How to consider the effects of time of day, beam strength, and snow cover in ICESat-2 based estimation of boreal forest biomass?

Spaceborne lidar sensors have potential to improve the accuracy of forest above-ground biomass (AGB) estimates by providing direct measurements of 3D structure of forests over large spatial scales. The ICESat-2 (Ice, Cloud and land Elevation Satellite 2), launched in 2018, provides a good coverage of the boreal forest zone and has been previously shown to provide good estimates of forest canopy height and AGB. However, spaceborne lidar data are affected by various conditions, such as presence of snow, solar noise, and in the case of ICESat-2, the power difference between the so-called strong and weak beams. The aim of this study was to explore the effects of these conditions on the performance of AGB modeling using ICESat-2 photon data in a boreal forest area. The framework of the study is multiphase modeling, where AGB field data and wall-to-wall airborne laser scanning (ALS) data are used to produce proxy ALS plots on ICESat-2 track positions. Models between the ALS-predicted AGB and the ICESat-2 photon data are then formulated and evaluated by subsets, such as only strong beam data captured in snowy conditions.Our results indicate that, if possible, strong beam night data from snowless conditions should be used in AGB estimation, because our models showed clearly smallest RMSE (27.0%) for this data subset. If more data are needed, we recommend using only strong beam data and constructing separate models for the different data subsets. In the order of increasing RMSE\%, the next best options were snow/night/strong (30.5%), snow/day/strong (33.6%), and snowless/day/strong (34.2%). Weak beam data from snowy night conditions could also be used if necessary (31.1%).

Seismic Assessment and Rehabilitation of a RC Structure Under Mainshock-Aftershock Seismic Sequences Using Beam-Column Bonded CFRP Strategy

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 RC structure under real scaled mainshock-aftershocks using nonlinear analysis. Verification was done in two 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 90% under the mainshock-aftershock sequence compared to the mainshock-only record. A beam-column bonded 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 78% 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 PGA to mainshock PGA could have an intensive effect on the seismic behavior of both rehabilitated and as-built structures.

New Types of Dissipative Streaming Instabilities

Two new, previously unknown types of dissipative streaming instabilities (DSI) are substantiated. They follow from new approach, which allows solving in general form the classical problem of an initial perturbation development for streaming instabilities (SI). SI is caused by relative motion of the streams of plasma components. With an increase in level of dissipation SI transforms into a DSI. The transformation occurs because dissipation serves as a channel for energy removal for the growth of the negative energy wave of the stream. Until recently, only one type of DSI was known. Its maximal growth rate depends on the beam density nb and the collision frequency ν in the plasma as ∼nb/ν. All types of conventional beam-plasma instabilities (Cherenkov, cyclotron, etc.) transform into it. The solution of the problem of the initial perturbation development in systems with weak beam-plasma coupling leads to a new type of DSI. With an increase in the level of dissipation, the instability in these systems transforms to the new DSI. Its maximal growth rate is ∼nb/ν. The second new DSI develops in beam-plasma waveguide with over-limiting current of e-beam. Its growth rate ∼nb/ν. In addition, the solutions of abovementioned problem provide much information about SI and DSI, significant part of which is unavailable by other methods.

A Comparative Study on Seismic Assessment of Building Using SMA in Base Isolation and Beam Column Joints

The seismic design of the moment-resistant plastic frames is aimed at forcing the structure to respond to the strong action of the weak beam, in which plastic loops are expected to form into beams on the faces of the columns. The regions of the khang are described in detail in such a way that the output of longitudinal steel bars allows to dissipate the energy of the earthquake. If SE SMA is used as a reinforcement instead of steel in the right places of the hinges or in the basic insulation, it will not only be able to dissipate adequate seismic energy, but also restore its original shape after the seismic event. Due to the higher cost compared to the cost of other building materials, SMA longitudinal ribs can be used together with steel ribs in the articulated areas of the beams. Such BCJs can allow design engineers to design connections that show minor damage and mitigate joint repairs after an earthquake. Keywords: Seismic, base isolation, SMA, beam, column & joints

