Prestress Level Research Articles

Study on the performance of cast-in-situ concrete wet joints in PCSBs under cyclic loading

The closure section of precast concrete segmental bridges (PCSBs) usually adopts the wet joint, the regular longitudinal reinforcement is discontinuous, which makes the section the vulnerable part. To study the performance of the wet joint in the closure section under cyclic loading, six specimens considering loading mode, interface treatment method, setting of regular reinforcement and prestressing are tested. Results show that the damage of the wet joint accumulates and the plasticity develops under cyclic loading, the specimens undergo residual deformation, strength attenuation and stiffness degradation. Increase in prestressing level can delay the cracking, the cracking load of specimens with a prestressing level of 8MPa and 10MPa is 21.9% and 32.8% respectively higher than that of the specimen with a stress level of 6MPa, and the results also confirm that excessive prestressing level cannot significantly improve the shear strength of the specimens. When the controlled displacement is small, the residual deformation of the specimen is small and the strength attenuates slowly; with the increase in controlled displacement, the residual deformation of the specimen increases and speeds up, the strength decreases continuously, and the development of the crack tends to be stable, leading to the leveling off of degradation of the stiffness.

Analytical model for RC beams with embedded prestressed Fe-SMAs

Prestressed iron-based shape memory alloy (Fe-SMA) strengthening is an effective means to enhance the performance of reinforced concrete (RC) structures. The applied prestress level significantly influences the strengthening efficiency. However, the absence of a reliable model predicting the applied prestress hinders the efficient design of prestressed Fe-SMA strengthening solutions. To fill this gap, the current study proposes an analytical model, with which a constant zone and a transfer zone are identified in strengthened RC beams. The constant zone, with zero interfacial shear stress, sustains a constant prestress level, while the transfer zone, experiencing non-zero shear stress, gradually reduces the Fe-SMA tensile stress from the prestress level to zero. Validated through experiments, the proposed model accurately predicts the applied prestress levels and prestress-induced deflections in RC beams strengthened with Fe-SMAs and more conventional carbon fiber reinforced polymers (CFRPs). Further analysis reveals that the transfer zone length ranges from 4 to 7 characteristic lengths, and it is proportional to the logarithm of the applied prestress level. Simplifying a constant prestress level within the beam span yields sufficiently accurate prestress analysis.

Threshold Voltage Recovery Time Measurement Technique Post VTH Instability in Normally-Off p-Gate GaN High Electron Mobility Transistors

In this study, we propose a simple measurement technique to quantitatively measure the time taken by threshold voltage of normally-off p-GaN AlGaN/GaN HEMTs to recover from a nominal operational gate stress-induced instability. The proposed technique eliminates the requirement to perform a full transfer characteristic sweep post-stress, thereby eliminating the measurement-induced instability effect, often colluding precise recovery time measurement. The rate of recovery and extracted recovery times hold significance in empirically correlating the location of traps in the p-GaN or AlGaN barrier region causing VTH instability. The gate of the HEMT is stressed at nominal operational drive voltages 1.5 V, 2 V, and 4 V for various time intervals from 500 μs to 100 s, and the time taken for the drain current to recover to prestress levels measured at near-threshold voltage (~1.1 VTH) is measured as the threshold voltage recovery time. With increasing gate stress voltages, 2DEG gets trapped at relatively deeper trap energy levels at the AlGaN/GaN interface requiring more emission time during the process of recovery, mandating larger recovery times. At higher stress voltage of 4 V, the Schottky gate leakage current is high enough enabling injected holes to cross the AlGaN barrier and counter-compensate for the deeply trapped 2DEG, requiring relatively the same recovery times as lower stress voltages where the gate leakage is negligibly small. With increasing stress time, the amount of 2DEG trapped increases, requiring more recovery time to de-trap and beyond a certain time, saturation of the trap density occurs causing the recovery time to plateau.

