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Purpose: To evaluate the effect of immersion in water on deforma8on of maxillary denture bases created with CAD/CAM and heat-polymerized resin fabrica8on techniques under loading condi8ons. Materials and Methods: 2-mm-thick denture bases were fabricated using four techniques: CAD/CAM milling (CCM; Polywax PMMA blank, Yamachi PMMA disk Yamahachi Dental); 3D prin8ng (3DP; BV005, NextDent Base); compression molding (CM; Luciton 199, Dentsply Sirona); and injec8on molding (IM; Ivobase, Ivoclar; n = 5 per group). Three sta8c 49-N loads were applied perpendicular to each denture base, and the mean strain value (MSV) was recorded with strain gauges a[ached to the denture surface. The denture bases were stored at 37°C in dis8lled water for 14 and 28 days, and the MSVs under the same sta8c load were recorded. Results: The highest MSVs were observed at the posterior palatal seal, tuberosity, and labial notches of the dentures. The lowest MSVs were recorded for the CCM group and then the CM and IM groups. The highest MSVs were recorded for the 3DP group. No significant differences in regional MSVs (P > .05) were observed among the CCM, CM, and IM aber 14 and 28 days in water. Large devia8ons in MSVs were recorded for the 3DP group across the measurement sites aber water exposure (P < .05). Conclusions: CCM had the lowest denture deforma8on under sta8c loading. Aber immersion in water, the deforma8on changes under sta8c loading were stable for CCM, CM, and IM. However, varia8ons among the materials used in 3DP group influenced the mechanical performance and presented larger deformations. [ABSTRACT FROM AUTHOR]

A novel laser thermal printing technique toward the fabrication of all‐in‐one flexible intelligent devices is presented in this work, addressing the existing challenges in their scalable manufacturing and multifunctional performance. The first‐ever application of this technique for the synthesis of a multifunctional intelligent cobweb structure is presented. The resultant cobweb integrates a conductive network of multi‐walled carbon nanotubes (MWCNTs) and NdFeB magnetic microparticles within a polydimethylsiloxane (PDMS) matrix, enabling seamless incorporation of sensing, stimulus response, and actuation functionalities. The cobweb exhibits multifunctional sensing characteristics, including a 2.37 strain gauge factor and a 0.312%·mT−1 magnetic field sensitivity, excellent stability exceeding 3500 cycles. Furthermore, the cobweb achieves accurate capture of a beetle on the basis of real‐time sensing of the beetle, verifying its rapid stimulus response characteristics. Meanwhile, the cobweb exhibits an electromagnetic ejection performance with an ejection height of over 33.5 times the size of the projectile, verifying its powerful actuating ability. These results demonstrate the successful integration of multifunctional sensing, stimulus response, and actuation within the cobweb structure, facilitated by the innovative laser thermal printing process. The laser thermal printing technique marks a significant advancement in the efficient fabrication of miniaturized and multifunctional flexible intelligent devices based on thermosetting materials. [ABSTRACT FROM AUTHOR]

Plantar shear stress may have an important role in the formation of a Diabetic Foot Ulcer, but its measurement is regarded as challenging and has limited research. This paper highlights the importance of anatomical specific shear sensor calibration and presents a feasibility study of a novel shear sensing system which has measured in-shoe shear stress from gait activity on both healthy and diabetic subjects. The sensing insole was based on a strain gauge array embedded in a silicone insole backed with a commercial normal pressure sensor. Sensor calibration factors were investigated using a custom mechanical test rig with indenter to exert both normal and shear forces. Indenter size and location were varied to investigate the importance of both loading area and position on measurement accuracy. The sensing insole, coupled with the calibration procedure, was tested one participant with diabetes and one healthy participant during two sessions of 15 minutes of treadmill walking. Calibration with different indenter areas (from 78.5 mm2 to 707 mm2) and different positions (up to 40 mm from sensor centre) showed variation in measurements of up to 80% and 90% respectively. Shear sensing results demonstrated high repeatability (>97%) and good accuracy (mean absolute error < ±18 kPa) in bench top mechanical tests and less than 21% variability within walking of 15-minutes duration. The results indicate the importance of mechanical coupling between embedded shear sensors and insole materials. It also highlights the importance of using an appropriate calibration method to ensure accurate shear stress measurement. The novel shear stress measurement system presented in this paper, demonstrates a viable method to measure accurate and repeatable in-shoe shear stress using the calibration procedure described. The validation and calibration methods outlined in this paper could be utilised as a standardised approach for the research community to develop and validate similar measurement technologies. [ABSTRACT FROM AUTHOR]

Copyright of Technisches Messen is the property of De Gruyter and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Technisches Messen is the property of De Gruyter and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper, the suitability of digital image correlation (DIC) technology in evaluating the flexural behaviour of as-built and carbon-fiber-reinforced polymer (CFRP) strengthened reinforced concrete beams was verified by conducting a four-point bending test on four large-size beams. The DIC data obtained during the tests were compared to the results measured using traditional techniques such as displacement sensors and electrical strain gauges, as well as the findings derived from finite element (FE) numerical simulations. A good agreement was achieved between the local displacement and strain measurements and the data from DIC as a function of the applied load. Moreover, the crack patterns generated by the FE modelling were validated by the corresponding patterns derived from DIC. This suitability study is expected to contribute to the future field implementation of DIC technology to monitor the CFRP-strengthened members of critical structures such as bridges. [ABSTRACT FROM AUTHOR]

Benign, locally aggressive tumors of the distal femur are typically treated with intralesional curettage and polymethylmethacrylate (PMMA) cementation. However, it is not known whether plate fixation should be added to biomechanically augment these PMMA‐filled defects. The purpose of this study was to evaluate the performance of two competing techniques for reconstruction of a distal femoral defect. For this biomechanical study, we used 12 composite femurs with properties comparable to bone. In nine femurs, identical contained medial distal femoral defects were created using a robotic arm. Group A contained three intact femurs, Group B three femurs with an unfilled defect, Group C three femurs reconstructed with PMMA alone, and Group D three femurs reconstructed with PMMA plus a medial locking plate. Locations of greatest stress concentration were determined by PhotoStress analysis, then three strain gauges were applied to each specimen at these high‐stress locations. Specimens were loaded within a physiologic range followed by loading to failure. Outcome measures included construct stiffness, strain along the distal femur, and load at failure. Results showed that stiffness and strain were not significantly different between reconstructive techniques; however, both techniques reduced tensile strain along the popliteal surface by approximately 40% compared to non‐reconstructed specimens. All specimens failed at the femoral neck before failing at the distal femur. These findings suggest that plate augmentation of PMMA‐filled distal femoral defects like the one in this study offers insignificant biomechanical benefit within physiologic loads and therefore may be unnecessary. [ABSTRACT FROM AUTHOR]

