Rutherford + Chekene

ABSTRACT We report precise radial velocity (RV) observations of HD 212657 (= K2-167), a star shown by K2 to host a transiting sub-Neptune-sized planet in a 10 d orbit. Using Transiting Exoplanet Survey Satellite (TESS) photometry, we refined the planet parameters, especially the orbital period. We collected 74 precise RVs with the HARPS-N spectrograph between August 2015 and October 2016. Although this planet was first found to transit in 2015 and validated in 2018, excess RV scatter originally limited mass measurements. Here, we measure a mass by taking advantage of reductions in scatter from updates to the HARPS-N Data Reduction System (2.3.5) and our new activity mitigation method called CCF Activity Linear Model (CALM), which uses activity-induced line shape changes in the spectra without requiring timing information. Using the CALM framework, we performed a joint fit with RVs and transits using exofastv2 and find Mp = $6.3_{-1.4}^{+1.4}$ $\, M_{\hbox{$\oplus $}}$ and Rp = $2.33^{+0.17}_{-0.15}$ $\, R_{\hbox{$\oplus $}}$, which places K2-167 b at the upper edge of the radius valley. We also find hints of a secondary companion at a ∼22 d period, but confirmation requires additional RVs. Although characterizing lower mass planets like K2-167 b is often impeded by stellar variability, these systems especially help probe the formation physics (i.e. photoevaporation, core-powered mass-loss) of the radius valley. In the future, CALM or similar techniques could be widely applied to FGK-type stars, help characterize a population of exoplanets surrounding the radius valley, and further our understanding of their formation.

ABSTRACT In recent years, Illinois bridge engineers developed an innovative “quasi-isolation” seismic bridge design methodology. The objectives of this study are to assess the seismic performance of prototype quasi-isolated highway bridges, to validate the design strategy, and to provide recommendations for improving bridge seismic performance. A matrix of bridges was computationally studied. Seismic assessment results validate that the current quasi-isolation design strategy is generally effective in preventing global collapse, but the response of a small number of bridges demonstrated a relatively high risk of bearing unseating and severe pier damage. Recommendations for calibrating the current design strategy have therefore been proposed.

The accuracy of several assumptions made when developing the methodology for nonlinear response history analysis of Chapter 16 of ASCE/SEI 7 is investigated. The major findings of this work include: (1) Modeling the gravity system's lateral influence can have a significant effect on system behavior, but it is generally conservative to neglect its contribution. (2) Exclusion of a residual drift check is acceptable when collapse prevention is the primary objective. (3) Spectrally matched ground motions should cautiously be used for near‐field sites. (4) The effects of nonlinear accidental torsion can be influential, and should be considered for the analysis of torsionally irregular buildings. (5) When analyzed using FEMA P‐695, a structure designed per ASCE/SEI 7 Chapter 16 may have a probability of collapse that is different than the target value associated with the system's risk category.

Chapter 16 of ASCE 7 governs the selection of ground motions for analysis of new buildings and requires recordings that meet specified criteria. If a sufficient number of recordings cannot be found, it allows the use of “appropriate simulated ground motions,” but does not provide further guidance. This paper outlines a procedure for generating and selecting a set of “appropriate” hybrid broadband simulations and a comparable set of recordings. Both ground motion sets are used to analyze a building in Berkeley, California, and the predicted structural performance is compared. The structural behavior resulting from recordings and simulations is similar, and most discrepancies are explained by differences in directional properties such as orientation of the maximum spectral response. These results suggest that when simulations meet the criteria outlined for recordings in ASCE 7 and properties such as directionality are realistically represented, simulations provide useful results for structural analysis and design.

This research proposes a new shear strength model, based on modifications to the UCSD shear model by Kowalsky and Priestley [2000], to calculate the shear capacity and predict the displacement ductility of reinforced concrete walls in diagonal tension. An experimental database is created from a literature review of experimental tests of reinforced concrete walls that exhibit strength degradation and shear failure during cyclic loading. This experimental database is used in the formulation of the proposed shear model and to test the accuracy of the model. The proposed model improves the accuracy of calculating pre-emptive shear and flexure-shear strength, correctly identifies the failure mode for all collected specimens, and provides the closest prediction of the ultimate displacement ductility. Based on this research, the proposed shear model is recommended for the calculation of the shear strength of reinforced concrete walls for either the assessment of existing buildings or the design of new structures.

Delhi, India faces substantial earthquake hazards from both distant, large-magnitude earthquakes in the Himalayas and smaller, local events. Delhi has many seismically vulnerable school buildings, in both government and private schools. GeoHazards International (GHI) has been working for several years with the Government of the National Capital Territory of Delhi and private sector partners, in order to reduce the earthquake risk to Delhi's schools. In the course of these efforts, GHI encountered a type of "semi-permanent," unreinforced brick school building with a particularly vulnerable type of roof constructed from steel I-beams and heavy, flat stone slabs. The stone slabs and beams are not attached to each other or to the supporting brick walls so that the building could, theoretically, be dismantled and moved to a new location. However, this lack of connection means that during strong shaking, stones could fall on students and teachers. This paper describes the unique design problem that these unusual semi-permanent buildings pose and the retrofit and conceptual new construction solutions that could reduce the earthquake risks that the buildings pose to students and teachers.

Built in 1927 from reinforced concrete, Bowles Hall is the oldest dormitory at University of California, Berkeley campus. In 2007 a fault-displacement hazard analysis commissioned by the University found that two corners of the structure sit atop a potentially active western fault trace of the Hayward fault. Rutherford & Chekene Structural and Geotechnical Engineers (R&C) evaluated the structure's seismic performance for shaking and for fault offset. To understand how buildings respond to ground offset, R&C reviewed reports of earthquakes where surface fault rupture occurred under structures. Based on the evaluation and retrofit design of Bowles Hall for earthquake fault offset, and on the review of research on fault-offset effects on structures, the authors have developed recommendations for designing for such a hazard. The recommendations include a general evaluation procedure, a consideration of influential variables, an identification of mitigation strategies, and draft building code requirements and commentary. Retrofit measures for Bowles Hall, constructed in July and August 2009, include new retaining walls at the hillside behind the building to limit soil pressure against the structure, and new foundation slabs over the fault zone. These measures are designed to allow surface fault displacement to occur without causing significant damage to the building.

The Australian coal industry is critical for the nation’s domestic energy supply and economy with an export value of almost A$24 bn in the fiscal year 2007/08. With almost 75% of production destined to the export market, Australia is also the world’s largest hard coal exporter and an essential secure source of energy particularly to meet both thermal and metallurgical coal demand in the fast growing Pacific Rim.

Efforts at improving earthquake recovery policies have been hampered by a lack of criteria and standards for evaluating and repairing damaged buildings. The Applied Technology Council has developed a performance-based methodology for the evaluation of earthquake-damaged concrete wall buildings and masonry wall buildings, recently published as FEMA 306/307/308. The methodology provides a way to quantify damage in terms of loss of seismic performance capability. It also provides guidelines for remedial measures to restore or improve seismic performance capability. In this methodology, the expected future seismic performance of a building is evaluated in its pre-event, damaged, and repaired conditions. Following the nonlinear static analysis procedure, displacement demands and capacities of the structure are used as indices of seismic performance. Identifying the governing mechanism of nonlinear deformation and the behavior mode of a structure and its components is shown to be a necessary first step towards evaluating expected seismic performance, interpreting indications of damage, and assessing their significance. The methodology provides a technical resource for understanding how buildings respond seismically on both global and component levels, and gives a basis for formulating post-earthquake policies.