In this paper the postbuckling behavior of multibay composite shear webs is explored. Several test specimens are designed through the use of advanced state of the art design methods taking into account material anisotropy. The panels are subjected to static as well as fatigue loading in a series of well instrumented and carefully conducted tests to determine various failure modes as well as failure loads. The experimentally ob- served failure modes and failure loads are compared with design loads and failure modes. Large deflection analysis is used to examine failure modes typical of composite panels. Composite shear webs are shown to have significant postbuckling strength and exhibit failure modes that are quite different from metal shear webs. TRINGER-STIFFENED shear panels are used extensively in many metal aircraft applications. In many of these applications buckling of the skin between the stringers is permitted to occur below limit load—sometimes well below. Composite materials are undergoing a rapid use escalation in new and projected systems. In order to make composite components weight efficient as well as cost competitive with their metal counterparts, the postbuckling strength of composite materials must be exploited. The available data in the literature indicate that composite materials have significant postbuckling strength. Postbuckling strength of boron-epoxy shear webs is demonstrated by Kaminski and Ashton.) In a similar study by Bhatia,2 graphite-epoxy shear webs are shown to have considerable postbuckling strength. In metal structures, the principal structural concern for postbuckled shear webs is that significant permanent set not occur for loading up to limit loads. Fatigue and ''wear out" are not of concern. For advanced composite stiffened panels, the concern about postbuckling behavior is much greater. Catastrophic failure can occur in the buckled skin due to high local compressive stresses or tension stresses; the relieving effects of yielding, as found in most metal structures, are not available in most practical composite layups. These com- pressive stresses, in addition to tension stresses present in shear webs, may result in severe strength degradation of composite laminates when subjected to repeated fatigue cycles. The purpose of this paper is to evaluate the behavior of realistically configured multibay panels- operating well into the postbuckled regime, to disclose specific failure modes, to assess the adequacy (or inadequacy) of available buckling and strength prediction methodology, to provide direction for future research, and to provide confidence in the viability of this useful type of construction. The main components of a shear beam are the web, uprights, and chords. The web transfers and/or resists the applied shear. The uprights are used to increase the buckling load of the web and to resist compression loads that are in- troduced from the tendency of the tension field forces in the web to pull the chords together. The chords together with the uprights prevent the structure from collapsing and are sub- jected to primary axial compression and tension loads due to primary bending of the beam as well as to secondary bending about their own axes due to the vertical component of the