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Mortar-less construction with interlocking bricks has many advantages, such as improved construction efficiency and relatively low requirements on labour skills. Nevertheless, the seismic performance of interlocking brick structures is not well understood yet. In this paper, laboratory tests and numerical modelling are carried out to investigate the seismic behaviour of interlocking brick walls. Laboratory shaking table tests are performed on a scaled reinforced mortar-less interlocking brick wall. The response and damage modes under in-plane seismic loading are investigated. A detailed numerical model is then generated and validated with the laboratory testing data. Unlike the conventional masonry wall that diagonal shear damage governs the failure, the interlocking brick wall exhibits rocking responses, whose damage is mainly at the two bottom corners of the wall. Full-scale interlocking brick walls are then modelled and compared with conventional concrete masonry unit (CMU) walls bonded by mortar. Comparisons are made between the seismic resistances and damage modes of the two walls. The influences of ground motion intensities, vertical components of seismic excitations and different seismic time histories on the seismic behaviour of the interlocking brick wall are examined. It is found that the interlocking brick wall has a higher seismic resistance capacity than the conventional CMU wall. Inter-brick friction is the main energy dissipation mechanism in the interlocking brick wall. Because of the rocking response, vertical component of the ground motion significantly influences the damage of interlocking brick wall. The interlocking brick wall is insensitive to velocity pulses of ground motions due to its relatively high natural frequency.

Multiple vibration modes of an engineering structure might be excited by earthquake ground motions. Multiple tuned mass dampers (MTMDs) are widely used to control these multi-mode vibrations. However, in the commonly used MTMD system, the mass element in each tuned mass damper (TMD) is normally assumed to be the same. To improve the performance of MTMDs for seismic-induced vibration control, non-uniform MTMD masses are adopted in the present study to improve the mass utilization of TMD, and a location factor is proposed to determine the best location of each TMD in the MTMD system. The effectiveness of the proposed method is validated through numerical study. The results show that the proposed method effectively reduces the seismic responses of the structure induced by multiple vibration modes.

This paper focuses on the ductility demand of self-centering structures with flag-shaped (FS) hysteretic behavior under near-fault (NF) pulse-like ground motions. To this end, the general features ...

Additive manufacturing (AM) is a relatively novel method to fabricate 3D objects by adding layer-upon-layer materials. As one of the most anticipated techniques in recent years, AM already made advances in design, production, and supply chain process of the manufacturing industry. AM is a digital manufacturing technology in which a massive amount of data is generated during the process. Accordingly, obtaining useful information from these data to improve current AM technology becomes a challenge. Meanwhile, Big Data research provides an ideal solution for dealing with the massive data obtained from AM processes. Besides the contributions in the AM research and production, Big Data analysis methods can also be used to help designers and engineers by collecting valuable information from clients and customers. From a business perspective, the manufacturing sector will benefit from the established Big Data sharing platform to promote and popularize new products. On the other hand, customers will obtain desired commodities with the help of a new-type 3D printing service system. The goal of this article is to summarize the contributions from the existing literature in the AM and Big Data field and prospect how Big Data methods can offer a better future for AM technology. It also introduces recent developments in AM technology combined with the internet of things (IoT), cloud, and cybersecurity. Future directions in AM and Big Data, which include AM data unification, completed AM data-sharing platform, and smart AM production process is pointed out as well.

To more effectively extract the vast wind energy in marine areas, offshore wind turbines have been constructed with slender tower and large rotor. External vibration sources such as aerodynamic, sea wave and seismic loadings can threaten the safety of these energy infrastructures. It is important to evaluate the reliability of offshore wind turbines subjected to external vibration sources. Previous research works on the wind turbine fragility analyses only considered the fragility of the tower by assuming the wind turbine was in the parked condition with the blade mass lumped at the top of the tower. The study of the fragility of the blade which is one of the most important components of a wind turbine has not been reported. In the present study, a detailed three-dimensional (3D) finite element (FE) model of the NREL 5 MW wind turbine is developed in ABAQUS, and the tower and blades are explicitly modelled to realistically estimate the aerodynamic loads and structural behaviours of the wind turbine. The uncertainties of the structural mass, stiffness and damping are taken into account to develop the probabilistic wind-induced demand models for the tower and blades. The dynamic behaviours of the wind turbine subjected to the simultaneous aerodynamic and sea wave loadings are investigated in a probabilistic frame and the fragility curves for both the tower and blades under the parked and operating conditions are derived and discussed.

