Prestressed Reinforced Concrete Research Articles

Failure-mode scale transitions in RC and PC beams

Current design Standards for reinforced concrete beams prescribe to respect a minimum, ρmin, and a maximum, ρmax, reinforcement ratio in the design of structures. Below ρmin a brittle failure due to unstable crack propagation is expected. On the other hand, for ρ > ρmax a brittle failure due to concrete crushing is obtained. In this framework, a reinforced concrete element with ρmin < ρ < ρmax presents yielded steel at Ultimate Limite State (ULS) with a stable behaviour and no catastrophic loss of bearing capacity. Design Standards define ρmin and ρmax limits on the basis of the Bernoulli’s hypothesis of plane sections, and completely disregard size-scale effects. Within the present paper, Dimensional Analysis is used to determine the Brittleness Numbers that govern the behaviour of reinforced concrete (RC) as well as of prestressed reinforced concrete (PC) beams. Therefore, parametric analyses carried out by means of the Cohesive/Overlapping Crack Model (COCM) are used to study the ductile-to-brittle transitions in RC and PC beams, and to highlight the size-scale dependency of the two above-mentioned reinforcement limits.

Experimentally validated numerical analyses on the seismic responses of extra-large LNG storage structures

Extra-large liquefied natural gas (LNG) storage tanks are comprised by a steel inner tank and an outer protective tank of prestressed reinforced concrete (PRC), both being very thin. These important lifeline infrastructures are prone to damage and even failure under earthquake during their service life. Convincing numerical simulation, verified by shake table tests, is a feasible tool to quantify the seismic responses and to mitigate the potential damage/failure of LNG storage structures. This work addresses systematically the three-dimensional finite element (FE) modeling, experimental validation and numerical simulations of such structures, with the soil–pile interaction of the foundation, the fluid–structure interaction of the inner tank and damage of the outer tank all properly accounted for. For the sake of computational efficiency with no loss of too much precision, the soil–pile interaction is described by the mass–damper–spring model, and the fluid–structure interaction by the mass–spring model with both the convective and impulsive components accounted for. Moreover, the nonlinear mechanical behavior of concrete is considered by the damaged-plasticity model regularized with the fracture energy. The concrete–steel interaction in PRC is practically dealt with by modifying the constitutive relations of concrete and steel rebars/tendons properly with the equilibrium and compatibility conditions accounted for. The FE modeling strategy is validated against the recently conducted benchmark shaking table test of a scaled extra-large LNG storage structure. The capability in capturing the overall dynamic responses, e.g., the hydrodynamic pressure and structural vibrations under seismic actions, etc., is sufficiently verified. Finally, the dynamic responses and structural reliability of an extra-large LNG storage tank under deterministic and stochastic seismic actions are numerically studied in details.

Seismic Response of a PC Continuous Box Girder Bridge under Extreme Ambient Temperature

To study the effect of temperature on the seismic performance of a prestressed reinforced concrete (PC) continuous girder bridge with laminated rubber bearings (LRBs), a two-linked continuous bridge was used as the background to consider the effect of extreme temperature on the properties of LRBs and pier concrete. First, the properties of concrete specimens were tested at different temperatures to obtain their mechanical parameters at extreme temperatures. Then, we obtained the effect of extreme temperature on the seismic response of consecutive bridges with LRBs by examining the seismic response of the pier moments, pier top displacements, and bearing deformations. The results show that compared with normal temperatures, the extreme temperature causes a change in parameters of the LRBs and concrete pier, which increases the internal force and displacement response of a pier under an extremely low temperature by 37.13% and 32.74%, respectively. The displacement of bearings under extremely high temperature conditions increases by 16.31%. The influence of temperature changes on the mechanical parameters of LRBs will change the connection stiffness of the pier and superstructure, resulting in significant changes in the seismic response of the pier and bearing, so that the internal force and displacement response of the pier are negatively correlated with the temperature.

