Stiffness Load Research Articles

Parameter identification procedure for hysteretic shear-resistant properties of beech wood dowels

To evaluate the shear-resistant behavior of wooden dowels used in Blockhaus shear walls under cyclic load, 19 specimens under ten groups of conditions were prepared and tested. The failure modes, hysteresis curves, mechanical properties, stiffness degradations, and energy dissipation capacities of the specimens were studied. The test results showed that with the increase in the number of dowels, the initial stiffness and peak load of the specimens increased greatly. The diameter of the dowels had little influence on the mechanical properties of the specimens. Furthermore, the test findings demonstrated that the pretension load between the walls greatly enhanced the initial stiffness and energy dissipation capacity of specimens. A simplified finite element model was established in Opensees. Considering the effect of material variability, the parameters of single dowel shear spring and friction spring were identified by Genetic Algorithm with modified objective function in Matlab. The identified parameters were applied to the finite element model of the multi-dowel specimens. The simulation results were in good agreement with the test results, and the validity of the numerical model and parameter identification method was verified.

Study of the Static Characteristics of Gas-Lubricated Thrust Bearings Using Analytical and Finite Element Methods

A study was conducted to develop a porous aerostatic rectangular thrust bearing model, with the aim of assessing how different operational conditions and geometric factors influence its static capabilities. Initially, the Reynolds equation was analytically solved. Subsequently, simulations were performed on the rectangular air bearing model. Analyzing the impact of throttle hole configurations, air film thickness, orifice size, and supply pressure revealed their significant effect on the bearing’s load capacity, air consumption, peak airflow speed in the air film gap, and rigidity. Experimental validations were further conducted on manufactured bearings, corroborating the theoretical findings. It was observed that extending the length of the rectangular throttle hole array progressively increases gas consumption and diminishes stability, while the load capacity and stiffness initially surge then taper off. A thinner air film enhances load capacity and reduces gas flow, contributing to increased stability. Conversely, enlarging the orifice diameter boosts both load capacity and stability but escalates mass flow and diminishes stiffness. Elevating gas supply pressure enhances load capacity, flow rate, and stiffness, albeit at the cost of reduced stability. A comparative analysis among experimental data, finite element analysis, and analytical solutions showed strong congruence, affirming the precision of the latter two methods for predicting the bearing’s performance. This investigation aids with refining bearing design for precision devices and offers insights to enhance bearing efficiency and lifespan and to reduce friction and wear. Given its lower computational demands, the analytical approach provides a rapid means to assess static characteristics, underscoring its utility alongside finite element techniques for optimizing aerostatic bearing parameters.

3D Textile Reinforced Cement (TRC) composites with integrated synthetic microfibres: Evaluation of mechanical response and crack formation in bending

This study explores the integration of short synthetic microfibres into 3D Textile Reinforced Cement (3D TRC) composites to achieve enhanced flexural capacity and improved crack control. The homogeneous distribution of microfibres within 3D TRCs was a challenge unaddressed in the current state of the art. The influence of the added microfibres on the bending behaviour and crack formation of the 3D TRCs was evaluated, along with the effect of crucial parameters such as the microfibre type (PP/PVA), length (3 mm/6 mm/8 mm) and content (0.5 %/0.7 %/1.0 %). Microfibre-enhanced 3D TRCs demonstrated a higher ultimate load and post-cracking stiffness, as well as more and narrower cracks.

Spherical Indentation and Implementation of S3/P for yield stress determination of brittle materials

A mathematically transparent and robust experimental method has been developed to estimate the yield stress of brittle materials through the analysis of depth-sensing spherical indentation. Employing Hertzian contact mechanics, an elastically invariant ratio based on the simple equation S3/P=6REr2, (where S and P are contact stiffness and indentation load, respectively) has been derived that enables more accurate and confident determination of the transition from elastic to inelastic deformation; a transition that the yield stress dictates and represents. Using two diamond spheres with radii of 3.2 and 8.6 μm, the indentation test method and analyses are applied to two vitreous silicates: Corning's HPFS 7980® fused silica and Vitro's Starphire® soda-lime silicate. The estimated yield strengths are 8.15 GPa ± 2.5 % for the fused silica and 6.1 GPa ± 3.3 % for the soda-lime silicate, and both were independent of indenter radius. Verification of this new experimental method is demonstrated with an as-drawn titanium by showing equivalence of measured yield stress by its spherical indentation and that from uniaxial compression testing. This method will enable easier and more confident estimation of yield stress in brittle materials - a property that historically has been elusive to measure for these materials using common laboratory mechanical test methods.

