Far-fault Ground Motions Research Articles

Seismic performance of frame‐bent structures subjected to near‐fault ground motions

Reinforced concrete frame-bent structures are one of the structural forms commonly used in industrial factory buildings. In order to study the seismic behaviour of frame-bent structures located near fault areas, eight pulse-like, eight non-pulse near-fault motions and eight far-fault ground motions have been selected in this paper. The finite element model of a reinforced concrete frame-bent structure was established to study seismic responses to near-fault and far-field ground motions. Numerical analysis results indicate that the maximum base shear of the structure under the action of near-fault ground motion was 5.10 times that of far-fault and 1.47 times that of non-pulsed near-fault ground motion; the maximum story drift angle under pulse-like near-fault ground motion was 3.8 times that of non-pulse and 19.7 times that of far-fault ground motion. Therefore, engineering designers should pay more attention to the seismic performance of frame-bent structures under the action of near-fault ground vibration.

Efficiency of Intensity Measures Considering Near- and Far-Fault Ground Motion Records

This paper focuses on the identification of high-efficiency intensity measures to predict the seismic response of buildings affected by near- and far-fault ground motion records. Near-fault ground motion has received special attention, as it tends to increase the expected damage to civil structures compared to that from ruptures originating further afield. In order to verify this tendency, the nonlinear dynamic response of 3D multi-degree-of-freedom models is estimated by using a subset of records whose distance to the epicenter is lower than 10 km. In addition, to quantify how much the expected demand may increase because of the proximity to the fault, another subset of records, whose distance to the epicenter is in the range between 10 and 30 km, has been analyzed. Then, spectral and energy-based intensity measures as well as those obtained from specific computations of the ground motion record are calculated and correlated to several engineering demand parameters. From these analyses, fragility curves are derived and compared for both subsets of records. It has been observed that the subset of records nearer to the fault tends to produce fragility functions with higher probabilities of exceedance than the ones derived for far-fault records. Results also show that the efficiency of the intensity measures is similar for both subsets of records, but it varies depending on the engineering demand parameter to be predicted.

Seismic Response of a Historical Masonry Bridge under Near and Far-fault Ground Motions

Historical masonry arch bridges which might be vulnerable to natural disasters are important part of the cultural heritage. Natural disasters, especially earthquakes can inflict damage to these structural systems. This paper aims to investigate a comparison of the effects of near and far-fault ground motions on the seismic response of masonry arch bridges under different earthquakes. Kalender masonry arch bridge which is located in Ergani, Turkey is selected as a numerical model. For this purpose, three-dimensional finite element model of the bridge is generated with ANSYS finite element software with macro modelling approach. Seismic response of the bridge is assessed by means of time-history analyses. The near-fault and far-fault ground motions, which have approximately equal peak ground accelerations, of 1979 Imperial Valley, 1999 Chi-Chi, 1999 Kocaeli and 2010 Darfield earthquakes are considered for the analyses. Comparisons between maximum displacements, maximum and minimum stress, which were acquired from the dynamic analyses of the masonry bridge subjected to each fault effect, are obtained. The study demonstrates that far-fault ground motions are as important as near-fault ground motions and it can be used together with near-fault ground motion for further evaluation of such historical masonry bridges.

Probabilistic seismic performance evaluation of nuclear containment structure subjected to far-fault ground motions

