Non-prestressed Reinforcement Research Articles

An integrated material-structural analysis of prestress concrete affected by corrosion of non-prestressed reinforcement

Corrosion-induced concrete cracking is a significant stage of structural deterioration in prestressed concrete (PC) structures. Most current research predominantly focuses on the corrosion of prestressed steel strands, while paying limited attention to the study of non-prestressed reinforcement corrosion. In this study, an integrated material-structural numerical approach was developed to simulate corroded PC beams, considering corrosion products migration in pores and cracks. The cracking patterns and prestress losses obtained from the simulation results agreed well with experimental observations. Subsequently, using the proposed numerical approach, the interaction mechanism of the prestress level and reinforcement corrosion was investigated. The simulation results indicated that corrosion of longitudinal reinforcement leads to cross-sectional damage, causing the redistribution of stress across the section and increasing long-term deformation, ultimately resulting in prestress losses. Meanwhile, stirrup corrosion leads to an initial increase in prestress due to expansion forces when the degree of corrosion is not so high, but finally it will also lead to a degradation of mechanical performance.

Dynamic serviceability and safety reliability analysis of aging PC girder bridges with non-prestressed reinforcement considering concrete shrinkage, creep and stochastic vehicle load flows

Prestressed concrete (PC) bridges’ service performance displays time-dependency due to several factors including concrete shrinkage, creep, resistance degradation, and stochastic vehicle load flows. These non-stationary vehicle load flows, combined with concrete shrinkage, creep, and resistance degradation, result in sequential alterations of internal forces and deformations in simply supported PC girder bridges, ultimately influencing their dynamic reliability. This study proposes a robust methodology that considers the impact of traffic loading, shrinkage, and creep to analyze the dynamic reliability of simply supported PC girder bridges through the development of a load probability model. A stochastic model for truck loads is generated using motion measurement data, which can be used to calculate bridge internal forces and subsequent quantitative analysis of structural deformation due to shrinkage and creep. Subsequently, the formula for the first exceedance probability under resistance degradation is presented and validated through Monte Carlo simulation. Reliability analysis is conducted for both serviceability and load carrying capacity limit states to assess the impact of shrinkage, creep, and increased mean vehicle load on structural reliability. The proposed method offers the theoretical foundation and practical guidance for assessing the structural health status of in-service bridges, thereby providing valuable insights into their long-term performance and maintenance requirements.

Seismic Performance at Beam Ends of Unbonded Prestressed Precast Concrete Frames

Numerical modelling was conducted to investigate the seismic performance at beam ends of unbonded prestressed precast concrete frames. The established finite element model was verified by the test results. Through numerical simulation, the influence of such factors as the presence or absence of energy-dissipating reinforcement, the length of the unbonded section of energy-dissipating bars, the amount of prestressed or non-prestressed reinforcement on the seismic performance at beam ends of unbonded prestressed precast concrete frames were further analyzed. The results show that all prestressed precast beam-end models have similar initial stiffness. The bearing capacity and energy-dissipating performance of beam-end models without energy-dissipating bars are the lowest. The length of the unbonded section of energy-dissipating bars has no significant effect on the bearing capacity and energy-dissipating capacity of beam-end models, though the yield displacement increases obviously with the increase of the length of the unbonded section, as the local stress of energy-dissipating bars is reduced by setting the unbonded section. The bearing capacity of beam-end models can be improved by increasing the amount of prestressed or non-prestressed reinforcement. In the case of the same amount of prestressed reinforcement, increasing the amount of energy-dissipating bars can significantly improve the energy-dissipating capacity.

Shaking table test of prestressed high-strength concrete pipe piles reinforced with non-prestressed steel reinforcement

Prestressed high-strength concrete piles reinforced with non-prestressed steel reinforcement (PRHC piles) have been developed to improve their seismic performance. In this study, the seismic response and failure mechanism of PRHC piles was investigated using a shaking table test. The dynamic characteristics, dynamic soil pressure, superstructure response, acceleration magnification factors, maximum curvature ductility demand, bending moment response, and failure mode identification of the PRHC piles were determined. The performance of PRHC piles was compared with that of prestressed high-strength concrete pipe (PHC) piles, which showed that the PRHC piles experienced higher energy dissipation and lower maximum curvature ductility demands than PHC piles. In addition, the PRHC piles suffered bending failure at the upper-middle positions, and the plastic zones were higher than those of the PHC piles. The adverse effects of long-period and pulse-type ground motions on pipe piles should be considered in designing for strong seismic events. The addition of non-prestressed reinforcement to a pipe pile allows longer segments of the pipe pile to be involved in providing resistance.

