Abstract: Based on existing macroscopic global seismic damage models, the Linear Modal Assurance Criteria (LMAC) method is used to consider modal transition that occurs commonly in lattice shells excited by strong earthquakes. In view of dynamic properties of lattice shells, a simplified modal damage model with modal contribution coefficient equal to 1.0 is presented and used to generate a global seismic damage index, with the assumption of total independence between modal damage. This simplified model is applied and numerically validated in the damage assessment of a 40m-span example Schwedler single-layer latticed shell excited by strong earthquakes. The damage indices generated from the model comply with the well-known positive S-type damage evolution curve, if modal matching and the contributions from higher modes are seriously treated. The assessment results also agree well with the responses, especially the maximum nodal displacement of the shell from incremental dynamic analysis (IDA) with three earthquakes. In addition, the simplified model is able to quantify the influence of initial imperfections on global damage, and to reveal the multiple modal properties of such influence. Although the results from IDA are strongly dependent on the selection of earthquakes, an ideal consistency has been shown in the computed damage indices corresponding to all characteristic points.