Advanced Materials Research Vol. 778

Abstract: Connections are key elements and the weak points for timber structures. The most commonly used bolted timber connections with slotted in steel plate have low lateral stiffness and poor ductility in post-and-beam construction. This paper introduces the prestressed-tube bolted connection to alleviate this problem. To evaluate its lateral resisting performance, the failure mode, strength, lateral stiffness, ductility, hysteresis curve and equivalent viscous damping ratio of the ordinary and improved connections, as determined by the monotonic and reversed cyclic loading test, are compared. The results demonstrate that the lateral stiffness of the prestressed-tube bolted connection has been significantly improved, and its ductility is also better than the normal bolted connection with no decrease in the ultimate moment resisting capacity. It is believed that the semi-rigid prestressed-tube bolted connection, as an alternative to current bolted solutions, may provide reasonable lateral stiffness and has good potential for use in post-beam timber construction.

Abstract: Considering wood currently used in construction domain, it may be observed that it possesses good strengths, but reduced modules of elasticity. This drawback may be prevented by creating structures with rigid nodes or by using hybrid or composed cross-sections for the structural elements.The paper consists of numerical analysis of a timber frame with rigid nodes, assuming composed cross-sections for the structural elements, made of four props with cross-sectional dimensions of 0.1x0.1 m each - for columns and two chords of 0.1x0.1 m each - for beams.Analyzing this type of structures by considering equivalent cross sections` properties of the structural elements, the real phenomena may not be covered, since it doesn`t consider all elastic characteristics of wood, resulting in different stress` distribution in the structural elements.The analyze of this structure considering both real solid cross-sections and all elastic properties of wood by using specialized software, leads to a laborious work because of the high number of finite elements. Thereby, a two-step analysis is proposed: the first one consists in solving the spatial timber frame with bar type finite elements and the elastic properties parallel to the grain, as provided by design codes. In the second step, an intermediary node is detached and loaded with the internal forces obtained from the first step, considering all elastic parameters of wood and using solid type finite elements.Currently, in the design process, only the first step in performed. The two-step analysis aims to compare the results with those obtained using the strength of materials methods, relieving the necessary corrections in the case of one-step design process.

Abstract: In traditional timber structures, hardwood connectors such as a nails, wedges, dowels and pegs have been used as reinforcement of carpentry joints or to fix wooden ceiling matts or floor boards. In the study reported, the possibility to rely on enhanced mechanical and technological properties of densified wood, for the production of wooden nails to be used in the repair of traditional timber structures is discussed. The wood used for connectors were domestic wood species; ash, beech, black locust and poplar. Wooden blocks were exposed to densification procedure with the purpose of increasing the materials density, dimensional stability and possibly, improve durability and selected mechanical properties. The densification ratio varied between 50 and 67%. A dedicated research has been performed in order to determine the effect of densification on the compression behavior of wood in the form of nails. The progress of pushing force during insertion of the wooden nails into wood samples was also monitored and served for insertion process control. A preliminary series of push-out tests have been carried out on timber-to-timber joints assembled with the densified nails.The results obtained show potential for using the novel wooden nail connectors for substitution or integration repair works in traditional timber systems.

Abstract: In this paper the transversal load distribution in timber-concrete systems is analysed and discussed. The analysis is based on experimental and numerical results obtained for real scale timber-concrete systems. Two situations are considered: a timber-concrete floor for a multi-storey building with dimensions of 3.39mx3.48m in plan view and a road bridge deck with dimensions of 5mx14m also in plan view. In both situations the systems were designed to the loads required by the European codes. The effect of the transversal load distribution was experimentally assessed by imposing concentrated loads in various locations, eccentric to both transverse and/or longitudinal direction. Additionally, FEM models were developed to describe the mechanical behaviour of the two composite timber-concrete systems. The results obtained with both methodologies are presented and discussed. Based on this discussion conclusions are drawn regarding the amount of transversal distribution that can be expected in this type of reinforcement solution.

