Contact force models for non-spherical particles with different surface properties : a review

This paper reviews the state-of-the-art contact force models for non-spherical particles, which describe the relationship between the contact force and the geometrical, material, and mechanical properties of the contacting particles. The review aims to select better contact force models to improve the current simplified contact force models used in discrete element method (DEM) simulations. First, the contact force models based on the extension of the classical Hertz theory are reviewed, in which a recent accurate geometrical contact force model is highlighted. Secondly, the research on the effects of different variables such as elastoplasticity, viscoelasticity, adhesion and surface roughness on contact force are reviewed respectively and then incorporated into the accurate geometrical contact force model. Thirdly, tangential force models for non-spherical particles in contact under various loading regimes are reviewed as well. Based on the review, a full set of improved contact force models for DEM is recommended. These contact force models can more accurately predict the contact force and contact area for non-spherical particles, which can be beneficial to the DEM simulation in emerging areas, such as nanoparticles and additive manufacturing

Assessment of seismic behaviour of SMRFS with RBS connections by means of mixed-based state-space approach

With an intention to implement a reliable numerical implementation of the mixed‐based state‐space strategy for steel structural systems, the paper presents a thorough seismic analysis of steel moment resisting frames (SMRFs) with reduced beam section (RBS) connections. Firstly, a model of beam‐column element inclusive of material and geometric nonlinearities is efficiently utilized derived from appropriate force interpolation functions. Moreover, with the present formulation, non‐prismatic properties of RBS region can be considered without the necessity of heavy discretization of elements. Contribution of panel zone is taken into account by considering a nonlinear rotational spring as well. In addition, the extension of Wen‐Bouc model to capture material inelasticity is applied that is apparently superior to other constitutive behaviour when it leads to both a smooth hysteretic model and rather precisely well‐mannered state‐space depiction capable of conveying several hysteretic features. The state‐space approach is then employed where nodal forces balance and constitutive equations are solved simultaneously. Secondly, three‐dimensional finite element analysis is surveyed to validate proposed macro‐element model. Finally, a set of nonlinear static and transient analyses of four‐ and eight‐storey frames with and without RBS connections are fulfilled. Then, structural demand parameters used to assess the global and local response of designated frames

A case study on the assessment of response modification coefficient and earthquake-induced collapse potential of a high-rise setback tower

This paper evaluates response modification coefficient (R-factor) and collapse potential of a high-rise tower with setback irregularity under spectral-matched ground motion records. The tower is comprised of two legs with three distinct lateral bearing systems in elevation and curved configuration in plan. Furthermore, it has a setback in elevation, recognised by inclined columns joining two legs of the tower in uppermost stories. These characteristics cause the tower to classify as a complex irregular structure in which using code-based R-factor is highly dubious. In this paper, initially, an analytical model of the tower was subjected to a suite of ground motions to estimate collapse potential and equivalent R-factor in accordance with FEMA P695. Alternatively, structural performance parameters including inter-storey drift ratios, residual drift ratios and plastic hinge rotations were compared to TBI acceptance criteria. To achieve consistent safety margin against collapse, the value of 8 was suitable for R-factor. In spite of satisfactory threshold in accordance with FEMA P695 and TBI guidelines, for a structure with irregular configuration and multiple bearing system, damages can be localised close to zones of change in lateral bearing system that may lead to partial collaps

Assessment of axial force effect on improved damage index of confined RC beam-column members

In recent years, different damage indexes have been introduced in engineering literature. The most prominent one among other counterparts is the 1985 Park and Ang's damage index (DIPA), which demonstrates well calibration against experimental results. Hence, it has traditionally had broad application in the field of structural engineering. Commonly, in DIPA relevant parameters are assessed based on plastic-hinge approach, which is not well suited to consider the coupled response between stress resultants (axial force and flexural moment) especially in grossly nonlinear domain. The reason is that named approach is utilized constant shape plastic moment-curvature curve, which is not capable of varying the shape throughout loading history. Another drawback of plastic-hinge method is the difficulty of representing precisely partial yielding of the cross-section. To remedy the situation, the fiber discretization technique is used in this paper. Based on the fiber discretization strategy, not only have the stiffness and strength degradation been characterized more accurately, but also the distribution of plasticity along the plastic zone has been considered. Besides, the multi-directional effect of axial force and flexural moment is considered to assess DI parameters. Additionally, this strategy directly incorporates the effect of transverse confinement into cross sectional constitutive behaviour

A case study on the soil–pile–structure interaction of a long span arched structure

Different concepts for modelling of soil-foundation in complete dynamic interaction analysis for a 110-m height 70-m span arched structure on 180 piles were investigated in this paper. The modelling approaches consisted of a sophisticated procedure to account for soil compliance and foundation flexibility by defining frequency-dependent springs and dashpots; namely, flexible-impedance base model. The results of this model were compared with those of the conventional modelling procedures; namely, fixed base model and flexible base model by defining frequency-independent springs. In the flexible-impedance base model, the substructure approach was employed through finite element modelling. To account for the kinematic interaction, the numerical model of the soil, foundation and piles were developed using a verified finite element model in ABAQUS. The free field time history and design spectrum were modified to obtain the foundation input motion. The impedance of pile groups with different length was obtained by the finite element model to assess the inertial interaction. The comparison of the results of the employed models showed that rocking and torsional responses were greatly affected by soil–structure interaction, indicating redistribution of seismic demands. It was also proven that the internal demands of the conventional model considering frequency-independent Winkler springs might be higher than those of the model including pile–soil–structure interaction effects

The efficiency of reduced beam section connections for reducing residual drifts in moment resisting frames

