Weak Beam Research Articles

Seismic performance of cruciform bolted joints with various reinforcing details in modular steel construction

Extensive research has been done on exterior T-shaped joints of modular structures. The modular structure consists of stacked modules that are not only connected vertically but also need to be connected horizontally. The horizontal connection between modules is another key for the modules to form an integral structure and resist lateral forces. This paper proposes a novel bolted joint that can be applied to multi-column module internal and external connections. By designing special loading supports, three internal cruciform joints and three external cruciform joints of the modular structure were tested under column end loading. The effects of different strengthening measures and the ratio of beam to column flexural bearing capacity on the seismic performance of the joints were compared. The results showed that all the joints had good seismic performance and satisfied the requirements of SMF systems in terms of inter-story drift ratio. The stiffness and bearing capacity of the internal joints after the beam-beam combination increased by 33.2% and 17%, respectively. However, the stiffness and bearing capacity of the cruciform joints strengthened by the cover plate are not significantly improved. For joints that meet the conditions of strong columns and weak beams, modular beams can reach full-section plasticity and can meet the requirements of full-strength joints.

Building Response to Excavation-Induced Ground Movements from a Nonlinear-Inelastic Perspective

The nonlinear-inelastic response of reinforced concrete moment-resisting frame buildings due to an adjacent excavation in soft to medium clays is presented. An advanced numerical model is used to account for building-soil-excavation interactions, post-yielding behavior of the structural members, and solid-fluid coupled behavior of supporting soils. The effects of the excavation on the internal force redistributions of structural members, lateral and vertical distortions, ground surface settlements, and lateral wall movements are presented in terms of angular distortions and drifts, curvature ductility, axial forces, and flexural moments. Results showed how beams progressively developed plastic deformations as deep-seated movements occurred during the excavation of soft and medium clays, reaching maximum curvature ductility ratios larger than 2. As the excavation advanced, maximum curvature ductilities of up to 5 were computed in beams closer to the excavation, causing localized inelastic mechanisms in the building. This paper shows how even well-designed buildings to withstand large levels of lateral load demands using strong column–weak beam approaches can still be subjected to significant excavation-induced nonlinear-inelastic demands that can cause damage.

Analysis on Seismic Performance of Prefabricated Building Box Formwork Combination

The outbreak of novel coronavirus pneumonia since the end of 2019 has posed a great challenge to the world's public health security. According to the statistics of COVID-19 epidemic released by the World Health Organization, the global epidemic has accumulated more than 500 million infections and more than 6.2 million deaths. However, if all hospitals at all levels are changed to designated hospitals, it may cause a run on medical resources. Container building has the advantages of simple construction, short construction period, recyclability and cost saving, and can be effectively used in the rapid transformation of talent apartment buildings and general wards into designated hospitals for efficient use. During the COVID-19, Wuhan Huoshen Mountain Hospital and Leishen Mountain Hospital adopted the container structure design, which is similar to Lego, combining containers one by one, giving full play to the advantages of container buildings. However, the current container building code stipulates that container buildings are only applicable to low and multi-storey buildings with six floors or less. In order to improve the seismic performance of container buildings and expand the application scope of container buildings, this paper proposes a box form composite structure based on traditional containers. Through the analysis of mechanical performance parameters, it is concluded that the "strong column and weak beam" yield mechanism of the box form composite structure is good, The initial rigidity of the weak axis is 133% higher than that of the traditional container structure, the yield strength is about 3 times that of the traditional container structure, and the ultimate bearing capacity is 2.5 times higher than that of the traditional container structure.

ICESat-2 for Canopy Cover Estimation at Large-Scale on a Cloud-Based Platform.

Forest canopy cover is an essential biophysical parameter of ecological significance, especially for characterizing woodlands and forests. This research focused on using data from the ICESat-2/ATLAS spaceborne lidar sensor, a photon-counting altimetry system, to map the forest canopy cover over a large country extent. The study proposed a novel approach to compute categorized canopy cover using photon-counting data and available ancillary Landsat images to build the canopy cover model. In addition, this research tested a cloud-mapping platform, the Google Earth Engine (GEE), as an example of a large-scale study. The canopy cover map of the Republic of Türkiye produced from this study has an average accuracy of over 70%. Even though the results were promising, it has been determined that the issues caused by the auxiliary data negatively affect the overall success. Moreover, while GEE offered many benefits, such as user-friendliness and convenience, it had processing limits that posed challenges for large-scale studies. Using weak or strong beams' segments separately did not show a significant difference in estimating canopy cover. Briefly, this study demonstrates the potential of using photon-counting data and GEE for mapping forest canopy cover at a large scale.