Mechanical properties and damage evolution features in uniaxial compression with non-coincident interlayer contact in double-block ballastless track

As interlayer cracking has become as a significant issue in ballastless tracks, investigating the mechanical properties and damage characteristics during uniaxial compression with non-coincident contact is vital for enhancing the operational performance of ballastless tracks. This study conducted experiments on interlayer non-coincident contact damage in double-block ballastless tracks with nominal normal pressures of 0.666 MPa, 1.244 MPa, 2.489 MPa, and 3.733 MPa. The research explored the relationship between normal load and normal deformation stiffness, analyzed the interlayer contact damage mechanism of concrete, and investigated the damage evolution mechanism under non-coincident contact conditions based on Acoustic Emission (AE) signals. The findings indicate that: I) When the nominal pressure is respectively less than and greater than 1.333 MPa, the normal deformation stiffness and normal load satisfy linear and power function relationships, respectively. II) The interaction of interlayer protrusions under non-coincident contact, combined with the outward expansion resulting from interlayer mutual compression deformation, are two significant factors contributing to the formation of tensile cracks, while the presence of significant shear stresses directly beneath the interlayer contact points is the primary cause of shear cracks. III) After loading, The ballastless track slab matrix remains undamaged, while the supporting layer matrix may experience comprehensive cracking when the nominal pressure exceeds 1.333 MPa. IV) During the stage of only interlayer interface damage, both tensile and shear cracks are the primary causes of concrete damage. In the stage where damage occurs to both the interlayer interface and matrix, tensile cracks play a dominant role. However, when comprehensive matrix cracking occurs, shear cracks take on a dominant role. The outcomes of this study contribute to a deeper understanding of the damage mechanisms of ballastless tracks under train loads following interlayer cracking. Particularly focusing on the evolution characteristics of damage under high interlayer pressure.

Long-term Pegvisomant Therapy of Acromegaly: Effects on Bone Density, Turnover and Microstructure Using HRpQCT.

Fracture rate is increased in patients with active acromegaly and those in remission. Abnormalities of bone microstructure are present in patients with active disease and persist despite biochemical control after surgery. Effects of treatment with the GH receptor antagonist pegvisomant on bone microstructure were unknown. We studied 25 patients with acromegaly (15 men, 10 women). In 20, we evaluated areal bone mineral density (BMD) by dual-energy X-ray absorptiometry and bone turnover markers (BTMs) longitudinally, before and during pegvisomant treatment. After long-term pegvisomant in 17, we cross-sectionally assessed volumetric BMD, microarchitecture, stiffness, and failure load of the distal radius and tibia using high-resolution peripheral quantitative computed tomography (HRpQCT) and compared these results to those of healthy controls and 2 comparison groups of nonpegvisomant-treated acromegaly patients, remission, and active disease, matched for other therapies and characteristics. In the longitudinal study, areal BMD improved at the lumbar spine but decreased at the hip in men after a median ∼7 years of pegvisomant. In the cross-sectional study, patients on a median ∼9 years of pegvisomant had significantly larger bones, lower trabecular and cortical volumetric density, and disrupted trabecular microarchitecture compared to healthy controls. Microstructure was similar in the pegvisomant and acromegaly comparison groups. BTMs were lowered, then stable over time. In this, the first study to examine bone microstructure in pegvisomant-treated acromegaly, we found deficits in volumetric BMD and microarchitecture of the peripheral skeleton. BTM levels remained stable with long-term therapy. Deficits in bone quality identified by HRpQCT may play a role in the pathogenesis of fragility in treated acromegaly.

