Edinburgh Napier University

  Buildings, roads, bridges and structures in general suffer many kinds of damages due to overstress caused by settlements of foundations, high winds, dynamic forces, passing traffic, vibration and unexpected external loads beyond the safe design forces. The damages manifest itself by cracks, falling of plaster and render uneven roads and some time complete collapse. The cost of maintaining and fixing damages caused by the above is quite high for the building and construction industry. The same phenomenon is common to many other structures like airplanes, wind turbine and machinery in general.
Structural Health Monitoring (SHM) is the engineering branch, which aims to give, at every moment during the life of a structure, a diagnosis of the "state" of the constituent materials, of the different parts of a structure. The state of the structure must remain in the domain specified in the design, although this can be altered due to usage or due to normal aging by the action of the environment, and by accidental events. By using special electronic sensors to monitor the unexpected high concentration of stresses or changes of these stresses throughout the life of the structure and pavement, reduces the cost of maintenance and repair. Historic buildings would also benefit from using such sensors to monitor the overstress in the old and frugally stones and bricks. The sensors can be embedded in the lime mortar joints and an electronic meter is used periodically to check for any unusual overstress during the life of the building.
The main aim of the proposed research project is to investigate the possibility of using thick-film technology stress sensors in masonry, concrete and building materials in general to monitor overstress and instability throughout the life of the structures. The sensors could be used in brick, block, stone, and concrete and they could be mounted on the surface or embedded in the materials.
There are many research studies on strain gauge devices in structural monitoring; Thick Film (TF) piezo-resistive sensors are proposed as a direct alternative to the widely used metal Foil Strain Gauges (FSG). Due to the low cost of TF sensors, their ease of use, suitability to integrate electronics on board, and to have different geometrical shapes, they could be deployed at different locations in a building, road or be distributed in arrays. This offers the continuous monitoring of stresses at any time by using a data logger on two points on the surface or by using wireless electronic transmission.
In this research, new thick film screen-printed ceramic piezo-resistive sensor has been developed and characterized as discrete device for deployment on surface of a structure and embedded into the structure during building material curing or after structure erection. The sensor response on different building materials has been experimented and compared. Mechanical and electronic simulation tools were used to characterise the sensor and to choose an adequate interface electronic circuit.
The experimental results of the simulated sensor and circuitry, showed the suitability of the sensor to be embedded in building materials during curing period and on erected structures. Materials used were wood, concrete, brick and plaster. In addition, the overall linearity of response of the sensors applied on building material surface was asserted which makes the technology a candidate for a more wide deployment in SHM field.