The role of steel connections is essential in structural fire design and analysis for steel-framed composite structures. The current structural design provisions provide strength reduction factors of load-carrying members and their end-connection elements at elevated temperatures, based on small-scale experiments under uniform heating conditions. The realistic thermal and structural evolution in member connections, especially as part of full-scale floor assemblies exposed to a large compartment fire, has not been well characterized. A large compartment fire experiment was recently conducted on a 9.1 m by 6.1 m composite floor assembly as part of a two-story steel-framed building. The test assembly had a total of ten shear-tab (fin-plate) connections subjected to combined fire and mechanical loading. This paper presents the measured thermal response of these connections to fire and comparison with the corresponding Eurocode 3 predictions with two methods (1) incorporating the beam bottom flange temperature at midspan and (2) the section factor method. The results show that the Eurocode 3 methods conservatively predict the maximum temperature during heating and the cooling rate but overestimate the high-temperature strength of connections when estimated using the section factor method, showing that the Eurocode 3 simplified approaches are not meant to provide the details of the failure mode for connections. This study suggests that estimating the strength of connections using strength reduction factors may not guarantee a safe structural fire design. In addition, this paper estimated the total axial force (from slab and beam) at the composite connection via using the strain gauge measurements close to the column bases which were not exposed to fire. It suggests realistic axial load and rotational demand on the shear connection due to restraints to thermal elongation or contraction of supported members should be considered in future design guidance as should designing and detailing the connections for ductility to withstand the inelastic deformation demands during the heating and the cooling phases. [ABSTRACT FROM AUTHOR]

Purpose: Torque is one of the main loads acting on the aircraft wing, the horizontal tail and the vertical tail. In flight load measurement, due to the significant influence of the bending moment and the shear force on the strain gauge, the accuracy of torque measurement is usually low. Therefore, aircraft torque measurement is difficult. Based on the characteristics of a certain type of horizontal tail, a measurement method for the torque with high accuracy was proposed in this paper. Design/methodology/approach: A new simplified torque measurement method for the all-moving horizontal tail was proposed based on the spiral driver. The feasibility of the method and key points of the tests were analyzed and studied through a virtual load calibration test. Findings: Based on the results of the real load calibration test, the torque load equation with high accuracy was established, and the torque measurement was achieved in load flight tests. Research limitations/implications: However, the proposed method is based on the structure of the spiral driver. If there is generally no spiral driver at the aircraft wings and vertical tails, then the appropriate torque measurement method needs to be derived according to the specific object. Originality/value: The research in this paper provides a new idea for the torque measurement of aircraft structures, which can be used for the torque measurement of subsequent aircraft types. [ABSTRACT FROM AUTHOR]

In recent years, cold regions have seen dramatic changes to the once-stable permafrost layers as a result of global warming. Changes in mean annual temperature directly impact the interaction between frozen ground and infrastructure systems such as piles and pipelines. Adfreeze, the controlling mechanism in a frozen soil–structure interface, is temperature dependent and weakens with rising temperature, while its cohesive nature may eventually change to a frictional one as pore ice turns into water. This paper studies the effect of temperature change on the behavior of steel piles in ice-poor soils subjected to pullout loading, especially during the transient melting state. A series of pullout pile load tests were carried out on a model steel pipe pile embedded in frozen sand and exposed to varying temperatures between −10∘C and 0°C. Strain-controlled pile load tests were performed to observe the pullout load transfer and failure mechanism of the pile, while constant-load tests were carried out to study the creep behavior of the pile exposed to different temperatures. Interface behavior was monitored by strain gauges and thermocouples mounted on the pile surface. Pullout capacities were found to vary linearly with temperature until entering the transient state near pore ice's melting temperatures. Creep rates under constant loads increased with the rise in temperature which eventually resulted in accelerated tertiary creep in the near-melting temperatures. Stress profiles showed severe variation close to the soil surface while changing to an almost average constant value toward the tip of the pile. Investigating the behavioral change during the step-wise temperature rise revealed the characteristics of the transition from a frozen to unfrozen soil–structure interface. [ABSTRACT FROM AUTHOR]

Background: There are a limited number of commercially available sensors for monitoring the deformation of materials in-situ during harsh environment applications, such as those found in the nuclear and aerospace industries. Such sensing devices, including weldable strain gauges, extensometers, and linear variable differential transformers, can be destructive to material surfaces being investigated and typically require relatively large surface areas to attach (> 10 mm in length). Digital image correlation (DIC) is a viable, non-contact alternative to in-situ strain deformation. However, it often requires implementing artificial patterns using splattering techniques, which are difficult to reproduce. Objective: Additive manufacturing capabilities offer consistent patterns using programmable fabrication methods. Methods: In this work, a variety of small-scale periodic patterns with different geometries were printed directly on structural nuclear materials (i.e., stainless steel and aluminum tensile specimens) using an aerosol jet printer (AJP). Unlike other additive manufacturing techniques, AJP offers the advantage of materials selection. DIC was used to track and correlate strain to alternative measurement methods during cyclic loading, and tensile tests (up to 1100 µɛ) at room temperature. Results: The results confirmed AJP has better control of pattern parameters for small fields of view and facilitate the ability of DIC algorithms to adequately process patterns with periodicity. More specifically, the printed 100 μm spaced dot and 150 μm spaced line patterns provided accurate measurements with a maximum error of less than 2% and 4% on aluminum samples when compared to an extensometer and commercially available strain gauges. Conclusion: Our results highlight a new pattern fabrication technique that is form factor friendly for digital image correlation in nuclear applications. [ABSTRACT FROM AUTHOR]

Flexible tactile sensors play important roles in many areas, like human-machine interface, robotic manipulation, and biomedicine. However, their flexible form factor poses challenges in their integration with wafer-based devices, commercial chips, or circuit boards. Here, we introduce manufacturing approaches, device designs, integration strategies, and biomedical applications of a set of flexible, modular tactile sensors, which overcome the above challenges and achieve cooperation with commercial electronics. The sensors exploit lithographically defined thin wires of metal or alloy as the sensing elements. Arranging these elements across three-dimensional space enables accurate, hysteresis-free, and decoupled measurements of temperature, normal force, and shear force. Assembly of such sensors on flexible printed circuit boards together with commercial electronics forms various flexible electronic systems with capabilities in wireless measurements at the skin interface, continuous monitoring of biomechanical signals, and spatial mapping of tactile information. The flexible, modular tactile sensors expand the portfolio of functional components in both microelectronics and macroelectronics. [ABSTRACT FROM AUTHOR]

Extrusion tests were conducted on recycled coarse aggregate concrete with circular steel tubes (RCCST, 100% replacement of recycled coarse aggregate) to investigate the impact of freeze–thaw cycles on bond properties. RCCST samples were subjected to 0, 25, 50, 75, 100, 125 and 150 freeze–thaw cycles and their bond properties were then compared with those of natural coarse aggregate concrete with circular steel tubes (NCCST) after 0, 100 and 150 freeze–thaw cycles. The experimental results indicate that freeze–thaw cycling damages the internal structure of RCCST, causing a significant decrease in interfacial bond strength with an increase in the number of freeze–thaw cycles. Freeze–thaw RCCST exhibits lower peak load and higher peak slip compared to NCCST, with increases of 25.2%, 73.2%, and 70.3% after 0, 100, and 150 freeze–thaw cycles, respectively. Regression analysis was used to derive an exponential equation that describes the relationship between longitudinal strain and strain gauge position. Additionally, a segmented fitting method was employed to obtain an expression for the bond slip of the freeze–thaw RCCST with a circular steel pipe. [ABSTRACT FROM AUTHOR]