Flexural Stiffness and Crack Width of Partially Prestressed Beams with Unbonded Tendons

The original concept of “Total Prestress” consists of creating compressions in concrete without generating tension stresses for service load, while in "Partially Prestressed” elements, tensions are allowed in the service stage, which would produce some cracking depending on applied loads that will be taken with non-prestressed reinforcement. Using criteria and design recommendations can guarantee maximum flexural capacity and admissible serviceability requirements of partially prestressed elements; however, there is insufficient research for estimating more accurately the required parameters for the design and review of these types of elements. Because of this, the present investigation consisted in the realization of experimental studies in continuous partially prestressed beams with unbonded tendons for the evaluation of the flexural behavior for different stages of load determining the actual stresses and the strains taking into account the structural stiffness decrease and its effect on deflections. The dimensions of the specimens were selected based on common dimensions presented on slabs. The tested specimens considered variables such as the relationship between the length of the continuous spans, the cross-section, and the partial prestressing ratio. Afterward, equations were proposed to predict the decrease in the structural stiffness, depending on the degree of cracking, the type of cross-section, the partial prestressing ratio, and the magnitude of the applied load and the tension and compression stresses to estimate the probable deflections for a particular loading stage. The crack width equation presented a difference of −16% to +18% with respect to the experimental data, while the flexural stiffness equation showed a highly accurate correlation to the experimental data.

Flexural response of UHPC beams post-tensioned with internal unbonded tendons: Experimental study

This paper presents the results of an experimental study that deals with the characterization of the complete flexural response of post-tensioned (PT) ultra-high-performance concrete (UHPC) beams with internal unbonded tendons. A total of 6 PT UHPC beams were monotonically loaded to failure. The variables investigated include volumetric fiber content, non-prestressed reinforcement ratio, and loading configuration. Flexural response is characterized in terms of crack pattern formation, propagation, and localization as well as failure mode identification. The influence of the investigated variables on change in: strand strain, UHPC compressive and tensile strains, strand stress, moment capacity, curvature ductility and member level ductility is presented including explanations of observed phenomena. The measured flexural response and capacity are compared with the predicted response using two mechanics-based methods and a numerical method. Prestress losses are quantified and used to obtain the predicted response. UHPC material characterization is conducted to obtain the necessary inputs for the prediction models. The measured to predicted ratio of flexural capacity and the corresponding COV for the considered prediction methods vary from 0.95 to 1.02, and from 6% to 11% suggesting good predictive capabilities. The use of nonprestressed flexural reinforcement in PT UHPC flexural members is recommended from the perspective of crack distribution, delay in the precipitation of flexural failure through crack localization and subsequent hinging, and member level ductility.

Experimental research on flexural behavior of post-tensioned self-compacting concrete beams with recycled coarse aggregate

Self-compacting concrete with recycled coarse aggregate (RCASCC) is a green concrete material with high performance. However, it bears the disadvantages of low elastic modulus and high brittleness compared with ordinary concretes. In this study, recycled coarse aggregate (RCA) obtained from C30 concrete block discarded in laboratory research and tests was used to produce post-tensioned self-compacting concrete (PSRC) beams, while coarse natural aggregate (NCA) was used to produce post-tensioned natural concrete (PNC) beams. The four-point bending tests were carried out on PSRC and PNC beams to analyze the variations between the flexural performance of PSRC and PNC beams. In addition, we discuss the applicability of the current design codes on PSRC beams. The results reveal that the failure mode of PSRC beams is similar to that of PNC beams, whereas it differs significantly in the number and scope of cracks. Moreover, the variations can be reduced by increasing the ratio of non-prestressed reinforcement. In general, the PSRC beam is more ductile than the PNC beam. The increase in the ratio of non-prestressed reinforcement reduced the ductility of the PSRC beam as well as the fluctuations in the ductility of PSRC and PNC beams. Compared with the PNC beam under the same conditions, the PSRC beam exhibited a similar flexural capacity, the cracking load and maximum crack width decreased significantly, and its working deflection increased slightly. According to the calculation and analysis, ACI318-08 can be applied for calculating the cracking load, flexural capacity, and working deflection of the PSRC beams, but not the maximum crack width; GB50010-2010 is applicable for calculating the cracking bending moment and flexural capacity of PSRC beams, but the calculation deviation of the working deflection and maximum crack width is large; EN1992-1-1:2004 is applicable for calculating the crack bending moment of PSRC beams, but it is not safe for evaluating the bending capacity, working deflection, or maximum crack width. Overall, the average crack spacing correction formula proposed through experimental tests in this study can be applied to determine the maximum crack width of PSRC beams, and its accuracy is higher than that of the above-stated specifications.

