Analysis of contact characteristics of ball screws under the combined loads considering non-uniform load distribution

YongJiang Chen,Jianghai Zhao,Chuangfan Yuan,Jingkai Sun 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.4

An analysis model of the contact characteristics of the double-nut preloaded ball screw which can consider the combined action of the axial load and the overturning moment is established, the model can consider non-uniform load distribution, and the validity of the model is verified by experiments. Based on this model, the influence of the combined action of axial load and overturning moment on the average value and distribution fluctuation value of the contact angle of the ball screw, the number of unloaded balls, the distribution fluctuation value of the contact load, and the static contact stiffness and other contact parameters are systematically analyzed, and get the following conclusions: The contact parameters of the ball screw are mainly affected by the axial load and the contact state between the ball and the raceway. The gradually increasing axial load basically reduces the influence of the overturning moment on the contact parameters of the ball screw. There is a critical value of the load in the axial direction within the range of the action value of the preload load. Only when the critical value is above the critical value, the contact parameters will change regularly with the changes in the axial stiffness and overturning moment. However, different critical values for the regular variation of contact parameters with axial load and overturning moment vary.

[미발표] 전철주기초의 마찰저항을 고려한 저항모멘트 산정방법 개발

이수형(Su-Hyung Lee) 한국철도학회 2012 한국철도학회 학술발표대회논문집 Vol.2012 No.10

철도선로 연변에 설치되어 전력을 공급하는 전철선이 고정되는 전철주는 노반에 매립된 각주 또는 원주 형태의 콘크리트 기초에 의해 지지된다. 전철선에 작용하는 하중은 기초로부터 일정거리 이상 이격되어 있으므로 전철주기초에는 큰 전도모멘트가 작용하게 되며 이에 저항하기 위하여 흙과 기초 사이에는 연직응력과 마찰응력이 발생하게 된다. 기존 전철주기초 설계에서는 기초에 작용하는 연직응력, 즉 수동토압의 분포만을 가정한 저항모멘트 산정 방법이 적용되고 있으나 보다 합리적이고 경제적인 설계를 위해서는 기초면에 작용하는 흙의 마찰응력을 고려할 수 있는 방법의 적용이 필요하다. 본 논문에서는 기존 전철주기초 설계방법에서의 폐쇄해적 방식을 개선하여, 기초 측면에 작용하는 수동토압과 마찰응력 뿐만 아니라, 기초 저부에 작용하는 토압까지 고려가 가능한 연립방정식 형태의 저항모멘트 산정방법을 개발하여 제시하였다. Railway electric poles are supported by foundations of square or cylindrical concrete columns. The forces acting on electric cables and their auxiliary parts are separated to the foundations by some distances and cause significant overturning moment. Vertical and frictional stresses developed between soil and foundation resist against the overturning to create the moment capacity. However the existing design methods consider only the passive soil pressure, i.e. vertical stress, and frictional resistance should be considered additionally for the more reasonable and economical design. In this study a new method to estimate the moment capacity of electric pole foundations considering frictional resistance is developed by adopting a simultaneous equation approach rather than closed form solution of the existing methods.

Effects of a floating wave barrier with square cross section on the wave-induced forces exerted to an offshore jacket structure

Osgouei, Arash Dalili,Poursorkhabi, Ramin Vafaei,Maleki, Ahmad,Ahmadi, Hamid Techno-Press 2021 Ocean systems engineering Vol.11 No.3

The main objective of the present research was investigating the effects of a floating wave barrier with square cross section installed in front of an offshore jacket structure on the wave height, base shear, and overturning moment. A jacket model with the height of 4.55 m was fabricated and tested in the 402 m-long wave flume of NIMALA marine laboratory. The jacket was tested at the water depth of 4m subjected to the random waves with a JONSWAP energy spectrum. Three input wave heights were chosen for the tests: 20 cm, 23 cm, and 28 cm. Results showed that the average decrease in the jacket's base shear due to the presence of a floating wave barrier with square cross section was 18.97%. The use of wave barriers with square cross section also resulted in 19.78% decrease in the jacket's overturning moment. Hence, it can be concluded that a floating wave barrier can significantly reduce the base shear and overturning moment in an offshore jacket structure.

