Masonry construction comprises a large portion of building construction in the U. S. and the world. Reinforced masonry construction use is increasing in moderate to higher seismic zones because of its apparent features of economy, fire safety, architectural flexibility and ease of construction. The present state of masonry structural analysis and design, and materials and construction technologies does not enable an accurate prediction of building behavior under lateral loads such as seismic loads. In the U.S., masonry buildings are designed and built with methods, codes and standards that rely upon a mixture of working stress methods, empirical rules, and questionable methods for determining allowable stress values. Masonry is also a complex building material because of the large number of design and construction variables which influence the final product configuration and its response under seismic loads. In order to describe the seismic response of masonry buildings it is necessary to develop the fundamental knowledge base to determine basic design methodologies consistent with safety and economic requirements. This research project concentrates on a lumped mass parameter floor slab spring system model to be used for dynamic analysis of buildings. This includes hysteretic modeling for horizontal floor systems consisting of composite steel-deck-reinforced slabs and concrete hollow-core precast plank slabs. This research develops an analytical non-linear model of load- displacement history of horizontal floor systems to provide associated displacements and stiffnesses for an integrated dynamic spring model. It provides a computer model using experimental data collected from other masonry researchers. This project is part of the U.S.-Japan Coordinated Program for Masonry Building Research and the Technical Coordinating Committee for Masonry Research (TCCMAR) Program.