The Design of a semi-prefabricated LVL-concrete composite floor

This paper describes the design of a novel semi-prefabricated LVL-concrete composite floor that has been developed in New Zealand. In this solution, the floor units made from LVL joists and plywood are prefabricated in the factory and transported to the building site. The units are then lifted onto the supports and connected to the main frames of the building and to the adjacent units. Finally, a concrete topping is poured on top of the units in order to form a continuous slab connecting all the units. Rectangular notches cut from the LVL joists and reinforced with coach screws provide the composite action between the concrete slab and the LVL joists. This system proved to be an effective modular solution that ensures rapid construction. A design procedure based on the use of the effective flexural stiffness method, also known as the “gamma method” is proposed for the design of the composite floor at ultimate and serviceability limit states, in the short and long term. By comparison with the experimental results, it is shown that the proposed method leads to conservative design. A step-by-step design worked example of this novel semi-prefabricated composite floor concludes the paper

Numerical analysis of timber-to-timber joints and composite beams with inclined self-tapping screws

In this paper, a Finite-Element (FE) numerical investigation on timber-to-timber joints and composite beams with inclined self-tapping screws (STSs) is presented. Based on past experimental data and numerical literature efforts, full 3D solid FE models of selected geometrical and mechanical configurations of technical interest are implemented in ABAQUS software package and analysed under static loading conditions. The typical push-out samples include GL24h timber members with several types (WT-T-8.2, 190\u202fmm and 220\u202fmm their length), layouts (2\u202f+\u202f2, 4\u202f+\u202f4, 2\u202f+\u202f2 X-shaped) and inclination of screws (up to \ub145\ub0). For the full-scale beam samples in bending (8\u202fm their span), composite systems consisting of GL24h timber beam, wooden plank, spruce floorboards and STSs are investigated. There, the STS joints take the form of two-rows or X-shaped connections, respectively (45\ub0 or 90\ub0 their inclination), including four screw types and different spacing. In both the push-out and full-scale cases, simple modelling approaches are taken from the ABAQUS library and adapted to the timber-to-timber structural system under investigation, so as to explore their structural performance in the elastic and post-damage phases, up to failure. A key role in the typical FE models is assigned to input material properties and mechanical contacts, including damage constitutive laws so as to reproduce possible local failure phenomena in the timber or steel components, as well as cohesive damage interactions for the joints. The presented FE models are calibrated in accordance with past research studies, and validated \u2013 for the examined structural typology \u2013 against experimental results available in literature. Comparative calculations are hence presented, based on the collected numerical, experimental and analytical estimations for the selected samples. As shown, the examined modelling approach can reasonably capture the expected performance of timber-to-timber joints and composite systems

Derivation of buckling design curves via FE modelling for in-plane compressed timber log-walls in accordance with the Eurocode 5

In \u2018Blockhaus\u2019 systems the structural capacity derives from surface interactions and friction mechanisms between multiple timber logs stacked horizontally one upon each other. Unlike masonry or concrete walls, timber log-walls are characterized by the absence of a full structural interaction between the basic components, hence resulting in \u2018assembled\u2019 rather than \u2018fully monolithic\u2019 structural systems characterized by high flexibility of timber and usually high slenderness ratios. The current Eurocode 5 for timber structures, however, does not provide formulations for the prediction of the critical load of log-haus walls under in-plane compressive loads. In this work, based on past experimental tests and detailed Finite-Element (FE) models, extended numerical investigations are performed on timber log-walls. A wide number of configurations (more than 900) characterized by different geometrical properties, timber log cross-sections, number and position of door and window openings, presence of in-plane rigid (RF) or fully flexible (FF) inter-storey floors, as well as initial curvatures and/or load eccentricities, are analyzed under monotonic in-plane compressive load. Careful consideration is also given to the influence of additional out-of-plane pressures (e.g., wind pressures) combined with the in-plane compressive load. In accordance with the buckling design approach proposed by the Eurocode 5 for timber columns, non-dimensional buckling curves are then proposed for timber log-walls under in-plane compression. These curves are based on an accurate calibration of the k c buckling coefficient and the related imperfection factors on the results of the numerical parametric study. The developed simple and conservative approach for the design of log-walls can be proposed for implementation in the new generation of the Eurocode 5

(INTER/48-2-1) Proposal of a Eurocode-based method for the buckling design of timber log-walls

Blockhaus structural systems are commonly obtained by assembling multiple timber logs, which are stacked horizontally on top of one another. Although based on simple resisting mechanisms, the structural behaviour of Blockhaus systems is rather complex to predict, and few design recommendations are available in current standards for timber structures. This paper focuses on the assessment of the buckling behaviour of a typical vertically compressed timber log wall

Non-linear modelling of the in-plane seismic behaviour of timber Blockhaus log-walls

This paper investigates the non-linear modelling of the cyclic behaviour of Blockhaus timber log-walls under in-plane lateral loads. The structural behaviour of Blockhaus log-walls in the examined loading condition strictly depends on the geometry \u2013 thus on the deformability and ultimate resistance \u2013 of the adopted corner joint, namely the joint between perpendicular log-walls. The presence of metal fasteners is in fact minimized and the structural interaction between the basic timber components is provided by simple mechanisms such as notches, tongues and grooves, multiple surfaces in contact. In this paper, a computationally effective FE-model is developed, in order to predict the cyclic behaviour of an entire Blockhaus log-wall once the cyclic behaviour of the adopted corner joint is known. The model uses non-linear hysteretic springs to describe the joint behaviour, where all typical features such as pinching behaviour, strength and stiffness degradation can be considered. By comparing the numerical and the experimental predictions of the cyclic response of full-scale Blockhaus log-walls, a general good agreement is found. Simulations confirmed the high flexibility of the studied structural systems, as well as the significant effect of possible openings such as doors and windows on their global resistance to in-plane lateral loads. In conclusion, the presented study confirmed that the proposed modelling approach can be used to estimate the load-carrying capacity and vulnerability to seismic events of Blockhaus shear walls, and that the same model could be extended to full Blockhaus buildings

