Wire Strain Gauges Research Articles

In-situ monitoring and analysis of tunnel floor heave process

Given that the forces acting on the inverts of high-speed railway tunnels are complex and their proper accommodation is critical to traffic safety, an in-situ stress test was conducted on the concrete of a reworked invert in the Fuchuan Tunnel on the Lanzhou–Xinjiang High-Speed Railway. In order to study the forces acting on the invert and the associated development of tunnel floor heave, vibrating wire strain gauges were embedded in the reworked invert concrete. The results show that the reworked invert first underwent compression before tensile stress developed in the central region, then stopped increasing and balanced the compressive stress. Based on the in-situ test results, the floor heave of the invert can be divided into slight, moderate, and severe phases. The progression between these phases is associated with the recharging and infiltration of groundwater into the expansive rock beneath the tunnel invert with the release of load, subjecting the concrete above to sharply increased stress. This causes cracking in the invert, leading to increasingly severe floor heave. The results of this study are of significance for the optimization of tunnel design and support systems and can be used to ensure tunnel traffic safety.

Verification of numerical creep and shrinkage models in an arch bridge analysis

AbstractThe highway arch bridge at Oparno in the Czech Republic is composed of the two independent almost identical structures; each of them carries one direction of the traffic. Each structure has a fixed end arch with the span of 135 m. The rise of the arch is 30 m. The bridge deck has a double T cross section and it is longitudinally prestressed. The arch was cast by cantilever method using temporary pylons with temporary stays. The arch is made of reinforced concrete and it is subjected preferably to compression. Therefore, it represents a suitable structure for comparison of strains and deflections obtained by measurements on the site and those obtained by a numerical analysis using different prediction models which may be applied in design calculations. The arch was equipped by vibrating wire strain gauges and the strains were recorded during the construction process and later during the early service life of the bridge. Additionally, the deflections of cantilevers during construction were also recorded. The measured values were used for adjustment of the form traveler and finally for evaluation of the prediction models. The bridge was built in the period 2008–2010. It was open to traffic significantly later (at the end of 2016) because the highway could not be finished earlier due to different nontechnical reasons.

Practical wireless safety monitoring system of long-span girders subjected to construction loading a building under construction

The primary goal of this paper is to address the challenges associated with the design and application of a practical wireless measurement system for the continuous safety monitoring of a large-scale structural members under construction. A practical wireless sensor network system (WSNS) was designed and real-time structural health monitoring (SHM) on long–span girders in a building under construction was performed. A WSNS consists of vibrating wire strain gauges (VWSGs) along with a sensor node, a master node, and a monitoring server. The field application of the WSNS using WVWSs was conducted on long-span plate girder and beam members of the K Art Hall during the construction of the building. It was possible to monitor the strain changes of the long-span plate girders and beams in real time as a function of the construction process and temperature changes.

Shaft resistance of pre-bored precast piles in Shanghai clay

Pre-bored precast piles with an enlarged base (PPEB piles) have been increasingly used in China over the past 5 years. However, the distributions of the shaft and toe resistance of the pile are still unclear. In order to reveal the ultimate bearing capacity and load transfer mechanism of PPEB piles in clay, three full-scale ultimate static loading tests were carried out in Shanghai. The test piles were instrumented with vibrating wire strain gauges to enable accurate measurement of the local shaft resistance along the pile shaft during the loading tests. The tests results revealed that about 75% of the pile bearing capacity was provided by shaft resistance when the ultimate load was applied and the majority of the shaft resistance was mobilised along the lower part of the test piles. After load testing, the soils around the test piles were excavated to evaluate the reliability and constructability of PPEB piles. The applicability of conventional methods (α-method and β-method) in estimating shaft resistance was assessed. In comparison with instrumented bored piles, the local shaft resistance of the PPEB piles in the lower stiff clays was significantly higher.

Developing Large Slab Airport Runways for the Next Century

The purpose of this research was to determine whether shrinkage-compensating concrete (SCC) made with Type K cement can create durable airport runways with fewer joints and reduced maintenance costs. The primary criterion examined was the ability of SCC to offset the effects of early-age drying shrinkage when the concrete is acted upon by external restraint. The interaction of restraint with SCC is important because restraint resists the expansive behavior that provides shrinkage compensation. Four sets of experiments were conducted, with increasing levels of Type K expansive mineral additive in each set. A set of test specimens consisted of four-inch diameter restrained columns. Each set consisted of three columns with varying degrees of stiffness in the restraint frame, including low, medium, and high-restraint stiffness. The medium-restraint column provides the theoretical response of new pavement cast against a mature slab, whereas the other two bracket the problem. The column specimens were instrumented using vibrating wire strain gages, which were embedded in the concrete, and load cells, which were affixed to the top of the columns. This research concludes that SCC can be effective even with a stiff boundary condition, and that SCC provides the potential for much longer-lasting airport runway slabs, as a result of reduced shrinkage and therefore fewer cracks.