Punching shear capacity of nonprestressed UHPFRC flat Plates: Evaluation of existing methods

An experimental database of 64 nonprestressed ultra high performance fiber reinforced concrete (UHPFRC) flat plates reported to fail in punching shear was generated and characterized. The selected plates featured round, end-hooked, and deformed steel fibers. All plates have uniform thickness with no shear reinforcement. Trends and correlations between the shear stress at failure and various parameters were investigated. The shear stress at failure was on average four times higher than the shear stress corresponding with the first crack. There was a notable positive correlation between nonprestressed flexural reinforcement ratio and shear stress at failure. Plate ductility at punching shear failure varied significantly. A total of 13 prediction methodologies were considered for final evaluation, 8 of which were developed for UHPFRC, 4 were developed for fiber reinforced concrete (FRC), and 1 was developed for high performance fiber reinforced concrete (HPFRC). The predictive performance of the various prediction models was evaluated using common statistical indicators, as well as a demerit point classification model. The average ratio of measured to predicted punching shear capacity ranged from 0.50 to 2.42. The corresponding coefficients of variation (COVs) ranged from 36% to 58%. Only five out of 13 prediction methodologies underpredicted, on average, the nominal punching shear capacity. The large COV suggests the need for more accurate prediction methods that capture fundamental phenomena observed during tests while being informed by parameters that are practical to obtain. Guidelines for casting methods that produce the desired distribution of fibers are essential in yielding a more predictable plate response.

Punching shear behavior of HSC & UHPC post tensioned flat slabs – An experimental study

Ultra-High-Performance Concrete (UHPC) and High-Strength Concrete are the concretes with superior characteristics comparing with the normal reinforced concrete. Their compressive strength starting with 120 & 60 MPa respectively. The punching shear capacity of posttensioned (UHPC & HSC) flat slabs without non-prestressed reinforcement is experimentally investigated in this research. Five slabs with different concrete compressive strength (100, 120 & 140 MPa) and different strands layout (uniform & bundled & gapped-bundled) were tested under the effect of a monotonic concentric static load. Test results were compared with the provisions of ACI & EC2. The outcomes of the study showed that the punching shear crack occurred at the angles of about 26 & 16° for uniformly and bundled distrusted strands respectively. (HSC) slabs showed good agreement with both ACI & EC2, while (UHPC) slab exceeded the theoretical capacity by about 65%. The bundle & gapped-bundle layout slab showed a slight enhancement in the ultimate punching capacity due to improving the efficiency of used strands, but also showed major reduction in deflection, angle of shear crack and dissipated energy.

A simplified approach to determine the prestress loss and time-dependent deflection in cracked prestressed concrete members, prestressed with fiber reinforced polymers or steel tendons

Based on the creep-transformed section method, a simple equation for the calculation of prestress loss in cracked, simply supported concrete girders, prestressed with FRP and/or steel tendons, is proposed. The equation is presented as a unit within a more global approach, where simple equations to calculate the change of forces in the concrete and the change in curvature are also presented. The novelty of the proposed equation is its application to cracked sections and that it directly considers the contribution of the concrete between the cracks, without the need to carry out multiple calculation stages. The proposed equation takes into account the effect of creep and shrinkage of the concrete, the relaxation of the prestressing tendons and the non-prestressed reinforcement. Furthermore, it can also be applied to the time analysis of continuous beams. The results predicted by the proposed equation are compared with experimental data and show good performance and concordance between the calculated and measured values.

