Acceleration Demands Research Articles

Development of Rocking Isolation for Response Mitigation of Elevated Water Tanks under Seismic and Wind Hazards

Elevated water tanks are categorized as strategic components of water supply systems in modern urban management. Past earthquake events have revealed the high vulnerability of these structures. This paper investigates the development of rocking isolation (RI) to these structures as a response mitigation technique. Using an analytical approach, a dynamic model is developed for two isolation cases: (1) at the pedestal base and (2) under the tank. The model incorporates a simplified analogy for simulating the liquid-tank system which is modified for a tank under rocking motions. Based on the dynamics of rocking structures, the equations of motion, impact, and uplift transitions are derived. Then, free vibration and seismic response history analyses are carried out on a sample structure. Discussions are made on the effect of RI on the dynamic and seismic responses of the pedestal and components of the liquid-tank system. Effects of various RI cases, pedestal heights, and tank filling levels are studied for a group of structures excited by an ensemble of ground motions. Considering that the system may be vulnerable to other lateral loadings, the combined effects of seismic and wind hazards are also studied. The wind loads are assumed to act statically and simultaneously with the seismic excitations. Results show that the first case of RI decreases the acceleration demands of mid-rise and tall structures, thus lowering the structural demands to 50% of the fixed-base system. However, the second case of RI has almost no effect on the performance of the system, upgrading only the response of mid-rise structures. Both RI cases also aggravate the wave oscillations and increase the freeboard requirements. Finally, while the combined seismic and wind hazards have almost no effect on the operational performances, the force demands of the structures are increased by 10%.

Performance comparison of BRBFs designed using different response modification factors

This paper presents details of the numerical examination and performance comparison of steel buckling restrained braced frames (BRBFs) designed with different response modification factors, using the next-generation performance assessment approach. Archetypal BRBF designs were conducted following the US provisions and considering response factors equal to or less than the codified limit. The archetypical buildings were subjected to ground-motions acquired from the FEMA P695 Far-Field record-set and scaled to MCE and DBE intensity levels. The FEMA P-58 performance assessment procedure was used to evaluate the results. The interstory drift ratio, residual interstory drift ratio, and peak story acceleration demands were determined and converted to performance quantities by using the Performance Assessment Calculation Tool (PACT). The repair time, probabilistic distribution of repair cost, unsafe placard probabilities, and irreparable residual drift probabilities were obtained, and a comparative study of response modification factors in terms of these results was conducted. The results show that designs with higher response factors result in higher repair costs, due to the damage of drift sensitive components and high residual drifts. On the other hand, BRBFs designed with lower response factors were found to experience higher accelerations, which result in an increase in the repair cost for acceleration sensitive components. An ideal response factor is proposed herein based on the consequence measures. The study was complemented by investigating the behavior of self-centering BRBFs and comparing their performance with those of conventional BRBFs.

Seismic upgrading of multistory steel moment‐resisting frames by installing shape memory alloy braces: Design method and performance evaluation

The installation of a damping bracing system is regarded as an effective means to upgrade the seismic capacity of steel moment-resisting frames (MRFs), a common structural form for buildings. However, conventional damping braces are incapable of eliminating residual deformation demand. Shape memory alloy (SMA) braces present an emerging seismic upgrading solution to this problem. However, the corresponding design method is yet to be developed. Therefore, this study proposes a simple and straightforward design method for seismic upgrading of MRFs through the installation of SMA braces. The maximum and residual interstory drift ratios are selected as performance target. Two benchmark frames with three or six stories are adopted to validate the proposed design method. A group of seismic ground motions corresponding to the design basis earthquake level are input to the frames with or without SMA braces. Seismic analysis results indicate that the frames equipped with properly designed SMA braces exhibit responses that satisfy the design target satisfactory. To quantify the seismic upgrading effect, peak and residual interstory drift ratios and peak floor acceleration demands are selected as critical factors to build single- or multiple-parameter indices. Based on the relevant performance indices, comparisons between the original and upgraded frames show that the overall seismic performance of MRFs can be improved by 10%–30% when SMA braces are installed. In addition, the reduction of residual deformation has a significant impact on the evaluation result because of the evident benefit to seismic performance.

