Prestressed Steel Bars Research Articles

Bending and shear strengthening of timber beams using prestressed steel and composite bars – experimental and numerical studies

The paper describes a program of experimental and numerical tests aimed at determining the mechanical properties of beams made of laminated timber (BSH) and laminated veneer lumber (LVL) reinforced with pre-stressed bars made of basalt, glass, natural and steel fibers, basalt mats with roving and composite, polyethylene and natural yarn. The paper presents various types of reinforcements, the purpose of which was to obtain higher load-bearing capacity and stiffness in bending with shear than for unreinforced beams. The effectiveness of different reinforcement schemes was compared for seventeen beams subjected to experimental tests on a test stand, the modes of destruction were described, as well as mechanical properties, deformations and deflections for reinforced and unreinforced beams under multiply variable and long-term loading. Based on the experimental studies, a significant increase in the load-bearing capacity and stiffness of the reinforced beams subjected to simultaneous bending and shear was confirmed, and it was indicated that the reinforcements by pre-stressed bars (steel, with polymer reinforcement or natural fibers) and composite mats eliminated local defects and discontinuities in the wood, without affecting the quality and strength of the FRP-wood connection. The numerical results of the analysis of the beam models using the finite element method showed compliance with the experimental studies in terms of deflections, linear and angular strains for the reinforced and unreinforced beams

Experimental study on deformation characteristics of new prestressed subgrade under static and dynamic loads

An in-deep comprehension of the static and dynamic operational characteristics of prestressed subgrade is essential for its analysis, design, and service performance evaluation. Based on the Buckingham π theory, a novel scaled static and dynamic model test system of the prestressed subgrade has been developed. The structural components, functional characteristics, and working mechanism of the test system were comprehensively elucidated, and a suite of static and dynamic model tests was conducted to study the deformation characteristics of the prestressed subgrade. It is demonstrated that the prestressed steel bars underwent prestress loss due to the additional stress induced creep of the soil elements below and adjacent to the load transfer plates (LTPs). Therefore, it is advisable to over-tension the prestressed steel bars in practical engineering. Upon the application of prestress, the subgrade surface experienced slight uplift deformation, which did not change the geometric shape and smoothness of the subgrade surface and demonstrated that the prestress reinforcement effect could diffuse to the subgrade surface. In the static double-load-plates tests, the prestressed subgrade presented obvious advantages in controlling the subgrade surface settlement and slope lateral deformation compared to the unreinforced subgrade, which could therefore improve the deformation resistance of the subgrade. In the short-term dynamic loading tests, both the acceleration and dynamic displacement of the subgrade approximately linearly decreased with an increase in the prestress, implying that the horizontal prestress had a notable beneficial impact on mitigating the subgrade vibration. Additionally, with the long-term dynamic loading, the prestress reinforcements could significantly restrain the cumulative plastic deformation of the subgrade, with the cumulative deformation decreasing as the applied prestress increased. The developed test system offers viable and implementable technical means for investigating the enhancement mechanism of a prestress reinforced subgrade, and the insights gained from the tests contribute to elucidating the effect of prestress reinforcements on the subgrade’s static and dynamic performance.

The Seismic Performance of Self-Centering Ribbed Floor Flat-Beam Frame Joints

To achieve rapid post-earthquake repair of self-centering ribbed floor flat-beam frame structures, a ductile hybrid joint consisting of dog-bone-shaped, weakened, energy-dissipating steel bars connected to the upper and lower column sections through high-strength threads is proposed based on the damage control design concept. By moving the ductile energy-dissipating zone out to the locally weakened section of the energy-dissipating steel bars and the locally unbonded prestressed steel bars in the core area, the residual deformation was limited and the seismic performance improved. Based on the working principle of hybrid joints, low cycle loading tests were conducted on two joint specimens to analyze the influence of lateral prestress on the seismic performance of the hybrid joints. Numerical modeling methods were used to compare the position of the energy-dissipating steel bars in the composite layer and the friction performance of the joints. The research results indicated that the hybrid joint had stable load bearing, deformation, and energy dissipation capabilities, with damage being primarily concentrated in the energy-dissipating steel bars. Even at an inter-story displacement angle of 5.5%, the upper and lower column segments remained elastic. After unloading, the connection seam at the joint was closed, and the self-centering performance was good. When the inter-story displacement angle reached 5.5%, the lateral prestress increased from 150 kN to 250 kN, the ultimate bearing capacity of the joint increased by 16.3%, and the cumulative energy consumption increased by 30.0%. The influence of the friction coefficient of the joint surface on the structural performance was set at a threshold of 0.7. When it was less than the threshold, the ultimate bearing capacity and initial stiffness of the joint increased with the increase in the friction coefficient. After reaching the threshold, the increase in the ultimate bearing capacity of the joint slowed down, and the rate of stiffness degradation gradually accelerated. This joint showed excellent seismic performance and can thus achieve post-earthquake repair of structures.

