Mid-span Deflection Research Articles

Experimental Study on the Flexural Performance of the Corrosion-Affected Simply Supported Prestressed Concrete Box Girder in a High-Speed Railway

Prestressed concrete box girders are commonly employed in the development of high-speed railway bridge constructions. The prestressed strands in the girder may corrode due to long-term chloride erosion, leading to the degradation of its flexural performance. To examine the flexural performance of corrosion-affected simply supported prestressed concrete box girders, eight T-shaped mock-up beams related to the girders used in the construction of high-speed railway bridges were manufactured utilizing similarity theory. Seven of the beams underwent electrochemical accelerated corrosion, and then each beam was subjected to failure under the four-point load test method. Measurements recorded and analyzed in detail during the loading process included the following: crack propagation, crack width at various loads, crack load, ultimate load, deflection, and concrete strain of the mid-span section. The results demonstrate that a corrosion rate of just 8.31% has a considerable impact on the structural integrity of the beams, as evidenced by a pronounced reduction in flexural cracks and a tendency towards reduced reinforcement failure. Furthermore, the corrosive process has a detrimental effect on mid-span deflection, ductility, and ultimate flexural bearing capacity, which could have significant implications for bridge safety. This study provides valuable insights for the assessment of flexural performance and the development of appropriate maintenance strategies for corroded simply supported box girders in high-speed railways.

Analysis of the response of wind-induced vibrations on flexible photovoltaic mounts

Abstract This article investigates a flexible photovoltaic bracket’s response to wind vibration. A finite element model is established using SAP2000 software for time course analysis. Representative units and nodes were selected to analyze internal force response, displacement response, and acceleration response. The prestress and span change rule of the flexible photovoltaic bracket are also explored, and quantitative research is conducted on the size of prestress and span size. The magnitude of the prestress affects a structure’s responsiveness to wind vibration. As prestress grows, so do deflection and acceleration, and the rate at which axial force is increasing also increases. Conversely, when prestress increases, the rate of deflection reduction falls. Consequently, considering the prestress size, it is advised that 50-kN prestressing be used for the support and wind cables. As the span rises, so do the mid-span span and the axial force of the wind cables, while acceleration also increases. The rate of mid-span deflection increases gradually with the flexible PV mount span, but the rate of axial force increase decreases. It is recommended to limit the span to below 50 m.

The impact of using prestressed CFRP bars on the development of flexural strength

Abstract The load-carrying capacity and ductility of conventional steel reinforcement may be greatly increased by using ordinary and prestressed carbon fiber-reinforced polymer (CFRP) bars, resulting in reinforced concrete structures with greater sturdiness. This research investigates the flexural behavior of CFRP-prestressed beams with bonded tendons as opposed to conventional steel-prestressed beams. This article examines a less explored topic that often fails because post-tensioned beams with unbonded CFRP tendons are crushed by concrete. The linear-elastic behavior of CFRP accounts for much of the experimentally observed considerable variations in flexural characteristics between CFRP and steel-prestressed beams. Compared to unbonded CFRP specimens, bonded CFRP specimens are much stronger. Our knowledge of CFRP reinforcement in concrete infrastructure is advanced by this work, which highlights the need for better design techniques to increase strength and ductility. It is recommended that CFRP bars be bonded with epoxy resin to restrict fast energy dissipation and avoid concrete failure. As a result, CFRP-reinforced concrete beams will react less linearly and more ductilely. CFRP may improve prestressed concrete beam performance and lifespan in a number of scenarios, as shown by comparative research with traditional steel reinforcement. Six 1,800–mm-long RC beams with a 200 × 300 mm cross-section were examined and divided into three groups, analyzing important loading phases (i.e., cracked, ultimate, and mid-span deflection) using CFRP bars as prestressed tendons to replace the bottom steel rebars. The load-carrying capabilities and ductility of CFRP-reinforced beams were much greater than those of the reference beam. A single beam using normal CFRP bars for reinforcement showed a 21.2 mm mid-span deflection and an ultimate load of 157.2 kN, with a 57.7-kN fractured load. Another beam with normal CFRP bars also showed enhanced performance, with a mid-span deflection of 21.2 mm, an ultimate load of 160.6 kN, and a cracking load of 57.5 kN.