Strength‐reduction factors for the design of light nonstructural elements in buildings

SummaryStrength‐reduction factors that reduce ordinates of floor spectra acceleration due to nonlinearity in the secondary system are investigated. In exchange for permitting some inelastic deformation to occur in the secondary system or its supports, these strength reduction factors allow to design the nonstructural elements or their supports for lateral forces that are smaller than those that would be required to maintain them elastically during earthquakes. This paper presents the results of a statistical analysis on component strength‐reduction factors that were computed considering floor motions recorded on instrumented buildings in California during various earthquakes. The effect of yielding in the component or its anchorage/bracing in offering protection against excessive component acceleration demands is investigated. It is shown that strength‐reduction factors computed from floor motions are significantly different from those computed from ground motions recorded on rock or on firm soils. In particular, they exhibit much larger reductions for periods tuned or nearly tuned to the dominant modal periods of the building response. This is due to the large differences in frequency content of ground motions and floor motions, with the former typically characterized by wide‐band spectra whereas the latter are characterized by narrow‐band spectra near periods of dominant modes in the response of the building. Finally, the study provides approximate equations to estimate component strength‐reduction factors computed through nonlinear regression analyses.

Design and field test of drilling composite impactor

When the PDC drill bit encounters the heterogeneous and highly abrasive formation, it comes up with problems such as serious stick-slip phenomenon, shallow depth of penetration and short service life, and meanwhile, the rapid drilling tool with a single impact function cannot meet the drilling acceleration demand of exploration and development in deeper and more complex formation. Therefore, as a complementary implement of the traditional percussion drilling tools, a efficient drilling composite impactor has been designed, which is capable of applying both the reciprocating torsional impact and the reciprocating axial impact. The impact characteristic parameters of the tool have been obtained through the ground performance test, which also verifying the reliability of the composite impact timing, in addition, the field application has been carried out in Tian17-Xie12 well. And the results show that the key drilling parameters, such as well inclination and azimuth, change stably, thus shortening the sliding drilling time, and compared with adjacent wells, the tool above-mentioned has improved the mechanical drilling rate by 38%.

Evaluation of Seismic Acceleration Demands on Building Nonstructural Elements

As proven by several past earthquakes, seismic losses associated with nonstructural damage in modern buildings are likely to significantly exceed those associated with structural damage. Hence, to satisfactorily assess the overall seismic performance of a building and consequently the associated losses, it is paramount to properly account for the nonstructural damage through the adequate estimation of acceleration demands that are imposed on its acceleration-sensitive nonstructural elements in any one-floor level during an earthquake. Component acceleration amplification factors, ap, which measure how much the acceleration of a component is amplified relative to the peak floor acceleration are evaluated by floor motions recorded during earthquakes on instrumented buildings in the United States. The study shows that component amplification factors currently used in codes significantly underestimate acceleration demands for components whose periods are tuned or nearly tuned to modal periods of the supporting structure. Simplified equations are proposed to estimate component acceleration amplifications. The study also evaluates inelastic floor acceleration spectral ordinates. As a result of the filtering and amplification of the ground motion by the structure, the results show that even small levels of nonlinearity in the nonstructural element or its attachment to the structure lead to significant reductions in acceleration demands.

Duration-Specific Peak Acceleration Demands During Professional Female Basketball Matches.

