Fling Effects Research Articles

Seismic Performance of Bridge Expansion Joints with and without Viscous Dampers during the 6 February 2023 Kahramanmaraş Earthquakes

Expansion joints render bridge structures highly vulnerable to damage during strong ground motions. Failures of expansion joints triggered by earthquakes not only jeopardize the post-earthquake serviceability of the bridge but also have a significant impact on the bridgeâs overall seismic performance. Despite extensive investigations and efforts to integrate these measures into design specifications aimed at mitigating the consequences of relative movements between adjacent bridge spans, major earthquakes have still revealed instances of damage related to expansion joints. On 6 February 2023, strong earthquake sequences occurred in KahramanmaraÅ, Turkey, with magnitudes of M7.7 and M7.6. The fault lines and epicenters of these shallow earthquakes were near the city and town centers and caused severe structural damage to buildings and infrastructures. There are approximately 1000 railway and highway bridges in the earthquake-affected region. Although both highway and railway bridges have generally performed well, some bridges experienced structural damage during the KahramanmaraÅ earthquakes. A large number of damage on the bridges is due to pounding and opening relative movements in expansion joints. This paper presents a comprehensive seismic evaluation of expansion joint failure mechanisms on bridges without viscous dampers during the 2023 KahramanmaraÅ earthquake sequences and an in-depth investigation into the seismic performance of bridge expansion joints equipped with viscous dampers and shock transmission unit devices are implemented utilizing the strong ground motion data collected throughout the earthquake sequences. It can be stated that the near-fault induced significant directivity and fling effects, resulting in notable velocity pulses and permanent tectonic deformations, and that these effects contributed to the failures of expansion joints, viscous damper devices, pot bearings, and shear keys.

Probabilistic damage evaluation of isolated steel box-girder bridge excited by near-field earthquakes

Modern civilization regards bridges as lifelines, and their failure due to significant earthquakes in the past has raised concerns about their seismic vulnerability. The effect of near-fault earthquakes on the bridge vulnerability is a significant problem that has not been well explored. The present work utilizes fragility analysis to assess the probabilistic seismic risk evaluation of a continuous isolated steel box girder bridge exposed to near-field ground motions (NFGMs). Probabilistic seismic demand models (PSDMs) of the bridge are explored to reliably associate key demand and intensity measures to capture the seismic performance of the system. This study examines a steel box girder bridge in Guwahati, India, isolated with lead rubber (LRB) bearings and a friction pendulum system (FPS). To achieve a comparable seismic response, each bearing system is designed for a similar isolation period. The PGV/PGA ratio is a useful metric for classifying ground motion suites and estimating their frequency content by classifying the input excitations into low- and high-frequency motions. To perform probabilistic seismic risk assessments, two ensembles of forward directivity records with PGV: PGA >160 cm/s/g (high frequency) and PGV: PGA <160 cm/s/g (low frequency) are considered. Moreover, one ensembles of near-field incorporating the fling effect and far-field are also utilized. The failure probability under the seismic hazards for isolated bridges is assessed utilizing different damage measures (DM) such as maximum displacement ductility of pier (DDP), displacement of deck (MDD), drift ratio of pier (PDR), and rotational ductility (RDP). The near-field earthquake damage probability is significantly impacted by the PGV/PGA ratio, as a high PGV/PGA ratio results in a greater probability of damage than a low PGV/PGA ratio. In conclusion, guidelines are provided that will help the design engineers for designing bridges with LRB and FPS isolators for seismic isolation in the event of varying ground motion characteristics.

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.

Mitigation of Structural Vibrations Due to Pulse-Type-Near-Fault Earthquake by the Compliant Liquid Column Damper

Pulse-type-near-fault (P-N) earthquake ground excitations can inflict serious damage to structures in built-up areas situated close to seismic faults. The high frequency content, high velocity pulses of long period, and fling effects cause P-N motions to impose large demands on both stiff and flexible structures. Among various passive control devices, the liquid column damper (LCD) is economical and its effectiveness is well-established for flexible structures under far-field earthquake ground motions. In this paper, the compliant form of the LCD (CLCD), which was specially developed to overcome the nonapplicability of the conventional LCD to stiff structures, is investigated for the vibration control of both stiff and flexible structures subjected to P-N ground motions. The study is carried out both in the frequency and in the time domain. Results indicate that the CLCD is successful in mitigating structural response to P-N ground motions. Some of the trends of response reduction with damper parameters are found to be different from those earlier reported for far-field earthquakes. Interestingly, in the case of flexible structures, while the CLCD is found to be fairly effective, the conventional LCD is rendered practically ineffective.

Are Near-Fault Fling Effects Captured in the New NGA West2 Ground Motion Models?

