Collapse Of Beams Research Articles

Deformational behavior and damage mechanism of R-UHPFRC beam subjected to fatigue loading

The fatigue behavior of a reinforced UHPFRC (Ultra High Performance Fiber Reinforced Cementitious composite) T-shaped beam under four-point bending is investigated. The beam was subjected to a fatigue loading range equal to 49% of the static resistance and failed after 0.88 million cycles. It was instrumented with extensometers, strain gauges and distributed fiber optic sensors for strain monitoring. The fatigue process consists of three stages: with rapid, stable and again rapid growth of strains during 10%, 80% and 10% of total number of fatigue cycles, respectively. Except of the first 10%, this process takes place locally; therefore, it cannot be followed with the deflection measurement. During the stable stage, growth of strain occurs at minimum loading level in the fatigue cycle, indicating a fatigue damage process under tensile-compressive response of UHPFRC. Advanced fatigue crack propagation in the reinforcement bar determines the location of rupture of the beam. When the remaining cross-section of the rebar does not suffice to carry the tensile load, stress is transmitted to the encompassing UHPFRC causing its fast deterioration. Complete rupture of the rebar occurs only at the end of the test, when the beam collapses.

Behavior of laterally unsupported monosymmetric steel I-section beams at elevated temperature under non-uniform moments

The steel sections are subjected to instability and buckling failure due to the rapid degradation of flexural rigidity under fire-loading conditions. The behavior of monosymmetric hot-rolled steel I-section beams are studied in this paper under uniform and non-uniform moment conditions. Validated finite element models in ABAQUS is used for parametric study, considering 1500 linear and non-linear simply supported beam models. Behavior of monosymmetric I-beams is analyzed under different uniform temperature conditions having shorter, intermediate, and longer spans with a height-to-width ratio greater than two (h/b > 2). The collapse of beams with longer span is not much affected by the non-linear material behavior. Only up to 17% increase from elastic capacity is observed for such beam under inelastic capacity. The interaction curves for the degree of monosymmetry and moment gradient are provided that can be used for estimating inelastic lateral-torsional buckling (LTB) capacities. Further, statistical analysis and comparison of FE-results with design predictions from Eurocode 3 part 1.2 showed that a single design buckling curve is insufficient in predicting the collapse capacity of hot-rolled beams under different loading conditions at elevated temperatures. Eurocode 3 part 1.2 generally provide highly conservative predictions at higher temperatures for beams under single curvature; however, it may provide unsafe results under double curvature for intermediate to shorter span beams.

Beam collapse and refractive index changes inside fused silica induced by loosely focused femtosecond laser

Femtosecond laser-induced optical and structural changes inside transparent materials are crucial to ultrafast laser micromachining. In this work, on-axis beam collapse has been predicted by theoretical simulations and further demonstrated by the experimental results where a femtosecond pulse was loosely focused into a fused silica with the energy far above the self-focusing threshold. A detailed discussion of the energy thresholds and the starting locations on the optical axis of beam collapse for different beam waist radiuses is given. In addition, the spatial distribution of the refractive index has been determined using a spectroscopic ellipsometer and a roughly uniform decrease of 0.1 has been observed in the laser-modified region. Further, the relationship between the spatial distribution of the refractive index and the pulse energy density has been discussed quantitatively. The observed modulation of the beam collapse and the refractive index distribution can be expected to be a useful tool for femtosecond laser micromachining.

Quantitative assessment of resistant contributions of two-bay beams with unequal spans

Following the sudden removal of an internal column from a steel-frame composite-floor system, the two-bay beams connected to the failed column play a key role in the internal force redistribution and rebalancing of the remaining structure. Moreover, the span–depth ratios of the adjacent two-bay beams have a significant influence on the collapse-resistant performance of the structure. To date, studies on structural progressive collapse of beams with unequal spans have been limited. In this study, based on the results of static loading tests on composite beam–column assemblies with cover-plate joints under three different span ratios, the finite element modeling method was validated and numerical models of the beam–column assemblies with three unequal spans were established. The influence of the unequal span of two-bay beams on the internal force development and load-resisting mechanisms of the composite beam–column assemblies were analyzed in detail. To gain deeper insight into the load-resisting mechanisms, the contributions of the flexural and catenary mechanism resistances to the total resistance of two-bay beams were quantitatively separated using the energy equilibrium theory, and it was found that the resistant contributions of the catenary mechanism, in general, account for less than a half of the structure’s resistance capacity. Moreover, theoretical formulas for the different resistant contributions of two-bay beams were proposed as recommendations for structural progressive collapse design and practical engineering applications. The analysis of results demonstrated that the span–depth ratios of two-bay beams determined the resistant contribution coefficients for the flexural mechanism, whereas the span ratios of two-bay beams determined the resistant contribution coefficient for the catenary mechanism, whereas the beam depth had little influence thereon.