Continuous fiber path optimization in additive manufacturing: A gradient-based B-spline finite element approach

Additive manufacturing of continuous fiber enables the control of local material distribution and mechanical characteristics. This localized control is realized through fiber path generation and optimization, which is one of the core problems in the additive manufacturing of continuous fiber. Current fiber path generation and optimization methods mostly try to infill topology-optimized parts or align the fiber with the maximum stress directions, which may lead to sub-optimality or time-consuming computations. This paper provides a different approach to optimize the fiber path directly by parameterizing it with B-splines and manipulating its control points. A finite element model with B-spline fiber parameterization is established, with an analytical fiber-in-element probability. This framework streamlines the computation of local and global stiffness and mass matrices, enabling effective and efficient prediction of loading responses, stiffness, and natural frequencies. The probability framework also allows efficient calculation of the gradients of the stiffness and mass matrices, leading to a gradient-based fiber path optimization. The effectiveness and accuracy of both the finite element and optimization methods are verified with simulation and experiment case studies. Results demonstrate enhancements in stiffness and strength with less fiber usage compared to a commonly adopted principal stress direction method.

Flexural response of sandwich structures comprising topologically perturbed cores

Enhancing the flexural stiffness of sandwich structures comprising honeycomb cores through perturbing their cellular cores is explored computationally in this work. In-plane sinusoidal perturbations are imposed on the ligaments of hexagonal cores to increase their second moment of inertia and flexural load-carrying capacity. The sensitivity of sandwich structures’ flexural strength, peak load and specific energy absorption to the imposed perturbation is investigated. Introduced perturbations are controlled through their amplitude and frequency. Results show that increasing the perturbation frequency and amplitude generally increases the flexural stiffness and peak loads of sandwich structures with perturbed cores without compromising their lightweight properties. However, low frequencies and amplitudes had a negligible effect on the sandwich structures’ mechanical properties.

Anterior Talo-Fibular Ligament Tensile Properties Compared to Suture Tape, Allograft, and Copolymer Augmentation Elements: An Isolated Biomechanical Study

Introduction/Purpose: The modified Brostrom-Gould (MB) technique incorporates the inferior extensor retinaculum for added strength of anatomic Anterior Talo-Fibular Ligament (ATFL) repair. A major limitation of the MB technique is the inability to restore native ATFL biomechanics. Surgical augmentation methods have been introduced to address the MB insufficiency. The purpose of this study is to investigate the isolated biomechanical performance of common MB augmentation elements including suture tape, allograft, and copolymer compared to that of native ATFL. Methods: A total of 24 samples were tested in this study, n=6 in each group. An electromechanical testing system (Instron, Norwood, MA) was used to investigate the biomechanical performance of native ATFL, UHMW-PE suture tape (FiberTape™, Arthrex, Inc., Naples, FL), allograft (Semitendinosus Graft), and copolymer (FlexBand™, Artelon, Marietta, GA). Native ATFL ligaments were isolated from cadaver specimens (mean age: 63 years; range: 45-80), semitendinosus allografts were obtained from LifeNet Health (Jacksonville, FL). Samples measured 20 mm between rigid fixtures and oriented parallel with the long axis of the load cell to simulate worse-case loading. Samples were loaded to failure at 305 mm/min. Biomechanical outcomes included elongation, stiffness, and ultimate load to failure. One-way ANOVA was used to evaluate significant effects of all biomechanical variables. If significance was observed, post-hoc comparisons of augment element and native ATFL were performed with either Tukey or Holm-Sidak test (SigmaPlot,14.0, Systat). Results: Stiffness was greatest for the suture tape group (246.4±52.1N/mm) and least for the copolymer (9.4±2.9N/mm). Significant differences were observed between all augment elements except when comparing ATFL to allograft (p=0.086). Ultimate load was greatest for the suture tape group (544.1±59.7N) and least for the copolymer (146.7±8.9N). Analysis revealed that suture tape ultimate load was statistically greater than copolymer (p < 0.001, Fig.1). Elongation at ultimate failure was greatest for the copolymer group (30.0±8.7mm) and least for suture tape (2.6±0.5mm). Significant interactions were detected for all ultimate load comparisons except for allograft and ATFL (p=0.691), allograft and suture tape (p=0.537), and ATFL and suture tape (p=0.436). See Figure 1 for all data and statistical outcomes. Conclusion: ATFL augmentation elements require thorough evaluation for clinical adoption. Copolymer was 79% weaker in ultimate load and elongated 131% more than the native ATFL. Conversely, suture tape group exhibited 47% greater ultimate load and 82% less elongation at failure compared to ATFL. Clinically, these results suggest the copolymer maintains elastic properties incapable of supporting ATFL ligament healing under load. ATFL augmentation with suture tape offers advantageous post- operative load-sharing support and may allow return to preinjury level activity sooner, as has been seen clinically.1 These results provide insight into how these augmentation elements perform in a static model. Elongation Under Load Figure. 1: Mean elongation data points by group at specified loads up to 550N as well as table that includes all load-displacement data mean and standard deviations. *All stiffness values statistically different from one another (p<0.086 for all comparisons) except for Native ATFL vs Allograft ***Copolymer elongation at failure was statistically greater than all other groups (p<0.001 for all comparisons) **Suture tape ultimate load was statistically greater than Copolymer (p<0.001)

