This thesis describes investigations on the inclusion of realistic considerations in vibration serviceability assessment of low-frequency steel-concrete composite office floors, aiming to represent their in-service conditions. The motivation for the research works presented is the continuous reporting of excessive vertical vibrations induced by walking loads in modern office floors that feature lightweight, slender, long-span structures, with “column-free” open-plan areas. The contribution of this thesis to knowledge is the 1) vibration serviceability check of framing configurations with both short- and long-span secondary beams, 2) investigation of modal properties and dynamic response of office floors with voids and layouts of full-height partitions, 3) serviceability assessment using calibrated vibration dose values, considering both different number of walk events and statistical distribution of pacing rates, and 5) environmental impact of modifications of floor depth and steel beam profiles to reduce floor vibrations. It was found that structural modifications can result in floors with excessive consumption of materials and high carbon footprint. Also, the consideration of voids and partitions led to a more realistic response, with excessive vibrations limited to a few panels, which suggests the use of local vibration control measures, instead of modifications on the whole structure. Finally, the use of calibrated vibration dose values with realistic assumptions resulted in leaner structures, depending on the acceptable limits used.