Lower Deflection Research Articles

Flexural and deflection behaviour of synthetic fibre reinforced concrete beams reinforced with glass fibre reinforced polymers bars under sustained service load

Glass fibre reinforced polymers (GFRP) bars have attracted increasing interest as a promising alternative for conventional steel reinforcement for its contribution towards sustainability and significantly improving the flexural performance of structural members. To mitigate the excessive deflections and crack widths exhibited by the FRP reinforced concrete members, fibre reinforced concrete (FRC) is employed which improves the toughness and cracking capacity of members. However, available research on the structural performance of FRC has focused on metallic fibres. The research presented in this paper is aimed at experimentally evaluating the influence of synthetic fibres on the time-dependent flexural behaviour of FRC beams reinforced with GFRP bars. Eight simply supported beams with varying synthetic fibre contents and GFRP bar diameters (but same reinforcement ratio) were tested under sustained service load. Creep under compression, concrete shrinkage, cracking moment, and deflection behaviour over 90 days were monitored and analyzed. Investigation revealed that the inclusion of synthetic fibres reduced the concrete deformations under creep and shrinkage by up to 22% and 26% respectively, increased the cracking capacity by 27%, increased the effective moment of inertia by 75%, and also resulted in up to 43% lower deflections. Suitability of several codes to predict the deformations and deflections under short and long-term conditions was also evaluated through comparison of the prediction models to the experimental results. Model proposed by ACI 440.1R-15 was found to predict the instantaneous deflection in beams without fibres with reasonable accuracy, however in FRC-GFRP beams, all models tend to overestimate the deflection. Presented research highlights the need for further investigation on non-metallic fibres and their contribution towards improvement of residual and flexural performance of FRC members to improve the validity of existing analytical prediction models.

Flexural behavior, porosity, and water absorption of CO2-cured amorphous metallic-fiber-reinforced belite-rich cement composites

The present study aims to scrutinize the flexural behavior and engineering properties of beams reinforced with amorphous metallic fiber (AMF) at varying dosages (0%, 0.25%, 0.50%, and 0.75% AMF according to the volume of mortar) and lengths (5 mm, 10 mm, 15 mm, and 20 mm). A total of fourteen mortar mixes, i.e., seven mixes for water curing (immersed in fresh tap water) and seven mixes for carbonation curing (60% relative humidity, 20 °C, and 10% CO2 concentration) were considered. The load–deflection behavior, flexural strength, pore structures, voids, and water absorption of the beams were investigated. The outcomes were justified with the mix containing 0.5% steel fiber (SF) and a length of approximately 20 mm. The results reveal that the load–deflection behavior and flexural strength were dramatically augmented for the beams with AMF as compared to the control beam (fiber-free beam), and the difference was more pronounced with an increase in both the dosage and the length of the AMF. Greater flexural strength with a lower deflection at failure was registered for the beam with AMF compared to that with SF. The voids and water absorption increased with an increase in the dosage and length of the AMF compared to the control specimen. It was also revealed that the carbonation-cured beams exhibited lower load–deflection behavior and lower flexural strength than those cured in water due to the substantially increased number of voids and greater water absorption driven by the better-connected pores. This study demonstrates that 0.50% AMF with a length of 20 mm can be used in cement-based materials due to the outstanding performance among all mixes.

Structural Dynamics of Bridges Under the Coupling Effect of Windmills and Bridges