Topological charge measurement in a four-level single layer graphene system

In this letter we have proposed a four-level graphene monolayer system for identifying the topological charge of Laguerre–Gaussian light. Here, we have shown that due to the four-wave mixing mechanism in the monolayer graphene system, a weak signal beam can be generated due to quantum coherence and interference effect. We have discussed the spatially dependent linear absorption spectrums of the weak probe and new generated signal beams via quantum mechanical density matrix formalism. We have found that by numbering the spot areas of the probe and signal beams, one can realize the topological charge of the Laguerre–Gaussian beam interacts by monolayer graphene system. Moreover, we have realized that for some topological charge the new generated signal beam can be amplified in the graphene system.

Beam Energy Dependence of the Linear and Mode-Coupled Flow Harmonics Using the a Multi-Phase Transport Model

In the framework of the A Multi-Phase Transport (AMPT) model, the multi-particle azimuthal cumulant method is used to calculate the linear and mode-coupled contributions to the quadrangular flow harmonic (v4) and the mode-coupled response coefficient as functions of centrality in Au+Au collisions at sNN = 200, 39, 27 and 19.6 GeV. This study indicates that the linear and mode-coupled contributions to v4 are sensitive to beam energy change. Nevertheless, the correlations between different-order flow symmetry planes and the mode-coupled response coefficients show weak beam energy dependence. In addition, the presented results suggest that the experimental measurements that span a broad range of beam energies can be an additional constraint for the theoretical model calculations.

Aperture-averaged scintillation for a weak underwater turbulence-affected Gaussian beam using the OTOPS model.

The calculation of optical system performance for laser beam propagation in optical turbulence, such as bit error rate (BER), signal-to-noise ratio, and probability of fade, requires the knowledge of scintillation. In this paper, we show the analytical expressions of the aperture-averaged scintillation using a new recently introduced power spectrum of the refractive index fluctuations for underwater turbulence, the oceanic turbulence optical power spectrum (OTOPS). In addition, we use this main result to investigate the impact of weak oceanic turbulence on free-space optical system performance for a propagating Gaussian beam wave. Similar to the atmospheric turbulence case, results show that aperture averaging can reduce the mean BER and the probability of fade several orders of magnitude if the receiver aperture is chosen with a diameter larger than the Fresnel zone, L/k. Being valid for weak turbulence regime in any natural waters, results present the variations of irradiance fluctuations and the performance of underwater optical wireless communication systems depending on the practical values of average temperature and average salinity concentration that can be encountered in any world's waters.

In situ EBSD/HR-DIC-based investigation on anisotropy mechanism of a near α titanium plate with strong transverse texture

The effect of strong transverse(T) texture on anisotropy deformation mechanism of Ti60 plate was in-situ investigated using the EBSD and the high resolution-digital image correlation (HR-DIC) technique. The yield strength and the ultimate tensile strength is in descending order: TD > RD > 45°, and the ductility shows the opposite trend. The tensile anisotropy related to the discrepancy of activated slip systems in RD, 45°, and TD. In yielding stage, prism<a> slip dominated in RD, basal<a> slip dominated in the 45° direction, while pyram <c+a > slip dominated in TD. The anisotropy coefficient χ was proposed to evaluate the resistance discrepancy based on all the activated slip systems, which well explained the trend of the tensile strength anisotropy. The ductility anisotropy has been analyzed through slip transmission and slip-GB interaction using HR-DIC technology, which is determined by residual dislocation under different tensile directions. The slip transmission can be easily achieved when the Burgers vector of incoming grain is a [2‾ 110] and the Burgers vector of outcoming grain is a [112‾ 0] in 45° direction, which can effectively weaken stress concentration on the grain boundary leading to the greatest ductility among three tensile directions. The dislocation structures in three directions have been analyzed under two-beam condition and weak beam dark field (WBDF) images.

Efficient diffraction control using a tunable active-Raman gain medium

We present a scheme to create an all-optical tunable and lossless waveguide using a controllable coherent Raman process in an atomic rubidium vapor in an $\mathcal{N}$-type configuration. We employ a Gaussian Raman field and a Laguerre-Gaussian control field to imprint a high-contrast tunable waveguidelike feature inside the atomic medium. We numerically demonstrate that such a waveguide is able to guide arbitrary modes of a weak probe beam to several Rayleigh lengths without diffraction and absorption. Our results on an all-optical waveguide-based scheme may have potential applications in lossless image processing, high-contrast biomedical imaging, and image metrology.

