Calculation of Maximum Permissible Load Currents under Cyclic Loading Conditions for Cables Laid in the Ground and in Pipes in the Ground

A method for calculating the maximum permissible load current under the conditions of cyclic daily load curve is developed. A system is suggested for parallel cables laid in the ground, including in pipes. The coefficients for determining permissible load currents are calculated for different laying variants. Calculated data for cables arranged in 2 × 2 and 2 × 4 blocks are presented.     

Effect of Weight and Compensation Loads on the Deformation of a Steam Conduit

The effect of hoop strain over the pipe perimeter and changes in the diameters of the cross section under long-term loading of the steam conduit due to the internal pressure and bending moment are considered. It is shown that the bending moment can be evaluated by measuring the residual strain of the pipe.     

基于安全余量的污染物总量控制方法评述

借助污染物最大日负荷量（TMDL）的相关研究成果,阐述安全余量（MOS）的特征。结合安全余量的表现形式,阐述隐式、显式、FOEA计算安全余量的流程。对安全余量的定量化及其负荷分配研究是推动TMDL策略完善的关键。在梳理以往研究成果的基础上,从安全余量的产生机理出发,分析与污染物总量控制相关的安全余量计算过程。在考虑安全余量的前提下,依据水环境质量的控制目标,结合环境容量所允许的污染物排放量,论述了基于数学模型测算、可持续管理策略的污染物总量控制方法。以永定河流域污染物容量总量分配为例,进行基于安全余量的污染物分配应用研究,对有效减少污染物排放总量、实现水功能区水质达标具有重要意义。     

水力条件对芦苇湿地系统DO质量浓度的影响

就水位及水力负荷对湿地系统中DO质量浓度的影响进行实验。结果表明：随着水位的不断提高,芦苇湿地系统中的DO质量浓度呈现出不断升高的趋势,且在300～550 mm水位区间增加趋势比较明显,随着水位的再度升高,在550～650 mm水位区间DO质量浓度增加趋势趋于平稳;随着水力负荷的不断增加,芦苇湿地系统中的DO质量浓度呈现先增加后减小的趋势,本实验中最适合的水力负荷在0.8968～1.2230 m3/（ m2＆#183; d）之间。     

Urban total phosphorus loads to the St. Clair-Detroit River System

The St. Clair-Detroit River System watershed is a large, binational watershed draining into the connecting channel between lakes Huron and Erie. In addition to extensive agricultural lands, it contains large urban areas that discharge phosphorus from point source facilities, runoff of impervious surfaces, and overflows of combined sewers. To help guide actions to reduce phosphorus input to Lake Erie, we analyzed the spatial and temporal dynamics of loads from the three largest urban areas in the watershed (southeast Michigan; Windsor, Ontario; and London, Ontario), and used a previously calibrated storm water management model (SWMM) to explore options for reducing loads around metro Detroit. Point sources in these three urban areas contribute, on average, 81% of the total urban load and 19% of the Detroit River’s total phosphorus (TP) load to Lake Erie, while combined sewer overflows and runoff both contribute about 10% each to the urban load and about 2.5% each to the Detroit River’s load to Lake Erie. Most of the urban load (56%) comes from a single point source, the wastewater treatment facility in Detroit; however, TP loads from that facility have decreased by about 51% since 2008 due to improvements in wastewater treatment. Model simulations suggest that increasing pervious land area or implementing green infrastructure could help reduce combined sewer overflows in certain upper portions of the metro Detroit sewer system, but reductions were much less expressed for wet-weather discharge from the system.     

Needed: Early-term adjustments for Lake Erie phosphorus target loads to address western basin cyanobacterial blooms

For Lake Erie, it is already time to revise the phosphorus target loads set to address the problem of cyanobacterial blooms in the Western Basin. Current targets were proposed by the Annex 4 task group in 2015, adopted by U.S. and Canadian governments in 2016, and set as objectives of domestic action plans in 2017. These targets, applicable to all spring discharges below the 90th percentile, set a maximum load for both total phosphorus (TP) and dissolved reactive phosphorus (DRP) equivalent to 60% of their 2008 spring loads. This essentially mandates 40% reductions in both particulate phosphorus (PP) and DRP loading relative to 2008 loads. These targets do not explicitly incorporate the difference in bioavailability between DRP (~100% bioavailable) and PP (~25% bioavailable). From 2008 to 2017, DRP comprised 24% of the spring TP load and over half (~56%) of the total bioavailable phosphorus (TBAP) load, while PP comprised 76% of the TP load but only ~44% of the TBAP load. Subsequent deposition of PP in the estuarine and nearshore zones further reduces its significance in bloom development. By ignoring differences in bioavailability, the current targets provide no guidance for choosing among practices based on their relative effectiveness in reducing DRP or PP and their combined reductions in TBAP loading. Current targets place more emphasis on PP than needed to efficiently reach targeted cyanobacterial bloom reductions. To clarify appropriate management approaches and lead to greater success in reducing cyanobacterial blooms, target loads should be based on TBAP.     