We evaluate how much of the fling effect is removed from the NGA database and accompanying GMPEs due to standard strong motion processing. The analysis uses a large set of finite-fault simulations, processed with four different high-pass filter corners, representing the distribution within the PEER ground motion database. The effects of processing on the average horizontal component, the vertical component, and peak ground motion values are evaluated by taking the ratio between unprocessed and processed values. The results show that PGA, PGV, and other spectral values are not significantly affected by processing, partly thanks to the maximum period constraint used when developing the NGA GMPEs, but that the bias in peak ground displacement should not be ignored.

Adding Fling Effects to Processed Ground-Motion Time Histories

Fling is the engineering term for the effects of the permanent tectonic offset, caused by a rupturing fault in the recorded ground motions near the fault. It is expressed by a one‐sided pulse in ground velocity and a nonzero final displacement at the end of shaking. Standard processing of earthquake time histories removes some of the fling effects that may be required for engineering applications. A method to parameterize the fling‐step time history and to superimpose it onto traditionally processed time histories has been developed by Abrahamson (2002). In this paper, we first present an update to the Abrahamson (2002) fling‐step models, in which the fling step is parameterized as a single cycle of a sine wave. Parametric models are presented for the sine‐wave amplitude ( D site) and period ( T f ). The expressions for D site and T f are derived from an extensive set of finite‐fault simulations conducted on the Southern California Earthquake Center broadband platform (see Data and Resources). The simulations were run with the Graves and Pitarka (2010) hybrid simulation method and included strike‐slip and reverse scenarios for magnitudes of 6.0–8.2 and dips of 30 through 90. Next, an improved approach for developing design ground motions with fling effects is presented, which deals with the problem of double‐counting intermediate period components that were not removed by the standard ground‐motion processing. Finally, the results are validated against a set of 84 empirical recordings containing fling.

Seismic performance evaluation of dam-reservoir-foundation systems to near-fault ground motions

Ground motion records obtained in recent major strong earthquakes have provided evidence that ground motions recorded near the near-fault regions differ in many cases from those observed further away from the seismic source. As the forward directivity and fling effect characteristics of the near-fault ground motions, they have the potential to cause more considerable damage to structures during an earthquake. Therefore, understanding the influence of near-fault ground motions on the performance of structures is critical to mitigate damage and perform effective response. This paper presents results of a study aimed at evaluating the effects of near-fault and far-fault ground motions on seismic performance of concrete gravity dams including dam-reservoir-foundation interaction. Koyna gravity dam is selected as a numerical application. Four different near-fault ground motion records with an apparent velocity pulse are used in the analyses. The earthquake ground motions recorded at the same site from other events that the epicenter far away from the site are employed as the far-fault ground motions. The seismic performance evaluation method based on the demand-capacity ratio, the cumulative overstress duration and the spatial extent of overstressed regions is presented. The concrete damaged plasticity model including the strain hardening or softening behavior is employed in nonlinear analyses. Nonlinear seismic damage analyses of the selected concrete dam subjected to both near-fault and far-fault ground motions are performed. The results obtained from the analyses show the effects of near-fault ground motions on seismic performance of concrete gravity dams and demonstrate the importance of considering the near-fault ground excitations.

Effects of near-fault and far-fault ground motions on nonlinear dynamic response and seismic damage of concrete gravity dams

As the forward directivity and fling effect characteristics of the near-fault ground motions, seismic response of structures in the near field of a rupturing fault can be significantly different from those observed in the far field. The unique characteristics of the near-fault ground motions can cause considerable damage during an earthquake. This paper presents results of a study aimed at evaluating the near-fault and far-fault ground motion effects on nonlinear dynamic response and seismic damage of concrete gravity dams including dam-reservoir-foundation interaction. For this purpose, 10 as-recorded earthquake records which display ground motions with an apparent velocity pulse are selected to represent the near-fault ground motion characteristics. The earthquake ground motions recorded at the same site from other events that the epicenter far away from the site are employed as the far-fault ground motions. The Koyna gravity dam, which is selected as a numerical application, is subjected to a set of as-recorded near-fault and far-fault strong ground motion records. The Concrete Damaged Plasticity (CDP) model including the strain hardening or softening behavior is employed in nonlinear analysis. Nonlinear dynamic response and seismic damage analyses of the selected concrete dam subjected to both near-fault and far-fault ground motions are performed. Both local and global damage indices are established as the response parameters. The results obtained from the analyses of the dam subjected to each fault effect are compared with each other. It is seen from the analysis results that the near-fault ground motions, which have significant influence on the dynamic response of dam–reservoir–foundation systems, have the potential to cause more severe damage to the dam body than far-fault ground motions.

