Far-fault Ground Motions Research Articles

The probabilistic performance-based seismic assessment of concrete bridge piers with SMASC reinforcing bars: Effect of pulse-like ground motion and vertical load-to-capacity ratio

Concrete bridge piers are critical components of bridge structures and their performance under seismic loading is of utmost importance. Traditional reinforced concrete bridge piers have shown limitations in terms of residual deformations and seismic resilience. This has led researchers to explore alternative reinforcement materials, such as Shape Memory Alloy (SMA) coupled with steel reinforcing bars, which have demonstrated promising attributes like energy dissipation as well as self-centering capacity. This study aims to fill this gap by evaluating the performance of concrete bridge piers with SMA-Steel coupled (SMASC) reinforcing bars under various intensities of vertical gravity loads and the action of pulse-like ground motion components, throughout a probabilistic framework. To this end, a group of bridge piers with different reinforcement types, including pure steel and SMASC are considered. These piers are subjected to 55 near-fault (NF) pulse-like records as well as 32 far-fault (FF) ground motions, throughout the Incremental Dynamic Analysis (IDA). The influence of distinct frequency components is analyzed by decomposing NF records into low-frequency pulses and high-frequency residual components. Also, the role of pulse to the 1st modal period of the piers (Tp/T1) is investigated by evaluating the piers’ response under the action of NF records, which were clustered into four groups. Results were assessed by evaluating the intensity measure and capacity of the studied piers at the desired performance objectives according to the FHWA manual. Moreover, the mean annual frequencies of exceeding performance limit states and the confidence levels of meeting performance objectives are studied. The results of the study indicate that the dominance of the component of NF ground motions depends on factors such as the intensity of gravity loads, ground motion characteristics, and the Tp/T1 ratio. The components of NF records within certain clusters of the Tp/T1 ratio are necessary for accurate response assessment, while FF records can be used for conservative design purposes, depending on the level of ground motion intensity and the intensity of applied gravity load. The SMASC-reinforced piers with specific λ factors (i.e. λ = 0.5 or λ = 1.0) and low intensity of gravity loads lead to a higher (1.6 times higher) mean annual frequency of exceeding a limit state, compared to pure steel rebars. Also, the confidence levels for meeting performance objectives vary depending on the ground motions, but, as gravity load intensity increases, confidence levels decrease, particularly for piers with a λ factor of 0.5.

Seismic Fragility Analysis of a Multi-Tower Super High-Rise Building Under Near-Fault Ground Motions

ABSTRACT Earthquake damage to engineering structures often occur in near-fault areas. Near-fault ground motion is characterized by high-energy velocity pulses, long action period, and strong destructiveness. This paper forces on the seismic analysis of a multi-tower super high-rise building that subjected to near-fault ground motions. The interactions between each tower makes the internal forces and dynamic responses much complex and totally different from single-tower super high-rise buildings. However, currently, multi-tower buildings in China are usually regarded as multiple single-tower buildings, and then separately designed based on the relevant provisions in seismic code for single-tower buildings. The mutual influence between the towers is almost not taken into account. Seismic response history analysis was carried on a three-tower super high-rise building using finite element method. Various near-fault and far-fault ground motions and high-energy velocity pulses were used as inputs. Through calculation of inter-story drift ratio and maximum displacement, the quantitative seismic fragility analysis was conducted for the main tower and sub-tower structures. The results show that the responses from near-fault ground motions to the structure are much greater than those from far-fault ground motions. The damage probabilities of various damage levels for near-fault ground motions are 12.5% higher than far-fault ground motions averagely. A further analysis reveals that the velocity pulses are the main factor causing structural damage in near-fault ground motions.