Purpose: Describing the most intense periods of match-play is important in player monitoring and the development of specific training programs. The aim of this study was to extract maximum accelerations during basketball match-play and describe those as a function over time durations.Methods: Twelve professional female basketballers were monitored during 13 official matches to calculate acceleration profiles. Moving medians of time durations ranging from 0.3 to 1,800 s were computed to extract peak acceleration and deceleration magnitudes for the resultant (|accres|), horizontal (|acchor|), and vertical (|accvert|) planes. The relationship between peak magnitudes and time durations was modeled by an exponential function. Distinct curve characteristics can be described by the function parameters scale and decrease rate, which refer to an athlete's ability to perform maximum acceleration intensities over short-time (scale) and middle-time intervals (decrease rate). Generalized linear mixed-models were calculated to determine plane-specific differences in acceleration and deceleration capacities.Results: Function parameters differed significantly between |accres|, |acchor| and |accvert| [effect size (ES) = 0.33–1.15]. Comparisons within each movement plane revealed significant differences between positive and negative |accres| for the parameters scale (ES = 0.34) and decrease rate (ES = 0.39). All function parameters differed significantly between |accvert|+ and |decvert| (ES = 0.39–0.71). Rank analyses between players revealed significant inter-individual differences for all function parameters in all groups.Conclusions: Modeling peak acceleration magnitudes as a function over log-transformed time durations provides an opportunity to systematically quantify the most intense periods of match-play over short, middle and long time intervals (0.3–1,800 s). Detailed knowledge about these periods may positively contribute to training prescriptions, which intend to prepare players for highest intensities experienced during match-play in order to improve performance and prevent injuries. Derived function parameters allow inter-individual comparisons and provide insights into players' physical capabilities. This study further examines plane-specific intensity demands of professional female basketball, emphasizing the need for coaches to prepare players for maximum decelerations in the vertical plane.

Risk-based mainshock-aftershock performance assessment of SMA braced steel frames

This study presents a methodology to generate probabilistic seismic demand models and hazard curves for steel frames with or without shape memory alloy (SMA) bracing systems under mainshock – aftershock sequences. First, three post-mainshock damage states were defined based on both peak inter-story drift and residual drift ratios. Incremental dynamic analyses (IDA) were performed considering only mainshock events to determine spectral acceleration demands corresponding to each mainshock damage level. Then, aftershock IDA were conducted on the post-mainshock SMRF and SMA frames at three damage states. To estimate the peak and residual drift response of SMRF and SMA braced frames subjected to a mainshock – aftershock sequence, empirical seismic demand models were developed. Next, a risk-based seismic performance evaluation study was conducted to generate seismic demand hazard curves for maximum and residual interstory displacement response. Results reveal the advantages of SMA braces in enhancing post-event functionality of steel frame buildings. In addition, defining damage states based on residual drifts is recommended while comparing the aftershock performance of conventional steel moment resisting frames with self-centering steel buildings.

Investigation and quantitative simulation of beam physics for 230 MeV SC cyclotron under construction at CIAE

In China, there is a strong demand of the medium-energy proton accelerators for proton therapy. A compact superconducting cyclotron named CYCIAE-230 is currently under construction at CIAE to provide 230 MeV proton beam. In this paper, the investigation and quantitative simulation of beam physics for CYCIAE-230 will be presented in detail, which mainly include: 1. The beam dynamics behavior in the ultra compact central region and the design challenges including the micro PIG ion source, the tips of magnetic poles and RF cavities; 2. the numerical simulation and optimization of the phase slip and tune diagram in acceleration region; 3. the orbit simulation in the extraction region, emphasizing on increasing the turn separation and the resonance study; 4. the fast intensity modulation, control of beam stabilization by a closed-loop feedback, and the basic algorithm for controlling the beam intensity, adjusting the phase and their implementations.

