Inelastic Behavior Research Articles

Seismic behaviour of structures under bidirectional ground motion: Does the angle of incidence have any influence?

Inelastic seismic behaviour of structures is needed to be predicted as accurately as possible. As during the seismic design, structures are allowed to undergo a stipulated amount of inelastic deformation in the dual design philosophy and its further extension of performance-based design. To obtain reasonably accurate behaviour in post-elastic ranges has manifold issues to be addressed together. The simultaneous effect of bidirectional ground motion is one of the major factors that need to be considered, and many studies also did the same. However, hardly any of them did consider the interaction between the deformations along two principal orthogonal directions on the yield criteria, post-elastic range excursion and the criteria of unloading. The present study makes an attempt to address these issues. Further, a few more studies mentioned that the angle of incidence of such orthogonal components of ground motion might influence the response of the structure. Hence, along with incorporating the effect of bidirectional interaction in the post elastic range, the issue of incidence angle is also studied extensively to reach a conclusive end. The detailed results presented in the study not only help to develop the physical insight but also maybe help in fine-tuning the design provisions.

A plastic-damage approach to the excavation response of a circular opening in weak rock

During opening construction, the accumulated wall displacement and the developing excavation damaged zone are the results of stress redistribution and inelastic behavior induced by both the microcracking damage and the irreversible plastic deformation. The current approach to predict ground response to excavation disturbance is usually based on the Convergence-Confinement Method, which fails to consider the rock damage and the plastic-damage coupled mechanism, resulting in inaccurate estimation of rock deformation, particularly in the case of the weak rock with high deformability. This study establishes a plastic-damage theoretical approach for a circular opening by a kinematic decomposition of strains into an elastic, plastic and damage parts within the framework of finite strain using a hypoelastic–plastic theory, in order to investigate the inelastic behavior-induced excavation response. In this regard, the damage model provides the effective stress to the plasticity model defining the yield criterion, in combination with the strength-stiffness degradation and damage evolution. The numerical implementation is given and two examples are considered for validation. Extensive works are then carried out to clarify some issues, including the capacity of the model to characterize the inelastic behavior, the role of rock damage and confining stress dependence on ground response, and the preliminary critical support pressure for the residual failure zone.

Investigation of Honeycomb Sandwich Panel Structure using Aluminum Alloy (AL6XN) Material under Blast Loading

In this study, we focused on the large inelastic behavior of a sandwich panel made of two solid plates as a stiffener and a honeycomb core shell subjected to blast load. The loading scheme was carried out using an explosive charge bullet mounted at a standoff distance of 100 mm with three mass variations of trinitrotoluene: 1, 2, and 3 kg TNT. The numerical simulations performed using ABAQUS/CAE were validated with the experimental results of a previous study. The geometrical effects of the sandwich panel on intact and damaged models were also numerically investigated. The panel was designed using a square and hexagonal honeycomb core. The effect of honeycomb core height was also observed by modeling the core using three height variations: 31, 51, and 71 mm. The results showed that the hexagonal core was more resistant to blast loads than the square design. The core height parameter determines the energy absorption based on these results. The structural strength is also affected by the damage. The findings of this study can be used to improve structural designs that utilize sandwich panels to withstand blast loads. Doi: 10.28991/CEJ-2022-08-05-014 Full Text: PDF

Characterization of site location versus the causative fault in seismic demands of structures

This paper aimed at investigating the effect of site location versus the causative fault on the seismic demand of structures and addressing the related parameters from different aspects in order to possibly bridge the gap between structural engineering and engineering seismology. To this end, fundamental studies were carried out using different SDOF and 2DOF systems to obtain the imposed seismic demands in terms of spectral displacement (Sd) contours, ductility demand contours (µ), Sdn/Sdp plots, and response resultant vectors. Both elastic and inelastic behavior regarding two ductility reduction factors (Rµ) were incorporated. In order to correctly address the influence of geometrical and seismological parameters on structural seismic demands, a total number of 273 ground motions at different locations were generated using a recently developed technique to perform more than 30,000 dynamic time-history analyses. In this regard, key parameters such as epicentral distance (R), angle (θ), slip distribution, rupture directivity, static offset, asperity location, pulse period (Tp), and pulse amplitude (Ap) were related to the structural responses and fully discussed. The results indicated that the vulnerability of structures could be rapidly and approximately assessed by elastic SDOF analyses or even by studying the ground motion characteristics such as pulse amplitude and pulse period. For low-period systems, the pulse amplitude (Ap) plays an important role, and for long-period systems, the pulse period (Tp) plays an important role. The relative rigidity of the structures vs. the pulse period plays a significant role in seismic demands. Finally, by getting far away from the epicenter, the Sdn/Sdp response ratio has been increased.