Dynamic response and seismic vulnerability assessment of the near-fault steep slope

Existing field data demonstrates that structures situated near faults, such as slopes, dams, and bridges, are particularly vulnerable to damage. Near-fault ground motions exhibit marked disparities from their far-field counterparts, necessitating thorough investigation. This study conducts a comprehensive analysis of ground motion characteristics utilizing response spectra, Hilbert-Huang Transform (HHT), and marginal spectra to discern near-fault pulse-like ground motions (PLGMs), near-fault non-pulse-like ground motions (NPGMs), and far-fault ground motions (FFGMs). PLGMs distinguished by their heightened energy content, typically induce more pronounced amplification effects compared to NPGMs and FFGMs. Employing an efficacy criterion, optimal intensity measures (IMs) are identified and linked to dynamic response, referred to as engineering demand parameters (EDPs). Velocity-based IMs demonstrate substantial correlations across diverse ground motion types for both plastic volume ratio (PVR) and crest displacement (Dc). Lastly, probabilistic seismic demand models are leveraged to establish seismic vulnerability curves for steep slopes exposed to PLGMs and NPGMs. Notably, with Dc as the EDP, the exceedance probabilities associated with the three IMs under PLGMs generally surpass those under NPGMs. This underscores the propensity of PLGMs to trigger larger displacements in slopes, rendering them more prone to failure.

Ambient Vibration-Based Seismic Evaluation of Long-Span Prestressed Concrete Box-Girder Bridges under Long-Duration, Near-Fault and Far-Fault Ground Motions

Ambient Vibration-Based Seismic Evaluation of Long-Span Prestressed Concrete Box-Girder Bridges under Long-Duration, Near-Fault and Far-Fault Ground Motions

Seismic performance of resilient self-centring bridge piers equipped with SMA bars

This study examines the seismic behaviour of precast post-tensioned segmental (PPS) bridge piers that are equipped with shape memory alloy (SMA) bars. PPS piers are designed to minimise overall and localised damage to bridges by incorporating natural hinges and rocking mechanisms. The introduction of super-elastic SMA bars has the potential to enhance the use of PPS piers in highly seismic regions. A parametric study is conducted to identify piers with the highest energy dissipation capacity, which are then subjected to dynamic analysis. The aim is to assess the energy dissipation capability of these systems by subjecting the selected piers, both with and without SMA bars, to far-field ground motions using a finite-element framework. The seismic performance of the piers is evaluated using incremental dynamic analysis (IDA) curves, which are obtained from analysing the piers under 44 far-fault ground motions. The IDA results indicate a significant reduction in the drift responses of the piers when SMA bars are utilised.

Fragility Assessment of a Long-Unit Prestressed Concrete Composite Continuous Girder Bridge with Corrugated Steel Webs Subjected to Near-Fault Pulse-like Ground Motions Considering Spatial Variability Effects

Prestressed concrete composite girder bridges with corrugated steel webs (PCCGBCSWs) are extensively employed in bridge construction because of their low dead weight, fast construction, and high prestressing efficiency. Moreover, PCCGBCSWs will experience deformation and failure of the corrugated steel webs, including steel fatigue and fracture, during earthquakes. These changes will introduce safety hazards, which can be addressed via bridge disaster prevention and mitigation. Because near-fault pulse-like ground motions (NFPLGMs) have high peak accelerations, these motions can easily cause damage to a bridge. Therefore, in this study, a seismic fragility assessment is performed for long-unit PCCGBCSWs subjected to NFPLGMs considering spatial variability effects, and a sensitivity evaluation of the seismic fragility is conducted considering girder type, bearing type, ground motion type, and apparent wave velocity to offer a point of reference for seismic design. The results show that PCCGBCSWs are less vulnerable than concrete bridges. The shock absorption effect of the friction pendulum bearing is better than that of the viscous damper. The impact of NFPLGMs on bridges is greater than that of near-fault non-pulse-like ground motions (NFNPLMs) and far-fault ground motions (FFGMs). The seismic fragility under nonuniform excitation conditions is greater than that under uniform excitation conditions, showing an increasing trend with decreasing apparent wave velocity.

Seismic fragility analysis of nuclear containment structure using Bayesian logistic regression model

Nuclear containment structure serves as the critical shielding structure in nuclear power plants, and must maintain structural integrity under various conditions. Following the Fukushima nuclear accident, seismic safety of nuclear power plant structures has become a significant concern in nuclear engineering community. This study presents seismic fragility analysis of the nuclear containment structure subjected to far-fault ground motion based on Bayesian logistic regression model. A refined finite element model of the nuclear containment structure was developed using layered shell element with considering material nonlinear behavior. The maximum tensile strain and roof drift of the nuclear containment structure were analyzed. MATLAB scripts for the seismic fragility analysis method based on Bayesian logistic regression model were developed. Posterior samples for the parameter of fragility function parameters were obtained using developed scripts. The sensitivity of the proposed Bayesian logistic regression based seismic fragility analysis method was verified. Seismic fragility curves of the nuclear containment structure obtained with the minimized sum of squared error, maximum likelihood estimation and Bayesian logistic regression methods were compared in depth.

