Passive Reinforcement Research Articles

Moment redistribution capacity in prestressed concrete continuous beams

In prestressed concrete continuous beams, building code provisions often allow for a reduction in the moment at a critical section (calculated through elastic analysis). This reduction is permitted as long as the moments in all other sections are adjusted to maintain equilibrium and support the designated loads. However, the allowable moment redistribution percentage (MRP) for prestressed concrete beams (PCBs) remains a topic of debate. Many codes currently assign a similar MRP limitation to both PCBs and reinforced concrete beams (RCBs). This approach might be over-simplistic for PCBs due to their unique behaviour. A method for identifying the maximum available MRP is proposed in this article. An in-depth study was conducted on the maximum available MRP of PCBs based on calibrated finite-element models. The results showed that parameters such as the passive reinforcement ratio, steel yield strength, slenderness ratio, eccentricity of prestressing tendons, concrete grade and load pattern, which are not considered in the codes, influence the maximum available MRP to an extent. Using the same permissible MRP as RCBs may thus be inappropriate. An equation is proposed to estimate the maximum available MRP for PCBs.

Influence of MgAl–NO2-LDHs on passivation of reinforcing steel in simulated geopolymer solution

Because of ion exchange properties, the presence of layered double hydroxides (LDHs) influences passivation process of reinforcement embedded in geopolymer concrete. In this study, the ion exchange behavior of MgAl–NO2-LDHs and its effect on the characteristics of passivation film and electrochemical behavior of passive reinforcement in simulated slag-fly ash-waste ceramic powders geopolymer solution (SGP) are extensively investigated. The results indicate that LDHs with layered structure improve the protection efficiency of adsorption layer in SGP. Further, the intercalated NO2− is efficiently exchanged with OH− in SGP, thus increasing the thickness and corrosion resistance of the formed passivation film. However, because the adsorption layer halts NO2− release process, the beneficial effect is mainly observed during later immersion stage.

Deformation and Failure Evolution Law and Support Optimization of Gob-Side Entry in Weakly Cemented Soft Rock under the Influence of Fault

Under the condition of weakly cemented soft rock in Western China, the surrounding rock deformation of gob-side entry is obvious, especially under the influence of fault, and the problem of surrounding rock control becomes increasingly prominent. To solve this issue, this paper firstly studied and obtained the evolution law of the ground pressure appearance of the gob-side entry in the fault area, then put forward the concept of surrounding rock control in the fault area of the gob-side entry, put forward a targeted pressure relief + increase preload + passive reinforcement parallel to the roadway surrounding rock strengthening control scheme, and carried out field applications. The results show that the roof subsidence and mining side heave of the roadway in the fault area increase significantly, accompanied by the characteristics of broken cables, the length of the broken cable is 0.2 m–0.6 m, and the breaking process is divided into multiple breaks. The stress evolution of gob-side entry in fault area presents a stage characteristic of “rapid growth-stable.” The surrounding rock control effect is improved under the bolt cable high pre-tightening support, and the roadway deformation is effectively controlled under the pressure relief + active + passive support, with a good application effect.

Numerical assessment of using FRP rebars as an alternative passive reinforcement in RC beams

AbstractRecent sustainable building strategies make the right decisions to be environmentally friendly and reduce carbon emissions. In some reinforced concrete (RC) elements, fiber-reinforced polymer (FRP) bars have been proposed as an alternative to conventional steel bars. The demand for using noncorrosive and/or nonmetallic reinforcing bars in various reinforced concrete projects has increased. Although these concrete elements are lightweight, have a long lifespan, and need little maintenance, their non-ductile nature and bond with the surrounding concrete create significant challenges. Several experimental investigations have been conducted to evaluate the behavior of RC elements, even with their high cost. This study aims to assess numerically the viability of using FRP bars instead of traditional steel ones in simply supported reinforced concrete beams (RCBs) as longitudinal reinforcement (passive reinforcement). Utilizing the three-dimensional (3D) nonlinear finite element analysis (FEA) software (ABAQUS), a total of eighteen models were carried out to validate the results available in reference case studies with FRP bars. The verification of the numerical results has been verified by comparing them with the reference experimental data. Next, in order to assess the rigidity of such RCBs with FRP bars, parametric research was carried out. The numerical results proved that RCBs with FRP bars have a positive impact on enhancing load-carrying capacities. But on the other hand, the strain energy of such RCBs with CFRP bars is reduced to about 75% of the strain energy of RCBs with steel bars, which leads to low beam ductility.