Impact of the Structural Defects on Risk Assessment of Concrete Bridges According to the Italian Guidelines 2020

The Italian infrastructure network of roads and bridges is one of the most complex in the world due to the territory orography. Italy is strongly interested in seismic and hydrogeological hazards, and, in addition, degradation and obsolescence phenomena are common in infrastructures nowadays approaching the end of their nominal life. Furthermore, these infrastructures are subjected to continuous traffic load increase over time. In 2020, the Italian Ministry of Infrastructure and Transport (MIT) published the guidelines for risk classification and management, safety assessment, and monitoring of existing bridges (LG2020) as an attempt to unify the multiple procedures of inspection, monitoring, and maintenance of infrastructures. The multilevel approach proposed in the Italian guidelines for the management of the complex existing system of bridges is herein discussed and investigated, focusing on an operational methodology to evaluate the impact of structural defects on the risk assessment. This study aims to develop an operational methodology for the application of the procedure generically depicted in the LG2020 for the attribution of the level of defectiveness based on the outcomes of the periodical inspections. In particular, such a methodology is applied to two of the most widespread bridge structural typologies in the Mediterranean area: reinforced concrete (RC) and prestressed RC (PRC) bridges. The defects’ extent and level to structural members are associated with the proposed procedure for different bridge risk ratings. The work presents a useful tool to proceed from the outcomes of the inspections to the assignment of a level of defectiveness for the bridge, which enters into the risk assessment. This is to drive decision-makers in the definition of future actions and interventions, such as the detailed assessment of safety level and relevant strengthening interventions or installation of continuous monitoring systems.

Non-Linear Analysis of R.C. and P.R.C. Girder Bridges

In professional practice, the design and verification of Reinforced Concrete (RC) and Prestressed Reinforced Concrete (PRC) structures are performed using a simplified calculation provided by the Eurocodes that limits resistance but that also includes a certain level of structural safety. Some aspects that directly affect the simplified methods involve the use of linear constitutive laws of materials. The use of non-linear laws is evident in the exploitation of reservoirs of strength and deformations of plastic materials in the Ultimate Limit State. The purpose of this research is to evaluate the increase in resistance to bending actions during the plasticization of the beam of existing bridges to support the decision-making process of the engineer in the assessment of existing structures. To achieve this, two codes (MEG Ductility, MEG Fiber Sections) were developed to provide the moment–curvature diagram of RC and PRC sections using non-linear bonds, and in this paper, the study of RC sections is reported. Furthermore, through a push-down analysis, two RC and PRC viaducts have been analyzed using the moment–curvature characteristics obtained from the realized codes and by varying the non-linear constitutive bonds. The results of this study provide valuable insights into the behavior of RC structures under bending actions and demonstrate the importance of considering non-linear material laws for accurate structural assessments. The findings contribute to the enhancement of the decision-making process of engineers when dealing with existing infrastructures.

Experimental Investigation of the Effect of Steel Fibers on the Flexural Behavior of Corroded Prestressed Reinforced Concrete Beams

Rebar corrosion and its consequences are one of the most common damages to reinforced concrete (RC) structures. In structures with greater sensitivity, such as prestressed reinforced concrete (PRC) structures, where steel elements, including prestressed tendons, play a more significant role in supporting the structure, the importance of this issue increases. Methods for repairing and reinforcing such structures have been developed, including incorporating fibers into the concrete mixture to improve its mechanical properties, particularly its bending resistance. This paper presents the results of an experiment that studied the influence of steel fibers on the flexural behavior of PRC beams subjected to accelerated corrosion. Twelve beams with a rectangular cross-section of 150 mm × 300 mm and a length of 2000 mm were fabricated. The steel fibers used in the experiment were corrugated and hooked-end types, with volume fractions of 0.5% and 1.0% in the concrete. Nine beams were subjected to accelerated corrosion testing, with three of them being without fibers and the remaining six being reinforced with steel fibers at volume fractions of 0.5% and 1.0%. Each group of three beams was exposed to three different levels of corrosion, namely 5%, 10%, and 15%. The specimens were tested after exposure to corrosion through a four-point bending load. The accelerated corrosion was induced using an electric current on the prestressing tendons. The results indicated that different levels of corrosion reduced the final bearing capacity and other behavioral characteristics of the specimen, including the amount of energy absorption, effective hardness, and midspan displacement. Adding fibers to the concrete mixture positively affects the compensation of these reduced capacities. Moreover, the amount of this compensation was directly correlated with the volume fraction of used fibers.