Investigation of dynamic responses of three-sided underpass culvert under near-fault and far-fault ground motions considering soil-structure interaction

Three-sided underpass culverts are structural systems used to provide passing vehicle or pedestrian. It is of great importance that such infrastructure systems remain useable, especially after disasters such as earthquakes that can cause great destruction, in order to ensure that infrastructure services can be maintained continuously. In this context, the aim of this study is to investigate using finite element method (FEM) the dynamic responses of three-sided underpass culvert system under near-fault ground motions with velocity pulse and far-fault ground motions. For this aim, the modal analysis of the soil-underpass culvert interaction system has been realized using proposed soil-structure interaction (SSI) model. The frequencies of the interaction system obtained from the finite element model developed using proposed approaches have been verified comparing with the results obtained from the literature and the site periods. After showing that the modes of the interaction system can be obtained with the help of the proposed numerical model, the full transient dynamic analyses have been performed in the time history using five near-fault and far-fault records, considering four different soil systems. The comparisons shows that the variations of the soil systems and the ground motion type can significantly affect the top peak relative displacements and the dynamic stresses of the three-sided underpass culvert.

Evaluation of damping reduction factors for displacement and acceleration spectra using code-compatible near-fault and far-fault ground motions depending on site conditions

Evaluation of damping reduction factors for displacement and acceleration spectra using code-compatible near-fault and far-fault ground motions depending on site conditions

Effects of near-fault and far-fault ground motions on nonlinear dynamic response and seismic damage of masonry structures

This study explores the seismic behavior of masonry buildings in close proximity to a fault rupture as compared to those located farther away. It takes into account the distinctive features of near-fault ground motions, such as forward directivity and the fling effect, which have the potential to cause significant earthquake-related damage. The study employs a dataset comprising 100 earthquake records, which represent both near-fault and far-fault ground motions and conducts an analysis of nineteen masonry buildings with varying typologies. Analytical models for each of these buildings are constructed using experimental data concerning the quality of masonry materials. Nonlinear static and dynamic analyses are carried out to evaluate the buildings' capacity to withstand seismic deformations and the extent of damage incurred. The findings indicate that near-fault ground motions exert a more significant influence on the dynamic response and result in greater damage to masonry structures when compared to far-fault ground motions.

Fragility evaluation of nuclear containment structure subjected to earthquake and subsequent internal pressure

Strong earthquake may lead to the rupture of pipeline inside the nuclear containment structure, which leads to overpressure of the nuclear containment structure. Therefore, nuclear containment structure suffers from the risk of subjected to earthquake and internal pressure sequence. However, studies on the performance evaluation of the nuclear containment structure subjected to earthquake and subsequent internal pressure sequence is very rare. This study presents fragility evaluation of the nuclear containment structure subjected to earthquake and subsequent internal pressure sequence. Firstly, detailed nonlinear finite element model of the nuclear containment structure is developed with layered shell element and concrete damage plasticity model. Then, 20 far-fault ground motion records are selected and scaled to different intensity levels to simulate different damage states of the nuclear containment structure. Nonlinear response of maximum strain, displacement and fragility of the nuclear containment structure subjected to earthquake and subsequent internal pressure sequence is analyzed. Results reveal that distribution of maximum strain and displacement of the nuclear containment structure subjected to earthquake and subsequent internal pressure are significantly different. Maximum displacement distribution of the nuclear containment structure subjected to earthquake is related to the ground motion intensity level. The variation of the median pressure capacity and logarithmic standard deviation presents a quadratic form with the increase of ground motion intensity level.

