Shear Distortion Research Articles

Objective detection of shear distortion of low-light-level image intensifier based on global scanning and image patch edge feature analysis

Objective detection of shear distortion of low-light-level image intensifier based on global scanning and image patch edge feature analysis

Testing of precast recycled aggregate concrete shear wall with pressed sleeve connection subjected to cyclic loading

AbstractThe pressed sleeve connection is a new type of connection technique reported in China recently. To explore the possibility of combining the advantages of pressed sleeve connections and recycled aggregate concrete (RAC) in precast concrete, the seismic performance of precast shear walls with pressed sleeves and recycled fine aggregate (RFA) concrete was investigated through a thorough experimental programme. A total of seven precast shear wall specimens and one cast‐in‐situ specimen were fabricated and tested under lateral cyclic loading, considering the effects of the aspect ratio, the axial compression ratio, and the RFA content. The failure modes, hysteretic behavior, bearing capacity, energy dissipation, stiffness and shear distortion of the specimens, as well as the strains of the steels, were reported and discussed. The test results demonstrated that the pressed sleeve connections were capable of transmitting both tensile and compressive forces between reinforcements, and the precast shear walls with pressed sleeve connections exhibited the same hysteresis behavior, strengths, ductility coefficient and energy dissipation capacity as the cast‐in‐situ counterpart. Moreover, the seismic behavior of the precast specimens with the RFA content of 30% was almost the same as those with natural aggregate concrete (NAC). The increase in the axial compression ratio and aspect ratio led to higher peak loads of the precast shear walls. Finally, existing design methods of ordinary reinforced concrete shear walls were evaluated for their application to the design of precast RFA concrete shear walls with pressed sleeves. Overall, the evaluation results revealed that the examined design methods offer generally accurate strength predictions for the proposed shear walls.

Raman Evidence of Multiple Adsorption Sites and Structural Transformation in ZIF-4

The zeolitic imidazolate framework, ZIF-4, exhibits soft porosity and is known to show pore volume changes with temperatures, pressures, and guest adsorption. However, the mechanism and adsorption behavior of ZIF-4 are not completely understood. In this work, we report an open to narrow pore transition in ZIF-4 around T ∼ 253 K upon lowering the temperature under vacuum (10-6 Torr) conditions, facilitated by C-H···π interactions. In the gaseous environment of N2 and CO2 around the framework, characteristic Raman peaks of adsorbed gases were observed under ambient conditions of 293 K and 1 atm. A guest-induced transition at ∼153 K resulting in the opening of new adsorption sites was inferred from the Raman spectral changes in the C-H stretching modes and low-frequency modes (<200 cm-1). In contrast to a single vibrational mode generally reported for entrapped N2, we show three Raman modes of adsorbed N2 in ZIF-4. The adsorption is facilitated by dispersive and quadrupolar interactions. From our temperature-dependent Raman results and theoretical analysis based on the density functional tight-binding approach, we conclude that the C-Hs are the preferred adsorption sites on ZIF-4 in the following order: C4-H, C5-H > C2-H > center of the Im ring (interacting with C-H centers) > center of the cavity. We also show that with an increasing concentration of N2 adsorbed at low temperatures, the ZIF-4 structure undergoes shear distortion of the window formed by 4-imidazole rings and consequent volumetric expansion. Our results have immediate implications in the field of porous materials and could be vital in identifying subtle structural transformations that may favor or hinder guest adsorption.

Anti-Aliasing Attention U-net Model for Skin Lesion Segmentation

The need for a lightweight and reliable segmentation algorithm is critical in various biomedical image-prediction applications. However, the limited quantity of data presents a significant challenge for image segmentation. Additionally, low image quality negatively impacts the efficiency of segmentation, and previous deep learning models for image segmentation require large parameters with hundreds of millions of computations, resulting in high costs and processing times. In this study, we introduce a new lightweight segmentation model, the mobile anti-aliasing attention u-net model (MAAU), which features both encoder and decoder paths. The encoder incorporates an anti-aliasing layer and convolutional blocks to reduce the spatial resolution of input images while avoiding shift equivariance. The decoder uses an attention block and decoder module to capture prominent features in each channel. To address data-related problems, we implemented data augmentation methods such as flip, rotation, shear, translate, and color distortions, which enhanced segmentation efficiency in the international Skin Image Collaboration (ISIC) 2018 and PH2 datasets. Our experimental results demonstrated that our approach had fewer parameters, only 4.2 million, while it outperformed various state-of-the-art segmentation methods.