Bolt loosening can significantly impact the accuracy, stability, and safety of equipment. The detection of bolt loosening in a timely manner is crucial for ensuring the safety, reliability, performance, and service life of equipment, structures, and systems. Various methods exist for detecting bolt loosening, such as strain gauges and ultrasonic waves. However, these technologies have some limitations that impede their widespread application. In this paper, for the high-pressure pipe manifolds that may experience leakage accidents due to the loosening of bolts, an early bolt loosening detection method based on digital image correlation is proposed. Initially, a model is established through tensile tests to relate the average strain on the side of the bolt head to the axial force. Subsequently, an industrial camera captures images of bolts with random speckles under operational conditions. Using digital image correlation technology, the average strain in a specific region on the side of the bolt head is calculated. By integrating the average strain into the established relationship model between the average strain and axial force, the axial force of the bolt under operational conditions can be predicted, enabling the early assessment of bolt loosening. The findings show that the average strain on the side of the bolt head increases proportionally with the axial force, indicating a strong linear relationship. This method enables accurate prediction of the bolt's axial force, offering a new approach for identifying the early loosening of bolts in high-pressure manifolds and monitoring structural health. [ABSTRACT FROM AUTHOR]

The checkerboard constitutes the best pattern for full‐field strain measurement because it maximizes image gradient. In the experimental mechanics community, employing this pattern is currently strongly limited because depositing it on the surface of specimens raises practical difficulties. A recent study shows, however, that it is technically possible by using a laser engraver. The present paper aims to push this solution forward by printing a checkerboard pattern on a thin polymeric film and then gluing the resulting laser‐engraved film on the specimen surface. The underlying idea is to separate the manufacturing process of this optical strain gauge on the one hand and its use on the other hand to help spread this strain measuring tool in the experimental mechanics community. The polymeric film employed here is the same as that used in the manufacturing process of classic electrical gauges, so one can rely on the know‐how of classic strain gauge bonding to glue this optical strain gauge on the specimen surface. The main difference between the proposed tool and classic electrical gauges is that the strain field beneath the polymeric support is measured instead of localized strain values. The paper is a proof of concept for this strain field measuring tool. The manufacturing and bonding processes are described in the paper. The localized spectrum analysis, a spectral technique developed for processing images of periodic patterns, is used to retrieve the strain fields from checkerboard images. Through two complementary examples, we show the ability of this new type of strain gauge to detect and quantify local details in the strain field beneath. A simplified 1D model is also proposed to assess the minimum width of the strain peak that can reliably be measured with this technique. [ABSTRACT FROM AUTHOR]

The interest in using new technologies to obtain recordings of on-water kinetic variables for assessing the performance of elite sprint kayakers has increased over the last decades but systematic approaches are warranted to ensure the validity and reliability of these measures. This study has an innovative approach, and the aim was to develop a new versatile jig including reference force sensors for both the calibration and validation of mutual static and dynamic stroke forces as measured with instrumented paddles at the high force levels used in elite sprint kayaking. Methods: A jig was constructed using a modified gym weight stack and a frame consisting of aluminum profiles permitting a fastening of custom-made kayak paddle shaft and blade support devices with certified force transducers combined with a data acquisition system to record blade and hand forces during static (constant load) and dynamic conditions (by paddle stroke simulation). A linear motion path incorporating a ball-bearing equipped carriage with sensors for the measurement of vertical distance and horizontal displacement was attached to the frame for recordings of various position measures on the paddle. The jig design with all components is extensively described to permit replication. The procedures for assessing the accuracy of the jig force instrumentation are reported, and with one brand of instrumented paddle used as an example, methods are described for force calibration and validation during static and dynamic conditions. Results: The results illustrate that the measured force with the jig instrumentation was similar to the applied force, calculated from the applied accurate mass (within a −1.4 to 1.8% difference) and similar to the force as calculated from the applied mass with the weight stack (within a −0.57 to 1.16% difference). The jig was suitable for the calibration and validation of forces in a range relevant for elite sprint kayaking under both static and dynamic conditions. During static conditions with a force direction equal to the calibration conditions and a force range from 98 to 590 N, all values for the instrumented paddle were within a −3.4 to 3.0% difference from the jig sensor values and 28 of 36 values were within ±2%. During dynamic conditions with paddle stroke simulations at 60 and 100 strokes/min and a target peak force of 400 N, the common force variables as measured by the instrumented paddle were not significantly different from the same measures by the jig (values at 100 strokes/min: peak force; 406.9 ± 18.4 vs. 401.9 ± 17.2 N, mean force; 212.8 ± 15.4 vs. 212.0 ± 14.4 N, time to peak force; 0.17 ± 0.02 vs. 0.18 ± 0.02 s, force impulse; 90.8 ± 11.2 vs. 90.5 ± 10.8 Ns, impulse duration; 0.43 ± 0.03 vs. 0.43 ± 0.03 s). Conclusion: A novel jig with several new functions is presented that enables the calibration and validation of force measurements with instrumented paddles by providing standardized conditions for calibration and force validation during both static and dynamic conditions in a force range relevant to elite sprint kayaking. [ABSTRACT FROM AUTHOR]

The development of systems for weighing vehicles in motion aims to introduce systems allowing automatic enforcement of regulations. HSWIM (high speed weight-in-motion) systems enable measurement of a mass of vehicles passing through a measurement station without disturbing the traffic flow. This article focuses on the calibration of a weighing station for moving vehicles, where strain gauge sensors are used to measure pressures. A solution was proposed to replace the calibration coefficients with calibration functions. The analysis was performed for two methods of determining wheel loads: based on the maximum of the signal from strain gauge sensors and on a method using the field under the signal and the vehicle's speed. Calibration functions were determined jointly for all test vehicles and separately for each of them. The use of a calibration function for a specific vehicle type made it possible to determine wheel pressure and gross weight with a level of accuracy that allowed the weigh-in-motion station to be classified as a direct enforcement system. The achieved improvement in the accuracy of weighing in motion did not require any interference with the measurement station. The proposed change in the method of calibration and, ultimately, determination of wheel loads required only a change in the algorithm for determining wheel loads. [ABSTRACT FROM AUTHOR]

The feasibility of using crushed limestone instead of sand in cement grout is examined in this work. This study entails performing several tests, including the Brazilian test, the compressive strength test, and the stress–strain correlation test. The curing times used were 7, 14, and 28 days for mixtures with various proportions of cement to limestone (1:1, 1:2, and 1:4). The conventional sand–cement grout laboratory tests were prepared using a similar methodology to examine the effectiveness of the suggested substitute. The findings show that the limestone-based grout has sufficient strength, but that it is less than that of the typical sand material. The values of the tensile strength and elastic modulus were determined. A focus was made on the tensile strength and stress–strain relationship. A special laboratory set-up was used to look at the progress of failure using strain gauges fitted to the cylindrical samples both vertically and horizontally. The angular shape of the particles' ability to interlock is responsible for the material's increase in strength. According to this study, crushed limestone can be used as a substitute for sand in circumstances where sand supply is constrained. The suggested grout can be used in the shotcrete of tunnels and rock surfaces. [ABSTRACT FROM AUTHOR]

