Electrical Strain Gauges Research Articles

ASSESSMENT OF TRAFFIC LOAD EVENTS AND STRUCTURAL EFFECTS ON ROAD BRIDGES BASED ON STRAIN MEASUREMENTS

Several technical and scientific publications have been made available focussing on Bridge Weight-in-Motion (BWIM) concerning railway bridges. On the contrary, BWIM analysis on road bridges are more scarce and therefore, this work intends to provide a contribution by presenting the BWIM analysis performed on two major road bridges in Portugal – Lezíria Bridge and Pinhão Bridge. These bridges are equipped with electric and optical strain gauges, acquisi­tion systems with features that allow high sampling rates. Based on the collected data and focussing on the bridges’ life­time, a probabilistic approach to quantify extreme traffic loads was implemented using extreme distribution functions. The bridges’ behaviour to these extreme traffic loads is numerically evaluated and a comparison with the alarm levels established by the bridge designers is performed. Although the bridge’s safety is not compromised, it was concluded that the representativeness of the observation period is a critical issue and the analysis of this kind of results must be care­fully considered. A comprehensive discussion about this matter is carried out at the end of this work.

Root Canal Surface Strain and Canal Center Transportation Induced by 3 Different Nickel-Titanium Rotary Instrument Systems

IntroductionRoot canal anatomy and canal preparation instruments affect the outcome of endodontic treatment. The purpose of this study was to determine the root surface strain (SS) generated and the extent of canal center transportation during canal shaping using 3 different nickel-titanium instruments. MethodsSimulated root canals in resin blocks (n = 10 per group) were prepared using adaptive rotary motion with twisted files (Twisted File Adaptive [TFA]; SybronEndo, Orange, CA), reciprocating rotary motion with WaveOne (WO; Dentsply Maillefer, Ballaigues, Switzerland) files, and continuous rotary motion with ProTaper Next files (PTN, Dentsply Maillefer). Electrical strain gauges at 3 sites recorded SS real time during canal shaping, and the blocks were scanned by micro–computed tomographic imaging to assess the canal center deviation at 3 sections after root canal instrumentation. The mean maximum SS and the canal center transportation for all groups and sites were derived and analyzed for a possible correlation between them. ResultsAn overall increase in root SS was observed after root canal instrumentation. A significant difference in the induced mean maximum SS between TFA, WO, and PTN at specific sites of curved root canals was observed. A statistically significant difference in the mean distance of canal center transportation was observed among the 3 shaping techniques at the apical section. Finally, the mean maximum SS values induced during canal shaping strongly correlated with canal center transportation in the apical section and the coronal section. ConclusionsThe curved canals prepared using TFA exhibited lower SS and less canal center transportation at the apical section than the WO and PTN systems. SS generated during canal shaping correlated with canal center transportation in a site-specific manner.

A strain measurement model using a limited number of sensors for steel beam structures subjected to uncertain loadings

The maximum stress of a structural member has been extensively adopted as a safety assessment indicator in structural health monitoring. Due to construction errors in the field and changes in the loading conditions during or after construction, it is impractical to accurately predict the location and magnitude of the maximum strain of a member a priori. To avoid the dependency of strain sensing methods on information of the structural and loading conditions, this paper proposes a strain distribution measurement model for steel beam structures subjected to uncertain loadings with uncertainties in magnitudes and shapes. With strains measured from a limited number of sensors, a general form equation of the strain distribution is determined for the estimation of the strain distribution. The performance of the strain distribution measurement model is verified by comparing estimated strain values from the proposed method and measured strains directly from fiber Bragg grating sensors or electrical strain gauges during static loading tests on single- and multi-span beam structures.

