Utilization of High Resolution 3D Optical Scanning of Crossties to Assess Cross-Sectional Parameters and the Effects of Long-Term Abrasion and Wear

2016 ◽  
Author(s):  
B. Terry Beck ◽  
Aaron A. Robertson ◽  
Naga Narendra B. Bodapati ◽  
Robert J. Peterman ◽  
Chih-Hang John Wu ◽  
...  
Keyword(s):  
Prestressed Concrete ◽  
Surface Strain ◽  
Scanning System ◽  
Cad Model ◽  
Surface Geometry ◽  
Transfer Length ◽  
Cross Sectional ◽  
Optical Scanning ◽  
3D Cad

Accurate unbiased assessment of transfer length for prestressed concrete railroad ties requires detailed knowledge of the longitudinal variation of geometrical cross-section parameters responsible for establishing the resulting surface strain profile. This is because the complex cross-sectional shape produces a non-uniform strain plateau region, which makes the accurate evaluation of transfer length more difficult. In particular, human judgment of a “plateau region” for assessment of the average maximum strain becomes subject to large uncertainty, and clearly this procedure cannot be used in any type of automated in-plant transfer length diagnostics. The important geometrical tie parameters include the cross-sectional area, centroid, moment of inertia, and the eccentricity of the prestressing wires. If a CAD drawing is available, this information can be digitally extracted from the CAD model representation of the crosstie. In fact, this digital extraction has been done and has already been in use for some time in assessing transfer length for one of the common crosstie manufacturer designs. However, current research efforts are investigating the characteristics of existing crossties which have been in track for many years, for which CAD drawings of the original designs are unlikely to be available. The objective of the current research is to develop a comprehensive understanding of the material characteristics that have caused splitting failures in prestressed concrete railroad ties, and those characteristics that have resulted in ties that have performed well after many years in track. As part of this effort, a three-dimensional (3D) Optical Scanning System is being used to accurately scan and quantify the surface geometry of previously manufactured ties that have been in service, so as to produce an accurate 3D CAD model for later analysis associated with the above long-term research objectives. For the initial phase of this work, a sample from the CXT crossties of known geometrical characteristics that were subjected to representative long-term loading at the TTCI Facility in Pueblo Colorado, was scanned so as to accurately map out detailed 3D tie surface geometry. These ties were cast using the same concrete materials but with different prestressing wires, and were all subjected to the same extreme in-track loading for a period of several years. A commercially-available 3D Laser-Based Optical Scanning System, having a maximum spatial resolution of approximately 0.1mm, was used to perform the surface scanning operations presented in this paper. The CXT tie provides a useful initial evaluation of the accuracy and general feature capture capability of the scanning procedure, since a 3D CAD model for this tie has been provided by the manufacturer. A detailed qualitative and quantitative analysis is presented which compares the 3D CXT CAD model geometry with the 3D geometry of the experimentally scanned ties. Illustrations as to how this 3D technique can reveal such features as abrasion and wear, along with the longitudinal variation of the above mentioned cross-section parameters associated with longitudinal surface strain and transfer length assessment, are included in this paper.

Accuracy of High Resolution 3D Optical Scanning of Crosstie Geometry for Assessment of Cross-Sectional Parameters and Long-Term Abrasion and Wear

2017 ◽  
Author(s):  
B. Terry Beck ◽  
Aaron A. Robertson ◽  
Robert J. Peterman ◽  
Kyle A. Riding ◽  
John Wu
Keyword(s):  
Cross Section ◽  
Accurate Determination ◽  
Surface Strain ◽  
Scanning System ◽  
Surface Geometry ◽  
Cross Sectional ◽  
Optical Scanning ◽  
Scanning Procedure ◽  
Optical Scanning System

