STR-931: TIMBER I-JOISTS WITH WEB OPENINGS: REINFORCEMENT, CAPACITY PREDICTION AND SENSITIVITY ANALYSIS

Timber I-joists are a popular product in light-frame wood construction in North America. The design with timber I-joists, however, has not yet achieved the same level of refinement compared to reinforced concrete or steel structures. One of the reasons is that timber I-joists have higher variability in their material properties than more homogeneous building materials. Additionally, although very commonly applied in practice, engineers and practitioners have limited knowledge and guidance for I-joists with web opening. As a result, in many cases the design of timber I-joists based on manufacturer’s specifications lead to very conservative solutions. The present research predicts the capacity of unreinforced and reinforced timber I-joists with openings from experimental results. A total of 100 unreinforced and 100 reinforced I-joists with opening were tested under four point loading. The capacity of the I-joists with opening was predicted from regression analysis. A sensitivity analysis was performed for the predicted equations using Meta-model of Optimal Prognosis (MOP) to evaluate the contribution of each parameter on the model responses. The research demonstrates that the reinforcement technique was efficient for I-joists with openings and the proposed equations were very accurate to predict the I-joists capacity

Evaluation of Remediation Techniques for Circular Holes in the Webs of Wood I-Joists

Remediation methods and strength predictions were evaluated for wood I-joists with single, circular holes in the webs, leaving utilities in place. A full-scale bending test using four equally-spaced point loads was applied to three depths of joists with varying flange widths and span lengths of 4.88 m and 2.44 m. Failure modes for long span joists without holes were in the flanges in tension, compression or lateral buckling; but once a hole was introduced the majority failed in shear. The curved beam approach and manufacturers software were employed to predict strength. Seven remediation techniques were investigated initially, and remediation effectiveness was evaluated based on strength, stiffness, and ease of installation/cost. The oriented strand board (OSB) collar remediation worked very well and returned 8 out of 12 series of joists to a strength statistically equivalent to the “No Hole” condition. The OSB collar was not quite as effective in returning stiffness to the joists, but was easier to install and less expensive than a laminated strand lumber patch.Keywords: wood structures, holes, joist

Timber and Timber-Timber Composite (TTC) Beams with Openings: Laboratory Experimentation and Nonlocal Finite Element Simulation

Introducing openings/holes in joists/beams of flooring systems is usually necessary to pass through building services without increasing the floor-to-floor height. In timber beams, the openings reduce the stiffness and limit the ultimate load-carrying capacity by promoting tensile stresses perpendicular to the grain and longitudinal splitting shear stresses. Furthermore, quasi-brittle failure of the timber in shear and tension (promoted by openings) leads to localisation of strain, spurious sensitivity of finite element (FE) simulations with respect to mesh size and orientation and ultimately poor or erroneous damage initiation and failure load predictions. Moreover, the interaction between the openings in the web and slabs of timber-timber composite (TTC) floors which have gained popularity in recent decade, remain largely unexplored in terms of experimental results, and numerical simulations, and design provisions are only limited to bare timber beams without slabs. Accordingly, this research project aims at producing benchmark experimental data and developing reliable FE models for assessing the effect of geometrical irregularities such as notches and openings on the failure mode and load carrying capacity of the timber and TTC beams. The research project consists of an experimental program and a numerical (FE) simulation that involves derivation, computer implementation and application of a nonlocal continuum-damage model for timber. In the first stage of laboratory testing, pushout tests were performed on symmetric LVLCLT and GLT-CLT joints with coach screw shear connectors to establish the load-slip behavior, stiffness, and peak load of the coach screw shear connectors. In the second stage, laminated veneer lumber (LVL) and glued laminated timber (GLT) beams with symmetric circular and square openings were tested under three-point bending tests to establish the governing failure mechanism, produce the load-mid span deflection curve and determine the reduction in stiffness and peak load of the LVL and GLT beams due to openings. In the final stage of laboratory experimentations, TTC beams were fabricated by connecting CLT slabs to LVL and GLT beams using coach screw shear connectors and then three-point bending tests were performed on the fabricated LVL-CLT and GLTCLT composite beams with web opening size, shape, and location identical to the LVL and GLT beams tested in the second stage of the testing program. The digital image correlation (DIC) results acquired during stages two and three of the experimental programs shed light on the mechanism of strain localisation and failure promoted by the openings. Moreover, the test results elucidated the major contribution of the coach screw shear connectors in conjunction with CLT slabs to the failure mode and load-carrying capacity of the TTC beams with web openings. After the experimental program, the existing design criterion for evaluating the ultimate load-carrying capacity of the bare timber beams with holes was modified and applied to TTC beams with web openings. In this regard, an analytical Timoshenko composite beam model was utilized to estimate the shear stress and normal stress profiles in the joist (web) cross-sections and accordingly, the relevant terms in existing design criterion were modified to take into account the composite action between the slab and joist and the reinforcing effects of the screws around the opening areas. The proposed modified design equation had a great agreement with the experimental results. The numerical part of this research project focused on development, implementation, and validation of a constitutive law for nonlinear FE analysis of timber beams with stress concentrators such as notches and openings. The complex orientation-dependent behaviour of timber accompanied with nonlinear ductile hardening and brittle softening of the timber in compression, tension and shear were captured by an enriched 3D multi-surface continuum damage model. To alleviate the localisation of strain and spurious FE mesh sensitivity associated with brittle/quasi-brittle behaviour of the timber in tension and shear, a nonlocal integral model was developed and incorporated into the 3D continuum damage material model of timber. Apart from a standard attenuation function that suffers from boundary effects at the edges of notches and openings, a symmetric attenuation function was adopted in the nonlocal integral model to minimise the boundary effects in the nonlocal FE simulations. The developed symmetric nonlocal material model was implemented as a user-defined material subroutine (UMAT) in ABAQUS software, and the nonlocal FE simulations of the tested timber and TTC beams with openings were carried out to demonstrate the adequacy and accuracy of the nonlocal FE model for predicting the failure mode, load-displacement, and peak load of the timber beams in the face of strain localisation. The results of experimental program and numerical simulations revealed that the CLT slab thickness and penetration length of screw shear connectors around the opening areas have major impact on the structural behaviour of the perforated timber beams. It was demonstrated experimentally that different opening shapes of equal area could result in similar reduction of the loading capacity in the perforated timber beams. In addition, the numerical models revealed that local constitutive models cannot simulate the failure of timber materials. Indeed, the local material models must be enriched with a strong localization limiter to prevent strain localization and mesh dependency associated with quasi-brittle failures (softening behaviour) of timber. In the numerical simulations, it was shown that adopting nonlocal integral technique in the material model of timber effectively resolves the strain localization and mesh sensitivity issues