Experimental and numerical study of cold-formed steel beams with web perforations

This study focuses on the experimental and numerical investigation of cold-formed steel (CFS) beams with web perforations to assess their shear performance. Twelve samples were tested, all processed from high-strength, cold-formed steel sheets of grade S235 with a thickness of 1.5 mm. The specimens, designated as CC, were formed by interlocking two C-sections and welded together. Various parameters were analyzed, such as the shear-span ratio, hole depth-to-web height ratio (dh/h), and web height-to-thickness ratio. The experimental setup involved mid-span single-point loading conditions to evaluate the mechanical behavior of the beams. Circular holes with different diameters were strategically placed at the mid-height of the webs in two shear zones. The experimental results were validated using finite element analysis (FEA) conducted in ANSYS, ensuring the accuracy of the finite element model. The findings indicate that the ultimate bearing capacity of the specimens decreases as the hole depth-to-web height ratio increases. When the hole depth-to-web height ratio was small (dh/h ≤ 0.4), the load-deflection curves declined rapidly after reaching the peak. Conversely, for a ratio of 0.5, the curves declined more gradually. Additionally, mid-span deflection decreased as dh/h increased, with significant variation observed for smaller ratios and stabilization for a ratio of 0.5. This research provides a comprehensive understanding of the shear behavior of cold-formed steel beams with web openings. It offers valuable insights into the design and optimization of these structures, contributing to the safe and efficient application of CFS beams in various engineering contexts.

Multiple impact tests on precast reinforced concrete beams with pressed sleeve connections

Buildings may experience impact loads or even multiple impacts during their service life. Precast concrete (PC) structures have been widely used in engineering, with PC beams serving as the primary load-bearing components in these structures. In this study, six PC beams and two cast-in-place reinforced concrete (RC) beams were designed and manufactured, and drop hammer impact tests were conducted. Additionally, static load tests were conducted on two corresponding PC and RC beams. The experimental study provided benchmark data examining the influence of varying drop hammer mass, impact velocity, and level of pre-damage on the dynamic response of the PC beams, including their failure mode, mid-span deflection, impact force, deflection recovery ratio, and deformation energy consumption. The experimental results confirmed the reliability of using pressure sleeve connection as the assembly and connection form of PC beams. Under equivalent energy conditions, an increase in impact mass simultaneously leads to a decrease in peak and residual deflection of PC beams. This reduction is accompanied by an increase in their average impact force. Under the same impact mass and velocity conditions, the peak deflection of beams exhibiting different degrees of damage exceeded that of undamaged beams, although their residual deflection was relatively lower. In addition, the deflection recovery rate of damaged beams is slightly higher than that of undamaged beams.

Shear behavior of reinforced concrete beams with high-strength reinforcements after high temperatures

This paper investigates the effect of steel reinforcement configured with different strengths after different high temperatures on the shear performance of the test beams, a total of 20 reinforced concrete (RC) beams, through experiments, numerical analyses and theoretical studies, in order to understand the key factors affecting the shear performance of the beams. The test revealed that the mechanical properties of concrete and steel reinforcement showed a trend of increasing and then decreasing after high temperatures. Increasing the stirrup ratio and stirrup strength can significantly improve the crack resistance and shear capacity of the beams, as well as the deformation performance of the beams. The residual shear strengths of test beams with high-strength stirrups after exposure to high temperatures are significantly greater than those of ordinary reinforced concrete beams. Specifically, the shear capacity of beams with high-strength stirrups after exposure to 800°C increased by 23.7 % compared to ordinary beams, and the mid-span deflection performance increased by 28.7 %. The stresses in the shear span region of the test beams after high temperature were more concentrated at the diagonal and the number of cracks was significantly reduced. In this paper, a simplified formula for calculating the residual shear capacity of RC beams after room and high temperatures is proposed, which can well predict the test results.