Static and dynamic experimental study of strengthened inforced short concrete corbel by using carbon fabrics, crack path in shear zone

The paper presents an experimental analysis of tracking the path of the cracks and crack growth in strengthened or repair reinforced concrete short corbels bonded by carbon fiber fabrics under static and dynamic loads. The reinforced short concrete corbel is a used precast element, for industrial buildings and structures. In fact, their functioning interestingly unconventional is compared to classical beam type elements. Then the effects of bending and shearing are combined in this case. The horizontal reinforced steel is localized to resist to tensile strength induced in bending top and a transversal strength-absorbing contribution. The introduction of carbon fiber composite in the field of Civil Engineering allows to strengthen or repair reinforced concrete structures using adhesive. So the carbon fiber material has many advantages as its low weight, flexibility, easier handling and also interesting physicochemical properties. However maintenance of civil engineering works is to protect them by ensuring better sealing or limiting corrosion. Then strengthening is to repair structures by using bonding technique to compensate their rigidity loss and limit the cracking. This allows to improve their performance and durability. Bonding of composite material in tensile zone of corbel retrieves most tensile stress and allows the structure to extend their load-bearing capacity. The local behavior of the structure is measured by means of the extensometer technique based on electrical strain gauges. This technique allowed to measure strains of steel, carbon fiber fabrics and concrete. The results of this investigation showed that strengthened reinforced concrete corbel bonded by carbon fiber fabrics can improve the ultimate load to twice and stiffens less than a third. The ultimate load, strain and displacement of the specimen are compared to reference experimental model of monotonic and cyclic applied loads. The success of strengthening depends strongly on surface preparation conditions. The cracking mechanisms and collapse modes under static and dynamic loadings are presented. The strengthened reinforced concrete short corbel behavior can be presented in three areas: overall elastic area, crack propagation area and opening of diagonal crack area.

Reliability of strain monitoring of composite structures via the use of optical fiber ribbon tapes for structural health monitoring purposes

In aerospace industry, a lot of effort has been focused on the practical implementation of optical fibers on composite subcomponents for health monitoring purposes during the service life of an aircraft. To this direction the fiber optic ribbon tapes (FORTs) concept was developed in order to ease the handling, the surface placement and the maintenance of such sensitive sensors. In this paper, we investigate the structural durability of this concept comparing two ways of mounting the FORT (co-bonding and secondary bonding) under fatigue loading conditions. Through long term fatigue tests and utilizing additional experimental (electrical strain gauges (ESG)), theoretical as well as numerical tools, it is concluded that the deviation of the experimentally measured strains using the FORT approach versus conventional ESG values are well within an error of maximum 6%. Moreover, they remain in this error bound for as much as 106 loading cycles, rendering FORTs a reliable solution for aerospace SHM. In the final part of the study, the effect of the FORTs placement on the stiffness of a structure is assessed through numerical analysis of the changes of the dynamic characteristics as well as the modal response of an aeronautical subcomponent representative of a wing front spar.

Architecture of Wireless Vehicle Weight Measurement System for Structural Health Monitoring in Civil Engineering Application

The following paper describes architecture of the Wireless Vehicle Weight Measurement System (WVWMS). The challenge was to design a road scale system enabling multipoint vehicle weight with the single network sink. The proposed platform is capable of weight measurement based on electrical strain gauge weight pads and in-node data processing. Communication is wireless, with mesh networking. The developed vehicle weight measurement is one of subsystems applied in the TULCOEMPA project. It is required to cooperate with Structural Health Monitoring and Truck Recognition Systems. Due to the absence of mains line, all installations are powered by Hybrid Power System. The authors propose Energy Harvesting Controller cooperating with both solar panels and wind generators. The controller enables efficient energy harvesting from both power sources as well as monitoring of generated and consumed power levels. Next challenge was a design of vehicle weight data acquisition software architecture. The solution includes application of modern architectural concepts in software design, Representational State Transfer (REST), Model-View-View Model (MVVM) paradigm, and cloud computing. Communication between vehicle weight measurement modules and server application is described.

