Seismic Behavior of Cross laminated Timber (CLT) Structural Systems: from Traditional Steel Connections to Low-Damage Solutions

Timber buildings have always showed great performances, even if past timber structural systems are no longer adequate to fulfil modern building standards. The key aspect of CLT buildings, as for timber constructions in general, are the connection systems. Nowadays, design of CLT wall connections is based on the hypothesis that hold-down connection is subjected only to tension, while angle bracket only to shear. Nevertheless, experimental highlighted that the two types of connection may be subjected to significant displacements in both directions, thus to coupled actions. The first part of this study presents results from an extensive experimental campaign conducted on traditional connections for CLT buildings using a specific setup that allowed to impose prescribed levels of displacements in secondary direction, varying at the same time the main direction displacement in a cyclic and monotonic manner. A total of fifteen specimens, for each connection type, are presented and critically discussed in terms of load-displacement curves, strength, stiffness, energy dissipation, strength degradation and ductility. The second part of the thesis focuses on an experimental and numerical investigation of a two storey 2/3 scaled CLT hybrid rocking wall. The applicability and the response of this relatively new low-damage solution has been studied for the first time applied on a CLT shear wall. The CLT wall included post-tensioned bars to provide self-centring capabilities and replaceable external steel dissipaters to accommodate energy dissipations. Furthermore, an experimental solution for the dissipater-wood panel link has been implemented. Results are presented in terms of achieved lateral force, overturning moment capacity, variation in the post-tension force, oscillation of the neutral axis depth and energy dissipation. Lastly, a numerical simulation accompanied experimental evidences, to examine the response of the rocking system for higher level of drifts, going beyond test limits

Seismic behavior of posttensioned self-centering precast concrete dual-shell steel columns

This paper describes an innovative bridge column technology for application in seismic regions. The proposed technology combines a precast posttensioned composite steel-concrete hollow-core column, with supplemental energy dissipation, in a way to minimize postearthquake residual lateral displacements. The column consists of two steel cylindrical shells, with high-performance concrete cast in between. Both shells act as permanent formwork; the outer shell substitutes for the longitudinal and transverse reinforcement, because it works in composite action with the concrete, whereas the inner shell removes unnecessary concrete volume from the column, prevents concrete implosion, and prevents buckling of energy dissipating dowels when embedded in the concrete. Large inelastic rotations can be accommodated at the end joints with minimal structural damage, since gaps are allowed to open at these locations and to close upon load reversal. Longitudinal posttensioned high-strength steel threaded bars, designed to respond elastically, in combination with gravity forces ensure self-centering behavior. Internal or external steel devices provide energy dissipation by axial yielding. This paper describes the main requirements for the design of these columns and also discusses the experimental findings from two quasi-static tests

Somatotipo e antropometria de indivíduos de 16 a 60 anos na região do polonoroeste do Brasil - dados de Jaurú/Mato Grosso

A Endomorfia, mesomorfia e ectomonfia foram antropometrica avaliadas pelo sistema Heath e Carter em uma amostra populacional de Jauru-itt, localizada em Amazônia. Foram avaliados indivíduos de ambos os sexos com idade variando de 10 a 59 anos. Os resultados mostraram que nos homens e mulheres com menos de 18 anos predominava a ectomorfia. A relação peso/altura e pregas cutânea apresentaram resultados superiores ao padrão nos indivíduos mais idosos. 0 somatotipo médio para homens de 10 a 17 anos foi 2,2 - 3,6 - 3,7; para homens com mais de 18 anos foi 4,1 - 4,5 – 2,3; para mulheres de 10 a 17 anos foi 3,1 - 3,3 - 4,0; e para mulheres com mais de 18 anos foi 4,9 - 4,2 - 1,0

Procedures for seismic characterization of traditional and modern wooden building types

The paper analyzes different wooden buildings types used in past and nowadays to realized Low-Rise and Mid-Rise timber structures from the seismic point of view. A preliminary overview about the procedures prescribed by codes for the seismic characterization of the timber building systems is given. Then the definition of the behaviour Q-Factor in the literature and its relevance in design of structures in seismic areas is treated. Available research methods for estimating the Q-Factor based on the verification of the nonlinear seismic response of entire buildings by means of experimental tests and numerical simulations are presented and analyzed. The relevance of a proper definition of the yielding limit and of failure condition in the seismic characterization of wooden building systems is treated. Moreover, a comparison between the Q-Factor estimations obtained using different calculation methods is presented. Lastly, the appropriate Q-Factor values are given for a reliable and safe seismic design of buildings realized using the examined wooden constructive systems

Procedures for seismic characterization of traditional and modern wooden building types

The paper analyzes different wooden buildings types used in past and nowadays to realized Low-Rise and Mid-Rise timber structures from the seismic point of view. A preliminary overview about the procedures prescribed by codes for the seismic characterization of the timber building systems is given. Then the definition of the behaviour Q-Factor in the literature and its relevance in design of structures in seismic areas is treated. Available research methods for estimating the Q-Factor based on the verification of the nonlinear seismic response of entire buildings by means of experimental tests and numerical simulations are presented and analyzed. The relevance of a proper definition of the yielding limit and of failure condition in the seismic characterization of wooden building systems is treated. Moreover, a comparison between the Q-Factor estimations obtained using different calculation methods is presented. Lastly, the appropriate Q-Factor values are given for a reliable and safe seismic design of buildings realized using the examined wooden constructive systems

