Evaluation of Peak Ground Velocity as a “Good” Intensity Measure for Near-Source Ground Motions

This paper investigates the “goodness” of peak ground velocity as a dependable intensity measure for the earthquake shaking of civil structures. The paper stresses the importance of distinguishing between acceleration pulses and velocity pulses, and identifies two classes of near-source ground motions: those where the peak ground velocity is the integral of a distinguishable acceleration pulse and those where the peak ground velocity is the result of a succession of high-frequency, one-sided acceleration spikes. It is shown that the shaking induced by the former class is in general much more violent than the shaking induced by the latter class of motions even when motions that belong to the former class may be generated by significantly smaller-magnitude earthquakes. Building on the dimensional analysis introduced in the companion papers this paper shows that both linear and nonlinear structural responses from a variety of records which exhibit distinguishable pulses scale better with the peak pulse acceleration than with the peak pulse velocity, indicating that the peak pulse acceleration is a more representative intensity measure of the earthquake shaking. This conclusion is further supported from the response analysis of linear and bilinear single-degree-of-freedom oscillators subjected to selected records from the 1999 Chi-Chi Taiwan earthquake that exhibit unusually high and long period velocity pulses. The paper shows that these high velocity pulses alone do not impose unusual demands on most civil structures. What is more detrimental are local, distinguishable acceleration pulses that override the long period velocity pulses.     

Empirical Predictive Models for Earthquake-Induced Sliding Displacements of Slopes

Earthquake-induced sliding displacement is the parameter most often used to assess the seismic stability of slopes. The expected displacement can be predicted as a function of the characteristics of the slope (yield acceleration) and the ground motion (e.g., peak ground acceleration), yet there is significant aleatory variability associated with the displacement prediction. Using multiple ground motion parameters to characterize the earthquake shaking can significantly reduce the variability in the prediction. Empirical predictive models for rigid block sliding displacements are developed using displacements calculated from over 2,000 acceleration–time histories and four values of yield acceleration. These empirical models consider various single ground motion parameters and vectors of ground motion parameters to predict the sliding displacement, with the goal of minimizing the standard deviation of the displacement prediction. The combination of peak ground acceleration and peak ground velocity is the two parameter vector that results in the smallest standard deviation in the displacement prediction, whereas the three parameter combination of peak ground acceleration, peak ground velocity, and Arias intensity further reduces the standard deviation. The developed displacement predictive models can be used in probabilistic seismic hazard analysis for sliding displacement or used as predictive tools for deterministic earthquake scenarios.     

Investigation of effect of near-fault motions on substandard bridge structures

The objective of this study was to investigate the effects of near-fault ground motions on substandard bridge columns and piers. To accomplish these goals, several large scale reinforced concrete models were constructed and tested on a shake table using near- and far-field ground motion records. Because the input earthquakes for the test models had different characteristics, three different measures were used to evaluate the effect of the input earthquake. These measures are peak shake table acceleration, spectral acceleration at the fundamental period of the test specimens, and the specimen drift ratios.For each measure, force-displacement relationships, strains, curvatures, drift ratios, and visual damage were evaluated.Results showed that regardless of the measure of input or response, the near-fault record generally led to larger strains,curvatures, and drift ratios. Furthermore, residual displacements were small compared to those for columns meeting current seismic code requirements.     

Three-dimensional baselines for perceived self-motion during acceleration and deceleration in a centrifuge

Three-dimensional motion trajectories were computed, representing the motions that would be perceived by a perfect processor of acceleration information during the acceleration and deceleration stages of a centrifuge run. These motions serve as "baselines" for perceived self-motion in a centrifuge, and depend on the initial perception of orientation and velocity immediately preceding the acceleration and immediately preceding the deceleration. The baselines show that a perfect processor of acceleration information perceives self-motion during centrifuge deceleration significantly differently from self-motion during centrifuge acceleration, despite the fact that the angular accelerations have equal magnitude (with opposite direction). At the same time, the baselines can be compared with subjects' reported perceptions to highlight limitations of the nervous system; limitations and peculiarities of the nervous system are identified as deviations from a baseline. As a result, peculiarities of the nervous system are held responsible for any perception of pitch or roll angular velocity or change in tilt of the body-horizontal plane of motion during the centrifuge run. On the other hand, baselines explain perception of tilt position during deceleration, linear velocity, possible lack of significant linear velocity during deceleration, and yaw angular velocity, including on-axis angular velocity during centrifuge deceleration. The results lead to several experimental questions.     