Flexural Performance and Stress Calculation of External Prestressed Fiber-Reinforced Polymer-Bar-Strengthened One-Way Concrete Slabs.

External prestressing is widely employed in structural strengthening engineering due to its numerous advantages. However, external prestressed steel bars are prone to corrosion when exposed to the service environment. This paper is dedicated to examining the use of fiber-reinforced polymer (FRP) bars as external prestressing materials to strengthen one-way concrete slabs. Five one-way concrete slabs were strengthened with externally prestressed FRP bars with different prestress levels and different amounts of FRP bars, while one non-strengthened slab was used for comparison. The effects of strengthening on the flexural behavior, specifically the cracking load, ultimate load, stiffness and failure mode, were analyzed systematically. Moreover, the ductility and cost-benefit optimizing properties of the reinforcing design were discussed. The results show that external prestressed FRP bars significantly improve the cracking load, ultimate load and stiffness of one-way concrete slabs. The absence of a bond between the concrete and FRP bars overcomes the brittleness of the FRP bars, while the strengthened slabs exhibit satisfactory ductility and a higher post-yield stiffness and bearing capacity. Additionally, the cost/benefit ratio is optimized by increasing the prestress level, while a higher number of prestressed FRP bars is beneficial to ductility. Finally, a method for calculating the stress in prestressed FRP bars at ultimate loads was proposed. Irrespective of the prestressing material, this method is applicable to both strengthened beams and one-way slabs.

Dynamic Stress Response in a Novel Prestressed Subgrade under Heavy-Haul Train Loading: A Numerical Analysis

To explore the dynamic transient characteristics induced by passing heavy-haul trains in newly-developed prestressed subgrade, two three-dimensional finite element models were constructed in the time domain using ABAQUS software. These models are categorized as train-track-prestressed subgrade and train-track-unreinforced subgrade. The numerical models also incorporated the vertical track irregularity commonly found in heavy-haul railways. The investigation aims to discern the dynamic stress response differences in both types of subgrades under three distinct train axle loads. Model validation occurred through comparisons with field tests gathered from various heavy-haul railways in China, as well as analogous numerical simulation cases. The findings indicate that track irregularity results in an asymmetric distribution of dynamic stress on the subgrade surface beneath both left and right rails, aligned transversely with the subgrade centerline. Additionally, this asymmetry is notably pronounced. The peak dynamic stress on the subgrade surface beneath the rails for both subgrades increases with escalating train axle loads. However, the prestressed reinforcement structure (PRS) effectively modulates this phenomenon, with the controlling advantage intensifying as train axle load increases. The average dynamic stress level in the prestressed subgrade is marginally lower than in the unreinforced subgrade within the roadbed layer beneath rails. Furthermore, train axle loads amplify the variation level of dynamic stress in the subgrade. However, the variable coefficient of dynamic stress in the prestressed subgrade is less than in the unreinforced subgrade, suggesting that PRS contributes positively to maintaining subgrade dynamic stability. In terms of the longitudinal distribution of peak dynamic stress, both subgrades exhibit normal distribution at varying depths within the roadbed layer. Lastly, the additional dynamic stress in prestressed steel bars also rises with increasing train axle loads. Nonetheless, it remains substantially lower than the static target pre-tensile stress. Moreover, the dynamic responses of prestressed steel bars in different rows attenuate as depth increases away from the subgrade surface. In summary, the study establishes that PRS significantly enhances the dynamic stability of railway subgrade.