Current research is attempting to develop a comprehensive understanding of the material and manufacturing characteristics that have caused splitting failures in prestressed concrete railroad ties, in contrast with those characteristics that have resulted in ties that have performed well after many years in track. As part of this effort, a three-dimensional (3D) Optical Scanning System is being used to accurately scan and quantify the surface geometry and volume (abrasion and wear) of a large sample of previously manufactured ties. A commercially-available 3D Laser-Based Optical Scanning System, having a maximum spatial resolution of approximately 0.1mm, is being used to perform the surface scanning operation. The scanning procedure ideally produces an accurate 3D CAD model of the tie geometry, which can then be analyzed to determine the desired geometrical features at any given cross-section. It can likewise yield a measure of the tie volume, the variation of which gives some direct indication of the extent of abrasion and wear. The feasibility of the scanning system has previously been demonstrated by extracting the detailed longitudinal variation of geometrical cross-section crosstie parameters of a typical CXT tie, including cross-sectional area, centroid, moment of inertia, and the eccentricity of the prestressing wires. These parameters are also known to be of importance to the accurate determination of transfer length from measured surface strain. The CXT tie geometry provides an excellent test case, and a challenge to the optical scanning system, since it has a complex scalloping along its length. While the basic feasibility of the system operation has been demonstrated, the repeatability of the geometrical information obtained from the overall scanning and subsequent post-processing of surface geometrical data has yet to be assessed. The main objective of this paper is to first demonstrate the volumetric measurement resolution experimentally by conducting repeated scans of the same tie by the same operator. The experimental scatter in scan results is presented for both cross-section parameter detail and tie volume assessment. The statistical variation in the measured tie volume ideally provides a reasonable measure of the expected volume resolution. In addition to assessing the statistics of these repeated scans, a CXT tie was subjected to induced abrasions of known (measurable) volume for direct comparison with the volume measurements obtained using the optical scanning procedure. This work represents an important next step toward identifying the accuracy of the assessment of abrasion and wear for the large number of ties currently being scanned after having been in long-term service.

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.

A High Resolution Automated Prestressing Wire Indent Profiling System for Verification of Wire-Concrete Mix Compatibility

2019 ◽  
Author(s):  
B. Terry Beck ◽  
Aaron A. Robertson ◽  
Robert J. Peterman ◽  
Adrijana Savic ◽  
Chih-Hang John Wu ◽  
...  
Keyword(s):  
High Resolution ◽  
Prestressed Concrete ◽  
Major Influence ◽  
Scanning System ◽  
Geometrical Parameters ◽  
Transfer Length ◽  
Ongoing Research ◽  
Load Bearing ◽  
Indent Depth ◽  
Sidewall Angle

It is well-known that the geometrical characteristics of the indents on prestressing wire used in the manufacture of prestressed concrete railroad ties affect the magnitude of the transfer length. In particular, it has been shown that such parameters as indent depth, indent volume and indent sidewall angle all affect transfer length, with indent volume being a major influence. Previous research has shown that the larger the indent volume, the shorter the transfer length. For full load bearing capacity, it is important that the transfer length not exceed the distance to the rail seat. Consequently, 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. Ongoing research, as well as previously published research results, also indicates that the geometry of the prestressing wire indents plays a major role in the formation of cracking. This is particularly important in the manufacture of concrete ties intended for high speed rail applications. Cracking and debonding of prestressing wires associated with ties in service can result in severe splitting and complete tie failure. It is therefore not sufficient to guarantee a safe transfer length alone, without consideration of the cracking propensity. The wire specifications in standard ASTM A881 are intended to promote quality prestressed railroad tie behavior; however, the detailed causes of cracking and splitting, and the specific indent features that are responsible, are not well-known from a quantitative perspective. Until recently, inspection of prestressing wire indent properties consisted of sampling a few indents from a small segment of wire, providing very limited statistical information on wire indent properties. To address this deficiency, a high-resolution automated non-contact optical wire indent scanning system has been developed for completely and rapidly characterizing all relevant indent geometrical parameters. The system is capable of measuring large segments of wire to yield statistically significant samples of all relevant indent parameters including indent depth, indent width, indent sidewall angle, indent pitch, and indent volume. The current state-of-the-art in this system development, along with some new insights based on recent indent scanning results, will be presented. This system represents a valuable tool to aid in identifying the key indent geometrical features related to cracking. The overall goal is to quickly assess critical indent parameters, so as to ensure high-quality bond and eliminate in-track tie splitting failures.

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.

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.

scholarly journals Experimental Technique for Measuring the Long-term Transfer Length in Prestressed Concrete

Strain ◽  
2012 ◽  
Vol 49 (2) ◽  
pp. 125-134 ◽  
Author(s):  
J. R. Martí-Vargas ◽  
L. A. Caro ◽  
P. Serna
Keyword(s):  
Experimental Technique ◽  
Prestressed Concrete ◽  
Transfer Length

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.