The Estimation Method of Stress Distribution for Beam Structures Using the Terrestrial Laser Scanning

This study suggests the estimation method of stress distribution for the beam structures based on TLS (Terrestrial Laser Scanning). The main components of method are the creation of the lattices of raw data from TLS to satisfy the suitable condition and application of CSSI (Cubic Smoothing Spline Interpolation) for estimating stress distribution. Estimation of stress distribution for the structural member or the whole structure is one of the important factors for safety evaluation of the structure. Existing sensors which include ESG (Electric strain gauge) and LVDT (Linear Variable Differential Transformer) can be categorized as contact type sensor which should be installed on the structural members and also there are various limitations such as the need of separate space where the network cables are installed and the difficulty of access for sensor installation in real buildings. To overcome these problems inherent in the contact type sensors, TLS system of LiDAR (light detection and ranging), which can measure the displacement of a target in a long range without the influence of surrounding environment and also get the whole shape of the structure, has been applied to the field of structural health monitoring. The important characteristic of TLS measuring is a formation of point clouds which has many points including the local coordinate. Point clouds are not linear distribution but dispersed shape. Thus, to analyze point clouds, the interpolation is needed vitally. Through formation of averaged lattices and CSSI for the raw data, the method which can estimate the displacement of simple beam was developed. Also, the developed method can be extended to calculate the strain and finally applicable to estimate a stress distribution of a structural member. To verify the validity of the method, the loading test on a simple beam was conducted and TLS measured it. Through a comparison of the estimated stress and reference stress, the validity of the method is confirmed. Keywords—Structural health monitoring, terrestrial laser scanning, estimation of stress distribution, coordinate transformation, cubic smoothing spline interpolation.

Theoretical and Experimental Studies of Timber Composite Beams Reinforced by Cold Formed Steel Sheets

This research deals with theoretical and experimental studies of timber composite beams reinforced by cold formed steel sheets, submitted to bending. A combination of different materials aims to the exploitation the advantages of each material, of manner to have a viable set, in constructive, structural and economic issues. For the accomplish of the research were tested three timber beams with dimensions 40mm x 120mm x 1050mm, six timber reinforced beams in the superior surface with metallic profile with dimensions 50mm x 25mm x 2mm and six timber beams reinforced in inferior surfaces and in the superior surface with the same metallic profile. The spacing between the connectors was of 100mm, 200mm and 300mm. With the objective of supplying the necessary dimensioning, theoretical formularizations for these studies were presented to the determination of internal moment and the estimated deflection. For this, the timber mechanical properties, the steel and the connectors were determined. With the results of the characterization tests of the materials, the simple and composite beams were tested in bending, for reading of stresses and maximum vertical displacements of the rupture on the inferior and superior extremities. Such values were performed by means of electric strain gauges and dial gauges. Also, were determined: the tensions in the elements of the beams and presented the chart of stresses x displacements. It was observed that, in relation to the timber simple beam, it had average increase at the ultimate load, for beams with reinforced parts in the compressed surface, of 20%, and 49%, when placed stiffeners in compressed and tensioned surfaces. In deflection values, it had the average reduction of 15%, when used stiffeners in the superior surface and of 49% in the parts with stiffeners, in the surfaces were performed to compression and tension. The biggest reduction in deflections happened in beams with lesser spacing between connectors, indicating that the influence of the interaction is bigger in relation to displacements, to bending moment. In stress distribution chart in the cross sections it was adopted, in all cases, the triangular form for the timber and for the profile, it was adopted a rectangular form. It was obtained results that differ from the experimental values in 17% for simple beams, in 16% for parts hardened with profile in superior surface and 21% for the parts hardened with profile, in the surfaces upper and lower, indicating that the proposal formularization can be applied with safety. In the calculation of deflections of geometric properties of composite section, in elastic regime, were performed with the homogenized section. It was presented the equation for the determination of correction factor of the estimated deflection for the studied cases.

Strain Profile Measurement for Structural Health Monitoring of Woven Carbon-fiber Reinforced Polymer Composite Bonded joints by Fiber Optic Sensing Using an Optical Backscatter Reflectometer

In order to monitor crack initiation and propagation under static and fatigue loading in adhesively bonded joints, strain profile measurement such as backface strain (BFS) is a very efficient technique. In single lap (SL) joints, crack initiation and propagation in the glue line can be monitored by detecting the negative peak of the strain profile. Therefore, the accuracy of the monitoring system greatly depends on detecting the strain profile correctly and accurately. Previously, an array of electrical strain gages as well as fiber Bragg grating (FBG) sensors had been used successfully to capture the profile of BFS of a SL joint by applying sensors on the backface of an adherend, near the overlap zone. In this work, the backface technique is improved by replacing an array of strain sensors by an ordinary optical fiber (without FBG sensors) connected to an optical backscatter reflectometer. The great advantage of this system over the more conventional arrays of FBG is that the entire length of the fiber can be used for sensing strains, and hence it provides a better spatial resolution. The experimental results are compared with finite element analyses, which were further validated by two-dimensional digital image correlation measurements.

