Post-tensioned Concrete Girder Research Articles

Transmission length of multiwire tendon in existing post-tensioned concrete structures

The paper presents unique research on real-scale post-tensioned concrete crane girders dismantled from an existing hall structure. The study aimed to determine the transmission length for bonded prestressing tendons in an anchorage failure situation, a critical factor for proper assessment of the safety of many building structures, mainly those built between the 1950s and 1980s. The results of the tests indicated the feasibility of prestressing force transmission from a 12Ø5 mm Freyssinet-type tendon to the element via bond stress, with implications extendable to the other 18Ø5 mm tendon type prevalent at the time. The key factor affecting transmission efficiency is the quality of tendon duct grouting, with good quality cement injection resulting in transmission length as short as 800 mm. Furthermore, a computational model for the transmission length of prestressing force in post-tensioned concrete members has been developed similarly to the Model Code 2020 for pretensioned concrete. The level I of approximation enables quick transmission length estimation, whereas refined analysis is possible with the level II approach. The developed model and the research findings facilitate a comprehensive assessment of the post-tensioned concrete members in anchorage or tendon failure scenarios. As a result of the analyses carried out, optimal strategies for the further use of the structures can be proposed, fostering a step towards sustainable management.

Field investigation and numerical analysis of horizontal cracking in ledge girders of post-tension concrete bridges

This research addresses the pressing issue of horizontal crack initiation in ledge girders of post-tensioned concrete (PTC) bridges, which is a significant concern for the safety and longevity of long-span bridges. With field observations and advanced engineering computations, the study identifies the primary causes of these cracks and explores potential mitigation strategies. The research pinpoints the primary causes of horizontal crack initiation in PTC girders by analyzing 3D finite element modeling and comparing the results with the analytical solution suggested by a design code. The study also probes the potential of using external prestressing with a post-tensioning bar to mitigate horizontal cracking. The findings underscore the significance of adhering to the design code requirements for hanger reinforcement, which notably mitigates crack width in PTC girders. The research also highlights that higher prestress losses correspond to increased crack width, emphasizing the need to consider prestress losses for maintaining structural resilience. Furthermore, the study reveals that in all strengthening cases, the maximum crack width is notably reduced at the point of failure, albeit less effectively than when using rebar as per the design code. These findings underscore the potential of post-tensioning as a strengthening technique and the importance of adhering to design standards.

Dynamical analysis of a 40 m span precast posttensioned concrete girder during lifting operations

AbstractCranes are employed to lift precast concrete girders during their construction. Presently, there is no recommendation for operational velocities during girder assemblage, particularly for long elements; simultaneously, several accidents have been reported during the transitory phase of girder motion. Since this mechanical problem has been examined in technical literature using a static approach, the present research study aims to investigate the dynamical behavior of a long, prestressed concrete girder by determining critical operational velocities according to crane movements. Prestressing cables' eccentricity and lifting loop position deviation were accounted for in 3D finite element simulations of a 40 m span precast prestressed concrete girder. Transient nonlinear analyses to obtain stresses and deflections were performed, so as to account for the large deformation behavior of the motion. A frequency domain approach was employed to analyze the time history results using the girder's natural frequencies obtained by modal analysis. The finite element model was developed to simulate upward, downward, and lateral girder movements. The most significant displacements and stresses were observed in the highest girder acceleration peaks, amplified by eccentricities. Safety against cracking and subsequent failure during vertical and lateral movements was ensured for crane operating accelerations of 0.02 g (v = 20 cm/s) and 0.007 g (v = 7 cm/s), respectively. Compared with the usual static analysis, for the critical case investigated, the inertial effect intensified the tensile stresses by 27 times, increased the compressive stresses by 11%, and increased the girder deflection by 3 times.

