Elisa Poletti

Full-Scale Experimental Testing of Retrofitting Techniques in Portuguese “Pombalino” Traditional Timber Frame Walls

Traditional timber frame walls are constructive elements representative of different timber frame buildings, well known as efficient seismic-resistant structures. They were adopted as a seismic-resistant solution in Lisbon’s reconstruction after the 1755 earthquake. To preserve these structures, a better knowledge of their seismic behavior is important and can give indications about possible retrofitting techniques. This article provides a study on possible retrofitting techniques adopting traditional solutions (bolts and steel plates). Static cyclic tests were performed on retrofitted traditional timber frame walls. The experimental results showed the overall good seismic performance of steel plates and the more ductile behavior of bolts retrofitting.

Structural Permanence in Pre- and Post-Earthquake Lisbon: Half-Timbered Walls in Overhanging Dwellings and in Pombalino Buildings

ABSTRACT Timber-framed walls represent a structural permanence in Portugal before and after the 1755 earthquake. Despite improvements made in the Pombalino buildings (late 18th century) for seismic design purposes, comparisons can be drawn with the use of mixed timber-masonry structure in overhanging medieval houses. The structural efficiency of medieval overhanging dwellings is due to the reduction in the weight from the lower to the upper floors, the ductile behavior, and the connections between the infill frame and the floor structure. A survey of examples still standing in Lisbon is carried out by the authors through archival dataset and on-site analysis. Special attention is paid to the degree of authenticity and state of conservation. Dissonances and continuities in the original construction and subsequent refurbishment are analyzed in three cases that are selected for their localization and remarkable architectural or typological features.

Single step joint: overview of European standardized approaches and experimentations

In the field of Built Heritage Restoration, engineers have to work with old structures made of poorly preserved timber elements. The assessment of timber elements and connections is a major issue for engineers involved in a restoration project. Before thinking about any intervention techniques, engineers have to properly understand how the carpentry connections fail, which parameters influence the failure modes (e.g. geometry of the joint, mechanical properties of the wood) and how the internal forces are distributed into the joint to finally figure out how to design the traditional carpentry connections. The present paper aims at raising those questions focusing on the Single Step Joint (SSJ) design. Even if this common joint between the rafter and the tie beam is geometrically simple, one may pick up three SSJ families from the past till today: the Geometrical Configuration Ideal Design, the Geometrical Configuration Perpendicular to the Tie Beam and the Geometrical Configuration Perpendicular to the Rafter. The first one is more recent because its geometry requires accurate timber cutting, using new technologies (e.g. Computer Numerical Control). For each one, some general design rules about the SSJ geometrical parameters are defined by some European standards (e.g. Eurocode 5 in Design of timber structures—part 1‐1: general—common rules and rules for buildings. CEN, European Standardisation Institute, Brussels, 8) or authors (e.g. Siem and Jorissen in Shatis’15: 3rd international conference on structural health assessment of timber structure, vol 1. Wroclaw, Poland, 9–11 Sept 2015, 11), but no detail is available on how to design this connection in order to prevent the shear crack at the heel depth in the tie beam, or the compressive crushing at the front-notch surface. Hence the design rules and the emergence of failure modes must be defined according to the SSJ geometrical parameters. In order to check the design equations and the failure modes, lab tests on the three SSJ families have been carried out, modifying the heel depth, the shear length and the inclination of the rafter.

Seismic Behaviour and Retrofitting of Timber Frame Walls

Half-timbered buildings are well known as one of the most efficient seismic resistant structure in the world, but their popularity is not only due to their seismic performance, but also to their low cost and the strength they offer. These structures generally consist of exterior masonry walls with timber elements embedded which tie the walls together and internal walls which have a timber frame with masonry infill and act as shear walls. Generally, different types of infill could be applied to half-timbered walls depending on the country, namely brick masonry, rubble masonry, hay, mud, etc. The focus of this paper is to study the seismic behaviour of the walls when no infill is present, i.e. considering only the timber frame, and then compare the results with those of the infill walls. Static cyclic tests have been performed on unreinforced timber frame walls and appropriate strengthening solutions have been applied in order to test the walls in a retrofitted condition, namely (1) steel plates with different configurations and (2) steel flat bars inserted with the NSM technique.

Numerical modelling of the cyclic behavior of timber-framed structures

Abstract The present paper presents a study on the applicability of numerical models in predicting the global response of timber-framed shear walls during earthquake events. Based on previous in-plane cyclic testing of traditional timber frames with and without masonry infill, numerical models were developed to describe the cyclic response of traditional timber frame walls including flexural behavior, pinching and strength degradation. The numerical models were developed in the finite element software OpenSees with calibrated springs representing nailed connectors found in traditional half lap joints. Based on the calibrated models a study was conducted on the timber frame wall with brick infill model by varying wall configuration and analysing cumulative energy dissipation and the effect of slenderness and load capacity with increasing drift. A good correspondence was obtained with the experimental data and future work will include the application of the model to whole buildings.

Numerical Approaches for the Analysis of Timber Frame Walls

Timber frame structures constitute an important cultural heritage of many countries, since they represent a typical anti-seismic construction adopted worldwide and are worth preserving. Recent experimental results have shown that the seismic response of traditional timber frame walls varies greatly with the type of infill, the type of connection and wall geometry. Two simplified 2D numerical models were created and in-plane monotonic tests were simulated and calibrated using recent experimental results. Material non-linearity was considered for all materials. Considering the numerous advantages of the use of simplified models, parametric analyses were carried out in order to evaluate the influence of parameters such as type of infill, infill-frame connectivity, timber type, connection type. The greater influence on the behaviour of the walls is given by the quality of the joints as well as the connectivity between timber and masonry, behaviour that is in accordance with experimental results. Additionally, the geometry of the wall influences its stiffness and load capacity.

An overview on the seismic behaviour of timber frame structures

Masonry and timber are materials used since ancient times in construction. Masonry buildings constitute an important percentage of the existing building stock and their preservation should be considered, since a large part of historic buildings are actually in masonry.

Seismic Performance of Traditional Half-Timbered Walls: Experimental Results

Half-timbered structures have been adopted as a typical seismic-resistant construction in many countries and they represent an important cultural heritage worth preserving. Little information is available on the performance of such structures when subjected to seismic actions; to overcome this lack of information, in-plane cyclic tests were carried out on real-scale half-timbered and timber frame walls, taking into consideration parameters such as vertical pre-compression and type of infill. Additionally, considering the great rehabilitation effort that has been taking place in the last decade, retrofitting solutions were proposed and tested on the already tested walls. Analysing the typical seismic parameters (e.g. ductility, energy dissipation, viscous damping), the influence of the type of infill and of the different retrofitting techniques were verified.