A new concept for superior energy dissipation in hierarchical materials and structures

We propose a new conceptual approach to reach unattained dissipative properties based on the friction of slender concentric sliding columns. We begin by searching for the optimal topology in the simplest telescopic system of two concentric columns. Interestingly, we obtain that the optimal shape parameters are material independent and scale invariant. Based on a multiscale self-similar reconstruction, we end-up with a theoretical optimal fractal limit system whose cross section resembles the classical Sierpiński triangle. Our optimal construction is finally completed by considering the possibility of a complete plane tessellation. The direct comparison of the dissipation per unit volume δ with the material dissipation up to the elastic limit δel shows a great advantage: δ∼2000δel. Such result is already attained for a realistic case of three only scales of refinement leading almost (96%) the same dissipation of the fractal limit. We also show the possibility of easy recovering of the original configuration after dissipation and we believe that our schematic system can have interesting reliable applications in different technological fields.Interestingly, our multiscale dissipative mechanism is reminiscent of similar strategies observed in nature as a result of bioadaptation such as in the archetypical cases of bone, nacre and spider silk. Even though other phenomena such as inelastic behavior and full tridimensional optimization are surely important in such biological systems, we believe that the suggested dissipation mechanism and scale invariance properties can give insight also in the hierarchical structures observed in important biological examples.

Micro and/or Nano-Silica modified moderate and high strength concrete: Rheology and synergistic effects on strength, elastic & inelastic behavior and microstructure

Synergistic effects of micro-silica (MS) and nano-silica (NS) on moderate and high strength concrete properties were investigated. Efficacy of micro and nano refinement remarkably increased as the W/Cm ratio decreased, and up to 37% improvement in compressive strength was obtained. Moreover, the linear-elastic region of the stress vs. strain diagrams significantly extended. As a result of the synergistic effect, a very dense interfacial transition zone was formed. The time-dependent evolution of the elastic modulus was much more effective than the compressive strength development. However, the combined use of MS and NS significantly decreased ductility.

COMPARISON OF MRF AND CBF STRUCTURAL RESPONSE TO EARTQUAKE IN OFFICE BUILDING SURABAYA

Indonesia is a country that prone earthquakes. Therefore, knowledge of earthquake-resistant building construction is needed in reducing the risk of damage caused by earthquakes. There are several methods of earthquake-resistant construction planning, one of which is the pushover analysis method. Pushover is a nonlinear static analysis method in which the structure is subjected to gravity loading and displacement-controlled lateral loads which continue to increase through elastic and inelastic behavior until the final condition. One of the popular construction materials in structural planning is steel construction, which has a uniform structure, lightweight, strong, and easy to work with. In modeling earthquake-resistant structures, several popular models are the MRF and CBF models. MRF is a structural configuration model configured on beams that are firmly connected to columns. Based on a rigid beam-column connection, the moment frame cannot be moved laterally without bending the beam or column depending on the connection geometry. Results The case study on the comparison of the two structural models concluded that in the design of earthquake-resistant steel structures using the pushover method, it was found that the MRF structure had higher ductility than the CBF, namely 2.1:1.6.

