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An experimental study is presented on the local and overall interaction buckling strength of welded built-up box columns made of high strength steel. A total of twenty-seven box columns with large width-thickness ratios were tested to failure, of which twenty-four columns were centrally loaded and the rest eccentrically loaded. Based on the test results, an empirical design formula is presented to predict the interaction buckling strength. Further, a discussion of an economical way of proportioning box sections is presented.

A finite difference procedure is used to determine the response of a single span curved single box beam bridge with any number of interior diaphragms. The bending and torsional distortions as well as cross-sectional distortions can then be determined throughout the curved box girder. The forces that are determined include bending moment and shear, pure torsion, warping torsion, and bimoment. These forces, in addition to distortional functions, yield resulting normal bending, normal warping, and normal distortional stresses. The technique is then used to determine the dead-load and live-load response of a series of typical curved box beams. A study of the data has resulted in a series of empirical design equations.

The problem of the inelastic lateral buckling of steel wide-flange beams is treated as an extension of the classical elastic buckling solution. The method is developed for the case of equal end-moments, about the major axis of the cross section, and for simply supported lateral and torsional boundary conditions. The influence of cooling residual stresses is considered in defining the boundaries of the elastic core. The lateral and the torsional stiffnesses are computed from the assumption that only the unyielded portions of the beams resist lateral buckling. The numerical work was performed for four representative wide-flange cross sections, and the results are represented as non-dimensional critical length-versus-critical moment curves. A simplified analytical method is given, and the analytical results are compared with two empirical design equations. A straight line transition equation is proposed in the report.

The behavior at various stages of loading of a flat slab reinforced with welded wire fabric is described. The design was based on the empirical design method of ACI 318-56. The test structure was loaded at 16 points in each of its nine panels to simulate a uniform load. From three of a series of tests conducted at different load levels and with different combinations of loaded panels, representative load-deflection curves are given. At working load, the behavior of the structure was characterized by small deflections and stresses. The structure was essentially uncracked after reaching design load. Under increased loading, the stresses and deflections increased at an increasing rate as cracking progressed at failure at 955 psf. Comparison of the computer and design unit moments showed the structure to be adequately designed. However, the distribution of reinforcement was inefficient. The indication of the tests is that high-strength steel can be used efficiently and that the empirical method of design can be made simpler.

Extensive tests on inverted umbrella and saddle-shaped models indicate that the design of thin-steel hypar roofs is usually governed by stiffness, rather than by stress limitations. The rise-span ratio and the shear rigidity of cold-formed decks are the most important factors determining the stiffness of the structure. Deck buckling is causd by the uniform shear stresses in the shear-diaphragm type of action of the shell which dominates the response of hypar shells. This experimental investigation yielded empirical design information in thin-steel hypars and also provided checks on other analytical studies.