons, and a five-ton blow, eighteen tons in all, was applied, that the cracks began to open out in the back of the wall. A vertical crack, which cut through the bricks, leaving the bonding mostly unaffected, opened in the upper part of the wall, and two horizontal cracks, which chiefly followed the zig-zag line of the mortar, spread to the two bottom corners. At this stage the wall had withstood a pressure of eighteen tons, or 3731 b to the square inch of pressing-plate surface, notwithstanding that the brickwork under test had only been up ten weeks, and would have been stronger if further matured. The pressure was released, and the wall sprang back half an inch, the cracks closing up.