Collapse of hybrid vector beam in Rb atomic vapor.

In recent years, many researchers have tried to control and design the collapsing behavior of light beams in nonlinear media. Vector beams coupling with spin and orbit angular momentum freedom have attracted more and more attention. In this Letter, we study the collapse of a hybrid vector beam (HVB) propagating through rubidium atomic vapor. First, the HVB collapses into filaments located at positions with linear polarization. As propagation distance in atomic vapor increases, the locations of the filaments switch from positions with linear polarization to those with circular polarization. In this process, the absorption of the medium plays an important role. Results indicate that the absorption can be used as a degree of freedom to modulate the filamentation. Furthermore, by analyzing the polarization angle of an elliptically polarized position on the transverse plane of the HVB, we demonstrate the evolution of polarization distribution of HVB during propagation. Such results could have application in manipulating other structured beams and could be potentially applied to realize optical switches or logic for information processing.

Nanomechanical properties of the ZEP-520 electron beam resist film

The ZEP-520 electron beam resist has been widely used in electron beam lithography and mask fabrication owing to its high resolution and good sensitivity. The stiffness and stability of the ZEP-520 resist are related to its mechanical properties, i.e., its hardness and elastic modulus. A higher hardness and elastic modulus can endow the ZEP-520 resist with higher stiffness, thereby allowing it to overcome the issue related to the collapse of the electron beam resist pattern. However, to date, only few studies have reported the mechanical properties of the ZEP-520 resist, and the relationship between the thickness of the ZEP-520 resist and its hardness and elastic modulus has not yet been determined. To obtain this information, in the present work, silicon is used as a substrate to analyse the hardness and elastic modulus of the ZEP-520 resist with different film thicknesses via nanoindentation. Additionally, a local area function method is proposed, through which the hardness of thin films can be conveniently and accurately obtained without being affected by the substrate effect. It is found that the true hardness increases with the decrease of the thickness of the ZEP-520 resist film; however, the true elastic modulus has no clear relationship with the film thickness. For a film thickness of 412 nm, the true hardness and elastic modulus of the ZEP-520 resist film are found to reach the maximum values of 0.52 and 11 GPa, respectively.

Evaluation of Structure Performance under Seismic Load with Non-Liner Time History on High-Rise Building Affected by Kendeng Fault Earthquake Simulation

Indonesia is a country located in the convergence of small plates and large plates. Furthermore, this causes Indonesia to be high potentially to earthquake hazards. The newest geological research published by Geophysical Research Letter (2016) shows the existence of Fault Kendeng, a fault stretches along 300 km from South Semarang, Central Java, to East Java with a movement of 0,05 millimeter per year [1]. As a result of its research, an evaluation using a non-linear time history analysis for structural buildings is necessary. The objective of this study is to evaluate structural buildings using a non-linear time history analysis. This study applies DSHA (Deterministic Seismic Hazard Analysis) method to obtain acceleration time history on bedrocks. Since the record of ground movement in Indonesia is limited, the attenuation function equation used to scale and match other country’s time acceleration history data. SSA (Site-Specific Analysis) is used to propagate earthquake acceleration from bedrocks to the surface. The earthquake acceleration on the surface generates as the earthquake load on the buildings. The results of Kendeng fault earthquake simulation using non-linear time history analysis shows that column members capacity is more robust than beam members capacity which the beam collapse mechanism occurs initially. From the maximum total drift ratio result, when the Kendeng fault earthquake occurs, the building structure performance level is at collapse prevention level Based on ATC-40 [2]. This research result shows that 96,7% of plastic hinge has not yielded. However, some elements are already damaged. Since most damage members are column, then it may require column strengthening to enhance maximum performance level at life safety condition category.

