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.

Determining the Remaining Prestress Force in a Prestressed Concrete Railroad Tie Through Loading in Direct Tension

2018 ◽  
Author(s):  
James D. Scott ◽  
Robert J. Peterman ◽  
B. Terry Beck ◽  
Aaron A. Robertson ◽  
Kyle A. Riding ◽  
...  
Keyword(s):  
Crack Opening Displacement ◽  
Prestressed Concrete ◽  
Applied Load ◽  
Crack Opening ◽  
Previous Method ◽  
Opening Displacement ◽  
Cross Sectional ◽  
Prestressing Steel ◽  
Prestressing Force ◽  
The Cross

Extensive research has been conducted by the research team in recent years to determine the prestressing steel and concrete properties that must be provided to ensure that the transfer length of a prestressed concrete railroad tie is shorter than the distance from the edge of the tie to the rail seat. In addition, a significant of amount of data has been collected that indicates high bonding stresses can produce longitudinal splitting cracks along the reinforcement. In a study of how prestressing steel and concrete properties relate to a ties propensity for longitudinal cracking, existing ties that have performed well in track for over 25 years without issues are being evaluated. One parameter of interest that affects the bonding stress is the amount of prestress force in a railroad tie, which is unknown for the existing ties being evaluated. The current paper focuses on a new method that was developed for determining the remaining prestress force in a tie. In a previous method for determining the prestress force, ties were first loaded in four-point bending to initiate flexural cracking. The crack opening displacement was measured in order to determine the applied load required to reopen the crack. Using this load and the cross-sectional parameters at the location of the crack, the prestress force in the tie can be calculated using static equilibrium. The issue with this method is that as a tie is being loaded and the crack propagates, there is a continuous change in the stiffness of the cross-section. This results in the load versus crack opening displacment curve being overly rounded. This increases the error when determining the load required to reopen the crack, and increases the uncertainty of the calculated prestress force. The new test method eliminates the problems associated with flexural testing by loading the ties longitudinally in tension. In the new proposed experimental method, ties that have been pre-cracked in the center are pulled in tension. Similar to the previous method, the crack opening displacement is measured while the tie is loaded. For the crack to fully open, the applied load must exceed the prestress force holding the crack closed. Prior to the crack opening, the applied load is resisted by the composite section of concrete and prestressing tendons. Once the crack as fully opened, the applied load is resisted by the prestessing tendons only. This creates two distinctly linear portions of the load versus crack opening displacement curve, one prior to the crack opening, and one after. The beginning of the linear portion post-crack opening marks a very clear upper bound for the amount of prestressing force in a tie. This method can estimate the remaining prestress force in a tie with much greater accuracy than the previous method, and eliminates the need of the cross-sectional parameters at the crack location. To verify this method, tests were first conducted on a smaller scale with prismatic beams with a known initial prestressing force. Then the method was applied to a full scale existing tie to determine the remaining prestress force. Results are presented for testing of both the prismatic beams, and the full scale tie.

Evaluation of web reinforcements in prestressed concrete box girders through shear-transverse bending domains

2020 ◽  
pp. 136943322098170
Author(s):  
Michele Fabio Granata ◽  
Antonino Recupero
Keyword(s):  
Analytical Model ◽  
Prestressed Concrete ◽  
3D Analysis ◽  
Box Girders ◽  
Element Analysis ◽  
Cross Sectional ◽  
Interaction Domains ◽  
Global And Local ◽  
Resultant Forces

In concrete box girders, the amount and distribution of reinforcements in the webs have to be estimated considering the local effects due to eccentric external loads and cross-sectional distortion and not only the global effect due to the resultant forces of a longitudinal analysis: shear, torsion and bending. This work presents an analytical model that allows designers to take into account the interaction of all these effects, global and local, for the determination of the reinforcements. The model is based on the theory of stress fields and it has been compared to a 3D finite element analysis, in order to validate the interaction domains. The results show how the proposed analytical model allows an easy and reliable reinforcement evaluation, in agreement with a more refined 3D analysis but with a reduced computational burden.