Abstract: The idea to combine the building materials timber and concrete is well known since the 20^th of the last century. While timber is beneficial in bearing tensile forces, concrete on the contrary sustains compressive forces very well. Thus, connecting both materials in the way that loads can be transferred between them, their advantages can be used to improve the load bearing capacity of structures. A lot of researches were carried out to investigate different problems of timber-concrete composite (TCC) constructions during the last years. Yeoh et al. [1] for example gave an overview of different full-scale short-term collapse tests in order to evaluate the load bearing behavior of different TCC systems. Nevertheless, some questions are still very few explored, among them is the lateral load bearing behavior of TCC constructions. These structures can be considered as 3 dimensional plane structures, being able to distribute loads along and perpendicular to the span of the timber beams. A concentrated load (applied to one beam of the TCC construction) will deflect it due to bending. All beams are connected with each other because of the concrete slab. For this reason adjacent beams also deflect even if no loads are applied to them directly. These beams contribute to the load bearing of the loaded beam and relieve it partly from the loads, reducing stress in this beam. The described behavior, of distributing loads perpendicular to the span, is called lateral load bearing behavior. This paper will report on short-term bending testes of TCC slabs, carried out at Leipzig University of Applied Sciences. Several slabs have been tested. Each of them had a span of 3.9 m, consisting of three timber beams (10/20 cm) and a connecting concrete slab (thickness 6 cm). Only the middle beam was loaded in the third part points. During the test deflections, as well as strains, at different points were recorded. Additionally, the concrete properties were determined and push out tests were carried out. Overall, seven TCC slabs were manufactured and tested. With the slabs several parameters have been varied, e.g. the type of concrete, the stiffness of the connection system, and the center distance of the timber beams. By varying these three parameters, their effect on the lateral load distribution was examined by measuring deflection and strain at different points of the composite slab. A timber beam ceiling, as reference sample, without concrete topping was tested additionally. The experiments and its results will be described in detail in the paper.

Abstract: Timber floors can be refurbished by connecting a concrete topping to the timber joists; stiffening the floor and reducing serviceability problems, including vibration. Research to date has focused on upgrade solutions with relatively thick toppings (40mm or greater). This paper presents a novel, ultra-thin topping solution where the topping is placed at a thickness of 20mm or less. Advantages of the solution include: reducing the mass added to the existing structure and minimising the change in floor to ceiling height whilst delivering a significant increase in floor stiffness. This paper reports the findings from the serviceability testing of an upgraded, full scale timber floor. Measurements prior to and after the upgrade are compared, including: elastic testing under static loads, vibration testing and short-term bending tests. The paper also compares the results with simple analytical approaches and design limits prescribed in Eurocode 5 Part 1-1.

Abstract: The rehabilitation of existing timber floors in seismic area should take into account the possibility to use both traditional and more modern materials and techniques. An extensive experimental program carried out at the University of Padova concerned full-scale wooden floors segments strengthened through the application of several solutions, belonging to the following three main categories: planks overlapping, diagonals, and nets.In detail, the following techniques were considered: single and double planking with an orientation of ±45° having different thicknesses; steel, CFRP, SRP or wooden diagonals; natural fibre (hemp) composites applied as nets with resin or vinyl glue; wooden nets applied with hardwood pins and screws.The study is aimed at characterizing the behaviour of strengthened floors for the selection of the most suitable solutions applicable in existing buildings, which are able to provide a proper in-plane stiffness for seismic load distribution among bearing walls. The test set-up was designed and realized on purpose to simulate the in-plane shear behaviour of timber floors. The experimental results and the comparison between unreinforced and strengthened floors under monotonic shear load are presented in the paper.

Abstract: In the paper, the results of an experimental study aimed at evaluating the mutual influence among the intervention techniques normally employed to improve separately the acoustic or the mechanical performance of timber floors are provided. The superimposition of planks having different thickness and arrangement or connections is usually considered to improve the in-plane stiffness of floors, especially in case of interventions on existing buildings in seismic zone, to take into account, if possible, also preservation criteria. On the other hand, the improvement of acoustic comfort is addressed to the use of specific noise-abating materials, like insulating boards (OSB) or sheathings, whose contribution, in terms of mechanical stiffness/strength is often neglected. This work proposes a combined interpretation of the two abovementioned requirements, through the characterization of the main parameters governing the involved physical and mechanical phenomena. The first results obtained on simple unidirectional full-scale specimens of floors are presented; seven combinations among various solution of boards and noise-abating materials are compared, first from a structural and subsequently acoustic point of view. The results allow identifying the solution, which is able to optimize at best both the mechanical and acoustic requirements, to be proposed for the intervention on existing timber floors.

Abstract: Within the bilateral scientific project between the Institute of Earthquake Engineering and Engineering Seismology - UKIM-IZIIS, St. Cyril and Methodius University, Skopje, Republic of Macedonia and the Civil Engineering Faculty, University of Zagreb, Croatia, experimental testing of full scale composite timber-glass innovative panels was carried out on the seismic shaking table at IZIIS for the purpose of defining their behaviour and stability under real earthquake conditions. The seismic excitations selected for the shake-table testing of the model were four representative accelerograms recorded during the following earthquakes: El Centro, Petrovac, Kobe and Friuli. The idea was to investigate the seismic behavior of the model under several types of earthquakes, considering their different frequency content, peak acceleration and time duration. The performed tests showed clearly the behaviour of the composite panels and the failure mechanism under strong earthquake motion.

Abstract: 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.