Behaviour of bamboo scrimber I-beam-box-column connections under static loads

As an eco-friendly construction material, bamboo scrimber has been increasingly investigated recently in terms of mechanical properties and member behaviour. However, limited test data about connection behaviour are available in published literature. This paper addresses the behaviour of bamboo scrimber I-beam-box-column connections under static loads. Two types of bamboo scrimber beam-column connections were tested, and the number of bolts connecting the beam flange and steel angles or T-stubs was also varied in the experimental programme. The moment resistance, failure mode and deformation capacity were obtained for connections. The shear strength and distortion of panel zones were quantified from experimental data. Comparisons were also made between the calculated shear strengths of panel zones and bamboo scrimbers. Finally, design methods were used to calculate the shear and moment resistances of bamboo scrimber I-beam-box-column connections subjected to static loads. Comparisons between experimental and calculated results suggest that the design methods could evaluate the shear and moment resistance of beams with good accuracy.

Shear-reduced seamless parametrization

Shear distortion has been a popular formal and informal measure, whether used quantitatively or visually, in assessing the quality of mappings or the shape of elements in a quad mesh. Nevertheless, well-known energies such as conformal- and isometric-based energies do not directly target lowering shear distortion but only bound it. Consequently, the shear distortion can be unnecessarily high.We introduce a new shear energy and offer an efficient way to incorporate it in the latest state-of-the-art optimization framework. The resultant mapping has substantially lower shear distortion, and the cost is a reasonably low addition of conformal or isometric distortion. The energy is minimized efficiently, and the run time of an iteration is of the same order of optimizing other popular energies. We also introduce a new scale-invariant, second-order smoothness energy that when combined with the shear energy, leads to smooth anisotropic mappings with low shear distortion.We demonstrate these energies and compare with the state of the art in the application of seamless parametrization, where the quality of mapping a checkerboard pattern is paramount since it directly affects the quality of an extracted quad mesh.

Damage and Failure of a Column-Supported RC Flat Slab Subjected to Impulsive Loading

RC flat slabs supported by an array of columns subjected to the action of impulsive pressure were investigated. The slabs were designed for static loads according to current standards. The dynamic responses of 4 × 4- and 8 × 8-column-supported slabs were similar, as were damage and failure. A simplified model consisting of a tributary area and a central column yielded similar results, demonstrating the accuracy of the simplified model and its reliability. These analyses exhibited modes of damage and failure characterized by large shear distortions in the slab–column connection zone. The rest of the span remained undamaged and in a horizontal position. In all analyses, the slab concrete around the column was fully damaged. The rebars failed within a limited zone at the slab–column connections. The early failure of integrity reinforcement indicated that it could not fulfill its duty; thus, a subsequent progressive collapse scenario was inevitable. All bent-up rebars failed, and their contribution to shear resistance was doubtful. The static analysis was entirely different from the dynamic failure mode. Impulsive loading damage and failure were similar to those in the case of slab-on-slab impact; in both cases, the slab underwent large displacement and severe damage in the narrow slab–column zone, whereas the rest of the slab remained almost completely flat and undamaged.