Embodied Energy Optimization of Prestressed Concrete Road Flyovers by a Two-Phase Kriging Surrogate Model.

This study aims to establish a methodology for optimizing embodied energy while constructing lightened road flyovers. A cross-sectional analysis is conducted to determine design parameters through an exhaustive literature review. Based on this analysis, key design variables that can enhance the energy efficiency of the slab are identified. The methodology is divided into two phases: a statistical technique known as Latin Hypercube Sampling is initially employed to sample deck variables and create a response surface; subsequently, the response surface is fine-tuned through a Kriging-based optimization model. Consequently, a methodology has been developed that reduces the energy cost of constructing lightened slab bridge decks. Recommendations to improve energy efficiency include employing high slenderness ratios (approximately 1/28), minimizing concrete and active reinforcement usage, and increasing the amount of passive reinforcement.

Failure Mechanism and Control Countermeasures for Argillaceous Surrounding Rock of Horsehead Roadway under High Stress.

The argillaceous surrounding rock of a horsehead roadway under high stress conditions is prone to deformation and failure, and the control of its long-term stability is difficult. Based on the engineering practices that control the argillaceous surrounding rock of a horsehead roadway in the return air shaft in the Libi Coal Mine in Shanxi Province, field measurements, laboratory experimentation, numerical simulation, and industrial tests are used to analyze the main influencing factors and mechanism of the deformation and failure of the surrounding rock of the horsehead roadway. We propose principles and countermeasures to control the stability of the horsehead roadway. The main factors of the surrounding rock failure of the horsehead roadway include the poor lithology of argillaceous surrounding rocks, horizontal tectonic stress, the superimposed influence of additional stress from the shaft and construction disturbance, the small thickness of the anchorage layer in the roof, and the insufficient depth of floor reinforcement. The results show that the shaft's presence increases the horizontal stress peak and stress concentration range in the roof, and the plastic zone range. The stress concentration and plastic zones and deformations of the surrounding rock increase significantly with the increase in horizontal tectonic stress. The control principles for the argillaceous surrounding rock of the horsehead roadway include increasing the thickness of the anchorage ring, the floor reinforcement exceeding the minimum depth, and reinforced support in key positions. The key control countermeasures include an innovative prestressed full-length anchorage for the mudstone roof, active and passive reinforcement technology with cables, and a reverse arch for floor reinforcement. The field measurements show that the control of the surrounding rock using the prestressed full-length anchorage of the innovative anchor-grouting device is remarkable.

Numerical analysis of bonded and unbonded prestressed RC beams using cohesive and non-compatible rod elements

This research presents a numerical approach to simulate prestressed RC beams. It combines state-of-the-art finite element models to simulate the concrete (including fracture), tendons, passive reinforcements, and the rebar–concrete interaction. This provides more realistic simulations and rich details on deformability, crack patterns, and axial and contact stress distributions in passive reinforcements and tendons. Concrete fracture is simulated using cohesive elements with a constitutive model based on the plasticity theory and fracture mechanics, enabling crack development and propagation prediction. Reinforcements are simulated using rod elements with incompatible nodes. Special contact elements link rod to bulk elements and are placed along the reinforcements and at tips. These contact elements also predict relative displacements between rebars and concrete. Prestressing is simulated by setting initial stresses in tendons and applying forces to its nodes simultaneously. The approach also includes two numerical techniques to improve the convergence of the highly nonlinear problem. Five experimental beams are simulated. In all cases, the numerical load–deflection curves agree with the experiments. Fracture patterns also match rupture modes. Finally, contact stress discontinuities in tendons due to crack development are examined in more detail.

