Drift Levels Research Articles

Numerical study of demountable shear wall system for multistory precast concrete buildings

The aim of this paper is to propose a demountable shear wall (DSW) system for multistory precast concrete buildings. For this purpose, instead of a large wall panel, several slender walls are used by connecting to adjacent beams. To evaluate the efficiency of the DSW system, nonlinear cyclic and time history analyses are performed on eighteen 4-, 8- and 12-story models, including three conventional shear wall models and fifteen DSW models with various wall numbers. The results indicate that for DSW system, when using more walls with a smaller width, the structural deformation tends from flexural-type to almost shear-type. This result prevents the plastic strain from concentrating on the columns and walls of the first story and causes the damage to be uniformly distributed on the walls of all stories. The DSW models exhibit hysteretic behavior without significant strength degradation at high drift levels. Also, DSW models with more walls, while increasing the ductility factor (up to 30%) and creating a more uniform distribution of drifts, reveal less value of maximum floor acceleration (up to 48%) and story shear (up to 53%), compared to conventional shear wall models.

Development of a double-stage yielding damper with vertical shear links

This study proposes a novel hybrid damper called vertical links system with double-stage yielding (VLDY). The VLDY damper consists of two replaceable vertical shear links connected in series, located within a moment-resisting frame (MRF). When the MRF sustains lateral deformation, the minor link yields in shear. The inelastic shear rotation of the minor link increases till the engagement of the lockout mechanism. Thereafter, the inelastic deformation occurs in the major shear link, and the entire system enters the second yielding stage. The minor link can be adjusted to dissipate the input energy in relatively small inter-story drift levels during moderate earthquakes, and the major link maintains the structural integrity under severe earthquake ground motions. A validated nonlinear finite element modeling protocol in ABAQUS/standard was utilized to examine the applicability and cyclic response of the proposed system. The results showed that the VLDY device could provide stable energy dissipation capacity in a wide range of inter-story drift levels ranging from 0.3% to 4%. In addition, the cyclic secant stiffness, energy dissipation capacity, and equivalent viscous damping ratio of the VLDY-equipped frames significantly increased compared with those of the bare frames. Based on the results, a minimum free span-to-depth ratio of 7 has been suggested to ensure the prevention of the steep moment gradient on the story beams.

Performance of new CFST square column-to-foundation connections for cyclic loads

Although the structural behavior of circular Concrete Filled Steel Tube (CFST) columns-to-foundation connections has been studied substantially, there are limited studies on connections for square CFST columns, which are more in demand in high-rise buildings. The acceptable behavior of these columns for their use in high-rise buildings require sufficient stiffness for controlling the drift, safe and efficient transfer of imposed loads, and adequate ductility for withstanding earthquake loads. In the present study, authors aim to develop two such column-to-foundation connections for the square CFST columns. The performance of the two square CFST column-to-foundation connections was assessed experimentally as well as numerically under cyclic lateral loading. The comparison of the connections was made with one of the prevalent square CFST column-to-foundation connections and a conventional RC connection to study the inelastic deformation capacity of connections under cyclic loads. The test results illustrate the efficient and improved behavior of the suggested connections. Numerical models were also developed, and the experimentally obtained results were predicted and compared. The developed numerical models were capable of predicting the experimental response of connections to large drift levels with acceptable accuracy. The numerical results were reasonably close to the experimental response.

