scholarly journals Considerations for Measuring Residual Stresses in Driven Piles with Vibrating Wire Strain Gauges

2021 ◽  
Author(s):  
James Ryan Bartz ◽  
James A. Blatz
Keyword(s):  
Residual Stresses ◽  
Temperature Effects ◽  
Strain Gauges ◽  
Pile Driving ◽  
Driven Piles ◽  
Vibrating Wire ◽  
Data Logger ◽  
Temperature Changes ◽  
Wire Strain ◽  
Below Ground

Vibrating wire strain gauges are often the preferred technology for measuring strain in driven piles. However, measuring the residual strain after pile driving is challenging to accomplish using vibrating wire gauges. The driving process can cause a shift in the no-load reading from a relaxation of locked-in manufacturing strains in the pile or relaxation of the gauge wire tension. Also, there are temperature effects from installing piles below ground. A test pile program was developed using driven steel H-piles instrumented with vibrating wire strain gauges. The piles were subjected to dynamic forces by striking against a steel plate in attempt to relax the locked-in manufacturing strain prior to installation. The strain gauges and thermistors were connected to a data logger during pile driving to record strain and temperature changes following installation. It was observed that applying a dynamic impact to the piles prior to installation resulted in a shift of 0 to 5 microstrain. Temperature effects from installing the piles in cooler ground resulted in a shifts of strain in excess of 60 microstrain in some strain gauges. It is concluded that temperature induced shifts to strain must be measured following pile driving to interpret residual stresses.

Evaluation of Negative Skin Friction on Bridge Abutment Piles

2021 ◽  
Vol 15 (2) ◽  
Author(s):  
Osama Drbe
Keyword(s):  
Skin Friction ◽  
Pore Water Pressure ◽  
Design Method ◽  
Water Pressure ◽  
Strain Gauges ◽  
Total Stress ◽  
Vibrating Wire ◽  
Negative Skin Friction ◽  
Drag Forces ◽  
Wire Strain

Piles are used to transfer loads of structures to deeper and stronger soil layers through skin friction and/or end bearing. Surcharge loads, site grading, or dewatering may induce downward movement of soil adjacent to piles installed in a compressible medium. This movement creates negative skin friction stresses acting downward at the pile-soil interface, which applies additional loads “drag forces” to the pile causing a maximum axial load in the pile shaft at the “neutral plane”. To evaluate the development of drag forces, a comprehensive field monitoring program was conducted over four years for three instrumented abutment H-piles as part of a three-span bridge project. The soil settlement and changes in pore water pressure in the soil adjacent to the piles due to the construction of an approach embankment were monitored using multiple-point extensometers and vibrating wire piezometers. The piles’ elastic settlement and strains were measured using single-point extensometers and vibrating wire strain gauges. The field measurements are presented and discussed in terms of responses time histories and load distribution along one pile shaft. In addition, the calculated forces from vibrating wire strain gauges are compared with the unified design method prediction considering the total stress method (α-method) for cohesive soils. The results show that the maximum drag force was developed after the complete dissipation of excess pore water pressure and that the location of neutral plane varied during the embankment construction stages. Employing the total stress method in the unified design method provided a reasonable prediction of the drag force and the neutral plane’s location.

scholarly journals Temperature and Strain Correlation of Bridge Parallel Structure Based on Vibrating Wire Strain Sensor

Sensors ◽  
2020 ◽  
Vol 20 (3) ◽  
pp. 658 ◽  
Author(s):  
Lu Peng ◽  
Genqiang Jing ◽  
Zhu Luo ◽  
Xin Yuan ◽  
Yixu Wang ◽  
...  
Keyword(s):  
Sensor Data ◽  
Parallel Structure ◽  
Strain Gauges ◽  
Final Conclusion ◽  
Vibrating Wire ◽  
Traceability System ◽  
Wire Strain ◽  
Time Work ◽  
Long Time ◽  
Dynamic Acquisition

Deformation is a ubiquitous phenomenon in nature. This process usually refers to the change in shape, size, and position of an object in the time and spatial domain under various loads. Under normal circumstances, during engineering construction, technicians are generally required to monitor the safe operation of structural facilities in the transportation field and the health of bridge, because monitoring in the engineering process plays an important role in construction safety. Considering the reliability risk of sensors after a long-time work period, such as signal drift, accurate measurement of strain gauges is inseparable from the value traceability system of high-precision strain gauges. In this study, two vibrating wire strain gauges with the same working principle were measured using the parallel method at similar positions. First, based on the principle of time series, the experiment used high-frequency dynamic acquisition to measure the thermometer strain of two vibrating wire strain gauges. Second, this experiment analyzed the correlation between strain and temperature measured separately. Under the condition of different prestress, this experiment studied the influencing relationship of temperature corresponding variable. In this experiment, the measurement repetitiveness was analyzed using the meteorology knowledge of single sensor data, focused on researching the influence of temperature and prestress effect on sensors by analyzing differences of their measurement results in a specified situation. Then, the reliability and stability of dynamic vibrating wire strain gauge were verified in the experiment. The final conclusion of the experiment is the actual engineering in the later stage. Onsite online meteorology in the application provides support.