Actuator Saturation and Control Design for Buildings under Seismic Excitation

Efficient design techniques are presented for improving the response of seismic-excited buildings under actuators with limited capacity. Information regarding the actuator capacity and estimated peak ground acceleration is used to fine tune the controller and reduce conservatism. Both state feedback and observer-based controllers are discussed. The observer-based controller uses the measurement of the ground acceleration, though this requirement can be removed easily. Sufficient conditions for feasibility of a feedback controller are expressed in terms of linear matrix inequalities. Performance of the proposed techniques is illustrated through simulations of a six-story building subject to earthquake ground motion.     

Responses of Buried Corrugated Metal Pipes to Earthquakes

This study describes the results of field investigations and analyses carried out on 61 corrugated metal pipes (CMP) that were shaken by the 1994 Northridge earthquake. These CMPs, which include 29 small-diameter (below 107 cm) CMPs and 32 large-diameter (above 107 cm) CMPs, are located within a 10 km2 area encompassing the Van Norman Complex in the Northern San Fernando Valley, in Los Angeles, California. During the Northridge earthquake, ground movements were extensively recorded within the study area. Twenty-eight of the small-diameter CMPs performed well while the 32 large-diameter CMPs underwent performances ranging from no damage to complete collapse. The main cause of damage to the large-diameter CMPs was found to be the large ground strains. Based on this unprecedented data set, the factors controlling the seismic performance of the 32 large-diameter CMPs were identified and framed into a pseudostatic analysis method for evaluating the response of large diameter flexible underground pipes subjected to ground strain. The proposed analysis, which is applicable to transient and permanent strains, is capable of describing the observed performance of large-diameter CMPs during the 1994 Northridge earthquake. It indicates that peak ground velocity is a more reliable parameter for analyzing pipe damage than is peak ground acceleration. Results of this field investigation and analysis are useful for the seismic design and strengthening of flexible buried conduits.     

Dynamics of the martial arts high front kick

Fast unloaded movements (i.e. striking, throwing and kicking) are typically performed in a proximo-distal sequence, where initially high proximal segments accelerate while distal segments lag behind, after which proximal segments decelerate while distal segments accelerate. The aims of this study were to examine whether proximal segment deceleration is performed actively by antagonist muscles or is a passive consequence of distal segment movement, and whether distal segment acceleration is enhanced by proximal segment deceleration. Seventeen skilled taekwon-do practitioners were filmed using a high-speed camera while performing a high front kick. During kicking, EMG recordings were obtained from five major lower extremity muscles. Based on the kinematic data, inverse dynamics computations were performed yielding muscle moments and motion-dependent moments. The results indicated that thigh deceleration was caused by motion-dependent moments arising from lower leg motion and not by active deceleration. This was supported by the EMG recordings. Lower leg acceleration was caused partly by a knee extensor muscle moment and partly by a motion-dependent moment arising from thigh angular velocity. Thus, lower leg acceleration was not enhanced by thigh deceleration. On the contrary, thigh deceleration, although not desirable, is unavoidable because of lower leg acceleration.     

3D Temporal Characteristics of Earthquake Ground Motion at Single Point

In this paper, we present the results of a study of the temporal 3D characteristics of earthquake ground motion at a single point, which are a completely different set from the frequently used spatial 3D characteristics. A ground motion trajectory from the 1995 Kobe earthquake is analyzed, based on the concept of temporal curvature and torsion. Kinematic turning and twisting of the ground motion are found to have occurred in the form of temporal curvature and torsion pulses. These pulses have typical durations of 100 or 20 ms, respectively. These two types of pulses offer some detailed characterization of the ground acceleration behaviors.     