Performance Evaluation of Whitetopping with Improved Design Practices in Texas

Abstract The design method of whitetopping in Texas is a method suggested by the American Concrete Pavement Association (ACPA). However, one of the limitations on this particular design method is that an existing asphalt pavement condition is not considered for slab thickness. Recently, the Texas Department of Transportation developed an improved whitetopping design procedure considering mechanistic-empirical (ME) behavior. In the present study, performance of whitetopping projects constructed by the ACPA design method in Texas were investigated, and improved design details were suggested in order to minimize distresses, such as corner break and slab movement, in transition areas. To evaluate the structural performance of whitetopping, various tests, including the falling weight deflectometer, ground penetration radar, and investigation of concrete coring were conducted on US 90. According to the field survey and tests results, most of the distress was caused by insufficient slab support conditions related to asphalt concrete pavement materials and inadequate slab thickness design. In addition, early-age behavior of whitetopping constructed by the improved ME design method was evaluated and analyzed, and various gage installations, such as vibrating wire strain gage, electric resistance-type strain gages, porous nonstress cylinder, and impervious nonstress cylinder, are discussed.

Early–Age Shrinkage of High-Performance Concrete Beam in Laboratory and Full-Scale

The beam is a significant element structure in bridge and high - rise building. The aim of this study is to obtain the difference of early age shrinkage between beam with laboratory scale and full scale. High-performance concrete with compressive strength of 60 MPa was used. This research was done experimentally in Indonesia for 24 hours. Three pieces of specimens measuring laboratory size of 150 mm × 150 mm × 600 mm, and one specimen measuring 200 mm ×600 mm ×3000 mm as full - scale specimen were used. All specimens were covered with styrofoam to eliminate transfer humidity. Early age shrinkage was obtained by using an embedded vibrating wire strain gauge for each laboratory size specimen and four embedded vibrating wire strain gauge for the full-scale specimen. As a result, the shrinkage type of full- scale specimen is a similar type to laboratory size. Shrinkage in laboratory size specimen is 31.5% larger than in full-scale specimen. Maximum shrinkage in a full-scale specimen is about 0.8E-04 occurs at the concrete age of 15.8 hours, while in laboratory size specimen is about 1.255E-04 occur at the age of 22.2 hours. Fluctuation expansion and shrinkage are smoother in full-scale than in laboratory size specimen. This is because in full-scale ettringite can expand more optimally so that it can come with stand shrinkage losses due to the growth of hydration products. High rate deformation of both specimens scale is occurring in the age range of 5-9 hours. Therefore, it is safe to assume the behavior of a real beam of high-performance concrete similar to laboratory size beam. Keywords : Beam, Concrete, Early, Shrinkage, Size DOI : 10.7176/CER/11-4-05 Publication date :May 31st 2019

Drying and shrinkage of massive concrete wall segments—3 years experiment and analytical observations

This paper presents 3 years lasting large scale experiment focusing on simultaneous measurements of drying profiles and shrinkage on massive concrete wall segments considering size effect. Three large specimens with thickness 20, 40 and 80 were accompanied by group of small specimens in order to measure additional parameters. Specimens were made from the same concrete mixture and placed in the same environment in the laboratory. Typical concrete mixture was used having water cement ratio 0.5 and average 28-days compressive strength 55 MPa. Pore relative humidity was measured in different depths using embedded plastic tubes and moisture meter, shrinkage (or swelling) strain was measured by embedded vibrating wire strain gauges. Special attention is paid and comments are stated to initial swelling up to 80 μm/m and to observed size effects in drying and shrinkage. Extensive data collected during this experiment were compared with results of various numerical models for shrinkage of concrete and with results of models for moisture transport in concrete. Discussion on the predictive capability of these models is provided. Calculation of apparent shrinkage from measured drying profiles of the wall segments using shrinkage point model is carried out and compared with measured shrinkage as well.