Experimental characterization of indented dry connections for precast double‐curved concrete shells

AbstractThis paper presents the experimental validation of a connections system to connect segmented precast long‐span thin‐shell structures made with lightweight ultra‐high‐performance fiber‐reinforced concrete (UHPFRC). The work comprises the segmentation of the large‐span ultra‐thin shell to meet the requirements of prefabrication (construction and transport limitations), and the design and characterization of the connections. Once the assembling of the shell required the use of post‐tensioned unbonded prestressing, an indented dry connection was chosen. The connections are experimentally characterized with in‐plane and out‐of‐plane shear tests for different prestressing levels. The results are presented and discussed, demonstrating the balanced behavior of the indented dry connection under shear loading. The connections exhibited high ductility in shear, capitalizing on the use of a UHPFRC to fabricate the shell. The prestressing also demonstrated its efficacy, significantly enhancing both the stiffness and the capacity of the indented dry connection.

Stability Conditions and Stiffness Variability of General Tensegrity Systems with Kinematic Joints

Abstract Tensegrity systems represent promising candidate mechanisms with in-situ stiffness variability through changing the cables' prestress levels. However, prestress-based stiffness behaviors of tensegrity systems with arbitrary kinematic joints have not been analyzed systematically. This paper adopts the natural absolute coordinates for static modeling of tensegrity systems consisting of rigid members and tension elements. Then, a generic stiffness analysis method is developed to formulate the reduced-basis tangent stiffness matrix, which is found to include three parts: positive semi-definite material and geometric stiffness matrices, and an indefinite constraint stiffness matrix. Based on these findings, a systematic stability-checking procedure is derived to determine prestress and super stability, which are qualitative indicators of the softening and stiffening effects in different tensegrity systems. Then, we proceed to quantify the range of prestress-based stiffness variability by formulating semidefinite programming problems that numerically pinpoint the maximum and zero stiffness points. Furthermore, this paper reveals the composable nature of multiple self-stress states, enabling the composability of stiffness properties in mechanism designs. Several numerical examples verify the efficacy and versatility of the proposed method and demonstrate interesting stiffness behaviors of tensegrity systems with kinematic joints.

Vascular endothelial cell morphology and alignment regulate VEGF-induced endothelial nitric oxide synthase activation.

Nitric oxide (NO) production by endothelial nitric oxide synthase (eNOS) inhibits platelet and leukocyte adhesion while promoting vasorelaxation in smooth muscle cells. Dysfunctional regulation of eNOS is a hallmark of various vascular pathologies, notably atherosclerosis, often associated with areas of low shear stress on endothelial cells (ECs). While the link between EC morphology and local hemodynamics is acknowledged, the specific impact of EC morphology on eNOS regulation remains unclear. Morphological differences between elongated, aligned ECs and polygonal, randomly oriented ECs correspond to variations in focal adhesion and cytoskeletal organization, suggesting differing levels of cytoskeletal prestress. However, the functional outcomes of cytoskeletal prestress, particularly in the absence of shear stress, are not extensively studied in ECs. Some evidence suggests that elongated ECs exhibit decreased immunogenicity and enhanced NO production. This study aims to elucidate the signaling pathways governing VEGF-stimulated eNOS regulation in the aligned EC phenotype characterized by elongated and aligned cells within a monolayer. Using anisotropic topographic cues, bovine aortic endothelial cells (BAECs) were elongated and aligned, followed by VEGF treatment in the presence or absence of cytoskeletal tension inhibitors. Phosphorylation of eNOS ser1179, AKT ser437 and FAK Tyr397 in response to VEGF challenge were significantly heightened in aligned ECs compared to unaligned ECs. Moreover this response proved to be robustly tied to cytoskeletal tension as evinced by the abrogation of responses in the presence of the myosin II ATPase inhibitor, blebbistatin. Notably, this work demonstrates for the first time the reliance on FAK phosphorylation in VEGF-mediated eNOS activation and the comparatively greater contribution of the cytoskeletal machinery in propagating VEGF-eNOS signaling in aligned and elongated ECs. This research underscores the importance of utilizing appropriate vascular models in drug development and sheds light on potential mechanisms underlying vascular function and pathology that can help inform vascular graft design.