Bending Strength of Connection Joints of Prestressed Reinforced Concrete Pipe Piles

The connection joint of prestressed concrete pipe piles is a typical steel–concrete structure, and its bending strength has evolved into a critical factor affecting the safety of supporting structures in underground engineering. Based on full-scale bending tests of five specimens of large-diameter prestressed reinforced concrete (PRC) pipe piles and connection joints, as well as the corresponding finite element numerical simulation, the bending bearing and deformation characteristics of connection joints of PRC pipe piles were analyzed, together with the effects of concrete strength, precompression stress, and connection mode of joints. The results showed that the crack resistance of the welded joint of PRC pipe piles was equivalent to that of the pipe pile shaft, but the ultimate bending moment of the joint was about 58–87% of that of the pile shaft. The bending failure mode of the pipe pile joint was mainly manifested in the end plate yielding into a drum shape, with the tension side of the pile hoop and the end plate clearly separated from the pipe pile, and crushed concrete at the upper edge of the pile hoop. The bending strength of the joint can be improved by increasing the bonding strength between the end plates of the joint or embedding Rachel reinforcement in concrete. In addition, synchronously increasing the strength grade and reinforcement ratio of concrete or strengthening the precompression stress of concrete are favorable measures.

Construction Technology of Pretension Prestressed Reinforced Concrete Structure of Multi-storey Logistics Warehouse

At present, there is a problem of too much prestress loss in the construction of multi-layer logistics warehouses in China. To meet the quality requirements of the project, this paper puts forward the research on the construction technology of pretension prestressed reinforced concrete structure of multi-layer logistics warehouse. The loss of prestress in the construction process can be effectively controlled by incorporating pre-tensioning technology into the construction process, placing prestressed tendons, and tensioning operations. Taking a logistics warehouse construction project as the construction object, using the construction technology designed in this paper to construct, the experiment proves that the construction technology of the pretension prestressed reinforced concrete structure of the multi-layer logistics warehouse proposed in this paper can effectively reduce the prestress loss caused by the instability of the construction structure, and can effectively improve the construction quality of the multi-layer logistics warehouse. This shows that the application and practice of pretension prestressing technology in the construction process of reinforced concrete structures has a positive reference significance, which can meet the needs of green engineering such as energy saving and emission reduction, and also provide a positive reference value for the construction technology of multi-layer logistics warehouse.

The finite element model of chloride diffusion in pre-stressed corroded reinforcement bars of reinforced concrete structures

Introduction. The general corrosion model, made for reinforced concrete structures, must include the initiation of environmental influences such as carbonation, cracking and chloride ion penetration. It depends on the rate and degree of corrosion, corrosive effects in reduced areas, as well as the lower strength of bond between pre-stressed and unstressed reinforcement bars and concrete. The majority of earlier studies were focused on one-dimensional diffusion problems with an assumed constant corrosion rate.&#x0D; &#x0D; Materials and methods. In the aftermath of general corrosion, localized corrosion is accompanied by a release of hydrogen and alkaline water, chlorine ions. Crack propagation in reinforcement wires is calculated using the transient finite element software for chloride diffusion, which is time-dependent.&#x0D; &#x0D; Results. In most cases, the diffusion equation does not have a closed form solution, and therefore, the finite difference method can be used. The authors have shown that the corrosion rate decreases with time if current density has different water-cement ratios. If the water-cement ratio increases, the corrosion rate increases, as well.&#x0D; &#x0D; Conclusions. In a pre-stressed reinforced concrete beam, the corrosion of one bar affects the total corrosion of all bars and the reduction in the cross-sectional area of bars that does not exceed 15 %.

SOIL REINFORCED WITH NONWOVEN GEOTEXTILE SHEETS IMPROVED CBR VALUE

Introduction: Building materials technology has allowed substantial advances in structural engineering to take place in the past. Using wood, building stone, concrete, and lately, prestressed reinforced concrete, it became feasible to create an even larger and more complex structure. Aim of the study: the main aim of the study is to Soil Reinforced with Nonwoven Geotextile Sheets Improved CBR Value. Material and method: Tests at NITTTR Bhopal have employed the campus soil as a subgrade for the experiments. CH soil is utilized in this project (Clay of high plasticity). Conclusion: In the laboratory, studies on the California bearing ratio (CBR) led to the following conclusions: Incorporating NW geotextiles into soils enhances CBR and, as a result, soil strength.