To analyze the coupled dynamics effects of existing railroad frame bridge structures under the action of traffic, a coupled train-ballast track-suspension bridge girder-soil dynamics model is established based on railroad large system dynamics and finite element theory. The joint ABAQUS-MATLAB simulation, time-varying coupling, and multi-step dynamic iterative solution strategies are introduced to numerically simulate the mechanical properties of existing railroad structures under the coupled effects of wind loads and traffic action. Specifically, (1) a dichotomous method is proposed to investigate the static behavior of the bridge in the bridge-forming state, and the maximum upper arch of the stiffened girder is 3.67 cm, which occurs at about 1/4 and 3/4 positions of the main span, and the lower deflection of the side span is larger, and the maximum lower deflection occurs at 11.04 cm in the span of the 110 m side span. The vertical acceleration in the span increases immediately with the maximum peak of 30 cm/s2, while the lateral acceleration is maintained within 20 cm/s22. (2) The effects of the stiffness of the rail fasteners and the bridge plate support stiffness on the dynamics were studied. (3) The results of the time-domain analysis are in general agreement with the simulation data, except for the error of the ambient vibration background existing at the peak. The correctness of the simulation model is verified.

Assessment of Flexural Performance of Reinforced Concrete Beams Strengthened with Internal and External AR-Glass Textile Systems

This paper is an experimental study of the effectiveness of using internal and external alkali-resistant glass fabric textile (AR-GT) layers for flexural strengthening of reinforced concrete (RC) beams. The experimental work compares internal single and triple layers of AR-GT as supplemental flexural reinforcement with textile-reinforced mortar (TRM) in RC beams subjected to four-point bending loading. In addition, a control beam specimen is cast with no AR-GT fabric. Monitoring the load–deflection curves, crack patterns, and strengthening layer performance showed that using AR-GT for internal and external layers increased the load-carrying capacity of RC beams. The failure patterns of beams with one external AR-GT layer and three internal AR-GT layers showed a similar trend, with higher loading capacity and lower deflections than the other beams. Three internal textile AR-GT layers recorded higher flexural strength (52%) than one internal layer (6.3%), compared to the control beam specimen. Moreover, using one layer of external AR-GT fabric exhibited higher flexural strength than using one or three internal layers (56.8%).

Experimental investigation on ultra high-performance concrete beams without shear reinforcement

Seven ultra high-performance concrete (UHPC) beams without shear reinforcement are tested in this work to examine their structural behavior as shear failure is a major concern in such members. Coarse aggregate was not used in two of the beams while the other five are made with coarse aggregate as 50% replacement of fine sand. Three longitudinal steel reinforcement ratios (1.14%, 1.64% and 2.46%) and three steel fiber ratios (0, 1% and 2%) are used. Results show that UHPC beams with coarse aggregate show higher ultimate loads (4.7% − 11.5%) than UHPC beams without coarse aggregate and incorporating 1% and 2% steel fiber raises ultimate loads by 60% and 131%, respectively for beams with coarse aggregate. Also, using 2% steel fiber changes failure mode from brittle shear failure by diagonal crack in beams of 0 or 1% steel fiber to ductile flexural failure by yielding of longitudinal reinforcement. Higher stiffness and toughness and lower deflections are observed with the increase of longitudinal reinforcement, steel fiber or coarse aggregate. Using 2% steel fiber highly improved toughness by more than 17 times. Lower rates of improvement are recorded for longitudinal reinforcement and coarse aggregate. However, it is recommended to perform more research to examine more parameters such as fiber types.

On the pressure–deflection relations and instability of carbon-based composite nonlinear pipes

In this paper, for the first time, the nonlinear buckling of curved pipes is investigated for different distributions of single-walled carbon nanotubes (SWCNTs) in the matrix. The curved pipe is subjected to uniformly distributed transverse pressure and experiences uniform temperature rise. Additionally, the pipe is in one-sided contact with an elastic nonlinear medium. Defined thickness-dependent and temperature-dependent material properties of SWCNTs are taken from the results of molecular dynamics (MD) simulations, well-established in the literature on the subject. Five technologically justified types of CNT distributions are considered. Shen’s rule of the mixture is applied to determine the effective properties of CNT-based composites. To avoid determining shear correction factor, the higher-order shear deformation theory is used. The nonlinear components of the Green–Lagrange strain tensor and the principle of virtual displacements are applied to derive the nonlinear system of partial differential equations of motion of the curved pipe. The solution to formulated boundary value problem is obtained by the perturbation technique for both simply-supported and clamped-clamped boundary conditions. The pressure–deflection curves of the curved pipe are obtained and discussed. The investigation of snap-buckling intensity and upper/lower limit load of the curved pipe is presented and new insights for its nonlinear stability are presented. For instance, it is shown that the V-type of CNT distribution profile affects on lower deflection of the curved pipe while the higher deflection exists for the Λ-type profile.