Experimental background behind new AASHTO LRFD specifications for partially partially debonded strands

To develop a unified approach for the design of partially debonded strands in prestressed concrete highway bridge girders, a coordinated analytical and experimental investigation was conducted. This investigation examined amounts of partial debonding, distribution of partially debonded strands within the cross section, debonded lengths, locations and staggering of termination of debonded strands, confinement of debonded regions and their termination points, and the impact of adding nonprestressed reinforcement in the region of partial debonding. The results from testing full-scale I- and U-shaped girders indicate that partially debonding strands does not result in deleterious performance if adequate reinforcement is provided to resist the longitudinal tension due to bending and shear. Crack patterns and angles were not noticeably affected by the amount of debonding. Regardless of the debonding ratio, the maximum measured crack widths at the capacities predicted by the eighth edition of the American Association of State Highway and Transportation Officials’ AASHTO LRFD Bridge Design Specifications remained small. The requirements for debonded strands were revised significantly in the ninth edition of the AASTHO LRFD specifications based on the presented research.

Performance of composite stone beams with prestressed NSM longitudinal CFRP reinforcement subjected to bending

This paper presents an investigation on the performance of stone beams reinforced with prestressed near-surface mounted (NSM) longitudinal carbon fiber reinforced polymer (CFRP) bars subjected to bending. Seven composite stone beams and four bare ones were tested. The test variables included the reinforcement ratio and prestressing level of CFRP bars, and the shear span to depth ratio of the tested beams. Test results showed that, the composite stone beams with either prestressed or non-prestressed reinforcement exhibited a ductile failure with visible deflection and multiple cracks. As the level of prestressing force increased, the cracking load and the shear capacity of composite stone beams increased but the deformation capacity decreased. The increase in reinforcement ratio could suppress the crack propagation and increase the flexural capacity of composite stone beams. As the shear span to depth ratio decreased, the cracking load, the shear capacity, and the peak load corresponding to flexural capacity of composite stone beams increased accordingly. Theoretical models for predicting the cracking and peak moments of composite stone beams were developed based on sectional mechanical analysis, and a good agreement with the experimental results was obtained.

Study on Flexural Performance of Prestressed Concrete Steel Strand Square Piles with Reinforcement

A new type of precast pile, namely steel strand square piles with reinforcement (PRS), is proposed in present study, which uses steel strand as a prestressed reinforcement and is equipped with hot-rolled reinforcement. Two kinds of full-scale pile specimens with different reinforcement were constructed to study the bending performance by the full-scale tests. The finite element model was also performed to study the differences in bending resistance, deformation capacity, crack resistance, and failure mode because of the reinforcement ratio. The results show that the steel strand in the pile was not pulled off, and the concrete in the compression zone was crushed. The finite element analysis results are close to the results of the full-scale test of the piles, which can simulate the flexural performance of the pile well. The experimental results were closer to the theoretical calculation of the cracking moment. The ultimate bending moment value is about 25% more than the theoretical value. The parametric analysis shows that for the PRS with 0.27% prestressed reinforcement, the best bending performance is achieved with 0.64% non-prestressed reinforcement. For the PRS with 0.64% of non-prestressed reinforcement, the best bending performance is achieved with 0.37% of prestressed reinforcement.

Research on calculation of unbonded tendon stress increment in prestressed concrete two-way slab during service stage

The finite element analysis model of unbonded prestressed concrete two-way slab supported by four sides and columns was established by using ABAQUS finite element software. The stress growth law of unbonded tendon in prestressed concrete slab during service stage was researched. The results of finite element analysis show that the stress increment of unbonded tendon increases with the increase of the composite reinforcement index, increases with the increase of the tensile strength of the non-prestressed reinforcement, and decreases with the increase of the rotational constraint level of the boundary of the prestressed concrete slab. According to the analysis results, the formulas for calculating the stress increment of unbonded tendons in service stage were established considering the influence of the composite reinforcement index, the four sides support conditions, the relative position of the prestressed tendon in the slab and the steel type of the non-prestressed reinforcement. The unbonded prestressed concrete two-way slabs supported by columns were divided into upper slab belt and mid-span slab belt. The influence of composite reinforcement indexes and steel types of unprestressed reinforcements on the stress increment of unbonded tendons was investigated respectively. The calculation expressions of stress increment of unbonded tendons in service stage were established for upper slab belt and mid-span slab belt.