Effects of floating wave barriers on wave-induced forces exerted to offshore-jacket structure

Arash Dalili Osgouei,Ramin Vafaei Poursorkhabi,Hamed Hosseini,Diyar N. Qader,Ahmad Maleki,Hamid Ahmadi 국제구조공학회 2022 Structural Engineering and Mechanics, An Int'l Jou Vol.83 No.1

The main objective of the present research was investigating the effects of a floating wave barrier installed in front of an offshore jacket structure on the wave height, base shear, and overturning moment. A jacket model with the height of 4.55 m was fabricated and tested in the 402 m-long wave flume of NIMALA marine laboratory. The jacket was tested at the water depth of 4 m subjected to the random waves with a JONSWAP energy spectrum. Three input wave heights were chosen for the tests: 20 cm, 23 cm, and 28 cm. Two different cross sections with the same area were selected for the wave barrier: square and rhombus. Results showed that the average decrease in the jacket’s base shear due to the presence of a floating wave barrier with square and rhombus cross section was 24.67% and 34.29%, respectively. The use of wave barriers with square and rhombus cross sections also resulted in 19.78% and 33.11% decrease in the jacket’s overturning moment, respectively. Hence, it can be concluded that a floating wave barrier can significantly reduce the base shear and overturning moment in an offshore jacket structure; and a rhombus cross section is more effective than an equivalent square section.

풍동실험에 기초한 풍방향 가스트하중계수 경험식에 관한 연구

신동현,하영철 한국풍공학회 2023 한국풍공학회지 Vol.27 No.4

The method of evaluating the wind load generated in buildings has developed a lot from the past. Among them, there is a relatively simple method, the gust loading factor method. This is a method of evaluating the equivalent static wind load by multiplying the static wind load by the dynamic coefficient and is used in the standards of many countries. Dynamic coefficients include Gust Effect Factor(DGEF) and Gust Loading Factor(MGLF). DGEF is displacement-based and can be calculated through theoretical assumptions, but the process is somewhat complicated. MGLF is based on the overturning moment and can be calculated by measuring the overturning moment through wind tunnel tests, but it takes a lot of time and effort to construct basic data. Therefore, in this study, we compared and analyzed the tendency of the along-wind mean wind force coefficient CF, mean overturning moment coefficien CM, and fluctuating overturning moment coefficient CM required when calculating MGLF to change according to aspect ratios( ), side ratios(D/B), and surface roughness(α). Through this, empirical formulas for the along-wind mean wind force coefficient CF, coefficients related to mean overturning moment Cg, and coefficients related to fluctuating overturning moment Cg were proposed, and basic data for MGLF calculation were presented. 건축물에 가해지는 풍하중을 평가하는 방법은 과거로부터 많은 발전을 이루었다. 그 중 비교적 간단한 방법인 가스트하중계 수법이 있다. 정적풍하중에 동적계수를 곱하여 등가정적풍하중을 평가하는 방법으로 여러나라 기준에서 사용되고 있다. 동적계수는 가스트영향계수(Gust Effect Factor:DGEF)와 가스트하중계수가(Gust Loading Factor:MGLF)가 사용된다. DGEF는 변위 기반으로서 이론적인 가정을 통해 산출할 수 있는 반면 그 과정이 다소 복잡하고, MGLF는 모멘트를 기반으로 하며 풍동실험으로 전도모멘트를 측정하여 산정할 수 있지만 기초자료를 구축하는 것에 많은 시간과 노력이 소요된다. 따라서 본 연구에서는 MGLF 산정 시 필요한 풍방향 평균풍력계수CF, 평균전도모멘트계수CM, 변동전도모멘트계수 CM 가 다양한 형상비( ), 변장비(D/B), 지표면조도구분(α)에 따라 변화하는 경향을 비교 분석하였다. 이를 통해 풍방향 평균풍력계수 CF, 평균전도모멘트 관련 계수 Cg, 변동전도모멘트 관련 계수 Cg 의 경험식을 제안하여 MGLF 산정에 대한 기초자료를 제시하였다.