Study Design: A prospective experimental study. Purpose: This biomechanical in vitro study aimed to examine the extent to which the use of a rod persuader (RP) leads to additional mechanical stress on the screw–rod system and determine its influence on the bony anchoring of primary pedicle screws. Overview of Literature: Degenerative spine diseases and deformities are the most common indications for the stabilization and fusion of spinal segments. The pedicle screw–rod system is considered the gold standard for dorsal stabilization, and an RP is also increasingly being considered to fit the spondylodesis material. Methods: Ten lumbar spines from body donors were examined. Bisegmental dorsal spinal lumbar interbody fusion of the L3–L5 segments was performed using a pedicle screw–rod system (ROCCIA Multi-LIF Cage; Silony Medical, Germany). In group 1, the titanium rod was inserted without tension, whereas in group 2, the rod was attached to the pedicle screws at the L4 and L5 levels, creating a 5-mm gap. To attach the rod, the RP was used to press the rod into the pedicle screw. The rod was left in place for 30 minutes and then removed. Results: The rod reduction technique significantly increased the mechanical load on the overall construct measured by strain gauges (p<0.05) and resulted in outright implant failure with pedicle screw pullout in 88.9%. Conclusions: In cases where the spondylodesis material is not fully attached within the pedicle screw, an RP can be used with extreme caution, particularly in osteoporotic bones, to avoid pedicle screw avulsion and screw anchor failure. [ABSTRACT FROM AUTHOR]

Open-ended pre-stressed high-strength concrete (PHC) pipe piles are susceptible to progressive distortion and even failure in the vicinity of the pile toe during driving into stiff soil or rock strata. This paper presents an experimental investigation conducted as part of a power plant construction in Huainan, China. After 50 piles were driven in the initial phase, the toe of 9 piles were detected as damaged using the sonic echo testing method. In the second construction phase, four piles were instrumented with longitudinal and circumferential fiber optic cables, as well as discrete strain gauges. The recorded responses of pipe piles throughout their driving process are analyzed to reveal the causes of damages. The results show that a maximum circumferential tensile stress developed at a distance of 1/6 pile length above the pile toe, with its value three times greater than that in other cross-sections. This high circumferential stress results in transverse cracks and the failure of open-ended PHC piles and is believed to be related to the formation of soil plugs. The findings provide valuable insights into performance evaluation of driven open-ended PHC piles. [ABSTRACT FROM AUTHOR]

Pile response in unsaturated soils is an area of interest due to its prevalence in real-world scenarios. Significant differences exist in the lateral behavior of single piles in partially saturated soils due to increased soil stiffness. In this study, a single pile was monotonically loaded laterally to investigate the performance of piles in soils with variable water table levels. Pile head lateral response showed that a mix of unsaturated-saturated soil led to an increase in lateral loads on the pile at a similar displacement compared with the fully saturated or dry soil conditions. The lateral response of the pile was obtained based on the curvature data from the strain gauges. A derivative method was used to generate the shear force and lateral resistance along the pile length based on finite differences at the seven strain gauge locations, thereby eliminating errors associated with curve fitting. Various lateral response plots, such as the normalized p-y curves, M-y curves, and maximum bending moment response plots, were used to assess the response to lateral load. Further, the effect of two different loading rates were assessed on the fully saturated and unsaturated-saturated soil, and the range of loading rates evaluated had minimal influence on the pile lateral response. Results indicated that considering the influence of the unsaturated soil could increase lateral resistance under similar lateral displacements. However, there is a risk of inducing large pile bending moments, potentially leading to pile flexural failure if the pile plastic moment is reached. [ABSTRACT FROM AUTHOR]

Structural health monitoring (SHM) is a technology aimed to monitor the soundness of the structures. Applications for aircraft structures are largely investigated. The goal is to utilize the information acquired during the monitoring to save maintenance costs, improve flight safety, and design lighter structures. Different issues, like load monitoring and impact detection, are investigated by SHM research. The most largely investigated issue is damage detection, i.e., developing a system that utilizes sensors to detect the damage in the structure. Damage detection can be performed with two sensors: dynamic and static. Dynamic sensors work by transmission of waves through the structures. Defects are identified by deviation and reflection of the waves by damages. The SHM approach described in this work is based on static sensors, like strain gages or fiber optics. The strain fields under load in pristine and damaged conditions are compared; the evaluation of the change in the strain field identifies damages. Two different algorithms for damage detection have been developed and patented in Leonardo Aircraft and are described in this work; they are based on the reverse finite element model (FEM) and neural network. The issues related to the strain field measurement are also briefly described. [ABSTRACT FROM AUTHOR]

In this study, the performance of recycled concrete aggregate (RCA/RSA) available in Agartala, Tripura (north-eastern regions of India), was studied in reinforced concrete members subjected to a severe artificially induced corrosive environment. The performance test was based on the non-destructive and destructive parameters of concrete. Due to the scarcity of normal stone aggregate (NSA) in this region, studying the effect of using such type of aggregate in reinforced concrete members help not only to mitigate the demand but also assists in waste management. The study also presents an innovative application of micro-bend opticalfibre sensors for corrosion monitoring and validated using other non-destructive instruments. The study presents an effective application of the micro-bend optical fibre sensor to predict the initiation of corrosion (de-passivation) and initiation of cracking (critical stress) due to corrosion in reinforced concrete specimens. Later, the results were validated using half-cell potentiometer and electrical strain gauge values. The specimen also presented different mechanical and durability properties with varying RCA percentages. A regression model to predict mechanical properties and corrosion amount (hoop strain) in reinforcement for different RCA-replaced concrete has been presented. The sorptivity and other porosity-related results were also presented for different RCA replacement percentage specimens. [ABSTRACT FROM AUTHOR]

As a cost-effective rock-supporting method, rockbolts have been widely used in geotechnical and mining engineering. Better understanding the load-transfer mechanism of rockbolts is of great importance for improving the accurate simulation of rockbolts applied in practical engineering. Numerous experimental studies on rockbolts have been conducted, and conventional instruments, such as strain gauges, have been used to monitor the deformation of rockbolts. Although researchers have reported on fiber optic-based monitoring, these data have not been verified by accurate strain gauges. In addition, there has been limited study on utilizing the fiber optic method to monitor the full range strain variation of rockbolts across varying rock strengths. In this study, distributed fiber optic sensing (DFOS), with an ultrahigh spatial resolution (0.01 mm), and strain gauges (SGs) were used to monitor the strain variation in rockbolts under pull-out tests, with the aim of comparing the performances of the DFOS and discrete strain gauges and determining the reliability and advantages of DFOS. It was found that: (1) the fiber optic data were able to perfectly reflect the complete decoupling mechanism of the bolt, which could not be observed in the strain gauge data; (2) the ultrahigh spatial resolution of the fiber optic method enabled it to accurately and fully exhibit the distribution of shear stress along the bolt; and (3) high rock strength can enhance the bonding performance of bolts and result in uneven stress distribution. [ABSTRACT FROM AUTHOR]