This study presents probabilistic seismic performance evaluation of nuclear containment structure subjected to far-fault ground motions. To achieve this objective, refined finite element model of nuclear containment structure is established and incremental dynamic analysis (IDA) is performed automatically using pre-processing and post-processing scripts. Cracking status, roof drift, damage dissipated energy and floor acceleration of the nuclear containment structure is discussed. Furthermore, probabilistic seismic safety margin of nuclear containment structure is quantitatively evaluated by median value method and confidence interval method. Finally, a closed-form solution for the annual frequency of exceedance for the roof drift of the nuclear containment structure is derived, and the effectiveness of the closed-form solution is verified by the classical direct numerical integration method. Annual frequency of exceedance for the roof drift of the nuclear containment structure corresponding to different performance levels is analyzed. Results indicated that the bottom of nuclear containment structure is the most vulnerable location. In general, nuclear containment structure subjected to far-fault ground motions is dominated by shearing cracks. When the ground motion intensity level is less than 0.4 g, damage dissipated energy of the nuclear containment structure is very small. In general, with the increase of elevation, acceleration amplification factor of the nuclear containment structure increases rapidly. Probabilistic seismic safety margin of the nuclear containment structure evaluated by median value method tends to be conservative. Analytical and classical numerical integration method provides almost the same prediction of the annual frequency of exceedance for the roof drift of the nuclear containment structure, which indicates the effectiveness of the proposed closed-form solution.

Seismic performance assessment of steel frame structures equipped with buckling-restrained slotted steel plate shear walls

The near-fault ground motion records may impose high seismic energy input to the building structures. The steel plate shear walls (SPSW) are one of the robust and efficient lateral-force resisting and energy-dissipating components and SPSWs are increasingly equipped in steel moment frame to form a dual structural system. A modified type of buckling-restrained SPSW with inclined slots has been proposed and applied in the steel frame. This paper presents the seismic performance of steel frame-SPSW system subjected to near-fault ground motions. Four multi-story (5-, 10-, 15- and 20-story) steel frame-SPSW structures were selected and designed. The accuracy of the SPSW models' predictions was assessed using previous experimental results. Nonlinear time-history analysis assuming two groups of 15 near-fault ground motions and 15 far-fault ground motions was used to predict the structures' interstory drift ratios, floor accelerations, residual interstory drift ratios and drift concentration factor. Incremental dynamic analysis was used to predict collapse probabilities using the same groups of ground motions. The analytical results can provide significant insights to the seismic behavior of steel frame-SPSW structures when subjected to near-fault ground motions.

Seismic Behavior of Historical Inclined Minarets under Near and Far Fault Ground Motions

ABSTRACT This study investigates the effects of near- and far-fault ground motion on the seismic behavior of historically inclined minarets. Inclined minarets built in Aksaray and Sivas, Turkey, are selected as numerical applications. The top of the Aksaray and Sivas minarets is 1.30 m and 1.23 out-of-plumb and the inclination values are 2.45° and 1.97°, respectively. Firstly, 3D finite element models of the minarets are created using solid elements by SAP2000 software and the numerical dynamic characteristics are determined numerically. 1992 Erzincan and 1999 Kocaeli earthquakes as near- and far-fault ground motion records are selected for the analyses. Maximum displacements, base bending moments, base shear forces, and principal stresses are determined using the finite element method. The results obtained for both earthquakes are compared with each other. It is clearly seen that near-fault ground motion has resulted in much larger response values for both minaret models when compared with far-fault ground motion and max stresses that occurred on the transition segments.

Quasi-static and nonlinear time-history analyses of post-tensioned bridge rocking piers with internal ED bars

Post-tensioned (PT) rocking piers have been recently emphasized for satisfactory self-centering capacity and accelerated bridge construction (ABC) technique in high seismic regions. In this paper, quasi-static cyclic and nonlinear time-history analyses (NLTHAs) are conducted on the PT rocking piers incorporating internal energy-dissipation (ED) bars, based on two modeling techniques. The influences of three parameters consisting of the transverse reinforcement ratio, the area of ED bars and the initial total axial load on the hysteretic behavior of PT rocking piers are studied. The emphases of the quasi-static analyses are on the concrete strain and the neutral axis depth which are seldom referred in the previous researches. Furthermore, NLTHAs are conducted on a set of PT rocking piers under two suits of near-fault and far-fault ground motions (NFGMs and FFGMs) to compare the seismic behaviors of PT rocking piers with different design parameters. The results reveal that the area of ED bars and the initial total axial load are the key parameters that affect the seismic performance of PT rocking piers. In addition, pulse-like NFGMs with a high ratio (>0.2 s) between the peak ground velocity (PGV) and the peak ground acceleration (PGA) result in larger structural seismic responses than FFGMs, except for the acceleration response. The maximum displacement response subjected to FFGMs is almost unaffected by the area ratio of ED bars.