Frequency drift in MR spectroscopy at 3T

PurposeHeating of gradient coils and passive shim components is a common cause of instability in the B0 field, especially when gradient intensive sequences are used. The aim of the study was to set a benchmark for typical drift encountered during MR spectroscopy (MRS) to assess the need for real-time field-frequency locking on MRI scanners by comparing field drift data from a large number of sites. MethodA standardized protocol was developed for 80 participating sites using 99 3T MR scanners from 3 major vendors. Phantom water signals were acquired before and after an EPI sequence. The protocol consisted of: minimal preparatory imaging; a short pre-fMRI PRESS; a ten-minute fMRI acquisition; and a long post-fMRI PRESS acquisition. Both pre- and post-fMRI PRESS were non-water suppressed. Real-time frequency stabilization/adjustment was switched off when appropriate. Sixty scanners repeated the protocol for a second dataset. In addition, a three-hour post-fMRI MRS acquisition was performed at one site to observe change of gradient temperature and drift rate. Spectral analysis was performed using MATLAB. Frequency drift in pre-fMRI PRESS data were compared with the first 5:20 minutes and the full 30:00 minutes of data after fMRI. Median (interquartile range) drifts were measured and showed in violin plot. Paired t-tests were performed to compare frequency drift pre- and post-fMRI. A simulated in vivo spectrum was generated using FID-A to visualize the effect of the observed frequency drifts. The simulated spectrum was convolved with the frequency trace for the most extreme cases. Impacts of frequency drifts on NAA and GABA were also simulated as a function of linear drift. Data from the repeated protocol were compared with the corresponding first dataset using Pearson's and intraclass correlation coefficients (ICC). ResultsOf the data collected from 99 scanners, 4 were excluded due to various reasons. Thus, data from 95 scanners were ultimately analyzed. For the first 5:20 min (64 transients), median (interquartile range) drift was 0.44 (1.29) Hz before fMRI and 0.83 (1.29) Hz after. This increased to 3.15 (4.02) Hz for the full 30 min (360 transients) run. Average drift rates were 0.29 Hz/min before fMRI and 0.43 Hz/min after. Paired t-tests indicated that drift increased after fMRI, as expected (p < 0.05). Simulated spectra convolved with the frequency drift showed that the intensity of the NAA singlet was reduced by up to 26%, 44 % and 18% for GE, Philips and Siemens scanners after fMRI, respectively. ICCs indicated good agreement between datasets acquired on separate days. The single site long acquisition showed drift rate was reduced to 0.03 Hz/min approximately three hours after fMRI. DiscussionThis study analyzed frequency drift data from 95 3T MRI scanners. Median levels of drift were relatively low (5-min average under 1 Hz), but the most extreme cases suffered from higher levels of drift. The extent of drift varied across scanners which both linear and nonlinear drifts were observed.

Unitized curtain wall systems joint performance with re-entrant corners under seismic racking testing

Understanding damage mechanisms and associated facility challenges for curtain wall systems with different boundary conditions is critical in their performance evaluation and selection during the design stage of a building's lifecycle, in particular if vulnerable to earthquake effects. While many different styles and configurations exist, limited research has been conducted on unitized four-sided structural sealant glazing (4SSG) with re-entrant corners under dynamic racking testing conditions. As such, this paper details a study on full-scale unitized 4SSG curtain wall system mockups featuring a re-entrant corner and subjected to cyclic racking displacements. Racking tests were carried out in accordance with the American Architectural Manufacturers Association (AAMA) 501.6 protocol. Glass fallout, sealant adhesive or cohesive failure, and glass cracking failure modes were identified as limit states and corresponding drift levels were determined. Results of these tests on full-scale specimens are presented here and some of the challenges in data collection and accuracy when using a racking facility are discussed.

Evaluation of seismic damage to Iraqi educational reinforced concrete building using FEMA P-58 methodology

The building seismic performance assessment can be defined as a posterior phase of investigation in which a detailed analysis is executed in order to evaluation of seismic damages and quantify the sequences of the earthquake for a building, this approach could be probabilistic evaluation or deterministic one. The aim of this paper is to perform seismic damage evaluation for educational multi-storey reinforced Concrete Building in Al-Mustaqbal University College (MUC) in Al-Hilla City, Babylon governorate in the middle of Iraq by using FEMA P-58 methodology. A 3D mathematical modelling, pushover analysis by using SeismoStruct software. In addition, incremental dynamic analysis (IDA) and fragility curve according to FEMA P-58 are developed in order to obtain damage limits in term of performance levels of the case study building. Fragility curves are useful tools for showing the probability of structural damage due to earthquakes as a function of ground motion indices. IDA is performed for those simulated building using twelve ground motions with scaling peak ground acceleration increased every 0.1g until it achieved 1.5g to determine the drift capacity of the building in four performance levels, operational (OP), immediate occupancy (IO), life safety (LS) and near collapse (NC) as defined in FEMA P-58. Based on those capacities, fragility curves were developed in terms of peak ground acceleration (PGA) and elastic spectral displacement for drift levels with lognormal distribution assumption.

