In situ measured cross section geometry of old timber structures and its influence on structural safety

Abstract

Old timber structures may show significant variation in the cross section geometry along the same element, as a result of both construction methods and deterioration. As consequence, the definition of the geometric parameters in situ may be both time consuming and costly. This work presents the results of inspections carried out in different timber structures. Based on the obtained results, different simplified geometric models are proposed in order to efficiently model the geometry variations found. Probabilistic modelling techniques are also used to define safety parameters of existing timber structures, when subjected to dead and live loads, namely self-weight and wind actions. The parameters of the models have been defined as probabilistic variables, and safety of a selected case study was assessed using the Monte Carlo simulation technique. Assuming a target reliability index, a model was defined for both the residual cross section and the time dependent deterioration evolution. As a consequence, it was possible to compute probabilities of failure and reliability indices, as well as, time evolution deterioration curves for this structure. The results obtained provide a proposal for definition of the cross section geometric parameters of existing timber structures with different levels of decay, using a simplified probabilistic geometry model and considering a remaining capacity factor for the decayed areas. This model can be used for assessing the safety of the structure at present and for predicting future performance.

Repairing of a Timber Truss Through Two Different Techniques Using Timber Elements and Screwed Metal Plates

“…The collar beam trusses were constructed with an iron tie at the base and a timber tie beam at mid-height, Fig. 1 [5]. The iron tie prevented problems associated to horizontal thrust which could be increased in an earthquake.…”

“…This type of roof structure was developed to provide more internal room height without increasing the overall height of the construction. The collar beam truss has a tie beam at the mid-height [5], with a different connection system to the inclined rafters from the tie beam of traditional king-post trusses [6][7][8]. The most common and dangerous damage for this type of truss structure, may occur at the joint connection of the rafters with the tie beam and at the rafters ends (e.g.…”

A Holistic Methodology for Probabilistic Safety Assessment of Timber Elements Combining Onsite and Laboratory Data

“…The assessment and intervention on common timber structures is often based on visual inspection of the structure and consequent elaboration of damage maps or datasheets that indicate the segments or regions of the structure that are of higher structural concern and in need of intervention (Macchioni et al, 2012;Alessandri et al, 2012;Lourenço et al, 2013).…”

“…For example, when the timber element is visually graded as class I, the reliability index is 5.82, while it may decrease down to 1.33 when the element is considered not suitable for structural use. This information, combined with the use of decay models (Lourenço et al 2013), may be used in the prediction of the future performance of the element, and therefore be useful in the definition of maintenance and intervention planning.…”

Use of Bending Tests and Visual Inspection for Multi-Scale Experimental Evaluation of Chestnut Timber Beams Stiffness

“…2. Location for the sequential bending tests (dimensions in centimeters): a) visual inspection segments; b) gauge length for E m,l (in shade); c) gauge length for E m,g (in shade) duction of the effective cross section (Lourenço et al 2013). Another purpose of the classification without the parameters of external damage is to obtain reference values for comparison with the smaller samples that will be taken in the following steps of the experimental campaign.…”