Plastic Beam Research Articles

A soft robot structure with limbless resonant, stick and slip locomotion

We present a smart robot structure that exploits anisotropic friction to achieve stick-slip locomotion. The robot is made out of three components: a plastic beam, a planar dielectric elastomer actuator and four bristle pads with asymmetric rigid metallic bristles. We show that when the robot is electronically activated at increasing frequency, its structure exploits the resonance condition to reach the maximum locomotion speed. The fundamental frequency of the structure is estimated both analytically and numerically, allowing the range of frequencies in which the top locomotion speed was observed during the experiments to be identified. The locomotion speed of the robot as a function of the actuation frequency is estimated with a frequency response analysis performed on a discretised model of the structure, revealing good agreement with the experimental evidence.

Calibration of nonlocal damping model based on numerical simulation results

The paper is devoted to polymer composite beams dynamic behavior simulation. The nonlocal damping model is used as a model of the internal friction. The vibration process is considered in this paper using the beam with fixed ends as an example. Equation of beam motion considering nonlocal damping is solved by Galerkin method to develop the model. The required number of eigenmodes is obtained for the beam under an instantly applied distributed load. The influence of nonlocal damping model parameters variation on the beam vibration process simulation results is considered under a periodic deterministic distributed load. The calibration of nonlocal damping model consists of defining its parameter known as influence distance which characterize the level of the nonlocal properties in material. Calibration is carried out with the least squares method using the numerical simulation data. For this purpose the results of 3D finite element modeling of thermoset vinyl ester fiber reinforced plastic beam vibrations under the instantly applied load were used. The 3D finite element model of the beam was created in SIMULIA Abaqus taking into account the orthotropic properties of the material. The calibrated model was justified for the beams with changed geometry. The results presented in this paper were obtained during the research for the PhD thesis.

Seismic Vulnerability Assessment of Hybrid Mold Transformer Based on Dynamic Analyses

In the present study, the seismic vulnerability of a hybrid mold transformer was investigated using a dynamic analytical approach incorporating the experimental results of shaking table tests. The analytical model consisted of linear springs and plastic beam elements, and it has six degrees of freedom simulating the hybrid mold transformer. The dynamic characteristics of the analytical model were determined based on the shaking table tests. The reliability of the analytical model was verified by comparing the test results and analytical results. In order to assess the seismic vulnerability, three critical damage states observed during the shaking table tests were investigated by incorporating the three performance levels specified in ASCE 41-17. Comprehensive dynamic analyses were performed with a set of twenty earthquakes in consideration of the variation of the uncertain parameters (such as the effective stiffness and coil mass) of the mold transformer. Based on the analytical results, fragility curves were established to predict the specified exceedance probability of the mold transformer according to the performance levels.

Fast simulation of stent deployment with plastic beam elements.

Coronary stent deployment is a reference cardiology intervention, used to treat atherosclerosis and prevent heart attacks. The outcomes of the intervention highly depend on the accuracy of the stent apposition, which could benefit from per-operative prediction tools. In this paper, we propose a fast and mechanically realistic 3D simulation of a coronary stent expansion. Our simulation relies on the finite element method and involves serially linked beam elements to model the slender geometry of a stent. The elements are implemented with a non-linear elasto-plastic behavior, describing realistically the complex deformation of a balloon-expandable stent. As a proof of concept, we simulated the free expansion of a coronary stent. The simulation output was compared with micro-CT data, acquired experimentally during the device expansion. Results show that the plastic beam model is able to reproduce successfully the final geometry of the stent. In addition, the use of 1D elements allows to achieve a significantly lower computational time than for equivalent literature simulations, based on 3D elements. This preliminary work highlights the compatibility of our method with clinical routine in terms of execution time. Further developments include the application of the method to more advanced simulation scenarios, with the addition of a personalized artery model.