Elastic-Plastic Seismic Behavior of Long Span Cable-Stayed Bridges

This paper investigates the elastic-plastic seismic behavior of long span cable-stayed steel bridges through the plane finite-element model. Both geometric and material nonlinearities are involved in the analysis. The geometric nonlinearities come from the stay cable sag effect, axial force-bending moment interaction, and large displacements. Material nonlinearity arises when the stiffening steel girder yields. The example bridge is a cable-stayed bridge with a central span length of 605 m. The seismic response analyses have been conducted from the deformed equilibrium configuration due to dead loads. Three strong earthquake records of the Great Hanshin earthquake of 1995 in Japan are used in the analysis. These earthquake records are input in the bridge longitudinal direction, vertical direction, and combined longitudinal and vertical directions. To evaluate the residual elastic-plastic seismic response, a new kind of seismic damage index called the maximum equivalent plastic strain ratio is proposed. The results show that the elastic-plastic effect tends to reduce the seismic response of long span cable-stayed steel bridges. The elastic and elastic-plastic seismic response behavior depends highly on the characteristics of input earthquake records. The earthquake record with the largest peak ground acceleration value does not necessarily induce the greatest elastic-plastic seismic damage.     

Equivalent Modal Damping of Short-Span Bridges Subjected to Strong Motion

In this paper four different methods are investigated for estimating the equivalent modal damping ratios of a short-span bridge under strong ground motion by considering the energy dissipation at the boundary. The Painter Street Overcrossing (PSO) is investigated because of seismic data availability. Computed responses using the response-spectrum method with the equivalent damping ratios estimates are compared with the recorded responses. The results show that the four methods provide reasonable estimation of equivalent modal damping ratios and that neglecting off-diagonal elements in the damping matrix is the most efficient and practical method. The equivalent damping ratio of the PSO was nearly 25% under an earthquake with peak ground acceleration of 0.55g, which is much higher than the conventional assumption of 5%.     

1D Time-Domain Solution for Seismic Ground Motion Prediction

A full time-domain solution for predicting earthquake ground motion based on the 1D viscoelastic shear-wave equation is presented. The derivation results in a time-domain equation in the form of an infinite impulse response filter. A solution in the time domain has several advantages including causality, direct modeling of impulsive and transient processes, and ease of inclusion of nonlinear soil behavior. The method is applicable to any arbitrarily layered silhouette presented as SH-wave velocity, damping coefficient, and mass density profiles for designated soil intervals. For nonlinear evaluations, an equivalent-linear formulation is incorporated and the standard modulus and damping degradation curves become part of the input set. Input motion can be either rock-outcrop or body-wave motions measured or estimated at the bottom of the geologic profile, and the output is the estimated ground motion time history. Application of the method to vertical array strong motion records from Garner Valley, and Wildlife Site, Calif., shows that predicted surface (and interval) ground motion is virtually identical to that measured. The differences between the results of linear and nonlinear analyses are negligible for most cases. A comparison of the time-domain model with SHAKE shows that SHAKE fails to accurately predict time histories in some situations, whereas the time-domain solution always yields satisfactory predicted surface ground motions.     

Wave Passage and Ground Motion Incoherency Effects on Seismic Response of an Extended Bridge

This paper investigates the implications of ground motion spatial variability on the seismic response of an extended highway bridge. An existing 59-span, 2,164-meter bridge with several bearing types and irregularity features was selected as a reference structure. The bridge is located in the New Madrid Seismic Zone and supported on thick layers of soil deposits. Site-specific bedrock input ground motions were selected based on a refined probabilistic seismic hazard analysis of the bridge site. Wave passage and ground motion incoherency effects were accounted for after propagating the bedrock records to the ground surface. The results obtained from inelastic response-history analyses confirm the significant impact of wave passage and ground motion incoherency on the seismic behavior of the bridge. The amplification in seismic demands exceeds 150%, whereas the maximum suppression of these demands is less than 50%. The irregular and unpredictable changes in structural response owing to asynchronous earthquake records necessitate in-depth seismic assessment of major highway bridges with advanced modeling techniques to realistically capture their complex seismic response.     

Modified Thermal Theory for Gravity Currents on Sloping Boundaries

In this study, we generalize the classic thermal theory to account for both entrainment and detrainment effects occurring in the acceleration and deceleration phases of gravity current motion. Although the original thermal theory qualitatively captures the two phases of gravity current motion, the pure entrainment model appears to underpredict the gravity current velocity and the distance before the maximum velocity is reached. We theoretically show that detrainment increases the predicted maximum velocity of gravity current and extends the predicted distance before the maximum velocity is reached. Furthermore, based on the experimental data reported in the literature, the detrainment coefficient appears to increase as the bottom slope increases.     

Implied velocity and acceleration induce transformations of visual memory.

