Grading of Low-Quality Wood for Use in Structural Elements

Timber is a sustainable resource, environmentally friendly and aesthetically pleasing. Using locally grown timber as building material leads to economic, social and environmental benefits. Being an organic material, timber is not homogeneous; hence, it is crucial to predict the base material quality. International codes require the use of wood previously graded according to the current regulations in order to verify its reliability when used as structural material. An exhaustive analysis of the state of art of different methodologies and code requirements for structural timber grading is presented herein. Structural timber grading methods and their applicability to low-strength timber is analysed and discussed with reference to Maritime Pine locally grown in Sardinia (Italy). Several physical and morphological parameters such as density, the presence of knots, clusters of knots, grain deviation, warping, annual ring width and moisture content had to be measured. Moreover, mechanical parameters (tensile strength and modulus of elasticity in tension) were measured and analysed in order to identify the strength class of Sardinian Maritime Pine. The operational issues related to the application of the different methodologies and code requirements for structural grading of low-quality wood are also discussed and analysed

from plastic waste to building material mechanical properties of recycled thermoplastic timber

The present paper illustrates the mechanical properties of a new structural product called Recycled Thermoplastic Timber (RTT), manufactured in Sardinia (Italy) and made of recycled plastics. The preliminary results of an experimental campaign aimed at assessing the main mechanical and physical properties of RTT are presented and discussed. Unreinforced and steel-reinforced thermoplastic timber profiles have been tested in laboratory and some mechanical and physical properties have been evaluated also varying the climatic conditions. Furthermore, weathering properties have been checked by testing the resistance to freezing and thawing. In light of the results since now achieved the prospect of using RTT as an eco-friendly alternative to wood and other building materials is discussed

Prove ultrasoniche su elementi in calcestruzzo rinforzati con rete in fibra di PBO

In the last decades externally bonded fiber reinforced materials have been increasingly used for strengthening and retrofitting of both new and existing structures due to their excellent mechanical and physical properties. However the structural efficiency of the reinforcement techniques is strongly dependent on a proper application and it is really important to realized a perfect bond in reinforcement/concrete interface. For this reason an important role is played by the quality control of the application of the reinforcement by using Non Destructive Techniques (NDT). This paper reports the results of an experimental campaign aimed at verifying ultrasonic test reliability in detecting adhesion reinforcement/concrete problems and defects. For this purpose 15 small concrete beams have been prepared and strengthened with PBO (Polyparaphenylenebenzobisoxazole) sheet material. During the application, some artificial defects have been deliberately settled in reinforcement/concrete interface realized with PTFE, collect glue and Plastic

Knowledge Acquisition of Existing Buildings by Means of Diagnostic Surveying. Case Studies

The issue of assessing the structural safety of existing buildings involves several problems when a unique and reliable strategy of modelling and analyzing is looked for. This is mainly related to the peculiarity of each construction in a context of broad variety. In this light the structural model and consequently the judgment on structural safety should be derived from a process of knowledge of the construction carried through steps of different reliability. This paper focuses on a fundamental step of the knowledge acquisition process, which is the surveying campaign aimed at assessing some of the parameters to implement into the structural model (geometry, detailing and properties of the materials). The main aspects of a proper and effective planning of the diagnostic campaign are issued and discussed also with reference to some case studies. Special emphasis is given to the usefulness of non-destructive testing methods, the criteria underlying their selection and the relevance of their calibration

In situ evaluation of concrete compressive strength: reliability of non destructive techniques

In the field of non destructive testing of concrete structures, several regulations propose correlations between cubic compressive strength and ultrasonic pulse velocity or pull out extraction force respectively. These correlations are expressed by means of coefficients derived from calibration through destructive tests carried out on cores. Aiming at evaluating the reliability of correlations in predicting concrete compressive strength, an experimental campaign has been started. Several concrete cubic specimens of different strength classes have been prepared and non destructive tested. Moreover, 16 cores have been extracted from the cubic specimens and ultrasonic and compressive tests have been carried out on them. Ultrasonic testing has been performed on both cubic specimens and cores in order to assess the influence of specimen form and dimension on the ultrasonic waves propagation. In this paper results of the experimental campaign are presented and discussed

NON-DESTRUCTIVE ASSESSMENT OF GLUING IN CROSS-LAMINATED TIMBER PANELS

Cross Laminated Timber (CLT) panels are wooden structural products consisting of finger jointed boards glued together and arranged in orthogonal layers. The lamination process reduces the scatter of the board properties so that minor strength reducing features such as knots and other defects are dispersed in the product. CLT panels have very high axial load-carrying capacity and bending strength, due to their large resisting areas, and high shear strength. However, the structural performance of CLT panels depends on the proper application of the glue between the layers. The bond set up at the interface between longitudinal and orthogonal layers can be seriously compromised by the lack of gluing occurring during the production process. For this reason, quality control is an essential tool for verifying the correct gluing process of CLT panels. This paper illustrates the preliminary results of an experimental programme aimed to test the effectiveness of Ultrasonic Testing (UT) in detecting adhesion anomalies and defects in CLT panels. UT was carried out on several CLT panels having different configurations (length, thickness of the layers, number of layers, timber species). For each panel, the velocity of longitudinal stress wave V was measured along several paths perpendicular to the plane of the CLT panels. V data was numerically processed and then for each panel the distribution of V on a horizontal plane was graphically represented implementing the iso-velocity curves. The match between the low-velocity areas resulting from data processing and the unglued areas visually assessed was evaluated and critically discussed

Prove, analisi e modellazione di un ponte in c.a.p. a campata semplice esistente

The aim of this paper is the evaluation of the structural safety of a single-span prestressed concrete bridge, placed in a thoroughfare, a few kilometres far from the city of Cagliari. The judgement on the reliability of the structure spreads from a diagnosis process starting from the visual inspection and passing through in situ tests, consisting in non-destructive tests and static and dynamic testing, whose results allowed the calibration of a finite element model, capable of representing accurately the stress-strain response of the structure. The validation of the numerical model is based primarily on the correlation between the results of the dynamic testing, in terms of fundamental frequency, and the numerical model modal analysis