Flexural behavior of coral aggregate concrete beams reinforced with BFRP bars under seawater corrosion environments

The combined utilization of fiber-reinforced polymer (FRP) composites with coral aggregate concrete (CAC) in remote island areas contributes to the reduced construction cost and construction period, offering a promising application. However, the evolution pattern and deterioration mechanism of flexural behavior for FRP bars reinforced CAC beams in marine service environments remains unclear. Thus, this paper investigates the flexural behavior of basalt-FRP (BFRP) bars reinforced CAC beams under seawater immersion and dry-wet cycle conditions using laboratory-accelerated aging methods. The research considers the effects of exposure temperature and corrosion age on their failure modes, flexural stiffness, ultimate loading capacity, and deformation deflection. The experimental results revealed that with the increase in corrosion age and exposure temperature, the amount of vertical cracks of CAC beams decreased and their crack depth also exhibited a slight reduction, but their crack width and spacing at failure significantly increased. After being attacked by seawater environments, the load-deflection curves of CAC beams experienced an enhanced slope of the ascending section (i.e., flexural stiffness), but this strengthened flexural stiffness did not result in an enhancement in the ultimate load capacity. Instead, with prolonged corrosion and higher temperatures, the ultimate load of CAC beams displayed significant degradation, accompanied by reduced mid-span deflection. After 12 months of seawater exposure to wet-dry cycle conditions at 60 °C, the ultimate load and mid-span deflection of CAC beams degraded by approximately 25.0 % and 56.6 %, respectively. The study also predicted the flexural bearing capacity of CAC beams utilizing existing specifications for FRP-reinforced normal aggregate concrete (NAC). It was concluded that the formulae for flexural loading capacity for FRP-reinforced NAC beams were still suitable for CAC beams.

Flexural capacity design model of reinforced concrete beams strengthened with hybrid bonded CFRP

In order to improve the calculation methodology for the flexural capacity of RC (Reinforced Concrete) beams strengthened with HB-CFRP (Hybrid Bonded-Carbon Fiber Reinforced Polymer), three-point bending tests were conducted in this study. The experimental setup involved 9 HB-CFRP strengthened T-shaped beams and 1 unstrengthened beam for comparison. The effects of anchor spacing, anchor pressure, CFRP thickness, and anchor distribution pattern on the flexural performance of strengthened beams were investigated. Additionally, the development of the full range load-deflection curves of the HB-CFRP strengthened specimens was analyzed. Two bond strength models (the Wu model and Liu model) were modified. Six parameters were considered in the modified model, namely, the CFRP elastic modulus, CFRP thickness, number of mechanical fasteners in the shear span, CFRP-concrete width ratio, concrete cylinder compressive strength and normal pressure applied to the mechanical fasteners. The accuracy of the modified models was compared on the basis of three specifications. Results indicated a notable enhancement in the flexural capacity of the strengthened beams, ranging from 61.1 % to 158.1 % compared to the unstrengthened beam. Taking the ACI specification as an example, the mean value and coefficient of variation (COV) of the flexural capacity obtained by directly using the Wu model were 1.187 and 0.169, respectively; the results obtained by using the modified Wu model based on the measured FRP strain were 1.038 and 0.125, respectively; and the results obtained by using the modified Wu model based on the ACI reversed-calculated strain were 1.012 and 0.106, respectively. After the strengthened beam reached the peak load, the load then decreased abruptly to the vicinity of the moment mid-span deflection curve of the reference beam. As the loading continued, the resistance improved by 27.4 %∼79.3 % due to the increase in interface friction in the mechanical fasteners and concrete.

Effect of shear span-to-depth ratio on flexural and fracture behaviors of reinforced UHPMC beams based on four-point bending test and acoustic emission monitoring