조경시공 관리에서 사다리 안전사고 예방을 위한 전도 안정성 평가 - 국내에서 사용되고 있는 삼각지지형 이동식 사다리를 대상으로 -

김은일,권윤구,이기열 한국조경학회 2023 韓國造景學會誌 Vol.51 No.5

본 연구는 조경시공 및 관리분야에서 수목관리, 전지 등과 같은 고소부위 작업을 위해 주로 사용하는 삼각지지형 이동식 사다리의 전도 안정성을 평가한 것이다. 산업현장에서 사용 빈도가 높은 이동식 사다리에 포함되는 삼각지지형 이동식 사다리는 작업 특성에 따라 바닥지지 형태가 일반적인 A형의 사면지지가 아닌 삼각지지 방식이고, 작업 높이도 이동식 사다리와 비교하여 2배 이상 높기 때문에 떨어짐과 함께 작업자의 안전을 위협하는 전도 발생 가능성이 매우 높다고 할 수 있다. 따라서, 국내에서 사용되고 있는 삼각지지형 이동식 사다리를 대상으로 관련 기준인 ANSI-ASC A14.7과 EN 131-Part 7에서 규정하고 있는 전도 안정성 평가를 기반으로 하여 작업 높이에 따른 전도모멘트와 저항모멘트를 계산할 수 있는 수식을 각각 유도하여 계산한 후, 이 값을 상호 비교하여 전도에 대한 안전율 및 전도 방향에 따른 안정성을 평가하였다. 각 기준에 따른 전도 안정성 평가 결과, EN 131-Part 7의 규정을 적용하면 후면방향 8단과 측면방향으로 6단 이상의 삼각지지형 이동식 사다리는 전도에 대해서 불안정한 것으로 평가되었으나, ANSI-ASC A14.7의 규정에 의하면 방향에 상관없이 모든 단수에서 전도에 대한 안정성을 확보하고 있는 것으로 평가되었다. This study evaluated the overturning stability of portable tripod ladders used for high-altitude work such as tree management and pruning work in landscaping construction and management. Portable tripod ladders, which are included in general mobile or portable ladders frequently used in industrial sites, are supported in a triangular support structure, not a 4-point support like common A-type Ladders. In addition, since the working height is more than twice that of a mobile or portable ladder, the possibility of an overturning accident that threatens the safety of workers with a fall accident is high. Therefore, based on the overturning stability test specified in ANSI-ASC A14.7 and EN 131-Part 7, which are related standards for about 130 types of portable tripod ladders sold and used in Korea. An equation to calculate each moment according to working height was derived. Then, each calculated moment was compared to evaluate the safety factor for overturning and stability. As a result of the overturning stability evaluation according to each standard, when the provisions of EN 131-Part 7 were applied, portable tripod ladders with 8 steps in the rear direction and 6 steps or more in the side direction were evaluated as unstable against overturning, but according to ANSI-ASC A14.7 regulations. It was evaluated that the stability against overturning was secured in all directions and number of steps.

크롤러 크레인에서 붐의 러핑각도에 따른 전도 모멘트와 와이어 로프 장력 사이의 관계

장효필(Hyo Pil Jang),한동섭(Dong Seop Han),한근조(Geun Jo Han) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11

An overload limiter is used to prevent the overturning accident of a crawler crane during an operating. Recently the simultaneous measuring method, which measures hoisting load and overturning moment of the crane, is demanded instead of the existing method, which measures load at the end of boom. The simultaneous measuring method is how to conduct the hoisting load and overturning moment as measuring the tension of luffing wire for a driving of boom. To develop this preventing device for an overturning, the relation between the hoisting load and the overturning moment and the tension of luffing wire according to the luffing angle of boom must be numerically defined. In this study, the relation formula is derived between the hoisting load and the tension of wire and between the overturning moment and the tension according to the luffing angle of boom. Next the formula is compensated by application of the deflection of boom that is obtained by conduction the finite element analysis.

