Diagonal Loading Research Articles

Evaluation of 3D-Printed Connectors in Chair Construction: A Comparative Study with Traditional Mortise-and-Tenon Joints.

The present paper investigates the possibility of replacing the traditional L-type corner joint used in chair construction with a 3D printed connector, manufactured using the Fused Filament Fabrication (FFF) method and black PLA as filament. The connector was designed to assemble the legs with seat rails and stretchers, and it was tested under diagonal tensile and compression loads. Its performance was compared to that of the traditional mortise-and-tenon joint. Stresses and displacements of the jointed members with connector were analyzed using non-linear Finite Element Method (FEM) analysis. Both connector and mortise-and-tenon joint were employed to build chair prototypes made from beech wood (Fagus sylvatica L.). Digital Image Correlation (DIC) method was used to analyze the displacements in the vicinity of the jointed members of the chairs. Seat and backrest static load tests were carried out in order to verify if the chairs withstand standard loading requirements. Results indicated that the 3D printed connector exhibited equivalent mechanical performance as the traditional joint. The recorded displacement values of the chair with 3D-printed connectors were higher than those of the traditional chair reaching 0.6 mm on the X-axis and 1.1 mm on the Y-axis, without any failures under a maximum vertical load of approximately 15 kN applied to the seat. However, it successfully withstood the loads for seating and backrest standard tests, in accordance with EN 1728:2012, without any structural failure. This paper presents a new approach for the chair manufacturing sector, with potential applicability to other types of furniture.

Evaluation of Tensile and Compression Bending Moment of L-Type Joints With 3D Printed Connectors

The paper investigates the bending moments under diagonal tensile and diagonal compression loads of L-type corner joints made of three wooden parts corresponding to the leg and the two stretchers used in chair construction. The wooden parts were jointed together with a 3D printed connector made of polylactic acid (PLA) filaments using Filament Fused Fabrication (FFF) as additive manufacturing technology. Larch (Larix decidua Mill.) wood was used to manufacture the wooden elements. In order to assess how the model orientation on the build platform influences the mechanical performance of the printed connector, two print positions were taken into account during the additive manufacturing (AM) process, namely horizontal and vertical. Mechanical testing under diagonal tensile and compression loads of the L-type corner joints, followed by the microscopic investigation of the fractured connectors with magnifications 50X, 80X, 100X were employed in this study. The results were compared with those of the reference L-type corner joint consisting of common mortise-tenon jointed wooden elements. The results show that the vertical orientation of the model on the build platform of the 3D printer is preferred for a better mechanical performance. The microscopy of the fractured connectors revealed the interlayer delamination of the filaments, especially in the case of the horizontal orientation of the model, which caused the wooden parts to slide out of the connector and record low values of the maximum failure loads.

Seismic performance enhancement of brick masonry walls by retrofitting with nominal RC bands: a study of diagonal compression tests

In-plane performance of un-reinforced brick masonry (URBM), retrofitted with nominal Reinforced Concrete (RC) bands, was investigated under diagonal compression tests using full-scale and half-scale specimens. The retrofitting technique is cost-effective, reliable, simple, easily implementable, and minimally intrusive. Six URBM wall specimens (three full-scale and three half-scale) served as control specimens, and similarly, six (three full-scale and three half-scale) were retrofitted with RC bands. All specimens were tested under diagonal compression in a computer-controlled servo-hydraulic universal testing machine using displacement-controlled scheme. Data on applied force and corresponding wall displacements were recorded. Responses of retrofitted specimens were compared with control specimens in terms of strength, deformation capacity, and failure patterns. Retrofitted specimens exhibited progressive damage due to ductile failure, showing a significantly increased deformation capacity and providing sufficient warning time before collapse. However, control specimens showed sudden catastrophic collapse due to sliding of bed-joints. Overall, retrofitted specimens demonstrated a significant enhancement of ductility. Next, a semi-empirical prediction formula for diagonal load capacity was established through macro-modelling approach and subsequent regression analysis to capture experimental results. From results, the proposed retrofitting scheme provides a promising solution for seismic risk reduction of existing deficient masonry structures in rural areas of the Indian subcontinent and elsewhere.

Experimental investigation of behavior of masonry wall under diagonal tension loading: Strengthening with CFRP versus TRM

Experimental investigation of behavior of masonry wall under diagonal tension loading: Strengthening with CFRP versus TRM

An Improved Reduced-Dimension Robust Capon Beamforming Method Using Krylov Subspace Techniques.

