FLUCTUATING STRESS GENERATING APPARATUS AND METHOD

Abstract: Apparatus for applying a fluctuating stress to, for example, a gable end (9) of a house includes means (6, 7) for defining with the end (9) a pressure enclosure. Air compression means (1) are connected to the pressure enclosure via a series of gauged valves (19) (20) whose position are continuously variable between limiting positions where the air compression means supplies all its output to, or takes all its output from the pressure enclosure. The effects of gusty winds can thus be simulated.

Description: Fluctuating stress generating apparatus and method This invention relates to testing apparatus and a method of testing using such apparatus. In particular, it relates to apparatus usable in the testing of buildings under wind stress. In the testing of buildings, a uniformly distributed load can be applied on to a horizontal test surface by weights or sand, provided there is no need to change the load quickly. However if an upward load is required, the test surface is not horizontal, or the load is to be varied quickly (to simulate wind effects, for example), it becomes impractical to generate proof loads in this way. Apparatus has therefore been devised in which a pair of co-operating valves may be coupled to an air circulating system to produce a rapidly fluctuating stress system. According to the present invention an apparatus for applying a fluctuating stress includes means for defining a pressure enclosure, air compression means having an intake and an outlet, and valve means continuously variable between a first position where the intake is connected to the pressure enclosure and the outlet is connected to atmosphere, and a second position where the intake is connected to atmosphere and the outlet is connected to the pressure enclosure, through intermediate positions where both intake and outlet are connected partly to atmosphere and partly to the pressure enclosure. In one form of the invention the apparatus includes means to compress air having an inlet port and an outlet port, first conduit means to conduct air from the outlet port, second conduit means to conduct air to said inlet port, first valve means having an inlet port connected to said first conduit means and having a pair of outlet ports together with adjustment means to divert air from a first to a second of its outlet ports, second valve means connected to said second conduit means and having a pair of inlet ports together with adjustment means to control the relative opening of its first and second inlet ports and an outlet port connected to said second conduit means, coupling, means to couple the adjustment means of said valve means, third conduit means connected to one outlet port of said first valve means and one inlet port of said second valve means, said third conduit means having a port which is connectible to a system under test to provide a fluctuating source of air pressure thereto. The valve means are preferably variable under computer controlled means whereby pressure within the pressure enclosure is varied according to a programme which may be predetermined or random. An embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which:- Figure 1 shows the general assembly of a test rig: Figure 2 shows a method of testing in which the test rig of Figure 1 is applied to a house; Figure 3 is a block diagram of a control system for use with, the test rig; Figure k is an assembly of control valves and air pump incorporated in the test rig; Figure 5 is a more detailed diagram showing the mechanical arrangement of the control valves of Figure k; and Figure 6a to c is an explanatory diagram for different air flow conditions. Referring now to the drawings, a test rig for applying a fluctuating stress to a building comprises a motor driven fan 1 with power supply 2 and silencer 3 coupled by means of a flexible hose to a control valve assembly 5. Directly coupled to the control valve assembly is a pressure containment cover 6 with seats 7 to couple it to a system under test 8. In use the test rig is attached to the system under test such as the gable end 9 of a house such that the cover 6 seats 7 and end 9 form a pressure enclosure (Figure 2). It may be held in position by support scaffolding 10. The control system for the control valve assembly 5 comprises a computer 11 coupled to an electronic controller 12 for a servo¬ motor 13 attached to the air supply control valve assembly 5. A position sensor on the servo-motor and a pressure sensor linked to the test enclosure 16 provide feedback to the electronic controller. The controlling air flow is generated by a centrifugal air pump 1 having an output conduit IT and an input conduit 18 consisting of flexible hoses. The output conduit is coupled to the inlet port of a first valve 19 of the control valve assembly. The input conduit is coupled to the output port of a second valve 20 of the control valve assembly. The valves are linked by a third conduit 21 having an output port 23 to the pressure enclosure. The control valve assembly (Figure 5) comprises a first valve 19 with a control motor 2k mounted on a mounting plate 25 to control a damper 26 which is continuously adjustable to divert air flow from the outlet conduit 21 to an exhaust port 27. The gate valve member 26 is coupled by a system of cranks 28-30 to a gate valve member 31 on a second valve 20 so that air may be taken in a continuously adjustable manner either from the atmosphere or from the links conduit 21. With this apparatus a record of fluctuating full-scale pressure is digitised at up to 10 Hz stored as a file in a portable computer (not shown). The computer reads the pressure into the test chamber every 25 mS and issues instructions to the servo¬ motor which adjusts the valve until this test pressure coincides with the filed record. Other operational procedures, such as a random variation of pressure generation by computer 22, will readily be apparent. With random generation a record of the pressure fluctuatic;:s may be kept on the portable computer or on computer 11.

Claims: CLAIM What is claimed is: 1. Apparatus for applying a fluctuating stress including means for defining a pressure enclosure, air compression means having an intake and an outlet, and valve means continuously variable between a first position where the intake is connected to the pressure enclosure and the outlet is connected to atmosphere, and a second position where the intake is connected to atmosphere and the outlet is connected to the pressure enclosure, through inter- mediate positions where both intake and outlet are connected partly to atmosphere and partly to the pressure enclosure. 2. Apparatus as claimed in Claim 1 whereas the means for defining apressure test enclosure includes a pressure containment cover and seats whereby in use the enclosure is defined between the cover, the seats, and a surface to which the fluctuating stress is to be supplied. 3. Apparatus for applying a fluctuating stress including means to compress air having an inlet port and an outlet port, first conduit means to conduct air from the outlet port, second conduit means to conduct air to said inlet port, first valve means having an inlet port connected to said first conduit means and having a pair of outlet ports together with adjustment means to divert air from a first to a second of its outlet ports, second valve means connected to said second conduit means and having a pair of inlet ports together with adjustment means to control the relative opening of its first and second inlet ports and an outlet port connected to said second conduit means, coupling means to couple the adjustment means of said valve means, third conduit means connected to one outlet port of said first valve means and one inlet port of said second valve means, said third conduit means having a port which is connectible to a system under test to provide a fluctuating source of air pressure thereto. . Apparatus as claimed in any one of Glai s 1 to 3 " including computer operated means whereby the positions of the valve means are varied. 5. Apparatus as claimed in ^laim h whereby the positions of the valve means are varied according to a predetermined programme. 6. Apparatus as claimed in Claim whereby the positions of the valve means are varied according to a random programme. 7. Apparatus substantially as herein described with reference to Figures 1 to β of the accompanying drawings. 8. A method of testing structure by ap. lying fluctuating stress thereto including steps of defining a pressure enclosure, connecting to the enclosure air compression means having an intake, an outlet -:nd valve means continously variable between a first position, where the intake is connected to the pressure enclosure and the outlet is connected to ..tmosphere, and a second position, where the intake is connected to atmosphere and the outlet is connected to the pressure enclosure, through intermediate positions where both intake and outle are connected partly to atmosphere and partly to the pressure enclosure, and applying varying pressure to the pressure chamber by operating the air compress means and varyiig the position of the valve means. 9. A method of testing structure substantially as herein described with reference to Figures 1 to o of the accompanying drawings.

Inventors: COOK NICHOLAS JOHN, COOK, NICHOLAS, JOHN
Applicants: SEC ENVIRONMENT BRIT
Application year: 1987
Main classification: G01M19
IPC codes: G01M5, G01M9, G01M19, G01N3, G01N17, G01N33