Cristiano Loss

Direct Displacement-Based Design of Glulam Timber Frame Buildings

We introduce a direct Displacement-Based Design methodology for glued laminated timber portal frames with moment-resisting doweled joints. We propose practical expressions to estimate ultimate target displacement and equivalent viscous damping, and we demonstrate that these expressions provide prior values that are close to those obtained a posteriori using a more refined model. Applied to case studies, the method yields base-shear forces lower than those obtained using the force-based approach of Eurocode 8. This is due to the high dissipation capacity of the specific connection technology, which apparently is conservatively accounted for in the q-factor of Eurocode 8.

On Estimating the Seismic Displacement Capacity of Timber Portal-Frames

An analytical model is proposed to estimate the seismic displacement capacity, at serviceability and ultimate limit states, of timber portal frame structures with dowelled joints. The predictions from the simplified formula are compared with the results of numerical analyses carried out on a sample of representative cases. These cases result from a simulated design procedure, consistent with Eurocode 8, and are generated via Monte Carlo sampling, with varying sizes, materials and load conditions and also uncertainties in these parameters. Based on the outcome of the analysis we propose a set of practical formulas which allow prediction of the displacement with a given percentile of overestimates. In addition, it is shown that these equations for displacement capacity can be used to generate fragility curves for performance-based earthquake engineering applications. Prescription of an overstrength factor in code provisions is recommended to avoid brittle failure.

Innovative construction system for sustainable buildings

This paper deals with a contemporary integrated and sustainable construction technology for new residential buildings. Specifically, this research aims at developing innovative steel-timber hybrid structures which allow a rapid assembly of the individual prefabricated components, minimizing the construction times and limiting the costs of the work. The numerical analyses performed on a multi-storey building for social housing will be presented and discussed. The in-plane behaviour of the floors and shear walls will be analysed, considering in particular the types and arrangement of the different timberand steel-timber joints. The connections to be used among the construction elements will be selected in order to develop a sufficient stiffness, ductility and bearing capacity according to the design criteria for seismic-resistant structures. These connections allow to enhance the on-site assembly operations, therefore working effectively also under harsh climatic conditions.

A New Method to Assess the Seismic Vulnerability of Existing Wood Frame Buildings

This paper aims at applying a direct displacement-based method to assess the seismic vulnerability of existing multi-storey wooden buildings. This procedure is consistent with Priestley’s direct methodology firstly developed for reinforced concrete structures. The distinctive characteristic of the proposed method is that the system response is quantified through the use of displacements instead of equivalent elastic strengths, according to the traditional force-based approaches. Consequently, in comparison to common force-based procedures, this method cannot only be considered as a rational alternative but also as a new seismic philosophy to design or assess structures. A representative timber construction system commonly used in Italy was selected as case study. The construction system illustrated in this work was analysed in detail, with special attention given to the mechanical connections typically used. The typical failure mechanisms and the energy dissipation capacity of the structure or of its members were identified on the basis of the mechanical properties of structural parts and connections, as well as of their geometry. In the proposed direct displacement-based assessment approach, the seismic intensity that would cause the limit state to be exceeded can be calculated by means of simple formulas. Therefore, the capacity to demand ratio can be simply derived. The procedure could be used to gauge the likelihood of losses, by combining it with simple loss models to account for probabilistic aspects.

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.