Dislocation contrast on X-ray topographs under weak diffraction conditions

The contrast of dislocations in 4H-SiC crystals shows distinctive features on grazing-incidence X-ray topographs for diffraction at different positions on the operative rocking curve. Ray-tracing simulations have previously been successfully applied to describe the dislocation contrast at the peak of a rocking curve.The present work shows that the dislocation images observed under weak diffraction conditions can also be simulated using the ray-tracing method. These simulations indicate that the contrast of the dislocations is dominated by orientation contrast. Analysis of the effective misorientation reveals that the dislocation contrast in weak-beam topography is more sensitive to the local lattice distortion, consequently enabling information to be obtained on the dislocation sense which cannot be obtained from the peak.

Seismic Behavior of Top-weld Bottom-bolt Joints between CFST Columns and H-beams

In recent decades, connections between concrete-filled steel tubular columns (CFST) and H-steel beams have been well designed and implemented. However, owing to poor construction quality, brittle failure often occurs at weld seams. In this study, an innovative joint was developed to connect CFST columns and H-steel beams using a top-weld bottom-bolt (TWBB) connection to minimize the effect of welding quality on the seismic resistance of joints. Six specimens were designed for cycle-reversed loading tests to discuss the seismic performance of this joint. Four configurations, including different connection methods, beam heights, column forms, and stiffener thicknesses, were considered in the test. The impacts of different configuration forms on the failure mode, strength, stiffness, ductility, and energy dissipation of the specimens were evaluated. The test results demonstrated that the columns with or without concrete had a significant effect on the deformation capacity. However, a smaller effect was observed on other indicators. The replacement of the through-diaphragm and an increase in the beam height adversely influenced the ductility of the joint. Moreover, changing the stiffener thickness and using a full-bolted connection affected the failure mode. The joint type analyzed in this study satisfies the strong column–weak beam design criterion and the related seismic provisions.

Seismic Analysis of Multi Storey Building Using Strong Column Weak Beam Ratio (SCWB) in Different Zones of India

An earthquake structures are mandatory to avoid significant damages (i.e., collapse) and aims that structure withstand a major earthquake without collapse. The design approach adopted is to ensure that the columns of the structure more capable to resist moments than beam; to avoid progressive collapse of structure due to failure of columns in lower level; it is necessary the columns have stronger than beams (strong column weak beam). The concept of SCWB is to ensure that plastic hinge formed in the beam not in the column; this help in dissipating the more energy along with providing ductility to the structure. If the plastic hinge is formed on the both ends of column then, the column is not able to spread the plasticity and collapse which are leads to global failure. The failure modes in all past earthquake is exactly opposite i.e, strong beam weak column; and comes to sway mechanism and fails to collapse. For this it is foreseen that the values of ratio of Mc/Mb (ratio of sum of ultimate moment of resistance of columns to sum of ultimate moment of resistance of beam) in the beam-column joint are stated by many design codes and the values are different ranging from 1.2,1.3,1.4,1.5 to 2, etc. Another effect of ratio Ic/Ib (ratio of moment of inertia of column to moment of inertia of beam) have been studied but the exact meeting of SCWB behaviour in the structures at the time of collapse not stated clearly. The Mc/Mb and Ic/Ib ratio are very important to prevent damage in the structure under seismic action. In the present work, attempts are made to achieve exact ratio of exact strong column weak beam. In this study, the combined effect of two ratio (Mc/Mb, Ic/Ib) simultaneously investigated in different zones of India to find out exact SCWB ratio’s value for to meet the SCWB behaviour. Different numerical examples are presented of combine ratios (Mc/Mb,Ic/Ib) and pushover analysis is performed on each ratio’s. The result of the investigation highlighted on the objective that is to find exact SCWB ratio value considering the parameter like target displacement, ductility ratio, hinge response etc.