On the accuracy of enhanced pushover procedures for seismic performance evaluation of code-conforming RC moment-resisting frame buildings subjected to pulse-like and non-pulse-like excitations

In this paper, the applicability and validity of enhanced pushover procedures in estimating the seismic demands of mid- and high-rise reinforced concrete (RC) building frames under pulse-like near-fault ground motions having forward-directivity and fling-step effects as well as non-pulse-like near-fault and far-fault ground motions are assessed through the comparison with the nonlinear response history analysis (NL-RHA). The enhanced pushover procedures including the modal pushover analysis (MPA), force-based adaptive pushover (FAP), displacement-based adaptive pushover (DAP), extended N2 method (EN2), single-run multi-mode pushover (SMP), and non-adaptive displacement-based pushover (NADP) procedures, as well as a conventional pushover method based on the first mode of the structure, are performed. To this end, three plan-symmetric buildings including the 9-, 12-, and 18-story RC frames designed in accordance with the provisions of ASCE 710 and ACI 318-14 are examined. The engineering demand parameters considered are the interstory drift ratios and story shears, which are representatives of the deformation and force demands, respectively. Additionally, the seismic performance of the RC buildings is assessed using the conventional and the enhanced multi-modal pushover procedures in accordance with the systematic evaluation scheme of the ASCE 41-17 standard. The comparative evaluation demonstrates that the accuracy of the NSPs varies with the type of the ground motions. Some methods result in satisfactory performance for pulse-like ground motions, some for non-pulse-like ones, and some for both of them. All in all, the MPA, EN2, and SMP procedures provide a relatively better prediction of the seismic demands of RC building frames.

Deformation-dependent peak floor acceleration for the performance-based design of nonstructural elements attached to R/C structures

This study introduces a simple and efficient method to determine the peak floor acceleration (PFA) at different performance levels for three types of plane reinforced concrete (RC) structures: moment-resisting frames (MRFs), infilled–moment-resisting frames (I-MRFs), and wall-frame dual systems (WFDSs). By associating the structural maximum PFA response with the deformation response, the acceleration-sensitive nonstructural components, and the building contents, can be designed to adhere to the performance-based seismic design of the supporting structure. Thus, the proposed method can accompany displacement-based seismic design methods to design acceleration-sensitive nonstructural elements to comply with the deformation target of the supporting structure. The PFA response shape is represented by line segments defined by key points corresponding to certain floor levels. These key points are defined by explicit empirical expressions developed herein. The maximum PFA response is correlated with the maximum interstory drift ratio (IDR) and other vital characteristics of the supporting structure such as the fundamental period. The proposed expressions are established based on extensive nonlinear dynamic analyses of 19 MRFs, 19 WFDSs, and 19 I-MRFs under 100 far-fault ground motions scaled to capture different deformation targets. Realistic examples demonstrate the efficiency of the proposed method to assess the PFA response at a given IDR, making the method suitable in the framework of performance-based design.

Seismic design lateral force distribution based on inelastic state of K-eccentric brace frames combined with high strength steel

The HSS-EBFs refer to the eccentrically braced frames combined with high strength steel, the ordinary steel (namely the nominal yield strength is lower than 345 MPa, such as Q345) is utilized for links, however the high strength steel is used for columns and beams. The columns and beams are kept in elastic under major earthquake and the plastic deformation is isolated to the links. Therefore the using of high strength steel brings many benefits, such as reduces the member sections with reducing the use of painting and welding, and increases indoor usable floor area, however it weakens the lateral stiffness of the structure. The lateral force distribution of HSS-EBFs is differing with the traditional EBFs, and the story stiffness of structure is changed from elastic to inelastic state. In this paper, four groups of K-eccentric brace frames combined with high strength steel with different story are designed to study the lateral force distribution under major earthquakes. The HSS-EBFs are conducted by nonlinear dynamic analysis using near-fault ground motions and far-fault ground motions, and the velocity pulse effect and the acceleration cumulative cyclic effect are considered. The lateral force distribution of the HSS-EBFs in inelastic state are proposed based on the mean values of the elastic–plastic story shear force, which is consistent with the code representation. The raised elastic to plastic lateral force distribution has a better accuracy than other existing distribution forms. The results of the study can provide reference for performance-based seismic design of HSS-EBFs.