Ultra-high performance manufactured sand concrete (UHPMC), using manufactured sand (MS) as aggregate, belongs to a brand-new ultra-high performance concrete (UHPC). Better understanding the failure behavior of UHPMC beams reinforced with steel reinforcement bars is crucial in structural design. This study investigates the effects of different shear span-to-depth ratios (λ = 1.2, 1.6 and 2.0) on the failure modes, mid-span deflection, concrete and rebar strain, flexural toughness, initial cracking load, ultimate load, energy dissipation capacity, and crack propagation patterns based on four-point bending tests for totally twelve reinforced UHPMC beams. Meanwhile, acoustic emission (AE) monitoring is used to evaluate corresponding fracture characteristics. Results reveal that an increase in shear span-to-depth ratio leads to a significant increase in mid-span strain and better ductility but lower equivalent stiffness. The maximum strain of specimen with λ = 1.2 is 24.8 % lower than that with λ = 2.0, and specimen with λ = 1.6 exhibits 22.3 % greater equivalent stiffness than that with λ = 2.0. Beams with larger shear span-to-depth ratios demonstrate superior ductility and energy absorption capacity, specimen with λ = 2.0 showing a ductility factor 2.85 times higher than that with λ = 1.2. The presence of MS significantly improves initial cracking load by 26.9 %, ultimate load by 4.5 %, and energy dissipation capacity by 37 %. MS also enhances toughness and delays crack propagation in the early stages. This effect can make the fracture transform into more rapid energy release in the later stages, indicating that MS could alter crack propagation patterns, forcing cracks to propagate along paths with greater resistance to crack propagation. These conclusions can offer insights for the safer and economical design and application of UHPMC beams, especially the balance among shear span-to-depth ratio, MS and mechanical performance in the environmentally friendly structures design and failure prevention process.

Construction control of rigid frame-continuous girder bridge based on grey theory

To address the issue of excessive mid-span deflection in rigid frame-continuous girder bridges during the later stages of normal use and to provide a basis for setting the pre-camber of this bridge type. This study focused on a specific rigid frame-continuous girder bridge. Based on the outcomes of finite element analysis, a GM(1,1) model developed using grey theory was utilized to forecast the vertical deflection of the primary girder in the construction phase of a rigid frame-continuous girder bridge, resulting in notable outcomes. The results suggest that the GM(1,1) model grounded in grey theory offers precise estimations of the vertical deflection of the primary girder during the prestressing tendon tensioning stage, displaying a minimal deviation of merely 1.73 mm compared to actual measurements. Consequently, applying the GM(1,1) model based on grey theory for projecting the vertical deflection of the primary girder in the construction process of rigid frame-continuous girder bridges can advance the accuracy of construction management. Through comparative analysis of measured values estimated values and theoretical values at the construction site, it is evident that the predictive model effectively controls the displacement, thus serving as a reference for construction control in similar projects.

Innovative demountable steel-timber composite (STC) beams: Experimental full-scale bending tests

This study introduces an innovative demountable steel-timber composite (STC) flooring system with potential for reuse. The flooring system consists of downstanding hot-rolled I-shaped steel profiles and laminated veneer lumber (LVL) slabs connected to the steel beams with novel shear connectors. This STC flooring system aimed at reducing embodied carbon and optimizing the use of resources, offer an alternative to traditional, carbon-intensive flooring systems. The novel shear connections implemented in the STC beams facilitate demountability, adaptability, reconfiguration, and relocation of structural components, aligning with circular economy principles. Moreover, this flooring system exhibits significant promise for modularization, standardization, and off-site serial production, making it ideal for prefabrication in standard sizes and modules. Two full-scale STC beams, each with a span of 10 m, an LVL slab width of 2.51 m and thickness of 144 mm connected to a steel profile IPE 400, were simply supported and tested in six-point bending to assess their flexural response. The two tested beams were identical in terms of geometry, materials, and shear connection distribution, but differed in the type of shear connection implemented. This contribution outlines the details of the innovative flooring system and the novel connections that enable demountability and reusability of the components. Specifics of the two STC beam specimens, their assembly, the test setup, the instrumentation, and the testing procedure are presented. The results of the two full-scale bending tests demonstrate their significant load-bearing and deformation capabilities as well as potential for reuse. Additionally, the results indicate the efficacy of the novel shear connections and the beams' overall structural integrity. Despite the extensive deformation of the STC beams, the shear connections remained undamaged and slip values of less than 7 mm were recorded in the last loading stages. Within the elastic range, maximum slip values of less than 1 mm were recorded, highlighting the structural components' potential for reuse. Midspan deflections exceeding l/20 demonstrate good ductility. Strain measurements on the timber slabs revealed that the slabs' width was not fully utilized, leading to the determination of an effective width of l/5.5.

