Prestressed Concrete Structures Research Articles

Experimental and numerical study on the dynamic behavior of prestressed concrete panels suffering low speed impact

Bidirectional bonded prestressed concrete (PS) structures have widely been used in energy infrastructure. Nonetheless, there has been a lack of research on the effect of the reinforcement ratio of longitudinal bars on the dynamic behavior of PS structures. Therefore, the low speed drop hammer impact tests of 4 reinforced concrete (RC) and 9 PS panels have been completed in this paper, firstly. The dynamic behavior of PS panels has been investigated through work, and the working mechanism of the reinforcement ratio on the dynamic behavior of the specimens is analyzed. The results show that the panels mainly suffer plastic deformation and damage; increasing the reinforcement ratio could improve the membrane force effect and enhance the confinement effect on concrete to improve the load-bearing capability of the specimen. However, it will expand the plastic damage area of the specimen. Furthermore, the numerical models have been verified based on the test results to deeply analyze the influence of reinforcement ratio on the energy dissipation mechanism of the specimen. It shows that the increase of the reinforcement ratio of reinforcement will increase the energy dissipation proportion of reinforcement, but it will also increase the plastic energy consumption ratio of the concrete and increase the prestress loss after the impact; while, the rise of the reinforcement ratio of prestressing bars is beneficial to use the reinforcement, prestressing bars and tensile bars fully. Therefore, the designer could increase the reinforcement ratio of prestressing bars to enhance the impact resistance of the structures.

Failure mode discrimination and theoretical prediction method for unequal span bonded prestressed concrete substructures against progressive collapse

Unequal-span prestressed concrete (USPC) structures have unequal spans on the left and right sides and are configured with prestressed steel strands on both spans. However, research on the progressive collapse resistance of these structures is lacking. The strength of the asymmetry of the USPC structure varies depending on the span ratio and reinforcement configuration, resulting in two distinct failure modes in progressive collapse. A parametric analysis was conducted using finite element software to determine how the resistance to progressive collapse and failure modes of USPC structures under middle column failure are affected by variables such as the span ratio, reinforcement configuration, and proportion of prestressing. Accordingly, a discrimination criterion for determining the failure modes of USPC structures was proposed. A theoretical approach for predicting the ultimate displacement and resistance of the progressive collapse of USPC structures was presented for different failure modes. This theoretical approach proposes an innovative stiffness combination and tension path method to establish displacement coordination and force equilibrium conditions, respectively. The theoretical prediction method was deemed valid after comparing it with finite element simulation results.

Effect of various factors related to the bond-type anchorage system on tensile performance of carbon fiber-reinforced polymer strand cables

Steel strands, which are most frequently used as internal/external tendons of prestressed concrete (PSC), are highly susceptible to corrosion, which degrades the structural stability of the PSC structures. Studies are underway to utilize carbon fiber-reinforced polymer (CFRP) strands in PSC structures as tendons to achieve structural performance comparable to that of existing steel strands, with the additional feature of corrosion resistance. However, such applications of CFRP strands require the accurate identification of the intrinsic properties of the material. This study conducted an analysis to establish a test method using bond-type anchorage that can evaluate the intrinsic properties of CFRP strands by setting several factors related to the bond-type anchorage system as variables. Tensile tests were conducted on the CFRP strands after fabricating the specimens according to the variables of the bond-type anchorage system (shape of the CFRP strand located inside the steel pipe and type of internal filler material). In addition, the compressive strength was measured to determine the mechanical properties of the cementitious filler materials. Based on the experimental results, the load-displacement curves, stress-strain curves, fracture shapes, and tensile strengths of various cases of CFRP strands were analyzed. The results of the study revealed that the split-strand CFRP fabricated with CP0.25 mixture as the bond-type anchorage system had the ability to fully obtained intrinsic tensile properties.

Corrosion monitoring of reinforced concrete structures: The DGZfP specification B12 Collaboration

AbstractCorrosion monitoring of reinforced or prestressed concrete structures has become increasingly important in recent years. Areas of application include components that are no longer accessible after completion or where potential field measurements cannot be carried out due to existing coatings. Corrosion monitoring can also be used to monitor the progress of corrosion in corroding systems, e.g. to prove the success of repair measures according to repair principle 8 in accordance with EN 1504‐9 or repair method 8.3 in accordance with the DIBt repair guideline. It also could be used to prove the functionality of cathodic corrosion protection systems in accordance with ISO 12696. Despite the increasing importance of corrosion monitoring, no guidelines or recommendations existed until 2018. This gap was closed by the English version of specification B12, “Corrosion Monitoring of Reinforced and Prestressed Concrete Structures,” of the German Society for Non‐Destructive Testing, which was published in 2021. This article introduces specification B12 by explaining the basic measurement principles and illustrating the potential of corrosion monitoring in new and existing buildings.