The architrave a tasselli

The architrave a tasselli is a peculiar design shape of the traditional stone lintels, which are widespread in Abruzzo, Italy: stone lintels are not usually monolithic elements, being formed by three pieces, the block spanning the opening and the tasselli, two small rectangular pieces. In the current paper, by means of an elementary Wrinkler-type beam model, it has been attempted to capture the behaviour of stone lintels, chasing the mechanical reasons supporting this traditional construction technique. Keywords: Architectural heritage, Theory of elasticity, Masonry building, Traditional constructive technique

COMPORTAMENTO A LUNGO TERMINE DI TRAVI COMPOSTE LEGNO-CALCESTRUZZO

1999/2000XIII Ciclo1967Versione digitalizzata della tesi di dottorato cartacea

Modelling the mechanical behaviour of typical wall-to-floor connection systems for cross-laminated timber structures

This paper proposes a numerical model capable of predicting the mechanical behaviour and the failure me- chanism of typical wall-to-floor connections for Cross-Laminated Timber structures. Such systems are assembled with angle brackets and hold-downs, anchored to the wall and floor panels with profiled nails and bolts. The metal connector and the elements to which it is fastened are modelled using 3D solid bodies, while the steel-to- timber joints are simulated as non-linear hysteretic springs. Shear and tension tests are reproduced on two connection systems and results are compared to the test data obtained from similar configurations. Simulations lead to accurate predictions of the mechanical behaviour (i.e. elastic stiffness, maximum load-carrying capacity, and shape of the hysteresis cycles) and energy dissipation. Finally, the performance when lateral and axial loads are applied simultaneously is investigated. Analyses are carried out by varying the inclination of the load, with respect to the axis of the connector, between 0\ub0 and 90\ub0. Results exhibit a quadratic interaction relationship between shear and tension loads, and prove that their coupled effect influences the stiffness and the maximum load-carrying capacity

Can Structural Timber Foster Short Procurement Chains within Mediterranean Forests? A Research Case in Sardinia

Background and Purpose: The aim of this paper is to present the idea of a timber short procurement chain as a means to provide an increased value to Mediterranean forests. It is based on the evidence that timber buildings are increasingly used for a number of reasons including sustainability, the speed of erection, and excellent structural and seismic performance. However, most of the timber currently used around the Mediterranean is imported from outside this area. Materials and Methods: The idea is to use the best part of the tree to produce timber boards, while all the remaining part of the tree including the production waste is used for energy production. Important issues to address are the generally low mechanical properties of locally-grown timber such as maritime pine in Sardinia, which would make some wood-based products such as glue-laminated timber not technically viable. Cross-laminated timber panels are a possible solution to this problem because this wood-based product is manufactured in such a way that even with low-quality timber boards it is possible to obtain a medium quality panel. The panel is made of layers of timber boards with the adjacent layers glued under pressure at a right angle. Another issue is the need to grade the local timber, for which a number of specimens must be tested to destruction in order to identify a visual or a machine-stress grading procedure. Last but not least, the panels must be tested to destruction to correlate their mechanical properties to the properties of the boards. Results: The preliminary mechanical tests carried out on Sardinia maritime pine confirm that the material is low-grade because it is characterized by large knots and a significant grain deviation. Nevertheless, when used in the cross-laminated panels, the properties are significantly improved due to the layout of the panel which reduces the influence of defects in the boards on the mechanical properties of the panel. Conclusions: A timber short procurement chain is a possible means to create job opportunities and reduce depopulation, which is particularly important in several regions of the Mediterranean. By adding value to the forests by means of timber production used in prefabricated components employed in low-rise timber buildings, it is also possible to improve forest management and even extend forested areas which have all positive effects on the environment, the landscape and the reduction of hydrogeological hazard

Rocking analysis of masonry walls interacting with roofs

This paper investigates the out-of-plane behavior of masonry walls interacting with roofs. Often, collapses of masonry portions supporting roofs may occur due to the roof thrust, which generates a destabilizing effect over motion. Nevertheless, the roof weight can produce a positive stabilizing effect for rotation amplitudes smaller than the critical value. The dynamics of a rocking masonry block interacting with roofs is discussed, by properly modifying the Housner equation of motion of the free-standing single degree-of-freedom block. The dependence of the restoring moment on the rotation angle is investigated and the minimum horizontal stiffness is calculated so that the same ultimate displacement as the system without roof thrust is obtained. Two case studies are presented as applicative examples of the proposed method: an unreinforced masonry structure tested on shaking table and a spandrel beam subjected to roof thrust that survived the Emilia Romagna earthquake. Inertia moments and radius vectors of different failure mechanisms are also provided to solve the equation of motion for different block shapes. Finally, a parametric analysis of a trapezoidal rocking block has been carried out by changing its geometrical shape. This analysis shows that the influence of the shape is relevant for the calculation of the failure load, although is not possible to determine an a priori most critical shape