Monitoring of loads in arch support with wire strain gauge

Monitoring of loads in arch support with wire strain gauge

Practical use of distributed fibre optic sensors in research on FRCM composites

This article describes research on FRCM (Fabric Reinforced Cementitious Matrix) composites, which unlike commonly used FRP (Fibre Reinforced Polymers) composites make use of a mineral matrix instead of epoxy resin, which allows to achieve much higher resistance to elevated temperatures. In the described studies, experimental measurement of deformations with the use of the DFOS (Distributed Fibre Optic Sensors) method was applied. This method allows for geometrically continuous measurement of deformations, which is its significant advantage compared to traditional electric resistance wire strain gauge, as it reduces the possibility of measuring deformations in a place where they are not representative. The tests were carried out using two reinforced concrete slab elements loaded to failure in the 4-point bending scheme. Fibre optic sensors were installed on an unstrengthened control element and on an element strengthened with FRCM composite. During the tests, deformations of the concrete under tension and the external surface of the FRCM reinforcing composite were determined. Measurements were carried out simultaneously in two manners: using the DFOS method, and strain gauges placed at the characteristic points of the element. The test results based on both methods were compared and analysed. The comparative analysis confirmed the usefulness and effectiveness of the DFOS method while measuring deformations in strengthening composites, and showed its significant advantages such as precise indication of the place of elements cracking as well as the possibility of conducting a global analysis of deformations.

Structural integrity assessment of nuclear containment through fracture characterization

AbstractThe paper deals with the study of structural response of partially cracked nuclear containment model structure in over pressurized condition with the simulated experiments conducted under severe accidents analysis program for Indian nuclear containment structures. In this research, the fracture characterization of concrete containment structure is also investigated through the over pressure experiments on the BARC Containment (BARCOM) test model structure, which represents 1:4 scale of the prototype 540 MWe Tarapur pre‐stressed nuclear containment structure. In addition to the surface‐type electrical resistance, strain gauges conventionally and commonly deployed for containment proof‐test and ultimate load capacity evaluation of containment models, embedded vibratory wire strain gauges (VWSGs), the digital image correlation (DIC) technique, and soap bubble tests are employed in this study. For fracture characterization, an optical crack profile (OCP) technique is developed through DIC full‐field experiment conducted at the identified critical locations with conventional strain gauges to evaluate the fracture energy and the characteristics of the fracture process zone of concrete containment model structure subjected to the over‐pressure condition for its performance assessment in the case of the beyond design basis accidents. The combination of conventional sensors and full‐field DIC deployed for the first time on the largest scale containment model along with the associated analysis is shown to be effective in fracture characterization and improved structural integrity assessment of the containment model.

Evaluation of tension-compression asymmetry of a low-carbon steel sheet using a modified classical compression test method

A modified classical compression test method was used to examine in-plane tension-compression asymmetry in a low carbon steel sheet. In this compression test method, interfacial friction between the compression platens and specimen surfaces was significantly reduced by use of polycrystalline diamond plates installed on the compression dies. Furthermore, crosshead displacement of the universal testing machine, which inherently includes deflection of the machine itself, was corrected to the net deformation of the specimen based on a series spring model. Consequently, precision of the compressive strains obtained with the present test method is equivalent to that attained in the standard tension tests using wire strain gauges. For tension and compression tests performed at in-plane directions of 0°, 45° and 90° relative to the rolling direction (RD), significant tension-compression asymmetry (i.e. strength differential effect (SDE)) was observed. In all the mechanical tests in the three testing directions, flow stresses in tension tests were smaller than those in compression tests.

Development of analytical models to estimate the increase in pile capacity with time (pile setup) from soil properties

This paper presents the analyses of twelve prestressed concrete (PSC) instrumented test piles that were driven in different bridge construction projects of Louisiana in order to develop analytical models to estimate the increase in pile capacity with time or pile setup. The twelve test piles were driven mainly in cohesive soils. Detailed soil characterizations including laboratory and in situ tests were conducted to determine the different soil properties. The test piles were instrumented with vibrating wire strain gauges, piezometers, pressure cells that were monitored during the whole testing period. Several static load tests (SLTs) and dynamic load tests were conducted on each test pile at different times after end of driving (EOD) to quantify the magnitude and rate of setup. Measurements of load tests confirmed that pile capacity increases almost linearly with the logarithm of time elapsed after EOD. Case pile wave analysis program was performed on the restrikes data and was used along with the load distribution plots from the SLTs to evaluate the increase in skin friction capacity of individual soil layers along the length of the piles. The logarithmic linear setup parameter “A” for unit skin friction was calculated of the 70 individual clayey soil layers and was correlated with different soil properties such as undrained shear strength (Su), plasticity index, vertical coefficient of consolidation (cv), over consolidation ratio and sensitivity (St). Nonlinear multivariable regression analyses were performed, and three different empirical models are proposed to predict the pile setup parameter “A” as a function of soil properties. For verification, the subsurface soil conditions and setup information for additional 18 PSC piles collected from local database were used to compare the measured versus predicted “A” parameters from the proposed models, which showed good agreement.