scholarly journals EM-Based Monitoring and Probabilistic Analysis of Prestress Loss of Bonded Tendons in PSC Beams

2018 ◽  
Vol 2018 ◽  
pp. 1-9 ◽  
Author(s):  
Zheheng Chen ◽  
Shanwen Zhang
Keyword(s):  
Probabilistic Analysis ◽  
Prestressed Concrete ◽  
Monitoring Methods ◽  
Prestress Loss ◽  
External Tendons ◽  
Material Environment ◽  
Key Factor ◽  
One Year

The prestress level is a key factor of prestressed concrete (PSC) beams, affecting their long-term serviceability and safety. Existing monitoring methods, however, are not effective in obtaining the force or stress of embedded tendons. This paper investigates the feasibility of elastomagnetic (EM) sensors, which have been used for external tendons, in monitoring the long-term prestress loss of bonded tendons. The influence of ambient temperature, water, eccentricity ratio, plastic duct, and cement grouts on the test results of EM sensors is experimentally examined. Based on the calibrated EM sensors, prestress loss of a group of PSC beams was monitored for one year. In order to further consider the high randomness in material, environment, and construction, probabilistic analysis of prestress loss is conducted. Finally, the variation range of prestress loss with a certain confidence level is obtained and is compared with the monitored data, which provides a basis for the determination of prestress level in the design of PSC beams.

scholarly journals Urinary Pesticide Levels in Children and Adolescents Residing in Two Agricultural Communities in Mexico

2019 ◽  
Vol 16 (4) ◽  
pp. 562 ◽  
Author(s):  
Erick Sierra-Diaz ◽  
Alfredo Celis-de la Rosa ◽  
Felipe Lozano-Kasten ◽  
Leonardo Trasande ◽  
Alejandro Peregrina-Lucano ◽  
...  
Keyword(s):  
High Performance ◽  
Public Health Problem ◽  
Cross Sectional Study ◽  
Urine Samples ◽  
Agricultural Activities ◽  
Cross Sectional ◽  
Agricultural Communities ◽  
Health Authorities

The use of pesticides in agricultural activities has increased significantly during the last decades. Several studies have reported the health damage that results from exposure to pesticides. In Mexico, hundreds of communities depend economically on agricultural activities. The participation of minors in this type of activity and their exposure to pesticides represents a potential public health problem. A cross-sectional study was conducted, in which urine samples (first-morning urine) were taken from children under 15 years of age in both communities. A total of 281 urine samples obtained in both communities were processed for the determination of pesticides with high-performance liquid chromatography together with tandem mass spectrometry. In 100% of the samples, at least two pesticides of the 17 reported in the total samples were detected. The presence of malathion, metoxuron, and glyphosate was remarkable in more than 70% of the cases. Substantial differences were detected regarding the other compounds. It is necessary to carry out long-term studies to determine the damage to health resulting from this constant exposure and to inform the health authorities about the problem in order to implement preventive measures.

scholarly journals Long-Term Characteristics of Prestressing Force in Post-Tensioned Structures Measured Using Smart Strands

2020 ◽  
Vol 10 (12) ◽  
pp. 4084 ◽  
Author(s):  
Sang-Hyun Kim ◽  
Sung Yong Park ◽  
Se-Jin Jeon
Keyword(s):  
Prestressed Concrete ◽  
Mechanical Strain ◽  
Prestress Losses ◽  
Prestressing Force ◽  
Eurocode 2 ◽  
Study Results ◽  
Girder Bridge ◽  
Creep And Shrinkage ◽  
Term Monitoring

