Browsing by Author "Vann, W. P."
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Item Behavior of steel beams subjected to alternating inelastic strains(1969) Ozier, Lynn Davis; Vann, W. P.This thesis reports an experimental study of the load deflection behavior and fialure characterisitcs of cantilevered rolled steel beams which undergo alternating inelastic strains. The beams are clamped into a rigid fixture to avoid connection problems, and are loaded cyclically between equal positive and negative values of end deflection which are of a magnitude such that fracture occurs at a relatively low number of cycles. The boundary conditions for twist and for lateral deflection are approximately "fixed-pinned". The development of flange, web, and lateral buckling is observed along with the effects of this buckling on the load capacity and the development of failure. The experimental parameters studied are the values of the flange width-to-thickness ratio, b/t (9.97 and 16.0); the web depth-to-thickness ratio, d/w (16.0and34.7); the length ratio, L/ry (30 and 60); and the magnitude of the end deflection at which each beam is cycled. It is found that, in general, after two or three cycles of loading the load-deflection hysteresis loops become smaller, due to a decrease in the peak cyclic loads and to a reduction in stiffness. These losses in load capacity and stiffness are related to the development of the different types of buckling.Item Cyclic loading of simple braced frames(1968) Houser, Conrad Bernard; Vann, W. P.The purpose of this study is to obtain experimental information about the load-deflection behavior under monotonic and reversed lateral loading of simple one-bay, one-story steel frames with corner-to-corner bracing. Model frames with pinned and with rigidly welded joints are considered. Slowly applied lateral loads that carry the structures well into the inelastic range of deformation are included, but vertical loading is not considered. The primary test variables are the stiffnesses and strengths of the bracing members and of the frames. It is found that diagonal members composed of cables with standard clamps cannot be counted upon to maintain their strength beyond the elastic limit but that mild steel diagonal members with larger effective areas at the ends than in the middle do provide useful strength and ductility in the inelastic range. For a pinned frame with diagonals of the latter type, the idealized elastoplastic "slip" model provides a good approximation to the load-deflection relationship of the structure, so long as strain-hardening effects are neglected and the compressive buckling loads of the diagonals are small compared to the tensile yield loads. For a rigid-jointed frame a more complicated idealized diagram made up of the "slip" model for the diagonals plus a conventional bilinear hysteretic model for the frame is found to provide somewhat less accuracy due to gradual yielding in the frame. It is found that in most practical cases the diagonals in a rigid-jointed structure of this type will yield at a lower deflection than the frame and will limit the deflection at which both components remain active. However, if the joints are welded, then local stresses in the welds may cause earlier fracture in the frame with cyclic loading.Item Dynamic response of certain elastoplastic systems of the shear beam type(1967) Sung, Leonard Chiuan-Lin; Veletsos, Anestis S.; Vann, W. P.A quantitative study is made by means of a digital computer of the dynamic behavior of certain elastoplastic systems of the shear beam type. The systems considered have from two to five degrees of freedom and particular distributions of mass, stiffness, damping, and yield level characteristics, but wide ranges of the fundamental frequency and the magnitude of the yield level are examined. The systems are subjected to two prescribed motions of the base, a simple pulse and an earthquake record. The response of each elastoplastic system is compared to that of an associated elastic system. Particular attention is given to the following aspects of the response: the location of the spring in which the maximum deformation occurs, the magnitude of the maximum deformation, and the effect of the number of degrees of freedom on the maximum deformation trends.Item Experimental buckling criteria for thin pierced plates(1971) Sehested, John H; Vann, W. P.Tests conducted with a pierced light-gage, cold-formed steel channel were used to evaluate four different criteria for experimentally determining the elastic buckling loads of thin plates. The single test specimen was a ten foot length of a 14-gage section with a nominal 8" web and nominal 3" lipped flanges. The section was loaded as a beam bent about its minor axis so that the web was placed in compression. A constant-moment mid-span region of five times the web width simulated a long plate subjected to in-plane compression. Tests of the unpierced specimen were followed by tests in which the specimen had a single hole in the center of the web. A repetitive process of flanging the plain holes and then cutting off the flanges created a succession of plain and reinforced holes of increasing diameter. A total of thirty-six tests were carried out. The specimen was instrumented with as many as forty electric strain gages and nine dial gages. The four buckling criteria considered were the maximum strain (or strain reversal) criterion, the top-of-the-knee criterion, the inflection point criterion, and the Southwell plot method. The last was judged to be the most accurate and appropriate, and it was applied in studying the effects of the hole on the elastic buckling load. The critical load was found to be insensitive to hole size for both plain and reinforced holes up to a hole diameter of about one-half the plate width. Tests were not conducted for large holes. The addition of a reinforcing lip increased the buckling load by over 50%. The experimental results agree fairly well with the results of a finite element study.