The in situ stress conditions of reservoirs are the fundamental parameters for determining the arrangements of horizontal boreholes and assessing borehole stability, especially for the exploration and exploitation of unconventional oil and gas. The borehole wall stress relief method (BWSRM) is a new technique that can directly measure three-dimensional (3D) stress without any assumptions regarding the stress field. In deep vertical borehole situations, a new experiment is proposed to prevent electronic components from becoming damp while simultaneously maintaining borehole stability. The effect of drilling fluid pressure on the strain measurement of the stress relief processes is studied. The finite-element model (FEM) simulates the stress relief process and verifies the theoretical solutions under different testing depths. The results show that complete stress relief is impossible under deep vertical borehole conditions, and the wall drilling process changes the stress conditions of the measured points from modified plane strain to triaxial compression. Therefore, the data measured by the strain gauges cannot be directly imported into the original relationships between the measured strains and far-field stress. The comparisons between the original theoretical solutions and FEM results indicate that if the confining pressure is ignored, then the maximum error between the measured and real in situ stress components is over 35%. After correcting the estimated strain data using the proposed methods, the stress tensors obtained from theoretical equations are consistent with the natural stress tensors. [ABSTRACT FROM AUTHOR]

This paper presents experimental testing evaluating the ability of a bridge deck deicing system to mitigate concrete deterioration from thermal stresses, frost action, and early-age cracking. Two experimental bridge deck models were constructed with embedded heat exchanger tubing and instrumented with thermocouples and strain gauges. Model 1 evaluated the efficiency of a deicing system in deicing and mitigating concrete deterioration from thermal stresses and frost action in concrete bridge decks, while Model 2 tested the effect of a deicing system on early-age cracking in bridge decks. The models were tested in a cold chamber laboratory under conditions representative of Montana's winter weather, with the system circulating warm fluid through the decks. Results showed the system succeeded in increasing concrete temperatures at all depths. While the system did not always raise temperatures above freezing, the consistent increases suggested that the system could enable deicing and mitigate frost action given certain conditions and higher inlet fluid temperatures. The system also successfully decreased thermal movement strain by up to 40% and reduced thermal shrinkage by decreasing the difference between peak cured and stabilized temperatures. Although the system did not eliminate thermal gradients, the maximum gradient induced was insignificant. Further testing is needed on strength impacts. Overall, the deicing system showed promise to reduce thermally induced deterioration in concrete bridge decks by regulating temperatures. [ABSTRACT FROM AUTHOR]

Many of the current fatigue design specifications for cross frames, especially those in composite steel bridge systems, have primarily been based on computational studies and component-level laboratory experiments. To fully understand the behavior of cross frames when subjected to in-service truck traffic and to critically evaluate legacy design provisions, in-service field monitoring of cross frames in various composite systems is important. Therefore, select cross frames in three bridges in the greater Houston area were instrumented with strain gage sensors—one straight bridge with normal supports, one straight bridge with skewed supports, and one horizontally curved bridge with radial supports. For each bridge, rainflow counting techniques and other postprocessing procedures were implemented for a monitoring period of one month to compare the measured cross-frame response. Among other key observations, the measured data demonstrated that load-induced force effects in the cross frames of the skewed bridge system exceeded those in the bridges with normal or radial supports and that cross-frame response was highly sensitive to the longitudinal and transverse truck positions. In all cases, though, the measured damage accumulated on all instrumented cross-frame members during their respective monitoring periods, if extrapolated to the entire service life, would likely not cause significant load-induced cracking in the critical welded gusset-to-member connections. [ABSTRACT FROM AUTHOR]

Hydrodynamic linear guides in machine tools offer a high load capacity and excellent damping characteristics, improving stability, precision, and vibration reduction. This study builds on previous research where floating heights were verified with a simulation model limited to measured floating heights. Advancements include incorporating pressure sensors into a fixed steel rail, enabling simultaneous measurement of oil film pressure and floating heights for a comprehensive understanding of lubrication conditions within the lubrication gap. The experimental results explore the effects of different lubrication methods, providing valuable insights into cavitation and lubrication adequacy. The results demonstrate the feasibility of utilizing pressure sensors to measure oil film pressure within the lubrication gap, providing a nuanced understanding of lubrication dynamics. By measuring both floating heights and pressure measurement, distinctions between hydrodynamic lubrication, mixed friction regions, and instances of lubricant deficiency become readily discernible. The variations in real-time oil film pressure and floating heights help to optimize the lubrication cycle for hydrodynamic linear guides, enhancing system performance and longevity. [ABSTRACT FROM AUTHOR]

This paper is devoted to a new gauge of small dynamic bending deformations of structures. Unlike previously existing strain gauges that measure elongation or compression at a certain point on the surface of a deformable body, the proposed gauge measures the change in curvature at a point on the surface of a deformable body and does not respond to elongation–compression strains. The gauge is a layered bar made of piezoelectric and elastic materials. It functions using the direct piezoelectric effect. In order to competently study the deformed state of a structure at points on a surface, it is necessary to determine all components of the strain tensor. The gauges currently used measure only elongational or compressive strains, which does not provide a complete picture of the strain state. It is very important to complement these deformations with bending strains measured by the new gauge. [ABSTRACT FROM AUTHOR]

This study focuses on the successful fabrication of a cost-effective strain sensor using exclusively additive manufacturing Fused Deposition Modeling (FDM) technology, enabling fast on-site production, which is particularly advantageous in maritime settings, reducing downtime, and supporting a circular economy approach by minimizing inventory needs and environmental footprint. The principle of operation of the developed device is based on the piezoresistive characteristics of a carbon nanotube (CNT)-enriched building material, from which the main sensing element consists. The prototype exhibited reliable piezoresistive properties, and a clear correlation was observed between the thermal treatment of the printed piezoresistor and the resulting gauge factor, linearity, and hysteresis. Its robustness, simple design, and single-step manufacturing process, together with its ability to be integrated into the readout circuitry through standard soldering, enhance its reliability and durability. The key advantages of the proposed device include its low cost, simple design, and rapid remote production. [ABSTRACT FROM AUTHOR]

Fastened joints still represent the most common method for joining components within the aerospace industry. For fastened joints that experience high cyclical stresses, the application of the Split Sleeve Cold Expansion (SsCxTM) process has proven to be highly effective in extending the total fatigue life. This paper provides experimental strain measurements from around holes subjected to the SsCxTM process. Measurements on aluminum alloy coupons were taken using strain gauges and fiber optic strain sensors, with those measurements being used to validate the results from a three-dimensional (3D) digital image correlation (DIC) system. These validated experimental results were then compared to three separate finite-element analysis (FEA) process simulations each performed using one of three different material hardening models, Chaboche, kinematic and isotropic hardening. A finite-element leveling process was then used to compare the FEA results to the DIC measurements to highlight which hardening model provided the best correspondence to the DIC measurements. Although all hardening models provided reasonable similarity to the DIC results, for this particular aluminum alloy, an isotropic hardening model provided the best results. [ABSTRACT FROM AUTHOR]