A Direct Comparison of the Traditional Method and a New Approach in Determining 220 Transfer Lengths in Prestressed Concrete Railroad Ties

2013 ◽  
Author(s):  
Weixin Zhao ◽  
B. Terry Beck ◽  
Robert J. Peterman ◽  
Robert Murphy ◽  
Chih-Hang John Wu ◽  
...  
Keyword(s):  
Prestressed Concrete ◽  
The United States ◽  
Laser Speckle ◽  
Surface Strain ◽  
Transfer Length ◽  
New Approach ◽  
Average Maximum ◽  
Concrete Mix ◽  
Strain Data ◽  
Length Determination

This paper presents the detailed analysis of surface strain data obtained at six prestressed concrete tie plants in the United States. These data were obtained by the authors by conducting a total of 220 transfer length measurements on prestressed concrete railroad ties with different concrete-mix designs and reinforcement variations. The surface strain profiles of the railroad ties were obtained using the traditional Whittemore gage, as well as a rapid non-contact technology, called laser-speckle imaging (LSI), that was previously developed by the authors. The LSI technique achieved a microstrain resolution comparable to that was obtained using mechanical gauge technology. The measured surface strain profiles were then analyzed by both the 95% AMS (95% Average Maximum Strain) method, and the ZL (Zhao-Lee) method that was recently proposed by the authors. The ZL method is an unbiased statistical method that provides a more accurate and reliable transfer length determination. A direct comparison between the 95% AMS method and the ZL method was achieved by applying both methods to determine the 220 railroad tie transfer length values. The comparison confirmed the bias of the 95% AMS method in estimating transfer length value, as predicated by theoretical analysis.

Determining the Remaining Prestress Force in a Prestressed Concrete Crosstie

2017 ◽  
Author(s):  
James D. Scott ◽  
Aaron A. Robertson ◽  
Robert J. Peterman ◽  
B. Terry Beck ◽  
Kyle A. Riding ◽  
...  
Keyword(s):  
Prestressed Concrete ◽  
Crack Opening ◽  
Systematic Evaluation ◽  
Load Testing ◽  
Opening Displacement ◽  
Cross Sectional ◽  
Prestressing Force ◽  
Bending Resistance

The research presented herein focuses on determining the amount of internal prestressing force and bending resistance that is necessary to provide a durable long-term concrete railroad tie. In order to accomplish this, the researchers conducted a systematic evaluation of existing concrete ties that successfully withstood over 25 years of service in track. An experimental method for determining the remaining prestress force in these existing prestressed concrete railroad ties is currently under development. The ties are first loaded in the upside-down orientation, with supports located at the rail seats, and two point loads applied at the center of the tie. A loading rate of 1,000 lb/min was used to initiate flexural cracking in the center of the tie. Once cracking was observed, the ties underwent 200 cycles of loading to reduce the friction between the prestressing tendons and the concrete. When the cycling was completed, the existing crack was instrumented with an extensometer to measure the Crack Opening Displacement (COD). The ties were loaded once more at 1,000 lb/min to develop a Load vs. COD relation. A systematic method of determining the load required to reopen the crack from the Load vs. COD relation is being developed using ties cast at a manufacturing plant that were instrumented with internal vibrating-wire strain gages. Using the load required to reopen the crack, along with the known cross-sectional properties at the center of the tie, the remaining prestress force is calculated through equilibrium of forces. This method allows for the determination of the remaining prestress force in a member with known section properties to be obtained through load testing.

Theoretical and Methodological Problems of a 10-Year Follow-Up Program Evaluation Study

2002 ◽  
Vol 18 (3) ◽  
pp. 229-241 ◽  
Author(s):  
Kurt A. Heller ◽  
Ralph Reimann
Keyword(s):  
Program Evaluation ◽  
Evaluation Studies ◽  
Evaluation Study ◽  
Control Groups ◽  
Cross Sectional ◽  
Long Term Study ◽  
Partial Inclusion ◽  
Methodological Problems

Summary In this paper, conceptual and methodological problems of school program evaluation are discussed. The data were collected in conjunction with a 10 year cross-sectional/longitudinal investigation with partial inclusion of control groups. The experiences and conclusions resulting from this long-term study are revealing not only from the vantage point of the scientific evaluation of new scholastic models, but are also valuable for program evaluation studies in general, particularly in the field of gifted education.

Sign in / Sign up

Export Citation Format

Share Document