Developing a Mg alloy with ultrahigh room temperature ductility via grain boundary segregation and activation of non-basal slips

Poor room temperature (RT) ductility is an inherent disadvantage of magnesium (Mg) alloys, which limits their wide application. Grain refinement is an accepted method to improve ductility and strength simultaneously. However, obtaining ultrafine grains (about 1 μm and below) usually requires severe deformation processes, which is not conducive to be widely used. Here, by utilizing a distinctive design strategy, i.e., introducing beneficial solute to achieve grain boundary (GB) segregation and effectively reduce the critical resolved shear stress (CRSS) ratio between non-basal slips and basal slip, thus efficiently activating non-basal slips, we obtained a Mg-0.3Er (at%) alloy with moderate-fine grains (∼8 μm) having elongation near 50% at RT. Based on the results of in-situ electron back-scatter diffraction and slip trace analysis, and weak beam dark-field observation, we confirmed that minor Er element and appropriate fine grains would contribute to the activation of considerable non-basal dislocations and the suppression of twinning. In addition, through energy dispersive spectrometry element analyses for systematic investigation, we found that the GB segregation level of the alloy annealed at 300 °C is higher than that of the alloy annealed at 360 °C. The higher GB segregation level would impact the cohesion strength and be conducive to activate more non-basal dislocations to accommodate local stress, thus suppressing the GB cracking and finally improving the ductility. This study not only suggests an effective way for large-scale development of high ductility Mg alloys at RT, but also provides a new insight to elucidate the origins of ultrahigh ductility by revealing the fraction of non-basal slips and the level of GB segregation.

Experimental and Numerical Studies on the Seismic Performance of New Assembled Concrete Frame Beam–Column Joints

A new type of assembled concrete beam–column joint based on a bolted connection was proposed, aiming to complete the post-earthquake node repair work by replacing precast beams and bolts. To study the seismic performance of the new beam–column joints, two full-scale components of the new joints were fabricated and subjected to low cyclic loading. The whole process from crack generation to component failure was investigated in detail, and seismic performance indicators such as the hysteresis curve, skeleton curve and stiffness degradation curve were compared and analyzed. Based on the experimental results, ABAQUS finite element software was applied to numerically simulate cast-in-place joints and test joints. Based on the failure mechanism of the new assembled beam–column semi-rigid joints, a stress analysis of semi-rigid joints was carried out. The research results show that the two new joints have good seismic performance and energy dissipation performance. Bolts and precast beams are the main stress components, and the repair of new joints can be completed by replacing bolts, which meets the seismic design concepts of “strong columns and weak beams” and “strong joints and weak components”. The larger the diameter of the bolts, the higher the load capacity and the lower the stiffness degradation rate. The finite element simulation results are high-accuracy and can well reflect the seismic performance of the components. It is found that cast-in-place joints are better in energy dissipation capacity than test joints, but the ultimate bearing capacity of test joints is better than that of cast-in-place joints. Based on the experimental stress characteristics of the nodal core zone, a mechanical analysis model of the nodal core zone of the new assembled concrete beam–column joints is proposed, and shear force calculation equations for the core zone of the new assembled concrete beam–column rigid joints and semi-rigid joints are derived.

Electron sheaths near a positively biased plate subjected to a weak electron beam

Electron sheaths have previously only been measured near a positively biased small electrode, in which a potential dip was often observed. In this paper, we present an experimental study on the electron sheath near a stainless steel plate in the presence of a weak electron beam. It is shown that the electron beam, though its density is much lower than that of the background plasma, will substantially alter the sheath structure, i.e., it causes the disappearance of the potential dip when the beam energy just exceeds the ionization potential of the neutral gas but later enhances the dip for higher energies. It is also shown that proper biases on the plate and chamber wall are the key to the formation of the electron sheath and the dip. For a fixed plate bias but with different electron beam energy, the measured thickness of the ion-free Child–Langmuir sheath agrees well with that of the theoretical model.

Experimental study of seismic performance of PEC column-steel beam 3D frame with endplate connection

The design and quasi-static test of a 1/3 scale down the single-story partially-encased composite structure of steel and concrete (PEC) column-steel beam 3D frame with endplate connection has been completed, confirming that the PEC is a new composite structural system that combines the advantages of concrete and steel structures. The damage mode and yielding mechanism of the frame by strain variation were analyzed, and its seismic performance was evaluated. The results show that the concrete filling in the node domain of the PEC column can activate the strut and tie mechanism for transferring the compression force between the column and the slab. The yield mechanism of the frame is “beam-column-node,” which satisfies the design principles of “strong column but weak beam” and “strong connection but weak component.” The full hysteresis curve has excellent energy dissipation capability. The strength degradation is stable, and the ductility coefficient is >2.85. The elastic inter-story and the elastic-plastic inter-story displacement drift meet the design requirements, which indicates that the frame has a stable bearing capacity, excellent flexibility, and anti-collapse capacity.

