Experimental Study on Flexural Performance of Glued-Laminated
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Materials and Structures (2018) 51:9 https://doi.org/10.1617/s11527-017-1135-2 ORIGINAL ARTICLE Experimental study on flexural performance of glued- laminated-timber-bamboo beams Qingfeng Xu . Yubing Leng . Xi Chen . Kent A. Harries . Lingzhu Chen . Zhuolin Wang Received: 13 September 2017 / Accepted: 29 December 2017 Ó RILEM 2018 Abstract Engineered bamboo, produced through the by tensile fracture of the bottom fiber in mid-span, technique of gluing and reconstituting, has better followed by horizontal tearing beside the broken mechanical properties than round bamboo and some surface. No relative slip between layers was observed wood products. This paper studies the flexural perfor- before failure, therefore the flexural capacity of the mance of laminated beams produced with timber and laminated beams can be predicted using equilibrium engineered bamboo. The six-layer beams were made and compatibility conditions according to the plane from Douglas fir, spruce, bamboo scrimber and section assumption. laminated bamboo, or a combination of these. It is confirmed that glued-laminated wood beams produced Keywords Engineered bamboo Á Bamboo scrimber Á with wood of weak strength, like spruce, can be Timber Á Laminated beams Á Flexural performance strengthened by gluing engineered bamboo lumbers on the outer faces, thus achieving better utilization of the fast growing economic wood species. Flexural failure of the laminated beams was primarily triggered 1 Introduction It is essential to develop green and environment- Electronic supplementary material The online version of friendly construction materials. Compared with con- this article (https://doi.org/10.1617/s11527-017-1135-2) con- tains supplementary material, which is available to authorized ventional building materials like steel, concrete and users. masonry, bamboo and wood are both renewable and biodegradable materials with low carbon emission & Q. Xu ( ) Á Y. Leng Á X. Chen Á L. Chen Á Z. Wang [1, 2]. The similarities between bamboo and wood, Shanghai Key Laboratory of Engineering Structure Safety, Shanghai Research Institute of Building Sciences, like high strength-to-weight ratios and excellent No. 75 South Wanping Road, Shanghai 200032, China seismic performance, prompt researchers to consider e-mail: [email protected] whether it is possible to use the two materials together to achieve better mechanical performance. Y. Leng School of Naval Architecture, Ocean and Civil New and innovative uses of wood have been Engineering, Shanghai Jiao Tong University, developed in recent decades driven by the consider- Shanghai 200240, China ations of sustainability and energy savings [3, 4]. Similarly, in recent years, engineered bamboo mate- K. A. Harries Department of Civil and Environmental Engineering, rials have garnered increased attention, as studies University of Pittsburgh, Pittsburgh, PA 15261, USA comparing bamboo to timber have mostly concluded 9 Page 2 of 14 Materials and Structures (2018) 51:9 Fig. 1 Engineered bamboo constituent products: a laminated bamboo; and b bamboo scrimber bamboo to be more sustainable and available than beams produced with such weaker wood can be timber [5]. Despite its long history, round bamboo has strengthened by gluing engineered bamboo lumbers at limited structural applications due to its slenderness, the outer faces, thus achieving better utilization of the natural variation, and limited geometrical sizes. fast-growing economic wood species. In glued lami- Engineered bamboo, including laminated bamboo nated timber manufacture different grades of wood and bamboo scrimber, overcomes these shortcomings. have been used together in the same member—with The mechanical properties of engineered bamboo are stronger harder wood as the outer layers (resisting comparable to, and in many respects better than flexure) and poorer quality wood in the middle comparable wood products [5–8]. (resisting shear) [11–15]. Other researchers have Laminated bamboo is fabricated by cutting laminae proposed similar approaches with weaker glued lam- from the bamboo stem and gluing them into rectan- inated beams reinforced with steel [16–18], FRP gular cross sections; in this case the original bamboo [18–23], natural fibers [24] and ultra-high perfor- wall cross section is maintained [6]. Bamboo scrim- mance concrete [25]. This study proposes an alterna- ber, also called parallel strand bamboo, is fabricated tive to the use of (possibly less readily available) better by cutting bamboo into strips and gluing them parallel wood species or other materials in the outer layers of to each other, typically in a mould under pressure such hybrid glued laminated members: engineered [9, 10]. In both materials, the process of gluing and bamboo. reconstituting result in a material that is more In this paper the flexural performance of 18 glued stable and less variable than the constituent natural laminated beams is studied. Twelve beams are