The proper distribution of prestressing force (PF) is the basis for the design of prestressed concrete (PSC) structures. However, the PF distribution obtained by predictive equations of prestress losses has not been sufficiently validated by comparison with measured data due to the poor reliability and durability of conventional sensing technologies. Therefore, the Smart Strand with embedded fiber optic sensors was developed and applied to PSC structures to investigate the long-term characteristics of PF distribution as affected by concrete creep and shrinkage. The data measured in a 20 m-long full-scale specimen and a 60 m-long PSC girder bridge were analyzed by comparing them with the theoretical estimation obtained from several design equations. Although the long-term decreasing trend of the PF distribution was similar in the measurement and theory, the equation of Eurocode 2 for estimating the long-term prestress losses showed better agreement with the measurement than ACI 209R and ACI 423.10R did. This can be attributed to the more refined form of the predictive equation of Eurocode 2 in dealing with the time-dependency of the PF. The study results also confirmed the need to compensate for the temperature variation in the long-term monitoring to derive the actual mechanical strain related to the PF. We expect our developed Smart Strand to be applied practically in PF measurement for the reasonable safety assessment and maintenance of PSC structures by improving several of the existing drawbacks of conventional sensors.

Determination of J-Integral Using the Load-COD Record for Circumferential Through-Wall Cracked Pipes

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
Nam-Su Huh ◽  
Yun-Jae Kim
Keyword(s):  
Crack Opening ◽  
Estimation Method ◽  
J Integral ◽  
Opening Displacement ◽  
Element Analysis ◽  
Load Line ◽  
Load Line Displacement ◽  
Η Factor ◽  
J Estimation

The present paper provides experimental J estimation equation based on the load-crack opening displacement (COD) record for testing the circumferential through-wall cracked pipe under combined tension and bending. Based on the limit analysis and the kinematically admissible rigid-body rotation field, the plastic η-factor for the load-COD record is derived and is compared with that for the load-load line displacement record. Comparison with the J results from detailed elastic-plastic finite element analysis shows that the proposed method based on the load-COD record provides reliable J estimates even for shallow cracks (small crack angle), whereas the conventional approach based on the load-load line displacement record gives erroneous results for shallow cracks. Thus, the proposed J estimation method could be recommended for testing the circumferential through-wall cracked pipe, particularly with shallow cracks.

The investigation and proposed rehabilitation of the Tsing Yi South Bridge, Hong Kong

1988 ◽  
Vol 15 (2) ◽  
pp. 190-198
Author(s):  
A. S. Beard ◽  
H. S. S. Tung
Keyword(s):  
Prestressed Concrete ◽  
Load Testing ◽  
Concrete Core ◽  
Box Girder ◽  
Expansion Joints ◽  
Radiographic Inspection ◽  
Core Extraction ◽  
Long Term Performance ◽  
Term Performance

The Tsing Yi South Bridge was constructed in the early 1970s to provide access between Tsing Yi Island and the mainland at Kwai Chung. It has a prestressed concrete box girder superstructure consisting of five independent units which are monolithic with their piers and have expansion joints at the mid-span shear hinges and the abutments. During routine maintenance it was found that the superstructure cantilevers were deflecting excessively, and consequently a thorough inspection and appraisal were commissioned. These included a complete visual inspection, concrete core extraction, radiographic inspection of prestressing tendons and a programme of load testing. The bridge was also reanalyzed to check its long-term performance. Subsequently, a rehabilitation scheme was designed to recover part of the deflection. This involved the introduction of additional prestress near the box girder's top flange. Key words: prestressed concrete, structural assessment, creep, shrinkage, radiographic inspection, rehabilitation, external prestressing.

Determination of crack-opening displacement by the method of caustics

1974 ◽  
Vol 9 (3) ◽  
pp. 197-205 ◽  
Author(s):  
P S Theocaris
Keyword(s):  
Crack Opening Displacement ◽  
Mechanical Characteristics ◽  
Crack Opening ◽  
Crack Tip ◽  
External Loading ◽  
Small Scale ◽  
Opening Displacement ◽  
Cracked Plates ◽  
Good Agreement