Effect of partial replacement of sand by plastic waste on impact resistance of concrete: experiment and simulation

The effect of partial replacement of sand by plastic waste on the mechanical properties of concrete under impact load was investigated experimentally and numerically. Specimens were prepared with 0%, 5%, 10% and 20% plastic waste as sand replacements. For each case, three beams of 100 mm wide, 50 mm deep and 400 mm long were loaded to failure in a drop-weight impact machine by subjecting it to 30 N weight from 400 mm height after 90 days, while another three beams of the same size and age were tested under static load. The load-displacement and fracture energy of the plain and concrete with plastic beams subjected to static and impact loads were studied. The dynamic beam behavior was also analyzed numerically using the finite-element method (FEM) based LUSAS software. In general, the experimental results reveal that the impact tup increase by 39% with 20% sand replacement by plastic waste, while the static peak bending load always decreases. The concrete with plastic waste is stronger and more energy-absorbing under impact loading, than under static loading. The predicted load against displacement behaviors of both plain concrete and concrete with plastic waste, are well matched with the experimental results.

EXPERIMENTAL STUDY ON CONTINUOUS BEAM TYPE SQUARE CFST BEAM-TO-COLUMN CONNECTION

Concrete-filled steel tubular (CFST) columns are used widely as building structure components because of their good performance. It can be complex, however, to connect beams into CFST columns, especially when rigid beam-to-column connections are required. In order to simplify the fabrication requirements and cost of these connections, a continuous beam type connection through the column is proposed. This can develop the full plastic moment capacity of the beam. In this paper, the experiment testing results of two types of CFST beam-to-column connection specimens are presented and the connection performance and load transfer mechanisms are examined. The continuous beam type connection performance is compared to that of traditionally used through-diaphragm type of connection, which is more complex and demanding to fabricate. Both specimens showed good seismic performance, exhibiting stable hysteretic behavior with high energy absorption. The maximum experimental strength exceeded the calculated value. For a continuous beam type specimen, there is the potential for the column flange to be affected by the local deformation from the steel beam under bending induced beam tension. However, such effects were not observed in practice until late in the test after extensive beam plastic action had occurred.

Cyclic Seismic Performance of Weak-Axis RBS Welded Steel Moment Connections

In this study, cyclic seismic performance of weak-axis reduced beam section (RBS) welded steel moment connections was experimentally investigated. Experimental results of this study again showed that the weak-axis RBS moment connection designed based on the procedure proposed by Gilton and Uang (J Struct Eng 122:1292–1299, 2002) performs well and developed an excellent seismic performance much better than 4% story drift with 80% of beam plastic capacity. However, it was also shown that the sharp corner of C-shaped fillet weld, used for attaching the beam web to the shear plate, can be the origin of crack propagation owing to stress concentration there. Slight trimming of the sharp corner is recommended to reduce notch effect. One specimen in this study eventually failed due to low cycle fatigue fracture as a result of cyclic flange local buckling that occurred at the butt joint between the beam flange and the horizontal continuity plate. The size of the weld access hole beneath the butt joint should be minimized if possible to suppress the occurrence of flange local buckling around the butt joint. The factors affecting the size of C-shaped fillet weld and the beam shear eccentricity for the weld design were also examined through a case study and simple analytical modeling. The sectional factor governing the beam shear eccentricity was shown to be the plastic section modulus ratio of beam section at RBS center to the beam flanges at welded joint. The elastic method neglecting the ductile behavior of the C-shaped fillet weld group was shown to be too conservative and should not be used in design in order to minimize welding heat affection to the thin beam web as well.