A Robust Density Estimation Method for Glacier-Height Retrieval From ICESat-2 Photon-Counting Data

Retrieval of glacier surface heights from ICESat-2 photon-counting data is significant to monitor glacier surface morphologies (e.g., crevasses) and their changes. However, existing methods are susceptible to complex glacier surfaces and diverse signal-to-noise ratios (SNRs). Therefore, we propose a robust density estimation method for glacier-height retrieval from ICESat-2 photon-counting data. A multi-scale random sample consensus (RANSAC) strategy is firstly employed to obtain the best elliptical neighborhood for each photon, to improve the consistency of neighboring photons. Then, a hybrid weighted density estimation method is developed to robustly describe the differences in the spatial distribution patterns between signal and noise photons. High-quality extraction of signal photons is finally implemented using adaptive thresholds in the local along-track segments. To test its performance, four datasets with strong and weak beams from the Jakobshavn Isbræ Glacier, western Greenland, were selected. Results showed that the proposed method achieved excellent performances in glacier-height retrieval in various glacier surface morphologies and diverse SNRs, due to discriminative densities between noise and signal photons were obtained. The average percentages of along-track segments with signal densities larger than noise densities for weak and strong beams were 92.0% and 99.9%. The average <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F₁-scores</i> reached 0.927 and 0.968 for the weak and strong beams, even the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F₁-score</i> reached 0.892 for the heavily crevassed complex surface with a low SNR. Moreover, comparison experiments with existing methods demonstrated that the proposed method showed superior performances in density estimation and glacier-height retrieval, and improved more than 17.33% and 16.10% in the most complex surface, respectively.

Seismic vulnerability assessment of RC frame structures subjected to seismic excitation: A review

Because of their unpredictable nature and high damage-causing ability, earthquakes pose a significant threat to buildings. As a result, loss of lives and significant loss of economy became a primary concern in many parts of the world. Damage to structures is one of the many reasons to examine their seismic behavior when subjected to seismic forces. The seismic vulnerability of a structure can also be defined as its vulnerability to damage caused by ground shaking of a certain intensity. A building fragility analysis is performed to assess its vulnerability. The analysis of structural fragility provides a better understanding of the response of structural and non-structural systems during seismic events. It also helps to reduce damage and the risk of loss of life. Fragility curves indicate the likelihood of failure when a building is subjected to earthquakes of varying magnitudes. This paper provides an overview of the studies published in the field of seismic vulnerability assessment of RC buildings using fragility curves. The adopted methods within the past studies were nonlinear static pushover analysis, nonlinear time history analysis, incremental dynamic analysis etc. This review study discusses the effects of aging, soil structure interaction, set back irregularities, effects of infill, effect of strong column and weak beam, soft story, construction quality etc. on the vulnerability of RC frame structures.

Numerical Study On Response Of Exterior Beam-Column Joint Under Cyclic Loading

In Present scenario, recent earthquakes have illustrated the severity of existing reinforced concrete (RC) beam-column joints to lateral loading. The sub-assemblage of Beam-Column are severe portion in reinforced concrete moment resisting frame as the high shear forces and larger moments getting attracted towards the joint. The Philosophy of Exterior beam-column joint are to observe its behaviour and has a significant role on the response of the reinforced concrete structure. This study includes numerical study on Exterior reinforced beam column joint with adequate shear reinforcement at joint as per IS: 13920-2016 and without shear reinforcement at joint as per IS: 456-2000. The seismic performance of G+5 RC Building of Zone III analyzed using SAP2000 and output of maximum shear force and bending moments are obtained, and one of the exterior beam-column joints at an intermediate storey is designed and satisfied for strong column and weak beam concept. The earthquake analysis of RC building of Zone III are carried out by incorporating all the modifications as per IS 1893:2002(Part-I) for Seismic loading, the loading is followed as per IS: 875 for dead and live loads and design as per code IS 13920:2016 and IS456:2000. Full scaled specimens were Numerically modelled in ANSYS 19.0 for constant axial load on column top and cyclic loading on beam end of each specimen, detailed as per IS 456:2000 and the other as per IS 13920:2016, were tested and response are obtained. This study outlined that model of IS13920:2016 performs more effective in controlling the seismic responses compared with model of IS456:2000. Further, there is significant reduction in Shear stress and observed improved ductility by providing adequate shear reinforcement in joint core of beam-column sub-assemblage.

