Development of a 5-Camera Transfer Length Measurement System for Real-Time Monitoring of Railroad Crosstie Production

2013 ◽  
Author(s):  
Weixin Zhao ◽  
B. Terry Beck ◽  
Robert J. Peterman ◽  
Chih-Hang John Wu
Keyword(s):  
Real Time ◽  
Measurement System ◽  
Laser Speckle ◽  
Surface Strain ◽  
Length Measurement ◽  
Plant Production ◽  
Automated System ◽  
Production Operation ◽  
Transfer Length ◽  
Strain Measurements

Knowledge of transfer length during production is critical for maintaining continuous production quality in the modern manufacture of prestressed concrete railroad crossties. Traditional laboratory methods for measuring transfer length, using manual instruments such as a Whittemore mechanical gauge or surface mounted resistance-type strain gauge, are simply not suitable for production operation. They are too time-consuming to implement, require extensive surface preparation, and can also require special operator training to provide accurate and reliable surface strain profiles from which the transfer length can be determined in a post-processing manner. In contrast with earlier manual methods, the newly developed non-contact Laser Speckle Imaging (LSI) technique has been shown to be capable of providing rapid and accurate surface strain measurement and consequently also rapid transfer length assessment. This system has recently been automated and combined with the new Zhao-Lee (ZL) least-squares strain profile fitting technique for quickly and reliably processing surface strain data. The automated system and processing procedure have been shown to provide an improved assessment of transfer length, unhampered by human intervention and subsequent potential human judgment bias. This paper presents recent progress toward the development of a 5-camera non-contact transfer length measurement system that is capable of continuous monitoring of railroad crossties in a production plant. This is made possible using an optimized version of the previously successful LSI system, which minimizes the number of surface strain measurements required to achieve reliable transfer length assessment. Experimental results and analysis will be presented for the latest multi-camera prototype concept for this new system design, demonstrating that only a few discrete surface strain measurements are required to achieve accurate and reliable transfer length assessment. Thus, for the first time it is now possible to envision practical real-time quality control monitoring of railroad crossties during an in-plant production operation.

In-Plant Testing of a New Multi-Camera Transfer Length Measurement System for Monitoring Quality Control of Railroad Crosstie Production

2015 ◽  
Author(s):  
B. Terry Beck ◽  
Robert J. Peterman ◽  
Chih-Hang John Wu ◽  
Naga Narendra B. Bodapati
Keyword(s):  
Quality Control ◽  
Measurement System ◽  
Surface Preparation ◽  
Production Quality ◽  
Surface Strain ◽  
Length Measurement ◽  
Transfer Length ◽  
Camera System ◽  
Strain Measurements ◽  
Strain Profile

Knowledge of transfer length is critical for maintaining continuous production quality in the modern manufacture of prestressed concrete railroad ties. Traditional manual laboratory methods for measuring transfer length are simply not suitable for production operation. They are much too time-consuming to implement, and typically require extensive surface preparation in order to obtain the required surface strain measurements needed for determining the transfer length. In addition, the traditional 95% Average Maximum Strain (95% AMS) method of assessing transfer length from the measured surface strain profile has been shown to possess bias. The accuracy of transfer length assessment using this method is generally influenced by individual operator judgment; therefore, making it unsuitable for use as a reliable production quality-control parameter. This paper presents recent in-plant testing of a newly developed prototype multi-camera non-contact transfer length measurement system, representing a major improvement over the traditional manual methods. The testing was conducted on concrete railroad ties at a manufacturing facility in North America. Concrete ties tested included those which were manufactured using indented prestressing wire as well as with 7-wire strand. The new device represents a next generation version of the previously successful Laser-Speckle Imaging (LSI) system developed by the authors. The multi-camera system is shown to provide nearly real-time surface strain profile measurements (subsequent to de-tensioning), with surface strain accuracy comparable to the mechanical Whittemore gage device, yet with little or no required surface preparation. Furthermore, with the previously demonstrated Zhao-Lee (ZL) transfer length processing algorithm built into a LabVIEW data acquisition and control interface, the multi-camera system is shown to provide assessments of transfer length within a nominal tolerance of +/− 1.5 inches using as few as six uniformly spaced surface strain measurements. This brings within reach the ultimate goal of providing the railroad tie manufacturer with the ability to measure the transfer length of every tie produced prior to leaving the plant, thereby ensuring that they are within an acceptable tolerance, and providing the means to quickly identify the need to modify production (e.g., concrete mix) if transfer length specifications fall out of desired range.

