Cable axial load measurement device and buckling sensor development

Usalan, Emine Ceren
Axial compression or tension carrying members may need to be monitored for their structural behaviors and/or damage detection. In this thesis, two different types of practical and cost efficient monitoring devices are proposed: The column buckling sensor and the cable tension measuring device. The columns of steel structures are prone to buckling due to their slender nature. The buckling sensor is developed by using strain gauges installed in half Wheatstone bridge and measures the strain level of the most critical section. The strain readings are used to determine the critical buckling condition based on tangent slope of the bending and axial strain graph. The readings are repeated in orthogonal directions for columns with symmetric cross section and the program gives warning when the specified load limit is reached. The buckling sensor is tested on rectangular hollow steel profiles with pin end restraints for both elastic and plastic buckling. The test results, which are compatible with the theory, prove that the buckling sensor works as intended. The cable tension measuring device is developed for measurement of axial load levels in the cables using a low tech sensor without assembling a complicated electronic setup. The device consists of a slender beam with a circular section attached in the mid-span, a laser pointer device at one end and a ruler at the other end for measuring the slope at supports. The beam is clamped to the cable at both ends to bend the beam around the middle circular section. As the slopes at the ends are measured, the bending shape as well as the force at the mid-span can be calculated. The mid-span force and deformed shape of the slender beam and cable can be used to calculate the axial force in the cable. The simplicity and size that permits mobility of the device are its advantages. A prototype is developed and tested for moderately stressed cables and the results are found to be compatible with the analytical studies.