Analytical And Numerical Solutions Of Metal High-Pressure Wave-Ring Gasket And Comparison With Experimental Results

Abstract The paper deals with experimental investigations of a set of metal wave-ring gaskets of different thickness and different assembly interference. The gaskets were examined under assembly conditions, i.e. pressed in their seats with no operating pressure applied. The electric resistance wire strain gauges were used to measure the circumferential and axial strains at the inner surface of the gaskets. The traces of contact at the working surface of the gaskets were measured after disassembly the gaskets from their seats. The material tests were carried out to determine the real mechanical properties of materials applied for the gaskets and the seats. The results of experiment were verified by FEM calculations and compared with the analytical approach based on the simplified shell model proposed for the gasket.

Ultimate Unbonded Tendon Stress in CFRP Strengthened Post-Tensioned Indeterminate I-Beams Cast with HSCs

Based on the bending experiment for two-span continuous post-tension beams with unbounded tendons and externally applied CFRP sheets, the analysis of the stress increment of unbonded tendons is monitored in the loading process. Since self-compacting concrete (SCC) is a suitable innovation,, understanding the implementation of this type of concrete on the ultimate unbonded tendon stress is critical. For these aims, results of four continuous un-bonded post-tensioned I-beams in two groups were cast and monitored by electrical strain gauges andare presented here. In the first group, the beams (UPN1-12, SUPN1-12) consisted of high strength normal concrete (HSNC), while in the second group (UPS1-12, SUPS1-12) high strength self-compacting concrete (HSSCC) were tested. The beams are made which are compared with the theory proposed by different codes, and a preliminary modification is given for each code equation. The results of standard error of estimate Sy/x , indicates that for two types of HSCs (strengthened and non-strengthened beams), the ACI 318-2011 provides better estimates than AASHTO-2010 model, whereas this model provides better estimates as compared toBS 8110-97.Comparison of increase in experimental ultimate tendon stress of beams indicates that the increase in tendon stress at ultimate state in strengthened beams is lower than that in non-strengthened beams cast with HSCs.

Comparison Between Finite Element Method Simulation, Digital Image Correlation and Strain Gauges Measurements in a 3-Point Bending Flexural Test

Mechanical testing holds a decisive role in structural components design. It supports and validates computer simulation models, spots design failures or critical sections and reveals the structure real behavior under static or dynamic loads. In order to reduce weight and/or improve durability of a train passenger car underframe, an alternative design was proposed based on an aluminium alloy modular components joined by laser beam welding. A section of this prototype was tested, according to a three-point bending flexural test configuration, and monitored with both optic techniques, such as digital image correlation and electric strain gauges. After processing, the resultant data was compared with the finite element method analysis for simulation model validation and structure inspection.

Root surface strain during canal shaping and its influence on apical microcrack development: a preliminary investigation