Reliable Transfer Length Assessment for Real-Time Monitoring of Railroad Crosstie Production

2014 ◽  
Author(s):  
Weixin Zhao ◽  
B. Terry Beck ◽  
Robert J. Peterman ◽  
Chih-Hang John Wu ◽  
Naga Narendra B. Bodapati ◽  
...  
Keyword(s):  
Real Time ◽  
Prestressed Concrete ◽  
Laser Speckle ◽  
Surface Strain ◽  
Experimental Comparison ◽  
Profile Measurement ◽  
Transfer Length ◽  
General Validity ◽  
Strain Profile ◽  
Average Maximum

Automated in-plant diagnostic testing of prestressed concrete railroad crossties is now within reach due to recent progress in robust surface strain measurement techniques. The newly developed non-contact Laser Speckle Imaging (LSI) technique has been shown to provide rapid and accurate surface strain profile measurement, which is a key requirement for rapid transfer length assessment. Accurate determination of transfer length is critical for maintaining continuous production quality in the modern manufacture of prestressed concrete railroad crossties. Conventional assessment of transfer length generally presumes the underlying existence of a bilinear prestressing force distribution and a corresponding bilinear surface strain profile. Furthermore, it is well-known that this bilinear profile is smoothed due to the effects of finite gauge length during the process of measuring surface strain. In addition, recent extensive crosstie measurements in concrete railroad tie plants have shown significant departures from this simple bilinear profile, which bring to question the general validity and reliability of the traditional 95% AMS (95% Average Maximum Strain) method. Deviations from the simple bilinear profile shape were shown to be partially due to the non-prismatic shape of typical concrete railroad ties. In addition, extensive comparisons between predicted and measured surface strain profiles on numerous crossties suggest that the underlying strain distribution for crossties is best represented by an exponential strain profile, with an asymptotic approach to the fully-developed compressive strain. This is in contrast with extensive testing of prisms with fixed cross-section and fixed prestressing wire eccentricity, for which the surface strain appears to be best represented by the simple bilinear strain profile. Clearly, departures from non-prismatic behavior have added complexity to transfer length measurement. If accurate and reliable measurements of this important quality control parameter are to be realized, these issues of transfer length uncertainty need to be addressed. This paper provides an experimental comparison of several possible alternative transfer length assessment procedures, in an attempt to answer important uncertainty questions which need to be addressed if rapid real-time transfer length is to be achieved. It is shown that in spite of considerable differences in the transfer length processing methods, and significant departures from prismatic behavior, the averaged results are in many cases consistent with the simple bilinear underlying strain profile assumption. Bias in the measurement of crosstie transfer length due to non-prismatic behavior will also be investigated in this paper.

Performance of a Continuously Traversing 2-Camera Non-Contact Optical Strain Sensor for In-Plant Assessment of Prestressed Concrete Railroad Crosstie Transfer Length

2016 ◽  
Author(s):  
B. Terry Beck ◽  
Aaron A. Robertson ◽  
Robert J. Peterman ◽  
Chih-Hang John Wu
Keyword(s):  
Measurement System ◽  
Prestressed Concrete ◽  
Strain Measurement ◽  
Production Quality ◽  
Step Change ◽  
Surface Strain ◽  
Length Measurement ◽  
Transfer Length ◽  
Measurement Systems ◽  
New System