Strengthening of Reinforced Concrete slabs using macro and micro synthetic fibers

Concrete is brittle and prone to cracking, especially under tensile forces. The gradual development and propagation of cracks would subsequently lead to brittle failure. The use of fibers is effective in restricting the propagation of cracks and improving the failure mode of cement composites. This study attempts to enhance the performance of Reinforced Concrete (RC) slabs under a four-point bending test by embedding synthetic fibers with distinct parameters. In the preliminary stage, experimental uniaxial tests were conducted in compression and tension to observe the stress–strain behavior of the developed Hybrid Fiber Reinforced Concrete (HyFRC). The obtained data are then used as input in Finite Element (FE) modeling for numerical analyses. In the primary stage, the numerical results were verified from the experimental data with respect to cracking behavior, ultimate load capacity, corresponding mid-span deflection, and steel reinforcement strain output. Based on the results, the HyFRC slabs exhibited positive improvements in terms of load-carrying capability by reducing stress in the concrete and rebars. The HyFRC slabs also experienced lower deflections with improved crack resistance and high flexural stiffness than the control slab. Additionally, the developed FE models presented a low margin of error compared to the experimental data for all assessed criteria.

The flexural behavior of Hollow core concrete slabs with different shape

Hollow slabs are slabs of reinforced concrete in which voids allow the concrete to be reduced in size. This type of slab results in reduced raw materials Consumption and increased insulating properties to achieve sustainability goals. This paper reported an experimental research program focused on the study of the bending behaviour of the elements of hollow slabs of normal-strength concrete. Three models of the one-way concrete slab were cast, It had dimensions of 1020 mm length, 420 mm width, and 100 mm thickness. The first model did not contain holes (solid) and the second model contained five circler opening holes with a 50 mm diameter, while the third model contained five square opening holes with 44 mm dimension, where the area of the second and third model were the same despite the difference in the shape of the opening. The results showed that the bearing capacity of the circular hollow core slab is higher by 12% compared to the square hollow core slab according to the type of voids and both of holes made the hollow core slab with a decrease in load capacity of 11% to 25% when compared to the solid slab. The solid slab has lower deflection value compared to the two hollow slabs whose weight is reduced by 23% compared to the solid slab.

In-situ monitoring and modelling of distortion in multi-layer laser cladding of Stellite 6: Parametric and numerical approach

Laser cladding is a direct metal deposition technique used for repair and rebuilding of worn-out components. In this process, the component is subjected to high heating and cooling cycles, which generate residual stresses and distortion affecting the part quality. The present work is to investigate and evaluate distortions generated during deposition using in-situ measuring method and also with numerical modelling. The role of different support conditions (simply, cantilever, and fixed) and process parameters (laser power, scan speed) on distortion are examined. A numerical model in COMSOL Multiphysics software was developed to generate thermal history and distortion in multi-layer cladding of Stellite 6. The temperature data shows large thermal gradients development along the thickness; allowing material to expand and contract at different rates, leading to substrate distortion. This was evidence in laser displacement sensor data and simulation. The results showed simple and fixed supports develop 40 - 50% and 60 - 70% less distortion than cantilever. Additionally, when the scan speed is decreased from 20 mm/s to 12 mm/s, distortion is lowered by 15 - 40%. An increase in laser power from 2400 W to 3400 W showed distortions to be 30 - 60% higher; while the second layer depositions have given 15 - 25% lower deflection. The simulation results are in good agreement with experimental values and reveals that support conditions are significant on distortion. Conclusion:- Laser cladding with simple and fixed supports developed 40 % - 50 % and 60 % - 70 % lower distortions than cantilever support; and increases with increase in laser power and decrease in scan speed.

