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The Structural Engineer

This paper compares the efficiency of mode superposition and direct integration methods for the dynamic analysis of offshore platform cranes. Newmark’s method and the central difference method, which integrate the equatiom of motion directly, are compared with the method of mode superposition on the basis of computer time, computer storage, and program complexity. Progruming techniques to improve the efficiency of the different algorithms are described. Results are presented that show the central difference method to be uneconomic in comparison with the other two methods. The method of mode superposition, while requiring marginally more computer storage, is shown to offer substantial savings in computer time over Newmark’s method. J.A.D. Balfour

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The Structural Engineer

A rapid method for assessing the ultimate strength of reinforced concrete members subjected to axial compression and biaxial bending is presented. The design procedure is computerised to full automation for arbitrary cross-sections, with or without voids. The concept of load fraction, which is the fraction of the applied load that can be adequately withstood, is introduced for quantitative measure of structural adequacy. The load fraction also provides useful guidelines to necessary redesign. An iterative procedure is evolved for making adequate provision for ultimate strength by gradually increasing the amount of rein forcement till the required load fraction is achieved. Reinforcement is always added at locations having the highest increase of load fraction/unit area of added reinforcement. Practical considerations in symmetry, nominal rein forcement, and steel congestion, etc., are taken into account. K.H. Kwan and T.C. Liauw

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The Structural Engineer

Moment resistant steel beam-column connections using endplates and high strength friction grip bolts have been tested under both static and pulsating loads to determine their energy absorption characteristics. The effect of endplate thickness on damping capacity has been considered for a constant bolt diameter and member cross- section. Six specimens, two each made using 20 mm, 16 mm, and 12 mm thick endplates were tested-three under static loads and the other three under pulsating loads. An optical technique was used for the measurement of rotations of the beam and column. Loss of bolt tension under pulsating loads was also considered. The use of a flexible endplate capable of transferring the full plastic moment of the beam is recommended for these connections. A.K. Aggarwal and Professor R.C. Coates

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