Evaluation, Modeling, and Retrofit of Flat-Slab Buildings subjected to Seismic Loading
Doctor of Philosophy thesis
Flat-slab buildings designed and detailed for gravity loads only typically do not have the ability to resist moderate earthquakes without experiencing severe damage. The damage potential of such seismically deficient buildings therefore needs to be assessed and strategies developed to improve their seismic resistance. Punching failure at slab-column connections in non-ductile flat-slab buildings during earthquakes can trigger progressive collapse of floor slabs. Based on the test results of a large number of interior and exterior connections, a methodology is developed to predict shear and unbalanced moment-transfer capacities of connections under combined gravity and lateral loads. Furthermore, a frame analysis procedure is developed based on the equivalent frame concept which targets both the moment-transfer capacity as well as stiffness of the interior and exterior slab-column connections. The approach employs a parametric hysteretic model and is based on the effective slab-width concept. The proposed procedure for evaluating the seismic capacity of flat-slab connections and frames is verified by comparing the calculated and measured responses of two-bay flat-slab subassemblies tested under earthquake-type loading. Seismic reliability against punching failure of slab-column connections in flat-slab buildings designed for gravity loads was investigated using the proposed equivalent frame approach. The reliability analysis indicated that the flat-slab buildings constructed prior to the 1960's could experience significant damage during moderate intensity earthquakes. By limiting the gravity load on floor slabs and by controlling the lateral drift, the potential for punching failure in flat-slab buildings can be minimized. The seismic resistance of older flat-slab buildings can be improved by retrofitting interior connections to protect against progressive collapse and by utilizing infill walls to control lateral drift. An economical connection retrofit scheme is proposed and verified experimentally. The equivalent strut concept is used to model masonry infills whose effectiveness in controlling the lateral drift is demonstrated through theoretical analysis of typical flat-slab frames.
Earthquake engineering; Buildings -- Earthquake effects