The predictive model for strength of inclined screws as shear connection in timber-concrete composite floor

Interest in timber-concrete composite (TCC) floors has increased over the last 30 years. TCC technology relies on timber and concrete members acting compositely together. Both timber and concrete exhibit a quite brittle behaviour in bending/tension and compression respectively whilst the shear connection is identified as the only contributor of ductile behaviour. Therefore, the strength, stiffness and arrangement of the shear connection play a crucial role in the structural design of TCC. There are only few investigations on analytical closed-form equation to predict the stiffness and strength of TCC joints as input values to design a partially composite floor. For example, Johansen's yield theory was adopted as European yield model in Eurocode 5. However, the equations are limited to vertically inserted dowels or screws and Eurocode 5 recommends that the strength and stiffness of unconventional joints should be determined by push-out tests. Previous investigations reported that the inclined shear connector significantly increase the initial stiffness and ultimate strength of the TCC joints and consequently composite floor. This paper presents a model for the strength ofTCC joint using crossed (±45°) proprietary screws (SFS Intec). The Johansen yield theory is extended to derive the strenght model of TCC joint with crossed (±45°) screws which are loaded in tension and compression. The model is an upper bound plastic collapse model that assumes the behaviour of timber and screw perfectly plastic with undamaged concrete. The failure modes considers of yield of screw, in tension or shear, and some combined modes assuming screw withdrawal, lateral crushing of the timber and the development of plastic hinges in the screw. The experimental aspect of the research consists of push-out tests and aims to verify the strength model of TCC joints with inclined screws. The failure modes are also investigated. The model seems to be reasonably accurate in predicting both the characteristic strength and failure mode. This research suggests the model to facilitate the design of inclined screw shear connections for TCC construction. © 2013 Taylor & Francis Group

Efficient finite element modelling of timber beams strengthened with bonded fibre reinforced polymers

This paper presents development and application of a simple and efficient frame finite element (FE) able to estimate the load-carrying capacity of timber beams flexurally strengthened with externally bonded fibre reinforced polymer (FRP) strips and near-surface mounted FRP bars. The developed element is able to model collapse due to timber crushing under compression, timber fracture under tension and FRP rupture and it is developed in the framework of a flexibility-based fibre element formulation. Furthermore, a novel method based on central difference method in conjunction with composite Simpson's integration scheme along the element axis is developed to take account of shear-slip. The developed model is employed to predict the loading capacity and the applied load-mid span deflection response of timber beams strengthened with FRP and the numerically simulated responses agree well with the corresponding experimental results. The major features of this frame FE are its simplicity and efficiency compared with more complex and computationally expensive FEs which makes it a suitable tool for practical use in design-oriented parametric studies. © 2011 Elsevier Ltd. All rights reserved

Cutting the mustard: New insights into the plant economy of Late Neolithic Tepe Khaleseh (Iran)

Excavations at Tepe Khaleseh, a small-settlement mound in the Zanjan Province of northwest Iran, have uncovered numerous structures dating to the second half of the sixth millennium B.C., including a pottery kiln. The charred plant remains recovered from the site provide evidence for the cultivation of a diverse spectrum of cereals, along with pulses, which are rare at contemporary sites in the region. Analysis of the archaeobotanical assemblage has also permitted a reconstruction of fuel use at the site, with wild mustards identified as having played a key role in the settlement’s fuel economy. The results presented here expand significantly on our understanding of plant management in northern Iran during the Late Neolithic, a period when we see the spread of farming out of the Fertile Crescent and into Eurasia

Experimental and analytical behaviour of steel-timber composite connections

The mechanical characteristics of steel-timber composite (STC) connections play an essential role in the safe and economical design of hybrid STC structures and floor systems. Accordingly, this study investigates the load-slip behaviour of lap Laminated Veneer Lumber (LVL) timber-steel plate composite joints. Push-out tests on four different types of STC lap joints connected by coach screws (with and without a reinforcing nail plate), high-strength bolts and a combination of glued and screwed joints are reported, and the load-slip behaviour and failure modes of the connections are characterised. The use of a nail plate is found to be effective in reinforcing the timber and in increasing the stiffness of STC lap joints with coach screws, but they did not produce a significant improvement of their strength. A non-linear regression is carried out and an empirical load-slip formulation for STC lap joints with coach screws and high strength bolted connectors is proposed in analytical form. Furthermore, simple formulae for the strength and stiffness of LVL-steel lap connections with coach screws are proposed