Axial stress-strain behavior of pre-stressed CFRP confined concrete columns

Bonded carbon fiber reinforced polymer (CFRP) confined concrete presents issues such as stress hysteresis and easy detachment at the interface between CFRP and concrete. Applying prestress to CFRP can improve this situation. To investigate the stress-strain behavior of prestressed CFRP strengthened plain concrete columns (PC) under axial compression, a total of 1 unreinforced concrete column, 9 bonded CFRP strengthened concrete columns, and 27 prestressed CFRP strengthened concrete columns were designed. Including CFRP layers and the level of prestress were taken as the study factors, and axial compression tests were conducted on each specimen to analyze their axial compression performance. The test results indicated that applying prestress to CFRP results in the core concrete being constantly subjected to triaxial compression, with initial transverse compressive strain and longitudinal tensile strain, thereby increasing the initial stiffness of the core concrete. In contrast to bonded CFRP-strengthened columns, the ultimate axial stress, ultimate axial strain, and initial stiffness of prestressed CFRP-strengthened columns increased with the level of CFRP prestress, with a more pronounced improvement observed in columns wrapped with a higher number of layers of CFRP. For a 4-layer CFRP strengthened column prestressed at 0.3, the ultimate axial stress and ultimate axial strain increased by up to 13 % and 20 %, respectively, compared to bonded 4-layer CFRP strengthened columns, with the initial stiffness increasing by up to 30 %. On the other hand, applying prestress to CFRP can significantly enhance the effective utilization of CFRP, but it is negatively correlated with the number of CFRP layers. Compared to bonded 1-layer CFRP strengthened columns, the effective utilization rate increased from 0.63 to 0.91, a 44 % increase, when prestressing CFRP at 0.3. Finally, based on existing relevant research, a peak stress and strain model considering the ratio of confinement stiffness to strain ratio was proposed. Based on the fundamental assumptions of curve analysis, the design-oriented axial stress-strain model suitable for prestressed CFRP strengthened concrete columns was established, with good match between theoretical and experimental curves.

Influence of the Initial Prestress Level on the Distribution of Regions of Dynamic Instability of Geiger Domes

This paper provides a parametric analysis of cable–strut tensegrity domes subjected to periodic loads. This analysis aims at determining the main regions of dynamic instability (unstable regions). From the point of view of the physical interpretation of the phenomenon, if the load occurs in these regions, the amplitudes of the resulting vibrations increase, posing a risk to the durability of the structures. The consideration includes cable–strut structures called Geiger domes. Four dome design solutions known from the literature are compared, i.e., regular (patented by Geiger) and modified domes with a closed and an open upper section. In contrast to conventional cable–strut structures, Geiger domes are characterized by a self-equilibrated system of internal forces (initial prestress), which affects the shape and range of unstable regions. The main purpose is to answer the question as to which type of design solution is more sensitive to the risk of excitation vibrations. A nondimensional parameter λ is introduced for this quantitative assessment. This parameter reliably determines the change in the area of unstable regions as the initial prestress level increases. The range of the parameter λ is defined as a value between 1 and 0. In the case of λ=1, there is potential for the excitation of unstable motion, whereas in the case of λ=0, such a risk is absent. The analysis presented in this paper can be employed in the process of optimizing the initial prestress level, which will constitute the subsequent stage of this research. A geometrically non-linear model is used to evaluate the behavior of the considered structures.

