Luca Pozza

An analytical formulation of q-factor for mid-rise CLT buildings based on parametric numerical analyses

The seismic response of cross-laminated timber buildings is analysed with the aim of assessing the correlation between the dissipative capacity (i.e., q-factor) and the assembling methodologies and geometrical properties. A parametric study was performed by means of incremental dynamic analyses on various building configurations with varying constructive features such as density of panel-to-panel joints and building slenderness. The results are firstly used to define parameters representative of the building geometry and assembling methodology and then to develop an analytical relationship to compute their most suitable q-factor starting from such parameters. The proposed method is finally validated referring to significant case studies available in literature.

Seismic design of floor–wall joints of multi-storey CLT buildings to comply with regularity in elevation

The effects of irregularity in elevation of cross-laminated timber buildings have not been fully analysed in literature to provide useful information for the design. In this work, a number of building configurations, regular or irregular in elevation, characterized by a different arrangement per storey of the floor–wall joints have been analysed by means of non-linear dynamic analyses. Comparative results in terms of ratio between the behaviour q-factor of the investigated irregular configurations and that of reference regular ones, show that less dissipative capacity can be expected if the building is irregular due to a disequilibrium among storeys between the actual and the required strength provided by the floor–wall joints. A correlation method to estimate the behaviour q-factor for perfectly regular cross-laminated timber buildings is here presented and extended to in-elevation irregular ones. A new empirical formulation to assess the reliable corrective factor accounting for the irregularity in elevation of cross-laminated timber buildings, according to Eurocode 8 provisions, is also proposed. A final discussion about the implications of in-elevation irregularity on the building design is reported.

Seismic analysis of multi-storey timber buildings braced with a CLT core and perimeter shear-walls

The seismic behaviour of multi-storey heavy-frame timber building superstructures braced by Cross-Laminated-Timber (CLT) shear-walls is investigated based on numerical linear dynamic simulations. All systems analysed have the same rectangular plan footprint dimensions, type of framework and shear-walls arrangement at each storey. For structural efficiency, the layout of lateral load-resisting systems combines a central building core with partial length perimeter shear-walls. What differs between cases is the number of storeys (3, 5, or 7), components specifications, and shear-walls anchoring methods. Special attention is paid to examining how the vertical joints between CLT shear-walls affect the seismic response. The properties of connections used in the analyses are obtained from testing of hold-down anchors and angle-bracket shear connectors. Results of the simulations demonstrate that mid-rise buildings are prone to effects of the lateral flexibility and transfer high uplift loads to the foundations during design level seismic events. By implication, special design measures may be necessary to limit the lateral drifts to the levels prescribed by the standards. Simplified representations of connection properties may yield to inappropriate predictions of lateral drifts of superstructures during seismic events, and to an improper design of connections. In future, the efficient realisation of multi-storey heavy-frame timber building superstructures braced by CLT shear-walls depends on the use of proper connection devices. Suitable devices may include metal tie-downs capable of reducing the inter-storey drift, while transferring forces to foundations in a manner that does not locally damage frameworks, shear-walls, or floor and roof diaphragms.

NUMERICAL SIMULATION OF THE COUPLED TENSION-SHEAR RESPONSE OF AN INNOVATIVE DISSIPATIVE CONNECTION FOR CLT BUILDINGS

This work presents a numerical macro-element model able to simulate the dynamic response of an innovative ductile and highly dissipative bracket for assembling of crosslaminated timber structures. This bracket resists to both tensile and shear forces and has been conceived to realize all the seismic-resistant joints of the building with a unique type of connection able to maximize the seismic capacity of the entire structure. The main issue of these kinds of connection is the reliability of numerical models in reproducing the coupled tensionshear behaviour and dissipative capacity with reduced computational effort, so as to simulate the non-linear response of complex buildings. With this aim, a numerical macro-element model was developed within the finite-element framework OpenSees using an assembly of linear beams and plastic hinges capable of simulating the complete tension-shear strength domain of the connection. The macro-element model was calibrated referring to the results from quasi-static cyclic-loading tests of the connector performed in pure shear and pure tension. The coupled tension-shear behaviour of the macro-element model was then validated on the results from independent numerical simulations performed using detailed 3D models with solid finite elements, including material and geometric non-linearity. Obtained results demonstrate that the developed macro-element model is able to describe accurately the hysteretic behaviour of the bracket with a very low computational effort. Therefore, it can be conveniently adopted to simulate the seismic response of complex structures. 247 Available online at www.eccomasproceedia.org Eccomas Proceedia COMPDYN (2017) 247-254

Dynamic simulation of an irregular masonry building with different rehabilitation methods applied to timber floors

Abstract. The in-plane stiffening of timber floors is normally supposed to be an improvement of the seismic performance of un-reinforced masonry buildings. A modelling strategy to simulate the non-linear behaviour of masonry buildings with simple or strengthened timber floors is presented: it allows to implement the in-plane hysteretic response of the floors and different types of failure of the masonry walls. This model was used to predict the modification of the seismic response of a two-storey masonry building subjected to different rehabilitation techniques applied to the timber floors. The case-study building is irregular in plan to study also torsional effects and out-of-plane deformation of the walls. The mechanical parameters of the non-linear elements representing masonry piers and floors were calibrated replicating experimental tests available in literature. The outcomes of this work were obtained with non-linear dynamic analyses, in order to allow the model to consider not only the actual elastic and post-elastic stiffness of the floors but also their energy dissipation capacity. Available online at www.eccomasproceedia.org Eccomas Proceedia COMPDYN (2017) 2269-2282