Experimental Study on Behavior of Precast UHPC Beam-Column Joints Subjected to Cyclic Loading

Ultra-performance concrete (UHPC) is a new material with many outstanding features such as compressive and tensile strength that are both very high compared to conventional concrete. In precast reinforced concrete structures, the beam-column joint is one of the most important parts. In this type of connection, the beam is connected to the column through post-tensioned prestressing steel bars (PC bars), making the connection resistant to bending moments as well as shear forces. This paper presents the behavior of this type of connection under the effect of seismic loads on the following criteria: flexural resistance, moment-rotational relationship, change of PC bars’ prestress during and after cyclic loading.

On the Role of Seismic Damage Tolerance on Costs and Life Cycle of CLT Buildings

This paper presents a contribution to reviewing the most common seismic design procedures of CLT buildings and their implications on structural features and technological solutions. Attention is particularly focused on the overall seismic performance, damage tolerance, construction costs and environmental impact. It is intended as a baseline for a more comprehensive study, thus the assessment is made with reference to a real building, representative of a class of common buildings recently designed and erected in many Italian regions exposed to low and moderate seismic hazards. As usual, the analysis was carried out according to a two-dimensional model of the panels, assumed to be elastic, varying the type of connections at the base, the presence of pre-stressing steel bars for rocking control and dissipative devices. The main outcomes of the study can be summarized as follows: (i) the structural seismic behavior of CLT buildings is significantly influenced by the structural schemes adopted for walls and connections; (ii) construction costs and environmental impact decrease whenever damage tolerance is accounted for in design procedures.

The Influence of the Prestressing Level of the Fully Threaded Anchor Bar on the Corrosion Rate

The article presents experimental research on the corrosion of prestressing steel bars with denotation CKT (fully threaded anchor bars), which are composed of high-quality prestressing steel of the grade Y 1050 (1050 MPa). The experiment was performed using an electrochemical accelerated test. The aspects of the electric current value influence, time dependence on the degree of corrosion, and especially the influence of the prestressing level in the prestressing steel bars on the degree of corrosion were observed and examined. The results of the experiment showed that if the sample was in a stressed state, its degree of corrosion increased. Specifically, for the maximal stress equal to 90% of the tensile strength, the corrosion degree was increased by approximately 7.3%, in comparison to the unstressed specimen. In this case, a 7.3% corrosion degree corresponds to a weight loss of 350 g. The theoretical degree of corrosion was calculated using Faraday’s Law, which allowed the prediction of a rough estimate of the corrosion degree obtained with known input data. The experimental results showed that there was no apparent difference in the corrosion morphology of the sample during the same time-dependent corrosion influence at the same prestressing level in the sample with the same electric current value.

Experimental and Numerical Study of a Rebar-Prestressed Cylinder Concrete Pipe (RPCCP) under Internal Load.

In order to study the load-bearing failure characteristics of a RPCCP under internal load, a field prototype test was designed, and a finite element model was established. An internal load was applied up to 2.0 MPa step by step and the force variation law of each part was obtained. During the production of the RPCCP, by wrapping prestressed steel bars around the concrete core with a cylinder, the core was subjected to an initial precompression stress. In the loading process, the protective cover cracked first, from where the concrete core gradually changed from the initial compression state to a tension state, finally cracking from the inner and outer diameter. The stresses of the cylinder and steel bars increased steadily with the internal load and did not yield. The finite element calculation results were in good agreement with the test results, and the influence characteristics of the tension control stress of the steel bar and the concrete strength on the failure of the RPCCP under internal load were discussed. The results showed that the internal load of the protective cover was independent of the tension control stress, but decreases with a decrease in concrete strength, while the load corresponding to the concrete core entering plasticity is related to the tension control stress and the concrete strength, and the relationships were basically linear.

