Case History on Prevention of the Landslide at Luoyiqi by Means of Rigid Frame Retaining Structure

This paper presents a new special type of retaining structure which prevents the large-scale landslide. It is named the rigid frame retaining structure. The author in this paper proposed a new computation method, i.e., analysis of the rigid frame within elastic foundation. The new formulations have been performed according to E. Ninkler\u27s theory and the difference principle and with the help of fundamental knowledge of strength of material and matrix algebra. The descriptions of the design and construction of the rigid frame retaining structure were given

Hermite polynomial normal transformation for structural reliability analysis

PurposeNormal transformation is often required in structural reliability analysis to convert the non-normal random variables into independent standard normal variables. The existing normal transformation techniques, for example, Rosenblatt transformation and Nataf transformation, usually require the joint probability density function (PDF) and/or marginal PDFs of non-normal random variables. In practical problems, however, the joint PDF and marginal PDFs are often unknown due to the lack of data while the statistical information is much easier to be expressed in terms of statistical moments and correlation coefficients. This study aims to address this issue, by presenting an alternative normal transformation method that does not require PDFs of the input random variables.Design/methodology/approachThe new approach, namely, the Hermite polynomial normal transformation, expresses the normal transformation function in terms of Hermite polynomials and it works with both uncorrelated and correlated random variables. Its application in structural reliability analysis using different methods is thoroughly investigated via a number of carefully designed comparison studies.FindingsComprehensive comparisons are conducted to examine the performance of the proposed Hermite polynomial normal transformation scheme. The results show that the presented approach has comparable accuracy to previous methods and can be obtained in closed-form. Moreover, the new scheme only requires the first four statistical moments and/or the correlation coefficients between random variables, which greatly widen the applicability of normal transformations in practical problems.Originality/valueThis study interprets the classical polynomial normal transformation method in terms of Hermite polynomials, namely, Hermite polynomial normal transformation, to convert uncorrelated/correlated random variables into standard normal random variables. The new scheme only requires the first four statistical moments to operate, making it particularly suitable for problems that are constraint by limited data. Besides, the extension to correlated cases can easily be achieved with the introducing of the Hermite polynomials. Compared to existing methods, the new scheme is cheap to compute and delivers comparable accuracy

Study of microstructure evolution in F/M steel T91 by in-situ synchrotron wide-angle X-rays scattering

T91 ferritic-martensitic (F/M) steel is one of the leading candidates for high temperature structural materials in advanced nuclear power applications. In situ Wide-angle X-ray Scattering (WAXS) was used to investigate T91 during tensile test under 3 different temperatures: room temperature (RT), 450C, 550C, respectively. By fitting scattering patterns, information of diffraction peaks and their variation trends with respect to macroscopic strain were recorded for further analysis of Fe matrix, M23C6 and MX precipitates. Lattice strain of Fe matrix and precipitates were obtained from peaks shift in WAXS pattern during tensile test. Load partitioning effect, which is known as precipitates can bear higher load than Fe matrix, was found to be less obvious within plastic regime with the increase of temperature from RT to 550C. Peak broadening, represented by full width at half maximum (FWHM), was carefully analyzed using modified Williamson-Hall (W-H) plots to separate strain and crystalline size effects due to their different theta dependence. It was found that dislocation density rho in Fe matrix behaved differently within different tensile regimes: before Ultimate Tensile Strength (UTS), they all increased; after UTS, it plateaued first then increased at end for RT, remained stable for 450C while decreased continuously for 550C. Coherent scattering length L310 calculated by Scherrer Equation using Fe(310) plane behaved as below: before UTS, they all decreased; after UTS, it decreased continuously for RT, remained stable for 450C and rose dramatically for 550C. The variation trends of both dislocation density and coherent scattering length L310 were impacted by combination effect from high temperature and tensile flow stress evolution. Scanning Electron Microscopy (SEM), Optical Micropy (OM) and Transmission Electron Microscopy (TEM) were also used to study the post-tensile samples. SEM found that at RT tensile fracture happened violently with huge cracks on necking center cross-section, while fracture happened slowly with voids and dimples on cross-section under higher temperatures. SEM Energy Dispersive Spectroscopy (EDS) mapping also found that rupture protrusions on necking center edges had higher C and N concentration than that of metallic elements. OM revealed the martensitic plates and ferrites in T91 after polishing and etching. Lastly, TEM experiment was also carried out using Focused Ion Beam (FIB) prepared specimen to characterize precipitates, dislocations and other microscale features, and to compare with the previous X-rays Diffraction (XRD) results