A simplified modal-based method to quantify delamination in carbon fibre-reinforced plastic beam

ABSTRACTThis study contributes to our knowledge about the detection and recognition of carbon fibre-reinforced plastic (CFRP) composites by using a modal analysis technique. Delamination was artificially induced during the manufacturing process of CFRP beams so that the dimension and location of the artificial delamination were known. The first three longitudinal bending modes were considered for detecting, locating, and evaluating the delamination. Contrary to what is commonly practised, the sensor placed on the CFRP structure had a large mass in order to contribute actively to restricting the delamination and hence modifying the structure’s natural frequencies, thus making it much easier to monitor its health condition. The technique was implemented on a beam with a delamination gap of 9% of the beam’s length, positioned within the span of the beam. The results demonstrate that the proposed technique can be effective not only to locate the delamination but also to measure its extent accurately.

Toward seismic design of tall steel moment resisting frames using the theory of plastic mechanism control

The kinematic approach and mechanism equilibrium curve in the rigid-plastic analysis framework are the basis of the theory of plastic mechanism control (TPMC). Applying this method for structural design will lead to a global collapse mechanism and prevent undesired collapse mechanisms. In this paper, to satisfy the TPMC conditions in tall moment-resisting frames (MRFs), linear programming (LP) is applied such that the TPMC conditions are defined as the optimization formulation. To investigate the effects of different structural constraints such as preventing the partial beam plastic hinge mechanisms (PBM), partial column plastic hinge mechanisms (PCM), and also to consider the strong-column weak-beam (SCWB) criterion in design MRFs by TPMC, a series of three (10, 15 and 20-story) MRFs is studied. Each frame is designed in the four different categories of the constraints: 1) PBM, 2) PBM + SCWB, 3) PBM + PCM, and 4) PBM + SCWB + PCM. The accuracy of the proposed design procedure is evaluated using pushover and nonlinear time history analyses. The results show that the designed structures reveal excellent seismic performance, and the global mechanisms are successfully achieved. The obtained nonlinear responses show that the seismic performances of the examined frames with different constraints are similar, and the PBM constraint is adequate for preventing undesired collapse mechanisms.

Non-linear Numerical Modeling of Partially Pre-stressed Beam-column Sub-assemblages Made of Reactive Powder Concrete

Three partially pre-stressed interior beam-column sub-assemblages (SI) and two partially pre-stressed exterior beam-column sub-assemblages (SE) made of reactive powder concrete as test specimens were numerically modeled using a finite element program. The objective of this study was to investigate the behavior of the SI and SE numerical models. The numerical model inputs were: material data, details of test specimen dimensions, and test specimen reinforcements. The numerical models were subjected to the same loads as those applied experimentally. The numerical modeling results were hysteretic and backbone curves and stress distribution contours. The numerical model outputs showed good similarity with the experimental results. The stress distribution contours of the numerical models correlated with the crack patterns in the joint zone of the test specimens. The behavior of the SI numerical models differed from the SE numerical models due to various stresses on the beam plastic joints and the joint zones.

Cyclic tests on high strength steel flange-plate beam-to-column joints

Improved beam-to-column joint configurations, with the beam plastic hinges shifted away from the column faces, were required in high strength steel frames to guarantee the seismic performance, and the flange-plate beam-to-column joints are expected to be one of the improved joint configurations that have good prospects in high strength steel frames because of the potential reinforcing effects and the negligible additional requirements for construction space. However, there have been few investigations on the high strength steel flange-plate beam-to-column joints and a lack of detailed design method for flange-plate joints. Considering three different combinations of Q345 or Q460 steel beams and Q460 or Q890 steel columns, a total of 6 full-scale specimens of flange-plate beam-to-column joints with middle columns in steel frames were designed and tested subjected to anti-symmetrical cyclic loads. The failure modes, the resistance, the stiffness and the ductility of the specimens were analysed, and the influences of the joint configurational parameters, including the panel zone thickness, the flange-plate lengths, the attached fillet welds in web connections and the fillet welds arrangements around the flange plates, were investigated. According to the test results, continuity plates with enough thickness were necessary in high strength steel flange-plate joints to avoid unexpected failure modes, and the panel zone shear rotation would make a considerable contribution to the total story drift angles and the plastic story drift angles of the high strength steel frames. Five of the tested specimens reached a story drift angle larger than 0.035 rad and one of them was larger than 0.04 rad, indicating that the flange-plate joint configurations could develop a considerable ductility, which, however, may still be insufficient when adopted in structures with high ductility demand. Based on the test results, design recommendations were proposed for flange-plate beam-to-column joints in high strength steel frames.