Developing Guidelines for Epoxy Grout Pourback Systems for Controlling Thermal/Shrinkage Cracking at Post-Tensioning Anchorages: Full-Scale Testing and Numerical Analysis

Epoxy grout pourbacks at end anchorages of post-tensioning tendons provide an essential level of corrosion protection. The tendon may fail because of strand corrosion, within a few years of installation, if it is not properly protected with epoxy grout pourbacks. Recently, the Florida Department of Transportation (FDOT) found cracking on larger epoxy grout pourbacks, possibly as a result of the exothermic nature of the epoxy grout curing, causing thermal stresses that increase the potential for pourbacks cracking. Coordinated laboratory and numerical investigations were undertaken to develop best practice guidance for eliminating cracking in epoxy grout pourbacks. Potential factors were determined to be the pourback size, shapes, and temperature of the concrete substrate. An epoxy grout pourback material was used to construct full-scale pourback systems consisting of rectangular (R-type) and irregular (S-type) pourbacks with volume to surface, V/ S ratios of 80, 98, and 113 mm. The full-scale specimens were instrumented with multiple thermocouples and a vibrating wire strain gauge, to capture the temperature profile and localized strain respectively. An ANSYS finite element model was developed to perform a parametric study to better understand the cracking mechanism and the influence of the V/ S ratio. The model was calibrated and validated using the data obtained from the full-scale test. Based on the research findings, it is recommended that the maximum value of the V/ S ratio of the epoxy grout pourbacks be limited to 91 for S-type and 107 mm for R-type shapes.

Indirect monitoring of distributed ice loads on a steel gate in a cold region

A steel gate is one of the major components of a hydraulic power station for storing water and monitoring the water level. In cold regions, the temperature decreases to well below the freezing point, and the water turns to ice, which can apply high loads on the steel gate, leading to large deformations and failure of the gate. This study aims to monitor and analyse the ice load distribution on a steel gate using an inverse method. As a case study, a steel gate at the hydraulic station on the Songhua River in Harbin is selected. The steel gate is equipped with several vibrating wire strain gauges, and deformation data for various locations on the structure was collected for 100 days. As experimental identification of the system transfer matrix requires information concerning the actual loads, which is not directly attainable, the transfer matrix was constructed using a finite element method. Five inverse methods were verified with a certain number of load patterns to determine the optimal method. The ice load distribution obtained using the optimal method is verified with the deformation data, indicating accurate load identification. Consequently, variation in the ice load distribution during the freezing period is monitored, and the relationship between the total ice force and temperature is obtained. During the winter of 2015–2016, the average ice line load gradually increased until reaching a maximum of approximately 25 kN/m on 11 Dec. 2015. Subsequently, the ice line load fluctuated between 17 and 25 kN/m. Finally, the ice released all of the force within 3 days beginning on 15 Mar. 2016.

Deformation of high performance concrete plate under humid tropical weather

This paper presents the relationship between surrounding relative humidity and temperature on deformation behavior of one sample concrete plate with compressive strength of 60MPa. This research was done in Indonesia that is in humid tropical weather. A specimens measuring 3000 mm × 1600 mm × 150 mm were used. The behavior was obtained by using four embedded vibrating wire strain gauges (VWESG). As a result there is a very strong relationship between humidity and deformation at the age range of 7 until 21 days. The largest deformation occurs in the corner and the fluctuation of deformation in side position is larger than in the corner and in the middle. The peaks of surrounding relative humidity were fully followed by the deepest valley of deformation on time in the corner, while in another position the range delay time was 8 - 11 hours. There is a strong relationship between surrounding temperature and deformation at the range of 7 until 14 days. The influenced of surrounding relative humidity to concrete behavior is faster and longer than surrounding temperature. The influence of surrounding temperature in humid tropical weather was shorter than in non-humid tropical weather.