Three dimensional seismic deformation-shear strain-swelling performance of America-California Oroville Earth-Fill Dam

Structural design of the vertical displacements and shear strains in the earth fill (EF) dams has great importance in the structural engineering problems. Moreover, far fault earthquakes have significant seismic effects on seismic damage performance of EF dams like the near fault earthquakes. For this reason, three dimensional (3D) earthquake damage performance of Oroville dam is assessed considering different far-fault ground motions in this study. Oroville Dam was built in United States of America-California and its height is 234.7 m (770 ft.). 3D model of Oroville dam is modelled using FLAC3D software based on finite difference approach. In order to represent interaction condition between discrete surfaces, special interface elements are used between dam body and foundation. Non-reflecting seismic boundary conditions (free field and quiet) are defined to the main surfaces of the dam for the nonlinear seismic analyses. 6 different far-fault ground motions are taken into account for the full reservoir condition of Oroville dam. According to nonlinear seismic analysis results, the effects of far-fault ground motions on the nonlinear seismic settlement and shear strain behaviour of Oroville EF dam are determined and evaluated in detail. It is clearly seen that far-fault earthquakes have very significant seismic effects on the settlement-shear strain behaviour of EF dams and these earthquakes create vital important seismic damages on the swelling behaviour of dam body surface. Moreover, it is proposed that far-fault ground motions should not be ignored while modelling EF dams.

Proposed minimum restoring force requirements for seismic isolated structures

In this research study, a new set of restoring force equations are proposed for seismic isolated structures subjected to far fault ground motions (FFGM) and near fault ground motions (NFGM). For this purpose, 110 FFGM and 49 NFGM are selected. Then, nonlinear time history analyses (NLTHA) of SDOF seismic isolated structures are performed using the selected ground motions to obtain their residual and maximum displacements. The analyses are repeated for an extensive range of parameters including peak ground acceleration, Ap, characteristic strength, Qd and post elastic period, Td, of the isolation system. Next, the variations of the residual and maximum displacements are plotted as functions of the various combinations of the parameters considered in the analyses. Then, nonlinear regression analyses are performed to formulate the residual and maximum displacements as functions of the parameters considered in the analyses. The developed equations are then used to formulate the upper limits of Td (restoring force equations) to ensure reasonable levels of residual and maximum isolator displacements. The developed restoring force equations are then compared with those of AASHTO and Eurocode-8 (EC-8) using the pool of residual and maximum displacement data obtained from NLTHA. It is observed that using the restoring force equations of AASHTO and EC-8 to check the design of seismic-isolated structures may, in some cases, produce unreasonably large levels of residual and maximum displacements. However, when the restoring force requirements proposed in this research study are applied, the residual and maximum displacements are observed to be within reasonable ranges.

Dynamic response analysis of story-adding structure with isolation technique subjected to near-fault pulse-like ground motions

The isolation technique is widely studied and applied in structural engineering due to its excellent seismic performance. However, the existing research mostly focuses on the conventional structure under the action of regular ground motions. In this paper, a story-adding seismic structure, a base-isolated structure, and a story-adding isolated structure were simulated by using numerical simulation methods. The dynamic response characteristics of the three structures under near-fault pulse-like ground motions are analysed and compared with the far-fault ground motions. The results showed that using the base isolation can significantly extend the period of the main structure and reduce the seismic response on the upper structure. The inter-story drift ratio, inter-story shear force, and the story acceleration of all three structures under near-field pulse-like ground motions were all larger than that of far-field earthquakes. Both base-isolated structure and story-adding isolated structure showed excellent damping performance. Besides, the damping properties of the base-isolated structure are better than the story-adding isolated structure.

