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This paper investigates experimentally and numerically the protective capability of skeletal muscle-inspired hierarchical tubular (MHT) structures made of aluminum under both quasi-static and dynamic impact conditions. In the quasi-static compression tests, structures with higher hierarchical order were more deformable and had lower contact force. Dynamic impact tests were conducted for the first time on MHT specimens of three different hierarchical orders using a drop tower facility. The results indicated a significant reduction in both the maximum and mean contact forces on the protected body when shielded by the second- and third-order MHT structures. This suggested that increasing the hierarchical order of the structure effectively enhanced impact protection capability. Numerical models were developed using ABAQUS/Explicit to accurately reproduce the deformation process and force-time functions of the dynamic impact scenarios. A parametric study found that the impact resistance performance of the MHT structures was robust against various impact velocities and masses. • Inspired by the internal structure of skeleton muscle tissues, the muscle-inspired hierarchical tubular (MHT) structure was proposed. • The energy absorption of the MHT structure was investigated experimentally and numerically. • Stress delocalization mechanisms significantly enhanced the energy dissipation of the MHT structure. • The effects of impact mass and velocity on the impact resistance of the MHT structure were investigated. [ABSTRACT FROM AUTHOR]

The present study reveals for the first time that some real earthquake ground motions would induce the absolute maximum response (AMR) of structural systems posterior to the end of the excitation. Under these ground motions, illustrated using single-degree-of-freedom (SDOF) systems, the peak responses calculated within the during-shaking phase might be significantly lower than the actual AMR. Extending the dynamic analysis to the post-shaking phase by half of the structural period is recommended when conducting response history analyses or calculating the response spectra of these ground motions. • Peak earthquake response of long-period structures occurs posterior to the earthquake shaking. • Extended analysis by half of the structural period is recommended after the earthquake shaking. • Ground motions requiring extended analysis are identified from the PEER-NGA2 database. [ABSTRACT FROM AUTHOR]

The innovative concept of geotechnical seismic isolation (GSI) system with the use of a continuous layer of low-modulus materials, such as rubber-soil mixtures (RSM), surrounding the foundation of structure has attracted considerable research interest on its performance at both system and material levels, since it was first proposed over a decade ago. The performance of the GSI system has been studied through a number of numerical, physical and hybrid modeling techniques; but due to the complexity of the problem, the isolation mechanism has not been thoroughly investigated. Hence, this article aims at initiating this aspect of development. A simple and efficient lumped-parameter analytical model is developed for analyzing the dynamic soil-foundation-structure interaction (SFSI) of the GSI system. Considering the importance of various nonlinearities involved, a theoretical approach for estimating effective shear strain is derived for capturing the nonlinearity of subsurface materials by the equivalent-linear method. The effectiveness of the analytical model is then demonstrated through a representative case study, based on which the main features of the isolation mechanism are investigated. The seismic isolation capability of the GSI system is founded on the reduced lateral stiffness of the RSM layer and the lower modulus of RSM that reduces the rocking stiffness. The proposed system could take advantage of the rocking isolation mechanism with reversible foundation deformations due to the higher elasticity of the RSM material. • First lumped-parameter analytical model for geotechnical seismic isolation system. • Nonlinearity of subsurface material incorporated in soil-foundation-structure model. • New theoretical approach for estimating effective shear strain in equivalent-linear method. • Demonstrated and explained the mechanism of GSI system through case study. [ABSTRACT FROM AUTHOR]

Highlights • Derivation of the key formulations for the implementation of single diagonal haunch. • Generalisation of formulation for seismic retrofit of RC joint using diagonal haunch. • Validation of generalized analytical procedure with available experimental data. • Effectiveness of single diagonal haunch demonstrated through a parametric study. Abstract Exterior beam-column joint is typically the weakest link in a limited-ductile RC frame structure. The use of diagonal haunch element has been considered as a desirable seismic retrofit option for reducing the seismic demand at the joint. Previous research globally has focused on implementing double haunches, whilst the performance of using single haunch element as a less-invasive and more architecturally favourable retrofit option has not been investigated. In this study, the feasibility of using a single haunch system for retrofitting RC exterior beam-column joint is explored. This paper presents the derivation of the key formulations for the implementation of a single diagonal haunch as well as the generalization of the formulations for all three systems: the non-retrofitted subassembly, the double haunch retrofitting system, and the single haunch retrofitting system. The formulations have then been validated by available experimental data for non-retrofitted subassembly and double haunch retrofitting system. Finally, the effectiveness of the single haunch retrofitting system is compared with that of the double haunch retrofitting system through a parametric study. [ABSTRACT FROM AUTHOR]