The new steel–concrete composite rigid-frame bridge (SCCRFB) with concrete-filled double skin steel tube (CFDST) piers has been verified showing superior seismic performance, and a promising structural solution for bridge constructions near or above active faults. Previous experimental and numerical studies revealed that the damages of this bridge type under across-fault ground motions mainly concentrate on the two CFDST piers. This paper investigates the effectiveness of damage mitigation measures for the SCCRFB with CFDST piers by using numerical simulations. Three detailed three-dimensional (3D) finite element (FE) bridge models are developed by using the explicit FE code LS-DYNA, in which Model A represents a reference SCCRFB with CFDST piers, and Models B and C employ different stiffeners at the two ends of the CFDST piers aiming to mitigate the damages induced by the effect of across-fault ground movements. Two pairs of across-fault ground motions with thrust and strike-slip mechanisms are considered, and the influence of fling-step is parametrically investigated. Numerical results including structural damages and responses are presented and the damage mechanisms are analyzed. Numerical results indicate that the strengthening measure used in Model C can effectively restrain local buckling of the steel tubes under both types of across-fault ground motions and is a practical option for SCCRFB with CFDST piers to mitigate the potential fault-crossing hazard. This study provides useful references for the seismic design of SCCRFB with CFDST piers crossing active faults.

The objective of this paper is to propose a novel fragility analysis method pertinent to the combination of the least squares support vector machine (LS-SVM) algorithm and JC method for the vulnerability estimation of deep-water high piers located in reservoirs under near-field ground motions. First, the uncertainties associated with the design parameters are considered and the LS-SVM algorithm is adopted to predict the cross-sectional critical curvature values of each damage state of the example pier and determine the probability distributions. Then, a group of finite element models of the example pier is developed using the OpenSees platform for considering the uncertainties related to the design parameters and near-field seismic waves; the Morrison equation is employed to calculate the added mass to simulate the hydrodynamic pressure. Meanwhile, the dynamical responses of the example pier with seven different water depth conditions are investigated using increment dynamic nonlinear analysis along the longitudinal and transverse directions under seismic excitations. Finally, the fragility functions are derived based on the JC method to consider the probability distributions of the cross-sectional critical curvature values and dynamical responses simultaneously; these functions are applied for assessing the damage probability at different damage states of the example pier. It can be concluded that the hydrodynamic pressure plays an important role in influencing the natural vibration period and mode shape of the deep-water high pier. In the slight, moderate, and extensive damage states, the damage probability of the middle-upper and bottom areas of the example pier is relatively large under longitudinal near-field seismic excitation; nevertheless, only the bottom is easily damaged under transverse near-field seismic excitation.

With the increment of cable length, long stay cables are prone to experience high-mode vortex-induced vibrations (VIVs) at normal wind velocities, and the VIV-prone mode range also becomes wider. Existing dampers cannot supply sufficient damping for such a wide range of high-modes. Inerter-based dampers (IBDs), which take advantage of the two-terminal inertial device dubbed inerter, have been proved to have a better control performance than conventional dampers. However, existing studies on IBDs only focused on the first several cable modes, which cannot cover the wide range of VIV-prone modes of long stay cables. The high-mode and multi-mode VIV control by using IBDs is investigated in this study. The governing equations of the cable-IBD systems under VIV are first established. The control efficiency of the IBDs and the influence of optimum design strategies are compared. The use of two IBDs to further enhance the control efficiency is also discussed. The results show that a three-element IBD in this study is quite effective for high-mode and multi-mode VIV control of long stay cables. Moreover, the multi-mode control efficiency can be further improved through using two IBDs. The results in this study can guide the design of IBDs for VIV control of long stay cables.

Many civil and mechanical engineering structures can be simplified as double-beam systems, i.e., a primary beam and a secondary beam connected to the primary beam. Many studies have investi...

Viscous dampers have been widely used for seismic mitigation of long-span double-tower cable-stayed bridges, and the effectiveness of seismic mitigation of cable-stayed bridges depends on t...

Vibration measurements have been widely used for structural health monitoring (SHM). Usually, wired sensors are required to attach on the testing structure, which may be arduous, costly and sometimes impossible to install those sensors on the remote and inaccessible part of the structure to be monitored. To overcome the limitations of contact sensors based vibration measurement methods, computer vision and digital image processing based methods have been proposed recently to measure the dynamic displacement of structures. Real-life structure subjected to bi-directional dynamic forces is susceptible to significant out-of-plane movement. Measuring the vibrations of structures under the out-of-plane movements using target-free vision-based methods have not been well studied. This paper proposes a target-free vision-based approach to obtain the vibration displacement and acceleration of structures subjected to out-of-plane movements from minor level excitations. The proposed approach consists of the selection of a region of interest (ROI), key-feature detection and feature extraction, tracking and matching of the features along the entire video, while there is no artificial target attached on the structure. The accuracy of the proposed approach is verified by conducting a number of experimental tests on a reinforced concrete structural column subjected to bi-directional ground motions with peak ground accelerations (PGA) ranging from 0.01 g to 1.0 g. The results obtained by the proposed approach are compared with those measured by using the conventional accelerometer and laser displacement sensor (LDS). It is found that the proposed approach accurately measures the displacement and acceleration time histories of the tested structure. Modal identification is conducted using the measured vibration responses, and natural frequencies can be identified accurately. The results demonstrate that the proposed approach is reliable and accurate to measure the dynamic responses and perform the system modal identification for structural health monitoring.