Common Defects of Prefabricated Prestressed Elements for Industrial Construction

This manuscript attempts to classify typical errors occurring during the design, production, and use of prefabricated and prestressed concrete girders and slabs manufactured in Poland for industrial buildings since the 1950s. Although the cases discussed concern Poland, most of them have a universal character, and as such are also found in other countries. The defects and errors are illustrated with examples and the causes of their occurrence are also discussed. A method of classifying flaws based on the period of their occurrence was proposed. Most of the examples discussed were encountered by the authors during their professional work. In most of the presented cases, repair was possible, enabling further safe operation. This paper shows how important it is to periodically check the technical condition of prestressed structures and how common and at the same time trivial mistakes may be made by designers and contractors of this type of structure, despite the experience of over 70 years of their mass use. The quality of modern prestressed structures is undoubtedly higher. Using the experience of previous generations, designers and contractors abandoned the less durable post-tensioned concrete lattice girders. Errors, if they appear, are most often at the stage of implementing new products or are the result of poor workmanship or disregard for unfavorable weather conditions.

Experimental Investigation on Nonlinear Flexural Behavior of Post-Tensioned Concrete Bridge Girders with Different Grouting Conditions and Prestress Levels

Experimental Investigation on Nonlinear Flexural Behavior of Post-Tensioned Concrete Bridge Girders with Different Grouting Conditions and Prestress Levels

Influence of strand rupture on flexural behavior of reduced-scale prestressed concrete bridge girders with different prestressing levels

In prestressed concrete (PC) bridges, high-strength prestressing steel plays a key role in the flexural response of girders. In both pre-stressed and post-tensioned PC bridge girders, damage induced by corrosion or impact of under-passing high vehicles may led to rupture of one or more strands, significantly affecting the load-carrying capacity against dead and traffic loads. This paper presents an experimental study on the response of PC girders affected by strand rupture at different locations. Four reduced-scale post-tensioned concrete girders with different levels of initial prestressing force were tested under four-point bending. Two specimens with a different level of prestress were initially tested in undamaged configuration to provide a basis for the assessment of damage effects. The other pair of specimens were intentionally damaged - having the same initial prestressing level of their undamaged counterparts - in the lower tendon to investigate their limited flexural response under different performance levels including serviceability and collapse. Damage turned into a different critical cross section outside the loading region, i.e. both cracking and collapse were attained 1.1m away from midspan. In the last section of the paper, a cross sectional analysis of the girder was developed at cracking and ultimate conditions for the prediction of damage impact on failure mechanisms, thus validating the experimental findings.

Grillage Analysis of Prestressed Concrete Girder Deck Superstructure for NH-16 Bridge Flyover; Part-1

Abstract: The bridge superstructure flyover built on National Highway route 16 (NH-16) near Benz circle in Vijayawada to act as grade separated highway for vehicles to cross over National Highway route 65 (NH-65) is made of precast and post-tensioned concrete girders. This article is the first part of the two phase study that focuses on the structural analyses of concrete bridge girders. The bridge girders are analyzed for vehicular loads considered as per Indian Roads Congress Specifications. The IRC Class of loads of 70R and Class A and their wheel load configurations are discussed. The bridge girders along with deck are modeled as grillage girder-slab members in Staad Pro analysis software. The bending moments and shear forces are computed for each of the IRC vehicular load configurations and the envelope forces for governing load configuration are presented for each of the girders. Finally, the article summarizes the maximum flexural and shear demands on the bridge girders. The pros and cons of grillage analysis modeling for prestressed girders and the alternate superior options for precise but quick modeling are also recommended.

An Investigation of a Post-tension Problem in a Conference Hall Roof

Introduction: Post-tensioning is a technique for strengthening concrete members by embedding tendons into the concrete before casting. When the concrete has acquired the desired strength, these tendons are tensioned using hydraulic jacks. This study deals with structurally analyzing and designing a 21 m × 25 m conference hall without interior columns contained within eleven stories building. Methods: The hall was located on the 9th floor. Many structural floor systems were proposed for the hall such as composite steel-concrete, waffle concrete, and post tensioned girder slab. The structural system of post-tensioned concrete girders with a top reinforced slab was chosen due to its advantages: low deflection and low risk of cracking, and increase of net floor height. Stressing of strands (live ends) was applied from the four sides of the concrete slab. Twenty-three live ends were placed in north-south direction and 20 live ends in east-west direction. Results: The ultimate strength of the stands was 1860 MPa. The jacking force, 209 kN, was applied in each strand which represented 75% of ultimate strength. The post-tension concrete slab was analyzed with Ram concept software, which revealed that the total elongation of strands in the E-W direction ranged from 116 mm to 152 mm, and the total elongation of strands in the N-S direction ranged from 120 mm to 172 mm. Conclusion: The problem of warping of nine live anchorage ends in the south-north direction was encountered during post-tensioning, which resulted in the movement of strands from their original locations. A rehabilitation plan was proposed to overcome the aforementioned problem.

