Efficacy Assessment of Timber Based In-Plane Strengthening of Wooden Floors on the Seismic Response of Masonry Structures by means of DEM Analyses

Masonry buildings are highly vulnerable to seismic loading, and their dynamic response is strongly influenced by the timber floor in-plane deformability and by the quality of the wall-to-floor connections. Understanding the behavior of timber floors and roofs and their interaction with the masonry walls is therefore important for the protection of historical buildings. In a previous research project, different timber-based dry-connected floor strengthening solutions were tested under in-plane loads. The experimental results show a significant increase in shear strength and stiffness. Discrete Element Method is here used to evaluate the effectiveness of the strengthening solutions in avoiding the triggering of the out-of-plane collapse of masonry walls, first on a simple masonry cell, and then on a heritage listed masonry building. A detailed cyclic model of the floor behavior was implemented: the unreinforced and reinforced floors were described by beams connected with nonlinear springs, reproducing the experimental hysteretic response. Both the case studies highlight the effectiveness of the strengthening solutions in reducing the out-of-plane displacements of masonry walls, confirmed also by a comparison with the ideal rigid diaphragm case. The reinforced floor is able to transfer the seismic forces to the shear-resistant walls. The out-of-plane displacements are compatible with the wall capacity, and the reinforced floor hysteretic cycles contribute to dissipate part of the input energy. Moreover, a proper connection design can also cap the transferred seismic forces to an acceptable level for shear-resistant walls

Evaluation of timber floor in-plane retrofitting interventions on the seismic response of masonry structures by DEM analysis: a case study

The seismic response of existing masonry structures is strongly influenced by floor and roof in-plane properties. A strengthening intervention is often needed for traditional timber floors to overcome their low in-plane stiffness and to preserve historical buildings. In this study, the effects of unreinforced and reinforced timber floors on the seismic behaviour of an existing listed masonry building are investigated with dynamic non-linear analyses by means of the Discrete Element Method (DEM). With this approach, the failure processes and collapse sequences of masonry structures can be captured in detail. A previously developed model of the floor cyclic behaviour, based on experimental data, is applied herein to DEM models of the masonry building. Different seismic ground accelerations, different floor types and different floor-to-wall connections are considered. The results highlight the effectiveness of the analysed floor strengthening solution in reducing the out-of-plane displacements of masonry walls. With adequate connections, the reinforced floor is able to transfer the seismic forces to the shear-resistant walls up to the shear-sliding collapse of the structural sidewalls. A comparison with the ideal rigid diaphragm case confirms the good performance of the strengthened floors. The small observed out-of-plane displacements are compatible with the masonry wall capacity, and the reinforced floor hysteretic cycles contribute to dissipate part of the input energy. Moreover, different designs of the connections can also cap the transferred seismic forces to an acceptable level for shear-resistant walls

Proposal of a CLT reinforcement of old timber floors

Despite the fact that, from the mechanical point of view, there is no ageing issues of timber elements when they are properly used, many old timber structures require important interventions because of changes in uses (which modifies the regulating rules for example), of material decay (misuse of timber) or possibly of a faulty design or construction. In particular, timber floors in old structures often present large deflections and most the time had been designed for a maximum load much lower than the one prescribed by contemporary rules. After an introduction about timber floors and a short review about the reinforcement technics that exist, the present paper presents a new proposal for their reinforcement. The solution developed in the present paper uses a Cross Laminated Timber (CLT) panel screwed over the existing floor, keeping a small gap between the panel and the existing joists. In this way, the new “composite” floor presents higher stiffness and the gap is used for horizontal line runs. For the design of such a “composite floor”, modified Johanssen’s equations (including the gap between the CLT panel and the joists) are proposed and their application on a case study is presented.- (undefined