EXPERIMENTAL CYCLIC TESTS ON CLT HOLD-DOWN CONNECTIONS SUBJECTED TO A COMBINATION OF SHEAR AND TENSION

Cross-Laminated Timber (CLT) structures dissipate energy during earthquake only in mechanical connections, which are located in few specific zones. The full definition of their structural behaviour and their correct design is then of crucial importance, especially in seismic conditions. Many studies were carried out on this topic during the last decade in Europe, North America and Japan in order to define monotonic and cyclic behaviour of mostly used connections when only one action (i.e. tension or shear) is prescribed. Nevertheless, some questions are still unanswered. In particular, during earthquakes, connections are subjected simultaneously to both shear and tension. The interaction between shear and tension forces may affect connector’s capacity in terms of strength, stiffness, ductility and dissipation capacity. Moreover, the possibility of brittle failure or excessive strength degradation of connections subjected to combined tension and shear action must be taken into account. This work presents the results of an extended experimental programme on CLT hold-down connectors conducted at CIRI Buildings & Construction Laboratory, University of Bologna. Cyclic tests were performed using a specifically developed test setup suitable to apply both tension and shear actions on the connections, simultaneously. In particular, the experimental tests on hold-downs were conducted prescribing a shear deformation and then loading the connection in tension according to the cyclic loading protocol prescribed by standards. The results of these tests, in terms of strength, stiffness, energy dissipation, strength degradation and ductility, are presented and critically discussed. A comparison between the experimental values of load-carrying capacity and stiffness and those obtained with calculations using existing design code provisions are given. Results obtained in this work allow to define some design guidelines and calculation rules for metal connectors in CLT structure. In addition, they provide the basic information for advanced and reliable investigation on the behaviour of CLT structure when subject to earthquake loadings

Axial – Shear interaction on CLT hold-down connections – Experimental investigation

Nowadays, the design of CLT wall connections is based on the hypothesis that hold-down connections are subjected only to tension and angle-brackets only to shear. Nevertheless, experimental investigations on CLT walls under seismic action highlighted that hold-downs may be subjected also to significant lateral displacement, and then to a tension-shear coupled action. The aim of this work is to experimentally investigate the axial-shear interaction in typical hold-down connections. To this purpose, an extensive experimental campaign was conducted with a specific setup allowing to impose prescribed levels of lateral displacement and varying the axial displacement in a monotonic or cyclic way. The test results on 15 specimens are presented here and critically discussed in terms of load–displacement curves, strength, stiffness, energy dissipation, strength degradation and ductility. Moreover, two different approaches for the definition of the connection's yielding limit are used, according to a tri-linear approximation of the experimental load–displacement curve. Forces and stiffnesses provided by these methods are compared with those predicted by code provisions

Seismic Behavior of Posttensioned Self-Centering Precast Concrete Dual-Shell Steel Columns

This paper describes an innovative bridge column technology for application in seismic regions. The proposed technology combines a precast posttensioned composite steel-concrete hollow-core column, with supplemental energy dissipation, in a way to minimize postearthquake residual lateral displacements. The column consists of two steel cylindrical shells, with high-performance concrete cast in between. Both shells act as permanent formwork; the outer shell substitutes for the longitudinal and transverse reinforcement, because it works in composite action with the concrete, whereas the inner shell removes unnecessary concrete volume from the column, prevents concrete implosion, and prevents buckling of energy dissipating dowels when embedded in the concrete. Large inelastic rotations can be accommodated at the end joints with minimal structural damage, since gaps are allowed to open at these locations and to close upon load reversal. Longitudinal posttensioned high-strength steel threaded bars, designed to respond elastically, in combination with gravity forces ensure self-centering behavior. Internal or external steel devices provide energy dissipation by axial yielding. This paper describes the main requirements for the design of these columns and also discusses the experimental findings from two quasi-static tests

Biophysical stimulation in osteonecrosis of the femoral head

Osteonecrosis of the femoral head is the endpoint of a disease process that results from insufficient blood flow and bone-tissue necrosis, leading to joint instability, collapse of the femoral head, arthritis of the joint, and total hip replacement. Pain is the most frequent clinical symptom. Both bone tissue and cartilage suffer when osteonecrosis of the femoral head develops. Stimulation with pulsed electromagnetic fields (PEMFs) has been shown to be useful for enhancing bone repair and for exerting a chondroprotective effect on articular cartilage. Two Italian studies on the treatment of avascular necrosis of the femoral head with PEMFs were presented in this review. In the first study, 68 patients suffering from avascular necrosis of the femoral head were treated with PEMFs in combination with core decompression and autologous bone grafts. The second one is a retrospective analysis of the results of treatment with PEMFs of 76 hips in 66 patients with osteonecrosis of the femoral head. In both studies clinical information and diagnostic imaging were collected at the beginning of the treatment and at the time of follow up. Statistical analysis was performed using chi-square test. Both authors hypothesize that the short-term effect of PEMF stimulation may be to protect the articular cartilage from the catabolic effect of inflammation and subchondral bone-marrow edema. The long-term effect of PEMF stimulation may be to promote osteogenic activity at the necrotic area and prevent trabecular fracture and subchondral bone collapse. PEMF stimulation represents an important therapeutic opportunity to resolve the Ficat stage-I or II disease or at least to delay the time until joint replacement becomes necessary