Porcelain surge arrester is common in electrical substation and is vulnerable in earthquakes. In most cases, surge arrester needs to be mounted on the top of a steel supporting structure. The seismic response behaviors and failure modes of a steel supporting structure – surge arrester system are critical for the safety and reliability of substations. This paper aims at investigating such interaction effects on the seismic responses of surge arrester. Porcelain surge arresters in 220 kV, 500 kV, 750 kV and 1000 kV are considered in this study. Earthquake induced flexural stress and displacement are identified as key response parameters of a steel supporting structure – surge arrester system based on a full-scale test of 1000 kV porcelain surge arrester. Analytical model of the system was then developed and verified by full-scale shaking table test. The effects of supporting structure on the bending moment and displacement responses are then investigated through time history analysis, modal analysis and a parametric study. Finally, a structural design procedure is proposed for selecting suitable value of flexural rigidity of the steel supporting structure. [ABSTRACT FROM AUTHOR]

Structural engineers design buildings according to the earthquake action (demand) specified in code of practice, whilst the rationale behind such requirement is commonly untold. In fact, even if a structure is designed strictly in accordance to the best standard and practice in the world, there is still a (small) chance of failure or collapse in an extreme earthquake event, due to the uncertainties in material properties and actual ground motions characteristics. This is the residual risk, which is unavoidable, and should be taken as a governing parameter for determining the performance goals of seismic design. This study attempts to establish the required (target) collapse risk limits for designing different types of ordinary buildings based on a well-accepted tolerable level of mortality risk and estimates of fatality rates in buildings. The proposed limits are compared with the target risk of collapse stipulated in the 2012 edition of the International Building Code (IBC). The risk-based approach presented in this paper should also be applicable for setting performance objectives for structural design of buildings and infrastructure against other natural, human-caused and technological hazards. [ABSTRACT FROM AUTHOR]

Design spectrum (DS) model is typically specified in a seismic code of practice for structural design. In a region of low-to-moderate seismicity where seismic code does not exist, a DS model in a well established code of practice is usually adopted, while the suitability of such model has seldom been evaluated. In this article, the elastic DS models for reference (rock) site stipulated in six major codes of practice (AS1170.4–2007, EN1998-1:2004, GB50011–2010, IBC–2012, NBCC–2010 and NZS1170.5:2004) have been compared and scrutinized. Three cities of low-to-moderate seismicity, namely, Melbourne (Australia), Hong Kong (China) and Karlsruhe (Germany), have been selected for illustrative purposes. Particular emphasis has been put on the parameterization scheme for DS model. It is found that huge discrepancies (over 100%) exist among the models, especially at the long period range, due to differences in spectral shapes and the recommended corner periods, which would lead to undesirable effects on the use of the displacement-based seismic design approach. It is urged that the values of corner periods should be determined specifically and cautiously based on the regional seismicity pattern and local geological conditions. [ABSTRACT FROM AUTHOR]

Abstract: Where a distinct soil–rock interface exists, the bedrock medium is commonly treated as elastic half-space and the bedrock surface as the lower boundary of the soil-column model for site response analyses (or the lower boundary of the finite element model for soil-structure interaction analyses). While shear wave velocity in bedrock varies with depth, there has been no consensus amongst scientists and practitioners over the value of “effective depth” into bedrock at which the “half-space” shear wave velocity value should be taken for modeling purposes. This paper reports an interesting and important observation that the effective depth into bedrock is sensitive to the shear wave velocity profile of the overlying soil sediments. A simple and heuristic method, namely Resonant Period Equivalence (RPE) Method, is proposed herein for representing a stratified elastic bedrock of inhomogeneous properties by an equivalent homogeneous elastic half-space medium, which is characterized by a single equivalent shear wave velocity (V R) value. The proposed calculation method has been verified by extensive comparative analyses involving the use of programs SHAKE and NERA and employing the complete shear wave velocity models of both the soil sediments and the underlying stratified bedrock. [Copyright &y& Elsevier]