Research on the Mechanism of the Passive Reinforcement of Structural Surface Shear Strength by Bolts under Structural Surface Dislocation

In order to study the local deformation of an anchor bolt and the improvement in the shear strength of a structural surface under the misalignment of an anchorage structure surface, FLAC3D software was used to simulate granite, sandstone, and coal specimens with anchorage angles of 90° to analyze the damage of the anchoring agent and the changes in the local axial and shear forces of the anchor bolts with the misalignment of the structural surface. The results show that the anchor bolt near the structural surface had significant local characteristics with the misalignment of the structural surface; that is, the length of the local deformation area of the bolt was approximately equal to the length of the damaged area of the anchoring agent, and the stress on the anchor bolt was in a coupled tensile–shear stress state when the bolt reached the yield state. For the fully grouted bolts, it was this significant local feature that made the shear strength of the structural surface increase rapidly under a small shear displacement so that the structural surface reached a stable state. The improvement in the shear strength of the anchoring structural surface was caused by the misalignment of the structural surface. This is referred to as the passive improvement of the shear strength of the anchoring structural surface, which is the mechanism of the bonding section anchor to control the shear displacement of the structural surface and realize the stability of the rock mass.

Optimal Design of Sustainable Reinforced Concrete Precast Hinged Frames

Sustainable development requires improvements in the use of natural resources. The main objective of the present study was to optimize the use of materials in the construction of reinforced concrete precast hinged frames. Proprietary software was developed in the Python programming language. This allowed the structure's calculation, verification and optimization through the application of metaheuristic techniques. The final cost is a direct representation of the use of materials. Thus, three algorithms were applied to solve the economic optimization of the frame. By applying simulated annealing, threshold accepting and old bachelor's acceptance algorithms, sustainable, non-traditional designs were achieved. These make optimal use of natural resources while maintaining a highly restricted final cost. In order to evaluate the environmental impact improvement, the carbon-dioxide-associated emissions were studied and compared with a reference cast-in-place reinforced concrete frame. The results showed designs with reduced upper slab and lateral wall depth and dense passive reinforcement. These were able to reduce up to 24% of the final cost of the structure as well as over 30% of the associated emissions.

CO2-Optimization of Post-Tensioned Concrete Slab-Bridge Decks Using Surrogate Modeling.

This paper deals with optimizing embedded carbon dioxide (CO2) emissions using surrogate modeling, whether it is the deck of a post-tensioned cast-in-place concrete slab bridge or any other design structure. The main contribution of this proposal is that it allows optimizing structures methodically and sequentially. The approach presents two sequential phases of optimization, the first one of diversification and the second one of intensification of the search for optimums. Finally, with the amount of CO2 emissions and the differentiating characteristics of each design, a heuristic optimization based on a Kriging metamodel is performed. An optimized solution with lower emissions than the analyzed sample is obtained. If CO2 emissions were to be reduced, design recommendations would be to use slendernesses as high as possible, in the range of 1/30, which implies a more significant amount of passive reinforcement. This increase in passive reinforcement is compensated by reducing the measurement of concrete and active reinforcement. Another important conclusion is that reducing emissions is related to cost savings. Furthermore, it has been corroborated that for a cost increase of less than 1%, decreases in emissions emitted into the atmosphere of more than 2% can be achieved.

Analysis on Spatial Disturbance Influence of Surrounding Rock Stress in the Staggered Roadways and Its Control Countermeasures

Combined with specific engineering examples, the spatial disturbance influence characteristics and laws of the surrounding rock stress in the staggered roadways are analyzed by numerical simulation. This paper concludes that (1) compared with the surrounding rock pressure behavior of the general roadway, the surrounding rock stability of the staggered roadway is relatively poor, showing the characteristics of the local serious roadway rock pressure behavior, such as the intensified destruction of the roadway side, the failure and fracture penetration of the surrounding rock between the roadways, and the relatively serious deformation of the surrounding rock. The reason is that the stress of the surrounding rock at the staggered roadway position is obviously superimposed and disturbed by each other; (2) the influencing factors of the failure and instability of the surrounding rock between interlaced roadways are as follows: the greater the buried depth and the smaller the distance between roadways, the more intense the superposition disturbance of the surrounding rock stress between roadways; the smaller the horizontal azimuth, the greater the influence range of superposition disturbance of surrounding rock stress between roadways; the more unbalanced the original rock stress field, the worse the stability of the surrounding rock between roadways, resulting in the more serious failure and instability of the surrounding rock between roadways; (3) for the staggered roadway layout, increasing the distance between roadways, the closer to the orthogonal layout and selecting the arch section of the lower roadway is conducive to the bearing stability of the surrounding rock between roadways; (4) constrained by the space conditions of staggered roadway, the role of bolt and cable support is limited. Passive support is the key to realize the safety and stability of surrounding rock of staggered roadway, so the control technical scheme of active and passive combined support in staggered roadway position is put forward, the combined support of the upper roadway “bolt + cable + shotcrete + concrete cushion of floor” and lower roadway “bolt + cable + U-shaped steel support passive reinforcement + shotcrete” within the spatial disturbance influence the range of surrounding rock stress in the staggered roadways, and the technical scheme can achieve satisfactory supporting effect.