Large coseismic displacements and tall buildings

SUMMARYSeismic demands imposed on tall buildings are sensitive to long‐period ground motions. A source of these motions can be near‐fault effects: rupture directivity and fling step (large coseismic displacements). The potential adverse effects of near‐fault motions on structures have been attributed to rupture directivity in previous studies. However, the influence of large coseismic displacement on tall building seismic response has not been widely investigated. This study explores the influence of coseismic displacements on the nonlinear response of tall buildings. Several nonlinear time history analyses were performed to evaluate the response of a reinforced concrete tall building to coseismic displacements. The ground motions used for these analyses were recorded in the proximity of faults where large coseismic displacements have been observed. Recorded motions from the Landers earthquake (1992), Kocaeli earthquake (1999), Tohoku earthquake (2011) and Chi‐Chi earthquake (1999) were selected for this study. The results from a parametric study of the response of a single‐degree‐of‐freedom system showed that the influence of the fling on the system response is dependent on (a) the ratio of fling rise time to the fundamental period of the system and (b) the yielding resistance of the structure. At the onset of yielding, the fling step can further drive the system into very large displacements. The results from the case study indicate a significant increase on the seismic response of a tall building when the fling effect is included in the ground motions. This issue is a concern for tall buildings in regions where faults are not mapped to a great extent and near‐fault fling effect could be produced by a large magnitude earthquake. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Earthquake fault‐induced surface rupture—A hybrid strong ground motion simulation technique and discussion for structural design

AbstractUnique to the near‐source region of a large earthquake is the occurrence of strong impulsive ground motion and surface faulting referred to as ‘fling‐step’ motion. The objective of this study is to synthesize broad‐band time histories over a wide range of frequencies by characterizing rupture directivity and fling effects from the comprehensive strong motion database of the near‐fault Chi‐Chi event. To aid in the generation of these special types of ground motions, a hybrid modeling technique is introduced based on the stochastic finite‐fault radiation method and an efficient analytical approach to incorporate the observed low‐frequency features in the records close to the ruptured fault. The results show that the overall agreement among the developed hybrid methodology and recorded waveforms and response spectra is quite satisfying. A brief discussion on the design of infrastructures near seismic fault is also included. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Enhancement of long period components of recorded and synthetic ground motions using InSAR

Tall buildings and flexible structures require a better characterization of long period ground motion spectra than the one provided by current seismic building codes. Motivated by that, a methodology is proposed and tested to improve recorded and synthetic ground motions which are consistent with the observed co-seismic displacement field obtained from interferometric synthetic aperture radar (InSAR) analysis of image data for the Tocopilla 2007 earthquake ( M w =7.7) in Northern Chile. A methodology is proposed to correct the observed motions such that, after double integration, they are coherent with the local value of the residual displacement. Synthetic records are generated by using a stochastic finite-fault model coupled with a long period pulse to capture the long period fling effect. It is observed that the proposed co-seismic correction yields records with more accurate long-period spectral components as compared with regular correction schemes such as acausal filtering. These signals provide an estimate for the velocity and displacement spectra, which are essential for tall-building design. Furthermore, hints are provided as to the shape of long-period spectra for seismic zones prone to large co-seismic displacements such as the Nazca-South American zone.

Seismic Response of Base-Isolated Structures with LRB and FPS under near Fault Ground Motions

Seismic response of structures in the vicinity of causative earthquake faults can be significantly different than those observed further away from the seismic source. In the near fault zone, ground motions are significantly influenced by the rupture mechanism and slip direction relative to the site and by the permanent ground displacement at the site resulting from tectonic movement. Forward directivity and fling effects have been identified by the seismologists as the primary characteristics of near fault ground motions. Because of the unique characteristics of the near-fault ground motions and their potential to cause severe damage to structures designed to comply with the criteria mostly based on far-field earthquakes, the estimation of seismic response of base-isolated structures for a project site close to an active fault should account for these special aspects of near fault ground motions. This paper investigates the seismic response of base-isolated structures with LRB and FPS isolators under near fault ground motions. A seismic evaluation of the building, isolated with the LRB and FPS, is performed using a nonlinear three-dimensional analytical model. The parametric study is concentrated on base shear, accelerations and displacements of isolated models. Large displacement and velocity pulses in records of near fault ground motions can significantly change the results of seismic response of base-isolated structures.

Characterization and modeling of near-fault pulse-like strong ground motion via damage-based critical excitation method

Near-fault ground motion with directivity or fling effects is significantly influenced by the rupture mechanism and substantially different from ordinary records. This class of ground motion has large amplitude and long period, exhibits unusual response spectra shapes, possesses high PGV/PGA and PGD/PGA ratios and is best characterized in the velocity and the displacement time-histories. Such ground motion is also characterized by its energy being contained in a single or very few pulses, thus capable of causing severe damage to the structures. This paper investigates the characteristics of near-fault pulse-like ground motions and their implications on the structural responses using new proposed measures, such as, the effective frequency range, the energy rate (in time and frequency domains) and the damage indices. The paper develops also simple mathematical expressions for modeling this class of ground motion and the associated structural responses, thus eliminating numerical integration of the equations of motion. An optimization technique is also developed by using energy concepts and damage indices for modeling this class of ground motion for inelastic structures at sites having limited earthquake data.