Optimal intensity measures in probabilistic seismic demand model of subway station

Ground motion intensity measure (IM), which is a key link between the seismic hazard analysis and structural seismic response analysis, plays an important role in the performance-based earthquake engineering framework. The objective of this paper is to evaluate the most commonly used IMs with respect to their capability to predict the seismic response of underground subway station structures. Because the properties of the surrounding soil has significant influence on the seismic response of subway station structure, four typical classes of engineering sites ranging from Class I to IV according to Chinese code for seismic design of urban rail transit structures are selected in this study. Dynamic time history analyses considering nonlinear soil-structure interaction (SSI) are performed on four two-dimensional finite element models consisting of two-storey three-span subway stations embedded in four different engineering sites in this paper. Both the near-fault without velocity pulse and far-fault ground motions are used as the seismic inputs for the nonlinear SSI models in this study. Ground motion excitation is converted into equivalent seismic load at the artificial boundary for the discretized finite element model to realize the seismic load input. The applicability of 20 ground motion IMs commonly used in earthquake engineering research are investigated in this study. Statistical regression analysis is carried out for those IMs and engineering demand parameters (EDPs) of the subway station structure measured by maximum inter-storey displacement ratio obtained from nonlinear time history analyses. Based on the criteria of efficiency, practicality, proficiency and sufficiency, the optimal IMs in probabilistic seismic demand model that can best estimate the seismic response of the subway station structure are identified among those commonly used IMs. It is found that for sites of Class I and Class II, the Arias intensity followed by the velocity spectrum intensity are the optimal candidates, and for sites of Class III and Class IV, the Arias intensity is the optimal IM.

Effects of the structural dimensions of multi-span historical arched masonry buildings under near-fault and far-fault ground motions

The seismic response of three multi-span masonry structures has been investigated through an advanced macro and micro-modeling FE-based approach. The structures with 1.27, 2.25 and 3.3 vault-to-spring ratios (L/B) are selected. Detailed three-dimensional FE models with a damage plasticity behavior for masonry have been developed, and non-linear dynamic analyses were done. The studies have highlighted the effects of geometrical features on the seismic behavior of the nine structures. The structures were subjected to six near-fault and far-fault accelerations. The structure with a square plan has a lower earthquake coefficient. But, in a rectangular plan with the length of one longer side, the earthquake coefficient increases significantly. It shows that a square plan has more ductility than a rectangular plan. The structure with the square plan showed the best stability. Changing the plan from square to rectangle, the structure's stiffness increases significantly with the increase the number of spans. On the other hand, the one to two-span structures with a rectangular plan have the highest increase in stiffness of about 56 %, which becomes about 23 % with the increase of the third span. The vertical component in near-field accelerations can increase displacement and damage by 83 %. The beginning of the damage process in the structures with the square plan is from the connection of the vault and spring to the roof, but in structures with a rectangular plan, the plastic strain starts from the connection of the spring to the roof. Some far-fault accelerations could have destructive effects, like did near-fault accelerations in the horizontal direction. It is better to state that the remoteness of the accelerations is not the reason for reducing the damage to the structure.

Numerical investigation of a proposed multidimensional isolator applied to large-scale domes subjected to earthquakes

A three-dimensional seismic isolation device that is effective in isolating both horizontal and vertical earthquake components has drawn the interest of researchers in recent years. This paper proposes a new three-dimensional isolator for large-scale dome structures, which is composed of a quintuple friction pendulum component and a stacked disc spring component in series in the vertical direction. The complex working characteristics of these components are investigated in detail. Numerical modeling methods are proposed to simulate this isolator for engineering application purposes, and the model accuracy is validated based on theory and experiments. Thus, the isolator is applied to a large-scale dome structure subjected to near- and far-fault ground motions. Numerical analysis shows that the proposed modeling methods can efficiently analyze the isolation performance of the isolator in a large-scale structure. The numerical results demonstrate that the isolator has excellent isolation performance not only for displacement and axial force demands but also for velocity and acceleration demands in all three directions. In addition, according to the comparative study of this paper, the isolation performance of the proposed isolator is better than that of other types of isolators under major earthquakes due to the adaptive sliding characteristics of the quintuple friction pendulum component and the flexibility of the stacked disc spring component prolonging the structural periods.

