Vibration Characteristics Research of Sandwich Structure with Octet-truss Lattice Core

Lattice sandwich beams are often subjected to vibrations when they are used. The aim of this study was to explore the vibration characteristics of the octet-truss lattice core sandwich beam by translating discrete octet-truss core to the continuous homogenization material. The natural frequencies of which are obtained by theoretical calculation and numerical simulation. The theoretical solutions are in good agreement with the numerical results. It demonstrates that the theoretical approach is effective to compute the natural frequency. Furthermore, the influences of truss member radius and thin sheets ply on the natural frequencies are also discussed. The outcomes indicate that the octet-truss lattice core sandwich beam’s natural frequencies are controlled via selecting the appropriate truss member radius and the face sheets thickness.

BUCKLING STRENGTH ANALYSES OF CORRODED TRUSS MEMBER WITH COMBINED CROSS SECTION

It will be important to forecast future the deterioration of remaining strength on corroded members for working out reasonable maintenance scenarios on steel structure. In this study, the buckling strength analyses, including future forecast, were conducted for the vertical member, which has the combined cross-section in actual aging truss bridge. For constructing the analytical model, a simple corrosion progress model was applied to generating the corroded steel surface. In this corrosion progress model, it assumes that corrosion pits are generated by the attack factors which can be decided by some control parameters for corrosion environment, corrosion form and corrosion area. And, the constant number of the attack factors per year fall all over the discretized steel surface. The corrosion surface in the future can be generated numerically by repeating mentioned above. The average thickness calculated from the numerical corrosion surface was applied to the local corrosion area in each analytical model. From these analytical results, a future forecast method applying a corrosion progress model was discussed by focusing on the aging deterioration of the buckling strength.

Analysis of rigid flange of bridge truss girder

Contemporary bridge truss girders have usually “W” bracing and spacing of cross beams smaller than spacing of truss nodes. The flange at deck level is loaded at its nodes and between them. It acts as a truss member and as a beam simultaneously. An analysis of the rigid flange in two stages is presented. The first stage of the analysis is aimed at computation of axial forces. Equivalent loading applied at truss nodes and truss member hinged connections are assumed. Ritter’s method is used to compute axial forces in rigid flange members. The second stage of analysis is aimed at computation of bending moments. A model of the rigid flange as a continuous beam on elastic supports with imposed settlements is assumed. In this stage additional model of truss girder as simply supported beam of equivalent moment of inertia is considered as well. Working example of application of presented analysis is given. Two computational models of rigid flange are analysed: model of rigid flange as member of truss girder and model of isolated rigid flange as continuous beam. Data recorded during test loading of two truss bridge spans are used for verification. Modelling isolated rigid flange as continuous beam and classical modelling of truss girder as plane frame provide similar accuracy of assessment of internal forces and vertical displacements distribution in rigid flange.

Experimentally Assisted Modelling of the Behaviour of Steel Angle Brace

Steel frame wind bracing systems are usually made of hot rolled profiles connected to frame elements directly or through a gusset plate. The behaviour of angle bracing members is generally complex since controlled by tension or compression, bending and torsion. The common practice is to transform the problem of complex behaviour into the buckling strength of a truss member. This paper deals with an analytical formulation of the force-deformation characteristic of a single angle brace subjected to compression. A strut model takes into consideration the effect of brace end connections and softening effect of its force-deformation characteristic. Two different boundary conditions, typical for engineering practice, are dealt with. Experimental program of testing the behaviour of angle brace in portal sub-frame specimens is described. Results of experimental investigations are presented. They are used for the validation of developed model. Conclusions are formulated with reference to the application of validated brace model in the analysis of braced steel frameworks.

Engineering modelling of structural details of a bridge

This paper presents a method of engineering modelling of structural details, which enables the analysis of local static and dynamic effects in a complex structure with the use of a personal computer. An analysed structural detail, modelled with the use of shell finite elements, is mounted to a spatial truss member system. Then, on the basis of prepared computational model, a static or dynamic analysis is carried out. The proposed model allows to detect the local effects in a theoretical. Conducted analyses confirmed the correct operation of such a computational model. Hence, the method of modelling presented in this paper allows to analyse the local effects on ordinary personal computer and more importantly, the results of such calculations are available within a relatively short period of time. The calculations are carried out by analysing the local effects in a steel node of the truss railway bridge.

Consideration of a Rotary Power Take-Off Mechanism as a Wave-Energy Converter on the WindFloat Platform

The possibility of incorporating a wave-energy extractor into a current design of the WindFloat platform is examined. First, to absorb wave energy, a rolling cam shape, with rotary power take-off, is attached to a tubular truss member of the WindFloat located above the calm-waterline. Based on the assumption that the extractor is operating in beam seas, numerical predictions for the coupled 3-DOF system (surge, heave and pitch motions) were completed for an ideal-fluid situation. The degradation of the performance of the wave energy extractor because of viscous effects was discussed in [1]. Second, a design of a versatile bi-directional rotary system, named the UC Berkeley Double-Ratchet Mechanism (UCB-DRM) was made. This mechanism can produce a unidirectional rotational motion, thus facilitating the power take off by a generator. A physical unit was constructed. The efficiency and performance of this mechanical system is assessed by introducing a known, bi-directional torque input and measuring the torque output.

Automatic generation of planar RC Strut-and-Tie models

This paper presents a proposal for determining Strut-and-Tie models of reinforced concrete plane elements. For the purposes of analysis, a computer program was developed and a discrete topological optimization was applied, using a truss member for the design of the stress-strain state of the real member. The method can be used for the analysis of a part or a whole member and it is particularly suitable for the usage in the places of sudden changes of static and/or geometric characteristics of members. The general principle of the method is that compressed members replace concrete parts of the element (surface or volume) and tension members replace the reinforcement.

Fatigue and Fracture Evaluation of a 70 Year Old Steel Bridge

Nen’jiang No.1 Bridge has been used for 70 year, so fatigue, fracture and corrosion dominate the remaining life of this bridge. Obviously the designer did not take into consideration the fatigue problem at that time. In order to keep this bridge in service economically as long as possible, bridge owner decides to take measures to preserve its service safety. Thus the remaining fatigue life and fracture failure risk need to be evaluated. The analytical results according to the fracture mechanic based concept show that the diagonal edge members U0L1 and U9L8 have the shortest remaining fatigue life, and some members have a potential risk of brittle failure. The fracture failure risk evaluation results show that the toughness of main truss member steel is lower than the code requirement, and members such as U0L1 and U9L8 have brittle fracture failure risk in cold winter. So this bridge should be temporarily closed traffic in winter.