Low-Cycle Reverse Loading Tests of the Continuous Basalt Fiber-Reinforced Polymer Column Filled with Concrete

The continuous basalt fiber-reinforced polymer column filled with concrete (BFRPC composite column) can well resist the erosion of the external environment, improve the durability of the structure, and reduce the life-cycle cost of the project. To evaluate the mechanical behaviors of the BFRPC composite column under cyclic lateral loading, laboratory low-cycle reverse loading tests were implemented on a BFRPC composite column specimen, a prestressed reinforced concrete (PRC) tube column specimen, and a prestressed high-strength concrete (PHC) tube column specimen. The failure features, hysteretic curve, and skeleton curve for these three types of column specimens were compared and analyzed through the load–displacement hysteretic curve. The results indicated that the BFRPC composite column possesses the better bearing capacity and deformation performance. The horizontal bearing capacity of the BFRPC composite column is at least three times better than that of PHC and PRC tube columns. Finally, the functional expression of the skeleton curves for the BFRPC composite column is fitted by the rational function fitting method.

Optimal strengthening by steel truss arches in prestressed girder bridges

This work focuses on the proposal and the evaluation of a new consolidation system for prestressed reinforced concrete (PRC) beams of girder bridges. The system consists of two arch-shaped steel trusses placed alongside the lateral faces of the beam to beconsolidated. The arches develop longitudinally along the entire span of the beam and in elevation using the available height of the PRC cross section. The consolidation system is characterized by its own external constraints, independent from those serving the pre-existing element. The efficiency of the system with respect to parameters variability is described also focusing on the ratio between the load discharged by the consolidation system and the total applied load. Referring to a case study, the consolidation of a PRC beam is presented adopting the proposed system with respect to the usually adopted external prestressing technique. The cross sections properties of the steel arch shaped trusses are defined by means of a structural optimization process using a genetic algorithm, identifying the minimum steel consumption. Finally, a preliminary cost-benefit analysis is performed for the proposed solution for a comparison with other commonly adopted techniques.

Numerical Analysis on Flexural Behaviors of Prestressed Reinforced Concrete Beams Strengthened with NSM CFRP Strips

This paper presents the numerical analysis of prestressed reinforced concrete (PRC) beams strengthened with near-surface mounted (NSM) carbon fiber reinforced polymers (CFRP). ABAQUS finite element software was used to simulate the existing test beams to investigate the flexural behaviors of PRC beams strengthened with NSM CFRP strips. The finite element model of beams strengthened with NSM CFRP strips was established. The finite element calculation results were compared with the experimental results to verify the accuracy and effectiveness of the model. Based on this model, the influences of concrete strength grade and amount of CFRP strips on the flexural behaviors of directly strengthened beams and the cycle numbers and overload amplitude on the flexural behaviors of damaged strengthened beam were further analyzed, and the load-carrying capacity calculation formula of PRC beam strengthened with NSM CFRP strips was established. The results showed that the simulation results and the theoretical calculation were consistent with the test results. With the increase of concrete strength grade and amount of CFRP strips, the ultimate load of directly strengthened beams increased significantly, with a maximum increase of 21.3% and 23.0%, respectively. When the concrete strength grade exceeded C50, the improvement of the ultimate load was limited. When the overload amplitude was less than 60% of the ultimate load, the cycle numbers (within 500 times) had little effect on the yield load, ultimate load, and deformation. When the overload amplitude was higher than 60% of the ultimate load, the deformation increased, and the ultimate load decreased with the increase of the cycle numbers. The larger the overload amplitude, the smaller the ultimate load, and the larger the deformation under the same cycle numbers.