A reduced-dimension robust Capon beamforming method using Krylov subspace techniques (RDRCB) is a diagonal loading algorithm with low complexity, fast convergence and strong anti-interference ability. The diagonal loading level of RDRCB is known to become invalid if the initial value of the Newton iteration method is incorrect and the Hessel matrix is non-positive definite. To improve the robustness of RDRCB, an improved RDRCB (IRDRCB) was proposed in this study. We analyzed the variation in the loading factor with the eigenvalues of the reduced-dimensional covariance matrix and derived the upper and lower boundaries of the diagonal loading level; the diagonal loading level of the IRDRCB was kept within the bounds mentioned above. The computer simulation results show that the IRDRCB can effectively solve the problems of a sharp decline in the signal-to-noise ratio gain and an invalid diagonal loading level. The experimental results demonstrate that the interference noise of the IRDRCB is 3~5 dB higher than that of conventional adaptive beamforming, and the computational complexity is reduced by 15% to 20% compared with that of the RCB method.

A novel damage localization method of Circular Phased Array using Minimum Variance Distortionless Response Beamforming with Autocorrelation Matrix Diagonal Loading

Damage localization methods based on Acoustic Emission (AE) can be classified into time-based and waveform-based. However, the former requires a large number of sensors while the latter is limited to 2D plane localization. In order to address the challenge of achieving more accurate 3D localization using a reduced number of sensors, this paper proposes a Circular Phased Array using Minimum Variance Distortionless Response (MVDR) Beamforming with Autocorrelation Matrix Diagonal Loading (AMDL) method. Firstly, a sparse circular array is utilized to form multiple beamforming for coherent shear wave signals, decomposing the original 3D localization problem into Direction Of Arrival (DOA) estimation. Secondly, azimuth angle, elevation angle and autocorrelation matrix diagonal loading methods are introduced, working in conjunction with the MVDR beamforming algorithm. Finally, spatial integration is performed through matrix decomposition to solve geometric overdetermined equations. The effectiveness of the proposed method is validated through numerical simulations and experimental verifications under various damage conditions. Results indicate that estimation errors for azimuth and elevation angles are both less than 2 %, while 3D damage source localization errors remain within a range of less than 3 %. This proposed method extends beamforming technology from 2D plane localization to 3D localization, significantly reducing the complexity of sensor arrangement and lowering the cost of structural health monitoring systems by utilizing a small number of sensors.

Experimental study on the in-plane behavior of mud brick walls strengthened with bamboo strip mesh and dried jute thread

Despite advancements in modern structural engineering, adobe and mud brick constructions persisted as important housing options for a significant percentage of the world's population. However, because of their low strength and brittle nature, they are susceptible to natural disasters, especially earthquakes, which is a concern for many mud-brick buildings found in seismically active areas. To address this issue, this research investigated the in-plane behavior of 4 ft x 4 ft mud-brick walls strengthened with locally available materials i.e. Bamboo Strips and Dried Jute Thread in mesh format with various spacing. The specimens were subjected to compressive and diagonal shear loading separately. The data collected was analyzed to determine the important mechanical properties such as compressive strength, modulus of elasticity, shear strength, modulus of rigidity, and energy absorption. Notably, the bamboo strips technique improved these properties by 30 %, 19 %, 96 %, 82 %, and 195 %, respectively. The dried jute thread wrapping technique, on the other hand, demonstrated even greater improvements with increases of 40 %, 69 %, 102 %, 110 %, and 314 % for the same properties. Based on the experimental results, the proposed technique can be applied to mud-brick wall in seismically active areas.

Robust wideband beamforming algorithm based on frequency difference technique

This paper investigates a novel robust wideband beamforming algorithm based on the frequency-difference (FD) technique. While FD technique can maintain good frequency invariance (FI) of the beamformer, it introduces cross terms that can adversely affect performance. To reduce the cross terms, a projection preprocessing is implemented prior to FD operation exploiting the approximate orthogonality between steering vectors (SVs). Then, a robust beamformer is designed based on the estimated cross terms covariance matrix (CTCM) and SV of the signal of interest (SOI). The output of beamformer is an FD SOI. To restore the SOI, we design a filtering system and apply a simple diagonal loading beamforming to obtain the amplitude and phase of SOI, respectively. The simulation results have verified the effectiveness and superiority of the proposed algorithm in the presence of array errors.

