The Structural Capacity of Laminated Timber Compression Elements in Fire: A Meta-Analysis

Modern building construction is increasingly applying laminated timber products as structural members for larger and more ambitious projects, both commercial and residential. As a consequence, designers require reliable knowledge and design tools to assess the structural capacity of laminated mass timber elements in fire. This paper reviews and assesses available data and methods to design for fire resistance of laminated mass timber compression elements. Historical data from fire resistance tests is presented and compared against the available design calculation methods. The underlying assumptions of the thermal and structural analyses applied within the presented calculation methodologies are discussed. The resulting meta-analysis suggests that the available methods are all able to make reasonable predictions (with an average mean absolute error (MAPE) of 22% across methods) of the fire resistance of glued-laminated columns exposed to standard fires; however, the available methods for CLT walls give inconsistent (MAPE of 46% across all methods and 30% excluding extreme outliers) and potentially non-conservative results (up to 88% of investigated cases are statistically non-conservative). Additional research on loaded compression elements is therefore needed

Influence of ply configuration and adhesive type on cross-laminated timber in flexure at elevated temperatures

This paper describes experiments on cross-laminated timber (CLT) beams exposed to uniform non-charring temperatures under sustained loading. Two different ply configurations and two different adhesive types were examined under sustained loads of both 30 and 50% of the ultimate ambient temperature flexural capacity. It was found that the adhesive type has a significant influence on the magnitude of the deterioration in structural stiffness during heating. From image correlation analysis this influence was attributed to increased shear strains along the adhesive lines between timber plies for specimens bonded with a polyurethane (PU) adhesive, when compared to those that used a melamine urea formaldehyde (MF) adhesive. It was also found that considerable deflections that were measured during heating were irrecoverable during cooling of the CLT, suggesting that these deformations were driven by creep of the timber – and possibly also the adhesives

Structural steel columns subjected to localised fires

In large open spaces within modern buildings, the application of standard compartment fire curves based on small compartments may be inappropriate for assessing the potential thermal actions imposed on structural members in fires. Instead, a localised fire approach should be considered for determining the fire protection requirements for steel structural elements in these situations. A series of experiments using real waste bin fires or controlled gas burners placed next to I-section steel columns is described. The goal of the research was to test the validity of the widely applied lumped thermal mass assumption, and potentially to propose alternative approaches. The experimental results show that steep temperature gradients developed both along the column length and over its crosssection, confirming that conventional thermal and mechanical analysis may be inappropriate for design. For the waste bin fires the maximum steel temperatures were controlled primarily by the burning duration

Structural response of cross-laminated timber compression elements exposed to fire

A set of novel structural fire tests on axially loaded cross-laminated timber (CLT) compression elements (walls), locally exposed to thermal radiation sufficient to cause sustained flaming combustion, are presented and discussed. Test specimens were subjected to a sustained compressive load, equivalent to 10% or 20% of their nominal ambient axial compressive capacity. The walls were then locally exposeFI to a nominal constant incident heat flux of 50 kW/m(2) over their mid height area until failure occurred. The axial and lateral deformations of the walls were measured and compared against predictions calculated using a finite Bernoulli beam element analysis, to shed light on the fundamental mechanics and needs for rational structural design of CLT compression elements in fire. For the walls tested herein, failure at both ambient and elevated temperature was due to global buckling. At high temperature failure results from excessive lateral deflections and second order flexural effects due to reductions the walls' effective cross-section and flexural rigidity, as well as a shift of the effective neutral axis in bending during fire. Measured' average one-dimensional charring rates ranged between 0.82 and 1.0 mm/min in these tests. As expected, the lamellae configuration greatly influenced the walls' deformation responses and times to failure; with 3-ply walls failing earlier than those with 5-plies. The walls' deformation response during heating suggests that, if a conventional reduced cross section method (RCSM), zero strength layer analysis were undertaken, the required zero strength layer depths would range between 15.2 mm and 21.8 mm. Deflection paths further suggest that the concept of a zero strength layer is inadequate for properly capturing the mechanical response of fire-exposed CLT compression elements. (C) 2017 Elsevier Ltd. All rights reserved

Percutaneous posterolateral approach for the simulation of a far-lateral disc herniation in an ovine model

This work describes a minimally invasive damage model for ovine lumbar discs via partial nucleotomy using a posterolateral approach. Two cadavers were dissected to analyze the percutaneous corridor. Subsequently, 28 ovine had their annulus fibrosus punctured via awl penetration under fluoroscopic control and nucleus pulposus tissue removed via rongeur. Efficacy was assessed by animal morbidity, ease of access to T12-S1 disc spaces, and production of a mechanical injury as verified by discography, radiography, and histology. T12-S1 were accessible with minimal nerve damage morbidity. Scar tissue sealed the disc puncture site in all animals within 6 weeks, withstanding 1 MP of intradiscal pressure. Partial nucleotomy led to a significant reduction in intervertebral disk height and an increased histological degeneration score. Inducing a reproducible injury pattern of disc degeneration required minimal time, effort, and equipment. The posterolateral approach allows operation on several discs within a single surgery and multiple animal surgeries within a single day.Peer reviewe

Characterization of encapsulated graphene layers using extreme ultraviolet coherence tomography

Many applications of two-dimensional materials such as graphene require the encapsulation in bulk material. While a variety of methods exist for the structural and functional characterization of uncovered 2D materials, there is a need for methods that image encapsulated 2D materials as well as the surrounding matter. In this work, we use extreme ultraviolet coherence tomography to image graphene flakes buried beneath 200 nm of silicon. We show that we can identify mono-, bi-, and trilayers of graphene and quantify the thickness of the silicon bulk on top by measuring the depth-resolved reflectivity. Furthermore, we estimate the quality of the graphene interface by incorporating a model that includes the interface roughness. These results are verified by atomic force microscopy and prove that extreme ultraviolet coherence tomography is a suitable tool for imaging 2D materials embedded in bulk materials

Non-destructive depth reconstruction of Al-Al2_2Cu layer structure with nanometer resolution using extreme ultraviolet coherence tomography

Non-destructive cross-sectional characterization of materials systems with a resolution in the nanometer range and the ability to allow for time-resolved in-situ studies is of great importance in material science. Here, we present such a measurements method, extreme ultraviolet coherence tomography (XCT). The method is non-destructive during sample preparation as well as during the measurement, which is distinguished by a negligible thermal load as compared to electron microscopy methods. Laser-generated radiation in the extreme ultraviolet (XUV) and soft x-ray range is used for characterization. The measurement principle is interferometric and the signal evaluation is performed via an iterative Fourier analysis. The method is demonstrated on the metallic material system Al-Al$_2$Cu and compared to electron and atomic force microscopy measurements. We also present advanced reconstruction methods for XCT which even allow for the determination of the roughness of outer and inner interfaces.Comment: First two authors contributed equally to this work and are ordered alphabetically. 14 page