Experimental Study on Transversal Stress of Precast Simply Supported Box Girder during the Pre-Tensioning and Initial Tensioning Stages

2011 ◽  
Vol 243-249 ◽  
pp. 1689-1693
Author(s):  
Zhang Rui ◽  
Wen Liang Lu
Keyword(s):  
Strain Gauges ◽  
Transverse Strain ◽  
Strain Development ◽  
Vibrating Wire ◽  
Box Girder ◽  
Simply Supported ◽  
Ballastless Track ◽  
Transverse Tensile ◽  
Wire Strain ◽  
Research Findings

Experimental research was conducted on the transverse stress of 32m post-tensioned precast simply supported concrete box girder with ballastless track. Vibrating wire strain gauges were embedded in the key sections to monitor the concrete transverse strain. The concrete strain development law was analyzed. The monitored results showed that there were low transverse tensile stresses and the cracking resistance of the girder was enough during pre-tensioning stage. The research findings provided effective experimental data for design and construction quality control.

scholarly journals Mechanical response of a thermal micro-pile installed in stratified sedimentary soil

2020 ◽  
Vol 205 ◽  
pp. 05007
Author(s):  
Brunella Casagrande ◽  
Fernando Saboya ◽  
Sergio Tibana ◽  
John S. McCartney
Keyword(s):  
Mechanical Response ◽  
Mechanical Performance ◽  
Thermal Response ◽  
Deep Understanding ◽  
Tropical Soil ◽  
Temperate Climate ◽  
Strain Gauges ◽  
Vibrating Wire ◽  
Wire Strain ◽  
Surrounding Soil

Data regarding the behavior of thermal piles in tropical countries is not as readily available as those in European or other temperate climate regions, where most applications are directed toward extracting heat from the subsurface. Similarly, a deep understanding of thermal piles constructed using the micropile technique has not been obtained. In micropiles, the installation process can disturb the surrounding soil, especially at the tip. This paper presents the results from a set of thermal response tests (TRT) performed on a 12 m-long instrumented thermal micro-pile installed in a sedimentary tropical soil. Vibrating wire strain gauges were installed in order to assess the mechanical performance of the pile when subject to thermal loads. Results indicate that the temperature distribution with depth is far from being homogeneous through the entire length of the pile. The resulting induced strains are strongly dependent on the subsoil conditions.

scholarly journals A Practical Monitoring System for the Structural Safety of Mega-Trusses Using Wireless Vibrating Wire Strain Gauges

Sensors ◽  
2013 ◽  
Vol 13 (12) ◽  
pp. 17346-17361 ◽  
Author(s):  
Hyo Park ◽  
Hwan Lee ◽  
Se Choi ◽  
Yousok Kim
Keyword(s):  
Monitoring System ◽  
Structural Safety ◽  
Strain Gauges ◽  
Vibrating Wire ◽  
Wire Strain

scholarly journals An Automatic Precipitation Gauge Based on Vibrating-Wire Strain Gauges

1985 ◽  
Vol 16 (4) ◽  
pp. 193-202 ◽  
Author(s):  
S. Bakkehøi ◽  
K. Øien ◽  
E. J. Førland
Keyword(s):  
Strain Gauges ◽  
Vibrating Wire ◽  
Sensing Element ◽  
Steel Wires ◽  
Wire Strain ◽  
Precipitation Gauge ◽  
The Relationship ◽  
Prototype Instrument ◽  
Small Steel ◽  
Better Than

The Norwegian Geotechnical Institute, NGI, has recently developed and tested a new automatic precipitation gauge for rain and snow which can measure accumulated precipitation with a resolution better than 0.1 mm. The gauge, which is a direct weighing device, is based on the use of vibrating-wire strain gauges. NGI's prototype instrument has a capacity of up to 300 mm precipitation before the gauge must be emptied. A new improved version designed by Geonor has a capacity of 600 mm precipitation. A diagram showing the relationship between the automatic observations and the manual measurements is included. In the NGI prototype the precipitation container is suspended from three small steel wires, each of which is in effect the sensing element in a vibrating-wire type strain gauge. When these gauge wires are set into vibration by an electromagnetic exciter, their resonant frequency of vibration is proportional to the square of the tension in the wire. Thus change in the frequency signals is a measure of the change in tension in the wires and correspondingly a measure of the accumulative weight of precipiation in the container. The distance between the precipitaion gauge and the monitoring station can be up to one kilometre without any loss in performance.

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