International Journal of High-Rise Buildings (국제초고층학회논문집)

Council on Tall Building and Urban Habitat Korea (한국초고층도시건축학회)
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Performance of Adhesives in Glulam after Short Term Fire Exposure

  • Published : 2018.12.01
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Abstract

As engineered timber such as Glulam is seeing increasing use in tall timber buildings, building codes are adapting to allow for this. In order for this material to be used confidently and safely in one of these applications, there is a need to understand the effects that fire can have on an engineered timber structural member. The post-fire resilience aspect of glulam is studied herein. Two sets of experiments are performed to consider the validity of zero strength guidance with respect to short duration fire exposure on thin glulam members. Small scale samples were heated in a cone calorimeter to different fire severities. These samples illustrated significant strength loss but high variability despite controlled quantification of char layers. Large scale samples were heated locally using a controlled fuel fire in shear and moment locations along the length of the beam respectively. Additionally, reduced cross section samples were created by mechanically carving a way an area of cross section equal to the area lost to char on the heated beams. All of the samples were then loaded to failure in four-point (laterally restrained) bending tests. The beams that have been burnt in the shear region were observed as having a reduction in strength of up to 34.5% from the control beams. These test samples displayed relatively little variability, apart from beams that displayed material defects. The suite of testing indicated that zero strength guidance may be under conservative and may require increasing from 7 mm up to as much as 23 mm.

Keywords

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Figure 1. Sample cross section of CLT (left) and Glulam (right). The laminates of CLT vary in direction between each layer while the laminates of Glulam are uniformly in one direction.

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Figure 2. Massive timber charring behaviour and response to fire exposure.

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Figure 3. Canadian timber adhesives standards summary (see Quiquero and Gales, 2017).

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Figure 4. Shear plane shown on unheated and heated samples (left) and shear apparatus test setup (right).

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Figure 5. Test setup of the heating portion of the experiment for the moment region (left) and the shear region (right).

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Figure 6. Mechanical loading of simply supported beam with four point loads.

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Figure 7. Total char depths measured on samples versus the heating duration.

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Figure 8. Typical failure mode of shear along an adhesive bond line.

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Figure 9. Comparison of remaining shear capacity versus area for all samples.

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Figure 10. Remaining shear capacity of samples versus different predictions of actual remaining shear area at full adhesive strength, compared with the measured char depths and the standard predicted sacrificial char method.

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Figure 11. Load versus slip behaviour for heated for different durations under a 50 kW/m2 incident heat flux.

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Figure 12. Failure mode of a Glulam undamaged control beam, whose failure originated along the adhesive bond lines within the moment region.

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Figure 13. Failure load of all beams damaged in the moment region, shear region, as well as the control beams.

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Figure 14. Load versus downward displacement beams damaged in the moment region (left) and shear region (right).

Table 1. Summary of the number of samples tested for each adhesive type, heat exposure and heating duration

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