Substitute Frame and adapted Fish-Bone model: Two simplified frames representative of RC moment resisting frames

This paper aims to develop simplified frame models applicable for Reinforced Concrete (RC) moment frames. For this purpose, the existing Modified Fish-Bone (MFB) model, which is usually used for steel moment frames, is adapted for RC moment frames using modified Ibarra-Medina-Krawinkler springs with deteriorating peak-oriented behavior. Pre-analysis demonstrates that the MFB model requires some modifications for RC moment frames to (a) eliminate the imposed redundant compressive forces to the single column which was caused by the unbalanced shear forces between two half-beams at each story, and (b) simulate the migration of contraflexure point in the beams of original RC frames. The challenges stem from (a) the different negative and positive moment capacities in RC beams, and (b) the peak-oriented hysteretic behavior of rotational springs representing beam plastic hinges. More detailed investigation indicates that eliminating the redundant compressive force is the most effective modification, but the migration of contraflexure point due to different negative and positive moment capacities and even the single curvature bending condition of original beams is not crucial. The reason is investigated using step-by-step incremental nonlinear analysis and illustrated that the contraflexure point is usually located in the mid-span at each step, except for a transient phase in the reverse loading. This minor effect is fundamentally based upon the peak-oriented hysteretic behavior of RC beams. Hence, two simplified models branch from the Modified Fish-Bone model: (i) the Adapted Fish-Bone (Adapted MFB) model in which the first crucial modification is applied, and (ii) the Substitute Frame in which both modifications are reflected and seems to be more compatible for RC moment frames. In the end, the accuracy of the proposed models is evaluated using two sets of far-fault and one set of near-fault ground motions. The comprehensive nonlinear dynamic analysis demonstrates that the two proposed models can estimate engineering demand parameters with high accuracy, while they greatly simplify the modeling process, computational effort and visualization of results.

Identification of traction-separation parameters by means of peel testing and in situ confocal microscopy

Delamination owed to environmental stress is a relevant concern in the field of microelectronics packaging. This study is focused on the adhesion of a photosensitive insulator to inorganic passivation layers and metal caps. Peel testing has been combined with confocal laser scanning microscopy to image the bent shape of the peeled layer in situ. Elastic plastic beam theory and finite element analysis have been used to identify a cohesive traction-separation law matching both the work of separation and the peel arm profile. The results indicate that the actual adhesion energy amounts to ~30% of the external work, whereas the rest is dissipated by plasticity. Being the latter related to the curvature of the peel arm during delamination, these results confirm the relevance of in situ imaging in the field of microelectronics reliability.

Elastic–plastic characterization of microstructures through pull-in 4 point bending test

This paper presents a simple design of gold MEMS, with a central test specimen undergoing tensile loading, for the experimental characterization of elastic–plastic behavior using electrostatic actuation. A kinematic model for the test microstructures is presented that relates the experimentally measured deflection in the test specimen to the developed axial and bending stress. Moreover, an elastic–plastic beam bending model is presented to analyze the development of plastic hinges in the central test specimen. The design of test microstructures allows us to achieve stress values higher than the yield stress of the gold specimen before the pull-in effect, thus allowing to analyze the effect of elastic–plastic behavior on the static deflection profile of the central test specimen under repeated loading. The actuation voltage-deflection tests under repeated loading, both in the elastic and elastic–plastic region, allowed to estimate the applied stress limit for the onset of plasticity in gold thin film based MEMS devices.