Strengthening of reinforced concrete slabs using carbon fiber reinforced polymers rods and concrete jacket with a mechanical anchorage system

This study presented the development of a new method for strengthening of Reinforced Concrete (RC) slabs using Carbon Fiber Reinforced Polymer rods (CFRP) and an Ultra-High Performance Fiber Reinforcement Concrete (UHPFRC) external jacket with a Mechanical Anchorage System (MAS). The mechanical anchorage system includes two components: high-carbon steel plates and the Mechanical Expansion Anchorage Bolt System (MEABS), and it’s employed to prevent any premature de-bonding between the existing concrete surface and the externally strengthening layers (CFRP rods and UHPFRC jacket). The efficiency of the proposed strengthening method was evaluated through conducting an experimental test on a few fortified slabs by applying cyclic loads using a dynamic actuator. For this purpose, three distinct concrete slabs were tested to assess various design parameters, including a control slab, a strengthened slab with the UHPFRC jacket only, and a strengthened slab with CFRP bars at the bottom of the slab with an external UHPFRC jacket. The results of experimental tests reveal that the proposed strengthening system significantly enhanced the load capacity of the slab and prevented premature debonding failures between the old concrete of the slab and the new UHPFRC layer until the stage of slab failure. Accordingly, the new proposed strengthening system played a crucial role in enhancing the tension zone of the slabs and delaying the occurrence of diagonal crack loads. On the other hand, embedding CFRP bars within the UHPFRC jacket in the strengthened slab led to a notable enhancement of 82 % in the ultimate load capacity of the slab. The FE and analytical models were developed to predict the behavior of the specimens. The models' outcomes were in good agreement with the experimental data. Consequently, the new proposed strengthening system emerges as a reliable technique for enhancing the performance of reinforced concrete slabs, eliminating the risk of debonding between old and new parts.

Behavior of ultra-high-performance concrete deep beams reinforced by basalt fibers

Abstract Deep beams are crucial for construction projects due to their load-carrying capacity, shear resistance, and architectural adaptability. Ultra-high strength concrete and ultra-high-performance concrete (UHPC) are used in their production. Basalt fiber is used as an alternative due to its corrosion resistance, tensile strength, and thermal stability. This study investigates the behavior of UHPC deep beams reinforced with basalt fibers. Three sets of 11 specimens were constructed without transverse reinforcement and reinforced with either fibers or steel fibers. The study also analyzes the impact of parameters like shear strength capacity, crack development, and load-deflection behavior on UHPC deep beams. The study discovered that the inclusion of basalt fibers in UHPC deep beam can effectively postpone the onset of diagonal cracks. Incorporating basalt fiber at concentrations of 0.5, 0.75, and 1.0% led to respective increases of 48.17, 70.07, and 86.66% in the diagonal fracture force, as compared to the inclusion of steel fibers which resulted in increases of 18.24, 56.93, and 98.54% in diagonal fracture loads. The ideal ratio for enhancing the maximum shear capacity was found to be 0.75% of basalt. This specific percent resulted in the highest measured force out of the three percentages that were examined. The addition of basalt fibers at concentrations of 0.5, 0.75, and 1.0% resulted in respective improvements of 11.62, 30.08, and 28.69% in the ultimate shear capacities. During that period, steel fibers significantly enhanced the ultimate shear capacity, resulting in an increase of 19.83, 34.49, and 55.24% compared to specimens without fiber reinforcement. Regarding the second parameter of this investigation, a drop in the shear span ratio is linked to an augmentation in shear capacity and a reduction in mid-span deflection to varying extents for both the utilization of basalt and steel fibers.

Axial mechanical response of concrete pipe jacking considering the deflection of the bell-and-spigot joint: Full-scale test and numerical simulation

The bell-and-spigot joints play a vital role in the axial mechanical response of pipe jacking. This paper investigates the influence of joint deflection on the axial stress distribution and jacking load transfer of concrete pipe jacking via full-scale tests and numerical simulation. The joint deflection contributes to the single-side eccentricity or diagonal eccentricity of the pipe segments. The increase in joint deflection influences the extension of axial stress concentration in the vertical direction near the joint, while the increase in jacking load enhances the maximum compressive stress of the pipe wall in the alignment direction. In addition, the nonlinear axial strain–stress property of the cushioning plank among the segments resulted in the nonlinear transfer of the jacking load. Moreover, the joint deflection also induces the visible tensile stress or inelastic stress of the pipe under diagonal loading mode, indicating a risk of structural damage.