Flexural Strengthening of Concrete Structures Using Externally Bonded and Unbonded Prestressed CFRP Laminates: A Literature Review

Carbon fiber-reinforced polymer (CFRP) materials have been widely used in prestressed and non-prestressed systems for the flexural strengthening of concrete structures in many construction projects worldwide. Strengthening with non-prestressed CFRP materials, which is known as passive repair, could lead to an increase in the ultimate capacity of the concrete member. However, it has little effect on its serviceability performance (e.g., cracking, yielding, and deflection properties). Flexural strengthening with prestressed CFRPs provides an active repair technique that positively effects the strength and serviceability of structures. In addition, strengthening with prestressed fiber-reinforced composites efficiently uses the material’s high tensile strength. Although different fiber-reinforced polymer (FRP) materials and forms have been used in prestressing applications, this paper focused on the use of CFRP laminates (e.g., sheets, strips, or plates). These laminates have been widely used due to their excellent mechanical properties, ease of application in various geometrical shapes, good conforming surface area of contact with structures, and low installation costs. A comprehensive literature review was presented on strengthening using prestressed CFRP laminates in conventionally and internally prestressed concrete structures (PCSs). The externally bonded and unbonded prestressed CFRP laminate applications that used different anchorage systems were presented. The flexural behavior, failure modes, and serviceability performance of the strengthened concrete members were discussed. The effects of the prestressing level on ductility and energy absorption and a summary of the recommended optimum prestressing level discussions were presented in this paper. Furthermore, a review of the theoretical studies that were conducted for prestressed CFRP applications was provided. The knowledge gaps in the research area and future research recommendations were presented.

Dynamic response of bidirectional bonded prestressed concrete slabs subject to low velocity impact: Impact energy and prestress degree

Bidirectional bonded prestressed concrete (PS) structures have been widely used in energy engineering. However, the systematic studies on the failure mechanism and dynamic response of this structure suffering from impact load are still inadequate. This paper has carried out nine drop hammer impact tests and corresponding numerical models. The results reveal that overall flexure and local punching co-occur in the bidirectional PS slabs under the impact, with the local punching failure as the failure mode. The dynamic response of the slab includes: inertia loading stage, load holding stage and rebound unloading stage. Due to the influence of the membrane force enhancing effect and specimen damage weakening effect, the impact force in the load holding stage may present three conditions. The compressive prestress applied to concrete can provide in-plane constraint and limit the appearance and development of cracks, resulting in decreasing the plastic damage of the specimen and the drop hammer displacement, while improving the bearing capacity and stiffness of the specimen. For impact energy of 5.48 kJ, when the prestress degree increase from 0% to 11.6%, the equivalent impact force increases 95%, the peak drop hammer displacement, equivalent spalling and scabbing diameter decrease 40%, 22.6% and 8.6%, respectively.

Investigation on tensile and creep behaviour of glass fiber reinforced polymer (GFRP) bars: A review

Corrosion has become a global issue primarily responsible for the deterioration of structural capacity of reinforced concrete structures (RCC) and prestressed concrete structures (PSC) leading to its premature failure. Across the globe, corrosion issue is critical in PSC structures, as the cross-sectional area of steel strands gets destroyed leading to the considerable reduction of load carrying capacity. A lot of case studies have been reported regarding the early failure of prestressed box girder bridges prior to their design life. The inspection of corrosion related issues is a complex affair, and it involves huge rehabilitation and maintenance cost. It has been reported that the expenditure estimated for maintenance and rehabilitation of structures due to corrosion is enormous inducing a significant loss in country’s GDP. To overcome this challenge in RCC and PSC structures due to corrosion of conventional steel reinforcement, Fiber reinforced polymer (FRP) bars could be used in place of steel bars. FRP bars distinct characteristics like light weight, excellent corrosion and fatigue resistance have attracted significant attention and priority as substitute over conventional steel reinforcement. The lack of proper design guidelines and specifications restricts the reliability and application of this technology in the construction field. However, the active research on glass fiber reinforced polymer (GFRP) bars indicated that it could be the best alternative due to its lower cost and superior tensile strength. Therefore, it is necessary to understand the preliminary characteristics of GFRP bars prior to its application as reinforcement in RCC and PSC. Hence, a critical review on tensile and creep characteristics of GFRP bars would be presented in this paper to contribute a vivid and detailed documentation for upcoming research on GFRP.