Accurate knowledge of transfer length has been shown to be crucial to the goal of maintaining continuous production quality in the modern manufacture of prestressed concrete railroad ties. Traditional manual laboratory methods, such as the conventional Whittemore method which requires the use of embedded reference points, are clearly not suitable for production operation or for use in reliable production quality-control. This paper presents the results of another advance in the development of automated transfer length measurement systems for practical in-plant operation. The new device offers a significant improvement over the previously successful automated Laser-Speckle Imaging (LSI) system developed by the authors. The earlier automated LSI strain measurement system has been modified to provide significantly improved optical resolution of longitudinal surface strain, with the ability to resolve longitudinal prestressed concrete crosstie surface strain without time-consuming special surface preparation. More importantly, the new system is also capable of making measurements of strain in a real-time “on-the-fly” manner over the entire distance range of interest on the tie associated with transfer length development. It features both a “jog” mode of operation, similar to its predecessor in which measurements of longitudinal surface strain are automatically captured in arbitrary spatial increments over the entire range of the computer-controlled traverse, and an “on-the-fly” mode in which measurements of longitudinal surface strain are captured without the need for stopping at each measurement location. This latter mode offers the potential of a much faster capture of the strain profile and should prove to be very beneficial for field testing and in-plant diagnostic applications. The performance of this new system is first demonstrated using a new calibrated step-wise uniform strain field setup which has been developed specifically for verification of this and other automated transfer length measurement systems. This verification system produces a calibrated step change in surface deflection, effectively subjecting the automated strain measurement system to an ideal step change in longitudinal strain for a given gauge length. In addition, the new automated system is demonstrated by conducting measurements of longitudinal surface strain on prestressed concrete crossties in a manufacturing plant. For this latter experimental in-plant testing, strain measurements using the new system are also compared directly with those from the recently introduced 6-camera transfer length measurement system, as well as with the traditional Whittemore gauge measurements. The agreement between these independent measurement systems is remarkable, and it is shown to even be possible to discern differences in strain profile and associated transfer length between adjacent crossties within a given casting bed. This new automated and high-resolution device should provide a very convenient and fast diagnostic tool for the manufacturer to quickly identify the need to modify production (e.g., concrete mix) if transfer length specifications fall out of desired range.

Determining Transfer Length in Pre-Tensioned Concrete Railroad Ties: Is a New Evaluation Method Needed?

2013 ◽  
Author(s):  
Weixin Zhao ◽  
B. Terry Beck ◽  
Robert J. Peterman ◽  
Chih-Hang John Wu ◽  
Grace Lee ◽  
...  
Keyword(s):  
Evaluation Method ◽  
Compressive Strain ◽  
Accurate Determination ◽  
Laser Speckle ◽  
Surface Strain ◽  
Bond Quality ◽  
Transfer Length ◽  
General Validity ◽  
Imaging Device ◽  
Average Maximum

The transfer length is perhaps the most significant KEY indicator of the bond quality between reinforcing wire/strand and concrete, and its measurement in pre-tensioned concrete railroad ties can enable concrete tie producers to identify problem ties before they are put into service. The 95% AMS method is the traditional method used to determine the transfer length from measurements of surface strain. The method generally presumes the underlying existence of a bilinear strain profile. During recent field trips to six concrete railroad tie plants, we conducted hundreds of transfer length measurements on concrete railroad cross-ties using a newly developed automated Laser Speckle Imaging device. It has been observed that many of the strain profiles depart significantly from this underlying bilinear profile, and bring to question the general validity and applicability of the 95% AMS (95% Average Maximum Strain) method. This paper discusses the difficulties with accurate determination of transfer length in various practical situations using the traditional 95% AMS method. Deviations of the strain profiles from the simple bilinear shape are shown to be partially due to the non-prismatic shape of typical concrete railroad ties. In addition, computational evidence suggests that the underlying strain distribution may be exponential in nature, with an asymptotic approach to the fully-developed compressive strain, potentially superimposed on the non-prismatic problem identified above. These departures are discussed along with proposed solutions to the basic problem of accurate transfer length assessment.

Real-time two-color laser speckle-shift strain measurement system

1998 ◽  
Author(s):  
Meg L. Tuma ◽  
Lawrence C. Greer III ◽  
Michael J. Krasowski ◽  
Lawrence G. Oberle ◽  
Kristie A. Elam ◽  
...  
Keyword(s):  
Real Time ◽  
Measurement System ◽  
Strain Measurement ◽  
Laser Speckle

Transfer Length Characterization of Entire Crosstie Plant Casting Bed Using Continuously Traversing Dual-Camera Non-Contact Optical Strain Sensors

2017 ◽  
Author(s):  
B. Terry Beck ◽  
Aaron A. Robertson ◽  
Robert J. Peterman ◽  
Kyle A. Riding ◽  
John Wu
Keyword(s):  
Quality Control ◽  
Real Time ◽  
Prestressed Concrete ◽  
Manufacturing Process ◽  
Control Parameter ◽  
Strain Sensors ◽  
Surface Strain ◽  
Manufacturing Plant ◽  
Transfer Length ◽  
Optical Strain