fabri- materials. The resulting engineered materials are cated with a single material (i.e., Douglas fir, spruce, believed to achieve better mechanical properties than laminated bamboo and bamboo scrimber, three spec- timber and round bamboo. The laminated bamboo and imens with each material). The remaining 6 hybrid bamboo scrimber products used in this study are specimens consist of different material layers. In the shown in Fig. 1. In practice, both engineered bamboo hybrid beams, the outer layers, especially the outer- and wood constituent materials are first fabricated into most tensile layer, are produced with engineered boards of desired thicknesses, and then processed into bamboo lumbers, and the inner layers, are composed glue-laminated structural members by cutting and of spruce. Such a combination is referred to as gluing under pressure at room temperature (cold press) ‘composite sandwiches’. The objective of the study [6, 9]. is to investigate whether the composite beams can Some fast growing wood species, like spruce, achieve better flexural performance, compared with typically exhibit relatively weak tensile and flexural the laminated wood beams. strengths. It is proposed that glued-laminated wood Materials and Structures (2018) 51:9 Page 3 of 14 9 Table 1 Design of the test beams Specimen Numbering of the laminate Cross section (mm) 1 2345 6 DF1, DF2, DF3 Douglas fir (DF) Sp1, Sp2, Sp3 Spruce (Sp) BS1, BS2, BS3 Bamboo scrimber (BS) LB1, LB2, LB3 Laminated bamboo (LB) ST1 Sp Sp Sp Sp Sp BS ST2 DF Sp Sp Sp BS BS ST3 BS Sp Sp Sp BS BS LT1 Sp Sp Sp Sp Sp LB LT2 DF Sp Sp Sp LB LB LT3 LB Sp Sp Sp LB LB The uniaxial stress–strain relationships of the four Test specimens having dimensions 115 mm constituent materials are first studied, to gain a better deep 9 45 mm wide 9 2400 mm long were designed understanding of the flexural behavior of the resulting in compliance with ASTM D198-15 [26]. All speci- hybrid glued laminated beams. mens had identical dimensions with six 19 mm thick glued layers (Table 1). According to ASTM D198-15, shear span/depth ratios between 5 and 12 are recom- 2 Experimental investigations mended for evaluation of flexural properties; in this study a shear span of 690 mm, resulting in a shear 2.1 Design of the test specimens span/depth ratio of 6.0 was used. The specific config- urations of the laminated beams are shown in Table 1. An experimental program was carried out to illustrate The adhesive used to bond the layers was the flexural performance of the beams glued laminated AQUENCE SL 3184, produced by the Henkel Chem- with different materials. Six series of laminated beams ical Technologies; the bond line thickness is with a total of 18 specimens were tested. The first negligible. (DF1 * DF3) and second series (Sp1 * Sp3) were produced with six layers of 19 mm thick Douglas fir 2.2 Test set-up and instrumentation and spruce, respectively. The third (BS1 * BS3) and forth series (LB1 * LB3) were produced with six Tests were carried out in a 100 kN capacity universal layers of 19 mm thick bamboo scrimber and laminated testing machine. The beams were simply supported on bamboo, respectively. The fifth series (ST1 * ST3) roller supports over a distance of 2070 mm and tested included 3 specimens produced with bamboo scrimber in four-point flexure with equal shear spans and at the tension face, spruce in the middle and varying constant moment regions of 690 mm. Tests were materials at the compression face. The sixth series conducted under mid-span displacement control at a (LT1 * LT3) included 3 specimens with laminated displacement rate of 5 mm/min. Figure 2 shows the bamboo at the tension face, spruce in the middle and loading geometry used. Loading was sustained until varying materials at the compression face. The six failure of the beam, after which the carrying capacity layer laminates are described in Table 1. dropped dramatically. By comparing the flexural behaviors of different Vertical displacements at mid-span, both loading series, the effectiveness of strengthening laminated points, and both supports were measured with dis- wood beams produced with wood species of low placement transducers. Strain gauges having a gage strength with engineered bamboo is discussed. Such length of 55 mm, oriented parallel to the longitudinal an approach is expected to result in better utilization of axis of the beams, were placed on the bottom, top and the fast growing and economical softwood species. lateral surfaces as shown in Fig. 2. Particular attention 9 Page 4 of 14 Materials and Structures (2018) 51:9 Fig. 2 Test set-up and instrumentation scheme was paid to the strain distribution through the depth of (the primary direction in which they were stressed in the beam at mid-span, where each lamina was the beams). instrumented with a strain gage on the lateral face of the beam in addition to gages on the top and bottom of 3.1 Parallel-to-grain tension and compression the beam. Load, displacement and strain data were behavior simultaneously recorded through a dynamic data logger.