Vol4 num4-6 Study of the influence of concrete on the thermal properties of vinilester-uretane composites vs accelerated tests

Specifically, the use of vinyl ester resins has been studied profusely in both the maritime and industrial sectors and with less time, in the use of reinforcement in civil engineering structures and architecture as passive reinforcements. The resin used in the present work is novel, and still little used. It is vinyl ester resin of bisphenol-A segment modified with urethane. This presents a greater resistance to chemical agents such as those of the petroleum industry, alkaline agents and vapors; together with a lower exotherm that facilitates the manufacture of thick laminates. A thermal and mechanical characterization has been carried out through the techniques of Differential Scanning Calorimetry (DSC), Infrared Spectroscopy (FTIR) and Thermogravimetry (TGA) of said resin reinforced with high grammage (780 g / cm2) fiber of E glass to evaluate the degradation of the composite and its mechanical properties to the interlaminar shear and bending. The influence of the contact with self-compacting concrete (HAC) on said material, imbedded inside its matrix as a reinforcement, as if it were a passive reinforcement, as well as an accelerated aging study in solution simulating the exudation liquid of the concrete pores (LPH) through said characterization. With the obtained results, it is evaluated and compared, from the point of view of degradation-stiffening vs. mechanical properties, with the traditional Bisphenol-A (VEBA) resins, as well as its suitability for the aforementioned applications, resulting in a resin with better properties than the VEBA.

Comparison of analysis between the classical ESIS method and the ASTM D-7905 standard, for obtaining shear fracture toughness

The present work is part of the characterization of glass fiber composites elaborated with a novel vinylester-urethane resin, with addition of poly for use in reinforcing materials for concrete, as a passive reinforcement or as a reinforcement for structures in use, as these resins have a higher Resistance to chemical agents, basics and vapors along with a lower exotherm facilitating the manufacture of thick laminates.Within Mode II fracture mechanics, until this 2014 there was no standard that would collect a procedure to quantify GIIC. Davies through the European Structural Integrity Society (ESIS) issued a mode II test protocol in 1992 known as ENF (End Notch Flexure) [1]ASTM D7905-14 encompasses a fairly complex procedure in which the basis for the characterization of shear fracture toughness in mode II using the final notch flexure (ENF) test is laid.This paper aims to verify the main differences between this classical procedure and the method of this standard to verify their similarities.For this purpose, a mechanical pre-characterization of the reinforced resin is carried out with high-grade fabric (780 g/cm2) with glass fiber E as well as a thinner carbon fiber composite. This characterization is performed by ENF bending tests, and the procedure of the new ASTM D-7905 standard.   [1] ASTM D5528-01, “Standard Test Method for Mode I Interlaminar Fracture Toughness of Unidirectional Fiber-Reinforced Polymer Matrix Composites”, American Society for Testing and Materials, 2001.

On-site corrosion monitoring experience in concrete structures: potential improvements on the current-controlled polarization resistance method

The need for proactive maintenance of reinforced concrete structures with non-destructive testing (NDT) is less disputable today than ever. One of the most promising strategies in this regard is the in-situ measurement of the reinforcement corrosion rate. This study explored the reliability of modulated current confinement method (hereafter MCC) based on a review of in-situ measurements made with that technique in real-life structures over a 13-year period. The most prominent problems detected included defective confinement of the polarization current in low-resistivity environments and over-polarization of passive reinforcement. The findings, which showed enhancement of MCC reliability to depend on improving the electrochemical current regulation and control methodologies presently in place, are being applied to improve the design of the next generation of corrosion meters.