Condition evaluation for through and half-through arch bridges considering robustness of suspended deck systems

Through and half-through arch bridges is one of the main bridge types in China, having arch ribs and simple suspended deck systems, which are connected by high-strength wire suspenders. However, due to the lack of robustness, the suspended deck systems of these types of bridges caused progressive collapse after the suspender corrosion damage. In this study, the internal structural factor of progressive collapse induced by suspender failure was revealed by comparison of five cases of suspender failure, and the robustness requirement of the suspended deck systems was proposed as redundancy to avoid transverse beam collapse when two supporting suspenders on both ends were broken at the same time. Meanwhile, a typical rigid-framed tied through concrete-filled steel tube arch bridge was investigated, and structural condition evaluation was carried out based on the Chinese standard (JTG/T H21-2011). It was found that the evaluation results of bridges with different deck systems were unreasonable, as the better the robustness was, the worse the condition of the deck system was rated, which would mislead the bridge maintenance decisions. A robustness-based evaluation method was then proposed by adopting different evaluation method according to the robustness of the suspended deck system, which is determined by qualitative classification or quantitative calculation. In addition, weight-adjusting method considering robustness was introduced in the evaluation process. The result showed that the new method could objectively reflect the condition of the bridge and thus fits the needs of bridge maintenance and management better.

Research on RC Frame Structure’s Resistance to Continuous Collapse

A typical 8-story RC frame structure model with floor is established by using ABAQUS finite element software. The nonlinear static analysis method and the incremental dynamic analysis method are used to explore the influence of the floor slabs after the demolition on the continuous collapse resistance of the RC frame structure at the same time. Determine the most reasonable amount of reinforcement that meets the requirements for continuous collapse resistance of the frame beams of each layer, and the layer height that is most beneficial to the structure’s continuous collapse resistance.It is concluded that the floor can greatly improve the continuous collapse resistance of the overall structure, and the nonlinear static analysis is conservative; the amount of longitudinal reinforcement in each frame beam should be increased by 1.9% ~ 2.9% to meet the most reasonable requirements for continuous collapse of the frame beam; the floor height is between 4.3 and 4.8 meters, which is the most ideal state for the structure to resist continuous collapse.

On the Lateral-Torsional Elastic Post-Buckling and Strength of Channel Steel Beams

This paper aims at shedding new light on the elastic post-buckling behavior and strength (elastoplastic collapse) of steel channel section beams undergoing lateral-torsional (LT) buckling. This new insight is acquired using a two-node geometrically exact beam finite element developed by the author, which can handle large displacements, including torsion-related warping, Wagner effects, plasticity, residual stresses and arbitrary initial configurations (namely geometrical imperfections). Several cross-sections and loading/support conditions are analyzed. The results obtained show that the LT buckling behavior of channels is asymmetric, meaning that the direction of the geometric imperfection can influence significantly the strength of the beams. Moreover, it is demonstrated that the loading and support conditions play a major role, leading to a significant scatter of results which hinder the definition of a single buckling curve for design purposes. Nevertheless, in all cases considered, the buckling strengths obtained fall significantly above those predicted by the current version of Eurocode 3.

Microstructure and structural analysis of polypropylene fibre reinforced reactive powder concrete beams exposed to elevated temperature

Despite the superior properties of reactive powder concrete (RPC), the possibility of spalling under fire conditions still exists, which can lead to a significant reduction in the fire endurance of reinforced concrete members. This study investigates the efficiency of using the different percentages of polypropylene fibres (PPFs) for enhancing the fire resistance of reinforced beams made from RPC. Five RPC beams were tested by applying two concentrated loads. One of them (without PPFs) was tested under monotonic load up to failure. The other four beams were subjected to service load, and then controlled fire was applied for 120 min in accordance with the fire temperature vs. time curve prescribed in ASTM E 119. Loading tests were then conducted on the beams that were not completely damaged through fire testing, in order to examine their remaining strength after cooling. Experimental results showed that non-fibrous reinforced RPC beams suffer early spalling during the fire test, thus causing beam failure after 38 min of fire exposure. The addition of PPFs in a low volume percentage (0.25%) decreases spalling and delays beam failure until 115 min, whereas PPFs in high percentages (0.75% and 1.25%) completely prevent the spalling and beam collapse. Moreover, an increase in PPF content reduces the total deflection of a beam and improves the residual strength and ultimate strength of fire-failed beams subsequent to cooling.