Experimental Study on Shear Performance of Post-Tensioning Prestressed Concrete Beams with Locally Corroded Steel Strands

To study the effect of the local corrosion of prestressed steel strands on the shear failure mode and shear bearing capacity of concrete beams, unilateral steel strands in four post-tensioning prestressed concrete (PC) beams are corroded, and the shear test of four PC beams are performed. Moreover, a simplified calculation method for the shear bearing capacity of concrete beams with diagonal steel bars is proposed considering the effect of cross-sectional reduction of steel bars, the degradation of mechanical properties, and the cross-sectional damage of concrete. Results shows that the crack propagation mode and failure mode are unrelated to the corrosion of prestressed steel bars when the shear span ratio of beam is the same. The shear capacity of the beam decreases with the increase of corrosion rate, but the decreasing rate is lower than the increasing rate of the corrosion rate. The growth rate of stirrup stress is much greater than that of load after concrete tension and compression loss cracking, and the yield of stirrup can be used as a sign of the ultimate bearing capacity of the beam. In addition, by comparing the experimental and numerical simulation results, the proposed simplified calculation method for the shear bearing capacity of concrete beams is of high accuracy.

Strengthening Shear Resistance of Beams without Web Reinforcements Using Vertical Prestressed Steel Bars

Ensuring the shear capacity of concrete structures is crucial. The vertical prestressed steel bar (VPSB) strengthening method is effective for improving the shear behaviour of concrete structures. Four concrete beams are investigated to reveal the effect of VPSBs on the shear capacity of concrete beams without web reinforcement. Test results indicate that the shear capacity of the test beam strengthened by VPSBs in the beam is significantly increased by more than 95%, and the failure mode of the test beam changes from diagonal tension failure to shear compression failure. Additionally, the results provide insights into the strengthening mechanism of VPSBs, i.e., the shear contribution of the VPSBs can be categorised into two stages. The vertical compressive stress provides shear contribution in the first stage and provides control in terms of crack development; meanwhile, in the second stage, the stirrup action by VPSBs contributes to shear.

Construction method of strengthening shear walls using prestressed steel bars for a high-rise building

2. In the shear wall reinforcement of a high-rise residence in Changzhou, China, the prestressed steel bar reinforcement method is innovatively used. This paper focuses on the reinforcement principle and construction method of the prestressed steel bar method for strengthening the shear wall. During the construction, combined with the engineering quality problems, the prestressed steel bar method is used to strengthen the shear wall. This method avoids the reduction of the use area caused by the increasing section reinforcement method and the stress lag caused by the replacement method, does not change the structural stiffness and the shape of structural members, and shortens the construction period. After monitoring by the monitoring unit, the reinforcement method has good effect. This study also passed the acceptance of the science and technology plan project of the Ministry of construction, and formed a complete set of construction method of prestressed steel bar strengthening shear wall. The effective implementation of this method can provide technical reference for the reinforcement construction of similar projects.

Model Construction and Simulation Study on Bending Performance of Strengthened RC Beam in Externally Prestressing Industrial Reclaimed Steel Wire

Strengthening with external prestressing is a kind of reinforcement method which imposes prestress on concrete by setting prestressed steel bar outside concrete, a new strengthening with external prestressing technology can be put forward by using industrial reclaimed steel wire instead of prestressing steel bar. High-quality steel wire is extracted from waste tire after stripping and derusting, and this kind of industrial reclaimed steel wire with high tensile strength and good toughness is applied to building reinforcement by externally prestressing method; it can provide a new research direction for the country’s green, low-carbon, and high-quality development. In this paper, the new strengthening with external prestressing technology is used to study the bending static load test of test beams under different working conditions. The influence of reinforcement material and rotational degree on the bending performance of RC beam is discussed. The results show that the ultimate bearing capacity of the flexural members with industrial recycled steel wire is more effective under the new external prestressed reinforcement method. Under the same reinforcement method, when the reinforcement materials are the same, the increase of prestress can effectively improve the bearing capacity of flexural members in the reinforced beams with prestress of 30%, 40%, and 50%, respectively. In order to verify the reinforcement effect of industrial recycled steel wire on the bending performance of RC beam from multiple perspectives, the numerical simulation was carried out on the concrete specimens reinforced with different degrees of woven reinforced wire, and the simulation results were in good agreement with the experimental results. This study provides a new research direction for the recycling of industrial reclaimed steel wire and the reinforcement of concrete components and has a good promotion, role, and theoretical support for subsequent research.