Nonlinear Finite Element Analysis of Corroded Reinforced Concrete Beams

Corrosion in reinforcing bars is a major cause of concern for sustainability of Reinforced Concrete (RC) structures exposed to extreme environmental conditions. Various RC structures, such as bridges and buildings are adversely affected due to the rebar corrosion, reducing its global load carrying capacity and ductility. In order to ensure an earthquake resistant design of any structure, the ductility of structural members is of chief concern. However, corrosion of reinforcing steel in RC members reduces its seismic performance. Thus, for safety and economic viability of any RC structure, an effective maintenance and repair work strategy is necessary. Based on the strong column - weak beam design concept of RC frames, the beams are the first structural members to absorb damage due to earthquake. Thus, to carry out maintenance and repair work, structural health assessment of RC beams considering the effect of reinforcement corrosion is of utmost importance. The present study aims at establishing a relation between the amount of corrosion induced and its effect on the ductility of an RC beam. A 3D Finite Element (FE) model of an RC beam including the effects of corrosion for nonlinear performance assessment has been modelled in ABAQUS. The FE model is validated with past experimental study including the effects of corrosion. Modelling of uniform corrosion in reinforcement bars involves defining the loss of bond between rebars and concrete, inducing spalling stresses on concrete and reduction in the cross-section area of the rebars. Bond-slip model between surface of concrete and reinforcement has been incorporated through cohesive surface. Spalling stress for uniform corrosion is applied in form of outward uniform pressure on the reinforcement and concrete interface. The cracking of cover concrete due to corrosion along with the flexural cracking in concrete due to incremental loading are implemented together in the present study. A comprehensive FE model is developed in order to obtain correct assessment of corroded beams. As observed from the FE model, the failure mechanism of the considered corroded RC beam is observed to be mostly shear failure as the corrosion level increases. Concrete crushing at the center of the RC beam is identified at the failure point of the beam due to corrosion induced damage. Evolution of displacement ductility index with respect to corrosion is determined for an RC beam based on the numerical study. It has been observed that the displacement ductility index of the beam is reduced significantly after considering a corrosion level of about 12%. Hence, the present study is an effort to establish a relation between structural performance of RC beams and level of reinforcement corrosion, which will be useful in proactive maintenance and repair work for corroded RC beams.

Atomic optical spatial mode extractor for vector beams based on polarization-dependent absorption

Vector beams with spiral phase and spatially varying polarization profiles have many applications from optical micromanipulation to materials processing. Here, we propose and demonstrate an atomic spatial mode extracting scheme for the vector beam based on polarization-dependent absorption in the atom vapor. By employing the linear polarization pump beam which induces polarization sensitive absorption in the atomic ensemble, a counter-propagated weak probe vector beam is extracted by spatial absorption, and extracted part still maintains the original polarization and the vortex phase. The topological charges of the extracted mode are verified by interfering with the Gaussian beam, and it can be found that the orbital angular momentum is conserved in the extracting process. Our work will have potential applications in non-destructive spatial mode identification, and is also useful for studying higher-dimensional quantum information based on atomic ensembles.

Experimental and numerical study of self-locking adaptable inter connection for modular steel structures

Compared to conventional steel construction, modular steel construction (MSC) is different. Instead of having a high degree of connectivity, the modules are connected at their corners only by inter-modular connections (IMC), which are the most vulnerable points of failure and require extra operation spaces. An adaptable connection was proposed in this study, and the working mechanism of the proposed connection was presented. Three full-scale connections consisting of square hollow section (SHS) members were tested under monotonic and cyclic loads to determine the seismic performance. The results showed that reinforced joints sustained 80% of the limit of the rigid joint at an inter-story drift ratio of 0.04 radian and satisfied the condition for strong column weak beam joint mechanism. Non-linear Finite Element Analysis (FEA) was conducted on this adaptable connection with a parametric study to study more influences of other related parameters. The findings indicated that the gap produced between connection and column under higher displacement was sensitive to the outer bolt and spring pin. This gap could be further reduced by increasing the number of outer bolts and by reducing tolerance between adapter and column walls.

Spatial weak form quadrature beam elements based on absolute nodal coordinate formulation

A new spatial nonlinear beam element allowing for arbitrary number of nodes is proposed. The element which embodies the idea of weak form quadrature is established on the basis of the absolute nodal coordinate formulation (ANCF). The order of Taylor expansion over the cross section can be chosen as desired, enabling the element to cope with complex cross-sectional behavior such as high-order shear and warping deformation. Four typical examples are presented and satisfactorily results are obtained, demonstrating the effectiveness of the formulation for the analysis of spatial beams with strong geometrical nonlinearity.