APPLICATION OF AN ORTHOTROPIC MACRO-STRIP PLATE ELEMENT WITH STIFFNESS DISCONTINUITIES

Several plate-type civil structures exhibit stiffness and/or cross-sec tional discontinuities in one direction. Examples for concrete slabs i nclude ribbed plates, slabs with drop panels, and slabs with varying c ross-section or reinforcement. Similarly, longitudinal stress-laminate d timber bridge decks stiffened with thin steel plates present sudden stiffness discontinuities along the deck width. When modeling such com plex structures with conventional finite elements, the drastic stiffne ss discontinuities can lead to ill-conditioning of the stiffness matri x, inaccurate results, and even singularity. To overcome this problem, we present in this paper the formulation and application of an orthot ropic macro-strip element suitable to model rectangular plates with di scontinuities along one principal axis. The stiffness jumps are descri bed by unit step functions, which are used to derive stiffness distrib utions for any number of segments within the element. The number of se gments selected does not increase the element degrees of freedom, and in contrast to the requirements of a finite element mesh with conventi onal plate or solid elements, the present model requires only a few ma cro-elements to model a structure. The system model is assembled and s olved with the mathematics software MAPLE. The present model is valida ted with finite element solutions using solid and plate elements. As a practical application, the present model is used to predict displacem ents for three stress-laminated timber bridges currently in service, a nd the results compare closely with field-measured values.