Analytical approach for bursting cracking analysis of post-tensioned anchorage zone

In prestressed concrete structures, improper design and detailing of the anchorage zone frequently cause bursting cracking along the tendon path. Due to the complex stress state in the anchorage zone, it is difficult to estimate the actual cracking load, even in well-controlled experimental tests. Previous studies on anchorage zone cracking are mainly based on numerical simulation. There is still a lack of explicit approaches for practical use. This study aims to provide an analytical approach for predicting the first bursting cracking loads in the post-tensioned anchorage zone. It is found that the stress ratio of compression to tension is significantly higher in the anchorage zone than in the split cylinder. Thus, a strength correction factor is derived to compensate for the tensile-strength reduction due to the effect of biaxial stress state. Besides, a tension chord model is developed to quantify the contribution of bursting reinforcement in enhancing the tensile strength of concrete. After clarifying the effect of biaxial stress state and the contribution of bursting reinforcement, direct equations are proposed for predicting the first bursting cracking loads in the anchorage zone. The analytical approach is compared with existing test data and is applied in the cracking analysis of an actual bridge, indicating that it is accurate and convenient for application.

Test Database for Corroded Prestressing Steel Strands Recovered from Aged Bridges

To evaluate the structural safety of corroded prestressed concrete structures, it is necessary to define the deteriorated mechanical behaviors of corroded prestressing steel strands. However, no standard provides a quantified relationship between the level of corrosion and the residual mechanical properties, and no consensus for such quantification has been reached. The aim of this study was to provide a test database for the residual mechanical properties of corroded prestressing steel strands. Strands recovered from aged bridges were naturally corroded, and an evaluation method for the corrosion level was suggested. In addition, corrosion assessment criteria were suggested based on characteristics of the corrosion appearance.

Review of the influence of concrete creep on the operation of pre-stressed steel-reinforced concrete structures of civil defense structures

Review of the influence of concrete creep on the operation of pre-stressed steel-reinforced concrete structures of civil defense structures

Analisis Kehilangan Gaya Prategang Girder Pada Jembatan Proyek Pembangunan Jalan Tol Tebing Tinggi – Inderapura

Currently, the construction of toll roads in several regions of Indonesia is being carried out. One of them is the construction of the Tebing Tinggi-Inderapura Toll Road. In this project there are several bridge constructions as a link between roads or as a pedestrian bridge. This bridge uses prestressed beams in which there are steel wires. The steel wire is tensioned by pulling it using a hydraulic jack. When stress is applied, the beam loses its prestressing force. The purpose of this study was to determine the percentage loss of prestressing forces that occurred in the bridge beam. Loss of prestressing force must not exceed the maximum that has been determined. There is some loss of prestressing force which is taken into account. Short-term prestress losses include elastic shortening of the concrete, friction along the tendons and anchor slippage. Furthermore, the loss of long-term prestressing forces is creep in steel, shrinkage in concrete and relaxation of steel. After all the loss of prestressing force is calculated, the total loss of prestressing force is 21.62%. To find out the maximum percentage of loss of prestressing force using calculations from the book Design of Prestressed Concrete Structures by T. Y. Lin H. Burns with the formula Pe/Ac and the value is 8.98 MPa. Where 8.98 MPa is 25%, so 21.62% is smaller than 25%, so it is still safe. In addition, an implementation method for installing girders on bridges is introduced..

Bayesian inference with correction of model bias for Thermo-Hydro-Mechanical models of large concrete structures

Drying and creep are mainly driving the continuous strain evolution in time of aging large prestressed concrete structures, and may jeopardize the safety of their environment. Therefore, it is crucial to dispose of an accurate assessment of structures’ long-term strain level so as to evaluate their integrity. In the framework of probabilistic modeling of the delayed mechanical analysis of aging concrete structures, Bayesian inference allows to update uncertainties related to input parameters of computational models through the assimilation of noisy monitoring data. In this paper, a Bayesian inference methodology aiming at updating uncertain parameters of computational models for large concrete structures is proposed. This methodology combines a powerful surrogate modeling technique named PC-PCE (Principal Component Polynomial Chaos Expansions) with the so-called BUS (Bayesian Updating with Structural reliability methods) framework, in order to efficiently draw samples from posterior distributions for a sensibly reduced computational cost. In particular, the methodology is based on a framework to account for model uncertainties and biases, which are usually disregarded in the existing literature related to large concrete structures, and it enables correction predictions through Bayesian inference. The proposed approach is illustrated through an application to a large aging prestressed concrete structure, namely a 1:3 scale mock-up of a Nuclear Containment Building. In this context, a thermo-hydro-mechanical computational model with uncertain parameters is adopted to model the time evolution of strains of the structure. Results emphasize that the proposed approach performs Bayesian updating for a reduced computational cost. The proposed Bayesian inference approach also enables the identification of model biases, and correction of strain predictions.

