Advancing performance-based design and assessment of exposed column base plates and welded column splices in steel moment resisting frames

Exposed column base plate (ECBP) and welded column splice (WCS) connections are critical load-carrying structural connections and are commonly used in steel moment-resisting frames (SMRFs). However, they have received relatively lower research attention than welded beam-to-column (WBC) connections, leaving several relevant aspects of their performance and their effects on the overall seismic performance of SMRFs not well investigated. For instance, although the current design approach for ECBP connections is relatively well-established from a mechanistic standpoint, the reliability of such designed connections (i.e., the structural performance of ECBPs at the design level) is not as well understood. Therefore, some prospective refinements to the current approach may be developed to ensure acceptable and consistent failure probabilities across the various components of the ECBP connections. In the context of WCS connections constructed before the 1994 Northridge earthquake (i.e., pre-Northridge WCSs), their potential fracture due to earthquake shaking has been recently revealed in some research studies. However, these studies did not take advantage of recent advancements in performance-based earthquake engineering (PBEE), and made several simplifying assumptions for practical purposes. Some refinements and research tools within the PBEE framework may be required to more accurately estimate the fracture demand and capacity distributions, and the associated fragility and risk of pre-Northridge WCSs. This doctoral dissertation attempts to address these mentioned issues in a rigorous manner. Specifically, this dissertation presents the following research studies: 1. Detailed reliability analysis of ECBPs designed as per the current design method and two modified approaches (improved from the current one) for a set of 59 design scenarios subjected to combinations of gravity, wind, and seismic loads. This also includes the Monte Carlo sampling to characterize the uncertainty sources in the load, material properties, component geometry, and demand/capacity models for various components within the connection. 2. Refined probabilistic fracture fragility assessment of pre-Northridge WCSs, accounting for the seismic demand and fracture capacity uncertainties. Optimal ground-motion intensity measures, the effect of vertical ground accelerations, and the WCS capacity uncertainties are included to improve the fracture fragility estimation. 3. Expanded fracture fragility and risk assessment of pre-Northridge WCSs in near-fault regions to address the effect of pulse-like ground motions on the distribution/increase of WCS seismic demands. Near-source probabilistic seismic hazard analysis is conducted to facilitate the fracture risk assessment. The findings of the first study can contribute to the better scientific knowledge of reliability-based design and assessment of ECBP connections in SMRFs, whereas the last two studies can help better understand the fracture risk of WCS connections in SMRFs, and inform the planning of retrofitting strategies

Gravitational waveform model based on photon motion for spinning black holes

The waveforms from binary black hole mergers include inspiral, merger and ringdown parts. Usually, the inspiral waveform can be obtained by calibrating from post-Newtonian approximation; The merger and ringdown ones can be gotten from the quasi-normal modes (QNMs) with black hole perturbation theory. However, for more general black holes, the calculation of the quasi-normal modes is not trivial. In this paper we use the photon sphere to get the quasi-normal modes of spinning black hole. Then we connect the ringdown wave with the inspiral part to get full waveforms and compare with the ones from numerical relativity(NR). We find that they match with each other very well. In principle this method can be extended to arbitrary black holes. As an example, the ringdown waveforms from parametrized axisymmetric black hole are obtained. We also use this method to get ringdown signals of the accelerating final black hole due to gravitational recoil during the merger. Even for the extreme cases, the acceleration due to the recoil can not produce detectable effects.Comment: 14 pages, 12 figure

Five-dimensional metric f(R)f(R) gravity and the accelerated universe

The metric $f(R)$ theories of gravity are generalized to five-dimensional spacetimes. By assuming a hypersurface-orthogonal Killing vector field representing the compact fifth dimension, the five-dimensional theories are reduced to their four-dimensional formalism. Then we study the cosmology of a special class of $f(R)=\alpha R^m$ models in a spatially flat FRW spacetime. It is shown that the parameter $m$ can be constrained to a certain range by the current observed deceleration parameter, and its lower bound corresponds to the Kaluza-Klein theory. It turns out that both expansion and contraction of the extra dimension may prescribe the smooth transition from the deceleration era to the acceleration era in the recent past as well as an accelerated scenario for the present universe. Hence five-dimensional $f(R)$ gravity can naturally account for the present accelerated expansion of the universe. Moreover, the models predict a transition from acceleration to deceleration in the future, followed by a cosmic recollapse within finite time. This differs from the prediction of the five-dimensional Brans-Dicke theory but is in consistent with a recent prediction based on loop quantum cosmology.Comment: 14 pages, 9 figures; Version published in PR

Clinical significance of stanniocalcin-1 detected in peripheral blood and bone marrow of esophageal squamous cell carcinoma patients

BACKGROUND: Stanniocalcin-1 (STC-1) is a potential marker of disseminated tumor cells (DTCs). The aim of this study was to examine STC-1 expression in peripheral blood (PB) and bone marrow (BM) of esophageal squamous cell carcinoma (ESCC) patients, and to evaluate its clinical significance. METHODS: A total of 85 ESCC patients treated with radical resection were enrolled in this study. Immunohistochemistry was used to detect STC-1 protein expression in ESCC tissues. Nested RT-PCR was used to detect STC-1 mRNA expression in PB and BM. RESULTS: There were 71 cases (83.5%) showed a higher level of STC-1 protein expression in tumor tissues than in adjacent normal tissues (P < 0.001). Furthermore, the frequencies of STC-1 mRNA expression detected in PB and BM were 37.6% (32/85) and 21.2% (18/85), respectively, and together increased sensitivity to 48.2% (41/85), which was much higher than that in patients with benign esophageal disease (5.0%, 2/40, P < 0.001). In addition, STC-1 mRNA expression either in PB or BM was correlated with lymph metastasis, advanced stage and adverse 2-year progression free survival (PFS). In a multivariate analysis using the Cox proportional hazard model, STC-1 expression in PB and/or BM was an independent unfavorable prognostic factor for ESCC, apart from lymph metastasis and clinical stage. CONCLUSIONS: STC-1 mRNA expression is a reliable marker for detection of DTCs in PB and BM of ESCC patients, and STC-1-positive DTCs may be a promising tool for diagnosis and prognosis assessment in ESCC