Corrosion-Fatigue Life Prediction of the U-Shaped Beam in Urban Rail Transit under a Chloride Attack Environment.

The coupled effect of the chloride attack environment and train load seriously affects the safety and durability of urban rail transit viaducts and dramatically reduces their service life. In this research, a corrosion-fatigue life prediction model of the prestressed concrete (PC) beam under the coupled effect of the chloride attack environment and train load was developed. This proposed model was illustrated by a 30 m-span PC U-shaped beam in an urban rail transit viaduct. The competitive relationship between concrete fatigue cracking time, non-prestressed reinforcement corrosion initiation time, and concrete corrosion-induced cracking time was discussed. The effects of train frequency, the chloride attack environment grade, and the environmental temperature and relative humidity were investigated on corrosion-fatigue life. Results indicate that train frequency, the chloride attack environment grade, and the environmental temperature can reduce the corrosion-fatigue life of a U-shaped beam by up to 30.0%, 50.7%, and 21.5%, respectively. A coupled chloride attack environment and train frequency can reduce the corrosion-fatigue life by up to 61.2%. Distinct from the environmental temperature, the change of relative humidity has little effect on the corrosion-fatigue life of the U-shaped beam.

Finite-element modeling of partially prestressed concrete beams with unbonded tendon under monotonic loadings

Purpose The partially prestressed concrete beam with unbonded tendon is still an active field of research because of the difficulty in analyzing and understanding its behavior. The finite-element (FE) simulation of such beams using numerical software is very scarce in the literature and therefore this study is taken to demonstrate the modeling aspects of unbonded partially prestressed concrete (UPPSC) beams. This study aims to present the three-dimensional (3-D) nonlinear FE simulations of UPPSC beams subjected to monotonic static loadings using the numerical analysis package ANSYS. Design/methodology/approach The sensitivity study is carried out with three different mesh densities to obtain the optimum elements that reflect on the load–deflection behavior of numerical models, and the model with optimum element density is used further to model all the UPPSC beams in this study. Three half-symmetry FE model is constructed in ANSYS parametric design language domain with proper boundary conditions at the symmetry plane and support to achieve the same response as that of the full-scale experimental beam available in the literature. The linear and nonlinear material behavior of prestressing tendon and conventional steel reinforcements, concrete and anchorage and loading plates are modeled using link180, solid65 and solid185 elements, respectively. The Newton–Raphson iteration method is used to solve the nonlinear solution of the FE models. Findings The evolution of concrete cracking at critical loadings, yielding of nonprestressed steel reinforcements, stress increment in the prestressing tendon, stresses in concrete elements and the complete load–deflection behavior of the UPPSC beams are well predicted by the proposed FE model. The maximum discrepancy of ultimate moments and deflections of the validated FE models exhibit 13% and −5%, respectively, in comparison with the experimental results. Practical implications The FE analysis of UPPSC beams is done using ANSYS software, which is a versatile tool in contrast to the experimental testing to study the stress increments in the unbonded tendons and assess the complete nonlinear response of partially prestressed concrete beams. The validated numerical model and the techniques presented in this study can be readily used to explore the parametric analysis of UPPSC beams. Originality/value The developed model is capable of predicting the strength and nonlinear behavior of UPPSC beams with reasonable accuracy. The load–deflection plot captured by the FE model is corroborated with the experimental data existing in the literature and the FE results exhibit good agreement against the experimentally tested beams, which expresses the practicability of using FE analysis for the nonlinear response of UPPSC beams using ANSYS software.