Raising the Reliability of Overhead Transmission Lines under the Action of Atmospheric Loads

Problems of reliability of overhead transmission lines (OTL) under the action of atmospheric loads are considered. It is assumed that the integral distribution function of, for example, ice loads, obtained from data of weather stations is a random statistical function that characterizes the frequency of an event (specific ice load) at a point (weather station area). The general population of statistical data is the most reliable base for analysis. Since the atmospheric loads are distributed in space and act on spatially distributed OTL systems, it is recommended to evaluate the proof load and the yearly reliability of OTL in terms of one integral statistical function composed of annual load maxima measured by weather stations located closest to the annual extremum of the ice load on a territory possessing common features (flat-bottom land, low land, elevation) that range within no more than 150 m with respect to the altitude. It is suggested that the Methodological Recommendations on Zoning of Atmospheric Loads on OTL Systems should be updated with allowance for the obtained data.     

方波加载对20CrMo钢焊缝疲劳裂纹扩展的影响

利用拉-拉疲劳法和金属磁记忆检测法研究了20CrMo钢焊缝在方波加载方式下疲劳裂纹扩展与自发射磁信号的相关性,用扫描电镜对疲劳断口特征进行了研究.结果表明,裂纹到达焊缝中心前,随着疲劳寿命的增加,焊缝处的自发射磁信号也随着增加,疲劳裂纹扩展速率先增加后减小,当裂纹越过焊缝后,随着疲劳寿命的增加,焊缝处的自发射磁信号开始减小,疲劳裂纹的扩展速率却迅速增加.在焊接接头的不同区域,疲劳裂纹扩展速率也不相同,其中热影响区扩展速度较快,而在其它区域扩展速率相对较慢.断口扫描分析表明方波加载方式下的疲劳断口为类解理断裂.     

Uncertainty in fatigue life prediction of structures subject to Gaussian loads

In this paper we shall concentrate on Gaussian (or close to Gaussian) loads acting on a structure. The goal is to compute a measure of risk for fatigue of a component during a specific time period and the so called “safety index” will be used to combine different types of uncertainties. The presented methodology can be applied in a more general situation of environmental loads which properties may vary with time of the year. The load is assumed to be “locally” stationary such that the mean load is constant (and taken to be zero) but the variance of the load can change slowly with time. Non-stationary hierarchical processes, separable into a stationary Gaussian process and a process describing the load amplitude and period, e.g. processes with Pierson–Moskowitz or JONSWAP spectrum, are treated in detail. The variability of a load, relevant for the fatigue accumulation process, will be described by means of rainflow cycles counted in the load. Moreover, common damage intensity approximations are reviewed and evaluated in a simulation study.     

Contact Interface Model for Shallow Foundations Subjected to Combined Cyclic Loading

It has been recognized that the ductility demands on a superstructure might be reduced by allowing rocking behavior and mobilization of the ultimate capacity of shallow foundations during seismic loading. However, the absence of practical reliable foundation modeling techniques to accurately design foundations with the desired capacity and energy dissipation characteristics and concerns about permanent deformations have hindered the use of nonlinear soil–foundation–structure interaction as a designed mechanism for improving performance of structural systems. This paper presents a new “contact interface model” that has been developed to provide nonlinear relations between cyclic loads and displacements of the footing–soil system during combined cyclic loading (vertical, shear, and moment). The rigid footing and the soil beneath the footing in the zone of influence, considered as a macroelement, are modeled by keeping track of the geometry of the soil surface beneath the footing, along with the kinematics of the footing–soil system, interaction diagrams in vertical, shear, and moment space, and the introduction of a parameter, critical contact area ratio (A/Ac); the ratio of footing area (A) to the footing contact area required to support vertical and shear loads (Ac). Several contact interface model simulations were carried out and the model simulations are compared with centrifuge model test results. Using only six user-defined model input parameters, the contact interface model is capable of capturing the essential features (load capacities, stiffness degradation, energy dissipation, and deformations) of shallow foundations subjected to combined cyclic loading.