Seismic in-plane displacement capacity of masonry barrel vaults: the role of constructive aspects

Historic masonry vaults are one of the most vulnerable elements with respect to the seismic action. Cracks are often detected after post-earthquake surveys. However, it is difficult to directly link the observed damage to causes. Different mechanisms can occur during an earthquake, such as in-plane horizontal shear distortion or longitudinal opening/closing of the abutments. These mechanisms are not necessarily associated to a specific crack pattern, since other factors are involved in the determination of the detected crack status. Among these factors, constructive aspects (such as the brick pattern) play a major role. This study aims at investigating the possible correlation between constructive aspects and the crack pattern in barrel vaults subjected to in-plane shear mechanism. Numerical simulations are carried out on an ideal circular vault with a rectangular base of dimensions 3.1 × 5.3 m, and rise of 1.175 m. Three brick patterns are considered: radial, diagonal and vertical. In order to investigate these aspects, a micro-modelling numerical approach has been adopted. Results are presented in terms of ultimate displacement capacity, collapse mechanisms and crack pattern charts.

Process Optimization of Injection Overmolding Structural Electronics with Regard to Film Distortion

The integration of structural electronics in injection-molded parts is a challenging step. The films-comprising of laminated stacks with electronics-are exposed to shear stresses and elevated temperatures by the molten thermoplastic. Hence, molding settings have a significant impact on the successful, damage-free manufacturing of such parts. In this paper, test films with polycarbonate (PC) sheets as outer and two different thermoplastic polyurethanes (TPUs) as middle layers incorporating conductive tracks on a flexible printed circuit board (flexPCB) are manufactured and overmolded with PC. Parameter studies investigating the influence of the melt temperature, mold temperature, injection speed and used TPU layer were performed. The molded parts were inspected visually and compared with a numerical simulation using injection molding software. A shear distortion factor for the TPU layer was derived based on the simulations that linked the shear stresses with the injection time and the softening (melting) of the TPU. The distortion of the films was found to reduce with higher melt temperature, lower mold temperature and faster injection speed. Films using the TPU with the higher melting temperature yielded significantly better results. Moreover, distortion on the films reduced with the increasing distance to the gate and a larger cavity thickness was found to be beneficial. All those relations could be correlated with the shear distortion factor.

Cyclic behavior of RC beams under artificial climate rapid freeze-thaw environment: A further research

Frost damage to concrete can make concrete beams more vulnerable under seismic forces. However, research on the seismic performance of frost-damaged reinforced concrete (RC) beams is still in its infancy. In this paper, the effects of freeze–thaw cycles (FTCs) and concrete strength on the seismic performance of frost-damaged RC beams are studied using an artificial rapid freeze–thaw climate and pseudo–static test in sequence. The seismic resistance of frost-damaged RC beams is assessed in the following respects: general damage behavior and failure pattern, hysteresis response, displacement, strength, cumulative energy consumption, and shear component. It turns out that, with the increase in the number of FTCs (NFTCs), the load and displacement under different characteristic states, ductility ratio, and cumulative energy consumption decrease stage by stage, while the shear distortion and the contribution of shear displacement under the entire cyclic loading process are progressively enhanced. Simultaneously, the strength of the cracking point is more susceptible to FTC action than to yield and peak points, and the declining rate of strength under different characteristic points gradually increases. Based on the test results, a calculation formula for the skeleton curve of frost-damaged RC beam–column is established, taking the influences of the pristine concrete strength, NFTCs, and axial force ratio into account.

Effect of Torsion on the Structural Response to Ground Movements

Structures, which are subjected to tunneling or open cutting-induced ground movements, are frequently skewed with respect to the direction of tunnel advance or the excavation face. The structures may be subject to a torsion, which is a type of shear (angular) distortion, due to differential settlement or out-of-plane distortion in 3D conditions and can be damaged more severely than structures with only in-plane distortion. Therefore, the effect of torsion should also be carefully considered when investigating a stuctural response to ground movements. This study examines the effects of torsion on the structural response to ground movemnts based on field case studies and 3D numerical tests.