Temperature-dependent pinned joint tensile behavior and failure analysis of CF/PEKK composites

The pinned joint tensile properties and failure behaviors of carbon-fiber-reinforced polyetherketoneketone (CF/PEKK) composites are sensitive to application temperatures. Herein, this study investigated the temperature-dependent mechanical behavior of CF/PEKK composites in a pinned joint configuration, emphasizing the impact on tensile behavior and bearing strength. Utilizing Solvay’s CF/PEKK prepreg with a quasi-isotropic stacking sequence, tensile tests were conducted at [Formula: see text]C and 230∘C. At [Formula: see text]C, increased load-pin displacement stiffness was observed, attributed to reduced polymer chain mobility, leading to increased peak load and concentrated bearing area around the pin contact region. Conversely, at 230∘C, a substantial reduction in stiffness and peak load was evident, emphasizing the severe deterioration of pin-load strength. Fracture analysis revealed distinct failure modes at different temperatures, highlighting localized compressive failure at [Formula: see text]C and severe permanent bearing failure at 230∘C. Understanding these temperature-dependent behaviors is critical for optimizing CF/PEKK composite applications in diverse industrial settings, providing insights for enhanced performance and reliability. The findings offer valuable information on the material’s behavior under extreme temperature conditions, contributing to the design and application of CF/PEKK composites in various industrial scenarios.

The effects of pre-loading on structural behavior of reinforced concrete beams under fire condition: a review

PurposeThis review paper seeks to enhance knowledge of how pre-loading affects reinforced concrete (RC) beams under fire. It investigates key factors like deflection and load capacity to understand pre-loading's role in replicating RC beams' actual responses to fire, aiming to improve fire testing protocols and structural fire engineering design.Design/methodology/approachThis review systematically aggregates data from existing literature on the fire response of RC beams, comparing scenarios with (WP) and without pre-loading (WOP). Through statistical tools like the two-tailed t-test and Mann–Whitney U-test, it assesses deflection extremes. The study further examines structural responses, including flexural and shear behavior, ultimate load capacity, post-yield behavior, stiffness degradation and failure modes. The approach concludes with a statistical forecast of ideal pre-load levels to elevate experimental precision and enhance fire safety standards.FindingsThe review concludes that pre-loading profoundly affects the fire response of RC beams, suggesting a 35%–65% structural capacity range for realistic simulations. The review also recommended the initial crack load as an alternative metric for determining the pre-loading impact. Crucially, it highlights that pre-loading not only influences the fire response but also significantly alters the overall structural behavior of the RC beams.Originality/valueThe review advances structural fire engineering with an in-depth analysis of pre-loading's impact on RC beams during fire exposure, establishing a validated pre-load range through thorough statistical analysis and examination of previous research. It refines experimental methodologies and structural design accuracy, ultimately bolstering fire safety protocols.