The fire performance of engineered timber products and systems

Timber is an inherently sustainable material which is important for future construction in the UK. In recent years many developments have been made in relation to timber technology and construction products. As the industry continues to look to construct more efficient, cost effective and sustainable buildings a number of new engineered timber products have emerged which are principally manufactured off-site. In terms of light timber frame, products such as structural insulated panels (SIPs) and engineered floor joists have emerged. For heavy timber construction, systems such as glulam and cross laminated timber (CLT) are now increasingly common. Despite many of the obvious benefits of using wood as a construction material a number of concerns still exist relating to behaviour in fire. Current fire design procedures are still reliant upon fire resistance testing and ‘deemed to satisfy’ rules of thumb. Understanding of ‘true’ fire performance and thus rational design for fire resistance requires experience of real fires. Such experience, either gathered from real fire events or large fire tests, is increasingly used to provide the knowledge required to undertake ‘performance based designs’ which consider both fire behaviour and holistic structural response. At present performance based structural fire design is largely limited to steel structures and less frequently concrete buildings. Many of the designs undertaken are in accordance with relevant Eurocodes which give guidance on the structural fire design for different materials. For the same approaches to be adopted for timber buildings a number of barriers need to be overcome. Engineered timber products, such as SIPs and engineered joists, are innovative technologies. However, their uptake in the UK construction market is increasing year on year. Little is known about how such systems behave in real fires. As a result the development of design rules for fire is a difficult task as failure modes are not well understood. To overcome this..

Timber Engineering - Principles for Design

This comprehensive book provides in-depth knowledge and understanding of design rules according to Eurocode 5. It is based on the first edition of the STEP (Structural Timber Education Programme) series, which was prepared in 1995 by about 50 authors from 14 European countries. The present work updates and extends the STEP compilation and is aimed at students, structural engineers and other timber structure professionals

Timber Engineering - Principles for Design

This comprehensive book provides in-depth knowledge and understanding of design rules according to Eurocode 5. It is based on the first edition of the STEP (Structural Timber Education Programme) series, which was prepared in 1995 by about 50 authors from 14 European countries. The present work updates and extends the STEP compilation and is aimed at students, structural engineers and other timber structure professionals

斜め格子パネルを用いた木質Ｉ形梁の開発および実用化に関する研究

東京都市大学2019年度（令和元年度

Proof of Concept for a Three-Dimensional Molded Core Wood-Strand Sandwich Panel

Sandwich composites are typically produced from two high strength facings bonded to a lower strength, lightweight core. Sandwich design has proven to be efficient for applications demanding high strength and low weight. Wood-based sandwich composites have been largely limited to non-structural applications with the exception of structural insulated panels and balsa core sandwich composites. This research presents a sandwich composite panel composed of oriented strand board (OSB) facings and a three-dimensional molded core produced from wood strands. Three-dimensional molded core panels (3DMCPs) were fabricated and subjected to bending, flatwise compression, in-plane shear, mechanical fastener, and small-scale shear wall testing. Results from these tests were compared to code-approved OSB sheathing to determine the feasibility of using this 3DMCP for structural sheathing applications