ANSYS Numerical Modeling of Confined Deep Beam with High Strength Concrete

In the numerical modeling presented, the deep beam is accounted for by means of a three dimensional FEA ANSYS 13.0 approach, in which the structure is modeled with load-displacement-based solid finite elements, whereas the internal work structure interacted by high strength concrete and reinforcement in full scale. Most deep beam collapse is dominated by the shear brittle collapse. Recently, confinement is the most effective way to improve the ductility of the reinforced concrete, whereas required to anticipate the occurrence of direct crack on the beam caused by quite large shear forces. Numerical models of deep beam with high strength concrete is done gradually by giving a variation of concrete strength, confinement and stirrup spacing. The two point load are applied with the ultimate load on all models. Then, analyzing of the deep beam is to be done with and without side reinforcement and also an analysis of the crack pattern of the beam to calculate the brittle area under the ratio of crack volume occurred. Concrete is modeled by SOLID65 and steel reinforcement using SOLID45 element. The collapses occurred are all ultimate flexural compressive collapse on the loading plate area, due to brittle shear collapse. The condition occurred on deep beam first crack was already considered a collapse, the density of reinforcement and the additional distance comprehensive reinforcement bar is most effective in terms of adding high ductility of high strength concrete beams. By using the stirrup reinforcement with confinement mode can significantly enhance the resistance of ultimate capacity, cracking ratio and reduced deflection.

Design and Analysis of Automobile Bumper

An automobile’s bumper is the front-most or rear-most part, ostensibly designed to allow the car to sustain an impact without damage to the vehicle’s safety systems. They are not capable of reducing injury to vehicle occupants in high-speed impacts, but are increasingly being designed to mitigate injury to pedestrians struck by cars. The automobile bumper weight is reduced by the utilization of composite and high- strength gilded sheet of a skinny material. Once the motor vehicle is hit from the front or behind, the bumper beam collapses. The impact force is transmitted to the left and right front frames on the bumper beam and bumper stays. The impact energy created throughout the crash is absorbed by plastic deformation on the bumper beam and bumper stays that square measure the specified elements of bumper For characteristic the foremost effective material, varied analysis like static analysis, impact or crash analysis, dynamic and modal analysis area unit required the target of the work is to counsel the foremost effective material for bumper that is ready to ensure rider safety, with high strength to weight quantitative relation through the static and dynamic analysis.

Revisiting an airgap split-optics mitigation for beam filamentation in high power lasers.

We extend the split-optic approach for mitigating filamentation in a thick optical component previously proposed for small beams to conditions relevant to high-power lasers. The split-optic approach divides a thick optic into two thinner optics separated by an airgap to reduce filamentation through diffraction management. Our numerical study focuses on filamentation of a flat-top beam with intensity modulation noise sources passing through a split-optic system. The improvement in the distance to collapse in glass is shown to be potentially substantial (>30%), yet has limited increase with the airgap size, unlike the common understanding when considering a collapse of a whole beam or a sole perturbation on a beam. The improvement in the collapse distance in glass asymptotes to an upper bound value that depends mainly on the beam mean intensity and its contrast for any airgap size above some value that depends mainly on the shortest spatial periods comprising the excitation noise source. Examining the difference in the simulation results for a periodic versus a randomly generated perturbation source-term suggests that the observed effect is governed by the statistical interference dynamics of the beam while propagating through the airgap.

A numerical study on the influence of internal corrugated reinforcements on the biaxial bending collapse of thin-walled beams

The Heat Treatment Forming and in-die Quench (HFQ) process allows for manufacturing of more complex geometries from Aluminium sheets than ever before, which can be exploited in lightweight automotive and aerospace structures. One possible application is manufacturing thin walled beams with corrugated internal reinforcements for complex geometries.This work considers different internal reinforcements (C-section and corrugated) to improve the energy absorption properties of thin walled rectangular beams under uniaxial and biaxial deep bending collapse, for loading angles ranging from 0 to 90 deg, in 15° increments. Using LS-DYNA simulations experimentally validated through unreinforced metallic tubes under quasi-static bending collapse, the finite element results demonstrate the stabilising effect of the reinforcements and an increase in the buckling strength of the cross section.Corrugated reinforcements showed a greater potential for increasing specific energy absorption (SEA), which was supported by investigating key geometric parameters, including corrugation angle, depth and number. This favourable response is due to an increased amount of material undergoing plastic deformation, which consequently improves performance of the beam undergoing post buckling and deep collapse. This concept is applicable to vehicle and aircraft passive safety, with the requirement that the considered geometries are manufacturable from Aluminium Alloys sheet only, using the HFQ process.

