Search

A mainshock is usually accompanied by a group of ground motions. In many design codes, the effects of the seismic sequences have been neglected or underestimated. Aftershocks can increase structural damage or even cause failure. The current study evaluated the seismic behavior of a rehabilitated and as-built reinforced concrete (RC) structure under real scaled mainshock-aftershocks using nonlinear analysis. Verification was done in three modes. The inter-story drift ratio, maximum residual, and relative displacements were studied. The seismic study of the as-built structure showed that the residual displacement grew, on average, more than 78% under the mainshock-aftershock sequence compared to the mainshock-only record. A beam-column bonded Carbon-fiber-reinforced polymers (CFRP) rehabilitation strategy using six layers of T-700 CFRP was chosen based on the specific performance level. The strategy showed the ability to transfer the plastic strain from the columns to the beams, which could be considered as a change from a weak column-strong beam concept to a strong column-weak beam concept. Compared to the as-built structure under the seismic sequences, the rehabilitated structure showed an average growth of − 81% in the first-story drift ratio, which was significant. Unlike the as-built structure, seismic sequences caused no growth drift in the rehabilitated structure. It also was observed that the ratio of aftershock peek ground acceleration (PGA) to mainshock PGA could have an intensive effect on the seismic behavior of both rehabilitated and as-built structures. [ABSTRACT FROM AUTHOR]

This paper investigates the performance of the Magnetorheological damper as a smart dissipating device in the isolated buildings for prevention of seismic pounding. To that end, an isolated building was modeled by considering the pounding effect with different gap distances. Multi-objective optimization was performed to optimize the fuzzy logic control of damper for each gap distance. The results showed that the optimized semi-active control system can prevent the pounding of the building and greatly improve the structure's behavior as compared to the isolated pounded building and even to the case without the pounding at some considered gap distances. [ABSTRACT FROM AUTHOR]

The core objectives of sustainable development are to develop access to renewable, sustainable, reliable, and cost-effective resources. Wind is an essential source of renewable energy, and monopile wind turbines are one method proposed for harnessing wind power. Offshore wind turbines can be vulnerable to earthquakes and liquefaction. This numerical study defined the effects of wind turbine weight on the seismic response of a wind turbine-monopile system located in liquefied multilayered soil with layer thicknesses of 5, 10, 15, and 20 m using four far-field records. OpenSees PL analysis indicated that if the liquefied sand had a lower density or a thickness of more than 10 m, then an increase in the earthquake acceleration beyond 0.4 g caused the pile to float like liquefied soil and to lose its vertical bearing capacity. Moreover, increasing the wind turbine power from 2 to 5 kW had no significant effect on the soil-structure interaction response. As the earthquake acceleration increased, the bending moment of the pile-column also increased as long as liquefaction did not occur and the pile-column deformation remained rotational-spatial in shape. As the acceleration and liquefaction increased and the pile began to float in response to its transverse motion, there was no significant difference in the pile-column displacement along the length, but there was a decrease in the pile-column bending moments. As this phenomenon increased and the pile continued to float, transformation of the pile increased the difference between the displacement of the pile-column along its length and further increased the bending moments. These results were derived from multiple correlation analysis, the bending moment relations, and lateral displacement of the pile-column of the wind turbine. [ABSTRACT FROM AUTHOR]

This study presents an energy-based procedure for the design of RC frames under earthquake strong motions. For this purpose, three RC frames having 4, 8, and 12 stories that were used in FEMA P695 were selected. The code-based designed frames were analyzed and redesigned employing the proposed energy-based procedure. A comparison was conducted between the performance of the code-based and energy-based designed models. Results reveal that the energy-based models appeared to perform more effectively under strong ground motions in terms of more optimized use of beam capacity for dissipation of energy, higher ductility values, and more uniform distribution of plastic hinges in height of structure. Comparison of pushover curves showed that ductility value in energy-based frames increases nearly 1.5–2.0 times the ductility of code-based frames. Calculated hysteretic energy demand in energy-based frames is also proved to decline by 50% in lower stories and, instead, the contribution of upper stories is increased. The same pattern for distribution of interstory drift ratio is also observed. [ABSTRACT FROM AUTHOR]