Development of a Rigid Full-Contact Mold for Preparing Biobeams through Microbial-Induced Calcite Precipitation

Abstract As a new environmentally friendly and sustainable technique for soil improvement, microbial-induced calcite precipitation (MICP) has been studied widely. A suitable sample preparation mold is the first step to prepare MICP treatment. The purpose of this study is to develop a rigid full-contact mold to prepare larger biobeam specimens for MICP treatments with an immersing method. Four different molds were developed, including a plastic beam rigid mold without a cover, a full-contact flexible mold, a rigid full-contact mold with geotextiles, and a rigid full-contact mold with filter paper. Beam-shaped specimens with different dimensions were treated with the four molds in the MICP process. A four-point bending test and a split tensile strength test were conducted to evaluate the flexural behavior of MICP-treated specimens from the four sample preparation molds. The results indicated that an MICP-treated sample prepared by the rigid full-contact mold with geotextiles can form the best beam shape and the most uniform calcite precipitation inside the sample. Additionally, the biobeam made by the rigid full-contact mold with geotextiles achieved the best mechanical properties. The flexural strength of the biobeam made by the rigid full-contact mold was 1,125 kPa at a failure flexural strain of 1.5 %, and the split tensile strength was 368 kPa with a failure tensile strain of 1.8 %.

Local contact behavior between elastic and elastic–plastic bodies

The loading–unloading behavior of local contact between elastic body and elastic-ideally plastic body is studied analytically and numerically. An analytical model is derived based on the simulating results pertinent to Brinell indentation and elastic–plastic beam impact. The observed linear and nonlinear contact characters from simulations are introduced into the proposed analytical model. The contact law is expressed in much easier formulations by four normalized contact variables, normalized average contact pressure H¯, relative strain Λ, normalized contact area c2 and relative contact force Ψ. The elastic loading is following Hertz contact theory. The linear contact laws for the elastic–plastic and fully plastic loadings and the nonlinear contact laws for the finite deformation loading are introduced in term of the finite element (FE) contact simulations pertinent to Brinell indentation. The coefficients in the contact law are determined by fitting the FE contact simulations and by satisfying the continuous conditions. The more suitable regime of Hertz solution and a refined force–indentation relation of unloading are introduced as well into the analytical model according to the FE impact simulations. The model is finally verified with the FE simulation and experiment of elastic-ideally beam struck by elastic sphere. The analytical model shows a very good agreement between the FE-simulations and the experimental data for either low or moderate velocity impacts, while Stronge model is dependent upon impact velocity. The loading and unloading laws are highly accurate, even for the finite contact deformation in which the nearly 90% of cross section has yielded and the contact radius a (normalized by the indenter radius R) is up to a/R = 0.217.

A robust frame element with cyclic plasticity and local joint effects

A robust elasto-plastic element is developed for analysis of frame structures. The element consists of a beam member with end joints with properties permitting representation of the effect of section forces in adjoining members, like axial forces. By use of the equilibrium formulation the deformations of beam member, plastic hinges and joints become additive and can be expressed in explicit form. The plastic deformations of the beam and the joints are represented by separate plastic mechanisms, described by the same generic cyclic plasticity format. This format is defined by an energy function, a yield surface, and a plastic flow potential for each plastic mechanism. In the cyclic plasticity model each component is characterized by the elastic stiffness, the yield capacity, the additional flexibility at initial yield, the ultimate capacity and a shape parameter describing the curvature of the hysteresis curve. The yield surface is represented by a recently developed generic format, combining the section forces into a homogeneous function of degree one and permitting smooth transition between regions with large and more moderate curvature. A robust return algorithm of approximately second order is developed, using a mid-step state to obtain representative information about the return path. The element is implemented in a co-rotational large-deformation computer program for frame structures. The formulation is illustrated by application to a couple of typical offshore frame structures, and comparison of different representations of the plastic effects illustrates the importance of a robust element with realistic representation of the cyclic plastic mechanisms.