Event‐triggering‐based robust optimal control for post‐stall pitching maneuver of aircraft

AbstractIn this paper, the problem of the post‐stall pitching maneuver of aircraft with lower deflection frequency of control actuator is studied by considering the unsteady aerodynamic disturbances (UADs). A nonlinear disturbance observer is employed to estimate the UADs in order to suppress their adverse effects. And the nonzero equilibrium adaptive dynamic programming (NEADP) control method derived from the reinforcement learning is adopted to achieve the optimal control of aircraft. Simultaneously, a critic neural network is constructed to approximate the value function in the Hamilton‐Jacobi‐Bellman equation so as to realize adaptivity. Furthermore, the event‐triggering (ET) scheme with an improved triggering condition is applied in the control method in order to decrease the deflection frequency of control actuator. In addition, the Lyapunov stability analysis method is used to prove that all signals in the closed‐loop control system are uniformly ultimately bounded. And the proof by contradiction is applied to confirm that the Zeno behavior is excluded with the analysis of the minimum dwell time. Finally, simulation results verify the effectiveness of the improved ET‐based NEADP control method.

Fatigue behavior of removable partial denture cast and laser-sintered cobalt-chromium (CoCr) and polyetheretherketone (PEEK) clasp materials.

To investigate the fatigue behavior of cast and laser-sintered cobalt-chromium (CoCr) and polyetheretherketone (PEEK) material for a removable partial denture (RPD) clasps. Dumbbell-shaped specimens were digitally designed with the center part of the dumbbell being a half-round shape at the cross-sectional dimension of 1.25 mm to simulate a typical clasp design and dimensions. A fatigue machine with an offset axis rotation system simulated a typical undercut depth of 0.25, 0.50, and 0.75 mm. Each group was subjected to 30,000 fatigue cycles (simulating 21 years) or till specimen failure. Before testing, the stress value at each undercut depth for each specimen was established in a universal testing machine and SN curves were plotted for each group. Data were statistically analyzed using Kruskal-Wallis and post hoc tests. The fractured surfaces were analyzed using SEM. The average fatigue cycles with 0.25, 0.50, and 0.75 mm undercuts were 27,155 ± 6277, 9298 ± 4033, 5642 ± 8785 for cast CoCr and 26,765 ± 6150, 11,318 ± 7931, 2861 ± 4803, for laser-sintered CoCr, respectively. Apart from three specimens, the PEEK groups did not fail during the simulation period. Clasps with 0.25 mm deflection showed significantly higher fatigue resistance than other groups (p < .001). There was no significant difference in fatigue behavior between the cast and laser-sintered CoCr. Microporosities at the fractured site along with irregular crack propagation were observed for cast and laser-sintered CoCr specimens. Fatigue-induced broken polymer crosslinking chains were observed in PEEK specimens. PEEK material exhibited the highest fatigue resistance and significantly lower deflection resistance. Cast and laser-sintered CoCr showed similar fatigue resistance and behavior.

Study on the Actuation Aspects for a Morphing Aileron Using an Energy–Based Design Approach