Dynamic Response Evaluation of Bridges Considering Aspect Ratio of Pier in Near-Fault and Far-Fault Ground Motions

The recent increase in earthquake activities has highlighted the importance of predicting the seismic response of structures. Damage to civil infrastructure, particularly bridges, can cause considerable human and property losses. The seismic performance of a structure should be evaluated based on the characteristics of structures and earthquakes. For this, this study defined the two main factors of ground motion and structural system that affect the seismic response of a structure. Ground motions, which are mainly dependent on the distance from the epicenter, were defined as near-fault and far-fault ground motions. Near-fault ground motion includes the characteristics of forward directivity and fling step. In addition to ground motion, the aspect ratio of the pier, as a representative factor of a structural system, influences the seismic behavior of bridges. Thus, this study assessed the seismic response of bridges with various aspect ratios under the near-fault and far-fault ground motion conditions. Nonlinear static analysis was first performed to evaluate the seismic capacity of the pier. Then modal and dynamic analyses were carried out to examine the effects of the aspect ratio and ground motion on the displacement and force response and the change in the natural frequency of the bridge.

The performance-based seismic response of special steel MRF: Effects of pulse-like ground motion and foundation safety factor

This study aims to investigate the effect of near-fault pulse-like earthquake ground motions as well as the foundation safety factor, on the performance-based seismic response (PBSR) of special steel moment-resisting frame (MRF). The Beam on the Nonlinear Winkler Foundation (BNWF) approach was employed for modeling the soil-foundation system. In this regard, values of 2, 3, and 5 were considered for the foundation vertical safety factor (FSv). The PBSR of the MRF has been assessed under 32 far-fault (FF) ground motions as well as 55 near-fault (NF) pulse-like records, through Incremental Dynamic Analyses (IDAs). The effects of extracted pulses and residual components of near-fault records were investigated as well. Results show that regardless of the earthquake record type, FSv has no considerable effect on the performance-based drift demand in the structure. However, larger settlement and rotation of the foundation are expected when a small FSv is accounted for. This leads to difficulties in providing the Immediate Occupancy (IO) performance objective for structures with operational performance levels. The effect of the input record type on the median foundation settlement is also inconsiderable. As well, a similarity was observed between the seismic performance of the structure under the residual components and the far-fault records. What’s more, neither the extracted pulses nor the residual components of near-fault earthquake records can represent the original near-fault pulse-like records. Also, the residual component plays an important role in the structural responses under low-intensity earthquake events.

Seismic fragility curves using pulse-like and spectrally equivalent ground-motion records

4- and 8-storey reinforced-concrete frame buildings are analyzed under the suites of the near-fault pulse-like, and the corresponding spectrally equivalent far-fault ground-motion records. Seismic fragility curves for the slight, moderate, extensive, and complete damage states are developed, and the damage probability matrices, and the mean loss ratios corresponding to the Design Basis Earthquake and the Maximum Considered Earthquake hazard levels are compared, for the investigated buildings and sets of ground-motion records. It is observed that the spectrally equivalent far-fault ground-motion records result in comparable estimates of the fragility curve parameters, as that of the near-fault pulse-like ground-motion records. As a result, the derived damage probability matrices and mean loss ratios using two suites of ground-motion records differ only marginally (of the order of ~10%) for the investigated levels of seismic hazard, thus, implying the potential for application of the spectrally equivalent ground-motion records, for seismic fragility and risk assessment at the near-fault sites.