Seismic Uplift Effect at End Spans of Long-Span Rigid-Frame Bridges Subjected to Near-Fault and Far-Fault Ground Motions

Miaoziping Bridge, a long-span rigid-frame bridge, uplift appeared at the end spans in the 2008 Wenchuan earthquake. Bearings and pad stones were damaged during the earthquake. In the past, the uplift mechanism and the seismic response under near-fault and far-fault ground motions were not sufficiently recognized. Here, a refined finite-element model of the Miaoziping Bridge was established considering the initial stress state and the nonlinear characteristics of the girder (e.g., cracking of concrete). The Wenchuan strong motion records and other 40 near-fault pulse-type and 40 far-fault ground motions were selected for nonlinear time history analysis. The uplift effect was realized by considering the compressive-only behavior of bearings. The results show that the seismic responses of the bridge under Wenchuan earthquake ground motions are in good agreement with the real seismic damage observed after the Wenchuan earthquake. The excitation of the near-fault pulse-type ground motion along the longitudinal direction is the dominant factor of the uplift at the end spans. When peak ground acceleration of the near-fault pulse-type ground motion is greater than 0.3g, the end spans are prone to uplift, and the maximum uplift displacement responses can reach 50 cm. There is little uplift possibility subjected to the far-fault ground motions. When the pulse period is in the range of 1–3 s, the pulse effect equals or even exceeds the full-wave effect. The end spans can hardly uplift subjected to vertical or transverse excitation individually. There is a slight difference between the uplift displacements subjected to single longitudinal ground motions and three-directional ground motions. The time of maximum uplift displacement is delayed considering the wave-passage effect. When the wave velocity is less than 1,000 m/s, the adverse effects of the wave-passage effect may be considered.

Nonlinear seismic analysis of irregular base isolated structures using a new modified lateral load pattern

Nowadays, seismic isolation systems are increasingly used by engineers for retrofitting existing structures and designing new ones. Nevertheless, limited studies have been conducted on the performance evaluation of the nonlinear static analysis methods for estimating the seismic demands of the base isolated structures. The current study proposes a new modified lateral load pattern for seismic analysis of base isolated structures using modified capacity spectrum method (MCSM). Moreover, this study investigates the applicability of the modal pushover analysis (MPA) and modified capacity spectrum methods for assessing the base isolated structures with setback irregularity. To this end, two types of steel moment resisting structures including 3-story (low-rise) and 9-story (medium-rise) with different irregularities in elevation are considered. All the structures are isolated by three types of lead rubber bearing (LRB) isolators with various stiffnesses. In order to consider the effect of ground motion, two types of near-fault and far-fault ground motions are selected. To evaluate the performance of the MCSM and MPA methods, the structural seismic demands estimated by these methods are compared with their benchmark values obtained by the nonlinear time history analysis method. The obtained results show the superiority of the modified capacity spectrum method and the effectiveness of the new modified lateral load pattern presented for this method.

Evaluation of ground motion intensity measures for time-history dynamic analysis of isolated bridges

The ground motion intensity measure (IM) is an important part of probabilistic seismic demand analysis and is used to predict the seismic response of structures. In this study, two typical isolation bridges are selected as cases, and 80 far-fault and 40 near-fault ground motions are used as inputs for the time-history analysis. By performing a comparison with 19 common IMs, it is proved that the IM based on the geometric mean of the response spectrum is an optimal choice for isolated bridges. The effects of response spectrum type and period range on this form of IM are investigated. The results show that the response spectrum type has a slight effect on the IM based on the geometric mean of the response spectrum, and the period range has a greater impact on the IM. The effects of the upper and lower limits of the period range of this IM are illustrated. The applicability of the IM to the far-fault ground motions and the near-fault ground motions is finally discussed. It can be concluded that when only near-fault ground motions are considered, the period range of the IM should be appropriately increased.