Simplified Model of PC Concrete Beams with Corroded Strands in Highway Viaduct: Case Study and Analytical Modeling

AbstractIn this paper, several cases of failure of prestressed reinforced concrete (PC) beams of a viaduct in Italy due to cable corrosion are presented. Therefore, a simplified model to determine ...

Full-scale experimental and numerical investigation on the ductility, plastic redistribution, and redundancy of deteriorated concrete bridges

Due to structural degradation, the performance of concrete bridges may degrade with time and result in catastrophic consequences. A novel approach is developed for evaluating the time-variant reliability of multi-girder concrete bridges considering the effects of the load-carrying mechanism and redundancy. By considering three failure modes at both the component and system levels, a new performance indicator is proposed for quantitatively evaluating the load elastic distribution and plastic redistribution among multiple girders. The adverse effects of material deterioration on the structural capacity, ductility, redundancy, load-carrying capacity, and failure mechanism are also investigated and incorporated into the analytical procedure, in which an incremental nonlinear finite element analysis of a 3D fiber beam element is used. Furthermore, the results associated with full-scale destructive tests of two in situ deteriorated bridges, a reinforced concrete (RC) and a prestressed RC (PRC) T-girder bridge, are adopted to evaluate the accuracy of the proposed approach. The feasibility and satisfactory performance of the proposed framework are evaluated using these two real-world bridges. The results demonstrate that the load-carrying mechanism and redundancy significantly affect the structural ultimate load-carrying capacity and time-variant reliability of deteriorating structures.

A cost-effective approach for assessment of pre-stressing force in bridges using piezoelectric transducers

Electromechanical impedance (EMI) technique based health monitoring has emerged as a promising technique over conventional monitoring techniques in the last two decades. This paper presents an experimental and statistical investigation to monitor residual post-tensioning force in the pre-stressed reinforced concrete (PSC) bridge using piezoelectric patches through the EMI technique. Lead Zirconate Titanate (PZT) sensors were bonded on the commercial load cells and their EMI signatures were captured in the laboratory using an impedance analyser (E4980AL, Keysight) in the frequency range of 20 kHz to 250 kHz for different axial load values ranging from 0 ton to 42 tons. Assessment models were developed and validated in the laboratory for three PZT-based load cells. The calibrated PZT-based load cells were installed on a four-span continuous PSC bridge to estimate the externally applied post-tensioning force during its rehabilitation. EMI signatures were captured once the full load was applied on the post-tensioned cables and then after 24 h of loading. Using the developed assessment models and the root mean square deviation (RMSD) values of the PZT-based load cells, the residual load in the post-tensioned cable was predicted and found a good agreement (overall error less than 14%) with that measured by the commercial load cell. This established the feasibility of a cost-effective approach of using inexpensive PZT-based load cells as an alternative to the well-established technique of using commercially available expensive load cells for the assessment of residual pre-stressing force during the increasing age of a prestressed concrete bridge.

Effect of concrete strength and tube thickness on the flexural behavior of prestressed rectangular concrete-filled FRP tubes beams

This paper presents the results of an experimental study aimed at evaluating the effect of important design parameters on the flexural behavior of unbonded post-tensioned rectangular concrete-filled fiber-reinforced-polymer (FRP) tubes (CFFTs) beams. Four full-scale beams were constructed and tested to failure in four-point bending over a simply supported span of 3,000 mm. The design parameters are the confinement effect of using FRP tube or steel stirrups, the concrete compressive strength, and the FRP tube thickness. The results showed that reinforced concrete (RC) rectangular CFFT beams prestressed with unbonded steel strands can achieve substantially higher flexural strength, inelastic flexural deformation, ductility, and energy absorption capacity than conventional prestressed RC beam without FRP tube. The ultimate strength, deformation capacity, ductility, and energy absorption were increased by 2.43, 1.89, 1.63 and 3.87 times than the prestressed RC beam. The results also showed that increasing the FRP tube thickness of the prestressed CFFT beams from 6.0 to 7.4 mm has led to the increase of the ultimate capacity, ductility, and energy absorption by 19%, 28% and 18%, respectively. Prestressed CFFT beams with high strength concrete (HSC, 70 MPa) enhanced the initial stiffness before cracking, increased the ultimate flexural moment capacity by 7%, with no significant change in the ultimate deflection, compared to normal strength concrete (NSC, 46 MPa). Based on the results of this study, the effect of increasing the FRP tube thickness is more effective in enhancing the flexural strength and stiffness of the prestressed CFFT beams than increasing the concrete strength. An analytical model based on plane sectional analysis using partially confined and unconfined concrete models as well as an empirical design equation are proposed to predict the flexural moment capacity of the tested beams. The proposed models using partially confined and unconfined concrete models and empirical equation successfully predict the flexural moment capacity with satisfactory accuracy on average of 1.06 ± 0.03, 1.23 ± 0.04 and 1.01 ± 0.08, respectively. It was also found that ignoring concrete confinement would highly underestimate the flexural strength. More investigations, however, are needed to assess the effect of a wide range of key influencing parameters to better model the flexural behavior of prestressed rectangular CFFT beams.