The service behavior of ductile metallic materials, when they have previously undergone technological plastic deformation, depends on the deformation conditions. These are represented, among others, by the deformation rate, the process temperature, the applied pressures, and the introduced stresses, as well as other process variables. The investigation of the mechanical properties obtained after plastic deformation is an important means that contains two characteristics: on the one hand, to determine to what extent the parameters of the technological manufacturing process influence the main characteristics of the final component; and, on the other hand, on the basis of these characteristics, to analyze whether the component subjected to plastic deformation will be able to function reliably and safely. In the present work, an experimental study was made of the residual stresses developed and hardnesses obtained both in the immediate vicinity of a highly plastically deformed area and in an area previously obtained by rolling, without additional plastic deformation. For the determination of the residual stresses, the tensiometric rosette drilling method was used. By determining the same quantities in a non-plastically deformed area, significant changes in the values of the two quantities in the plastically deformed area were found. An increase in the maximum principal normal stresses by approx. 60 MPa and an increase in the Rockwel hardness by approx. 10 HRC was found. A sample was taken from the area under a plastic deformed circular shape, and was analyzed microscopically. [ABSTRACT FROM AUTHOR]

Effective transmission of stress between fillers and the host matrix is instrumental in enhancing the properties of nanocomposites and optimizing filler reinforcement. This study delves into understanding stress transfer in materials, exploring the impact of synthesis methods and matrix materials through a comprehensive examination of a bilayer graphene (BLG)‐polydimethylsiloxane (PDMS) nanocomposite. BLG was synthesized via chemical exfoliation and subjected to various strain conditions within a PDMS matrix. A precisely controlled strain, ranging from 0% to 0.19%, was applied using a meticulous 4‐point bending method, monitored with a standard strain gauge. The study unveiled significant shifts in the Raman spectra's 2D band, indicating a direct linear relationship with applied strain. Utilizing contour mapping techniques on well‐defined Raman spectra and stress‐induced band shifts, we mapped strain distribution within the BLG layer. The results revealed a gradual increase in strain from the lower to the upper end of the BLG structure, resembling strain behaviors observed in differently shaped fibers. These compelling findings advance our understanding of strain dynamics within BLG‐PDMS nanocomposites, highlighting the crucial role of strain mapping methodologies in scrutinizing the material's structural response to deformation. Highlights: The study reports successful synthesis of high‐quality bilayer graphene (BLG) using a chemical exfoliation method, as evidenced by the sharp 2D and G Raman peaks.Significant shifts in 2D band exhibited linear correlation between applied strain; observed within precise strain levels of 0% to 0.19%.Contour maps revealed a gradual increase in strain from the lower to the upper end of the BLG structure, akin to strain behaviors observed in differently shaped fibers. [ABSTRACT FROM AUTHOR]

Flexible strain sensors are widely used in the fields of human motion monitoring, electronic skin, and soft robotics. In this work, to satisfy the demand for high‐sensitivity, low‐cost, and fast‐response flexible strain sensors for these fields, embedded 3D printing (E‐3DP) technology is employed to fabricate highly sensitive and fast‐responding flexible strain sensors. The effects of conductive carbon paste concentration and printing process parameters by establishing the E‐3DP system on the piezoresistive behavior of the sensor were investigated. The results show that the gauge factor of the strain sensor is about 36.1 and 247.67, under the strain of 0%–40% and 40%–45%, respectively. Its response/recovery time is about 250/350 ms. On this basis, the sensor can also accurately sense and distinguish the motion in distinct parts of the human body, demonstrating that the flexible strain sensor manufactured by the method possesses the potential to be widely used in the fields of human motion monitoring, electronic skin, and soft robotics. [ABSTRACT FROM AUTHOR]

Tactile texture sensors are designed to evaluate the sensations felt when a human touches an object. Prior studies have demonstrated the necessity for these sensors to have compliant ridges on their surfaces that mimic human fingerprints. These features enable the simulation of contact phenomena, especially friction and vibration, between human fingertips and objects, enhancing the tactile sensation evaluation. However, the ridges on tactile sensors are susceptible to abrasion damage from repeated use. To date, the healing function of abraded ridges has not been proposed, and its effectiveness needs to be demonstrated. In this study, we investigated whether the signal detection capabilities of a sensor with abraded epidermal ridges could be restored by healing the ridges using polyvinyl chloride plastisol as the sensor material. We developed a prototype tactile sensor with an embedded strain gauge, which was used to repeatedly scan roughness specimens. After more than 1000 measurements, we observed significant deterioration in the sensor's output signal level. The ridges were then reshaped using a mold with a heating function, allowing the sensor to partially regain its original signal levels. This method shows potential for extending the operational lifespan of tactile texture sensors with compliant ridges. [ABSTRACT FROM AUTHOR]

To better address mechanical behavior, it is necessary to make use of modern tools through which it is possible to run predictions, simulate scenarios, and optimize decisions. sources integration. This will increase the capability of detecting material modifications that forerun damage and/or to forecast the stage in the future when very likely fatigue is initiating and propagating cracks. Early warning outcomes obtained by the synergetic implementation of NDE-based protocols for studying mechanical and fatigue and fracture behavior will enhance the preparedness toward economically sustainable future damage control scenarios. Specifically, these early warning outcomes will be developed in the form of retopologized models to be used coupled with FEA. This paper presents the first stage of calibration and the combination of a system of different sensors (photogrammetry, laser scanning and strain gages) for the creation of volumetric models suitable for the prediction of failure of FEA software. The test objects were two components of car suspension to which strain gauges were attached to measure its deformation under cyclic loading. The calibration of the methodology was carried out using models obtained from photogrammetry and experimental strain gauge measurements. [ABSTRACT FROM AUTHOR]

Silicone elastomers are continuously gaining importance in a variety of industrial applications, including strain gauges, electrical heaters, electromagnetic interference, and electrostatic discharge protection coatings. But these materials have certain drawbacks such as high cost, poor resistance to solvents, low tear strength, limited high-temperature resistance, difficulty in bonding and limited abrasion resistance. Therefore, unique nanocomposites of organosilicon elastomers with metals have been prepared using MWCNTs. The prepared nanocomposites demonstrated nano-diameter structures (15–60 nm) with micron-sized fibrous structures (12–60 μm). Aluminum elongated inclusions (60 µm in size) and bronze spherical inclusions (12–30 µm) were observed in the nanocomposites. The composites containing MWCNTs, Co-Mo/Al2O3-MgO catalyst and bronze (3 wt. %) had the maximum thermal and electrical conductivity. The prepared nanocomposites were used to make the heaters. The heating of the heaters was carried out by applying a voltage of 12–24 V. The Highest temperature achieved was more than 50 °C in all the heaters. By supplying 12–24 V electricity to the heaters in the ventilation and heat recirculation system, the interior of a minibus or living space can be heated. The developed electric heater has another important economic application in temperature-controlled materials. [ABSTRACT FROM AUTHOR]

The project case of Qiwu Bridge using link slab action between simply supported composite spans is introduced. The 60 m-span girder of Qiwu Bridge is the longest and heaviest among the composite girders erected by bridge-erecting machine in China. Qiwu Bridge consists of a series of 3 simply supported spans built with composite girders and connected at the pier supports by a link slab. This solution has both advantages of (1) smooth driving condition and enhancement of durability by removing expansion joints and (2) clear structural behavior as simply supported spans. A finite element model was established to simulate and predict the mechanical response of this semi-continuous solution. Numerical results showed that the removal of the shear connection around the link slab decreased the stress level but also caused a stress mutation. Qiwu Bridge was also monitored by vibrating wire strain gages to follow its actual structural response. From preliminary monitoring data and numerical results, it can be concluded that the proposed construction method and the static scheme is safe for the 60-span composite girder with a large safety margin. Further experimental results will be obtained during the service stage of the bridge to validate the in-service performance of the proposed steel-concrete composite bridge with link slab. [ABSTRACT FROM AUTHOR]