Abstract: Site classification is an important procedure for a reliable site-specific seismic hazard assessment. On the other hand, the site conditions at strong-motion stations are essential for accurate interpretation and analysis of the recorded ground motion data obtained from different regions of the world. For some countries with insufficient data on the subsurface geological settings, the required site condition information is not available. This paper presents a new and efficient approach for site classification based on artificial neural networks (ANN) along with a selected set of representative horizontal to vertical spectral ratio (HVSR) curves for four site classes. The nonlinear nature of ANN and their ability to learn in a complex environment make it highly suitable for function approximation and solving complicated engineering problems. Two types of radial basis function (RBF) neural networks, namely, probabilistic neural networks (PNN) and generalized regression neural networks (GRNN) were chosen in this study, as no separate training phase is required, rendering them particularly suitable for site classification. The proposed approach has been tested using data of the Chi-Chi, Taiwan, earthquake (Mw=7.6) recorded from 87 stations at which the site conditions are known. Analyses show that both the PNN and the GRNN perform very well with similar accuracy in estimating site conditions, with successful rates of 78% and 75%, respectively. [Copyright &y& Elsevier]

We propose a skeletal muscle-inspired hierarchical structure for the alumina ceramic layer in ceramic composite armour structures to achieve greater energy dissipation under impact. We mimic the nano-architecture of skeletal muscle tissues by introducing hierarchy both with self-similarity using a fractal design, and without self-similarity in the hierarchical levels to explore the function of hierarchy in improving the protective capability of the armour structure. The numerical simulations showed that increasing the structural hierarchy can boost stress reduction by up to 30% for the third order hierarchical structure without self-similarity compared to the first order hierarchical structure with the same weight. The underlying mechanism that increases the impact resistance in the higher order hierarchical structures is the delocalisation of the damage over multiple crack paths in the different hierarchical levels. This bio-inspired concept can be used to generalise the design of future impact-resilient structures which optimise the suppression of stresses and reduce the associated weight penalty for use in protective gear and armoured structures. [ABSTRACT FROM AUTHOR]

Owing to the repeatedly observed long-duration ground motions (GMs), the duration effect is becoming increasingly critical for the seismic design and assessment of important infrastructures. In this study, dynamic analyses are performed to evaluate the influence of GM duration on the inelastic seismic response of subway stations. Based on the Daikai subway station in Kobe, Japan, a two-dimensional numerical model incorporating a concrete damage plasticity model and a soil nonlinear model is developed. Twenty-five spectrally matched records with different significant durations (D 5-95) are selected for dynamic analyses. The responses are evaluated based on various engineering demand parameters (EDPs) including the internal force, drift ratio, element damage index, and the total damage of the structural member. The results show that for weak earthquakes (PGA = 0.15 g) the duration has a negligible influence, while for strong earthquakes (PGA = 0.45 g) the duration effect is particularly pronounced due to the significant cyclic degradation of stiffness and strength of the material. Compared to the location-dependent maximum internal forces and the element damage index, the maximum drift ratio and the total compressive damage index are suitable EDPs, since they correlate well with D 5-95. On average, for every 10-s increase in D 5-95 of strong GMs used in this study (PGA = 0.45 g), the maximum drift ratio of the side wall and center column increases by 0.12 % and 0.2 % while the total compressive damage index of the side wall and center column increases by 0.01 and 0.04, respectively. The duration effect is more pronounced for the center column implying that damage to the weak structural member is exacerbated by long-duration GMs. The increased column stiffness or elastic soil behavior may reduce the duration effect. This study highlights that strong GMs having similar amplitude and response spectrum with different significant durations can significantly affect the inelastic seismic response of subway stations. • Correlations between different demand measures with significant duration are quantified. • Maximum drift ratio and total compressive damage index are two suitable indicators for evaluating duration effect. • Response of the center column is much more exacerbated under long-duration ground motions compared to the side wall. • Duration should be considered in the specification and selection of ground motions. [ABSTRACT FROM AUTHOR]