Seismic vibration control of an innovative self-centering damper using confined SMA core

Using confined shape memory alloy (SMA) bar or plate, this study proposes an innovative self-centering damper. The damper is essentially properly machined SMA core, i.e., bar or plate, that encased in buckling-restrained device. To prove the design concept, cyclic loading tests were carried out. According to the test results, the damper exhibited desired flag-shape hysteretic behaviors upon both tension and compression actions, although asymmetric behavior is noted. Based on the experimental data, the hysteretic parameters that interested by seismic applications, such as the strength, stiffness, equivalent damping ratio and recentering capacity, are quantified. Processed in the Matlab/Simulink environment, a preliminary evaluation of the seismic control effect for this damper was conducted. The proposed damper was placed at the first story of a multi-story frame and then the original and controlled structures were subjected to earthquake excitations. The numerical outcome indicated the damper is effective in controlling seismic deformation demands. Besides, a companion SMA damper which represents a popular type in previous studies is also introduced in the analysis to further reveal the seismic control characteristics of the newly proposed damper. In current case, it was found that although the current SMA damper shows asymmetric tension-compression behavior, it successfully contributes comparable seismic control effect as those having symmetrical cyclic behavior. Additionally, the proposed damper even shows better global performance in controlling acceleration demands. Thus, this paper reduces the concern of using SMA dampers with asymmetric cyclic behavior to a certain degree.

A highly stable reliable SRAM cell design for low power applications

The growth in demand for power-efficient neural network accelerators has generated an intense demand for low power static random access memory (SRAM). In this context, a power-efficient transmission gate based 9-Transistor (TG9T) SRAM bitcell has been proposed in this work. In order to assess the relative performance of the proposed design in terms of major design metrics, it has been juxtaposed with contemporaneous designs such as the feedback-cutting 7T, fully differential 8T (FD8T) and single-ended disturb free 9T (SEDF9T) bitcells, while the reliability of such SRAM designs when subjected to process variations has also been analyzed. In terms of read stability (RSNM), the TG9T shows 2.87×/3.36× higher RSNM and 2.90×/2.67× narrower spread in RSNM, respectively, as compared to 7T/FD8T. In addition, it also exhibits 1.4×/6.55× higher write ability (WSNM) and 1.01×/5.05×/1.06× narrower spread in WSNM when compared with FD8T/SEDF9T and FD8T/SEDF9T/7T respectively. Moreover, a 1.15×/1.06× narrower spread in read delay (TRA) and 1.54×/1.38× narrower spread in read current (IREAD) are also exhibited by the proposed design in comparison with 7T/FD8T. The reliable nature of TG9T is indicated by the narrower spread in read stability, write ability, read delay and read current. Furthermore, in comparison with 7T/FD8T, TG9T consumes 2.92×/1.04× lower hold power. Additionally, the proposed cell shows 10.80×/17.81× lower write power consumption and 1.43×/18.37× lower read power consumption when compared to that of SEDF9T/FD8T and 7T/FD8T respectively. Amongst all SRAM bitcells used for comparison, the proposed bitcell yields the lowest VDD,min. The TG9T cell achieves all the aforementioned improvements at the cost of 1.22×/1.34× longer TWA and 1.93×/1.93× longer TRA when compared with 7T/SEDF9T and 7T/FD8T, respectively, at a supply voltage of 0.7 V.

Critical Assessment of Estimation Procedures for Floor Acceleration Demands in Steel Moment-Resisting Frames

Performance-based earthquake engineering has increased the need for practical ways to assess the response of non-structural components (NSCs), which may be affected by deformation and/or acceleration demands of the superstructure. In the research study detailed in this paper, peak floor accelerations (PFAs) and floor response spectra (FRS) are computed using nonlinear response-history analysis (NTHA) for a comprehensive suite of 30 steel moment-resisting frame (MRF) archetypes, designed in accordance to Eurocode 8, considering different levels of nonlinear seismic demand. The mean trends observed were compared with the most recent approaches proposed in the literature for the prediction of acceleration demands. It was found that for PFAs, the available methods provide accurate predictions of the actual structural response under elastic and inelastic demands. However, the estimation procedures for the FRS yielded relevant differences in comparison to the observed elastic and inelastic responses, which points to the need for further development of such methods. It was also concluded that the existing PFA and FRS estimation methodologies present in several guidelines for seismic design and/or assessment do not provide reliable estimates of the acceleration demands imposed to buildings. This highlights the very important need for an improvement of these codified procedures for a more reliable prediction of seismic response.