A Robust Sidelobe Cancellation Algorithm Based on Beamforming Vector Norm Constraint

Sidelobe cancellation (SLC) is a well-established beamforming technique for mitigating interference, particularly in the context of satellite communication (SATCOM). However, traditional SLC suffers from the issue of partially canceling the desired signal at high signal-to-noise ratio (SNR), primarily due to unconstrained beamforming processing. Extensive research has been conducted to address this problem; however, existing algorithms have limitations such as dependence on knowledge of signal array vectors or number of interferers and involve high computational complexity. In this paper, we propose a robust SLC algorithm based on beamforming vector norm constraint. Our proposal offers a practical solution by only requiring knowledge of the earth station antenna gain and maximum auxiliary array gain to the desired signal, both of which are fully known. Furthermore, compared to traditional SLC, our proposed method introduces additional computational complexity that only scales linearly with the size of the auxiliary array. Simulation results demonstrate comparable performance between our proposed method and existing techniques such as diagonal loading and spatial degrees-of-freedom control-based algorithms.

Farklı Duvar ve Harç Malzemeleri İle Üretilen Duvarların Mekanik Özelliklerinin Belirlenmesi

Walls produced using different masonry materials and mortars are among the structural elements that carry horizontal and vertical loads. In this context, the mechanical properties of walls produced with different wall and mortar materials have been investigated. In the production of wall samples, Harman Brick (HB), Masonry Brick (MB) and Bimsblok (BB) were chosen as the mesh material Reinforced Mortar (RM) and Polypropylene Fiber Added Mortar (PM) were used as binding materials in the construction of the walls produced in 900x900 mm dimensions. The volumetric mixing ratios of the mortar used were prepared as sand:cement:lime=6:1:1, according to the TSE 2510 standard. The bricked wall samples were subjected to diagonal loading tests after being kept in the laboratory environment for 28 days. Flexural and compressive strengths of the mortars used in wall building, displacement values of the walls, shear strength, rigidity modulus, energy absorption capacity and collapse patterns of the walls were determined. The graphs of the displacement values obtained by examining the behaviors observed in the test samples and the cracks formed were interpreted. It was observed that the shear strength of the walls built using PM was higher than the shear strength of the walls built using RM. The energy absorption capacity was highest in the fibrous specimen laid with masonry bricks. The average vertical load value of the wall specimens built with fibrous mortar, which is the BB of the masonry material, was 30% higher than the specimens built with non-fiber mortar.

Analysis on the effect of lateral force variation induced by the lubrication condition between wheel and rail for diagonal wheel load unbalance of railway bogie

Analysis on the effect of lateral force variation induced by the lubrication condition between wheel and rail for diagonal wheel load unbalance of railway bogie

Source Enumeration Utilizing Adaptive Diagonal Loading and Linear Shrinkage Coefficients

Source Enumeration Utilizing Adaptive Diagonal Loading and Linear Shrinkage Coefficients

Donatılı Zeminler için Alternatif Hafif Kompozit Panel Elemanları

Steel reinforced concrete facing members, which are used to fix geosynthetic reinforcements working against tensile forces inside soils and to resist active lateral earth pressures, have certain disadvantages, such as massiveness and corrosion. In addition, the aforementioned conventional panels are not economical since they frequently require maintenance and repair in terms of long-term stability. In this study, the utility of alternative composite panels is evaluated with the various arrangement and type of fiber reinforcements and a typical foam concrete. Panel tests and three-point bending tests are realized to determine the experimental behavior of steel, carbon fiber (CFRP) and glass fiber reinforced (GFRP) specimens, as well as unreinforced examples. Although CFRP wrapped specimens cannot reach expected levels, samples with GFRP present favorable performance as well as being cheaper. Specimens with mat GFRP enhance both strength and deformation capacities according to the results of axial and lateral deformations under diagonal loading condition. In addition, chopped GFRP applied foam concrete specimens have more strength in terms of bending test results, but CFRP reinforcements increase their displacement capacity.