Calculation of creep deformation of stiffness-degraded RC beams after strengthening with increased cross-section

The strengthening of existing reinforced concrete beams (RCBs) has mainly focused on short-term mechanical properties such as flexural resistance and shear resistance, while long-term deflection of RCBs has seldom been studied. In this study, six RCBs with different types and degrees of damage were designed and strengthened by the section enlargement method. Mid-span deflection and concrete strain were used to evaluate the influence of stiffness degradation due to fatigue or corrosion damage on the creep behavior of strengthened RCBs (SRCBs). The experiment results revealed that time-varying curves of creep deformation from fatigue or from corrosion-damaged SRCBs were consistent among the six specimens. Creep in a damaged SRCB was found to increase faster than that in an undamaged beam, and to reach over 90 % of final creep in about six months. Based on the mean curvature method and creep models, taking fatigue and corrosion damage as examples of stiffness degradation, a calculation method for creep deformation of SRCBs was established, and sensitivity analysis of stress levels, reinforcement height, consolidation time, and other parameters were carried out. The research results can provide a theoretical basis and guidance for evaluating creep deformation of stiffness-degraded RCBs after reinforcement with increased cross-section.

Nonlinear behavior of existing pre-tensioned concrete beams: Experimental study and finite element modeling with the constitutive Serial-Parallel rule of mixtures

The performance of existing prestressed concrete (PC) beams and their time-dependent behavior have been concerns for bridge maintenance services. In this paper, laboratory tests of three PC void slab beams taken away from an obsolete bridge were conducted and an alternative more efficient finite element (FE) method was developed. In preparing the three beam specimens, two retained their original reinforced concrete (RC) overlay and one chiseled off its RC overlay. Through the four-point loading tests, the load response plots of the beams from elastic to plastic failure were carefully documented, including the strains along the mid-span section, the strains of longitudinal rebars and strands, and the mid-span deflection. The test results showed that no interface slip was observed between the RC overlay and the top of void slab during the whole loading process, and the yield load of the test beams with the overlay was approximately 45 % higher than that without the overlay. Regarding the proposed nonlinear numerical formulation, the modelling process avoided the treatment of complex reinforcement and prestressing tendon layouts. The prestressed concrete was simulated as a composite material whose behavior is depicted by a constitutive serial-parallel rule of mixtures (SP-RoM). The generalized Maxwell model and generalized Kelvin model were applied to calculate the time-dependent losses of prestress. All the developments have been implemented within the open-source FE code Kratos-Multiphysics environment and are fully available. Compared with the test outcomes, it shows that the numerical results are in good agreement with the solutions in terms of stiffness, load-deflection curves, and damage evolution. The differences between the experimental and numerical values of ultimate load for the specimens with and without RC overlay were all within 10 %. Furthermore, the proposed nonlinear models can also predict the time-dependent prestress losses of existing PC beams.

Using Machine Learning Algorithms to Develop a Predictive Model for Computing the Maximum Deflection of Horizontally Curved Steel I-Beams

Horizontally curved steel I-beams exhibit a complicated mechanical response as they experience a combination of bending, shear, and torsion, which varies based on the geometry of the beam at hand. The behaviour of these beams is therefore quite difficult to predict, as they can fail due to either flexure, shear, torsion, lateral torsional buckling, or a combination of these types of failure. This therefore necessitates the usage of complicated nonlinear analyses in order to accurately model their behaviour. Currently, little guidance is provided by international design standards in consideration of the serviceability limit states of horizontally curved steel I-beams. In this research, an experimentally validated dataset was created and was used to train numerous machine learning (ML) algorithms for predicting the midspan deflection at failure as well as the failure load of numerous horizontally curved steel I-beams. According to the experimental and numerical investigation, the deep artificial neural network model was found to be the most accurate when used to predict the validation dataset, where a mean absolute error of 6.4 mm (16.20%) was observed. This accuracy far surpassed that of Castigliano’s second theorem, where the mean absolute error was found to be equal to 49.84 mm (126%). The deep artificial neural network was also capable of estimating the failure load with a mean absolute error of 30.43 kN (22.42%). This predictive model, which is the first of its kind in the international literature, can be used by professional engineers for the design of curved steel I-beams since it is currently the most accurate model ever developed.