There Is Little Difference in the Peak Movement Demands of Professional and Semi-Professional Rugby League Competition

Previous research has quantified the peak movement demands of elite rugby league match-play, but the peak accelerometer load or the semi-professional peak demands remain unknown. The aim of this research was to determine the peak movement demands of professional and semi-professional rugby league competition. Wearable microtechnology devices tracked the physical activity profiles of players during 26 professional (n = 351 files) and 22 semi-professional (n = 267 files) matches. Following each match, data were exported in raw form to extract the peak 1- to 10-min periods for speed, average acceleration, and accelerometer load of each player, using a rolling average method. To determine the difference between playing levels (professional vs. semi-professional) and position (forwards vs. backs), linear mixed models were used. The intercept and the slope were calculated based on the power law relationship to provide the peak, and rate of decay, of each dependent variable. Cohen’s effect size (ES) statistic was used to determine the magnitude of differences between positions and playing level. There was little difference between playing standards, with only small differences in running speed, with a greater intercept and slope for the professional forwards compared with semi-professional forwards (intercept ES: 0.37; 90%CL: 0.19 to 0.55; slope ES: 0.35; 0.15 to 0.55). For positional comparisons (forwards vs. backs), there was no difference in running speeds at the professional level, but there was substantially greater running speed for backs compared to forwards in semi-professional competition, with small to moderate differences (ES range: 0.60–0.39). Both professional and semi-professional forwards showed small to moderately higher accelerometer load compared to backs, which increased with period duration (ES range: 0.22–0.79). Similarly, acceleration demands were greater for forwards compared to backs across both playing standards, with moderate to large differences (ES range: 0.52–0.96). Overall, the results of this study show that there is a small difference in the peak running speed for forwards in professional competition, but otherwise there are no meaningful differences in movement demands of professional and semi-professional rugby league match-play. Forwards display greater acceleration and accelerometer load across a number of rolling average durations compared to backs.

Seismic shear and acceleration demands in multi-storey cross-laminated timber buildings

A realistic estimation of seismic shear demands is essential for the design and assessment of multi-storey buildings and for ensuring the activation of ductile failure modes during strong ground-motion. Likewise, the evaluation of seismic floor accelerations is fundamental to the appraisal of damage to non-structural elements and building contents. Given the relative novelty of tall timber buildings and their increasing popularity, a rigorous evaluation of their shear and acceleration demands is all the more critical and timely. For this purpose, this paper investigates the scaling of seismic shear and acceleration demands in multi-storey cross-laminated timber (CLT) buildings and its dependency on various structural properties. Special attention is given to the influence of the frequency content of the ground-motion. A set of 60 CLT buildings of varying heights representative of a wide range of structural configurations is subjected to a large dataset of 1656 real earthquake records. It is demonstrated that the mean period (Tm) of the ground-motion together with salient structural parameters such as building aspect ratio (λ), design force reduction factor (q) and panel subdivision (β) influence strongly the variation of base shear, storey shears and acceleration demands. Besides, robust regression models are used to assess and quantify the distribution of force and acceleration demands on CLT buildings. Finally, practical expressions for the estimation of base shears, inter-storey shears and peak floor accelerations are offered.