Structural behaviour of 3D printed concrete beams with various reinforcement strategies

3D concrete printing (3DCP) offers many new possibilities. This technology could increase the productivity of the construction industry and reduce its environmental impact by producing optimised structures more efficiently. Despite significant developments in materials science, little effort has been put in developing reinforcement strategies compatible with 3DCP and on the characterisation of their structural behaviour. Consequently, 3DCD still lacks compliance with structural integrity requirements. This study presents an experimental investigation consisting of nine four-point bending tests on extrusion 3DCP beams reinforced with various types of reinforcement. As interlayer shear reinforcement, aligned end-hook fibres (0.3 and 0.6%) or steel cables (0.1%) placed between the layers of printed concrete were used. As longitudinal reinforcement, unbonded post-tensioning and conventional bonded passive reinforcement were explored. The crack patterns and their associated kinematics were tracked using digital image correlation. The results show that the post-tensioned beams failed in a brittle manner due to the crushing of concrete in bending, with deformations localised in a few bending cracks. In the beams with conventional bonded longitudinal reinforcement, both bending as well as shear cracks were generated, and the brittle failure of the interlayer shear reinforcement limited the ultimate load. Estimations based on the measured crack kinematics show that the interlayer shear reinforcement carried most of the applied shear force. Based on these results, a simple mechanical model is developed to understand the mechanical behaviour and to pre-design the required amount of interlayer shear reinforcement.

Innovative passive reinforcements for the gradual stabilization of a landslide according with the observational method

A large number of landslides occur in North-Eastern Italy during every rainy period due to the particular hydrogeological conditions of this area. Even if there are no casualties, the economic losses are often significant, and municipalities frequently do not have sufficient financial resources to repair the damage and stabilize all the unstable slopes. In this regard, the research for more economically sustainable solutions is a crucial challenge. Floating composite anchors are an innovative and low-cost technique set up for slope stabilization: it consists in the use of passive sub-horizontal reinforcements, obtained by coupling a traditional self-drilling bar with some tendons cemented inside it. This work concerns the application of this technique according to the observational method described within the Italian and European technical codes and mainly recommended for the design of geotechnical works, especially when performed in highly uncertain site conditions. The observational method prescribes designing an intervention and, at the same time, using a monitoring system in order to correct and adapt the project during realization of the works on the basis of new data acquired while on site. The case study is the landslide of Cischele, a medium landslide which occurred in 2010 after an exceptional heavy rainy period. In 2015, some floating composite anchors were installed to slow down the movement, even if, due to a limited budget, they were not enough to ensure the complete stabilization of the slope. Thanks to a monitoring system installed in the meantime, it is now possible to have a comparison between the site conditions before and after the intervention. This allows the evaluation of benefits achieved with the reinforcements and, at the same time, the assessment of additional improvements. Two stabilization scenarios are studied through an FE model: the first includes the stabilization system built in 2015, while the second evaluates a new solution proposed to further increase the slope stability.

Assessment of posttensioned concrete beams from the 1940s: Large‐scale load testing, numerical analysis and Bayesian assessment of prestressing losses

AbstractThe UCO textile factory was built in Ghent (Belgium) in the period 1947–1948. The roof structure covered an area of about 35,000 m2 and consisted of 100 primary beams and 600 secondary beams. These post‐tensioned beams were designed by prof. Gustave Magnel, who was a world‐leading expert in the field of prestressed concrete. This project was one of the first important large‐scale applications of prestressed concrete in industrial buildings in the world and also the first large scale application of on site prefabrication. Recently, part of the factory building was demolished and a primary beam and secondary beam of the roof structure were transferred to the Magnel‐Vandepitte Laboratory for Building Materials and Structures for testing at an age of approximately 70 years. The primary beams have a span of 20.5 m and a maximum depth of 1.7 m. The secondary beams have a span of 13.7 m and a depth of 1 m. Only prestressing tendons (Blaton–Magnel system with Ø 5 mm wires) were present in the beams but no passive reinforcement nor stirrups are present except for the reinforcement in the corbels and the end blocks. This article describes the results of the loading tests up to failure on the beams. The experimental results are compared with results from analytical calculations. Furthermore, a nonlinear finite element model was developed and validated. Subsequently, this numerical model was used for a Bayesian‐based assessment of the prestressing losses in these beams. As such, the article presents novel information related to time‐dependent prestress losses after 70 years in service as well as the structural performance of such existing post‐tensioned concrete structures dating from that pioneering period.