A Hybrid Force/Displacement Seismic Design Method for Reinforced Concrete Infilled-MRFs and Wall-Frame Dual Systems

ABSTRACT A hybrid force/displacement (HFD) performance-based seismic design method is proposed for two types of plane reinforced concrete structures, i.e., infilled moment-resisting frames (I-MRFs) and wall-frame dual systems (WFDS). The HFD seismic design method is a force-based method which controls with high accuracy both structural and non-structural deformation limits. The behavior factor is related here to the inter-storey drift ratio and the member plastic rotation by taking into account both geometrical and dynamic structural characteristics. The HFD is herein developed through an extensive parametrical study involving non-linear time-history analyses of 19 I-MRFs, and 19 WFDS under 100 far-fault ground motions.

Statistical seismic performance assessment of tuned mass damper inerter

In this study, the robust optimum design of a recently developed passive control device, i.e., tuned mass damper inerter (TMDI) is investigated to control a 10-story base-excited shear building benchmark. The H2 and H∞ of three different objective functions (i.e., minimizing roof displacement, minimizing 7th-story displacement, and maximizing the TMD stroke) are selected as objective functions for two different single and double inerter configurations. Optimum free vibration parameters of the TMDI (i.e., natural frequency and damping ratios) are calculated using a metaheuristic technique for two different structural damping values. Additionally, the performance of the optimum designed damper and its robustness under 25 far-fault (FF) ground motions are assessed in the time domain with 12 different performance criteria (i.e., the mean and standard deviation of the maximum and norm of response histories for roof displacement, roof acceleration, and the total kinetic energy of the building). Based on current work, the best performance index for single TMDI for all three objective functions is the roof absolute acceleration, showing a maximum of 45% reduction in the mean maximum roof acceleration for 25 earthquake records. Therefore, the TMDI is most effective when the goal is to reduce the floor accelerations. The double inerter configuration shows approximately the same values for the performance indices for all three objective functions and demonstrates similar reduction for a single TMDI. However, it increases the robustness of the control method by adding redundancy and enhancing the performance for different combinations of inertance and mass ratios.

Seismic resilience evaluation of base-isolated RC buildings using a loss-recovery approach

Seismic isolation systems, especially friction pendulum bearings (FPBs), are used as ideal seismic protection strategies in performance-based design. Furthermore, FPBs can increase the functionality of buildings by minimizing interruption of use of the facility (e.g., operational performance level) and reducing seismic demands on the structural and non-structural elements. The primary objective of this paper is to investigate the seismic resilience of reinforced concrete (RC) buildings, especially essential buildings in compliance with a loss-recovery approach. To this end, an analytical examination is conducted concerning a six-story RC building, which was mainly designed under the Uniform Building Code (UBC in International Conference of Building Officials, Whittier, CA, 1997) for a high-risk seismic zone. The incremental dynamic analyses of the fixed-base and base-isolated structures subjected to a set of near and far-fault ground motions are carried out for getting seismic fragility and functionality curves as well as the resilience of structures using a loss-recovery approach. The proposed methodology is employed to special buildings such as hospital buildings, with and without using the FPBs considering different seismic hazard scenarios that could occur within the investigated region. At the end of the paper, a parametric study is conducted by changing the building and pendulum parameters. The benefit of the suggested approach is found in terms of loss-recovery and seismic resilience that will be well recognized by the decision-maker for better planning to decrease seismic losses, rather than waiting for an earthquake and paying for it afterward.

Assessment of Near-Fault Ground Motion Effects on the Fragility Curves of Tall Steel Moment Resisting Frames

Nowadays it is common to use the fragility curves in probabilistic methods to determine the collapse probability resulting from an earthquake. The uncertainties exist in intensity and frequency content of the earthquake records are considered as the most effective parameters in developing the fragility curves. The pulse-type records reported in the near-fault regions might lead to the major damages in the structures having moderate and long periods since response spectra of near-fault ground motions within the long period range are different from those of the far-fault ground motions. In the present study, the influence of this type of earthquake records on the fragility curves of the steel special moment resisting frames, SMRFs, was examined. The results indicated that the median value of the collapse capacity (i.e.ŜCt Parameter, which defines the earthquake intensity leading to the collapse of the structure in half-set of the chosen records) due to near-fault ground motions was 76% that of the far-fault records for the ten-story example SMRF.