Exploring flexural performance and abrasion resistance in recycled brick powder-based engineered geopolymer composites

BackgroundDue to growing global concerns regarding the management of construction waste, this study investigates the feasibility of creating engineered geopolymer composites by replacing traditional industrial by-products (slag) with construction waste, specifically recycled brick waste powder.ResultsPolyvinyl alcohol fibers were incorporated into the engineered geopolymer composite mixtures. The substitution of slag with recycled brick waste powder was carried out at varying percentages: 0, 20, 40, 60, 80, and 100%, resulting in six different engineered geopolymer composite mixtures. The study evaluated the flexural strength, sorptivity, water absorption, and abrasion resistance of the engineered geopolymer composites, and also, microstructural characterization was conducted using scanning electron microscopy. The findings demonstrated that incorporating recycled brick waste powder into the engineered geopolymer composite mixes resulted in a decrease in flexural strength by 35.59% and a notable increase in midspan deflection by 339% when slag was replaced. Concurrently, there was a significant rise in water absorption and sorptivity by approximately 304 and 214%, respectively, when slag was entirely substituted with recycled brick waste powder. Conversely, abrasion resistance decreased, with the inclusion of recycled brick waste powder resulting in an 84% increase in volume change. The scanning electron microscopy (SEM) analysis showed active geopolymerization of recycled brick waste powder within the engineered geopolymer composite mixtures.ConclusionsThe results of this investigation demonstrate that it is feasible to produce engineered geopolymer composites using recycled brick waste powder instead of slag. The greater ductility and increased midspan deflection point to areas that require further optimization, even in spite of the observed decreases in flexural strength and abrasion resistance. The SEM examination reveals an active geopolymerization, highlighting the potential of recycled brick waste powder to produce environmentally friendly and sustainable construction materials. These results offer a good starting point for further studies that try to maximize the durability and performance of these composites.

Experimental and numerical investigation on deck system of a 102 m simply supported prestressed UHPC box-girder highway bridge

To address two main challenges (excessive mid-span deflections and numerous cracks in the main girder) in long-span prestressed concrete (PC) box-girder bridges, this paper proposes a long-span simply-supported UHPC box-girder bridge. In comparison to conventional PC box-girder bridges with three-dimensional prestress, the proposed UHPC box-girder consists only one-dimensional (longitudinal) prestress, and the thickness of the bottom/top plate and web of the UHPC box-girder are relatively thin and are strengthened with dense diaphragms and stiffening ribs. The 4th Beijiang River Bridge adopts this type of bridge with a span of 102 m, which is the longest span simply supported prestressed UHPC box-girder highway bridge in the world. Considering the fact that the thickness of the top plate of the UHPC box-girder is relatively thin (only 20 cm) and the transverse prestress is removed from the top plate, thus, under the direct action of wheel loads, the risk of bridge deck cracking may correspondingly increase. To investigate the mechanical behavior of the deck system of UHPC box-girder bridges, a 1:2 scaled experimental specimen associated with the field bridge is tested. The mechanical behavior of the new deck system is investigated and discussed. It is found that because the support strength of the stiffening rib is significantly weaker than that of the web, the UHPC deck slab should still be regarded as a two-way slab rather than a one-way slab in the elastic stage. In addition, although the test load location is unfavorable to the UHPC deck slab and the first crack appears on the UHPC deck slab, this deck system finally suffers from bending failure of the transverse rib. Furthermore, finite element analysis is carried out to study the mechanical behavior of this new deck system. Parametric analysis considers some factors including the reinforcement ratio in the transverse rib, the height of the transverse rib, and the space between transverse ribs. The results provide a good reference for design and optimization in the new deck system of UHPC box-girder bridges.