풍압적분법에 의한 풍응답변위의 평가

김병조,하영철 한국풍공학회 2014 한국풍공학회지 Vol.18 No.2

고층 건축물의 내풍설계 시 다차모드 해석의 수행이 필요하다. 고층건축물의 다차모드 해석을 위해서 풍압적분법과 1차모드 해석을 수행하였으며, 풍압적분법을 활용하여 층별 시간이력 전도모멘트를 산출하였다. 층별 전도모멘트를 산출하기 위해 풍압적분법을 활용하였고, 그 방법으로 임의의 층까지의 누적 풍력데이터로부터 층별 시간이력의전도모멘트를 산출하였다. 풍응답변위는 각 층별 전도모멘트로부터 1차 모드 해석을 수행하여 평가하였다. 본 연구 결과의 그 유효성을 높이기 위해, 건축물 전체에 작용하는 풍력데이터에 의해 얻어진 풍응답 결과와 비교하였다. 두 연구 결과는 유사한 것으로 나타났다. When planning wind resistant design for tall buildings, multi-modal analysis is needed. In order to calculatethe wind load of multi-modal for tall buildings, Pressure Integral Method and first-modal analysis were used. The timehistory of overturning moments were calculated by using Pressure Integral Method. Overturning moments on eachstories were calculated by using cumulative wind force data of each stories. The wind response displacement wasestimated from overturning moments of each stories by using first-modal analysis. To increase the validity on the resultsof this study, it was compared with the results of wind response displacement which was estimated by wind force dataacting on a whole building. The results of those were similar.

The effects of vertical earthquake motion on an R/C structure

Selcuk Bas,Ilker Kalkan 국제구조공학회 2016 Structural Engineering and Mechanics, An Int'l Jou Vol.59 No.4

The present study investigated the earthquake behavior of R/C structures considering the vertical earthquake motion with the help of a comparative study. For this aim, the linear time-history analyses of a high-rise R/C structure designed according to TSC-2007 requirements were conducted including and excluding the vertical earthquake motion. Earthquake records used in the analyses were selected based on the ratio of vertical peak acceleration to horizontal peak acceleration (V/H). The frequency-domain analyses of the earthquake records were also performed to compare the dominant frequency of the records with that of the structure. Based on the results obtained from the time-history analyses under the earthquake loading with (H+V) and without the vertical earthquake motion (H), the value of the overturning moment and the top-story vertical displacement were found to relatively increase when considering the vertical earthquake motion. The base shear force was also affected by this motion; however, its increase was lower compared to the overturning moment and the top-story vertical displacement. The other two parameters, the top-story lateral displacement and the top-story rotation angle, barely changed under H and H+V loading cases. Modal damping ratios and their variations in horizontal and vertical directions were also estimated using response acceleration records. No significant change in the horizontal damping ratio was observed whereas the vertical modal damping ratio noticeably increased under H+V loading. The results obtained from this study indicate that the desired structural earthquake performance cannot be provided under H+V loading due to the excessive increase in the overturning moment, and that the vertical damping ratio should be estimated considering the vertical earthquake motion.

단면의 변의 수가 초고층 건물의 공력특성에 미치는 영향

김용철,반디 에스와라 쿠마,유키오 타무라,요시다 아키히또,윤성원,Kim, Yong-Chul,Bandi, Eswara Kumar,Tamura, Yukio,Yoshida, Akihito,Yoon, Sung-Won 한국공간구조학회 2013 한국공간구조학회지 Vol.13 No.3

A series of wind tunnel tests were conducted on 7 super-tall buildings with various polygon cross-sections, including triangle, square, pentagon, hexagon, octagon, dodecagon, and circular. The primary purpose of the present study is to investigate the effect of increasing number of sides on aerodynamic characteristics for super-tall buildings. Wind tunnel tests were conducted under the turbulent boundary layers whose power-law exponent is 0.27. Fluctuating wind pressures from more than 200 pressure taps were recorded simultaneously, and time series of overturning moments were calculated considering tributary area of each pressure tap. The results show that the overturning moment coefficients and the spectral values decrease with increasing number of sides, and the largest mean and fluctuating overturning moments were found for the triangular super-tall building, and the largest spectral values were found for the square super-tall building. The analysis should be conducted more in detail, but currently it can be roughly said that there seems to be a little differences in the aerodynamic characteristics for the super-tall buildings whose number of sides is larger than 5 or 6.