To determine the root surface strain (RSS) generated during root canal shaping and its effects on apical microcrack development. Twenty-five extracted human mandibular premolars were selected and decoronated. The teeth were instrumented with either the ProTaper (PT) or WaveOne (WO) (Dentsply Maillefer) NiTi rotary systems (n=10 per group) or used as controls (n=5). Instrumented root canals were enlarged to ProTaper F4 (size 40, 0.06 taper) or using WaveOne LARGE (size 40, 0.08 taper) instruments according to the manufacturer's instructions. An electrical strain gage (KFG02-120-C1-16, Kyowa Dengyo, Tokyo, Japan) was fixed on the proximal root surface and connected to a strain amplifier via a bridge box in order to measure RSS. During canal shaping, the strain output of the amplifier was recorded. The instantaneous RSS induced by each instrument and the maximum RSSs were determined. All teeth were then stained with contrast media and imaged with micro-computed tomography (micro-CT) at an isotropic resolution of 10μm to detect microcracks. The mean maximum RSS values (microstrain) and mean number of microcracks recorded for both groups were tested for statistical significance using Mann-Whitney U-test. Presence/absence of microcracks in both groups was compared by chi-square tests. Increased baseline RSS from strain accumulation during canal shaping was observed, with similar maximum RSS (mean±SD) for PT (416.6±185.1 μstrain) and WO (398.2±163.8 μstrain) (P=0.94). The interevaluator reliability for microcrack detection using micro-CT had a kappa value of 0.998. Compared to the PT group, there was a trend for fewer samples with microcracks in the WO group (P=0.051). On the micro-CT images, apical microcracks were detected in 20 PT and 11 WO samples (P=0.10). The microcracks were observed in the buccolingual direction in all WO and 81% of PT samples. No vertical root fractures were found. The maximum RSS obtained during canal shaping was poorly correlated with the number of microcracks found (R(2) =0.093). Based on these preliminary data, canal shaping appears to cause apical microcracks regardless of the type of rotary instrument motion. Contrast-enhanced micro-CT was able to identify microcracks in roots.

Electrical and magnetic properties, and FLAPW electronic band structure of magnetostrictive Tb0.27Dy0.73(Fe0.7−xNixCo0.3)2 compounds

Abstract The structural and physical properties of nickel-diluted Tb 0.27 Dy 0.73 ( Fe 0.7 − x Ni x Co 0.3 ) 2 intermetallics were studied by X-ray diffraction, four-probe dc electrical measurements and standard strain gauge method. X-ray analysis shows that all samples crystallize in a cubic Laves structure. The lattice parameter decreases linearly with the nickel content. Electrical resistivity was measured in a temperature range of 15–1100 K. The parameters involved in the dependence of resistivity on temperature and composition were determined. Residual, phonon and magnetic resistivity were separated from the electrical resistivity using both the Matthiessen and Bloch-Gruneisen formulas. The compounds’ Curie temperatures, which decrease nonlinearly with x, were obtained from the magnetic resistivity curves. The maximum values of magnetostriction attained for the Tb 0.27 Dy 0.73 ( Fe 0.6 Ni 0.1 Co 0.3 ) 2 compound exceed about 851 ppm. Electronic 3d-band structure and magnetic moment calculations were performed using the Full-Potential Linearized Augmented Plane Waves method. The distribution function for the densities of 3d-states was used to characterise the transition metal subbands.

Measurement of early-age strains in mortar specimens subjected to cyclic temperature

As well known, the volume change induced by environment temperature variation can lead to cracking at the surface of cementitious materials with low water-cement ratio. Thus, it can be said that there is a pressing need to reveal the early-age performance of cementitous materials in a variable environment temperature. Conventional thermocouple and strain gauge have been widely used for measuring temperature and strain in cementitious materials, respectively. However, conventional sensors have several limitations for measuring strain and temperature in cementitous materials such as too many cables for multipoint measurement, short circuit, and electromagnetic interference. Compared to conventional electrical strain gauge, fiber Bragg grating (FBG) has several inherent advantages including multiplexable, resistance to electromagnetic interference, and stable signal in long distance transmission. In this study, two lines mutiplexed with FBG strain and temperature sensors were fabricated and employed to measure the quasi-distributed strain and temperatures in mortar specimens subjected to cyclic temperature.

Monitoring and theoretical losses of post-tensioned indeterminate I-beams

Self-consolidating concrete is a desirable achievement in reinforced concrete structures. This non-vibrating concrete has had a significant impact on the prestressed concrete industry because it increases productivity in the casting of durable prestressed or precast members without mechanical vibration. In the design of prestressed concrete structures, the immediate and time-dependent losses in tendon stresses are important. The main objective of this study is to investigate the losses in tendon stresses of indeterminate (continuous) post-tensioned unbonded beams consisting of two different types of concrete (high-strength self-consolidating concrete (HSSCC) and high-strength normal concrete (HSNC)). Six continuous, unbounded, post-tensioned I-beams in two groups were cast and monitored by electrical strain gauges for a duration of 60 d and the losses were measured. Results were compared with the Association of State Highway and Transportation Officials (Aashto) third and fourth edition methods, the Precast/Prestressed Concrete Institute (PCI) method and the Eurocode 2 model. It was found that the Aashto third edition, PCI and Eurocode 2 methods were conservative and the Aashto fourth edition method was non-conservative for estimating time-dependent losses in post-tensioned beams cast with high-strength concretes. The amount of experimental time-dependent losses in beams consisting of HSSCC was slightly lower than that of beams prepared using HSNC with almost the same concrete strength.