Investigated the phenomenon of representational momentum as reported by the 1st 2 authors (see record 1984-16934-001) in cases where visual memories are distorted by implied motions of the elements of a pattern, conducting 3 experiments with 48 undergraduates. It was predicted that these memory distortions should be sensitive not only to the direction of the implied motions but also to changes in the implied velocity. Ss observed a sequence of dot-pattern displays that implied that the dots were moving at either a constant velocity or constant acceleration, but in separate directions. Discrimination functions for recognizing the final pattern in the sequence revealed that Ss' memories had shifted forward, corresponding to small continuations of the implied motions. The induced memory shifts increased in size as the implied velocity and acceleration of the dots increased but were eliminated when the display sequence implied a deceleration of the dots to a final velocity of zero. It is suggested that mentally extrapolated motion may have some of the same inertial properties as actual physical motion. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Angiotensin-converting enzyme (ACE) inhibitors revert abnormal right ventricular filling in patients with restrictive left ventricular disease

OBJECTIVES: Our aim was to determine mechanisms underlying abnormalities of right ventricular (RV) diastolic function seen in heart failure. BACKGROUND: It is not clear whether these right-sided abnormalities are due to primary RV disease or are secondary to restrictive physiology on the left side of the heart. The latter regresses with angiotensin-converting enzyme inhibition (ACE-I). METHODS: Transthoracic echo-Doppler measurements of left- and right-ventricular function in 17 patients with systolic left ventricular (LV) disease and restrictive filling before and 3 weeks after the institution of ACE-I were compared with those in 21 controls. RESULTS: Before ACE-I, LV filling was restrictive, with isovolumic relaxation time short and transmitral E wave acceleration and deceleration rates increased (p < 0.001). Right ventricular long axis amplitude and rates of change were all reduced (p < 0.001), the onset of transtricuspid Doppler was delayed by 160 ms after the pulmonary second sound versus 40 ms in normals (p < 0.001) and overall RV filling time reduced to 59% of total diastole. Right ventricular relaxation was very incoordinate and peak E wave velocity was reduced. Peak RV to right atrial (RA) pressure drop, estimated from tricuspid regurgitation, was 45+/-6 mm Hg, and peak pulmonary stroke distance was 40% lower than normal (p < 0.001). With ACE-I, LV isovolumic relaxation time lengthened, E wave acceleration and deceleration rates decreased and RV to RA pressure drop fell to 30+/-5 mm Hg (p < 0.001) versus pre-ACE-I. Right ventricular long axis dynamics did not change, but tricuspid flow started 85 ms earlier to occupy 85% of total diastole; E wave amplitude increased but acceleration and deceleration rates were unaltered. Values of long axis systolic and diastolic measurements did not change. Peak pulmonary artery velocity increased (p < 0.01). CONCLUSIONS: Abnormalities of RV filling in patients with heart failure normalize with ACE-I as restrictive filling regresses on the left. This was not due to altered right ventricular relaxation or to a fall in pulmonary artery pressure or tricuspid pressure gradient, but appears to reflect direct ventricular interaction during early diastole.     

Ground Motion Induced by Train Passage

Two methods are illustrated to effectively calculate the ground motion induced by constant speed moving loads. On the one hand, the dynamic Betti–Rayleigh reciprocity theorem allows one to take full advantage of the availability of Green’s functions for a homogeneous or a horizontally layered half-space. On the other hand, the spectral element method allows one to deal with complicated configurations, including dynamic soil-structure interaction, with an accuracy that is significantly higher than classical finite element or finite difference methods. Both the Betti–Rayleigh and spectral element methods are considered in three dimensions. After validating both methods, the decay of peak ground motion with distance is analyzed as a function of load speed and frequency. For speeds lower than the Rayleigh wave velocity in the soil, the decay turns out to be much faster than for a stationary point load. This effect is studied in detail by an analytical approach and interpreted in terms of destructive interference. Finally, the previous analytical and numerical results are checked against the records obtained at Ath, Belgium, during a field experiment to study ground motion induced by high-speed trains in soft soil conditions.     

