The performance of structural screws in Canadian Glulam
Bibliographic record
Abstract
The development of engineered wood products (EWPs), such as glued laminated timber, has led to the production of structural members with increased strength and spanning capabilities compared with solid sawn lumber and timber, and similar to what one could attain with commonly sized steel and reinforced concrete members. An important reason for the underutilisation of wood for heavy construction is the limitation of the CSA O86 Wood Design Standard especially as it applies to the design of fastenings for highly loaded connections. This thesis addresses the connection design of glulam and sawn wood using structural self-tapping/self-drilling screws from Europe.The CSAâO86 Standard provides formulas for the design of both lag and wood screws in Canada. Recently in Europe structural screws have been developed which combine the advantages of both lag and wood screws. These screws have high load carrying capacities and withdrawal strengths and are also self-tapping/self-drilling, hence in most cases do not need lead holes. However CSA O86 has no specific design provisions for these screws. To assess their viability for use in Canada, two test programs were carried out; the first on the withdrawal resistance of the screws and the second on the performance of inclined screws in joist-to-header connections. Douglas fir Larch(20f-E), Spruce Pine (20f-E) and Nordic Lam (24f-1.9E) glulam in conjunction with a variety of 6, 8, 10 and 12mm diameter European structural screws were used for the withdrawal tests, while the joist to header connections were made of No.2 white pine timber connected by double threaded 8.2mm WT-T screws from SFS intec. In all 1960 withdrawal test were carried out. The test setup and procedure was modelled after ASTM D1761.The joist to header test set-up, involving 14 tests was modelled after ASTM D7147. The main aim of the withdrawal test program was to recommend a generic equation for use in the design of these screw connections with Canadian glulam. In the process the effects of Canadian wood density, depth of penetration, screw diameter and lead holes on the withdrawal resistance of the screws were assessed. The aim of the joist to header connection test program was to compare the performance of dry specimen with that of the same connection in wet timber.The test results demonstrated that the withdrawal strength per unit length increases with denser wood, except 6mm and 8mm in Nordic Lam glulam. The depth of penetration affects the withdrawal strength, where for larger screws an increase of slightly more than double was obtained for 12d penetration compared to 6d.The orientation of the glulam, that is either top or side, was insignificant other than the effect it had on the scatter of the strength results. The use of lead holes was shown for both the 8mm and 10mm not to influence the withdrawal strength. However the lead holes improved the ease of installation for the larger screws, especially in the dense glulam.The tests results were compared with the predicted characteristic and average withdrawal resistance values, which were calculated using formulas found in timber codes around the world, namely CSA O86 (Canada), NDS (USA), Eurocode 5 (Europe), DIN 1052 (German) and from other researchers including Frese and Blaβ (GER), Pirnbacher and Schickhofer (AUT) and McLain (USA). All methods resulted in a reasonable prediction of the withdrawal resistance except for the CSA O86 formula for lag screws which was very conservative. The McLain formula for lag screws provided the closest prediction of the test result, but bearing in mind the variability of wood, all the other methods could be considered as acceptable except for the CSA O86 lag screw equation. Regarding the joist-to-header cross screw connections, the dry tests were measured to have a 35% increase in resistance compared with the wet specimens; furthermore, the Kevarinmäki formula provided the most accurate prediction of the resistance.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".