Powder-flow behavior and process mechanism in laser directed energy deposition based on determined restitution coefficient from inverse modeling

In order to clarify the transportation mechanism of particles in continuous coaxial powder feeding (CCPF) process, a trial-and-matching method is developed to quantify the restitution coefficient which is used to describe the inelastic collision between the particle and the nozzle wall. The consistency of the outlet velocity and the spatial concentration distribution of particles between the experimental statistic and the numerical calculation shows that the restitution coefficient of 0.9 can be used to measure the inelastic collision behavior between particles and the nozzle wall. Employing the determined restitution coefficient, a semi-quantitative method based on optical diagnostic and quantitative analysis derived from numerical calculation are proposed to study the powder-gas flow transport characteristics from single-layer to multi-layer jet flow. It is found that the outer shielding gas flow (OSGF) has a great influence on the multi-layer jet flow field, and it is most conducive to powder focusing at the OSGF of 20 L/min. The velocity distribution of CGF determined by the inner structure of CCPFN and the inelastic collision between the particle and the wall are the two mutually coupled factors that determine the outlet velocity of particles. Frequent inelastic collisions and the decrease of the CGF velocity lead to velocity dispersion and trajectory fluctuation of particles. When the inlet velocity of particles is 1.33 m/s, the outlet velocity ranged from 0.4 m/s to 0.9 m/s. This paper aims to provide a general method to determine the restitution coefficient and offer a comprehensive understanding of transportation mechanism of power particles both inside continuous coaxial powder feeding nozzle (CCPFN) and multi-layer jet zone between substrate and the CCPFN outlet.

Electrospun POSS integrated poly(carbonate-urea)urethane provides appropriate surface and mechanical properties for the fabrication of small-diameter vascular grafts

This study developed a platform for fabricating small-diameter vascular grafts using electrospun poly(carbonate-urea)urethane bonded with different concentrations of POSS nanocage. The characteristics of electrospun POSS-PCUUs were investigated by ATR-FTIR, 1HNMR, EDS, SEM, AFM, WCA, and DSC analyses. Besides, mechanical attributes such as tensile strength, modulus, elastic recovery, and inelastic behaviors were monitored. The survival rate and cellular attachment capacity were studied using human endothelial cells during a 7-day culture period. The results showed that electrospun nanofibers with 6 wt.% POSS-PCUU had better surface properties in terms of richness of POSS nanocage with notable improved mechanical strength and hysteresis loss properties (p < 0.05). The surface roughness of electrospun 6 wt.% POSS-PCUU reached 646 ± 10 nm with statistically significant differences compared to the control PCUU and groups containing 2, 4 wt.% POSS-PCUU (p < 0.05). The addition of 6 wt.% POSS increased the ultimate mechanical strength of nanofibers related to control PCUU and other groups (p < 0.05). The expansion of human endothelial cells on the 6 wt.% POSS-PCUU surface increased the viability reaching maximum levels on day 7 (p < 0.05). Immunofluorescence imaging using DAPI staining displayed the formation single-layer endothelial barrier at the luminal surface, indicating an appropriate cell-to-cell interaction.

Assessment of cyclic degradation effects in composite steel-concrete members

This paper investigates the inelastic behaviour of composite steel concrete beams, with particular emphasis on cyclic deterioration effects. A detailed continuum model is firstly developed to represent the hysteretic response of composite steel beam and concrete slab assemblages, validated against available experimental cyclic results on both steel and composite members. The proposed model is then adopted to perform detailed parametric assessments which are used to gain insights into the key response characteristics related to the inelastic cyclic performance of composite steel/concrete members, including their stiffness, capacity, and ductility. A synthetically generated numerical database is subsequently used to develop relationships governing the plastic rotation and cyclic degradation of dissipative composite beams as a function of the main geometric and material properties, with focus on members designed to European codified procedures. The deterioration effects are shown to be dependent on a number of key factors including, most significantly, the composite beam depth and the steel cross-section slenderness. In addition to the asymmetry in behaviour under sagging and hogging moments, it is shown that composite members typically exhibit 20% more degradation under cyclic loading compared to their bare steel counterparts. Importantly, the proposed cyclic degradation expressions for composite beams also enable the calibration of widely used uniaxial deterioration models which are suitable for implementation in computationally efficient nonlinear inelastic frame analysis for structural systems. These expressions also provide fundamental information required for idealised pushover representations for practical seismic assessment and design purposes.