Topology-optimized lattice enhanced cementitious composites

In this work, the topology-optimized lattices structures were designed to serve as ductile nylon reinforcements in lattice-enhanced cementitious composites. The mechanical behavior of the prepared composites was examined via a flexural test where the strength and mid-span deflection were especially concerned. The digital image correlation (DIC) approach was employed to monitor and evaluate the failure pattern and strain distribution. Further investigation was conducted on the mechanical effects of two major optimization factors in the lattice design process, namely cell size and optimization volume fracture. Finally, the improved ductile performance of the suggested composites was compared to that of prior works. The results indicated that the proposed topology-optimized lattices significantly promote the mechanical performance of the prepared composites, i.e., strength and ductility. It may present a higher ductility enhancement efficiency than homogenous lattices under an identical volume. The cell size of lattices is inversely related to the enhancing effects, and more extensive optimization volume fracture enhances composite strength and ductility. Compared with previous works, this study gained advancement in terms of printing materials, unit topology, and cement types. The topology-optimized lattice generally provides a novel solution to the ductility enhancement effect, providing both superior performance and greater design flexibility.

Monitoring and Analysis of Prestress Loss in Prestressed Box Girder Bridges Strengthened with External Prestressing.

To investigate the effects of long-term prestress loss on concrete box girders strengthened with external prestressing, a large-span box girder, in service for over 20 years and strengthened with external prestressing, was monitored for four months. Prestress loss in the longitudinal, vertical, and transverse directions of the box girder was calculated according to Chinese code requirements. Magnetic flux rope force transducers were used to monitor the prestress loss in the external prestressing cables. Fiber Bragg Grating (FBG) sensors were used to monitor deflection changes at the mid-span of the bridge. Finally, the effect of prestress loss in the longitudinal, vertical, and transverse tendons on mid-span deflection was investigated through simulations using ABAQUS software. The results show that instantaneous prestress loss accounts for most of the total loss compared to long-term loss, and that longitudinal prestress loss has the most significant effect on mid-span deflection. The impact of longitudinal prestress loss on deflection before and after strengthening was also compared. The downward deflection and up-ward arch caused by longitudinal tendon prestress loss were reduced after strengthening, con-firming the effectiveness of the external prestressing method.

Shear behavior of seawater sea-sand concrete beams reinforced with BFRP bars after seawater dry-wet cycling

The shear behavior of 27 basalt fiber-reinforced polymer reinforced seawater sea-sand concrete (BFRP-SSC) beams after seawater dry-wet cycling was comprehensively investigated. Parameters considered included stirrup diameter and spacing, shear span-to-depth ratio, stirrup surface treatment, cycling duration, concrete cover thickness, and seawater temperature. Results indicate that seawater dry-wet cycling increases cracking load and decreases bending stiffness in BFRP-SSC beams. Increasing shear span-to-depth ratio from 1.55 to 2.35 led to load reductions of 31.3 % and 49.7 % at 6.5 mm mid-span deflection. Seawater dry-wet cycling, particularly temperature and duration, significantly impacts the mechanical properties of stirrups. This results in diminished shear contribution and reduced efficacy in inhibiting diagonal crack propagation, leading to a shift in beam failure mode from diagonal compression failure to shear compression failure and diagonal tension failure. Increasing cycling duration from 60 to 120 days decreased tensile strength retention by 19.1 % and 33.3 % respectively. Based on experimental data, Arrhenius theory, and the time shift factor (TSF) method, a predictive model was developed for the shear capacity retention of beams subjected to seawater dry-wet cycling. Results indicate that after 100 years in a tidal environment (70 % and 90 % relative humidity), shear capacity damage factors of 0.77 and 0.52, respectively, can be applied to account for the impact of seawater dry-wet cycling on the shear capacity of BFRP-SSC beams.

Leveraging clay formwork 3D printing for reinforced concrete construction

ABSTRACT Robotic clay formwork three-dimensional printing combined with incremental concrete casting controls concrete's hydrostatic pressure and enables the production of building-scale structures. Clay formwork is self-demolding and less carbon intensive than concrete and polymer, often used in formwork additive manufacturing. This research investigates the recycling and reuse of clay to re-print formworks and tailors a self-compacting concrete formula with 60% reduced cement content and 90% larger maximum aggregate size. The study then explores integrating steel fibers and longitudinal rebars into the fabrication process to provide shear and bending reinforcement. When comparing the load-bearing behaviour of the fabricated beams against those cast traditionally using wooden formworks, the fabricated beams demonstrated 20% lower load-bearing capacity, with peak load mid-span deflections staying in a similar range. While more investigation is required to address formwork deformations using mixed steel fibers and recycled clay, this research paves the way for more sustainable concrete construction practices.