Papers by Keyword: Strain Gages

Abstract: Modern tunnel structures are presently implemented primarily by conventional excavation, using the New Austrian Tunneling Method. Two linings are usually used to support the excavated area. The primary tunnel lining serves for consolidation of the extracting during tunneling and the secondary tunnel lining ensures the safe use of the structure during its life time. The design and evaluation of the tunnel lining is a comprehensive process that involves a lot of input conditions. We are not always able to define these inputs exactly. In order to specify the amount of secondary lining load, we must know not only the load by the rock but also e.g. the hydrostatic load and deformation behavior of concrete during its aging. The lining is also influenced by local climatic conditions. It is necessary to include effects of various temperatures on the lining in our design. The measurements carried out in the already completed structures serve us for a more exact determination of these temperatures. Based on the results from these measurements, we can determine the distribution of temperatures in the profile and the behavior of the construction versus the climate change more exactly. Monitoring the temperature development takes a long time. The specification of this behavior should lead to a material saving when new constructions are designed.

Abstract: In this contribution the experimental program is summarized. The experiments were aimed especially at the accurate yield point determination on specimens made out of structural low carbon ÈSN 41 1523.1 steel after normalization annealing (ÈSN 411523, ASTM A623-Gr.C). These tests were carried out in the Laboratory of material diagnostics of Institute of Thermomechanics AS CR in Pilsen. Several methods for deformation and force controlled loading and various types (single with one measuring grid, rosette) of strain gages were used for achieved measurements. Likewise, the specimen made from different material batch was tested for comparative purposes. Strain gages were glued on both sides of the specimens for evaluation of coaxial alignment. Reached results are compared with those of tensile tests. All obtained data are evaluated and optimal solution is exported as output. The accurate determination of the yield point is very important for next tests of ratcheting and distortional hardening computation.

Abstract: Structural design, regardless of construction material, is based mainly on deterministic codes that partially take into account the real structural response under service and environmental conditions. This approach can lead to overdesigned (and expensive) structures. The differences between the designed and the real behaviors are usually due to service loads not taken into account during the design or simply to the natural degradation of materials properties with time. This is particularly true for wood, which is strongly influenced by service and environmental conditions. Structural Health Monitoring can improve the knowledge of timber structures under service conditions, provide information on material aging and follow the degradation of the overall building performance with time.A long-term monitoring control has been planned on a three-floor structure composed by wooden trusses and composite concrete-wood slabs. The structure is located in Nantes, France, and it is the new extension to the Wood Science and Technology Academy (ESB). The main purpose of the monitoring is to follow the long-term structural response from a mechanical and energetic point of view, particularly during the first few service years. Both static and dynamic behavior is being followed through strain gages and accelerometers. The measurements will be further put into relation with the environmental changes, temperature and humidity in particular, and with the operational charges with the aim to improve the comprehension of long-term performances of wooden structures under service. The goal is to propose new improved and optimized methods to make timber constructions more efficient compared to other construction materials (masonry, concrete, steel).The paper will mainly focus on the criteria used to design the architecture of the monitoring system, the parameters to measure and the sensors to install. The first analyses of the measurements will be presented at the conference to have a feedback on the performance of the installed sensors and to start to define a general protocol for the Structural Health Monitoring of such type of timber structures.

Abstract: Many engineering specifications, manufacturing procedures, inspection and quality control have begun to require that the residual stress of a particular component be evaluated. This is becoming as commonplace as the demands on the mechanical properties. In the country there are few research laboratories qualified to perform these tests and also found a worrying lack of skilled labor. Studying the formation and distribution of residual stress fields will improve the operational criteria of wheel safety, among other gains. It is known that these residual stress fields could be added to the effects of system load (tare weight plus occupation of vehicle traction, braking and torque combined). The results obtained used drilling method and rosette type strain gages, are convergent with similarity to those obtained using FEA simulation over critical region for global and superficial in principal stresses mode. The relevance of the present study and research on residual stresses meets safety improvements in cars wheel industry.