Genomic signatures of clonality in the deep water kelp Laminaria rodriguezii.

The development of population genomic approaches in non-model species allows for renewed studies of the impact of reproductive systems and genetic drift on population diversity. Here, we investigate the genomic signatures of partial clonality in the deep water kelp Laminaria rodriguezii, known to reproduce by both sexual and asexual means. We compared these results with the species Laminaria digitata, a closely related species that differs by different traits, in particular its reproductive mode (no clonal reproduction). We analysed genome-wide variation with dd-RAD sequencing using 4,077 SNPs in L. rodriguezii and 7,364 SNPs in L. digitata. As predicted for partially clonal populations, we show that the distribution of FIS within populations of L. rodriguezii is shifted toward negative values, with a high number of loci showing heterozygote excess. This finding is the opposite of what we observed within sexual populations of L. digitata, characterized by a generalized deficit in heterozygotes. Furthermore, we observed distinct distributions of FIS among populations of L. rodriguezii, which is congruent with the predictions of theoretical models for different levels of clonality and genetic drift. These findings highlight that the empirical distribution of FIS is a promising feature for the genomic study of asexuality in natural populations. Our results also show that the populations of L. rodriguezii analysed here are genetically differentiated and probably isolated. Our study provides a conceptual framework to investigate partial clonality on the basis of RAD-sequencing SNPs. These results could be obtained without any reference genome, and are therefore of interest for various non-model species.

Genetic history of Calabrian Greeks reveals ancient events and long term isolation in the Aspromonte area of Southern Italy

Calabrian Greeks are an enigmatic population that have preserved and evolved a unique variety of language, Greco, survived in the isolated Aspromonte mountain area of Southern Italy. To understand their genetic ancestry and explore possible effects of geographic and cultural isolation, we genome-wide genotyped a large set of South Italian samples including both communities that still speak Greco nowadays and those that lost the use of this language earlier in time. Comparisons with modern and ancient populations highlighted ancient, long-lasting genetic links with Eastern Mediterranean and Caucasian/Near-Eastern groups as ancestral sources of Southern Italians. Our results suggest that the Aspromonte communities might be interpreted as genetically drifted remnants that departed from such ancient genetic background as a consequence of long-term isolation. Specific patterns of population structuring and higher levels of genetic drift were indeed observed in these populations, reflecting geographic isolation amplified by cultural differences in the groups that still conserve the Greco language. Isolation and drift also affected the current genetic differentiation at specific gene pathways, prompting for future genome-wide association studies aimed at exploring trait-related loci that have drifted up in frequency in these isolated groups.

Seismic fragility of steel special truss moment frames with multiple ductile vierendeel panels

Special truss moment frames (STMFs) are used as the lateral force-resisting systems in buildings. Under seismic loading, the hysteretic energy dissipation in STMFs mostly occurs through the flexural plastic hinges developed in the special segments only. This study presents the seismic fragility assessment of low to high-rise STMFs with ductile Vierendeel panels as the special segments. Four building frames (i.e., 3-, 6-, 9-, and 15-story) with three different configurations of special segments in STMFs have been considered as the study frames. Nonlinear incremental dynamic analyses of the study frames have been carried out using computer software PERFORM-3D using forty-four ground motion records. The probability of exceeding the drift levels corresponding to three performance levels, viz., immediate occupancy (IO), life safety (LS), and collapse prevention (CP) of the study frames have been investigated under the design-basis earthquake and maximum considered earthquake hazard levels. The presence of intermediate vertical members in the Vierendeel panels resulted in the gradual loss in the post-peak lateral strengths of STMFs. The use of multiple Vierendeel panels significantly reduced the probability of failure of low-rise (namely, 3- and 6-story) STMFs. However, STMFs with single Vierendeel panels are found to be beneficial in 9- and 15-story building frames. The inter-story drift limits have been proposed for the performance levels of IO, LS, and CP of STMFs.