Ground motions induced by pore pressure changes at the Szentes geothermal area, SE Hungary

Excessive thermal water volumes have been extracted from porous sedimentary rocks in the Hungarian part of the Pannonian Basin. Thermal water production in Hungary increased significantly from the early 1970s. Regional-scale exploitation of geothermal reservoirs without re-injection resulted in basin-scale pressure drop in the Upper Pannonian (Upper Miocene) sediments, leading to compaction. This compaction resulted in ground subsidence primarily through poro-elastic coupling.We investigated surface deformation at the Szentes geothermal filed, SE Hungary, where the largest pressure decline occurred. Subsequently, hydraulic head recovery in the western part of the geothermal reservoir was initiated in the mid-1990s. We obtained data from the European Space Agency’s Envisat satellites to estimate the ground motions for the period of November 2002–December 2006. We applied inverse geomechanical modeling to estimate reservoir properties and processes. We constrained the model parameters using the Ensemble Smoother with Multiple Data Assimilation, which allowed us to incorporate large amounts of surface movement observations in a computationally efficient way. Ground movements together with the modeling results show that uplift of the Szentes geothermal field occurred during the observation period. Since no injection wells were operated at Szentes before 2018, and production temperatures remained relatively constant through the entire production period, we explain ground uplift with pore pressure increase due to natural recharge. The estimated decompaction coefficients of the reservoir system characterizing the elastic behavior of the Szentes geothermal reservoir varies between ~ 0.2 × 10–9 and 2 × 10–9 Pa−1. Compaction coefficients of the reservoir system corresponding to the earlier depressurization period, from ~ 1970 to the mid-1990s, may be significantly larger due to the potential inelastic behavior and permanent compaction of clay-rich aquitards. The improved parametrization enables better forecasting of the reservoir behavior and facilitates the assessment of future subsidence scenarios that are helpful for the establishment of a sustainable production scheme.

Seismic Performance of I-shaped Beam-column Joint with Cubical and Triangular Slit Dampers Based on Finite Element Analysis

From the layout of a metallic structure`s beam-column connection w, while the seismic design is inside the dissipative method, precise contributors and zones ought to admit the growth of plastic deformation, and many metallic second resisting frames fail on the beam-column joints. This examines designed a unique structural machine with diverse slit dampers to triumph over this challenge, which can be easier to deliver overall seismic performance in the structural device that has been proposed. Plastic deformation is confined to the slit dampers at the end flange, which is the machine's key characteristic. The recommended connection's seismic overall performance changed into confirmed the use of the Abaqus software program utility to software systems with diverse slit damper forms. The proposed hyperlink exhibited first-rate hysteretic conduct in accordance to check results. Furthermore, on this machine, strength dissipation and plastic deformation focus on the diverse shapes of slit dampers, while the inelastic behaviour of the beams and columns is prevented via a suitable ability layout. The conduct of triangular and cubical shapes of slit dampers withinside the connection among a metallic beam and a container column is defined in this paper.

Creep behavior of intermetallic compounds at elevated temperatures and its effect on fatigue life evaluation of Cu pillar bumps

In electronic devices, intermetallic compound (IMC) can normally be found in solder interconnects, and it can pose significant effects on mechanical integrity of interconnects. It is widely accepted that IMC is brittle and normally assumed to be elastic in related mechanical simulations. However, in this work, temperature-dependent inelastic deformation behavior of Cu6Sn5, a common intermetallic compound in lead-free solder joints, was identified to exist at both room temperature and high temperature up to 180 °C and therefore was systematically investigated by nanoindenation. Young's modulus and hardness of IMC generally decreased linearly with increasing temperature. Creep deformation of IMC during dwelling period in nanoindentation was confirmed and further analyzed. The maximum creep displacement was found to increase from 4.90 nm at room temperature to 186.10 nm at 180 °C. Creep stress exponent was found to decrease from 3.32 to 0.37 as temperature rose, indicating significant improvement of deformation capability. Finite element modeling with and without IMC creep shows that inelastic deformation of IMC can compensate the mismatch between adjacent solder and pad in interconnects. Without considering IMC creep, fatigue life of Cu pillar bump can be severely under estimated in modelling.