With the increasing application of thin-film sensors in high-temperature applications, there is an escalating demand for insulation layers that provide enhanced resistance to elevated temperatures. However, failure often occurs because of the mismatch in thermal expansion coefficients between the insulation layer and the substrate. This study proposes an underlayer comprising a double ceramic layer of CeYSZ and Al 2 O 3 , which preserves the high thermal expansion coefficient and corrosion resistance of CeYSZ while enhancing its electrical insulating properties. The high-temperature electrical insulation performance of underlayers with different ceramic layer structures was experimentally evaluated. The results indicate that the CeYSZ/Al 2 O 3 double ceramic layer exhibits an electrical resistance of 2.1*106 Ω at 800 °C and minimal drift after 5 h, demonstrating high stability. Finally, PdCr thin-film strain gauges were fabricated on CeYSZ/Al 2 O 3 double ceramic layer, revealing the stability of the electrical resistance at high temperatures. The porosity of the underlayer cross-sections was also compared, revealing that the double ceramic layer coating effectively fills pores and cracks inherent in single-layer coatings. This mitigation of conductive pathways reduces the occurrence of such defects, thereby enhancing the high-temperature insulation performance of the underlayer. © 2014 xxxxxxxx. Hosting by Elsevier B.V. All rights reserved. [ABSTRACT FROM AUTHOR]

A screw micropile is a multi-sectional pile typically consisting of a smooth segment at the top, a threaded segment in the middle and a tapered segment at the bottom. Although the axial behavior of this pile type has lately been studied, response to lateral loading and contribution of the threads to lateral capacities are yet to be investigated. To facilitate the design of this pile type for applications where wind or seismic loads are concerned, there is a necessity to examine the lateral behavior and capacities of screw micropiles and effect of the threads on the lateral capacities. Hence, lateral load field test programs were carried out on six types of screw micropiles at two cohesive soil sites and a cohesionless soil site. Selected piles were instrumented with bending moment strain gauges along the pile shaft. A geotechnical site investigation was carried out at each site to obtain soil profiles and properties. The lateral load versus displacement curves and the bending moment distribution were obtained. The lateral capacity and failure mode of the piles were determined from existing methods and analysis of the field test results. The lateral capacities of the piles were estimated using the Broms method without considering the effects of the thread. The estimated and measured lateral capacities were in a good agreement. This suggested that the effects of the threads on the lateral capacities were minimal. In addition, the effects of the tapered segments on the lateral response of the piles were negligible. This research was the first one for screw micropiles subjected to lateral loading and the outcome may support the engineering of the piles and further studies on soil-screw micropile interaction. [ABSTRACT FROM AUTHOR]

This paper outlines an experimental investigation conducted at the INCAS trisonic wind tunnel, focusing on the determination of pitch damping coefficient. The model used for this investigation is the Basic Finner Model, a standard model for dynamic tests which consists in a cone-cylinder body with four rectangular fins. The study aims to evaluate the influence of various parameters—including the Mach number, angle of attack, reduced frequency, center of rotation, and roll angle—on pitch damping coefficient. The employed method for determining these coefficients is the free oscillation method which consists in measuring the model oscillation in free stream after an initial perturbation. In order to perform these dynamic tests in the wind tunnel, a dedicated rig was developed to initiate the model's oscillation using a linear servo-actuator and to record its oscillation using a strain gauge. The results obtained from the experiments illustrate how each parameter impacts the pitch damping coefficient, highlighting the precision of the measurements. The paper's conclusion presents that the developed rig and the method used provide accurate results, and the variation in different parameters can change the damping coefficient. [ABSTRACT FROM AUTHOR]

Cutting force is one of the most basic signals that can reflect the information of the cutting process, so it is very necessary to study the strain elastic element of strain gauge wireless rotating dynamometers. This paper proposes a strain elastic element with a double-layer cross floating beam that can be applied to the strain gauge wireless rotating dynamometer, which can simultaneously obtain the four-component cutting force/torque information of F X , F Y , F Z , and M Z . Based on the proposed strain elastic element, a compact strain gauge wireless rotating dynamometer is designed, which is composed of a tool holder, upper connection flange, strain elastic element, lower connection flange, tool base, and data acquisition and wireless transmission system. The static model of the double-layer cross floating beam on the strain elastic element is established by the segmented rigid body method, and the relationships between the material, force, structural parameters, and the strain and deformation of the floating beam are obtained. The static model is consistent with the finite element solution, which proves the rationality of the static model. Based on the established static model, the sequential quadratic programming algorithm is used to optimize the structural parameters of the double-layer cross floating beam to maximize the sensitivity of the floating beam. The overall structure of the strain elastic element is analyzed by finite element software, and the strain of the structure under simulation conditions is obtained, which provides a reference for subsequent calibration tests and circuit design. The calibration matrix and dynamic performance of the strain elastic element are obtained by the static calibration test, dynamic calibration test, and cutting test. The results show that the proposed strain elastic element has high sensitivity and low cross-sensitivity error, and can be applied to the strain gauge wireless rotating dynamometer to measure medium- and low-speed cutting forces. [ABSTRACT FROM AUTHOR]

The wind turbine design process requires performing thousands of simulations for a wide range of inflow and control conditions, which necessitates computationally efficient yet time-accurate models, especially when considering wind farm settings. To this end, FAST.Farm is a dynamic-wake-meandering-based mid-fidelity engineering tool developed by the National Renewable Energy Laboratory targeted at accurately and efficiently predicting wind turbine power production and structural loading in wind farm settings, including wake interactions between turbines. This work is an extension of a study that addressed constructing a diurnal cycle evolution based on experimental data. Here, this inflow is used to validate the turbine structural and wake-meandering response between experimental data, FAST.Farm simulation results, and high-fidelity large-eddy simulation results from the coupled Simulator fOr Wind Farm Applications (SOWFA)–OpenFAST tool. The validation occurs within the nocturnal stable boundary layer when corresponding meteorological and turbine data are available. To this end, we compared the load results from FAST.Farm and SOWFA–OpenFAST to multi-turbine measurements from a subset of a full-scale wind farm. Computational predictions of blade-root and tower-base bending loads are compared to 10 min statistics of strain gauge measurements during 3.5 h of the evolving stable boundary layer, generally with good agreement. This time period coincided with an active wake-steering campaign of an upstream turbine, resulting in time-varying yaw positions of all turbines. Wake meandering was also compared between the computational solutions, generally with excellent agreement. Simulations were based on a high-fidelity precursor constructed from inflow measurements and using state-of-the-art mesoscale-to-microscale coupling. [ABSTRACT FROM AUTHOR]