Evaluating the impact of morphing devices in terms of actuation energy is a promising approach to quantify, from the earliest stages of wing design, the convenience of active camber morphing compared to the use of conventional control surfaces. A morphing wing device consists of an adaptive structure coupled with an actuation system. The starting point for the design of the adaptive structure is a three-dimensional parametric-geometry-representation technique working on the definition of the external morphing shape. The morphing shape is defined to be feasible from the structural point of view and able to meet the aerodynamic design requirements. The new method presented here enables the computation of the actuation energy as a combination of strain energy and external aerodynamic work. The former is the energy required to deform the skin and can be computed in an analytical way, based on the same quantities used by the parameterization technique. The latter is used to compute the energy needed to counteract the external aerodynamic loads during the deformation. This method is applied to the design optimization of a morphing aileron which is installed on a 24 m span wing, starts at 65% of both the chord and the semi-span and extends for one third of the span. A parametric study shows the superiority of the morphing aileron, compared with an equivalent hinged aileron, in terms of energy saving, weight penalty reduction and ease of on-board installation. The morphing aileron is more compact and requires a lower actuation energy combined with a lower deflection, while providing the same roll moment.

Process-induced failure mode transition of compression molded discontinuous carbon fiber composites: From coupon to component level

Discontinuous carbon fiber composites have been reported to be damage tolerant materials with insensitivity to notches and defects. Meso-scale damage mechanisms and crack arresting are responsible for high apparent fracture toughness and pseudo-ductility. This work studies the effect of manufacturing and structure formation on the mechanical behavior of stochastic carbon fiber sheet molding compounds based on thermosetting prepreg platelets with a fiber length of 50 mm. The process–structure–property–performance relationship is analyzed by non-destructive characterization and mechanical bending tests on the component level. Model components of various preform and stack placement scenarios were compression molded to investigate different flow conditions, weld lines and artificially introduced defects. The experimental findings revealed a process-induced failure mode transition from pseudo-ductile to brittle failure behavior. Low-flow scenarios showed a highly non-linear response with large deflection values and high energy absorption. Higher in-mold material flow and weld lines caused brittle failure at significantly lower deflections with a considerable reduction of energy absorbing capacity. Increased material flow also reduced component stiffness and maximum load values. Weld lines exhibited major strength reduction compared to the pristine material configuration. Full-scale and high-resolution X-ray computed tomography scans revealed differences in local fiber orientation state, increased levels of fiber waviness and porosity, as well as asymmetric distribution of defects.

Validation of Aeroelastic Actuator Line for Wind Turbine Modelling in Complex Flows

The actuator line method is a widely used technique to model wind turbines in computational fluid dynamics, as it significantly reduces the required computational expense in comparison to simulations using geometrically resolved blades. Actuator line coupled to an aeroelastic solver enables not only the study of detailed wake dynamics but also aeroelastic loads, flexible blade deformation and how this interacts with the flow. Validating aeroelastic actuator line predictions of blade loading, deflection and turbine wakes in complex inflow scenarios is particularly relevant for modern turbine designs and wind farm studies involving realistic inflows, wind shear or yaw misalignment. This work first implements a vortex-based smearing correction in an aeroelastic coupled actuator line, and performs a grid resolution and smearing parameter study which demonstrates significant improvement in the blade loading and in the numerical dependencies of predicted thrust and power output. A validation is then performed using a 2.3 MW turbine with R = 40 m radius, comparing against blade resolved fluid-structure interaction simulations and full-scale measurement data, in both laminar and turbulent inflows including both high shear and high yaw misalignment. For an axisymmetric laminar inflow case, the agreement between blade resolved and actuator line simulations is excellent, with prediction of integrated quantities within 0.2%. In more complex flow cases, good agreement is seen in overall trends but the actuator line predicts lower blade loading and flapwise deflection, leading to underpredictions of thrust by between 5.3% and 8.4%. The discrepancies seen can be attributed to differences in wake flow, induction, the reliance of the actuator line on the provided airfoil data and the force application into the computational domain. Comparing the wake between coupled actuator line and blade resolved simulations for turbulent flow cases also shows good agreement in wake deficit and redirection, even under high yaw conditions. Overall, this work validates the implementation of the vortex-based smearing correction and demonstrates the ability of the actuator line to closely match blade loading and deflection predictions of blade resolved simulations in complex flows, at a significantly lower computational cost.