Long-term hybrid galvanic corrosion protection of reinforced-concrete structures

Hybrid corrosion protection (HCP) can be used to provide corrosion arrest and prevention in degrading reinforced-concrete structures to increase their service life. The proprietary technology is a relatively new electrochemical treatment for concrete structures, having been patented in 2005 (patent GB2426008B). Due to this fact, accurate and reliable empirical data over the life span of a structure protected by an HCP system does not yet exist. This paper is the first to present over 10 years of empirical data, from one of the very first installations of HCP, providing a rigorous and reliable assessment of the structure's long-term performance. Results demonstrate that hybrid galvanic anodes exhibit a responsive behaviour to maintain the concrete environment and respond to corrosion hazards. Even after prolonged periods of low current output, the anodes respond to changing environmental conditions, providing the higher current output required to afford the necessary polarisation to the reinforcement, and hence the protection to the structure. Steel potentials also continued to trend towards more positive values, a generally agreed indication of passive reinforcement. Overall, this study is unique, being the first to present continuous, long-term performance data on hybrid galvanic anodes for the corrosion protection of reinforced-concrete structures.

Comparison between methods to determine the fibre orientation factor of an HPFRC bridge box girder

Due to high volume fraction of steel fibres allied to improved rheology and packing density of cementitious matrices, materials like HPFRC and UHPFRC have been providing the possibility of partial or total replacement of passive reinforcement, expanding their applications to structures like footbridges, motorway bridges, and roof shells. When performing ultimate limit state design, the tensile strength curve obtained from tests of prismatic specimens moulded in laboratory must be adjusted by the so-called fibre orientation factor to consider the actual distribution and orientation of the fibres in the structural element. As this factor is influenced by the formwork geometry and the casting process, a representative mock-up of the actual structure must be constructed. In this context, this work aims to compare two methods for determining the orientation factor for a proposed bridge girder. The first method is based on 3-point flexural tests, and the second, on the number of fibres crossing a fracture plane. For their application, a box girder mock-up was built and prismatic specimens were extracted. The results showed both methods provided similar orientation factors in more than half the analysed specimens. However, in the remaining ones large differences were found which were then significantly reduced when the number of fibres crossing the tensile region of each specimen was considered in the calculation instead of the whole area. Moreover, the discrepancy shown amongst the post-cracking behaviour of the specimens indicates that steel fibre-reinforced concrete materials cannot be treated as isotropic without prior investigation.

Design of filling self-stressing concrete to use in strengthening of columns by prefabricated jacketing

This study proposes the design and characterization of an expansive self-compacting concrete (SCC) with self-stressing properties for its use as a filling in reinforcement systems by external prefabricated jacketing. The self-compacting characteristic ensures the correct filling of the inner space and the characteristic of expansiveness (self-stressing) guarantees a correct transmission of tensions from the column to the prefabricated reinforcement jacket. In the design, a K-type expansive agent based on calcium sulfoaluminate is used in the doses of 10% and 15% and the influence of its addition on the fresh properties and the compressive strength on the reference mix of SCC is analysed. The restrained expansion is evaluated in prisms by the standard method ASTM C878 and by means of an alternative method based on a double ring device that simulates the configuration of reinforcement systems using carbon fiber reinforced polymers (CFRP) or steel external jacketing. Finally, the efficiency of the proposed strengthening system is compared to that usually used for CFRP jacketing directly glued on the element like concrete specimens and reinforced concrete columns. The results show that the double-ring based test device presents a high degree of correlation with the prism-based standard method and that the proposed strengthening based on filling self-stressing SCC and external prefabricated jacketings is an efficient solution that allows to move from a passive reinforcement system (CFRP jacketing glued directly to the column) to an active one that allows the reinforcement to contribute from the initial moments of the cast-in-place of the self-stressing SCC.