Showing papers on "Bending moment published in 2018"

Bending and wrinkling of composite fiber preforms and prepregs. A review and new developments in the draping simulations

Abstract: Bending properties play a significant role in the forming of textile composites reinforcements, particularly in determining the shape of wrinkles. The physics related to the bending of fibrous reinforcements is specific. Bending is due to slippage between the fibers and since the fibers are quasi-inextensible, standard plate and shell theories are irrelevant. To measure bending characteristics, three experimental tests (and their variants) have been developed in the last decades, and efforts are currently devoted to extending and improving these tests. From their results, simulations can be performed by introducing a flexural energy related to the bending moment and the curvature. In particular, wrinkles during forming can be simulated. In the case of 3D modeling of thick reinforcements, the use of generalized continuum mechanics model is necessary because of the bending stiffness of each fiber and the slippage between fibers. In order to simulate textile reinforcements with shells, some shell approaches, different of the standard theories, can correctly calculate the rotations of textile reinforcement normals.

Stress-strain relationship of FRP confined concrete columns under combined axial load and bending moment

Abstract: The stress-strain relationship of FRP confined concrete columns under eccentric loading is different from that under concentric loading However, eccentric loading can have different load paths, eg constant axial force with increasing load eccentricity or constant load eccentricity with increasing axial load The effect of different load paths on the stress-strain behavior of eccentrically loaded columns has remained unclear to date It was believed previously that such difference in load paths could be insignificant for the stress-strain behavior of FRP confined concrete columns under eccentric loading Unexpectedly, the study in this work on two different load paths demonstrates that the stress-strain behavior can be very different A new stress-strain model for FRP confined circular concrete columns under constant axial force and increasing load eccentricity is developed in this work for engineering applications

An efficient frequency-domain model for quick load analysis of floating offshore wind turbines

Abstract: . A model for Quick Load Analysis of Floating wind turbines (QuLAF) is presented and validated here. The model is a linear, frequency-domain, efficient tool with four planar degrees of freedom: floater surge, heave, pitch and first tower modal deflection. The model relies on state-of-the-art tools from which hydrodynamic, aerodynamic and mooring loads are extracted and cascaded into QuLAF. Hydrodynamic and aerodynamic loads are pre-computed in WAMIT and FAST, respectively, while the mooring system is linearized around the equilibrium position for each wind speed using MoorDyn. An approximate approach to viscous hydrodynamic damping is developed, and the aerodynamic damping is extracted from decay tests specific for each degree of freedom. Without any calibration, the model predicts the motions of the system in stochastic wind and waves with good accuracy when compared to FAST. The damage-equivalent bending moment at the tower base is estimated with errors between 0.2 % and 11.3 % for all the load cases considered. The largest errors are associated with the most severe wave climates for wave-only conditions and with turbine operation around rated wind speed for combined wind and waves. The computational speed of the model is between 1300 and 2700 times faster than real time.

A comparative study on empty and foam-filled hybrid material double-hat beams under lateral impact

Abstract: In previous research, an innovative hybrid material double-hat thin-walled beam has been proposed for vehicle bumper system, which has demonstrated great potentials for improved pedestrian safety and reduced weight. In this work, we have used aluminum foam to fill the hybrid double-hat beam to further its application in vehicle bodies with increased bending resistance and energy absorption efficiency. Bending behaviors of both empty and foam-filled hybrid beams were numerically investigated using the validated LS-DYNA models. Three representative loading positions including the mid-span, 50 mm and 100 mm offsets from the mid-span were simulated to reveal the effect of load position uncertainty. It was found that the foam filler could increase the specific energy absorption (SEA) by more than 30% and double the bending moment (Mb) of the empty hybrid beam by changing its deformation pattern. Moreover, the foam-filled beam shows more robust crashworthiness performance against load position variation. Using radial basis function (RBF) metamodels, the multi-objective design optimization (MDO) problems were formulated for both empty and filled hybrid beams to maximize SEA and Mb and minimize the initial peak force (Fip). The multi-objective particle swarm optimization (MOPSO) was used to seek the Pareto fronts of the MDO problems. The MDO results show that the foam-filled beam has much broader performance space in terms of Fip, SEA and Mb and has great potentials for high-energy crash applications. It was also found that the Pareto front varies for different loading positions for either empty or filled hybrid beam. Including multiple loading positions could achieve a more robust design against load uncertainty. Appropriate weighting factors should be chosen for different loading positions to yield realistic and more robust designs of the proposed hybrid beams.

Overall instability performance of concrete-infilled double steel corrugated-plate wall

Abstract: This paper proposes a new type of composite walls, namely concrete-infilled double steel corrugated-plate walls (CDSCWs). The CDSCW consists of a wall element that is formed by two steel corrugated-plates, where they are interconnected through high-strength bolts, and the spacing between the two steel corrugated-plates is filled with concrete. Additionally, two concrete-infilled steel tubes (CFSTs) are assigned as vertical boundary elements at both sides of the wall element. Not only the corrugated configuration of steel sheets themselves would significantly improve the load-bearing efficiency of CDSCWs, but also the interactions and combined actions among steel corrugated-plates, high-strength bolts and concrete could provide much better load-bearing capacity and seismic performance for CDSCWs. In addition, industrial mass production of the CDSCWs can be achieved by adopting integrated cold-formed steel rolling techniques. Therefore, the CDSCWs are much more suitable for applications in high-rise building structures as shear wall structural systems that carry axial loads and bending moments as well as shear loads. This paper mainly investigates the overall instability performance of I-section CDSCWs under uniform compressions and corresponding design formulae are recommended. Firstly, Finite Element (FE) eigenvalue buckling analyses are carried out to investigate the overall elastic buckling behavior of CDSCWs subjected to vertical compressive loads. The formulae for estimating the elastic buckling loads of CDSCWs and corresponding normalized slenderness ratios λn are obtained based upon the form of Euler's formula. The overall instability performance of CDSCWs under compressions is then studied by FE nonlinear analyses, leading to the overall stability coefficient φ as well as φ-λn curve for their strength design. Moreover, an I-section CDSCW specimen has been designed and tested under uniform compressive load, and its overall instability performance is investigated experimentally. The results obtained from the experiment show an agreement with those obtained from FE numerical analyses, which also verifies the safety and validity of φ-λn curves for the strength design of CDSCWs.

Centrifuge shaking table tests on 4 × 4 pile groups in liquefiable ground

Abstract: A series of centrifuge shaking table model tests are conducted on 4 × 4 pile groups in liquefiable ground in this study, achieving horizontal–vertical bidirectional shaking in centrifuge tests on piles for the first time. The dynamic distribution of forces on piles within the pile groups is analysed, showing the internal piles to be subjected to greater bending moment compared with external piles, the mechanism of which is discussed. The roles of superstructure–pile inertial interaction and soil–pile kinematic interaction in the seismic response of the piles within the pile groups are investigated through cross-correlation analysis between pile bending moment, soil displacement, and structure acceleration time histories and by comparing the test results on pile groups with and without superstructures. Soil–pile kinematic interaction is shown to have a dominant effect on the seismic response of pile groups in liquefiable ground. Comparison of the pile response in two tests with and without vertical input ground motion shows that the vertical ground motion does not significantly influence the pile bending moment in liquefiable ground, as the dynamic vertical total stress increment is mainly carried by the excess pore water pressure. The influence of previous liquefaction history during a sequence of seismic events is also analysed, suggesting that liquefaction history could in certain cases lead to an increase in liquefaction susceptibility of sand and also an increase in dynamic forces on the piles.