GB857222A - Methods and apparatus for measurement of stresses and the main components influencing them such as temperature, pore-water pressure, strains as well as deflections in concrete or like constructional material - Google Patents

Abstract

857,222. Measuring stresses; strains, and pressures. GLOTZL, F. Feb. 20, 1957 [Feb. 20, 1956], No. 5775/57. Class 106 (2). [Also in Group XX] Apparatus for measuring mechanical stresses or mechanical values, such as temperature, pressure or strain, which can be converted thereto comprises a valve-type pick-up 2 built into part of a structure 1 in which the stresses or values are to be measured, a pipe 7 supplying a pressure medium, and a pipe 6 returning the medium to its supply source, the pick-up 2 being constructed as an hydraulic pressure-relief valve V so that the mechanical stress or value being measured controls the pressure at which the valve opens. As shown in Fig. 1 for measuring the stress in a concrete building, a resilient capsule 2 is built into the concrete during construction and provided with inlet and outlet pipes 7, 6. Pipe 7 enters the capsule at an arbitrary but not central point, and pipe 6 enters at the centre of the lower diaphragm 4 the central portion of which is accurately ground to bear against an accurately ground surface on the upper diaphragm 3 and from a valve V. In use, liquid is pumped through inlet 7 until the pressure inside the capsule 2 equals the external pressure due to the stress in the concrete. At this point the valve V opens and excess liquid returns by pipe 6. Thus, the maximum pressure recorded on a pressure recorder 10 gives a measure of the stress at that time. This operation may be repeated at any desired interval. Fig. 3 shows the apparatus used for temperature measurement. A bimetallic tube 21 is held in a fixed frame 20, the base 25 of the tube being freely movable and having a ring 23 secured to it. Thus, a valve V similar in action to that in Fig. 1 is formed by the ring 23 and the base 26 of the frame 20. The action is as before, fluid being pumped in until its pressure equals the pressure acting on the base of the tube 21 derived from the temperature in the concrete. When this happens, the valve V opens and excess liquid returns via the pipe 6, the temperature being represented by the maximum pressure indicated or recorded at 10. Other embodiments (not shown) describe the measurement of the strain in the building and of the pressure of the water in the pores of the concrete.