Fast fracture in toughened glass when impacted randomly by Ice

Modelling the triggering of fracture at a pre-existing flaw is an evolving method of predicting ultimate failure in glass. This fracture mechanics approach of modelling has been shown to give more reliable predictions than a calibrated probabilistic distribution model (as is commonly adopted) when dealing with hail impact which is highly transient in nature. The dynamic stress intensity factor controlling fast crack growth is sensitive to the complex stress state surrounding the critical flaw. Finite element simulations of localised stresses in 3D could incur high computation cost which is compounded by the need to repeat computations until convergence and to simulate multiple strikes in emulating a storm scenario. In this study, closed-form expressions were developed to waive away the need of any simulations. With hail impact, boundary conditions of the glass panel need not be factored into the modelling, as the highly transient stresses are wave controlled. Input parameters are the thickness and level of prestress in glass; offset of position of strike from the known crack and its depth; and the size, velocity, and temperature of the ice impactor. Results from 40 test scenarios involving 5 offset distances, 3 crack depths, 2 glass thicknesses, and 2 sizes of ice were used to validate the prediction, and to reveal the sensitivity of the outcome of the impact to changes in the impact position relative to the known crack.

An experimental analysis of dynamic deformation and settlement resistance in a novel prestressed railway subgrade

ABSTRACT The dynamic deformation characteristics of track-subgrade systems under moving train loads provide valuable insights for vibration and serviceability assessment of the track-subgrade. This study developed three 1:5 scale track-subgrade models incorporating the novel prestressed subgrade structure and conducted two series of dynamic tests to examine how the heavy-haul train axle loads and prestress levels affected the track-subgrade dynamic deformation. The primary frequency of the subgrade dynamic displacement was observed closely aligned with the input loading frequency of 2 Hz, indicating the validity of the test setup. The track-subgrade dynamic displacement decreased with increasing distance from the loading source, of which the elastic deformation near the subgrade shoulder attenuated by approximately 79% compared to that at the sleeper end. The elastic deformation at the monitoring points approximately linearly increased with the axle load at rates ranging from 0.0018 to 0.0029 mm/t. Conversely, increasing prestress reduced the track-subgrade elastic deformation with average rates of 22.8 and 1.63 μm/100 kPa at the sleeper end and subgrade shoulder, respectively. Furthermore, application of prestress enhanced the track stiffness, with the equivalent track stiffness rising by 16.3% and 17.7% when the prestress increased from 0 to 50 kPa and from 50 to 100 kPa, respectively. The study also showed that the prestressed reinforcement structures could significantly mitigate the cumulative track-subgrade settlement over 60%, comparing the prestressed subgrade with 50 kPa prestress to the unreinforced subgrade, which highlighted the superior deformation resistance of prestressed subgrades under the train loads.

Predictive Analysis of Corrosion Dynamics in Prestressed Concrete Exposed to Chloride Environments

This study investigates the corrosion behavior of 5 mm diameter prestressed wires in concrete beams under chloride attack, a prevalent issue for coastal infrastructure. The study simulated aggressive chloride environments to understand their impact on structural integrity and service life. Utilizing a combination of advanced digital image correlation (DIC) techniques and a novel machine learning-based predictive model, the research provides a nuanced analysis of the interplay between stress levels, corrosion rates, and concrete strength. Empirical findings reveal a significant correlation between increased prestress levels and accelerated corrosion, indicating a crucial consideration for the design and maintenance of prestressed concrete structures. Notably, this study found that beams with a 95% prestress level exhibited a corrosion rate of 0.64 mm/year, significantly higher than the 0.37 mm/year for non-prestressed beams. The predictive model’s accuracy was validated with a mean squared error of 0.517 and an R2 value of 0.905, offering a valuable tool for quantifying the impact of corrosion. Therefore, the predictive model is a valuable tool for quantifying the impact of corrosion, enhancing the ability to assess and improve the durability of such infrastructure. This study’s insights highlight the necessity for a balanced approach to design and regular monitoring, especially in chloride-rich environments. By helping to develop more resilient construction practices and contributing to sustainable development goals, this study can significantly impact the safety and service life of coastal bridges and structures, aligning with global efforts to create more sustainable and durable infrastructure.