Effects of pulse-like ground motions on tunnels in saturated poroelastic soil for obliquely incident seismic waves

It has been widely recognised that near-fault ground motions can be distinctly different from far-fault ground motions, in terms of their amplitudes and spectral characteristics, and there are a number of studies investigating the effects of near-fault ground motions on the structural response. However, only a few studies focus on underground tunnels, and most of them consider vertically incident seismic waves, neglecting the wave passage effect which is critical for long tunnels. This paper investigates the consequences of near-fault pulse-like ground motions on the seismic tunnel response, with an example of a tunnel embedded in saturated poroelastic soil. The input motions are represented by obliquely incident P1 waves, and the wave passage effect along the longitudinal direction is considered by a 2.5D modelling technique. The seismic tunnel response for near-fault pulse-like and far-fault ground motions is compared. Additionally, artificial ground motions, which have consistent acceleration response spectra with the near-fault pulse-like ground motions, but without velocity pulses, are generated to gain further insight into the contribution of velocity pulses. It is shown that the near-fault pulse-like ground motions can noticeably increase the tunnel internal forces, due to large seismic energy associated with the velocity pulses. For pulse-like ground motions with similar acceleration response spectra, the fling-step velocity pulse can be more detrimental to the tunnel than the forward-directivity velocity pulse. Moreover, the amplification effect of the near-fault pulse-like ground motions on the tunnel internal forces tends to be more prominent for large vertical angles of incidence, highlighting the significance of considering the oblique incidence case for seismic design.

Implications of Arch Warp Altitudes on an Ancient Masonry Bridge under Ground Movements

Although only a few of the ancient masonry arch bridges (MABs) are in fairly good condition today, many ancient arch bridges are still in use. Over time, the condition of the masonry bridges declines and the safety requirements change. Therefore, it is important to examine these bridges under different influences. The strengthening of MABs is generally not essential. The major cause of damage to MABs is their insufficient width and height, and thus, it is not the safety but the usability that has restricted the life-time of the MABs. Therefore, in this investigation, the effect of the arch height on the static and dynamic behavior of a single-span MAB was investigated. For this aim, the Ancient Tokatlı Bridge, built in Karabük, Türkiye, was selected for investigation under near-fault (NF) and far-fault (FF) ground motions (GMs). To observe the altitude of the arch warp on the ancient MAB, first, the finite element model (FEM) was utilized, using ANSYS and SAP 2000. Furthermore, to constitute the arch warp’s influence on a MAB, the FEM was remodeled considering the different arch warps between 7.0 and 9.0 m. Moreover, GMs were applied to the FEM to investigate the effect of dynamic behavior. Under these GMs, stresses and strains (compression and tensile) were observed and compared with each other. Consequently, at the end of these investigations, it was observed that the maximum motions were reduced, while the height of the one-span MAB was increased under NF and FF GMs, and this was also true for the contrary situations. The compression stresses were not observed to be hazardous at the point of destruction, while the altitude of the one-span MAB increased.

Adaptive linear quadratic regulator for optimal structural control based on wavelet transform and genetic algorithm

PurposeIn real life, excitations are highly non-stationary in frequency and amplitude, which easily induces resonant vibration to structural responses. Conventional control algorithms in this case cannot guarantee cost-effective control effort and efficient structural response alleviation. To this end, this paper proposes a novel adaptive linear quadratic regulator (LQR) by integrating wavelet transform and genetic algorithm (GA).Design/methodology/approachIn each time interval, multiresolution analysis of real-time structural responses returns filtered time signals dominated by different frequency bands. Minimization of cost function in each frequency band obtains control law and gain matrix that depend on temporal-frequency band, so suppressing resonance-induced filtered response signal can be directly achieved by regulating gain matrix in the temporal-frequency band, leading to emphasizing cost-function weights on control and state. To efficiently subdivide gain matrices in resonant and normal frequency bands, the cost-function weights are optimized by a developed procedure associated to genetic algorithm. Single-degree-of-freedom (SDOF) and multi-degree-of-freedom (MDOF) structures subjected to near- and far-fault ground motions are studied.FindingsResonant band requires a larger control force than non-resonant band to decay resonance-induced peak responses. The time-varying cost-function weights generate control force more cost-effective than time-invariant ones. The scheme outperforms existing control algorithms and attains the trade-off between response suppression and control force under non-stationary excitations.Originality/valueProposed control law allocates control force amounts depending upon resonant or non-resonant band in each time interval. Cost-function weights and wavelet decomposition level are formulated in an elegant manner. Genetic algorithm-based optimization cost-efficiently results in minimizing structural responses.