Mode‐superposition has been extensively used in computing the dynamic response of complex structures. Two versions of mode‐superposition, namely the mode‐displacement method and the mode‐acceleration method, have been employed. The present paper summarizes the results of a systematic study comparing the accuracy of the mode‐displacement and mode‐acceleration methods when applied to structures with various levels of damping or various excitation frequencies. The paper also discusses several details concerning the implementation of the mode‐acceleration method.
An accurate computation of the joint load factors is critical for the safe design of bolted connections. This study provides a four-step procedure for the direct computation of the joint load factors for a variety of bolt diameters, joint thicknesses, individual plate thicknesses, and plate material combinations. The finite element method was used to calculate the bolt and plate deformations necessary to directly compute the load factor for 4424 unique combinations of the four joint design parameters. The procedure developed in this study provides accurate estimates of the joint load factor over the entire range of the four joint design parameters. All 4424 joint designs originally analysed with the finite element method were recomputed using the proposed procedure. The root mean square error was found to be 0.58 per cent with a correlation coefficient between the load factors computed by using the original finite element analyses and the proposed procedure to be 0.9998.
Airport pavement thickness design procedures predict a significant amount of interaction between the loads from multiple-wheel and closely spaced multipletruck landing gear configurations. But the true degree of interaction is not known, and measurements from full-scale tests are required to determine how closely wheels and trucks can be spaced without significant load interaction. As a supplement to traffic tests run to failure at a later date, pavement response tests were performed to study the wheel load interaction effects. Pavement responses (stresses, strains, deflections, etc.) were measured at various depths in each of the nine pavement test items at the National Airport Pavement Test Facility (NAPTF) for different combinations of wheel configurations, truck configurations, and load levels. Moving loads were applied at a speed of 0.15 m/sec (0.5 feet/second). A total of 522 tests were performed on six flexible pavement test items and 108 tests were performed on three rigid pavement test items. This paper describes the response test objectives and test procedures. Some typical pavement responses are presented. Data from the response tests is being analyzed at the FAA Center of Excellence for Airport Technology at the University of Illinois. The raw data is also available from the FAA for independent analysis.
There are numerous situations in machine component design in which curved beams with cross-sections of arbitrary geometry are loaded in the plane of curvature, i.e. in flexure. However, there is little guidance in the technical literature concerning how the shear stresses resulting from out-of-plane loading of these same components are effected by the component's curvature. The current literature on out-of-plane loading of curved members relates almost exclusively to the circular and rectangular cross-sections used in springs. This article extends the range of applicability of stress concentration factors for curved beams with circular and rectangular cross-sections and greatly expands the types of cross-sections for which stress concentration factors are available. Wahl's stress concentration factor for circular cross-sections, usually assumed only valid for spring indices above 3.0, is shown to be applicable for spring indices as low as 1.2. The theory applicable to the torsion of curved beams and its finite-element implementation are outlined. Results developed using the finite-element implementation agree with previously available data for circular and rectangular cross-sections while providing stress concentration factors for a wider variety of cross-section geometries and spring indices.
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