Experimental investigation of the effective parameters on the lead extrusion damper performance

Lead extrusion dampers (LED) are employed for seismic response control of various structures due to their advantages over other energy-dissipative devices. However, a reliable design algorithm and an optimization process are essential to ensure optimal performance within the host structural system. Thus, the influence of device parameters on the damper behavior must be clearly understood. In the first part of this comprehensive study, the effect of different parameters on the LED performance was experimentally investigated. To this end, 23 specimens with different prestressing levels, bulge-to-shaft diameter ratios, shaft-to-bulge transition zone geometries, and device length ratios were cyclically tested under varying displacement amplitudes, i.e., 5 mm, 10 mm, and 20 mm, and loading rates, 0.5 mm/s, 1.0 mm/s, and 2.0 mm/s. Subsequently, they were exposed to a ramp-type loading up to the amplified design displacement. After satisfactorily completing the experimental tests, the behavior of the LEDs was compared in terms of their hysteretic behavior, energy dissipation capacities, temperature change, and stable behavior. It was concluded that the most influential parameters on the LED behavior were the bulge-to-shaft diameter ratio and the prestressing level on the lead. In addition to its effects on improving the hysteretic behavior, having a smooth shaft-to-bulge transition zone geometry was essential to guarantee a stable damper behavior.

Flexural performance of the negative moment region in bonded steel-wire-rope-strengthened reinforced concrete T-beams at different prestressing levels

This work examines the performance of reinforced concrete (RC) beams strengthened using bonded steel wire rope (SWR) at various prestressing levels. The strengthening approach has, however, been applied to the flexural strengthening of RC T-beams in the negative moment region, in order to determine its advantages. For this purpose, four RC T-beams were fabricated and tested under monotonic four-point bending: one control beam (S00), one beam strengthened with non-prestressed SWR (S20), and two beams strengthened with SWR (prestressed at 10% and 20% of their ultimate tensile strength: S21 and S22). The results indicate that the strengthened beams exhibit higher load-carrying capacities. Specifically, the cracking load, yield load, and ultimate load of S20, S21, and S22 increase by 10%–30%, 30%–50%, and 50%–90%, respectively, compared to S00. Additionally, there is an improvement in stiffness and energy absorption capacity. However, these strategies may have a dual effect on the specimens, resulting in a reduction in their ductility index. Finally, the tested beams were replicated using a three-dimensional finite element model, which has proved effective in predicting the behavior of such structures and, therefore, was found to be appropriate for use in future studies.

Horizontal shear behavior of self-compacting lightweight concrete composite beams with dry joints and unbonded reinforcements

This study aims to investigate the horizontal shear behavior of self-compacting lightweight concrete (SCLC) composite beams with dry joints and unbonded transverse reinforcement. For this, the experimental program included different concrete types, joints configurations, and the use of unbonded high-strength bars with varying levels of prestressing and transverse reinforcement ratios in composite beams. Two precast beams were fabricated using a match-cast method and integrated horizontally to form composite beams, utilizing unbonded transverse reinforcements. The composite beams incorporating lightweight aggregates (LWA) instead of normal weight aggregates (NWA) exhibited a decreased ultimate shear strength of 19.5 %; however, the addition of steel fibers into the mixtures mitigated this decrease, resulting in a 22.8 % increase in strength compared to mixture without steel fibers. The vertical prestressing level significantly influenced the horizontal shear behavior and failure mode of composite beams, with adequately prestressed composite beams exhibiting similar ductile behaviors to the monolithic beam. Composite beams with keyed joints exhibited higher horizontal shear strength, up to 65.3 % more than the beam with flat joint, attributed to the interlock provided by the shear keys. Increased slip between two precast beams activated the dowel action of unbonded reinforcements, effectively resisting horizontal shear. Predictions of the horizontal shear strength, as per current codes, were compared to the experimental results. The results indicate that the design approach in Eurocode 2 provides reasonable estimations of the strengths of composite beams with dry joints and unbonded reinforcements.