Influence of the spatial confinement on the self-focusing of ultrashort pulses in hollow-core fibers

The collapse of a laser beam propagating inside a hollow-core fiber is investigated by numerically solving different nonlinear propagation models. We have identified that the fiber confinement favors the spatial collapse, especially in case of pulses with the input peak power close to the critical value. We have also observed that when using pulses in the femtosecond range, the temporal dynamics plays an important role, activating the spatial collapse even for pulses with input peak powers below the critical value. The complex self-focusing dynamics observed in the region below the critical power depends on the temporal evolution of the pulse and, also, on the interaction between the different spatial modes of the hollow-core fiber.

AAM for Structure Beams and Analysis of Beam without Shear Reinforcement

Advances in technology and sustainability requirements create substantial demand for material research. In construction industry, possibilities of innovation of concrete are opened by using recipes based on new activation methods, where alkaline activated composites can be included. This article focuses on this area where the results of the recipe verified under industrial conditions are presented, and the way of processing is significantly different from the laboratory conditions. The aim of the article is to present the material properties and differences of alkali activated specimens that are compared with series of common concrete material properties based on composition from the same aggregate material base. It was found that the most significant differences are the modulus of elasticity. In both of the recipes, the same design cube compressive strength is used. The article presented also experiment and nonlinear analysis of the alkali-activated beam without shear reinforcement, which was used to study the mechanism of damage and collapse of AAM beam. Nonlinear analysis was used thanks to complex knowledge of material properties. Numerical modelling uses the ATENA software. Test of small structural element is complemented by an advanced crack detection diagnosis with the use of acoustic emission.

Failure Mechanism of Composite Frames Under the Corner Column-Removal Scenario

The beams and the slabs of a composite structure act jointly as an integrated floor system to resist progressive collapse. Ignoring the composite slab’s contribution to strength and ductility will result in significant underestimation of the vertical force resistance. In order to investigate the effect of composite slabs on the failure mechanism and the distribution of the resistance, a series of simulation and theoretical studies have been conducted on the progressive collapse of beam–slab substructures by removing corner column. This article discusses the contribution of several mechanisms on the load-carrying capacity. It is found that the composite slab can significantly improve the progressive collapse resistance of the composite structure. Under catenary mechanism, the peak load of the beam–slab specimen is approximately 1.15 times the beam specimen. In addition, the maximum angle in the beam end of the beam–slab specimens reaches 1.33 times that of the beam specimen. The progressive collapse process of the structure can be sectioned into four stages which are the elastic stage, the elastoplastic stage, the plastic stage and the collapse limit stage. Before the elastoplastic stage, the collapse resistance is contributed by the flexural strength of the composite frame. Sometimes the longitudinal shear bearing capacity of the composite slab will significantly affect the flexural strengths. After the elastoplastic stage, the collapse resistance is mainly determined by the catenary mechanism of the beams and tensile membrane action of the steel sheet.

Self-trapped pulsed beams with finite power in Kerr media excited by time-diffracting, space-time beams.

We study the nonlinear propagation of space-time pulsed beams, also known as time-diffracting beams, a recently introduced class of diffraction-free spatiotemporal wave packets whose temporal-transversal structure is that of diffraction in time. We report on the spontaneous formation of propagation-invariant, spatiotemporally compressed pulsed beams carrying finite power from exciting time-diffracting Gaussian beams in media with cubic Kerr nonlinearity at powers below the critical power for collapse, and also with other collapse-arresting nonlinearities above the critical power. Their attraction property makes the experimental observation of the self-trapped pulsed beams in cubic Kerr media feasible. The structure in the temporal and transversal dimensions of the self-trapped wave packets is shown to be the same as the structure in the axial and transversal dimensions of the self-focusing and (arrested) collapse of monochromatic Gaussian beams.

Suppression of collapse for optical beams by linear anisotropy

Evolutions of (1 + 2)-dimensional optical beams in local Kerr nonlinear media with linear anisotropy are discussed both analytically and numerically. The suppression of collapse of both circular and elliptic beams is predicated by variational solutions, and confirmed by numerical simulations. If the anisotropic parameter is large enough, the beam width can become even larger during nonlinear propagations when the optical power is larger than the critical power.