Seismic Performance of Assembled Shear Wall with Defective Sleeve Connection

In this paper, three kinds of shear walls with full sleeve grouting, fully defective sleeve and partially defective are designed for finite element analysis to analyze the influence of defects on the seismic performance of shear walls. The research shows that at the beginning of loading (5 s), the three models begin to appear compressive damage at the bottom of the wall in all three models. The damage of the defect-free model develops rapidly, and the damage of the fully defective model is basically the same as that of the partially defective model. With the gradual increase of displacement control (15 s), the compressive damages at the foot of the wall in the defect-free and partially defective grouting model are obvious, with plastic hinge formed in the foot of the wall, and the phenomenon of development along the pier body showing up. When the structure is damaged, the overall compressive damages of the wall in the defect-free and partially defective models are obvious, and the damage on the defective side of the partially defective model is slightly deficient. While the maximum stress of pre-stressed reinforcement in the defect-free model is concentrated at the top of the sleeve, the maximum stress of the pre-stressed steel bar in the fully defective model appears at the end of the steel bar in the sleeve. The hysteresis curve shape of the non-defect model and partially defective model are basically the same, showing a “shuttle” shape with a sound energy dissipation effect. The hysteresis curve shape of the fully defective model appears an obvious “pinch” phenomenon. The yield displacement levels of the defect-free and partially defective models are smaller than that of the fully defective model structure. The stiffness degradation curves of the three models basically overlap with one another. Before the limit displacement, the stiffness results of the non-defect model and the partially defective model are greater than that of the fully defective model. When the displacement is loaded to 20 mm, the stiffness degradation of the three models is equivalent.

Investigations on Integrally Lifted Prefabricated High-Performance Concrete Cap Beams

This research proposes two new types of prefabricated high-performance concrete cap beam structures, which solve the problem that the traditional large cap beam needs to be split into two to three parts during assembly construction, and the construction efficiency is reduced. Using new materials such as ultra-high performance concrete (UHPC) and new technology such as high-performance composite structure, two new types of cap beams are studied. Taking prestressed concrete cap beams as the control group, the calculation model of each cap beam is established, and then the mechanical performance of each cap beam is tested and analyzed. At the same time, the self-weight, cross-sectional size, quantity of prestressed steel bars, and manufacturing material cost of each cap beam are also analyzed and compared, and the applicability of each cap beam is given. The research results show that compared with ordinary concrete, the use of UHPC can significantly improve the mechanical performance of the cap beam, reduce the cross-sectional size of the cap beam, and reduce the self-weight of the cap beam. Calculation results show that the steel-UHPC composite cap beam can achieve the smallest lifting weight. In summary, the two new prefabricated high-performance concrete cap beams proposed in this paper can significantly reduce the self-weight of the cap beam and improve the construction efficiency.

Experimental and analytical investigations on flexural behavior of bamboo beams strengthened with steel bars

The embedding of steel bars is proposed to enhance the load-bearing performance of bamboo beams. Based on laboratory tests, the bending behavior of bamboo beams reinforced with steel bars or prestressed steel bars was analyzed using finite element software. Comparing the finite element simulation results with those measured in tests, it can be found that the load–displacement curves coincide with each other, and the strain development processes in the mid-span are basically the same. The prediction by the finite element simulation has good accuracy. The embedding of steel bars and prestressed steel bars can effectively improve the ultimate bearing capacity (up to 27.0%), bending stiffness at the serviceability limit state (up to 42.61%), ductility (up to 22.9%), and material utilization efficiency (up to 34.1%) for the bamboo beams. The embedding of steel bars makes the bamboo in the compression zone of the beams develop with higher efficiency, and applying the prestress for steel bars can produce reverse bending deformation and reduce the actual deflection for the reinforced bamboo beam under service load. Under the same reinforcement ratio, the prestress level has a relatively small influence on the ultimate bearing capacity (up to 4.5%) and stiffness (up to 4.5%) of the reinforced beam.