Manufacturing, Testing and Recycling of a small recyclable wind turbine blade

Thermoplastic resins are likely to replace thermoset resins in wind blade manufacturing, as their similar structural properties together with their recyclability would enable the reuse of the raw materials in other composites at the end of life. This paper presents the manufacturing, testing and recycling process of a 1 m thermoplastic composite wind turbine blade compared to a similar thermoset blade. The results showed that the static and centrifugal performance of the two blades were similar, but the thermoplastic composite blade had a lower deflection compared to the epoxy blade. The different components of the thermoplastic blade were recovered by immersion in a suitable solvent for their possible reuse in the manufacture of a new wind turbine blade. Thus, this study provides an example of the use of circular economy principles in a strategic renewable sector, wind energy, validating the use of a new thermoplastic resin in the design and recycling of wind turbine blades, without changing their current manufacturing process.

Selective layer-by-layer fillering and its effect on the dynamic response of laminated composite plates using higher-order theory

In this work, a fifth-order shear deformation theory is computed using the layer-wise model to determine non-dimensional fundamental frequencies. The theoretical, experimental, and finite element analysis (FEA) results are compared for a standard isotropic material. Hand layup technique is used to prepare glass fiber reinforced polymer composites (GFRPC) with selective layers filled with graphene and flyash. This technique helps to reduce the fabrication cost as the whole structure is not to be strengthened by the fillers. Six classes of the laminated-composite-plate (LCP) such as outer layer graphenated LCP (O-LCP), core layer graphenated LCP(C-LCP), functionally graded LCP (FG-LCP), LCPs only rich in graphene (G-LCP), LCPs only rich in flyash (F-LCP) along with a neat epoxy-glass LCP (N-LCP) are fabricated. A low-cost frequency measurement module is set-up to measure the fundamental frequency (FF) of the fabricated LCPs. FFs, amplitudes, non-dimensional stress parameters, and central deflection of the LCPs under harmonic load, the buckling strength, and displacements of the LCPs are calculated. It is found that harmonically excited C-LCP and O-LCP have better stability accompanied by lower deflections, followed by G-LCP as compared to other kinds of LCPs. Also, the addition of graphene increases the buckling strength of LCPs, which portrays that the local layer filling is a useful technique to enhance the strength of the LCPs.

Flexural response of FRP-strengthened lightweight RC beams: hybrid bond efficiency of L‐shape ribbed bars and NSM technique

This paper presents the results of an experimental study on employing near surface mounted (NSM) fiber-reinforced polymer (FRP) reinforcement technique, and L‐shape ribbed bars, for flexural strengthening of lightweight reinforced concrete (RC) beams. 18 RC beams including 14 lightweight RC beams and four normal-weight concrete beams were designed. The beams were strengthened with glass fiber-reinforced polymer (GFRP) bars and carbon fiber-reinforced polymer (CFRP) laminate in bending tests. Test parameters included: (1) different FRP materials (glass bars and carbon sheets), (2) longitudinal steel reinforcement ratio, and (3) type of strengthening technique used (NSM reinforcement or hybrid). The ultimate tensile strength, deflection, compressive and tensile strain of concrete, and failure mode of the beams were examined under four-point flexural test. Results showed that the ultimate strength of all RC beams increased between 33 and 105% compared to the control beam. The ultimate strength of beams reinforced with CFRP in the mid-span region was 10% higher than that of beams strengthened at both ends, although the former exhibited 28% lower ultimate deflection. The ultimate strength and deflection of RC beams strengthened with combined steel reinforcing bars and GFRP bars were 10% and 108% higher, respectively, compared to those of RC beams strengthened with GFRP bars only. Hybrid L‐shape ribbed bars beams showed a considerably higher ductility (up to 170% increase in the ultimate deflection) compared to other beams. The comparison of the experimental results of the ultimate strength of the beams with ACI440-2R guidelines indicated a reasonable and conservative prediction of the code expression.