Experimental research on flexural behaviors of damaged PRC beams strengthened with NSM CFRP strips

This paper investigates the flexural behaviors of the damaged prestressed reinforced concrete (PRC) beams strengthened with near surface mounted (NSM) carbon fiber-reinforced polymers (CFRP) strips under overloading. A bending test was carried out to evaluate the effects of three variables: the cycle number, overload amplitude and strengthening under loading or unloading. Different damage degrees were mainly controlled by cycle number and overload amplitude. The test results showed that strengthening with NSM CFRP strips could effectively inhibit crack development. Compared with the un-strengthened beam, the flexural load-carrying and stiffness of the strengthened beams were enhanced evidently. With the increase of cycle number and overload amplitude, the yield loads increased. The yield load of strengthened beam under unloading was higher than that of strengthened beams under loading. These three variables had limited influence on the ultimate bearing capacity. The deformations of the strengthened beams were smaller than that of the control beam, and decreased with the increase of cycle number, but increased with the increase of overload amplitude. The deformations of the strengthened beams under loading were slightly greater than that of the strengthened beam under unloading in the early phase but smaller in the later phase. The ductility of strengthened beams was evidently reduced compared with that of the control beam. The displacement ductility factors of the strengthened beams under loading decreased with the increase of cycle number and overload amplitude, and were smaller than that of strengthened beam under unloading.

On the Evaluation of Prestress Loss in PRC Beams by Means of Dynamic Techniques

In the last few decades, prestressing techniques have been used to build very important structures and infrastructures. Since the serviceability and the safety of prestressed reinforced concrete (PRC) elements rely on the effective state of prestressing, development of tools and procedures capable of estimating the effective prestress loss would be very useful. Amongst other techniques, dynamic identification has proved to be an economical, quick and reliable method to evaluate structural integrity. However, the influence of prestressing in the dynamic behavior of PRC elements is not completely clear. In fact, while many references in the literature state that the prestressing force does not affect the frequencies of vibration, almost every experimental test carried out on PRC beams shows an increase in the eigenfrequencies for increasing value of the prestressing force. This paper aims to contribute to the debate, investigating the dynamic behaviour of PRC beams taking into account properties, such as nonlinearity, softening, confinement and micro-cracking of concrete subjected to compression and tension stress states, and the variation of the flexural stiffness of the PRC beam along its length according to bending stress distribution. Non-linear discrete modelling, in combination with system identification and optimization was used to define the dynamic properties of PRC beams, taking into account the effect of prestressing level. The proposed model was applied to four PRC beams with known mechanical and dynamic properties in literature. The influence of the prestressing force on the trend of frequencies of vibration was closely captured for each beam, with errors less than 3% of the estimated frequencies. The results of this investigation thus indicate that dynamic identification techniques can potentially be used to identify the prestressing force level, and consequently the prestress loss, provided the complete concrete mechanics is taken into account.

Discussion on Construction Technology of Prestressed Reinforced Concrete Pipeline of Municipal Water Supply and Drainage

Prestressed reinforced concrete pipe has the advantages of good bending resistance, good anti-corrosion, anti-seepage, low price and so on. It is very common in municipal water supply and drainage engineering. This paper mainly explore the analyze the construction technology of the prestressed reinforced concrete pipe in municipal water supply and drainage engineering.