Colonizing other planets, like Mars, marks a significant milestone in the pursuit of a multi-planetary existence. Millions of people would settle on Mars in self-sufficient bases. Colonizing Mars is a long-term mission that demands self-sufficient, secure habitats and comprehensive planning. Importing structures, such as inflatable structures, from Earth is cost-prohibitive, making the utilization of in-situ resources and onsite construction the most viable approach for preparing the required buildings. Studies have shown that it is possible to produce and craft several kinds of binders and concretes with appropriate mechanical behavior using Martian soil composition; however, determining the optimal option for onsite construction remains a challenge. This study investigates available cement/concrete options for onsite construction on Mars from a structural engineering perspective, taking into account the available resources and technologies. In this regard, the observations and data provided by Martian landers, rovers, orbiters and methods such as Viking-1 & 2, Pathfinder, Spirit, Opportunity, Curiosity, Mars Express, Ultraviolet–visible/Near-infrared reflectivity spectra and Alpha particle X-ray spectrometer were used to obtain a comprehensive and detailed investigation. Eleven types of Martian cement/concrete based on the in-situ resources, soil composition, and available technologies were compared based on the criteria and indices defined in accordance with the structural engineering point of view to select the best practical option for onsite construction. These criteria encompass factors such as mechanical behavior, Martian structural loads, raw material accessibility, available sources, energy required for production, water requirement, curing and hardening time, possibility of using 3D printers, byproduct usefulness, conditions required for hardening and curing, importation requirements from Earth, production complexity, long-term durability and behavior under galactic cosmic rays (GCRs) and solar energetic particles (SEPs). The pros and cons of each cement/concrete option are thoroughly assessed, considering the harsh conditions on Mars. Additionally, the study highlights extra considerations that are crucial for onsite construction on Mars. To determine the best practical option for onsite construction and sustainable colonization, the proposed cements/concretes were compared using multi-scale spider/radar diagrams and a quantitative point of view. This perspective was enabled by assigning weights to each criterion through expert consultation, experimental data, and literature review, ensuring that the diagrams accurately reflect the features of each concrete mix. This comprehensive investigation aims to provide valuable insights into selecting the most suitable cement/concrete for onsite construction on Mars, considering the structural engineering perspective and the long-term goal of sustainable colonization. • The Martian soil composition is investigated using data from Martian landers and orbiters. • Eleven types of Martian concrete/cements are proposed based on available resources and technologies. • Structural engineering criteria and indices are defined to select the best option for onsite construction. • The best practical option for onsite construction is determined using multi-scale spider/radar diagrams. [ABSTRACT FROM AUTHOR]

This study numerically evaluated the retrofitting of RC columns using different transverse rebar arrangements and retrofitting methods using European standard I-section profile (IPE) and fiber-reinforced polymer (FRP) coatings. The degree of deformation, failure pattern of the element, and residual axial strength of the RC columns after exposure to a blast were the performance criteria. Fifteen different models were evaluated to determine the effect of spacing and arrangement of rebars and the effect of FRP and IPE retrofitting. The results indicated that the RC element with transverse rebars with branches showed the least amount of deformation. Furthermore, the damage and deformation of the structure against blast loading decreased by 25% and 20%, respectively, when applying I-shaped profiles and RC columns with FRP coating. The residual capacity of the columns was highest in the models retrofitted with FRP and IPE. [ABSTRACT FROM AUTHOR]

The current study compares the effect of structure-soil-structure interaction (SSSI) on the dynamic responses of adjacent buildings and isolated structures including soil-structure interaction (SSI) with the responses of fixed-base structures. Structural responses such as the relative acceleration, displacement, drift and shear force were considered under earthquake ground motion excitation. For this purpose, 5-, 10- and 15-story structures with 2-bay moment resisting frames resting on shallow foundations were modeled as a group of buildings in soft soil media. Viscous lateral boundaries and interface elements were applied to the soil model to simulate semi-infinite soil media, frictional contact and probable slip under seismic excitation. The direct method was employed for fully nonlinear time-history dynamic analysis in OpenSees using 3D finite element soilstructure models with different building positions. The results showed that the responses of the grouped structures were strongly influenced by the adjacent structures. The responses were as much as 4 times greater for drift and 2.3 times greater for shear force than the responses of fixed-base models. [ABSTRACT FROM AUTHOR]

A parametric survey was conducted to capture the dynamic response of a thin beam subjected to a varying speed moving mass. The existing literature lacks a comprehensive study on the beam dynamic behavior under a varying speed moving mass with arbitrary constant acceleration and mass ratio. The current work represents midpoint response spectra for a thin beam acted upon by a varying speed moving mass for a wide range of design parameters. Findings show that for a given mass ratio, higher response amplitudes are observed in decelerating motion compared to accelerating one. Moreover, increasing the mass ratio of the moving mass generally leads to higher beam dynamic response. Among the methods that can be utilized to calculate beam response, the Eigenfunction expansion method (EFM) and Orthonormal polynomial series expansion method (OPSEM) were used. Then an improvement technique was applied on both aforementioned methods and computational efficiency and convergence rate of all utilized methods was compared. [ABSTRACT FROM AUTHOR]

The major obstacle to Martian colonization is the mission cost which requires significant reduction. From the structural engineering point of view, importing materials and structural elements from Earth or massive excavations on the surface of Mars require an enormous amount of energy; thus, inflatable and under-surface structures as the main options for Martian colonization seem unrealistically expensive. Construction of affordable buildings onsite using only in situ sources may represent an ideal solution for Martian colonization. On the other hand, solar energy, at the early stage of colonization, would be the only available, practical, and low-cost energy source on Mars. Though, for sustainable and broad colonization, the energy required for construction and the construction cost should be minimized. Here, we propose three types of simple (relatively optimized), perforated, and algorithmic shape-optimized Martian structures to minimize the material and energy required for construction as well as the construction cost using only in situ resources. These structural forms can be considered remarkable steps towards sustainable structural construction and colonization on Mars. Also, these innovative structures were designed to minimize the tensile stress (maximize the compressive stress) and enable the use of in situ concrete. Our data indicate that compared to our previous study, the material and energy required for construction as well as the construction cost can be reduced by more than 50%. Acceptance criteria and limitations appropriate to the Martian environment, and desirable structural and material behaviors were defined to evaluate whether or not the behavior of a structure under the applied loads and conditions will be acceptable. To detect potential issues for onsite construction and evaluate the geometry of the models, a 1:200 3D model of the best structural form was printed. [ABSTRACT FROM AUTHOR]