A new experimental technique based on the method of caustics is presented for the measurement of the distance between the lips of a crack near the crack-tip. The two parts of the caustic formed by reflections from the front and rear faces of the specimen lie at a distance from each other. The gap between these parts depends on the total c.o.d. (crack-opening displacement), that is the initial opening and the opening due to loading, as well as on the optical and mechanical characteristics of the material By increasing the external loading of the cracked plate, the gap between the parts of the caustic was changed and this gap measured the instantaneous c.o.d. due to loading. The method was applied to the measurement of small c.o.d.s. due to small-scale loading, with satisfactory results. Therefore it can certainly be used to measure c.o.d.s at large loading steps, up to fracture, because the gap between the parts of the caustic becomes significant and easy to measure. Measurements with cracked plates made of p.m.m.a. (polymethylmethacrylate) and polycarbonate showed that the results obtained are in good agreement with theory. Thus, it has been proved that the method of caustics yields a very sensitive means for measuring c.o.d.s, especially in small-scale deformations, where measurement of c.o.d by conventional methods is inaccurate. A great advantage of the method is that it measures the c.o.d.s at a well defined region, which always remains near to the crack tip.

scholarly journals Long-term Deflections in Balanced Cantilever Prestressed Concrete Bridges

2009 ◽  
Vol 4 (1) ◽  
pp. 22
Author(s):  
Eltayeb Hassan Onsa ◽  
Elsafi Mohamed Adam ◽  
Abdalla Khogali Ahmed ◽  
Mohamed Elmontasir Elbagir
Keyword(s):  
Prestressed Concrete ◽  
Concrete Bridges ◽  
Live Load ◽  
Prestressed Concrete Bridges ◽  
Prestressing Force ◽  
Load Tests ◽  
The Moment ◽  
Aashto Lrfd ◽  
Made In

Long-term deflections in balanced cantilever prestressed concrete bridges are reviewed. Burri and Shambat Bridges are taken as cases study to calculate long-term deflection. The two bridges were constructed at Khartoum State in the years 1972 and 1962, respectively. Due to the shortage of the basic data regarding the two bridges the AASHTO-LRFD is used to estimate and calculate the missing data in the two bridges. The Moment Area method is used to calculate the long-term deflections due to the dead load, live load and prestressing force. The calculated long-term deflections are compared with measured live load deflections obtained from load tests made by a Chinese contractor requested to evaluate the two bridges. Remarkable differences between theoretical and measured deflection at the end of cantilevers are encountered. The differences are probably due to the basic assumptions made in the formulations of deflection calculations. Some adjustments in the long-term deflection formulae are suggested to bring the calculated deflections in compatibility with measured ones.

scholarly journals Mechanical behaviour and permeability of geopolymer mortars

2020 ◽  
Vol 322 ◽  
pp. 01043
Author(s):  
Mateusz Sitarz ◽  
Marta Choińska ◽  
Izabela Hager ◽  
Abdelhafid Khelidj
Keyword(s):  
Gas Permeability ◽  
Crack Opening ◽  
Industrial Wastes ◽  
Opening Displacement ◽  
Granulated Blast Furnace Slag ◽  
Alternative Materials ◽  
Short And Long Term ◽  
Splitting Tensile Test ◽  
Positive Effect

Geopolymers may be considered as an alternative materials to Portland cement ones, providing an opportunity to exploit industrial wastes or co-products with promising short and long-term performances in the construction field, f.ex. for reparation issues. However, these materials are porous and consequently their durability depends on the risk of intrusion of aggressive agents. In order to assess their durability, we propose to investigate in this study gas permeability of sound and mechanically loaded specimens. Loading is performed using a splitting tensile test driven by a crack opening displacement up to a level of 50 microns. Tests are performed on four types of blended fly-ash (FA) and ground granulated blast furnace slag (GGBFS) geopolymer mortars, containing four different levels of GGGBF slag in the binder: 0%, 10%, 30% and 50% wt. Results show a positive effect of blending with slag in terms of modulus of elasticity and tensile and compressive strength, as well as the permeability. However, permeability recovery after cracking is the lowest when blending is the highest.

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