On-site testing of masonry shear walls strengthened with timber panels

The effectiveness of a method to strengthen/repair unreinforced masonry (URM) by using timber-based products was investigated through experimental in situ testing. The strategy consists of timber-based panels connected to the masonry by means of screw fasteners. URM piers obtained from a century-old building were subjected to in-plane semi-cyclic quasi-static loading in as-built, repaired and retrofitted configurations. The application of the reinforcement on previously damaged piers led to a notable increase in the in-plane capacity while the initial stiffness of the repaired specimens was found to be consistent with that of the specimens tested as-built. When applied to undamaged masonry, the retrofit system allowed an in-plane force 40% higher than the capacity of the unreinforced walls, with the initial stiffness comparable with that of the repaired specimens. Both repaired and retrofitted specimens exhibited remarkable displacement capacity (drift levels &gt; 2.0%) and energy dissipation.

Influence of historic roof structures on the seismic behaviour of masonry structures

Historic buildings are complex structures in which all the composing elements work together. Studies of heritage structures after seismic events have shown that timber roof structures strongly influence the seismic response of masonry structures, being able to reduce or enhance the out-of-plane displacement of the structure. Starting from these observations, three different types of roof structures, from the eighteenth, nineteenth and twentieth centuries, were introduced in the finite-element simulation software SCIA Engineer. The roof structures were subsequently placed on the same eighteenth-century masonry building with a ground floor and two upper floors, respecting its geometric features. Simulations were performed considering successively rigid, hinged or sliding connections between the roof and the masonry structure. At the same time, the traditionally crafted joints of the roof structures were consecutively modelled as hinged, rigid and semi-rigid (determined using three different methods). Ultimately, the top horizontal displacement, inter-storey drift and damage level of the masonry structure were compared. The main aims of this study were to observe if roof structures have an influence on the seismic behaviour of masonry buildings and to determine if selected parameters suffer any changes depending on the roof structure type, the roof–wall connections and joints’ axial stiffness.

Graph-Based Proprioceptive Localization Using a Discrete Heading-Length Feature Sequence Matching Approach

Proprioceptive localization refers to a new class of robot egocentric localization methods that do not rely on the perception and recognition of external landmarks. These methods are naturally immune to bad weather, poor lighting conditions, or other extreme environmental conditions that may hinder exteroceptive sensors such as a camera or a laser ranger finder. These methods depend on proprioceptive sensors such as inertial measurement units and/or wheel encoders. Assisted by magnetoreception, the sensors can provide a rudimentary estimation of vehicle trajectory which is used to query a prior known map to obtain location. Named as graph-based proprioceptive localization, we provide a low cost fallback solution for localization under challenging environmental conditions. As a robot/vehicle travels, we extract a sequence of heading-length values for straight segments from the trajectory and match the sequence with a preprocessed heading-length graph (HLG) abstracted from the prior known map to localize the robot under a graph-matching approach. Using the information from HLG, our location alignment and verification module compensates for trajectory drift, wheel slip, or tire inflation level. We have implemented our algorithm and tested it in both simulated and physical experiments. The algorithm runs successfully in finding robot location continuously and achieves localization accurate at the level that the prior map allows (less than 10 m).

Coronavirus and Influenza Viruses: An Overview of Their Differences and Similarities

SARS-CoV-2 is a new virus that is the cause of the current COVID-19 pandemic. We currently do not have a cure and immunity against this pathogen. Influenza viruses, on the other hand, are constantly evolving and undergo various levels of antigenic drift and shift that will become less recognizable by our immune system. This makes it difficult to develop a widespread effective influenza vaccine and also poses a risk of pandemics by leading to the emergence of new strains of zoonotic Influenza. Both Coronaviruses and Influenza viruses are enveloped RNA viruses and one of the primary pathogens affecting human respiration. COVID-19 and Influenza infections have similar transmission routes and symptoms. The reviewed literature indicates that there are important structural differences between COVID-19 and Influenza. These include differences in genome structures, surface proteins, number of strain and subtypes. In addition, incubation times, risk groups, asymptomatic transmission and transmission rate are important difference between the two viruses. However, unlike Influenza, the lack of vaccines and treatments for COVID-19 poses serious difficulties in controlling the spread of the disease. As a result, Coronavirus is spreading rapidly and due to the risk of possible co-infection with Influenza virus, it is extremely important to evaluate COVID-19 and Influenza infection together and developing public health measures accordingly.