In most framed structures anticipated deformations in accordance with current codes fall into acceptable limit states, whereas they go through substantial residual deformations in the aftermath of severe ground motions. These structures seem unsafe to occupants since static imminent instability in the immediate post-earthquake may be occurred. Moreover, rehabilitation costs of extensive residual deformations are not usually reasonable. Apparently, there is a lack of detailed knowledge related to reducing residual drift techniques when code-based seismic design is considered. In this paper, reduced beam section connections as a positive approach are taken action to mitigate the huge amount of residual drifts which are greatly amplified by P-Δ effects. To demonstrate the efficacy of RBS, a sixteen-story moment resisting frame is analyzed based on a suite of 8 single-component near field records which have been scaled according to the code provisions. The results are then processed to assess the effects of RBS detailing on drift profile, maximum drift, and residual drift. Besides, a special emphasis is given to estimate overall trend towards drift accumulation in each story in the presence of RBS assembly. A main conclusion is that using this connection predominantly alleviates the adverse effects of P-Δ on amplifying residual drifts

Seismic fragility analysis of liquid storage steel tanks considering shell buckling and anchor failure by added-mass method

Liquid storage tanks are vulnerable to a wide variety of failures under severe seismic excitation. Among all failure modes shell buckling and anchor bolt failures are the most critical forms of damage. Sometimes combination of different modes intensifies or accelerates liquid storage tank’s damage. Although the effect of each different failure modes has been studied separately by a number of researchers, few studies may have considered combination of main failure modes concurrently. Hence, in this paper, a cylindrical steel tank has been selected in order to study multiple damages due to dynamic loadings on the tank. All anchor bolts and steel thin wall and reinforced concrete pedestal have been modeled counting material and geometric non-linearity. The methodology for finite element modeling of fluid-structure interaction has included applying the added-mass strategy, followed by performing the numerical analyses. A suite of ground motions has been selected and matched to the target spectrum. Afterwards, incremental dynamic analyses have been conducted to obtain fragility curve according to simultaneous modes of failure. The results have indicated that anchor bolt failures along with shell buckling significantly have contributed to more flexible behavior of the thin-walled steel tank and distribution of buckling to uppermiddle part of tank which might increase seismic effects on the tank. Also, the design of steel tanks needs more considerations beyond current codes in major earthquake prone zones

Assessment of different failure modes in liquid storage tanks under horizontal ground motion

Steel storage tanks are generally vulnerable to dynamic failure under strong ground motion. The reason for that is partly because of small thickness of tank walls which contribute to either elastic buckling or inelastic post-buckling mechanisms. The tank aspect ratio plays a pivotal role in developing different failure modes. In order to investigate different failure mechanisms, case study tanks considering different aspect ratios that are fully anchored at the base are introduced. Dynamic fluid-structure interaction is utilised based on so-called added-mass method and tank walls are modelled using general purpose finite element platform to detect potential failure modes. Seven strong ground motions are selected from NGA database and spectrally matched with target spectrum. Incremental dynamic analyses are conducted to identify critical failure modes and construct fragility curves. The results demonstrate that changing tank aspect ratio contributes to different modes of failure ranging from elephant foot and diamond shape to secondary buckling modes

In-plane lateral behaviour of PVC modular concrete form squat walls : experimental and numerical study

The in-plane lateral performance of modular concrete form squat walls comprising prefabricated Polyvinyl Chloride (PVC) permanent forms and reinforced concrete cores was experimentally and numerically undertaken. The PVC encasement make additional confinement to the reinforced concrete core that makes the formwork attractive, however, the interaction between the encasement and the concrete make an irregular internal concrete core and therefore further studies are required. Eleven wall specimens of different aspect ratios ranging from 0.5 to 2.0 were subjected to incrementally increasing monotonic drifts to failure after imposing eccentric vertical loads as indicative of gravity loading conditions. Two samples were further selected and investigated by adopting push-out tests to measure in-plane shear capacity of PVC form walls. The experimental measures including concrete crack propagation and crushing, loads and displacements pertinent to capping and failure stage, and ductility capacity were discussed. After stripping the form off, a failure mode in walls demonstrated discontinuity in the concrete crack propagation due to penetration of the form web into the concrete core which did not act as a solid concrete wall. Finite element simulations were undertaken according to suggested modelling techniques and the credibility of the numerical method was investigated through comparison with experiment results. Implications of change in design parameters including axial load ratio, wall aspect ratio, concrete strength, vertical, horizontal reinforcement ratio, and cyclic loading regime were further examined through a detailed parametric study. It demonstrated that the peak lateral load capacity and post-peak negative stiffness of PVC form squat concrete walls were highly influenced by axial load ratio. The influence of concrete strength on peak lateral response of the walls was in direct proportion to the axial load ratio. Increasing horizontal reinforcement ratios showed the modest influence on the peak lateral load capacity of the walls

A revisit of common normal method for discrete modelling of non-spherical particles

Discrete element method (DEM) is prominent for studying granular materials at particle scale. However, how to model non-spherical particles in DEM is still challenging. In light of the present contact detection algorithms in the literature, common normal (CN) and geometric potential (GP) are two methods used for particles with smooth surfaces. Yet it has been long believed that CN gives erroneous results while GP is more preferable since they were firstly proposed for ellipsoidal particles decades ago. A revisit of CN in this work identifies two problems in the original CN, and then a new CN is proposed which can overcome these problems. Based on the comparison to sub-particle scale finite element analyses, the new CN has been further shown to be able to predict the contact plane more accurately than the original CN and GP. Such an advantage is found for the modelling of ellipsoidal and superquadric particles. The study not only proposes an improved CN algorithm but also demonstrates that CN should receive more attentions in DEM, though GP is now much more widely used