Nonlinear Response of Deep Immersed Tunnel to Strong Seismic Shaking

Critical for the seismic safety of immersed tunnels is the magnitude of deformations developing in the segment joints, as a result of the combined longitudinal and lateral vibrations. Analysis and design against such vibrations is the main focus of this paper, with reference to a proposed 70?m-deep immersed tunnel in a highly seismic region, in Greece. The multisegment tunnel is modeled as a beam connected to the ground through properly calibrated interaction springs, dashpots, and sliders. Actual records of significant directivity-affected ground motions, downscaled to 0.24 g peak acceleration, form the basis of the basement excitation. Free-field acceleration time histories are computed from these records through one-dimensional wave propagation equivalent-linear and nonlinear analyses of parametrically different soil profiles along the tunnel; they are then applied as excitation at the support of the springs, with a suitable time lag to conservatively approximate wave passage effects. The joints between the tunnel segments are modeled realistically with special nonlinear hyperelastic elements, while their longitudinal prestressing due to the great (7?bar) water pressure is also considered. Nonlinear dynamic transient analysis of the tunnel is performed without ignoring the inertia of the thick-walled tunnel, and the influence of segment length and joint properties is investigated parametrically. It is shown that despite ground excitation with acceleration levels exceeding 0.50 g and velocity of about 80?cm/s at the base of the tunnel, net tension and excessive compression between the segments can be avoided with a suitable design of joint gaskets and a selection of relatively small segment lengths. Although this research was prompted by the needs of a specific project, the dynamic analysis methods, the proposed design concepts, and many of the conclusions of the study are sufficiently general and may apply in other immersed tunneling projects.     

Effects of Seismically Induced Pounding at Expansion Joints of Concrete Bridges

This paper presents the result of a study on the effect of pounding at expansion joints on concrete bridge response to earthquake ground motions. An engineering approach, rather than continuum mechanics approach, is emphasized. First, the dynamic behavior of a damped multidegree-of-freedom bridge system separated by an expansion joint involving an impact is examined by means of the finite element method. Second, the sensitivity analysis of the stiffness in gap elements is performed. Third, usefulness of the analysis method for simulation of pounding phenomena is demonstrated and the effect of pounding on the ductility demands measured in terms of the rotation of column ends is investigated. Two-dimensional finite element analysis using a bilinear hysterestic model for bridge substructure joints and a nonlinear gap element for the expansion joint is performed on a realistic bridge with an expansion joint. The effects of the primary factors on the ductility demand such as gap sizes and characteristics of earthquake ground motion are investigated through a parametric study. The major conclusions are (1) the effect of impact most directly depends on the size of momentum (or pounding magnitude); and (2) the pounding effect is generally found to be negligible on the ductility demand for wide practical ranges of gap size and peak ground acceleration, but is potentially significant at the locations of impact.     

Numerical Modeling of Seismic Response of Rigid Foundation on Soft Soil

A numerical model was developed to simulate the response of two instrumented, centrifuge model tests on soft clay and to investigate the factors that affect the seismic ground response. The centrifuge tests simulated the behavior of a rectangular building on 30?m uniform and layered soft soils. Each test model was subjected to several earthquakelike shaking events at a centrifugal acceleration level of 80g. The applied loading involved scaled versions of an artificial western Canada earthquake and the Port Island ground motion recorded during the 1995 Kobe Earthquake. The centrifuge model was simulated with the three-dimensional finite-difference-based fast Lagrangian analysis of continua program. The results predicted with the use of nonlinear elastic–plastic model for the soil are shown to be in good agreement with measured acceleration, soil response, and structural behavior. The validated model was used to study the effect of soil layering, depth, soil–structure interaction, and embedment effects on foundation motion.     

Failure Analysis of Modular-Block Reinforced-Soil Walls during Earthquakes

Several modular-block reinforced-soil retaining walls failed during the 1999 Ji-Ji (Chi-chi) earthquake of Taiwan. Similar walls showed distress during the 1994 Northridge, Calif., earthquake. The instability or failure of these walls offered an opportunity to validate the simplistic pseudostatic limit-equilibrium procedures. In this study, the Ta Kung Wall of the Ji-Ji earthquake is analyzed, and the Gould and Valencia Walls of the Northridge earthquake are revisited with an improved estimation of local site acceleration. The local acceleration was estimated by using simple attenuation relationships obtained through the earthquake records. The results of analysis indicate that these three walls had adequate internal stability under estimated site acceleration. The geosynthetic length was inadequate to resist compound modes of failure where the potential failure surface extends beyond the reinforced zone. The external stability was most critical in the presence of horizontal and vertical accelerations.