Advancing the Structural Safety & Efficiency of Modular Construction Connections under Normal and Extreme Loading Conditions

Lack of experimental investigation of the structural performance of beam-to-column connections (i.e. intra-module connections) within corner-supported modular steel buildings (MSBs) has resulted in these connections typically being assumed as fully rigid. However, this is rarely the case due to the use of square hollow sections (SHS) columns in which the wall of the SHS welded to the adjoining beam can deform locally under concentrated load from the beam. A new computationally efficient phenomenological beam element model (BEM) with bilinear/trilinear moment-rotation relationship (initially validated through experiments by others) of the intra-module connections proposed herein has initially shown that the vertical displacement following the notional removal of one support in one module is at least 16% higher, compared to model with fully rigid intra-module connections. Despite the investigation only analysing one module, it showed how the semi-rigid intra-module connections affect its vertical stiffness. Therefore, the influence of accurate moment-rotation behaviour on a full building numerical model needs to be investigated. Hence, two types of eccentrically connected welded intra-module connections, typically found at the floor and ceiling levels of corner-supported steel modules, were experimentally tested to identify their precise moment-rotation (M-φ) response. The obtained response allows the actual behaviours of these connections to be better represented in the numerical model of the modules. In the experiments, two full-scale connections each of 5 repeat tests, showed that failure was governed by weld fracture between the cap plate and the column in all connections, under concentrated bending load from the beam. Similar failure patterns were observed in the validated numerical shell element model (SEM) of the connections. The influence of axial compression load in the column on the connections’ M-φ response was also investigated numerically using the validated model. It was found that the presence of axial compressive load in the column reduced the ultimate bending capacity of the connections, on average, by 17%. Furthermore, the numerical results showed that the commonly used deformation limit of 0.03b_0 to predict the ultimate bending capacity of hollow sections connections may not be applicable when the members are connected eccentrically to the SHS column. Local failure (tearing or bearing) at the side wall of the column occurred in almost all connections with column walls less than 10 mm thick. This is due to the nature of the eccentrically connected intra-module connections that transfer most of the bending load directly into the side wall of the column. For connections with column wall thickness larger than 10 mm, greater numbers of local crushing/yielding failure (i.e. plastic hinge) as a result of excessive rotation were observed in the beam. Following the experimental and numerical investigations of the intra-module connections, a full-scale 10-storey corner-supported MSB with experimentally and numerically validated semi-rigid intra-module connections throughout the building was created. The robustness assessment of the full building model demonstrated that disproportionate collapse was prevented in all ground floor corner removal (CR), external removal (ER) and internal removal (IR) scenarios in both cases where the ground floor columns were separately designed to axial loads at 100% and 110% their buckling capacity at ultimate limit state (ULS) before the notional removal. These results suggest that the structural design of the columns on the ground floor could be optimised to be more efficient. Furthermore, ER scenarios were found to be more severe than CR scenario where the latter was commonly deemed the most onerous in traditional framed buildings. Additionally, all the partially yielded intra-module connections, following the notional removal of column(s) for all the removal scenarios investigated