Effect of magnesium phosphate cement mortar coating on strand bond behaviour

Surface coating on prestressing strand is an effective and economic measure to prevent pre-tensioned prestressed concrete structures from corrosion. The effects of magnesium phosphate cement (MPC) mortar coating on the strand bond behaviour are investigated experimentally in the present paper. Ten pull-out specimens with different MPC mortar coating thickness are designed to study the effect of coating thickness or thickness ratio on the bond failure mode, bond strength and force-slip response. Experimental results demonstrate that the bond failure mode changes from pull-out failure accompanied with strand rotation to cover splitting failure when coating thickness and thickness ratio exceed 10 mm and 0.15, respectively. Compared with the uncoated and epoxy coated control specimens, coating thickness ranging from 25 mm to 35 mm or thickness ratio ranging from 0.37 to 0.52 contributes the most to the increase of bond strength and stiffness. Beyond that range, the facilitation in both bond strength and stiffness gradually decreases. Besides, an analytical model, which considers the composite cover confinement provided by the coating and concrete, is proposed to reproduce the bond strength evolution. Comparison of experimental and prediction results show that the proposed model can be used to reasonably evaluate the bond strength.

Deep Learning-Enriched Stress Level Identification of Pretensioned Rods via Guided Wave Approaches

By introducing pre-compression/inverse moment through prestressing tendons or rods, prestressed concrete (PC) structures could overcome conventional concrete weakness in tension, and thus, these tendons or rods are widely accepted in a variety of large-scale, long-span structures. Unfortunately, prestressing tendons or rods embedded in concrete are vulnerable to degradation due to corrosion. These embedded members are mostly inaccessible for visual or direct destructive assessments, posing challenges in determining the prestressing level and any corrosion-induced damage. As such, ultrasonic guided waves, as one of the non-destructive examination methods, could provide a solution to monitor and assess the health state of embedded prestressing tendons or rods. The complexity of the guided wave propagation and scattering in nature, as well as high variances stemming from the structural uncertainty and noise interference PC structures may experience under complicated operational and harsh environmental conditions, often make traditional physics-based methods invalid. Alternatively, the emerging machine learning approaches have potential for processing the guided wave signals with better capability of decoding structural uncertainty and noise. Therefore, this study aimed to tackle stress level prediction and the rod embedded conditions of prestressed rods in PC structures through guided waves. A deep learning approach, convolutional neural network (CNN), was used to process the guided wave dataset. CNN-based prestress level prediction and embedding condition identification of rods were established by the ultrasonic guided wave technique. A total of fifteen scenarios were designed to address the effectiveness of the stress level prediction under different noise levels and grout materials. The results demonstrate that the deep learning approaches exhibited high accuracy for prestressing level prediction under structural uncertainty due to the varying surrounding grout materials. With different grout materials, accuracy could reach up to 100% under the noise level of 90 dB, and still maintain the acceptable range of 75% when the noise level was as high as 70 dB. Moreover, the t-distributed stochastic neighbor embedding technology was utilized to visualize the feature maps obtained by the CNN and illustrated the correlation among different categories. The results also revealed that the proposed CNN model exhibited robustness with high accuracy for processing the data even under high noise interference.

Distributed displacement estimation of pre-stressed concrete beams with random cracks using long-gauge strain sensing

Large pre-stressed concrete structures are usually confronted with random cracks and down-warping. Aiming to these structure diseases, a strategy for estimating distributed displacement of pre-stressed concrete beams with random cracks based on long-gauge strain sensing is presented in this article. First, an indirect method of calculating displacement of beams considering the presence of random cracks and pre-stress effect is derived. The method only relies on the collected strain responses and material parameters, and is irrelevant to external load. Then, a pre-stressed beam subjected to static load is designed for prove the effectiveness of the strategy. In the experiment, variable neutral axis position, curvature, concrete stress and vertical displacement are extracted under different load steps. Experiment results indicate that the estimated displacement has large relative error if random cracks are neglected. When the influence of random cracks is taken into account, the identified displacement agrees well with the directly monitored one by displacement sensors. Meanwhile, the results using different sensor arrangement are also compared. The presented strategy without the necessity of reference point could be an alternative for displacement monitoring of pre-stressed structures.

