The aim of this research is to evaluate the dynamic response of steel concentrically braced frames (CBFs) considering the nonlinear response of embedded footings in granular soils through the Beam on Nonlinear Winkler Foundation (BNWF) approach, which allows to the vertical, rotational, and horizontal response of the soil-foundation system to be modelled using backbone curves. To model the vertical stress-displacement behaviour of footings, it is possible to define a backbone curve capable of reproducing the total response by adding in series the behaviour of the compression zone with that of the tension zone. The shape of the compression zone is described by an elastic response with a slope that represents the dynamic stiffness of rigid foundations combined with a non-linear zone calibrated through field tests. Furthermore, the moment-rotation behaviour is captured via the distribution of vertical springs placed along the footing length. When uplift of the soil-foundation system is allowed, some authors simplify their models by considering the maximum tension capacity to be 0% to 10% of the ultimate bearing capacity (qu), or even neglecting it in some cases. However, it is necessary to consider the horizontal stresses of the native soil on site and the degree of compaction of the soil mass above the footing to avoid significant deviations between the analysis results and the real response. The nonlinear response of the tension zone has been modelled taking into account these parameters, which are defined by the soil properties and the construction method used in several countries, characterised in some cases by deeper embedment depths of 1 to 3 metres. This research project proposes a procedure whose implementation has been validated through various pushover and time-history analyses on an archetype CBF structure for different soil conditions, considering various embedment depths. The procedure can predict the influence of the uplifting mechanism of the footing on the dynamic response, using non-linear springs calibrated according to field and laboratory experimental data. The results suggest that the dynamic response of the structure is influenced by the stress-displacement behaviour of the footing tension zone. The proposed model could be used to simulate the flexible support condition of embedded footings to estimate the nonlinear dynamic response of the structure when carrying out performance-based design procedures.