Study on the influence of wedge-shaped steel plate hoops and steel strands wire mesh-PCM on seismic performance of damaged RC columns

This paper presents an experimental investigation on the use of polymer cement mortar (PCM) and steel strands wire mesh (SSWM) for strengthening damaged reinforced concrete (RC) columns. A new type of anchor device, wedge-shaped steel plate hoops (WSSPHs), was developed to maximize the resistance of the steel strands. The study aimed to analyze the impact of spacing and prestressing level on the mechanical properties of the damaged RC columns. Six columns were constructed and tested under low-cycle reciprocating quasi-static tests, including three control columns and three strengthened columns. The research focuses on the strengthening mechanism of WSSPHs and explores the influence of steel strand prestressing level and spacing on factors such as failure modes, hysteresis behavior, stiffness degradation, and cumulative energy dissipation of the strengthened columns. The test results showed that while the strength and stiffness of the strengthened specimens were not fully restored due to significant damage, the ductility and energy dissipation of the columns were improved. Moreover, columns with higher steel strand prestressing levels and narrower spacing demonstrated better strengthening effects. The study assessed the level of damage in specimens using the Park-Ang model, confirming the effectiveness of the proposed strengthening method.

Flexural strengthening of RC beams using PGFRP bars embedded in strain-hardening cementitious composites (SHCC)

The application of the near surface mounted (NSM) fiber reinforced polymer (FRP) as an additional reinforcement at tension side of flexural members is efficient to upgrade the flexural strength. However, this technique must be applied to concrete beams having hard concrete cover to avoid premature failure induced by concrete cover deterioration. The current research aims to improve and evaluate the flexural behavior of reinforced concrete (RC) beams strengthened with embedded prestressed glass fiber reinforced polymer (PGFRP) bars, based on replacement of weak concrete cover with a layer of strain hardening cementitious composites (SHCC). For this investigation, one reference beam (without strengthening) and nine flexural strengthened beams were tested under a four-point bending scheme. All beams had the same reinforcement and geometry, 150 mm width, 300 mm total depth, a total length of 3000 mm and the effective span was 2700 mm. The test parameters were: (1) the strengthening technique (conventional NSM-PGFRP bars, NSM-PGFRP bars covered with external SHCC layer and PGFRP bars embedded in SHCC replaced cover), (2) the prestressing levels in the GFRP bars (0, 10 % and 20 % of the ultimate bar strength) and (3) the thickness of the SHCC layer (30, 40 and 50 mm). Compared to the conventional NSM strengthened beams, the conjunction of SHCC with PGFRP bars not only prevented the spalling of the concrete cover but also increased the load carrying capacity up to 26.5 % and the ductility up to 16 %. A model for the prediction of flexural capacity of the strengthened beams having SHCC replaced cover was conducted, the predicted ultimate loads have a good consistency with the test results.

Impact of psychosocial stress on facial emotion recognition in schizophrenia and controls: an experimental study in a forensic sample.

Psychotic disorders have been associated with dysregulated stress reactions and adaptation. Little is known about the neuroendocrine responses to psychosocial stress in justice-involved individuals with schizophrenia. Using an experimental research design, the present study aims to examine differences in the subjective and neuroendocrine responses to psychosocial stress and its impact on facial emotion recognition (FER) and performance on an arithmetic task in chronically ill justice-involved individuals with schizophrenia (PAT) and a healthy control group. PAT undergoing treatment in forensic psychiatric inpatient wards (n = 17) and a healthy control group (n = 17) were assessed regarding sociodemographic and clinical characteristics. Additionally, salivary cortisol levels, measured before and after performing a psychosocial stress task [Montreal Imaging Stress Task (MIST)], and performance on an arithmetic problem-solving task and two FER tasks were recorded. Two participants dropped out, one from each group. Therefore, the final sample consisted of 32 individuals. Significant group differences in FER were recorded. There was a significant rise in subjective perception of momentary strain relating to the induction of psychosocial stress in both groups. Notably, the pre-stress level of subjective strain was higher in the PAT group than controls. Acute psychosocial stress induced an increase in FER performance in a sub-task related to naming emotions in individuals with schizophrenia spectrum disorder. The results underline the importance of psychosocial and therapeutic interventions aimed at strengthening stress resilience in individuals with schizophrenia spectrum disorders.