Loading and structural stiffness of tandem bicycle frames

Tandem bicycles are used for all para-cycling events for visually impaired athletes. Tandems are structurally more challenging to design than solo bicycles: they must resist higher loading over a longer wheelbase, yet must still fit between the legs of the riders. Despite this, there is limited published work on tandem design. This paper presents a method for determining maximal loading of a tandem bicycle frame in racing scenarios. The only inputs required are the dimensions of the frame and the torques exerted by the riders. Outputs are the forces acting on the frame. The method is used to provide loads for structural analyses of tandem frames of different topologies. Twisting of the frame under a starting effort is shown to be the worst load case. The “double diamond” is shown to be the most efficient tubular frame design, on a stiffness per weight basis, but is only 2% superior to an “open” topology.

Analysis of deformations of road embankments founded on displacement columns improving soft subsoil

Drilled displacement columns, constructed in the form of unreinforced or reinforced concrete elements, are currently a very commonly used method of improving soft subsoil, creating an alternative to more expensive pile foundations. A frequently used solution for improving soft soils of road or railway embankments is to design a regular pattern of columns of relatively small diameter. Columns along the perimeter of the improved area are reinforced with rigid steel profiles, while the internal ones are made as concrete elements. Column heads are usually covered with a load transfer platform (layer of compacted granular fill) which is additionally reinforced with geosynthetics. The application of soil improvement with displacement columns is not always successful. It is due to the errors and shortcomings occurring at the design stage, including simplifications in modelling, to construction faults, which may include insufficient experience of contractors and/or improper supervision. Referring to the real object that failed, the article provides the results of numerical parametric analyses taking into account the influence of the key design parameters such as: the stiffness of the load transfer layers, the amount and stiffness of the geosynthetic reinforcement as well as the column spacing. The article presents comparisons of numerical results obtained with the finite element analyses for various approaches to geometry modelling (axisymmetric, 2D and 3D). The simulations indicate that the use of the axisymmetric model of a single column in routine design may lead to the deformations exceeding the serviceability limit states.

Anti-osteoporotic effects of Yi Mai Jian on bone metabolism of ovariectomized rats.

Yi Mai Jian herbal formula (YMJ) is formulated with Eucommiae Folium, Astragali Radix, Ligustri Lucidi Fructus, and Elaeagnus Fructus to improve bone function in traditional Chinese medicine. The anti-osteoporotic effects of YMJ in bone metabolism were evaluated in ovariectomized (OVX) rats. The skeletal structure of the femur and vertebrae was analyzed after treating OVX rats with YMJ for 114days. The results showed that YMJ significantly increased the bone mineral density (BMD) and trabecular number (Tb. N) of the femur and 5th lumbar vertebrae and reduced trabecular separation (Tb. Sp). Moreover, trabecular bone volume/total tissue volume (BV/TV), bone stiffness, and maximum femur load were significantly increased. The serum concentrations of NTX1 and PYD were significantly decreased. According to these results, YMJ could ameliorate osteoporosis in ovariectomized rats. Eucommiae Folium and Elaeagnus Fructus inhibited osteoclast differentiation, Ligustri Lucidi Fructus inhibited calcium reabsorption, Astragali Radix stimulated osteoblast proliferation, and Astragali Radix and Eucommiae Folium stimulated mineralization. Therefore, the combination of the four herbs into one formula, YMJ, could alleviate bone remodeling caused by low estrogen levels. We suggest that YMJ could be a healthy food candidate for preventing post-menopausal osteoporosis.

Fracture Behavior of Crop Circle Ceramic Tiles: Experimental and Numerical Study

This research investigates the effect of three-dimensional (3D) bee-crop-circle tiles on load deformation, initial cracking and propagation, and stress redistribution. Experimental tests provide limited data due to the small specimen size and brittle nature of the material. A finite element (FE) model is constructed and validated by laboratory data to analyze the stress-strain responses and failure mode. The model enables a detailed description of stress patterns, stress propagation, and redistribution of layers beneath the bee design. The study concludes that a 3D crop circle-inspired design significantly influences the ultimate load-carrying capacity and stress-related behavior. The load-deformation response is nonlinear, and the coloring influences the thickness of coatings, further affecting the ultimate load and initial stiffness. Furthermore, designs with convex details result in an arc action, deviating the stress concentrations away from the line of loading. The FE model slightly overestimates the initial stiffness but represents the ultimate load and load-displacement response with high accuracy.