INVESTIGATION OF STRONG COLUMN – WEAK BEAM RATIO IN MULTI-STOREY STRUCTURES

It is expected that the engineering constructions should carry the vertical and horizontal loads during the service within the determined safety margin. Basic principal of having strong column weak beam preference is essential for earthquake resistant structures for all construction types including concrete, steel, wood and prefabricated. The major criteria for having earthquake resistant structure is to ensure that the columns are stronger and carry the most load than the beam in the nodes. This criterion has been widely adopted in earthquake codes in Europe, USA, Japan and India. It is possible to absorb and consume the earthquake energy via beam plastic joint hinges if the columns are constructed to be more durable than the beams. For this, it is foreseen that the ratio of the ultimate strength of the upper and lower columns to the right and left beams (β) should be greater than one (β = 1.2) in the beam-column joints as stated in the Turkish Earthquake Code. This coefficient is usually greater than 1.2 in the earthquake codes adopted in the world. It was observed that many structures were damaged or collapsed due to not meeting the coefficient criteria stated above. This criterion is the most effective one among many to prevent the damage in the structure under seismic action. In this study, the effect of the change in the coefficient on the column and beam moments is investigated under the Turkish Earthquake Code. Different numerical examples are presents for the coefficient of 10. The results of the investigation highlighted that irregularity in the strong column weak beam composition may negatively affect the other irregularities in the structure.

Collapse mechanism analysis of a steel moment frame based on structural vulnerability theory

This paper presents an improved method to analyze the collapse mechanism of steel moment frames based on structural vulnerability theory (SVT), in which the failure processes of the essential components are defined according to the damage characteristics of their ductile and brittle members. The improved method can accurately identify possible collapse modes of steel moment frames, because the transformation processes of such connections as beam-column joints and support joints from rigid connections to pinned ones were considered. Structural vulnerability analysis is performed on a 4-story steel frame structure by using the improved method, the results show that the collapse caused by joint failure in the first story had the maximum vulnerability index, so that the weakness of the steel frame may be located in the first story; while the collapse behaving as a “beam plastic hinge” failure, as an expected failure mode, had the minimum value. Moreover, the improved method was validated by a shaking table test due to the consistence between the experimental results and the collapse modes calculated to have the maximum vulnerability index, which demonstrates that such improved method could be effectively to predict the collapse modes of steel frame structures.

Numerical analysis of the counter-intuitive dynamic behavior of the elastic-plastic pin-ended beams under impulsive loading with regard to linear hardening effects

The counter-intuitive behavior where the permanent deflection of elastic-plastic beam come to rest in the opposite direction of the impulsive loading, normally appears and disappears abruptly, in certain small ranges of loading and structural parameters. One of the most important issues in the study of this phenomenon is the determination of the influence of different parameters. This work is aimed to study the effects of hardening in counter-intuitive dynamic behavior of elastic-plastic pin-ended beams under impulsive loading. This has been done by developing the proposed Galerkin numerical model and presenting a novel algorithm. The Galerkin method as well as the commercial finite element code ANSYS/LS-DYNA is applied to study this phenomenon. In order to account for the hardening effects in Galerkin method, a new algorithm is proposed. The time history curves for mid-span of the beam is studied in detail and the region of the occurrence of the counter-intuitive behavior is determined. Furthermore, using the finite element software, energy diagrams of the beam are also derived. It has been found that the counter-intuitive behavior is a phenomenon, which is very sensitive to loading, therefore it may appear with a little change in the amount of loading. The results also show that although both methods predict one continuous region of loading for the occurrence of this phenomenon in elastic-perfectly plastic beams, still there are two continuous distinct regions of loading, when considering the hardening effects, for this phenomenon. In addition, this anomalous behavior would occur in the proper ratios of kinetic to internal energy and when considering the linear hardening effects, the possibility of the occurrence of the counter-intuitive behavior exists in a wider domain of energy ratio.