Study on the damage quantification model for exterior beam-column joints with headed bars in RC buildings based on the experimental data

The main purpose of this work is to suggest formulas for estimating strengths external of beam-column (B/C) joints with headed bars in reinforced concrete (RC) buildings, with respect to the main failure modes, under cyclic loading. At first, this work collects relevant experimental data to confirm existing models and code formulas for the strength of external B/C joints with headed bars related to side-face blowout failure or concrete breakout failure. Furthermore, for the damage control, models to estimate the shear distortion and shear crack width of external B/C joints are proposed. Finally, a simplified procedure for controlling damage is developed.

Experimental verification of a beam element for thin-walled beams with torsion, distortion, and shear lag

Beam-type elements based on the theories of Euler–Bernoulli, Timoshenko, and Vlasov are widely used in civil engineering. However, shell and solid finite elements are often used when the effects on normal stresses of either shear deformation or distortion are considered important. Numerically validated in an earlier study with finite element models for shell-type structures, the same one-dimensional finite element model is further developed in this study with a low number of degrees of freedom per node that includes all the structural mechanisms without using 3D finite element models. Laboratory testing of an instrumented steel box girder is conducted, to improve validation of the goodness of fit of the finite element model with real structural behavior.

Seismic demands of steel moment resisting frames with inelastic beam‐to‐column web panel zones

AbstractThis paper intends to provide quantitative seismic response characteristics of steel moment resisting frames (MRFs) with inelastic beam‐to‐column panel zone joints. Two modeling approaches are proposed for this purpose along with a methodology to consider the fracture potential at the bottom beam flange in steel MRFs due to panel zone kinking. Both approaches, which are validated with available experiments, preserve the behavioral insights of inelastic panel zones. Nonlinear static and dynamic analyses are then conducted to quantify the seismic demands of 32 prototype steel MRFs while their panel zones exhibit various levels of inelastic deformations. Engineering demand parameter hazard curves are developed to interpret the results for a risk‐targeted seismic performance. The results demonstrate that steel MRFs with panel zone shear distortions of 10 to 15 times the shear distortion at yield, , have a mean annual frequency of collapse ranging from to , which is up to two times lower than corresponding results with code‐compliant steel MRFs (i.e., It is shown that steel MRFs with inelastic deformations of 10 in their panel zones, (a) enjoy up to 50% reduction in residual story drift ratios at a design basis earthquake; (b) their beam‐to‐column connections do not experience fractures due to panel zone kinking; and (c) local buckling in steel beams is very limited even at low probability of occurrence earthquakes. The above hold true when the current detailing and fabrication practice is employed. The findings have implications on seismic design and the post‐seismic repairability of steel MRFs.

First-Principles Study of the Physical Properties of CuV-=SUB=-2-=/SUB=-S-=SUB=-4-=/SUB=- under Pressure

The structural, electronic, mechanical, thermodynamic, and optical properties of CuV2S4 have been studied under pressure (0-50 GPa) by employing first-principles computation depending on the density functional theory. The optimized structural constraints are in good accord with the experimental results. By employing different pressure, the variation of single crystal elastic constant Cij as well as polycrystalline mechanical parameters are evaluated and discussed in detail. The increment of elastic constant with the increase in pressure guaranteed that CuV2S4 turn ought to be more resilient to shear distortion with pressure. The linear response of elastic moduli under pressure confirms that hardness of CuV2S4 rises with increasing pressure. The Pugh's ratio ensured the ductile nature of CuV2S4. Band structure and DOS calculations have been confirmed the electrically conductive nature of CuV2S4. The population analysis validates the presence of dominant covalent bonding. Optical properties, i.e., absorption, conductivity, reflectivity, and loss function are also explored with the variation of pressure. These optical functions demonstrate that the compound exhibits high reflectivity in the low-energy range, which assures the application of this compound as coating material. The thermodynamic properties are also investigated under pressure and discussed. Keywords: first-principles study, spinel-type compound CuV2S4, mechanical properties, electronic properties, optical and thermal properties.