WCTE 2016 - World Conference on Timber Engineering

Concrete is the most widely used construction material in the world. This material causes formation and release of CO2 and high energy consumption during manufacturing. One way to decrease concrete consumption negative consequences is to replace it with lower needed primary energy materials, like timber. The engineered wood products such as laminated veneer lumber (LVL) and cross laminated timber (CLT/X-lam) with improved structural characteristics, durability and fire resistance have made it possible for structural engineers to design and construct large multi-storey multi-bay buildings. Use of timber in structures is beneficial from both structural and environmental points of view. To name a few advantages, it has low carbon foot print, less energy consumption to be manufactured, less demand of work force, deconstruction capability, fast installation and low self-weight that ultimately lead to smaller size for structural component (e.g. beams and columns and foundation dimensions). In this paper, at first behaviour of Steel-Timber Composite (STC) simple 2bay beam with prefabricated cross banded LVL slabs with coach screws (self-tapping screws are assumed to be utilised for transferring the interface shear between the steel girder and the prefabricated timber slab and providing a composite connection) is captured by a nonlinear finite element model and the results are compared with similar Steel-Concrete Composite (SCC) system. Concrete hybrid structures have slightly higher strength and stiffness in compare to timber hybrid structures; On the other hand, timber structures are lighter, less pollutant and green to the environment, have simpler and faster and cheaper fabrication process and can be dismantled to recycling its structural components. Moreover, in a 1bay simple beam, effect of different parameters such as screw size, screw spacing, length of beam, timber slab and beam size on the load carrying capacity and composite efficiency of the STC system with LVL slab are evaluated. Results show that, screw spacing effect is more than screw size effect. In other words, in order to reach high strength and stiffness and appropriate composite action between slab and beam, also to avoid brittle failure, it is highly recommended to use many smaller diameters screws instead of few large diameters ones

Experimental and numerical investigation of short-term behaviour of CLT-steel composite beams

This paper concerns the short-term behaviour of innovative steel-timber composite (STC) floors comprising of cross-laminated timber panels connected to steel girders by various mechanical fasteners and/or glue. The results of four-point bending tests performed on full-scale STC beams are reported and the structural behaviour (the load-deflection response, short-term stiffness, peak load capacity, and failure modes) of the proposed STC system is studied. In addition, extensive non-linear 1D and 2D finite element (FE) analyses of STC beams are carried out and the numerical results are verified against the test results. It is shown that 1D and 2D FE models are adequate in capturing the structural response of the STC beams. Using the FE and experimental results, the composite efficiency of STC beams that can significantly influence their structural behaviour beams is determined and reported in the paper

Experimental and analytical investigation of short-term behaviour of LVL-concrete composite connections and beams

This paper reports the results of experimental push-out tests on three different types of timber-concrete composite (TCC) connections, including normal screw, SFS and bird-mouth. The load-slip diagrams obtained from lab tests are employed to calculate the slip modulus of the connections for serviceability, ultimate and near collapse cases based on Eurocode 5 recommendations. Additionally, four full-scale TCC beams with normal screw, SFS and bird-mouth are constructed and tested under four-point bending within the serviceability load range to verify the slip modulus of connections which derived from the push-out tests. Further, based on the experimental results and using nonlinear regression, an analytical model each one of the connections is derived which can be easily incorporated into nonlinear FE analyses of TCC beams. © 2012 Elsevier Ltd. All rights reserved

Cutting the mustard: new insights into the plant economy of Late Neolithic Tepe Khaleseh (Iran)

Excavations at Tepe Khaleseh, a small-settlement mound in the Zanjan Province of northwest Iran, have uncovered numerous structures dating to the second half of the sixth millennium B.C., including a pottery kiln. The charred plant remains recovered from the site provide evidence for the cultivation of a diverse spectrum of cereals, along with pulses, which are rare at contemporary sites in the region. Analysis of the archaeobotanical assemblage has also permitted a reconstruction of fuel use at the site, with wild mustards identified as having played a key role in the settlement’s fuel economy. The results presented here expand significantly on our understanding of plant management in northern Iran during the Late Neolithic, a period when we see the spread of farming out of the Fertile Crescent and into Eurasia

Nonlinear long-term analysis of timber-concrete composite structures with finite element-finite difference scheme

Long-term analysis of timber-concrete composite (TCC) structures is a challenging task owing to the time-dependent behaviour of timber, concrete and connections which are highly nonlinear under variable environmental conditions (i.e. temperature, humidity). In this paper an efficient numerical method that takes advantage of a finite element-finite difference (FE-FD) scheme is presented. The differential equations governing the long-term behaviour of TCC section under variable humidity are solved using the FD scheme and the differential equations governing the mechanical behaviour of the composite beam are solved by a FE formulation recast in the framework of force-interpolation concept. The comparison between experimental data and numerical results shows the sufficient accuracy of the proposed FE-FD model for capturing long-term behaviour of TCC members. © (2014) Trans Tech Publications, Switzerland