Empirical Stock Return Prediction as an Extension of Merton’s Asset Return Model

We extend Merton’s 1976 asset return analysis which relied on intraday trade data to estimate volatility by introducing drift estimation and equity premium dynamics leading to predictability of short run daily returns under appropriate conditions. We find empirical support for the identification of trade dates associated with commencement of change in return behavior as compared to recent past behavior. We show that drift level, change in drift, equity risk premium level, change in equity risk premium level and local variance shock are individually and jointly predictive to determine macro epoch return behavior, as well as identify optimal buy/sell trade dates and price. Our empirical model can be viewed as a super-set framework congruent with Merton’s (1976) findings as well as Lo’s (1995) findings as a subset. Empirical results concur in theory, distributional arguments and time series analysis of previous work on predictability of equity return processes.

Experimental Testing and Numerical Modeling of Robust Unreinforced and Reinforced Clay Masonry Infill Walls, With and Without Openings

This paper presents an overview of the experimental results obtained by combined in-plane/out-of-plane (IP/OOP) tests carried out on robust clay masonry infill walls. The combined tests were carried out on eight full-scale one-bay, one-story infilled reinforced concrete (RC) frames, plus one reference RC bare frame. In four cases, the masonry walls fully fill the RC frame: two walls are made of unreinforced masonry (URM), whereas the other two are made of reinforced masonry (RM), with both vertical and horizontal reinforcement. Each pair of specimens was tested up to different levels of IP drift before carrying out the OOP tests. Four other specimens, still made of URM and RM walls, are characterized by the presence of a central opening, and in one case, the effect of a lintel is analyzed. On the basis of the tests carried out, an analytical model was developed for the analysis of the OOP behavior. It was used to calibrate IP damage degradation models based on the experimental results to define limits for the applicability of well-known flexural and arching mechanism models for the evaluation of the OOP capacity of the infill walls and to evaluate the efficiency of vertical reinforcement. In this work, the experimental campaign is presented, and the results of both experimental tests and numerical analyses are discussed.

A Numerical Investigation on the In-Plane Behavior of Perforated Unreinforced Masonry Walls

Considering architectural constraints, the existence of openings in unreinforced masonry (URM) walls is inevitable. Moreover, the observations of damaged URM buildings after previous earthquakes and the results of experimental studies on the seismic performance of masonry shear walls confirm that the in-plane behavior of perforated walls depends on the coupling of piers and spandrels. Accordingly, some improvements have been made in recent editions of international seismic retrofitting codes. This study is concerned with the in-plane behavior of perforated URM walls through a finite element (FE) study. For this purpose, 3D micromodeling is utilized for the simulation of the masonry walls in the FE software ABAQUS. At first, the FE model is verified using the results of an experimental study on large-scale perforated walls under simultaneous gravity and lateral in-plane loads. The numerical and experimental results show a good agreement with each other which confirms the reliability of the model for the simulation of URM walls. Subsequently, a parametric study is conducted by means of the validated FE model. The pier width and spandrel depth of the walls as well as the intensity of the gravity load on the piers are considered as the influential variables in the numerical investigation. Finally, the results of the numerical study are presented in terms of load–displacement curves, ultimate mode of failure, and the proportions of the internal shear force induced in piers at different story drift levels. According to the results of the current study, the geometrical properties of the walls and the gravity load have a substantial effect on the in-plane strength of the walls. Additionally, the role of spandrels in the global seismic performance of URM walls and piers is not negligible and should be considered in the seismic vulnerability assessment of existing buildings.