Experimental response of unreinforced exterior RC joints strengthened with prestressed steel strips

The response of unreinforced beam-column joints represents a key issue in seismic vulnerability and fragility assessment of existing Reinforced Concrete (RC) buildings. A great attention has been focused on the investigation of the experimental response of unreinforced joints and their possible strengthening strategies.In this study, an experimental investigation of the response of exterior RC beam-column joints strengthened with prestressed steel strips is presented. Four full-scale specimens were tested, two non-strengthened and two strengthened. The non-strengthened specimens were built with (specimen S) or without (NS) stirrups in the joint panel and were tested for reference and comparison purposes, in order to reproduce a seismic code-compliant and a non-conforming RC joint, respectively. The strengthened specimens had two different layouts characterized by a higher (CAM1) or lower (CAM2) complexity of installation and level of building disruption.The response of specimen NS was controlled by joint panel failure following beam yielding, whereas the specimen S showed a ductile response, controlled by beam flexural failure. The response of specimens CAM1 and CAM2 demonstrated the effectiveness of the adopted technology. For CAM1, a ductile response was observed, similar to specimen S. For CAM2, a joint panel failure following beam yielding was observed, as for specimen NS, but with a significantly higher global ductility.The presence of prestressed steel strips led to a delay in the onset of diagonal cracking, with a slight increase in strength at this condition, i.e. by 8%, but a significantly higher deformation capacity, with the drift increasing, on average, by 122%. The strengthening led to a relatively slight increase in the resistance of the subassemblage, which was very similar in specimens S, CAM1 and CAM2, and, on average, 11% higher than in specimen NS. Instead, a much more significant difference was observed in terms of deformation capacity, with the drift at conventional ultimate condition in specimens CAM1 and CAM2 77% and 61% higher than specimen NS, respectively.The experimental results are reported, and the effectiveness of the tested strengthening solutions is discussed, in terms of global response of the subassemblage, observed damage evolution, energy dissipation capacity, and local response, such as joint shear distortion and measured strain of strengthening steel strips.

Experimental investigation on seismic performance of two types of member-panel zone unified joints for precast concrete moment-resisting frame

Recently, precast concrete (PC) moment-resisting frame (MRF) is widely used for lateral load-resisting systems in buildings such as semiconductor factories requiring a short construction period and high quality of materials, but its application is limited to high-seismicity regions due to complex in-situ assembly between PC members and low seismic performance of joints. This paper presents the evaluation on cyclic behavior of two types of member-panel zone unified PC joints, in which the panel zone is unified with a PC beam or column, designed for use in high-seismicity regions. Two specimens of the member-panel zone unified joints and a benchmark specimen of cast-in-place joint (CIP) were tested under cyclic loading and were analyzed about crack patterns, failure mode, hysteretic behavior, shear distortion, and reaction moment of beams to compare the cyclic behaviors of PC joints with the CIP joint. The seismic performance of each specimen was evaluated in terms of allowable drift ratio, strength & stiffness degradation and energy dissipation capacity suggested in the current code. The maximum strength of the beam-panel zone unified PC joint was comparable to that of the CIP joint, and the crack pattern and failure mode were found to be similar to that of the CIP joint with shear failure of the panel zone. The seismic performance of the beam-panel zone unified PC joint satisfied the criteria applicable to special MRF. On the other hand, the column-panel zone unified PC joint exhibited the flexural failure of the PC beam due to a biased distribution with a high bending moment on either beam, which significantly contributed to a low maximum strength than that of the CIP joint. In spite of relatively low strength, the seismic performance of the column-panel zone unified PC joint satisfied the criteria except for the allowable drift ratio. It was shown that the member-panel zone unified PC joint can be applied as the special MRF by improving the workability and securing high seismic performance. • Cyclic tests on two types of member-panel zone unified PC joints were conducted to investigate seismic performance compared to cast-in-place joint. • Two distinct failure modes were observed depending on PC members unified with panel zone. • Gap-opening between PC beam and panel zone significantly reduced strength of joint contrary to gap-opening between PC column and panel zone. • Column-panel zone unified joint showed low strength due to biased bending moment to one side of PC beam generated by gap-opening. • Beam-panel zone unified joint had comparable seismic performance with conventional cast-in-place joint in terms of strength, stiffness, and energy dissipation capacity.