• Martian colonization using onsite construction requires a structural load combination. • Probable Martian structural loads are calculated and studied. • The valid data from landers, rovers, and orbiters are used for the study. • Martian structural loads are calculated based on the worst-case scenario. • A combination of loads is proposed for the design of Martian buildings. Multiplanetary life has been studied by scientists as a way to supply energy or sustain human life in the future. Mars is likely to be man's first destination, colonization using onsite structural construction would be one of the main options. The first step to designing a reliable building is to know the applied structural loads and to have an accurate design load combination. Due to lack of complete knowledge, short span of recorded data, Martian environment, and hazardous environment that Martian structures face, constructed Martian structures should behave appropriately under the highest likely live, dead and environmental loads either simultaneously or as a worst-case scenario. The present study evaluated and calculated probable Martian structural loads, including live, internal pressure, snow, gravity (dead), dust accumulation, thermal stress, wind, marsquake, asteroid, and meteoroid impact loads and their effects. Information was gathered from previous studies and valid data from Martian landers, rovers and orbiters. Wind loads were calculated based on the over 6.5 years of data recorded by Vikings 1 and 2, temperature and winds for InSight (TWINS) sensor. A wind shear exponent and wind profile have been proposed for a Martian flat terrain construction site. Marsquake lateral loads, frequency content and seismicity were assessed using data from the seismic experiment for interior structure (SEIS) and the Viking 2 seismometer. Considering the high influx of micrometeoroids, their penetration distance, impact loads and their effects on structures were calculated. The annual probability of an asteroid impact on a settlement was assessed for a 30-year mission. A load map for Martian residential buildings that considers the worst-case scenario in which a Martian structure should be designed based on them has been proposed. [ABSTRACT FROM AUTHOR]

A new bending connection between a steel beam and concrete-encased composite column (CEC S) with a bolted flange plate is proposed which maintains the integrity of the column and allows for the interchangeability of the beam for improvement of the connection. The confinement of the steel plates and the central steel core (H-section column) is provided by reinforced concrete and cover plates, thus lateral torsional and local buckling of the through plate (TP) and the central core is prevented. Three full-scale samples of the proposed exterior connection with variable TP thickness and different bending capacities under lateral cyclic and constant axial loads in the column were tested. The moment contribution in the components and seismic behavior of the connection were studied. The load transfer to the panel zone occurred through four components in the bending plane; TP, concrete performance, tensile studs, and side plates. The average share of the resistant elements which is immediately behind the front plate were determined as 56%, 26%, 12.50%, and 5.5%, respectively. The internal panel zone remained undamaged and the stresses were below the yield limit, so that the plastic hinge could occur outside the connecting members in the beam. In general, the specimens with sufficient pre-tensioning in the connection bolts had stable hysteresis curves and less pinching. In addition, these specimens showed acceptable energy dissipation that provided a high ductility index. • Integrity of the column and continuity of the longitudinal reinforcement in the internal panel zone • No requirement for transverse reinforcement in the region of the internal panel zone • The confinement of the through plate and the central steel core by reinforced concrete and cover plates • Determination of moment contribution of the connection components using analytical method and experimental tests • Showing acceptable cyclic behavior and appropriate energy dissipation [ABSTRACT FROM AUTHOR]

Aim: The aim of this study was to compare the different phases of chronic Hepatitis B virus (HBV) infection with different values for normal ALT. Background: For many years, the upper limit of 40 IU was considered normal for ALT for both sexes, but in recent years this value is challenged and some guidelines have lowered their limit. Methods: In this cross-sectional study, 2000 HBsAg positive patients who were referred to Taleghani Hospital, Tehran, Iran, from 2011 through 2018 were classified in four groups according to American Association of the study of the liver disease (AASLD), European Association of the study of the liver (EASL) /Asian-Pacific Association of the study of the liver (APASL) and American Collage of Gastroenterology (ACG) guidelines. The frequency of each group based on 3 different guidelines was compared. Results: In HBeAg positive patients (n=100), the percentage of immune tolerance phase was 43% according to AASLD cutoff for normal ALT (35 IU for men, 25 IU for women), while it was 68% and 28% with regard to EASL/APASL and ACG (30 IU for men, 19 IU for women) cutoffs respectively. In HBeAg negative patients (n=1900), 66.68% were inactive carriers according to AASLD, but the percentage changed to 82.89% and 52.42% considering EASL/APASL and ACG values, respectively. Conclusion: Using ACG and to a lesser extent AASLD cutoff for ALT, many patients shift from immune tolerance and inactive carrier state into the immune active phase. Thus, more patients are candidates for treatment or intensive workup to determine the extent of liver damage. [ABSTRACT FROM AUTHOR]