Long-Term Monitoring of Concrete Building Structure

Long-term deformations of the concrete are important for determination of behavior of concrete structures. For prediction of the long-term deformations rheological models are used. The models are usually derived from measurements on laboratory specimens. There are only few measurements performed on real structures. The objective of the realized experimental program is to compare predicted values of strains and strains measured on a real structure. Vibrating wire strain gauges have been installed in two columns in underground floors of eight-storey office building. Target of this paper is evaluation of measurement from the initial period (7 to 8 months). Measured values have been compared with results of first calculations and with values measured on laboratory specimens placed at the construction site.

Evaluation of pile capacity from CPT and pile setup phenomenon

Piles driven in cohesive soils usually experience a large increase in capacity over time, known as setup or freeze. This paper presents the field results of two test piles that were driven in two different locations of Louisiana to evaluate the pile setup behavior. Laboratory and in situ soil testings (cone penetration test, CPT) were conducted to characterize the subsurface soil properties. Several dynamic load tests (DLTs) and one static load test (SLT) were conducted on each test pile at different times after end of driving (EOD) to quantify the magnitude and rate of setup. The test pile in one site was instrumented with vibrating wire strain gages to calculate the load-distribution along the length of the pile during the static load test. With the aid of Case Pile Wave Analysis Program (CAPWAP®) analyses and load distribution plots from strain gages, skin friction and end-bearing capacities were measured separately. The load test results showed that the setup was mainly attributed to increase in skin friction with time and end-bearing capacity remained almost constant. The load test results also showed that setup behavior was more significant in soft cohesive soil. The pile capacity of one test pile was also evaluated using different CPT methods (such as Schmertmann, De Ruiter and Beringen, LCPC). The result showed that all the methods can estimate the pile capacity with good accuracy.

Performance Characteristics of Fiber-Optic Strain Sensors as Compared With Electrical Resistance and Vibrating Wire Strain Gauges

Abstract This paper presented experimental results of fiber-optic sensor performance in terms of its accuracy, repeatability, and reproducibility. Strain sensors were embedded in concrete specimens, which were then subjected to the same known static and dynamic load, and their responses were compared to each other on the same basis. In addition to evaluating the response due to load, the measurements due to concrete drying shrinkage were also evaluated. According to the experimental test results, the fiber-optic strain sensor (FOS) showed an average error of 2.7 με, as compared with average errors of 5.7 and 5.6 με for an electrical resistance strain gauge and a vibrating wire strain gauge (VWSG), respectively. In addition, the repeatability of the FOS in terms of coefficient of variation (COV) was 7.5 % as compared with COVs of 4.4, 5.6, and 9.6 % for three different electrical resistance strain gauges and the reproducibility of the FOS in terms of COV was 9.8 % as compared with COVs of 5.4, 5.7, and 10.1 % for three different electrical resistance gauges. When compared with the strains measured by a calibrated LVDT in a concrete drying shrinkage test where the strains varied from 0 to around 250 με, the FOS showed an average difference of 30.37 με, whereas the VWSG showed an average difference of 34.04 με. However, these difference were statistically insignificant at 95 % confidence level. Based on these results, it can be concluded that the FOS is found to have similar accuracy, repeatability, and reproducibility as compared to electrical resistance and VWSG.

Long Term Deformation of Beams and Columns of High Performance Concrete

The columns of a building must be stronger than the beams. The aim of this study is to obtain the cause of the long-term deformation difference by shrinkage between the beams and columns of high performance concrete with compressive strength of 60 MPa. This research was done experimentally in Indonesia during 410 days. Specimens measuring 150 mm × 150 mm × 600 mm were used, 3 pieces for the beams and 2 pieces for the columns. Deformation was obtained by using an embedded vibrating wire strain gauge for each specimen. The difference of long-term deformation in columns and beams is in their autogenous deformation behavior. This is because during the autogenous phase, swelling abnormally occurs in the column before shrinkage occurs. The abnormal swelling is caused by the press of its own weight. This phenomenon does not occur in beams. In the age range of 1 to 200 days, the behavior of the beam deformation has a similar pattern to the deformation behavior of the column with a high deformation rate. After that, at 200–410 days, column deformation changes to a very slow deformation rate. Long-term deformation in columns is lower (64%) than in the beams at 410 days age. Keywords Beam; Column; Concrete; Deformation; Shrinkage