To investigate the performance of in-service skewed bridges, two continuous two-span steel I-girder bridges, one skewed 45° with integral abutments and the other skewed 41° with stub abutments, were instrumented during construction for long-term field monitoring. The bridges are located near each other and experience similar traffic volume and thermal variation, from roughly −18°C to 38°C (0°F to 100°F). Critical girders and cross-frames were instrumented with strain gauges and/or tiltmeters, and temperature was recorded at each sensor. Superstructure response over more than 2 years of data collection was recorded and studied, including for the in-service first-stage half bridges (temporarily for 6 months) and the full bridges. Girder cross-sections and cross-frames were within the elastic range during field monitoring, so stress directly relates to measured strain. The bridge superstructures experienced cyclic stress variation under thermal loading—there was clear linear correlation between bridge response and seasonal temperature variation, especially for decomposed girder axial stress and strong-axis bending stress. Deviation from the correlation was observed due to changes in abutment restraint during seasonal temperature variation and thermal gradient under daily temperature changes. Exterior girders were frequently unevenly heated by direct sunlight, which induced a diverging daily stress–temperature relationship compared to long-term observations. Thermal response of exterior girders is more complex than interior girders regarding both strong-axis and lateral bending, which is often not incorporated in standard bridge design procedures. Several girder bottom flanges and cross-frame members exhibited atypical increasing stress that started during the first cold-weather period; some of the stress development continued over time, regardless of long-term thermal cycles. [ABSTRACT FROM AUTHOR]

Corrosion is a major cause of deterioration in conventional steel-reinforced prestressed concrete (PC) piles installed in aggressive (marine) environments. As foundation members in bridges, deteriorated piles may result in failure or expensive repair or reconstruction. Corrosion resistant alternatives for reinforcing piles longitudinally and transversely include carbon fiber composite cables (CFCC) and stainless-steel (SS). However, the cost of these alternatives is prohibitive, which in turn increases the production cost of PC piles. To mitigate the high cost of CFCC and SS piles, the spirals in these corrosion resistant piles can be safely replaced by glass fiber–reinforced polymer (GFRP) bars in spiral form. In this research, the effectiveness of GFRP spirals in confining PC piles is presented by showing results of impact experiments conducted on full-size specimens. One control pile was reinforced with steel strands and spirals, while another pile was reinforced with steel strands and GFRP spirals. The spirals within the piles were instrumented at critical locations with strain gauges to record spiral responses. Externally, pile driving analyzer strain gauges and accelerometers were installed for pile response along loading direction. In addition, to further understand the spatial response of the piles tested, three-dimensional finite-element (FE) models were developed using a commercially available code to simulate the impact test. For the FE model, concrete behavior of was modeled using concrete damaged plasticity model, the behavior of steel strands was simulated using a bilinear elastoplastic material, and the GFRP spiral behavior was modeled using a linear elastic material. The results of the research show that PC piles can be confined with GFRP spirals, without decreasing the load-carrying capacity of the pile. Practical Applications: This research brought forth valuable insights with practical implications, particularly regarding the use of glass fiber–reinforced polymer (GFRP) spirals within prestressed concrete applications. The practical applications encompass several key points that stand to influence engineering practices. Notably, both experimental results and finite-element studies assert that prestressed concrete piles reinforced with GFRP spirals exhibit performance comparable to their traditional counterparts employing steel spirals. This similarity extends to a robust response under impact loads, indicating that prestressed concrete piles featuring GFRP spirals as lateral reinforcement can effectively withstand pile driving forces, rendering them suitable for practical applications. Furthermore, the study introduces the prospect of enhancing corrosion resistance in prestressed concrete piles by incorporating GFRP spirals in combination with corrosion-resistant strands. This development expands the feasibility of deploying corrosion resistant prestressed concrete piles for bridge foundations in marine environments. Engineers engaged in bridge construction projects are thus encouraged to explore the adoption of GFRP-reinforced prestressed concrete piles, anticipating enhanced durability and longevity for bridge structures, especially in regions subject to harsh environmental conditions. This plays a pivotal role in advancing resilient and sustainable infrastructure practices within the realm of civil engineering and construction. [ABSTRACT FROM AUTHOR]

Borehole strain gauges play a crucial role in geophysical, seismological, and crustal dynamics studies. While existing borehole strain gauges are proficient in measuring horizontal strains within vertical boreholes, their effectiveness in capturing vertical and oblique strains is limited due to technical constraints arising from the cylindrical probe's characteristics. However, the accurate measurement of three-dimensional strain is essential for a comprehensive understanding of crustal tectonics, dynamics, and geophysics, particularly considering the diverse geological structures and force sources within the crustal medium. In this study, we present a novel approach to address this challenge by enhancing an existing horizontal-component borehole strain gauge with a bellows structure and line strain measurement technology to enable vertical and borehole oblique strain measurements. Integrating these enhancements with horizontal strain measurement capabilities enables comprehensive three-dimensional borehole strain measurements within the same hole section. The system was deployed and tested at the Gongxian seismic station in Sichuan Province. Clear observations of solid tides were recorded across horizontal, oblique, and vertical measurement units, with the tidal morphology and amplitude being consistent with the theoretical calculations. The achieved measurement sensitivity of 10-10 meets the requirements for borehole strain measurement, enabling the characterization of three-dimensional strain states within boreholes through association methods. [ABSTRACT FROM AUTHOR]

As the basic application of fiber optic sensing technology, strain measurement accuracy as a key index needs to be further calibrated and analyzed. In this paper, accuracy calibration experiments and the related analyses of two fiber-optic sensing technologies, the fiber-optic grating (FBG) and optical frequency domain reflectometry (OFDR), are carried out using a standard beam of equal strength and a mature resistive strain gauge (ESG). The fiber-optic single-point strain data for loading and unloading changes of the beams of equal strength show good continuity and linearity, with good cyclic stability, and the error in the strain test data is less than 2% after repeated loading. At the same time, using finite element theory to analyze the data and using the measured data error within 5%, a good strain test curve linearity is achieved and R2 is better than 0.998. After repeated loading and unloading tests, it is verified that the fiber grating and the distributed optical fiber in the strain test have good stability in repeatability accuracy. The calibration experiments and data analysis in this paper further illustrate the three sensing technologies in determining the strain test accuracy and the advantages and disadvantages of the indicators, and the development of the fiber optic sensing technology application provides basic technical support. [ABSTRACT FROM AUTHOR]

The critical crack lengths of wet-sieved concrete and fully graded concrete obtained from experimental measurements, numerical simulation and an analytical solution based on linear elastic fracture mechanics were quantitatively compared. Experiments were conducted on wedge-splitting specimens with depths of 200–1500 mm and a maximum aggregate size of 150 mm. Strain gauges and clip gauges were pasted and mounted along the direction of crack growth to measure the critical crack length. Numerical and analytical methods were used to calculate the critical crack length. The average relative error between the analytical calculations and measurements was still 14%, even for a specimen depth of 1500 mm. The effective fracture toughness was calculated by combining the peak load and critical crack length, resulting in an average relative error of 17%. These results indicate that the existing analytical method for determining the critical crack length is inadequate. Consequently, a modified analytical method was adopted, using 95% of the peak load in the post-peak region and the corresponding crack mouth opening displacement, which provided results that agreed well with the experimental data. Furthermore, the effective fracture toughness could be reasonably derived using the critical crack length from the modified analytical method. [ABSTRACT FROM AUTHOR]