Homogenized finite element analysis of distal tibia sections: Achievements and limitations

High-resolution peripheral quantitative computed tomography (HR-pQCT) based micro-finite element (μFE) analysis allows accurate prediction of stiffness and ultimate load of standardised (∼1 cm) distal radius and tibia sections. An alternative homogenized finite element method (hFE) was recently validated to compute the ultimate load of larger (∼2 cm) distal radius sections that include Colles' fracture sites. Since the mechanical integrity of the weight-bearing distal tibia is gaining clinical interest, it has been shown that the same properties can be used to predict the strength of both distal segments of the radius and the tibia. Despite the capacity of hFE to predict structural properties of distal segments of the radius and the tibia, the limitations of such homogenization scheme remain unclear. Therefore, the objective of this study is to build a complete mechanical data set of the compressive behavior of distal segments of the tibia and to compare quantitatively the structural properties with the hFE predictions. As a further aim, it is intended to verify whether hFE is also able to capture the post-yield strain localisation or fracture zones in such a bone section, despite the absence of strain softening in the constitutive model.Twenty-five fresh-frozen distal parts of tibias of human donors were used in this study. Sections were cut corresponding to an in-house triple-stack protocol HR-pQCT scan, lapped, and scanned using micro computed tomography (μCT). The sections were tested in compression until failure, unloaded and scanned again in μCT. Volumetric bone mineral density (vBMD) and bone mineral content (BMC) were correlated to compression test results. hFE analysis was performed in order to compare computational predictions (stiffness, yield load and plastic deformation field pattern) with the compressive experiment. Namely, strain localization was assessed based on digital volume correlation (DVC) results and qualitatively compared to hFE predictions by comparing mid-slices patterns.Bone mineral content (BMC) showed a good correlation with stiffness (R2 = 0.92) and yield (R2 = 0.88). Structural parameters also showed good agreement between the experiment and hFE for both stiffness (R2 = 0.96, slope = 1.05 with 95 % CI [0.97, 1.14]) and yield (R2 = 0.95, slope = 1.04 [0.94, 1.13]). The qualitative comparison between hFE and DVC strain localization patterns allowed the classification of the samples into 3 categories: bad (15 sections), semi (8), and good agreement (2).The good correlations between BMC or hFE and experiment for structural parameters were similar to those obtained previously for the distal part of the radius. The failure zones determined by hFE corresponded to registration only in 8 % of the cases. We attribute these discrepancies to local elastic/plastic buckling effects that are not captured by the continuum-based FE approach exempt from strain softening. A way to improve strain localization hFE prediction would be to use longer distal segments with intact cortical shells, as done for the radius. To conclude, the used hFE scheme captures the elastic and yield response of the tibia sections reliably but not the subsequent failure process.

Design and Analysis of a Novel Variable Stiffness Joint Based on Leaf Springs

In response to challenges like the complexity and limited scalability of existing variable stiffness joints, a novel variable stiffness joint, based on leaf spring elements, is introduced in this paper. The joint stiffness can be adjusted in real time by changing the effective length of the leaf spring via the use of an Archimedean spiral groove. The stiffness adjustment range and load capacity of the joint can be defined by manually configuring the number of springs involved during offline joint operations. A stiffness model for the joint is established based on the cantilever beam theory of material mechanics. The coupled effects of the design parameters of the variable stiffness mechanism on joint stiffness, elastic torque, and stiffness adjustment resistance torque are analyzed. A dynamic model for the joint is developed, while a PID controller is designed for simulation purposes. The motion characteristics of the joint are analyzed, confirming that this approach has certain advantages in terms of stiffness adjustment speed and accuracy.