Bond behaviour of prestressed basalt textile reinforced concrete

Innovative Textile Reinforced Concrete (TRC) composites, although holding a significant potential, usually have poor performance under serviceability conditions. Addressing this limitation requires applying innovative techniques, such as prestressing, to utilise its potential fully. However, successful design and application of prestressing require a comprehensive understanding of the prestressing effect across scales, including the textile-to-matrix bond behaviour. To address this need, this study investigated the influence of key parameters such as prestressing level, prestressing release time and matrix age on the bond behaviour of basalt textile reinforcement. Test results show a significant influence of prestressing level and release time on textile-matrix bond behaviour. A 1-day prestressing release time resulted in a 25 % increased stiffness with only a 5 % peak load reduction followed by a further 13.7 % increase in the pull-out energy when the prestressing level was 13 %. At 35 % prestress level, 1-day released samples showed a significant reduction of 48.4 % in the peak load and 76 % reduction in the debonding energy. The positive effect of prestressing on the bond behaviour became more evident at prolonged release durations. The 7-day release samples showed a 17.4 % increase in the peak load at both prestress levels. Meanwhile, at 35 % prestress level, 34 % further increase in the debonding energy was observed. The obtained data are then utilised for providing indications on the effect of prestressing on saturated crack spacing of TRC components.

Fatigue performance simulation of reinforced concrete beams externally strengthened with side bonded CFRP sheets

Damaged Reinforced Concrete (RC) beams are commonly strengthened by bonding Carbon Fiber Reinforced Polymer (CFRP) strips to their soffits. However, inaccessible or narrow soffits limit the use of bottom-bonded CFRP strips. The Side Bonded (SB) CFRP technique overcomes this, yet studies on SB-CFRP-reinforced beams' fatigue behavior are limited. This paper presents a Finite Element (FE) model for simulating the fatigue behavior of RC beams externally strengthened with SB-CFRP sheets. The model incorporates cyclic-dependent CFRP-concrete interface degradation. Existing experimental results are utilized to validate its accuracy. Computational analyses are undertaken to explore the effects of CFRP dimensions, load and prestress levels, and end-U-shaped wrapping on fatigue performance. A simple model is proposed to predict fatigue life considering load and prestress levels. The FE model effectively predicts fatigue performance. Parametric studies indicate that narrow CFRP strips are unable to prevent concrete failure under high loads. Fatigue failure modes include rebar ruptures and CFRP delamination. Besides, the end-U-shaped wrapping reduces interface damage, extending fatigue life. The study emphasizes the sensitivity of vibration excitation method to CFRP debonding. The proposed equation efficiently predicts the fatigue life of RC beams with externally bonded CFRP strips on their sides.

Experimental and numerical investigations on flexural behavior of stress-laminated timber-concrete composite decks with butt joints

Stress-laminated timber (SLT) products are increasingly used in the field of timber bridges. However, existing butt joints and significant vibrations of SLT greatly hinder its application. Allying a concrete slab on the top of an SLT deck to form a composite structure can effectively ameliorate these deficiencies. In this study, the flexural behavior of SLT-concrete composite decks (SCCD) was investigated via four-point bending tests. The test parameters include prestress level, butt joint frequency, and concrete slab thickness. Comparative analysis against the SLT deck revealed substantial improvements in the load-carrying capacity and initial bending stiffness of SCCD, with increases of 30.2 % and 86.2 %, respectively. Additionally, the improvement is more significant when the concrete slab thickness increases. The presence of butt joints reduces the structural performance of SCCD, and its stiffness reduction degree is slightly greater than that of the SLT deck at the same butt joint frequency. Furthermore, a finite element (FE) model for the SCCD was established, and the numerical simulation showed good agreement with the test results in terms of failure modes and bending performance. Finally, the bending stiffness reduction coefficient for the SCCD was recommended by considering various butt joint frequencies based on tests and numerical simulations, which can serve as a reference for practical engineering.