On buckling collapse and failure analysis of thin-walled composite lipped-channel columns subjected to uniaxial compression

The paper deals with buckling of short thin-walled lipped-channel columns, simply supported on both ends and subjected to uniformly distributed compressive load. The main objective of the study was to investigate the structure׳s work in far post-buckling state and at collapse corresponding to the moment of the column׳s stiffness loss. The following measuring devices and methods were applied: electrical strain gauges for strain measurements, a laser sensor to measure the displacements, and the Acoustic Emission method. Along with running the experimental tests, the non-linear stability of compressed composite columns was analyzed with the Finite Element Method. The numerical and experimental results showed good agreement.

Assessing Shot-Peening Residual Stresses by Using the Incremental Hole-Drilling Technique and Laser Interferometry (DSPI)

The incremental hole-drilling technique was applied to determine residual stress profiles in shot-peened steel layers. The accuracy of using an enhanced Digital Speckle Pattern Interferometry technique for measuring the strain relaxation arising around the drilled holes and, consequently, the in-depth residual stress distribution induced by shot-peening, was evaluated. The experimental results were systematically compared with those determined using standard electric strain-gauges. The X-ray diffraction technique was chosen as reference due to its high accuracy to determine shot-peening residual stresses.

Stress analysis of clamped-free grid composite cylindrical shell under various end loadings

Stress analysis of cylindrical grid-stiffened composite shells was conducted under transverse loading, pure bending, torsion and axial compression under clamped-free boundary condition. Electrical strain gauges were employed to measure the strains in transverse loading case to validate the finite element analysis which was conducted using ANSYS software. Good agreement was obtained between the two methods. It was observed that stiffening the composite shell with helical ribs decreased the average equivalent Von Mises stress on the shell. The reduction of the stress seemed to be higher in the intersection of two ribs. It was also seen that the stress reduction ratio was higher when the structure was under bending compared to torsion and axial compression. The reduction ratio was approximately 75% in pure bending in the intersection point of the ribs, while it was approximately 25% in torsion. Therefore, it is concluded that the presence of the ribs is more effective under bending. Failure analysis was done using Tsai-Wu criterion. The ribs were observed to result in maximum and minimum increase in the failure load of the structure under transverse bending and torsional loading, respectively.

Quantitative Sensitivity Analysis of Surface Attached Optical Fiber Strain Sensor

Optical fiber strain sensors, in particular, the fiber Bragg grating (FBG) type, are widely applied in different applications. The most common installation method is surface-attached. In principle, the optical fiber strain sensor with adequate sampling and signal processing techniques is usually more accurate than electrical resistive strain gauge. However, the strain of the surface of structure may not transfer to the sensing element perfectly. The ratio between the measured and actual strain can be correlated by a strain transfer factor (STF). However, it depends on the material and geometrical properties of the optical fiber and adhesive. It is noneconomical and impractical to measure the STF for every installed sensor. It is desirable to identify the most of the sensitive parameters on the variation of the STF so that the quality control and assurance procedure can be performed more efficiently. In this paper, a quantitative global sensitivity analysis, called extended Fourier amplitude sensitivity test will be performed to compute the first-order and total sensitivity indexes based on a well-established semi-analytical/empirical mechanical model of three material and five geometrical parameters of both integral and optical FBG type optical fiber strain sensor with two different kinds of polymeric coating under three types of strain field in 16 different configurations. From the detail analysis, the most of the sensitive parameters on the STF are bond length, the thickness of adhesive beneath the optical fiber and the deviation of grating position, which are related to workmanship instead of the material properties of the optical fiber and adhesive.