Patent ID: 8781795

Claim:
A computer-implemented strut and tie method for waffle slabs, comprising the steps of: building a 2-D strut and tie truss model for each rib in both directions, wherein for each 2-D truss, a bottom reinforcement represents a bottom tie, a portion of concrete top slab along the ribs represents a top strut, stirrups or concrete at rib intersection represents the vertical tie, nodes of trusses are defined by intersections of top and bottom chords with vertical ties, and a compressive force-resisting diagonal strut member interconnecting top and bottom nodes is provided lengthwise along each rib; connecting each 2-D strut and tie truss representing a rib to perpendicular trusses at rib intersections, thereby forming a 3-D strut and tie structural model defining a plurality of waffle openings; providing cross-bracing at the top of the 3-D strut and tie structural model, the cross-bracing simulating action of an exemplary three-dimensional concrete waffle slab; applying structural loads including self weight to the top nodes of the 3-D strut and tie structural model; analyzing the 3-D strut and tie structural model either by linear or 3-D nonlinear analysis to obtain an axial force in each said diagonal strut member; using said axial force in each said diagonal strut member in a design of each of the diagonal strut members; recommending a nonlinear analysis with nonlinear material properties; predicting strength and mode of failure of the slab based on the nonlinear analysis recommendation; and applying linear analysis at service loads when materials are in linear elastic range.