Characterization of mechanical behavior of different types of masonry with a detailed investigation of full-field strain using digital image correlation

This article presents an experimental study on the mechanical characterization of three different types of masonry: burnt clay bricks, fly ash bricks, and autoclaved aerated concrete (AAC) blocks, with a detailed focus on strain distribution and failure mechanism. The specimens were subjected to direct and diagonal compression loading, and the stress–strain curves and failure modes were studied. Digital image correlation (DIC) was used to obtain full-field strain data, allowing for detailed analysis of failure mechanisms, tracking of crack propagation, and examination of other intricate details. The DIC analysis showed that in burnt clay brick and fly ash brick masonry, failure under compression was initiated by the tensile splitting of the brick, while in AAC block masonry, it was initiated by the tensile splitting of the mortar. Additionally, the study identified that the failure modes under diagonal compression were different for each type of masonry, with bed joint sliding being the dominant failure mode in fly ash brick and AAC block masonry. In contrast, the failure mode in burnt clay brick masonry was due to vertical splitting along the loaded diagonal. In the diagonal compression test, the shear strain along both diagonals was negligible, and principal strain directions were observed to be aligned along the two diagonals.

Lamb wave based damage imaging using an adaptive Capon method

As plate-like structures are widely used in railway vehicle systems, structural health monitoring and nondestructive testing of those structures are important. The Lamb wave, as an ultrasonic guided wave propagating in plate-like structures, is an effective tool for fault diagnosis. The Capon method is widely used in Lamb wave based damage imaging due to its superior performance in suppressing background noise compared with the conventional delay-and-sum method. As the conventional Capon method is sensitive to modeling errors like the inaccuracy of the look-direction, diagonal loading is usually adopted to regularize the inverse of the covariance matrix. However, the degree of diagonal loading is related to the accuracy of the given look-direction and is hard to determine accurately. Aimed at improving the imaging quality of the conventional Capon method, an adaptive Capon method with adaptive diagonal loading is proposed. In the proposed method, the dispersion and the amplitude caused by wave diffusion are first compensated for each imaging point using the virtual time reversal technique. The correlations among the compensated waveforms after windowing are used to determine the degree of diagonal loading. In the process of regularizing the inverse of the covariance matrix, a large diagonal loading factor will be applied when the correlations among the compensated waveforms are large. As correlations are closely related to the signal phase, both the amplitude and the phase of scattering signals are utilized in the proposed method. The numerical and experimental validations on an aluminum plate are carried out to verify the effectiveness of the proposed method. The results show that compared with the conventional Capon method, the proposed method can obtain images with higher imaging quality, fewer artifacts, and lower noise.

Broadband Beamforming Using the Least Square Method Improved via Adaptive Diagonal Loading

The least square method (LSM) is a commonly used beamforming method. However, it limits the beamforming frequency bandwidth and is vulnerable to noise; therefore, diagonal loading is used to overcome these limitations. The diagonal loading proposed in this study can be used for broadband beamforming in cases in which noise does not exist, and it makes the loading factor adaptive to a singular value distribution. The simulation results show that the proposed method works stably above the beamforming frequency limit, even for an extended beamforming frequency. We expect that the proposed method can be used to form frequency-invariant beam patterns used in monopulse algorithms to detect signals of unknown frequencies.

Failure Mode Prediction of Unreinforced Masonry (URM) Walls Retrofitted with Cementitious Textile Reinforced Mortar (TRM)

The brittle failure of unreinforced masonry (URM) walls when subjected to in-plane loads present low shear strength remains a critical issue. The investigation presented in this paper touches on the retrofitting of URM structures with textile-reinforced mortar (TRM), which enables shifting the shear failure mode from a brittle to a pseudo-ductile mode. Despite many guidelines for applying composite materials for retrofitting and predicting the performance of strengthened structures, the application of TRM systems in masonry walls is not extensively described. A thorough retrospect of the literature is presented, containing research results relating to different masonry walls, e.g., bricks, cement, and stone blocks strengthened with TRM jackets and subjected to diagonal compression loads. The critical issue of this study is the failure mode of the retrofitted masonry walls. Available prediction models are presented, and their predictions are compared to the experimental results based on their failure modes. The novelty of this study is the more accurate failure mode prediction of reinforced masonry with TRM and also of the shear strength with the proposed model, Thomoglou et al., 2020, at an optimal level compared to existing regulations and models. The novel prediction model estimates the shear failure mode of the strengthened wall while considering the contribution of all components, e.g., block, render mortar, strengthening textile, and cementitious matrix, by modifying the expressions of the Eurocode 8 provisions. The results have shown that the proposed model presents an optimum accuracy in predicting the failure mode of all different masonry walls strengthened with various TRM jackets and could be taken into account in the regulations for reliable forecasting.