A New Macromodel of Beam-Column Joints for Progressive Collapse Analysis of Reinforced Concrete Structures Under Blast Loading

The macromodel, by which the beam and column are simulated by fiber beam elements, has been extensively used in the progressive collapse analysis of reinforced concrete (RC) frames due to its high computing efficiency as compared to the solid element model. However, there exist some problems that need to be solved to improve the accuracy of the macromodel. One typical issue is to develop an accurate beam-column joint model. In current practice, the beam-column joint is as part of the rectangular frame with rigid elements, neglecting the shear damage and bending moment distribution in the core region of the joint, although they are crucial to progressive collapse analysis. In this paper, a new macromodel that considers the shear damage and bending moment distribution in the core region of the beam-column joint is developed for the progressive collapse analysis of RC frame structures under blast loads. Nonlinear springs are used in the joint connection interfaces to consider the force transfers from the beams or columns to the joint. Also, nonlinear shear springs are used in the core region of the joint, whose characteristics are derived based on the actual force-deformation relationship of the sub-assemblage due to joint shear distortion, to model the shear damage of the joint under blast loading. The proposed beam-column joint macromodel is validated with the available test data in the literature. The results indicated that the proposed macromodel for beam-column joints is more accurate than the traditional beam-column joint macromodel, while the computing efficiency remains almost unchanged in progressive collapse analysis of RC structures, especially when the RC frame structures are seriously damaged or collapse under blast loadings.

Critical Comparison of Assessment Codes for Steel Moment Resisting Frames

AbstractMany existing steel multi‐storey frame buildings worldwide were designed prior to the introduction of modern seismic design provisions or based on outdated hazard maps considering low values of seismic intensity. This often resulted in buildings showing low performances with respect to earthquake loads. Assessment codes, such as the Eurocode 8 Part 3 and the ASCE 41, have been conceived to provide tools to assess the seismic performance of existing structures, to evaluate their adequacy with respect to the current safety standards and the need for seismic retrofit. However, recent research studies have revealed the necessity for a revision of these codes. In particular, for steel moment resisting frames, the current European regulation shares many similarities with older versions of the American codes, but has failed to incorporate changes based on the state‐of‐the‐art knowledge. In addition, the undergoing update of other parts of the Eurocode motivates a full revision of the current standards. This paper compares the assessment procedures of the European and American codes. Two low‐code steel Moment Resisting Frames were considered for case study purposes and the assessment was performed based on three local Engineering Demand Parameters (EDPs), i.e., column's rotation, beam's rotation and panel zone's shear distortion, and the inter‐story drift as global EDP. Incremental Dynamic Analyses were performed for the development of component and system fragility curves. The present work aims to identify some challenges and to provide some preliminary insights for the revision of the Eurocode 8 Part 3.

Analytical Solution for Longitudinal Dynamic Responses of Long Tunnels under Arbitrary Excitations

In this paper, an analytical solution is proposed for longitudinal dynamic responses of long tunnels under arbitrary excitations. For the derivation, the tunnel is assumed as a Timoshenko beam resting on a visco-Pasternak foundation. The Timoshenko beam theory is employed to consider both effects of the shear distortion as well as the rotary inertia of the tunnel, which are neglected by the Euler–Bernoulli beam. The visco-Pasternak foundation is applied to represent the viscoelastic compressive and shear resistance of soil. The governing equations of motion are transformed from partial differential forms into algebraic forms through integral transformations, and thus the solutions are conveniently obtained. The analytical solutions of the tunnel under several specific dynamic loads, including impulsive loads, moving line loads as well as traveling loads, are presented in detail and verified by comparing to the known degraded solution in literature and finite element results. Several examples are also conducted to investigate the influence of the relative stiffness ratio between the soil and the tunnel structure on the tunnel responses.