Past seismic events have shown that pile-supported wharves are susceptible to severe damage during earthquakes, and thus it is important to assess the seismic performance of pile-supported wharves. Seismic fragility analysis is recognized as an effective means for seismic performance assessment of infrastructural systems exposed to seismic hazards since it quantifies the probability of seismic damage conditioned on the various ground motion intensity levels. This study systematically investigates the seismic fragility of a large-scale pile-supported wharf at both component and system levels. It is well known that pile-supported wharf is a typical soil-pile-structure system, and the soil-pile-structure interaction will significantly affect its seismic performance. In this regard, a solid-fluid, fully-coupled nonlinear finite element (FE) model is developed for the seismic analysis of this large-scale pile-supported wharf. Additionally, to determine the quantitative seismic demand bounds for different damage states, this study proposes the use of the pushover analysis-based procedure rather than engineering judgment or engineering common sense which is subjective to a degree. Furthermore, the soil permeability is another parameter that may evidently influence seismic fragility of wharf structures, so its influence is also discussed in detail through parametric studies.

In current practice the shear load-slip behaviour of bolted steel connections is estimated based on the friction coefficient and bolt preload. The friction coefficient is approximated by the slip factor, which is determined experimentally through testing of standard specimens. A linear load-slip (F-d) behaviour is typically assumed, with an arbitrary initial stiffness depending on the slip load and an assumed slip displacement. However, even for the standard slip factor test specimens, the F-d behaviour in the initial stage is not necessarily linear. To enable the development of more accurate models for bolted steel connections, it is essential to understand the F-d behaviour of standard specimens constructed using AS/NZS 3678-350 steel, known as G350, a common Australian steel with limited data in the current literature. An experimental program was performed to investigate the effect of surface finish on the shear behaviour. In addition, numerical simulation was carried out and the results were compared with the experimental results including the F-d behaviour. An empirical formula was proposed for the initial slip behaviour and a good fit was demonstrated. The improved understanding of the shear behaviour could be applied to the design of connections for modular buildings which provide suitable site assembly tolerances while controlling the possible cumulative slip displacement.

Reynolds-Averaged Navier-Stokes (RANS) method equipped with the shear stress transport ( S S T ) K − ω model is widely used to simulate the vortex-induced vibration (VIV) of elastically-mounted rigid cylinders subjected to fluid flow. Previous studies show that this method is very difficult to capture the maximum response of the cylinder occurring in the upper regime. Moreover, previous numerical studies by using this method mainly focus on the two-dimensional (2-D) simulations. In reality, VIV is a three-dimensional (3-D) phenomenon, the 3-D effect must then be incorporated in the numerical simulations. To improve the accuracy of the RANS method with S S T K − ω , the low-Reynolds numbers ( R e ) correction technique is applied to the numerical model in the present study and the 3-D VIV responses of an elastically-mounted cylinder subjected to the subcritical fluid flow regime are numerically investigated. The two-way coupled Fluid-Structure Interaction (FSI) framework is developed and computational fluid dynamics (CFD) analyses are performed for a range of Reynolds numbers R e = 2000 − 12000 . Numerical results show that the present method can lead to more accurate VIV response estimations compared to the previous numerical studies. Moreover, the formation of the wake vortex shedding modes and its transition are well captured by this method.

Offshore wind turbines (OWTs) are more and more widely used to produce electrical energy nowadays. Besides the constant wind and wave loads, earthquake excitation can be another important vibration source to the OWTs since many OWTs have been/will be constructed in the seismic prone areas. Extensive research works have been carried out to understand the dynamic behaviours of OWTs when they are subjected to multi-hazards (e.g. the simultaneous wind, wave and/or earthquake loadings). However, when seismic excitations are considered, the onshore earthquake records are normally used as inputs in the analyses due to the lack of offshore data and the difficulty in synthesizing the offshore seismic motions. This practice may lead to inaccurate structural response estimations since it is well known that the seawater can significantly suppress the seafloor vertical motions near the P wave resonant frequencies of the seawater layer, which in turn results in the different characteristics of onshore and offshore earthquake recordings. Moreover, the earthquake motions along the pile of OWTs are different from those at the ground surface, i.e. the earthquake motions vary with the soil depth. Recently, a method to stochastically simulate the earthquake ground motions on the offshore site was proposed, in which the influence of seawater layer was considered and the earthquake motions at any soil depth could be obtained. This paper carries out numerical simulations on the dynamic behaviours of OWTs subjected to the combined wind, wave and earthquake loadings, and the depth-varying offshore seismic motions are used as inputs in the analyses. The seismic responses of OWTs obtained from the onshore and offshore earthquake motions are calculated and compared. The influence of depth-varying ground motions on the dynamic responses of OWTs is discussed.