Assessment and strengthening of post-tensioned concrete box-girder bridges

Post-tensioned concrete box girders have been widely adopted for the construction of medium- to long-span bridges since the mid-20th century. Since the construction of the first such bridges, there has been rapid growth in the volume and weight of heavy vehicles, as well as an increase in exposure to adverse environmental conditions. At the same time, it is estimated that more than 50% of existing bridges in higher-income countries are over half-way through their design life and thus bridge owners are challenged with the management of aging structures. When deterioration in prestressed concrete bridges is identified during inspections, it leads to specific assessments and is usually followed by the need for bespoke strengthening design solutions. In many cases, the challenge in implementing the strengthening resides in maintaining structural capacity to minimise traffic disruption before the works are complete. This article covers the technical and asset management aspects related to the assessment and subsequent strengthening design for post-tensioned concrete box-girder bridges through the lens of case studies on two successful post-tensioned bridge rehabilitations. The strengthening solutions presented have been implemented with minimal disruption to traffic and have had a positive environmental impact by avoiding demolition and full deck reconstruction.

Numerical Investigation of Cracks at Girder Ends of Prefabricated Post-Tensioned Prestressed Concrete I-Girders

Prefabricated post-tensioned prestressed concrete (PTC) girders with high degrees of prestressing have been developed continuously in recent bridge designs to reach longer spans, higher quality, and larger load-bearing capacity. However, during the prefabrication process, several inclined and horizontal cracks were observed at the ends of a new style post-tensioned concrete girder, which could have a negative impact on the girders' longevity. In this study, a nonlinear finite element analysis technique was utilized to illustrate how concrete reacts and the mechanisms behind typical cracking patterns during the actual post-tensioning sequence. The prestressing load of a PTC girder was simulated with an improved cooling temperature method that accounts for immediate prestress losses. The field of principle tensile strain patterns and primary strain trajectories explained the overall mechanism underlying typical cracking behaviors. The results showed that the horizontal cracks under the anchorage plate (behavior 1) were generated by the bursting force, whereas the inclined cracks (behavior 2) and the horizontal cracks between the strands N1 and N2 anchor plates (behavior 3) were caused due to the spalling force. The effects of self-weight, girder end forms, as well as the transfer length of the prestressing strands, were discussed. The result demonstrates that both the self-weight and girder end shapes have a considerable effect on the behaviors of the anchorage zone. It is suggested that the transfer length of the anchor head be greater than 26 times of strand diameter to achieve the same effective stresses as the theoretical values.

EXPERIMENTAL AND THEORETICAL INVESTIGATIONS FOR BEHAVIOR OF PRECAST CONCRETE GIRDERS WITH CONNECTIONS

This research presents experimental and theoretical investigation of 15 reinforced concrete spliced and nonspliced girder models. Splices of hooked dowels and cast in place joints, with or without strengthening steel plates were used. Post-tensioning had been used to enhance the splice strength for some spliced girders. The ANSYS computer program was used for analyzing the spliced and non-spliced girders. A nonlinear three dimensional element was used to represent all test girders. The experimental results have shown that for a single span girder using steel plate connectors in the splice zone has given a sufficient continuity to resist flexural stresses in this region. The experimental results have shown that the deflection of hooked dowels spliced girders is greater than that of non-spliced girder in the range of (17%-50%) at about 50% of the ultimate load which approximately corresponds to the serviceability limit state and the ultimate loads is less than that of non-spliced girder in the range of (12%-52%). For other spliced girders having strengthening steel plates at splices, the results have shown that the deflection of the spliced girder is less than that of non-spliced girder in the range of (2%-20%) at about 50% of the ultimate load and the ultimate loads for spliced girder is greater than that of nonspliced girder in the range of (1%-7%). The post-tensioned concrete girders have shown a reduction in deflection in the range of (26% - 43%) at a load of 50% of the ultimate load as compared with that of ordinary girders. Moreover, post-tensioning increases the ultimate loads in the range of (70% - 132%). The results obtained by using the finite element solution showed a good agreement with experimental results. The maximum difference between the experimental and theoretical ultimate loads for girders was in the range of (3-11%).

