Socioeconomic disadvantage in childhood as a predictor of excessive gestational weight gain and obesity in midlife adulthood

BACKGROUND: Lower childhood socioeconomic position is associated with greater risk of adult obesity among women, but not men. Pregnancy-related weight changes may contribute to this gender difference. The objectives of this study were to determine the associations between: 1. childhood socioeconomic disadvantage and midlife obesity; 2. excessive gestational weight gain (GWG) and midlife obesity; and 3. childhood socioeconomic disadvantage and excessive GWG, among a representative sample of childbearing women. METHODS: We constructed marginal structural models for seven measures of childhood socioeconomic position for 4780 parous women in the United States, using National Longitudinal Survey of Youth (1979–2010) data. Institute of Medicine definitions were used for excessive GWG; body mass index ≥30 at age 40 defined midlife obesity. Analyses were separated by race/ethnicity. Additionally, we estimated controlled direct effects of childhood socioeconomic disadvantage on midlife obesity under a condition of never gaining excessively in pregnancy. RESULTS: Low parental education, but not other measures of childhood disadvantage, was associated with greater midlife obesity among non-black non-Hispanic women. Among black and Hispanic mothers, childhood socioeconomic disadvantage was not consistently associated with midlife obesity. Excessive GWG was associated with greater midlife obesity in all racial/ethnic groups. Childhood socioeconomic disadvantage was not statistically significantly associated with excessive GWG in any group. Controlled direct effects were not consistently weaker than total effects. CONCLUSIONS: Childhood socioeconomic disadvantage was associated with adult obesity, but not with excessive gestational weight gain, and only for certain disadvantage measures among non-black non-Hispanic mothers. Prevention of excessive GWG may benefit all groups through reducing obesity, but excessive GWG does not appear to serve as a mediator between childhood socioeconomic position and adult obesity in women

Small-scale laterally-unrestrained corrugated web girders: (I) LTB tests and numerical validation

The lateral–torsional buckling (LTB) of corrugated web girders (CWGs), which have been used extensively in bridges worldwide, is investigated in this paper. In consideration that available flexural strength proposals of CWGs have been based largely on numerical/theoretical investigations, besides the scarce of physical tests and the risk of collapse by LTB, three small-scale simply-supported CWGs specimens are designed and tested, and their results are presented in this paper. An innovative test setup, containing special loading plates as well as end and lateral supports, is prepared to ensure that the tests are under pure bending moment through the four-point bending without any stabilising or destabilising effect for the applied load. The main test parameter is the web depth of the girders, while other parameters are evaluated numerically in the companion paper. Accordingly, the related experimental works are currently introduced and several conclusions are drawn. The effect of the web depth is evaluated, which shows that the ultimate buckling moments of the girders, and also the stiffness, increase with the increase in the girder\u27s height. Moreover, the tests indicate that the too thin corrugated webs (CWs) may be affected by web distortion which may not be very obvious in the deformed configuration, even though CWs do not withstand longitudinal stress. The corresponding finite element (FE) models are then developed taking into account the elastic and inelastic buckling analyses. Through comparisons with the tests, FE simulations show good agreement and ability to provide the behaviour of small-scale CWGs. Accordingly, they are used to generate parametric studies in the companion paper with the goal of providing the fundamental behaviour of small-scale CWGs as well as appropriate design methods. Additionally, FE modelling outcomes confirm that the entire sections of CWGs do satisfy the plane section assumption

Small-scale laterally-unrestrained corrugated web girders: (II) Parametric studies and LTB design

As shown in the companion paper, innovative tests of corrugated web girders (CWGs) were performed followed by validation of the finite element (FE) model. Accordingly, this paper continues investigating the lateral–torsional buckling of small-scale corrugated web girders through parametric studies. This is to expand the available data required to unveil their behaviour and strength. The layout of the tested girders is considered herein, where the webs of small corrugation dimensions are under pure bending moment with symmetrical boundary conditions. This study deals with the linear and nonlinear buckling analyses of the lateral–torsional buckling (LTB) of CWGs using ABAQUS software. Accordingly, 108 models are conducted, considering the effects of the girder length, web overall dimensions, corrugation dimensions, flange dimensions and different steel grades. The results show that increasing the girder length decreases consequently the ultimate flexural strength and stiffness of CWGs. With regard to the web overall dimensions, increasing the web depth is found to have a significant effect on the strength of CWGs in contrast to the effect of the web thickness value, which has insignificant effect on strength. Furthermore, the results revealed that increasing the flange dimensions increases subsequently the strengths of CWGs. In addition, it is noted that the lower the steel grade, the more effectively the material is used especially for girders failing elastically. Additionally, the critical and design LTB strengths of small-scale CWGs with small corrugation dimensions are evaluated. The comparisons show that the critical LTB stress requires modifications to accord well with FE results. Furthermore, comparisons of the ultimate FE strengths with those of Lindner\u27s equation (1990), EC3 (2004) and AISC (2010) are provided. The comparisons exhibit that the predictions of Lindner\u27s equation (1990) are suitable, while the predictions of EC3 (2004) and AISC (2010) are highly conservative. Therefore, modifications are made for EC3 (2004) and AISC (2010) design models to provide more appropriate design strengths for CWGs with small corrugation dimensions for use in buildings

Experimental characterization and numerical simulation of riveted lap-shear joints using Rivet Element

In aeronautical and automotive industries the use of rivets for applications requiring several joining points is now very common. In spite of a very simple shape, a riveted junction has many contact surfaces and stress concentrations that make the local stiffness very difficult to be calculated. To overcome this difficulty, commonly finite element models with very dense meshes are performed for single joint analysis because the accuracy is crucial for a correct structural analysis. Anyhow, when several riveted joints are present, the simulation becomes computationally too heavy and usually significant restrictions to joint modelling are introduced, sacrificing the accuracy of local stiffness evaluation. In this paper, we tested the accuracy of a rivet finite element presented in previous works by the authors. The structural behaviour of a lap joint specimen with a rivet joining is simulated numerically and compared to experimental measurements. The Rivet Element, based on a closed-form solution of a reference theoretical model of the rivet joint, simulates local and overall stiffness of the junction combining high accuracy with low degrees of freedom contribution. In this paper the Rivet Element performances are compared to that of a FE non-linear model of the rivet, built with solid elements and dense mesh, and to experimental data. The promising results reported allow to consider the Rivet Element able to simulate, with a great accuracy, actual structures with several rivet connections