Numerical Development and Assessment of 3D Quintuple Friction Pendulum Isolator Element Based on Its Analytical and Mathematical Models

ABSTRACT This paper aims to develop, assess, and numerically implement analytical models for the newly introduced Quintuple Friction Pendulum Isolator (QFPI) which can identically capture its real experimental performance and also have the ability to capture the bi-directional, tri-directional, and vertical-horizontal coupling behavior of it, raising the predictive capability of nonlinear response history analyses and also lowering computational and experimental complexity and cost. The mathematical formulation proposed in this paper aims at addressing the variability of the coefficient of friction based on experimentally obtained data from prototype test on QFPI system. The formulation accounts for variation in the coefficient of friction with the instantaneous change of axial load and sliding velocity at the isolator contact interfaces. Furthermore, it considers the experimentally discovered phenomena such as the static frictions developed at the very first initiation of motion, breakaway, or at motion reversals, stick-slip. The proposed model has been coded three-dimensionally by a series model in the object-oriented finite element software OpenSees based on its mathematical formulations. The primary assumptions in developing the friction models and corresponding parameters are validated by available experimental data and suggestions. A case study has been considered to validate the developed element and also to investigate and demonstrate the prediction capability of it when applied to real situations, such as variations have been made in displacement, base shear, and acceleration demand for this system under dynamic behavior of earthquakes. Moreover, the effects of vertical-horizontal coupling behavior of QFP isolated system on its horizontal responses have been investigated numerically and justified analytically under the existence of vertical acceleration, by subjecting the system to a variety of X and XY (horizontal only) and 3D (horizontal plus vertical) input excitations for comparison.

How do granular columns affect the seismic performance of non-uniform liquefiable sites and their overlying structures?

This paper presents results of a series of three dynamic centrifuge experiments to evaluate how granular columns affect the seismic performance of level and gently sloped sites that include a non-uniform liquefiable deposit and an overlying, 3-story structure. A slight variation in the thickness of the liquefiable layer is shown to produce unacceptable permanent lateral ground deformations, even in the absence of a surface slope or a structure. The presence of a gentle slope further amplified lateral displacements but did not influence settlements notably. Granular columns (with an area replacement ratio of 20%) were successful in reducing the extent and duration of large excess pore pressures, void redistribution, and shear strain localization in such layered deposits. Hence, they generally reduced settlements, rotations, and lateral displacements both near and away from structures, but not necessarily to acceptable design limits. Granular columns could increase the acceleration demand transferred to the foundation and superstructure by increasing soil stiffness and reducing damping. The impact of this mitigation on roof accelerations and beam/column bending strains was shown to depend on the intensity and frequency content of the input motion in relation to the modal frequencies of the structure. The presented experimental results highlight the importance of considering even slight variations in liquefiable layer thickness as well as soil-foundation-structure interaction when designing liquefaction mitigation strategies in the context of system performance.

Optimal tuning and assessment of inertial dampers with grounded inerter for vibration control of seismically excited base-isolated systems

In this paper, the concept of an ideal grounded linear inerter, endowing supplemental inertia to passive linear tuned mass-dampers (TMDs) through its inertance property without increasing the TMD mass, is considered to reduce lateral displacement demands in base isolated structural systems (BISs). Optimal tuned mass-damper-inerter (TMDI) design parameters are numerically determined to maximize energy dissipation by the TMDI under stationary white noise support excitation. Performance of these optimally designed TMDI-equipped BISs is assessed for stationary white and colored noise excitations as well as for four recorded earthquake acceleration ground motions (GMs) with different non-stationary frequency content. It is found that for fixed mass ratio the inclusion of the grounded inerter reduces significantly secondary mass displacement and stroke for all considered excitations while it improves appreciably BIS displacement demands except for the particular case of a near-fault accelerogram characterized by early arrival of a high-energy low-frequency pulse as captured in its wavelet spectrogram. More importantly, it leads further to reductions to BIS acceleration demands with the exception of colored noise excitation for which an insignificant increase is noted. The positive effects of the inerter saturate with increasing inertance and BIS damping ratio demonstrating that small inertance values are more effective in vibration suppression of BISs with low inherent damping. Overall, it is recommended to combine low damping isolation layers with large inertance and low secondary mass TMDIs.