Comparison of RCC and Post-Tensioned Flat Slabs Using ETABS

Flat slabs are widely used nowadays. The system’s insufficient punching shear capacity is a major and serious flaw. There are numerous approaches to increasing the punching shear strength of concrete slabs to solve the problem of punching failure. Increasing the thickness of the slab adjacent to the column, as well as the thickness of the column, contradicts the architectural intent. In developing countries such as India, the benefits of prestressing, particularly post-tensioning, have yet to be recognized. In this study, the technique of post-tensioning is used to strengthen a flat slab. RCC flat slabs are compared to post-tensioned flab slabs with different tendon profiles. Tendons are available in two forms: distributed and banded. The models were built as per ACI 318-14. These slab models were created using ETABS software, and the following parameters were compared: thickness, supporting reactions, punching shear, and deflection. When compared to traditional flat slabs. The results indicate that post-tensioned flat slabs have a higher punching shear capacity even at shallower depths, resulting in more cost-effective sections. The provision of tendons also results in lower deflection.

Bond Strength and Deflection of Four Types of Bonded Lingual Retainers.

Objectives This study aimed to assess the bond strength and deflection of four types of bonded lingual retainers. Materials and Methods In this in vitro, experimental study, 160 extracted, mandibular incisors were mounted in acrylic blocks in sets of two and randomized into four groups for bonding of 1.0.010 × 0.026-inch Bond-A-Braid®, 0.012 × 0.027-inch Retanium®TM, 0.038 × 0.016-inch Ortho FlexTech®, and 0.0175-inch three-strand retainer wires; 15 mm of passive wire was adhered to the lingual tooth surface using Transbond XT composite. The shear (SBS) and tensile (TBS) bond strength values were measured. The adhesive remnant index (ARI) score and deflection of wires were also determined under a stereomicroscope. Data were analyzed by the chi-square test and ANOVA. Results The four groups were significantly different regarding the ARI scores (P < 0.05). Significant differences were noted between the three-strand and all other groups in deflection (P < 0.05). The Retanium group had significant differences with other groups in peak SBS (P < 0.05). A significant difference was found between the Retanium and Ortho Flex groups in break SBS (P < 0.05). Significant differences were also reported between the three-strand and all other groups in peak TBS (P < 0.05). Conclusion The Retanium retainer had the maximum SBS, while the three-strand retainer had the maximum TBS. The three-strand and Retanium wires can probably better tolerate intraoral forces and have higher resistance to fracture due to having higher TBS. Also, the three-strand wire had lower deflection rate, which highlights its higher resistance to occlusal forces. Retanium and Ortho FlexTech wires had the most favorable failure modes.

Deflection bowl parameters for falling weight deflectometer testing: data collection and threshold benchmarking

ABSTRACT Deflection Bowl Parameters (DBP) has been used widely to evaluate pavement structural performance based on deflection data from Falling Weight Deflectometer (FWD). However, due to different pavement layers, materials configuration, test load, and climatic temperature, DBP thresholds need to be established for urban streets in tropical countries like Singapore. Around 130 km of field data in the network was collected every 25 m span, processed using Elmod 6 software before regression analysis. Based on the high coefficient of determinations (R-squared > 0.65), the DBP thresholds were proposed mainly for the middle layer condition (using Middle Layer Index, Lower Layer Index and Maximum deflection) and subgrade condition (via Lower Layer Index). In contrast, there were still some uncertainties in parameters related to HMA surface layers (by using Base Layer Index and Radius of Curvature) due to lower levels of R-squared (≅ 0.5). Our results have filled the research gaps of field-validated DBP thresholds for FWD 50 kN on the thick bituminous base pavement: Hot Mix Asphalt 130-170 mm, Graded Granite Aggregate Base 200-250 mm, and infinite subgrade. The findings have contributed to newly established DBP thresholds for immediate implementation in Singapore and other countries sharing similar pavement configurations.