Flexural stiffness of RC beams with high‐strength steel bars after exposure to elevated temperatures

AbstractIn this paper, the flexural stiffness of the reinforced concrete (RC) beams reinforced with high‐strength steel bars after exposure to different elevated temperatures was investigated experimentally and theoretically. The effects of the elevated temperature (room temperature, 200°C, 400°C, 600°C, 800°C, and 1000°C), high‐temperature duration time (0 h, 1 h, and 2 h), and steel bar types (HRB600 and HRB500) on the load–deflection response, load–stiffness response, and crack distribution of tested beams were investigated. The results showed that when the temperature is below 600°C, the effect of high temperature on the stiffness reduction of high‐strength RC beams is not significant, while the beams reduced the stiffness when the exposure temperature reached 800°C and 1000°C, regardless of the type of the steel bars. The elevated temperature accelerated the development of the deflection of RC beams, and the bending stiffness of the RC beams decreased more severely as the increase of duration time. By using appropriate degradation factors, the residual stiffness of the beams was predicted well by the analysis calculation method and the effective inertia moment calculation method, for example, the prediction accuracy is over 91% and 85.8% for the cases under and over 800°C, respectively. However, for the beams at 1000°C, a correction coefficient (0.652) was applied to improve the accuracy of the calculative stiffness of the HRB600 RC beams at the service load stage.

Experimental and numerical study of the flexural behaviour of semi-precast slab reinforced with prestressed FRP bars

The performance of semi-precast slabs with prestressed basalt fibre-reinforced polymer (BFRP) bars under load is explored in this paper, using both experiments and computer simulations. The semi-precast slabs consist of precast concrete panels and cast-in-situ layers. The Precast panels are reinforced with BFRP bars prestressed at varying levels from 0% to 50% of their ultimate tensile strength. The experimental programme encompasses four-point bending tests conducted on five semi-precast slabs. For the numerical study, an ABAQUS model was used to perform finite element (FE) analysis, which aimed to simulate how the semi-precast slabs bent and to study how different factors affected their bending performance. The study parameters in this study were the grade of concrete and the reinforcement ratio. The results of this study show that prestressed BFRP bars significantly enhance load capacity and stiffness, while steel offers superior ductility. The computer models and the experiments matched well, as the average error between the two sets of data was less than 10%. Additionally, the parametric study reveals that enhancing the concrete grade or the reinforcement ratio can effectively enhance the flexural capacity and stiffness of the semi-precast slabs. In conclusion, this paper advocates for the utilisation of prestressed BFRP bars as an efficient and long-lasting reinforcement solution for semi-precast concrete slabs.

Experimental study on flexural performance of prestressed concrete beams strengthened by Fe-SMA plates

Shape memory alloy (SMA) is an innovative intelligent material, capable of restoring its shape before deformation upon reaching the critical activation temperature. This property promotes its promising applications in civil engineering. This paper proposes a novel reinforcement method and aims to investigate the reinforcing effect of iron-based shape memory alloy (Fe-SMA) plates on prestressed concrete (PC) beams through four-point bending tests on one reference beam without reinforcement and three Fe-SMA reinforced beams, as well as with three beams reinforced by carbon fiber-reinforced polymer (CFRP). The results show that Fe-SMA can effectively reduce concrete cracks, and improve stiffness and characteristic loads of beams without negative effects. Under the same loading conditions, new cracks of Fe-SMA reinforced beams were relatively fewer than those of CFRP reinforced beams. Besides, Fe-SMA exhibited superior performance when utilizing the same cross-sectional reinforcement material to enhance the bending capacity of beam, and proved more advantageous for improving stiffness and characteristic loads of beam under the identical initial tensile force. Furthermore, the reinforcing effectiveness of Fe-SMA positively correlates with the cross-sectional area (thickness) and recovery stress (pre-stretch level and activation temperature) of Fe-SMA. Increasing the thickness of Fe-SMA plates by 100%, while maintaining other parameters constant, resulted in a 33% increase in cracking load. Similarly, elevating the recovery stress from 314 MPa to 340 MPa led to a 12.5% rise in cracking load. This paper investigates the reinforcement effect of Fe-SMA plates on PC beams, and provides a reference for the application of Fe-SMA in PC beam reinforcement, laying a foundation for promoting the utilization of Fe-SMA in civil engineering.