In-plane-out-of-plane single and mutual interaction of masonry infills in the nonlinear seismic analysis of RC framed structures

In the aftermath of earthquakes poor seismic response was evidenced by non-structural elements such as enclosure masonry infills (MIs), characterized by a combination of in-plane (IP) and out-of-plane (OOP) damage mechanisms. The present work is aimed at identifying the effects of this mutual interaction on the nonlinear seismic behaviour of reinforced concrete (RC) framed structures. To this end, an extensive parametric study is carried out considering a spatial one-bay multi-storey shear-type model with MIs constituted of two leaves of clay hollow bricks, which is assumed as equivalent to infilled RC framed buildings. An extensive GIS aided structural mapping of the town of Rende (Italy) is adopted in order to obtain benchmark models as close to real structures as possible, focusing on total height, in plan dimensions and maximum and minimum bay lengths of the buildings. The dependence of the results on the variation of the following design parameters is considered for the i-th cluster of buildings characterized by the same number of storeys: i.e. fundamental vibration period; behaviour factor of the bare structure; aspect ratio of MIs, defined as the ratio between the panel length and height. A five-element macro-model comprising four (diagonal) nonlinear beams and one (horizontal) central nonlinear truss for the prediction of the OOP and IP behaviour of MIs, respectively, is first implemented in a homemade computer code. The proposed algorithm addresses the issue of the nonlinear mutual interaction of MIs by modifying stiffness and strength in the OOP direction on the basis of simultaneous or prior IP damage and vice-versa. A lumped plasticity model describes the inelastic behaviour of the RC frame members. Finally, a review of the current Italian, European and American seismic code provisions is performed by means of comparison with results of nonlinear dynamic analyses. To this end, bidirectional spectrum-compatible accelerograms are considered at ultimate limit states.

Eulerian constitutive equations for the coupled influences of anisotropic yielding, the Bauschinger effect and the strength-differential effect for plane stress

Recently, an Eulerian formulation based on evolving microstructural vectors was used (Lee and Rubin, 2020) to model anisotropic inelastic deformation rate in sheet metals. In contrast to Lagrangian formulations, the Eulerian formulation is insensitive to arbitrariness of reference and intermediate configurations. Here, additional constitutive equations are introduced to model asymmetric inelastic behaviors, such as the Bauchinger effect, permanent softening and the strength-differential effect within the context of the Eulerian formulation. The resulting model is calibrated to produce good agreement with several material data sets. In addition, example data sets are used to demonstrate advantages of the new model, especially for severe anisotropic response and large deformations.

Effect of reinforcement on the response of continuous steel-concrete composite beams

This paper presents a comprehensive assessment on inelastic behavior of continuous steel-concrete composite (SCC) beams, focusing on the effect of reinforcement in slab. A finite element model is formulated and verified against laboratory tests. Numerical assessment is conducted on two-span SCC beams with various reinforcement types and areas. The results indicate that using carbon fiber reinforced polymer (CFRP) reinforcement is more effective in reducing the crack width in concrete slab over the center support than using glass fiber reinforced polymer (GFRP) or steel reinforcement. The reinforcement hardly influences the ultimate response at midspan but markedly affects that at the center support. The ultimate load of SCC beams with steel reinforcement is close to that with CFRP reinforcement while higher than that with GFRP reinforcement. At ultimate, CFRP reinforcement leads to greater support moment but substantially lower moment redistribution while GFRP reinforcement results in lower moment but comparable moment redistribution, when compared to steel reinforcement.