Deterministic and probabilistic representation of near-field pulse-like ground motion

The response and damage assessment of engineering structures under near-field ground motions is currently of great interest. Near-field ground motion with directivity focusing or fling effects produces pulse-like ground motion that has characteristics different from those of ordinary records. This paper develops simple deterministic and probabilistic models for near-field pulse-like ground motions. These models belong to the class of engineering models that aim to replicate some of the gross features observed in near-field records. The ground velocity is expressed as a steady-state function or a stationary random process modulated by an envelope function. Both models account for the non-stationarity and the multiple pulses in the ground velocity. While the deterministic model is similar to some of the models developed earlier, the probabilistic model facilitates handling uncertainties in the ground motion and variability in the structure's properties. For instance, this model combined with structural reliability methods can be used for reliability assessment of structures under near-field random ground motion. The reduction of the structural response by adding supplemental dampers is also investigated.

Effects of Fling Step and Forward Directivity on Seismic Response of Buildings

This paper investigates the consequences of well-known characteristics of near-fault ground motions on the seismic response of steel moment frames. Additionally, idealized pulses are utilized in a separate study to gain further insight into the effects of high-amplitude pulses on structural demands. Simple input pulses were also synthesized to simulate artificial fling-step effects in ground motions originally having forward directivity. Findings from the study reveal that median maximum demands and the dispersion in the peak values were higher for near-fault records than far-fault motions. The arrival of the velocity pulse in a near-fault record causes the structure to dissipate considerable input energy in relatively few plastic cycles, whereas cumulative effects from increased cyclic demands are more pronounced in far-fault records. For pulse-type input, the maximum demand is a function of the ratio of the pulse period to the fundamental period of the structure. Records with fling effects were found to excite systems primarily in their fundamental mode while waveforms with forward directivity in the absence of fling caused higher modes to be activated. It is concluded that the acceleration and velocity spectra, when examined collectively, can be utilized to reasonably assess the damage potential of near-fault records.

A Theoretical Method for Computing Near-Fault Ground Motions in Layered Half-Spaces Considering Static Offset Due to Surface Faulting, with a Physical Interpretation of Fling Step and Rupture Directivity

An efficient mathematical method is presented for computing the near- fault strong ground motions in a layered half-space, giving explicit consideration to the static offset due to surface faulting. In addition, the combined effects of and on the near-fault ground motions are investigated. First, after checking the fault integration in the representation theorem, it is found that when an observation point is close to the fault plane, Green's functions exhibit near singularities, which consist of extremely sharp peaks in a narrow band close to the observation point. Therefore, direct numerical integration becomes quite onerous for computing near-fault ground motions, because the dynamic Green's functions must then be distributed very densely in order to evaluate accurately the effects of the near singularities. Instead, a new form of the representation theorem is introduced, which exploits the property that the dynamic Green's functions can be approximated by the corresponding static Green's functions in the vicinity of the singularities. The modified theorem, which involves the device of adding and subtracting the static Green's functions from the dynamic ones, is the sum of two fault integrations. The first integration involves the difference of the dynamic and the corresponding static Green's functions, while the second contains only the static Green's functions. This formulation requires much less CPU time than the original one when near-fault ground motions are considered, because the near singularities of the dynamic Green's functions in the first integration are completely eliminated by subtracting the static Green's functions. While the second integration does require a densely distributed set of points to capture the near-singular behavior of the static Green's function, it needs to be performed only once, as it is valid for all frequencies. Subtraction of the static Green's functions from the dynamic functions has the added benefit of making the integration over the wavenumber in the determination of the Green's functions much more efficient, especially for surface faulting. This is because the difference of the dynamic and static integrands converges rapidly to zero with increasing wave- numbers, whereas the original integrands diverge in the case of a source point on the free surface. The proposed methodology is used to investigate the two most important effects in near-fault ground motions, fling step (e.g., Abrahamson, 2001) and rupture direc- tivity (e.g., Somerville et al., 1997), by paying special attention to the contribution of static and dynamic Green's functions. It is found that the fling effects stem mainly from the second integral in the modified representation theorem, which involves the static Green's function. The fling effects are dominant in the slip direction only in the vicinity of the surface fault and are negligible for buried faults, because the static Green's function attenuates rapidly with distance from the fault, r, as the order of (1/r 2 ). Also, more importantly, when an observation point is located above a buried fault, the medium has to remain continuous, and thus cannot fling. By contrast, the directivity effects stem mainly from the first integral, which involves the dynamic Green's function, and attenuate much more slowly than the fling, on the order from 1/r to . The directivity effects are dominant in the fault-normal direction, especially