Steel, Timber and Plastic structures

A study on the dynamic response of single-storey steel frames equipped with a novel friction damper device (FDD) is presented. Extensive testing was carried out for assessing the friction pad material, damper unit performance and scaled model frame response to lateral harmonic excitation. Numerical simulations based on non-linear time history analysis were used to evaluate the seismic behaviour of steel frames with inserted FDD. The governing parameters were identified and their influence was traced and summarised along with implications for practical design. The application of the new FDD presents a feasible alternative to the conventional ductility-based earthquake-resistant design both for new construction and for upgrading existing structures. 

A scaled specimen representing single-storey partially-composite steel plate shear wall was tested under cyclic loading. The slender steel web panel had a single-sided reinforced concrete encasement attached with headed shear studs in order to prevent the shear buckling and tension-field action of the slender web when subjected to lateral seismic forces. A specific feature of the tested specimen was the use of semi-rigid beam-to-column connections and purposely made gaps between the boundary steel frame members and the concrete encasement. The testing was conducted using the recommended testing procedure of ECCS and showed that the specimen has stable hysteretic behaviour and dissipative capacity superior to that of its pure steel counterpart tested under the same conditions. Parallel numerical simulations based on simplified and more refined nonlinear models were carried out in order to provide insight into the complex interaction between the shear wall components. Both experimental testing and numerical simulation revealed that the cyclic response of the specimen was affected by the formation of local tension-field action in-between the shear stud rows, which is an indication that the seismic codes shall improve their provisions for the design of reinforced-concrete encasement and its shear stud connection to the slender steel web panel.

The paper presents an overview on nonlinear modeling and numerical evaluation of the seismic response of two steel single-storey concentrically braced frames with X-brace configuration previously tested by other researchers. The numerical simulations included series of nonlinear time history analyses using OpenSees computational framework. The brace members were modeled with fiber frame finite elements with distributed plasticity taking into account their initial imperfections. The material model accounted for the low-cycle fatigue effects based on the approach proposed by several other research works on the topic. The maximum response displacements of the investigated specimens were also evaluated following the procedure given in Annex B of EN 1998-1 (Eurocode 8). However, the previously conducted shake table testing and the herein presented numerical results indicated that this procedure may significantly underestimate the displacements of single-storey dissipative short-period CBFs designed with high values of the behaviour factor. It was also found that the numerical estimation of the maximum and residual lateral response displacements of the analyzed CBFs based on nonlinear time history analysis is very sensitive to small variations of the material properties and assumed damping model (damping matrix definition). Therefore the experimentally-obtained response displacements can be realistically predicted only if the parameter variations are taken into account in the numerical analyses. The authors believe that the use of high values for the behaviour factor in the design of low-rise CBFs may result in excessive residual displacements and low-cycle failure of the brace members. It is suggested the further revisions of Eurocode 8 impose lower reference values of the behaviour factor for the short-period steel CBFs with slender braces in order to reduce their ductility demand and related damage in strong earthquakes.