Analysis of Influence Factors on Line Shape of High-speed Railway Beam-Arch Combination Bridge

Taking the prestressed continuous beam-arch composite bridge on the Zheng Wan High-speed Railway as a research object, which across the South-to-North Water Transfer in Zhang Liang Town, the space finite element model of the bridge was established by Midas/Civil, the cantilever casting construction process of the main beam was simulated, and the influence of many different parameters on beam line shape of the bridge was investigate. The results show that the unbalanced weight of the hanging basket and the prestressed steel bar parameters have less influence on the beam line shape; the bulk density of concrete and the arrangement length of counterweight have a great influence on line shape, therefore, these should be considered as key control parameters during construction, the counterweight of boom beam can reduce the deformation of bridge’s mid-span, it is advantageous for the Analysis of Influence Factors on Line Shape of High-speed Railway Beam-arch Combination Bridge line shape control of the bridge.

Bending Performance of Prestressed Continuous Glulam Beams

The limited transferring moment capability of Glulam (glued laminated wood) joints results in insufficient joint stiffness. Therefore, most of the connections are hinged joints. Based on the previous studies, one novel end‐connection device was proposed to form prestressed continuous Glulam beams. The prestressed beams were composed of prestressed low‐relaxation steel bars, the deviator block, the anchorage device, and the novel end‐connection apparatus. These prestressed steel bars were tensioned by the deviator block to exert prestress. Then, 18 prestressed continuous beams and two prestressed simply supported beams were subject to the bending tests to explore the impact of reinforcement ratio and prestress on the prestressed Glulam beams from aspects such as failure modes, bearing capacity, load‐deflection relationship, and load‐strain relationship. The results show that, given the same prestress level, compared with beams with a reinforcement ratio of 1.92%, the bearing capacity of beams with a reinforcement ratio of 3.84% and 5.76% is increased by 20.3%–29.4% and 30.51%–36.36%, respectively. Given the same reinforcement ratios, compared with beams without prestressing, the bearing capacity of beams with a prestressing force of 7 kN and 14 kN is increased by 2.39%–10.14% and 6.49%–13.26%, respectively. In addition, compared with simply supported beams, the bearing capacity of continuous beams is increased by 40%, and the deformation is reduced by 13%. Therefore, as a novel prestressed beam, the bending performance of Glulam beams can be improved effectively.

Effects of differential subgrade settlement on damage distribution and mechanical properties of CRTS II slab track

Differential subgrade settlement adversely affects the slab track. In this study, a three-dimensional model of a slab track based on damage mechanics theory was established for analysing the effects of differential subgrade settlement on the damage distribution and mechanical properties of the slab track. The prestressed steel bars and ordinary steel bars in the precast slab of the slab track were refined. The rail supporting forces were employed as the train loads. The damage distribution, deformation, and longitudinal stress of the track under differential subgrade settlement cases were calculated using the model. The results indicated that with the increasing of settlement amplitude, the concrete base is damaged first. If the settlement amplitude continues to increase, the precast slab is damaged. The critical subgrade settlement amplitude of the initial damage of the track structure increases with the increasing of settlement wavelength. Under differential subgrade settlement, the steel bars in the precast slab were subjected to additional loads. However, the precast slab may also crack. Damage to the precast slab and concrete base destroys the integrity of the longitudinal connection system of the CRTS II slab track. Subgrade with differential settlement should be repaired in time to avoid serious damage to the track structure.

Research on prefabricated concrete beam-column joint with high strength bolt-end plate

Many prefabricated concrete frame joints have been proposed, and most of them showed good seismic performance. However, there are still some limitations in the proposed fabricated joints. For example, for prefabricated prestressed concrete joints, prefabricated beams and prefabricated columns are assembled as a whole by the pre-stressed steel bar and steel strand in the beams, which brings some troubles to the construction, and the reinforcement in the core area of the joints is complex, and the mechanical mechanism is not clear. Based on the current research results, a new type of fabricated joint of prestressed concrete beams and confined concrete columns is proposed. To study the seismic performance of the joint, the quasi-static test is carried out. The test results show that the nodes exhibit good ductility and energy dissipation. According to the experimental fitting method and the fixed point pointing law, the resilience model of this kind of nodes is established, and compared with the experimental results, the two agree well, which can provides a certain reference for elasto-plastic seismic response analysis of this type of structure. Besides, based on the analysis of the factors affecting the shear capacity of the node core area, the formula of shear capacity of the core area of the node is proposed, and the theoretical values of the formula are consistent with the experimental value.