A new empirical model for residual flexural capacity of corroded post-tensioned prestressed concrete beams

In this paper, a total of 70 experimental flexural tests of corroded post-tensioned prestressed concrete (PC) beams were gathered from the published literatures. Using the experimental data, a comprehensive databank of flexural capacity of the corroded PC beams was established. Meanwhile, four existing empirical models for calculating the residual flexural strength of the corroded PC beams were also gleaned and contrasted with each other based on the databank. It turns out that three of the four existing empirical models underestimate the flexural capacity. To deeply analyze the factors affecting the flexural capacity, numerous factors were discussed, e.g., the corrosion ratio, beam width, effective height of the beam section, concrete compressive strength, and the ratio of strength between the tensile reinforcement (including prestressed and non-prestressed reinforcement) and concrete. It is found that the corroded post-tensioned PC beams’ residual flexural capacity is affected most by the corrosion ratio. In the end, a better empirical model is proposed for computing the residual flexural capacity of corroded PC beams, which provides accurate and effective predictions in a wide range of corrosion ratio for engineering practice.

Numerical investigation on compressive arch action of prestressed concrete beam-column assemblies against progressive collapse

To investigate the compressive arch action (CAA) of prestressed concrete beam-column assemblies, bonded prestressed concrete (BPC) assembly models were established and validated using previous experimental data. The beneficial effect of CAA on the progressive collapse resistance of BPC structures is quantified by the load increase factor η, and the CAA of BPC assemblies with four layout schemes of prestressed tendons is investigated. Furthermore, the effect of seven parameters on the progressive collapse resistance of BPC assemblies with parabolic strands is determined. A model is proposed to evaluate the CAA of BPC assemblies. The results indicate that the CAA capacity of BPC assemblies differs with different strand layout schemes. Parabolic strands aggravate the failure of the area near the middle column; the contribution of linear strands is the smallest; the resistance of parallel strands is similar to that of X-shaped strands. Moreover, the ratio of prestressed tendons, the ratio of non-prestressed reinforcement at the top and bottom of the beam, and the section dimensions of the column have a significant impact on the load increase factor. The proposed models were validated against both experimental and simulation results with a mean error of less than 5%.

Time-dependent analysis of simply supported and continuous unbonded prestressed concrete beams

An equation to estimate the prestress loss in continuous unbonded prestressed concrete beams is proposed in this paper. The equation accounts for the creep and shrinkage of the concrete and the relaxation of the prestressing steel. In addition, a numerical model is developed based on the finite element method for the time-dependent analysis of these types of concrete beams. The approach also accounts for the presence of non-prestressed steel reinforcement and the friction between the tendons and their ducts. Furthermore, a well-justified integral-form equation is proposed to compute the strain at each section of the unbonded prestressing steel accounting for the friction between the tendons and their ducts. This equation is based on the equation for frictional loss accepted by different standards. The strain at each section of the unbonded prestressing is calculated from the strain in the concrete at the level of the prestressed tendon along the whole beam. Numerical and experimental results are compared to validate the proposed equation and the finite element approach and the good performance of both in modelling the behaviour of this type of prestressed concrete member over time is shown.

Deflection of a Concrete T-beam with Prestressed and Non-prestressed Fiber Reinforcement Polymers at Elevated Temperatures

Prestressed concrete members have gained popularity as an efficient and effective way of designing a structural member with the best engineering and material properties. The method of prestressing a structural concrete member has the capability of controlling increased service loads with less depth over longer spans. However, deflections from over-loading or loading over time give a disadvantage to the common steel reinforced concrete members by the effect of corrosion as the structural concrete develop cracks. To prevent corrosion of a structural concrete member, exchanging of steel reinforcement with Fiber Reinforcing Polymers (FRP) has sparked engineering interest in recent years. Both prestressed and non-prestressed FRP reinforcement can reduce tension in concrete. However, the performance of such structural members under elevated temperatures is currently unknown. The knowledge and application of this may lead to a cost effective, and practical consideration in fire safety design. In this article, an analytical model is developed using flexural rigidity of a concrete T-beam with both prestressed and non-prestressed FRP reinforcement to study the deflection behavior at practical elevated temperatures. The model is compared with the finite element model (FEM) of a T-beam with both prestressed and non-prestressed reinforcement subjected to practical elevated temperatures. In addition, comparison is also made with an indirect reference to the real behavior of the material. The results of the analytical model correlated reasonably with the FEM and the real behavior, and were within the accepted range of the American Concrete Institute (ACI) specifications.