Fusion of NDE Scanning and Photogrammetric Data for Concrete Bridge Decks and Girders Condition Assessment

The first case history would present 3-D results of Impact Echo Scanning and Ground Penetrating Radar (GPR) Scanning plus Spectral Analyses of Surface Waves tests of post-tensioned concrete bridge girders. The NDE results were overlaid on photogrammetric images of visible corrosion/cracking damage to the concrete bridge girders of an aging bridge due to de-icing salts and a marine environment. Cart-based scanning with GPR and Impact Echo and Spectral Analyses of Surface Waves NDE methods is commonly being conducted of both bare concrete decks and asphalt overlaid decks to map both top and bottom delaminations and depth of concrete cover. The data is being used in conjunction with chlorides and carbonation testing of concrete cores to recommend repairs and evaluate remaining service lives for bridges. Photogrammetric images of bare concrete in particular are being used to visibly compare areas of spalling, delamination and deck patching for improved interpretation, visualization and mapping of internal deck delaminations and other concrete damage with this data fusion approach to provide more accurate surface and full-depth images of bridge deck conditions.

Behavior of Post-Tensioned Concrete Girders Subject to Partially Strand Damage and Strengthened by NSM-CFRP Composites

Studies on the flexural behavior of post-tensioned beams subjected to strand damage and strengthened with near-surface mounted (NSM) technique using carbon fiber-reinforced polymer (CFRP) are limited and fail to examine the effect of CFRP laminates on strand strain and strengthening efficiency systematically. Furthermore, a design approach for UPC structures in existing design guidelines for FRP strengthening techniques is lacking. Hence, the behavior of post-tensioned beams strengthened with NSM-CFRP laminates after partial strand damage is investigated in this study. The testing program consists of seven post-tensioned beams strengthened by NSM-CFRP laminates with three partial strand damage ratios (14.3% symmetrical damage, 14.3% asymmetric damage, and 28.6% symmetrical damage). The experimental results showed that the use of CFRP laminates significantly increases the flexural capacity by up to 17.4 to 20.4%, corresponding to a strand damage ratio of 14.3 and 28.6%, respectively, enhances the stiffness, and reduces strand strain by up to 15.8 to 22.2%. However, the flexural stiffness of strengthened beams during serviceability phases is critical as strand damage ratios increase. Additionally, semi-empirical equations were proposed to predict the actual strain of unbonded strands whilst considering the effects of CFRP laminates. The suggested equations provide accurate predictions with little variance. Doi: 10.28991/CEJ-2022-08-07-013 Full Text: PDF

Probabilistic structural analysis of a real-life corroding concrete bridge girder incorporating stochastic material and damage variables in a finite element approach

A combined probabilistic approach based on response surface sampling (RSS) and importance sampling (IS) is developed to efficient assess the structural reliability of corroding concrete structures. In this approach, the failure probability and the corresponding reliability index can be calculated for any stochastic system, independent of the material and model complexity or the limit state function(s). The combined approach is applied to a real-life example where a corroding post-tensioned concrete bridge girder is considered. This bridge girder is modelled in a dedicated finite element analysis to assess the structural reliability under corrosion damage. Serviceability and ultimate limit state requirements are taken into account and the material and damage properties are the stochastic variables. A converged solution is found in 8 and 128 limit state function evaluations for the RSS and IS, respectively. The importance factors for the different variables are calculated. The full analysis highlights non-important parameters (strength of the traditional reinforcement) and indicates that the ultimate limit state of the girder is the limiting factor in all analyses. Further computational optimizations are proposed and implemented, highlighting the capabilities of the reduced model and the robustness of the proposed approach.