Safety roller barrier (SRB) is an innovative road safety device that utilises foam rollers to absorb and convert shock energy into rotational energy, showcasing its remarkable ability to minimise the risk and severity of casualties in road accidents. In this study, a simulation-based optimisation approach was employed to obtain the optimal design for the SRB. Quasi-static and dynamic mechanical properties of the construction materials were experimentally obtained. SRB finite element (FE) models were then created based on installed systems in multiple Australian cities. The model was validated using full-scale TL4 crash tests according to the specifications outlined in the Manual for Assessment of Safety Hardware (MASH). Subsequently, a parametric study was conducted to explore the influence of design parameters such as post spacing, rail height, and roller number. Finally, a parallel Bayesian optimisation algorithm was applied to re-design the SRB system with enhanced performance and reduced cost. This optimisation process yielded several sets of optimal parameters, paving the way for a more effective and economically viable SRB design. • Numerical model of safety roller barrier (SRB) crash was built and validated. • Parametric studies were conducted to reveal optimal designs of SRB. • The geometry of SRB was optimised using parallel Bayesian optimisaiton method. [ABSTRACT FROM AUTHOR]

Directivity is a phenomenon perceived during fault ruptures wherein the ground motion and spectral response in the direction of the rupture is more significant than in any other direction. The objective of this study is to evaluate the variability in characteristics of near-fault ground motions as well as the ductility demand on structures due to directivity based on simulations of strike-slip earthquake events by employing SPECFEM3D, a physics-based ground motion simulation code. To understand the finite fault propagation effect, a source effect, the vertical strike-slip fault is considered to be embedded in an elastic half-space, to prevent the influence of path and site effects. Two scenarios are designed based on the positioning of nucleation asperity (NA): (1) in the middle of the fault face to simulate bilateral (BL) rupture and (2) shifted to one end for the case of unilateral (UL) rupture. The ground motions at near-fault stations, located in a racetrack configuration around the surface trace of the fault, are analyzed. In addition to a high spectral content in the forward directivity stations as a result of UL rupture, directivity velocity pulses identified in the fault-normal components are higher than the fling step velocity pulses in the fault-parallel component for the racetrack stations considered. Furthermore, the study examines the correlation between ductility demands computed based on elastoplastic rheology with direct point parameter and ground motion intensity measures for directivity and fling step stations. • Rupture dynamics based simulations were performed for directivity and non-directivity ground motions. • A unilateral scenario (hypocenter to one side of the fault) and a bilateral rupture (hypocenter at the middle along strike. • Influence of Nucleation Asperity (NA) on pulse period is shown for five locations arranged around the fault on a racetrack. • The effect of NA on ductility demand of structures displaying low, moderate, and high natural periods was highlighted. • Correlation of inelastic response with directivity correction factors in literature, and intensity measures discussed. [ABSTRACT FROM AUTHOR]

In predicting the capacity of screw anchors under static tensile loading, the Concrete Capacity (CC) method is the state-of-the-art prediction model which covers concrete cone capacities in uncracked and cracked concrete up to 0.3 mm crack width. However, in seismic applications, anchors may be subjected to large crack widths of up to 0.8 mm. With large crack width, the behaviour of small-sized (typically 6 mm) screw anchors has not been studied. In this study, experimental investigations were conducted for a total of 29 anchors in uncracked and cracked concrete with large crack widths up to 0.8 mm. The experimental results showed that the load-carrying capacity of screw anchors significantly dropped resulting in a reduction factor of 0.13–0.47 for cracked concrete with 0.8 mm crack width (significantly lower than 0.7 assumed by the CC method for a crack width of up to 0.3 mm). This paper focused on developing modelling technique for predicting the performance of screw anchors in cracked concrete with a crack width of up to 0.8 mm since screw anchor in cracked concrete has not been studied using finite element analysis. Three-dimensional finite element models were developed for screw anchors in uncracked and cracked concrete and validated by the experimental results. Further, parametric analysis showed that dilation angle and shape factor are the two most influencing parameters among other of the concrete damage plasticity model. • Behaviour of 6 mm screw anchors in cracked concrete of large crack width up to 0.8 mm. • Finite element analysis of screw anchors in cracked concrete with large crack width. • Parametric analysis of concrete parameters of concrete damaged plasticity (CDP) model. [ABSTRACT FROM AUTHOR]