Quantifying Mean Peak Running Intensities in Elite Field Hockey.

Delves, RIM, Bahnisch, J, Ball, K, and Duthie, GM. Quantifying mean peak running intensities in elite field hockey. J Strength Cond Res 35(9): 2604-2610, 2021-To replicate match demands in training, field hockey (FH) coaches typically prescribe intensities based on whole-match data. Such data may underestimate peak competition periods, potentially underpreparing athletes for competition. This study then aimed to quantify maximal mean running intensities during elite FH competition to facilitate enhanced training prescription. Ten-Hertz Global Positioning System data were collected from 17 male and 11 female FH athletes who competed in the 2016 and 2017 Australian Hockey League tournaments. Maximal mean values for speed, acceleration, and metabolic power (Pmet) were calculated over a 1- to 10-minute moving average by position. Summary match statistics were also analyzed. Linear mixed models were constructed to determine the effect of position on moving average and summary variables. Pairwise comparisons between groups were made using magnitude-based inferences. In female competition, speed and Pmet intensities were greater in midfielders, whereas defenders were lowest in acceleration demands over the 10-minute window and in corresponding intercepts. In male competition, acceleration was greater in defenders during the 10-minute window and in subsequent intercepts compared with midfielders, whereas defenders were lowest in speed intercepts. In comparison with previously reported summary match variables, intensities from the 1-minute moving average interval were 50-65% greater in male competition and 30-50% greater in female competition. The 10-minute moving average framework has identified FH running intensities that are greater than previously reported whole-match averages. This information enhances the understanding of the demands of FH, assisting practitioners to prepare their athletes for the most demanding instances of play.

Dimensionless fragility analysis of seismic acceleration demands through low-order building models

This paper deals with the estimation of fragility functions for acceleration-sensitive components of buildings subjected to earthquake action. It considers ideally coherent pulses as well as real non-pulselike ground-motion records applied to continuous building models formed by a flexural beam and a shear beam in tandem. The study advances the idea of acceleration-based dimensionless fragility functions and describes the process of their formulation. It demonstrates that the mean period of the Fourier Spectrum, T_m, is associated with the least dispersion in the predicted dimensionless mean demand. Likewise, peak ground acceleration, PGA-, and peak ground velocity, PGV-based length scales are found to be almost equally appropriate for obtaining efficient ‘universal’ descriptions of maximum floor accelerations. Finally, this work also shows that fragility functions formulated in terms of dimensionless varPi-terms have a superior performance in comparison with those based on conventional non-dimensionless terms (like peak or spectral acceleration values). This improved efficiency is more evident for buildings dominated by global flexural type lateral deformation over the whole intensity range and for large peak floor acceleration levels in structures with shear-governed behaviour. The suggested dimensionless fragility functions can offer a ‘universal’ description of the fragility of acceleration-sensitive components and constitute an efficient tool for a rapid seismic assessment of building contents in structures behaving at, or close to, yielding which form the biggest share in large (regional) building stock evaluations.

Nonlinear 3D path following control of a fixed-wing aircraft based on acceleration control

This paper focuses on the design of a novel path following control concept for fixed-wing aircraft, which systematically incorporates the nonlinearities of the flight dynamics. By introducing an acceleration based inner loop control, feedforward acceleration demands of nonlinear 3D paths can be directly taken into account. Furthermore, the nonlinear effects of airspeed, orientation, and gravity are considered separately by implementing a cascaded design and feedback linearization. As a result, robust performance of the path following control is achieved even for wind speeds in the order of the aircraft’s airspeed and path accelerations significantly higher than the gravitational acceleration. By further including direct lift control, a high-bandwidth vertical acceleration control is developed. Results of flight experiments show that the designed control concept is particularly beneficial in terms of the tracking performance for 3D paths, the incorporation of input constraints, the robustness against wind and turbulence effects, and the ease of implementation as well as the low computational complexity.