Analysis of Short-Term Prestress Losses in Post-tensioned Structures Using Smart Strands

The proper estimation of prestressing force (PF) distribution is critical to ensure the safety and serviceability of prestressed concrete (PSC) structures. Although the PF distribution can be theoretically calculated based on certain predictive equations, the resulting accuracy of the theoretical PF needs to be further validated by comparison with reliable test data. Therefore, a Smart Strand with fiber optic sensors embedded in a core wire was developed and applied to a full-scale specimen and two long-span PSC girder bridges in this study. The variation in PF distribution during tensioning and anchoring was measured using the Smart Strand and was analyzed by comparison with the theoretical distribution calculated using the predictive equations for short-term prestress losses. In particular, the provisions for anchorage seating loss and elastic shortening loss were reviewed and possible improvements were proposed. A new method to estimate the amount of anchorage slip based on real PF distributions revealed that the general assumption of 3–6-mm slip falls within a reasonable range. Finally, the sensitivity of the PF distribution to a few of the variables included in the equation of the elastic shortening loss was examined. The study results confirmed that the developed Smart Strand can be used to improve the design parameters or equations in PSC structures by overcoming the drawbacks of conventional sensing technologies.

Evaluation of the Performance and Ductility Index of Concrete Structures Using Advanced Composite Material Strengthening Methods.

The performance of concrete structures deteriorates over time. Thus, improving their performance using fiber-reinforced polymers (FRPs), PS strands, and various strengthening methods is important. Reinforced concrete (RC) and prestressed concrete (PSC) structures develop initial cracks in concrete during bending tests, and destruction occurs over a certain period of time after a certain load is generated, and then after the reinforcements and strands yield. However, in the case of FRP structures, after an initial concrete crack occurs, FRPs exhibit a rapid shape deformation of the structure after yielding. Thus, in this study we used FRP and PS strand materials and evaluated the ductility index using the load-displacement results obtained from structural tests conducted using various strengthening methods. The ductility index evaluation method compares and analyzes the change rates in the ductility index of PSC and RC structures based on a method that uses structural deflection and the derivation of the energy area ratio. The ductility evaluation results based on the energy area ratio at the crack, yield, and ultimate points showed that all the RC structures, except for the specimens strengthened with reinforcing materials from company H, were in the ductility and semi-ductility sections. Thus, all the PSC structures, except for the control specimens and PH4NP, were found to be brittle.

Comparison of fire spalling behaviours between ring-restraint and pre-stressed concrete specimens during fire

Pre-stressed concrete (PC) structures have higher explosive spalling risk during fires than reinforced-concrete structures, because of the initial compressive stress due to the pre-stressing force. The Japanese Concrete Institute (JCI) has standardised a ring-restraint heating test. Herein, we investigated the explosive spalling of uniaxial PC beam specimens and ring specimens made of concrete with the same mix proportions. A fire test was performed by exposing the specimens at the bottom ends to one-sided heating. RABT 30 and ISO 834 heating curves were used. The spalling was evaluated using spalling indexes specified by the JCI in terms of the maximum spalling depth, spalling area ratio, spalling volume ratio, and maximum spalling depth ratio. The spalling behaviour depended on the shape, degree of restraint, and difference in the pre-stress levels of the specimens. We demonstrated the need to consider the spalling area, depth, and volume in spalling evaluations.

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.

Fire resistance of bi-directionally prestressed concrete under extreme fire loading

Infrastructures such as prestressed concrete containment vessels (PCCVs) and liquid gas storage tanks are constructed as bi-directional prestressed concrete (PSC) structures to ensure outstanding leak-tight storage and shielding performance. However, PSC structures exhibit severe vulnerability to high-temperature fire due to the high-strength concrete used and the application of prestressing (PS) stresses to increase the strength of the structures. The PCCV of a 1400 MW advanced power reactor was selected as the target for study. A scaled-down model of the PCCV outer wall was fabricated and tested to determine its resistance to a standard fire-loading scenario. Furthermore, different PS forces were applied to the specimens to evaluate the effect of concrete confinement on the fire resistance. Test data of temperature distribution, PS force loss and residual strength capacity were obtained. The experimental data were used for calibration of a commercial finite-element simulation program (Midas FEA) for structural fire analysis of real-scale concrete structure and infrastructure. The simulation and test results showed significant similarity and the result trends were accurate.