Experimental study on one-way arching masonry specimens under monotonic and cyclic loads

Characterizing the behavior and the mechanical properties of masonry assemblies subjected to out-of-plane static loading is a fundamental step towards the understanding of their response to more complex loading scenarios. The more challenging case is that of arching walls where the load resistance mechanism couples bending and axial components. This study presents a combined experimental and theoretical effort aiming at gaining insight into the behavior of such arching walls. The experimental phase is conducted on small-size one-way specimens that are comprised of two or four masonry units loaded in a four-point-bending scheme. The experimental methodology aims at collecting new quantitative data on the response under monotonic and cyclic loadings. The 2-block configuration mimics the basic form of arching walls and focuses on the interaction between the masonry units and the mortar layer, features that are essential for any quantitative, analytical or numerical assessment of such walls. The 4-block configuration mimics the more complex response when additional mortar joints are part of the structural system. Along with the global load–displacement curve, the experiments also monitor the arching force, as well as local aspects such as the axial deformations at the tensed and compressed extreme fibers of the mortar joints. The latter aims at studying the constitutive behavior of the mortar joints. The complete set of test results is then used as a benchmark for comparison with an analytical model. The comparison examines the model capabilities, reveals further aspects of the physical behavior, and explores the cracking process, the deformation profile, and the effect of inelastic behavior of the mortar material. The combined experimental and theoretical findings reveal the spectrum of phenomena governing the behavior of masonry walls and highlight the role of the arching mechanism through macro and micro perspectives.

Numerical Analysis of Multilevel Eccentric Chevron Braced Frame for Improved Inelastic Behavior

AbstractThis paper presents a renovation strategy to upgrade the conventionally constructed chevron braced (both concentric and eccentric) steel frames in such a way that each set of the upgraded b...

Performance based design of a new hybrid passive energy dissipation device for vibration control of reinforced concrete frames subjected to broad-ranging earthquake ground excitations

This paper evaluates a new hybrid passive device that comprises two different passive energy dissipation categories, namely, viscoelastic damper and friction damper. The device operates as a synergic unit using a novel locking mechanism. The hybrid passive device offsets the drawbacks of individual devices and facilitates improving the performance of structures for multiple excitation vibration levels due to wind and seismic events. Both devices are connected in a parallel combination using locking mechanisms and exhibit distinct hysteretic characteristics under small and significant deformation. The viscoelastic damper alone will be activated for extreme winds and minor to moderate earthquakes, and both devices will work simultaneously for strong earthquakes. Considering the advantages of such a new device, this article presents a new seismic design method structures equipped with a hybrid passive dampers device using the energy-balance concept. The method accounts for the structural member's inelastic behaviour, phase transformation of the stiffness and the energy dissipation capacity of the energy devices to achieve the intended performance level under the design earthquake hazard. The proposed method has been applied on a six- and a twelve-storied reinforced concrete building. The seismic performance is verified through nonlinear time history analysis using a set of near and far-field ground motions. Numerical results are investigated in terms of the inter-story drifts, the residual drifts, the floor acceleration and the yield mechanisms. The structure's performance corresponds well with the target performance levels.

Local buckling behaviour of high-strength steel tubular columns subjected to one-sided cyclic loading and implications in seismic design of steel MRFs

After yielding, steel structures progressively exhibit an asymmetrical hysteretic behaviour under earthquakes biased in one direction (ratcheting effect). This response may be favourable to structural components because of the absence of symmetrical cyclic loading reversals. To evaluate the inelastic behaviour of components to asymmetrical cyclic loading, this study develops a set of one-sided cyclic loading histories for columns on the basis of a parametric study on the asymmetrical hysteretic behaviour of steel moment-resisting-frames (MRFs). Experimental and computational results indicate that steel tubular columns subjected to one-sided cyclic loading may exhibit 15%–71% higher ductility compared with that under symmetrical cyclic loading showing adequate resistance to local buckling initiation and sufficient ductility afterwards. These reduced ductility demands may permit the use of high-strength steels in energy dissipative zones, such as high yield-to-tensile strength ratio (Y/T) steels, resulting in reduced material consumption and more economical seismic design of buildings. The above findings are utilized in the seismic design of a MRF employing high Y/T steel, which enjoys almost the same lateral strength as a corresponding conventional steel MRF but nearly 25% smaller cross-sectional area in columns. Nonlinear time-history analyses revealed that the high Y/T MRF behaved elastically under frequent events, whilst the ground floor columns of the conventional MRF yielded. Under rare seismic events, the average story drift ductility demand for the high Y/T MRF was only 1.77, while for the conventional MRF was 2.57. The former MRF successfully resisted the earthquake loads without experiencing local buckling in columns.