• Limited ductile high-strength RC columns are tested under bidirectional earthquake actions. • Axial load ratio and the type of bidirectional loading history are the variables of the study. • A non-linear biaxial force-drift backbone model for RC columns is proposed and validated. This paper endeavors to enhance the understanding of the non-linear force-displacement hysteretic behavior of reinforced concrete (RC) columns subjected to bidirectional earthquake actions with different loading paths and magnitudes of lateral displacement in the two axes. RC column testing in literature has traditionally been focused towards the unidirectional testing of both normal and high strength concrete columns or the bidirectional testing of normal strength concrete columns only. This study will address this important knowledge gap by experimentally investigating the biaxial lateral capacity of high-strength RC columns with limited ductile detailing. The results of this experimental study and other previous studies are also used to develop a simplified model for predicting the non-linear backbone force-displacement behavior of RC columns. The paper will firstly present the six full-scale column specimens, the test setup, and the loading procedure. The test results will then be presented and analyzed. Three different bidirectional loading protocols were adopted to study the effects of loading history. The important effects of axial load ratio on the collapse behavior (i.e. maximum drift) are also examined in detail. The paper will conclude with an overview of the proposed backbone model for predicting the force-drift behavior of RC columns subjected to bidirectional loading. [ABSTRACT FROM AUTHOR]

• UBPRC column has larger post-yield stiffness and smaller ultimate displacement. • UBPRC column shows better self-centering behavior but weaker energy dissipation. • FPC column suffers severe prestress loss. • The self-centering performance index can be adopted in designing UBPRC column. Unbonded prestressed reinforced concrete column (UBPRC column) has become an attractive approach in the field of bridge seismic design due to its superior self-centering behavior. Unbonded prestressing bar in a UBPRC column functions as a self-centering element and longitudinal mild reinforcement functions as an energy dissipator. Quasi-static cyclic test was carried out in this study to compare the seismic performance of reinforced concrete column (RC column), UBPRC column and fully prestressed concrete column (FPC column). The result shows that the UBPRC column has higher post-yield stiffness and smaller quasi-static residual displacement, but lower energy dissipation capability than the RC column. The FPC column suffers from the least quasi-static residual displacement, but has the lowest energy dissipation capability, the least ultimate displacement and the most severe prestress loss. The quasi-static residual displacement and residual crack width of the UBPRC column are around 66% and 73% of those of the RC column, respectively. The failure patterns of the RC column and the UBPRC column are similar, while the failure pattern of the FPC column is similar to that of a rocking column. The self-centering behavior of the three columns was analyzed and quantified using a self-centering index, which can be recommended for use in the seismic design of bridge columns. [ABSTRACT FROM AUTHOR]

Inter-module connections (IMC) are a research focus closely related to the robustness of steel volumetric buildings (VB). Many IMC have been proposed by numerous researchers and engineers, experimentally tested and numerically studied using finite element models. However, there are insufficient IMC macro models available, which imposes challenges for engineers to construct a global numerical VB model. Hence, this study aims to close the gap with a component-based macro-mechanical model for the macro-modelling of IMC in steel VB. In this paper, a comprehensive IMC database was collected to identify and characterise the active components. Two types of macro-mechanical models (H-shape and Q-shape) consisting of P-V-M links have been proposed and a novel uplifting mechanism has been derived for a typical IMC (bolted tie plate with shear key). The proposed macro-mechanical model and other existing macro-models were then compared with existing pushover experiments from an IMC subassembly. The proposed macro-mechanical model shows a good match to the existing experimental results, and it is adaptable to existing IMC. • A component-based macro-mechanical model for inter-module connections (IMC) is proposed. • A comprehensive IMC database was collected to identify and characterise the active components. • A novel uplifting mechanism is derived for a typical IMC (bolted tie plate with shear key). • The proposed macro-mechanical model is compared with existing pushover experiments of IMC subassembly. [ABSTRACT FROM AUTHOR]

Glass fiber reinforced polymer (GFRP) composite is a desirable alternative to porcelain for insulators of cylindrical electrical equipment in electrical substation. However, mechanical properties of composite insulator in an event of earthquake are not fully known yet. This study aimed to investigate both the static and dynamic properties of GFRP composite insulators and electrical equipment through impact hammer test, quasi-static flexural tests and full scale shaking table tests. The flexural properties, in terms of flexural stiffness, damping and hysteretic behavior, were investigated, based upon which a mechanical model was proposed. Moreover, the possible failure modes were identified in order that a design and qualification procedure was recommended for engineering application. The procedure has been further validated by a full scale shaking table test of 1000 kV cylindrical composite electrical equipment. [ABSTRACT FROM AUTHOR]