COMPARATIVE STUDY OF PERFORMANCE BASED BEHAVIOUR OF MOMENT RESISTING FRAMES WITH STRUCTURAL SHEAR WALLS, CONCENTRIC BRACED FRAMES &amp; BUCKLE RESISTING BRACED FRAMES

Performance evaluation and design of civil facilities against earthquakes is a challenge to engineers because of the large uncertainty in the seismic demand and capacity of structures. The purpose of the study is to perform comparative analytical investigation of performance-based behavior between Moment Resisting Frames with Structural shear Walls, Concentric Braced Frames &amp; Buckle Resisting Braced Frames of a concrete structure by using ETABS-2017 software. The comparative analytical evaluation of the study will be based on the parameters such as displacement, inter-story drift, pushover curve and life expectancy level. The purpose of the study is to obtain a structural system which is more efficient, reliable and strong in its nature and strength.

Impact of bi-directional loading on the seismic performance of C-shaped piers of core walls

Reinforced concrete structural walls are commonly used as the primary lateral load resisting system in modern buildings constructed in high seismic regions. Most walls in high-rise buildings are C-shaped to accommodate elevators or other architectural features. C-shaped walls have complex loading and response including: (1) symmetric response in the direction of the web, (2) asymmetric response in the direction of the flange and (3) high compression and shear demands when used as a pier in a coupled-wall configuration. A research study was conducted on C-shaped walls tested under (1) uni-directional and (2) bi-directional loading of an isolated walls and (3) bi-directional loading of a c-shaped pier in a coupled wall system. Each of the walls failed in flexure with strength loss resulting from low-cycle fatigue of the boundary element longitudinal reinforcement with buckling followed by fracture. The damage progression was as follows: (1) cracking at the wall-foundation interface, (2) concrete spalling in the web, (3) buckling and fracture of web reinforcement, (4) spalling in the flanges, (5) buckling and fracture of the bars in the boundary elements. Concrete spalling and steel bar damage occurred at lower strong-axis drift levels for the bi-directionally loaded, resulting in lower drift capacities for these loading protocols. However, for the strong-axis direction, bi-directional loading does not reduce flexural or shear effective stiffness values suggesting that current values are appropriate for design and evaluation of buildings with c-shaped walls.

Influence of bond property of longitudinal bars on seismic behaviour of reinforced-concrete columns

Four circular fly-ash concrete columns reinforced by steel rebars with different bond levels were tested to investigate the influence of bond strength of longitudinal steel rebar on the seismic behaviours of reinforced-concrete (RC) members. Furthermore, a fibre-element method considering steel bond slip was used to investigate the influence of bond properties of steel rebar on seismic responses of circular RC columns, with the test results used to validate reasonability. The comparison of results shows that the anchorage of the steel rebar has a significant influence on, and the plastic hinge length no effect on, the seismic behaviours of the columns. The analytical and test results show that low bond strength delays the yielding process of steel rebars adjacent to the beam–column interface, which can improve the deformability of RC columns, but does not obviously influence the moment resistance. However, the stiffness of the cross-section is reduced from a certain drift level. Six equations are proposed to predict with very good accuracy the reduced ratio of the stiffness of the cross-section, the enhanced ratios of the drift at the ultimate moment and the drift at the maximum lateral load of the column models reinforced by bonded or unbonded steel rebars.

Investigating the efficiency of DDBD approaches for RC buildings

Direct displacement-based design (DDBD) approach attempts to alleviate the shortcomings of force-based design (FBD) approach to achieve seismic resistance of structures. Many simplified procedures for DDBD proposed in the literature are conceptually similar, yet differ in their considerations for crucial parameters such as target displacement profile, equivalent viscous damping equation and base shear distribution pattern in the design process. Due to variation in the aforementioned parameters, seismic force, their distribution and element design differs, leading to significant changes in the inelastic behavior of the building. The present numerical study compares the performance of low, medium and high-rise RC frame buildings designed using six DDBD approaches for two drift levels. The seismic performance of the considered buildings has been deliberated by both nonlinear static pushover as well as nonlinear dynamic time-history methods. From analysis results, it is observed that the 84th percentile of the sample mean storey displacement of low-rise buildings designed for low storey drift exceeds the target profile, whereas, this behavior is contrary in high-rise buildings designed for higher storey drift. The analysis also highlighted that the parabolic displacement profile consideration for mid and high-rise buildings is rational than the linear displacement profile consideration. In the present case, it seems that equivalent viscous damping estimation and displacement spectra modification factors are conservative for all the DDBD approaches and needs modification to improve its rationality.