Transfer length has been identified as a key diagnostic parameter for evaluating the load bearing capability of prestressed concrete railroad crossties. Furthermore, it has been proposed for use as a valuable quality control parameter. However, until quite recently the capability to easily and accurately measure transfer length has been limited primarily to a laboratory setting. This is especially true for measurements made in the harsh environment of a tie manufacturing plant. The development of portable non-contact optical strain sensors has opened the door to rapid in-plant transfer length measurement. The measurement capability of these devices has been repeatedly demonstrated not only in the laboratory, but more importantly also through actual testing at multiple tie manufacturing plants. The latest version of the automated Laser-Speckle Imaging (LSI) system developed by the authors offers improved optical resolution of longitudinal surface strain, with the ability to resolve longitudinal prestressed concrete crosstie surface strain without time-consuming special surface preparation. The new system is also capable of making measurements of strain in a real-time “on-the-fly” manner over the entire distance range of interest on the tie associated with transfer length development. This faster capability to capture the strain profile with high resolution makes this new technology very beneficial for field testing and in-plant diagnostics applications. It has been demonstrated to be capable of resolving minor differences in longitudinal surface strain profiles associated with ties even in adjacent cavities. As a logical next step toward eventual implementation of transfer length as a quality control parameter, it is important to evaluate the expected variation of transfer length during the tie manufacturing process. This paper presents the results of extensive in-plant assessment of transfer length in an attempt to characterize experimentally the in-plant manufacturing variations that can occur in practice. To the best of the authors’ knowledge, this is the first time extensive real-time measurements to this extent have been attempted in an actual tie manufacturing plant with the expressed purpose of statistically characterizing the variations in transfer length that take place over an entire casting bed. A sampling of transfer lengths from well over 50 ties was determined during the manufacturing process (corresponding to over 100 transfer length measurements). The sampled tie measurement locations were distributed at different “form” locations along the casting bed, and included samplings of ties from several different “cavities” within a given form. The entire bed was 45 forms in length, each form having 6 tie cavities, for a total bed size of 270 ties. The statistical distribution of overall transfer length measurement results is presented, along with what may be typical variations in strain profile and resulting transfer length as a result of variations that took place in the manufacturing process. The overall range of transfer length observed, along with an investigation of possible bias due to position within the casting bed, and apparent variations of transfer length within a given form, are identified and discussed.

Long-Term End-Slip Measurements and Corresponding Transfer Lengths in Pretensioned Concrete Railroad Ties Fabricated With 15 Different Reinforcements

2015 ◽  
Author(s):  
Robert J. Peterman ◽  
Naga Narendra B. Bodapati ◽  
B. Terry Beck ◽  
Chih-Hang John Wu
Keyword(s):  
Surface Strain ◽  
Manufacturing Plant ◽  
Transfer Length ◽  
Strain Measurements ◽  
Pretensioned Concrete ◽  
Concrete Mix ◽  
Different Types ◽  
Low Humidity ◽  
Wire Strand

Fifteen different reinforcements that are widely employed in manufacturing of railroad ties worldwide were selected for the study presented in this paper. Selected reinforcements include; 12 number of 5.32 mm diameter wires, two 3/8-inch diameter 7 wire strands, and one 5/16-inch diameter 3 wire strand. Twelve wire reinforcements are differed by surface indent geometries with one wire being smooth surfaced profile. Strand reinforcements consisted one smooth and one indented 7 wire strand, and one smooth 3 wire strand. All reinforcements were stored in low-humidity environment to avoid rust. Later, pre-tensioned concrete railroad ties were fabricated at a tie manufacturing plant with the selected 15 different reinforcements in January 2013. Same concrete mix proportions were used during the fabrication of the ties with these 15 reinforcement types. Reinforcement end-slips were measured for each concrete tie at every reinforcement location during August 2014 (after one and half years). Simultaneously, transfer length measurements were measured on all these ties through surface strain measurements. Detailed analysis of the measured end-slips for the ties fabricated with 15 reinforcements is presented. This analysis includes the variation of end-slip measurements at different locations in the cross-section. Variation in end-slip measurements for different types of reinforcements is also discussed. Transfer lengths are compared with end slip measurements and an equation to predict transfer lengths from long term end-slip values is presented.

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