Full-scale investigation of post-tensioned prestressed concrete bridge girders subjected to frost heaving in cold regions

Frost heaving is one of the major diseases of post-tensioned prestressed concrete structures in cold regions. This study investigates the effects and underlying mechanisms of frost heaving damages on the mechanical behaviors of full-scale post-tensioned prestressed concrete girders of a highway bridge. Forensic investigations were performed for three bridge girders through destructive tests, which included borehole, anatomy, and flexural tests, with an intact girder as the control. Three-dimensional nonlinear finite element models of the girders were established to understand the mechanisms of the effect of frost heaving. The results show that frost heaving reduced the effective prestress, mechanical properties of concrete, and bond between concrete and tendon, thus reducing the crack resistance and durability of the girders. This study provides new insights into post-tensioned prestressed concrete girders under frost heaving. The results are useful to improve the safety, serviceability, and durability of prestressed concrete bridges in cold regions.

Failure Analysis of Dapped-End Cracking in Posttensioned Bridge Girder

Abstract This paper will examine in detail a posttensioned concrete (PTC) girder bridge with dapped-end connections, with a re-entrant corner diagonal crack that is typical of these types of bridge...

Test of 90-Foot Post-Tensioned Concrete Girder with Unbonded Tendons

Test of 90-Foot Post-Tensioned Concrete Girder with Unbonded Tendons

The effect of wire rupture on flexural behavior of 45-year-old post-tensioned concrete bridge girders

Current maintenance practices for aging prestressed concrete bridges are facing challenging tasks to judge structural adequacy and remaining service life even with insufficient information and invisible deterioration. For prestressed concrete bridges, remaining prestress forces and corrosion of strands are the most crucial data. To accumulate the data, full-sized and deteriorated 45-year-old prestressed concrete bridge girders were recovered from an existing bridge. The post-tensioned girders were tested to observe key performance indicators such as cracking, yielding and crushing. The proposed strain compatibility method considering average tested material properties and measured prestressing force provides reasonable estimation of the flexural capacity of the old prestressed concrete girders. From the observed flexural behavior, a flexural cracking can give a good indication of the residual prestressing force. Based on the experiment, discussion on the assessment of existing bridges and shift from safety-oriented limit states to quantitative approach for extended service life.

Elements of Pathway for Quick and Reliable Health Monitoring of Concrete Behavior in Cable Post-Tensioned Concrete Girders.

The paper discusses the problems connected with long-term exploitation of reinforced concrete post-tensioned girders. The scale of problems in the world related to the number of cable post-tensioned concrete girders built in the 1950s and still in operation is very large and possibly has very serious consequences. The paper presents an analysis and evaluation of the results of measurements of the deflection and strength and homogeneity of concrete in cable–concrete roof girders of selected industrial halls located in Poland, exploited for over 50 years. On the basis of the results of displacement monitoring in the years 2009–2020, the maximum increments of deflection of the analyzed girders were determined. Non-destructive, destructive, and indirect evaluation methods were used to determine the compressive strength of concrete. Within the framework of the indirect method recommended in standard PN-EN 13791, a procedure was proposed by the authors to modify the so-called base curve for determining compressive strength. Due to the age of the analyzed structural elements, a correction factor for the age of concrete was taken into account in the strength assessment. The typical value of the characteristic compressive strength is within the range 20.3–28.4 MPa. As a result of the conducted tests, the concrete class assumed in the design was not confirmed, and its classification depended on the applied test method. The analyzed girders, in spite of their long-term exploitation, can be still used for years on the condition that regular periodical inspections of their technical condition are carried out. The authors emphasize the necessity for a permanent and cyclic diagnostic process and monitoring of the geometry of girders, as they are expected to operate much longer than was assumed by their designers.

3D printing of a post-tensioned concrete girder designed by topology optimization

In this paper, the digital design and manufacturing of a post-tensioned concrete girder is presented. We bring together two emerging technologies that show great potential for realizing highly-efficient concrete structures: topology optimization for simulation-driven design and 3D concrete printing (3DCP) for manufacturing of optimized shapes. While this is not the first-ever 3D-printed concrete structure, it is the first demonstration of how topological design in combination with 3D concrete extrusion printing allows for creating efficient structures with reduced use of materials. As the implementation of a specific optimization procedure for post-tensioned concrete structures is so far available in 2D only, some design post-processing was necessary, and a 3D finite element analysis was performed. After realization of the 3DCP element (i.e. printing and assembly), the girder's structural performance was experimentally verified using digital image correlation. The deflection of the girder was compared with the numerical results. The manuscript includes thorough discussions on the manufacturing challenges – including printing setup, assembly and integration of reinforcement.