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- Crocetti, Roberto, et al.
(författare)
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An Innovative Prefabricated Timber-Concrete Composite System
- 2014
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Ingår i: Materials and Joints in Timber Structures. - Dordrecht : Springer Netherlands. - 2211-0844 .- 2211-0852. - 9789400778108 ; 9, s. 507-516
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Konferensbidrag (refereegranskat)abstract
- A novel type of timber-concrete composite floor, consisting of longitudinal glulam beams with a fibre reinforced concrete (FRC) slab on the top is proposed. In order to check some relevant mechanical properties of such a floor, full-scale laboratory tests along with numerical analyses were carried out. The shear connector system used in the investigation consisted of self-tapping screws driven at an angle of 45 degrees to the grain direction of the glulam beams. The manufacture of the structure occurred according to the following steps: (a) the screws were inserted on the top of the glulam beams; (b) the beams were rotated 180 degrees about the longitudinal axis and placed in a concrete formwork; (c) the FRC was cast into the formwork; (d) after curing of the FRC, the composite floor was again rotated 180 degrees about the longitudinal axis into its right position, i.e. with the FRC slab on the top side. Long term tests and quasi-static bending tests were performed. It was found that the proposed connection system showed a very high degree of composite action both during the long-term testing and at load levels close to the failure load. Furthermore, the assembly of the prefabricated timber-concrete composite system revealed to be very fast and easy.
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| 2. |
- Crocetti, Roberto, 1968, et al.
(författare)
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Anchorage systems to reduce the loss of pre-stress in stress-laminated timber bridges
- 2010
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Ingår i: Proceeedings of the International Conference Timber Bridges. - 9788251926805 ; , s. 11-
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Konferensbidrag (refereegranskat)abstract
- Stress-laminated timber (SLT) decks consist of a number of planks, boards or glulam elements,placed edgewise, side by side, in which holes are pre-drilled at regular intervals along thelongitudinal axis. High-strength bars are then inserted into the holes and pre-tensioned. The pretensioningof the bars introduces compressive stresses in the transverse direction of the deck. Oneof the main problems with SLT decks has been the loss of tension in the pre-stressed bars, whichleads to a reduction in the structural efficiency of the deck. A phenomenon of this kind is mainlycaused either by local indentation of the wood at the anchorage system and/or by long-term effects.This paper describes the results of laboratory tests and numerical simulations conducted on SLTreinforced in the anchorage zones by means of self-tapping screws. The loss of tension in the prestressedbars has been recorded both instantaneously and after a few months in a climate chamberwhere they were exposed to moisture variation.
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| 3. |
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| 4. |
- Crocetti, Roberto, et al.
(författare)
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Experimental and numerical investigation on the shear strength of glulam
- 2010
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Ingår i: International Council for Research and Innovation in Building and Construction: Working Commission W18 ‑ Timber Structures — 2010. - Nelson : University of Canterbury.
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Konferensbidrag (refereegranskat)abstract
- According to EC5, the shear resistance of a structural timber element should be determined on the basis of the characteristic shear strength of the material, along with classical beam theory. For glulam, the characteristic strength values are given by the European standard EN 1194 [3], which assumes a direct relationship between tensile strength and shear strength of the lamination. As an example, the characteristic shear strength of glulam class GL28c, consisting of inner laminations with characteristic tensile strength ft,0,k = 14.5 MPa, would be fv,k = 0.32·(14.5)^0.8 = 2.9 MPa. However, recent investigations both on glulam members [4] and on timber members [5] have shown that the shear strength of spruce is higher than the shear strength obtained by means of the model proposed by EN1194. Moreover, the studies show that the shear strength is nearly constant, regardless the strength class of the timber material.
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| 5. |
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| 6. |
- Crocetti, Roberto, et al.
(författare)
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Strengthening of large diameter singel dowel joints
- 2010
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Rapport (refereegranskat)abstract
- A preliminary study for implementation of a novel truss node is presented. For this purpose, the load-slip behaviour of double-shear loaded single large dowel joints was investigated. Out of a total of 26 laboratory shear tests, 5 were performed on non-reinforced specimens. The remaining 21 tests were performed on specimens reinforced by means of self-tapping screws. All laboratory tests were conducted under monotonic quasi-static loading. The distance between the dowel and the loaded edge of the timber element was considerably smaller than the minimum distance suggested by building codes. The influence of both i) the placement and ii) the diameter of the reinforcing screws on the load-slip behaviour of the joint was studied. The study shows that the scatter in test results is considerably reduced when reinforcing screws are used. The study also shows that the reinforcing screws prevent the joint to fail due to premature splitting. Thus, due to the presence of the reinforcing screws, no reduction of load-carrying capacity of the dowel caused by the short distance between dowel and loaded edge of the timber element needs to be applied. Further, the reinforced specimens exhibited a very ductile load-slip behaviour and - after the first drop in the load-slip curve occurred - the joints still showed a significant reserve of load-carrying capacity.
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| 7. |
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| 8. |
- Crocetti, Roberto, et al.
(författare)
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Takras avslöjar allvarliga brister
- 2011
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Ingår i: Samhällsbyggaren. - 2000-2408. ; :5, s. 22-27
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- SP har etablerat en databas med 180 rasade eller skadade tak. Det framgår, att det var övervägande stål- och träkonstruktioner, som hade rasat. Endast en skadad betongkonstruktion rapporterades. Byggnadernas ålder spänner över cirka 100 år, men 60 % är uppförda från 1980 och framåt. Taken är förhållandevis flacka. Ca 30 % är lantbruksbyggnader. De dominerande rasorsakerna är dimensioneringsfel och utförandefel. Till dimensioneringsfel räknas bl a, att man inte har dimensionerat över huvudtaget, och att man inte har beaktat snöfickor mm. Detta är några av slutsatserna i den utredning, som SP har utfört tillsammans med Skanska, Lunds tekniska högskola och Lantbruksuniversitetet, och som publicerades den 1 juni 2011.
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| 9. |
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| 10. |
- Ekholm, Kristoffer K J, 1982, et al.
(författare)
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Full-Scale Ultimate-Load Test of a Stress-Laminated-Timber Bridge Deck
- 2012
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Ingår i: Journal of Bridge Engineering. - 1084-0702 .- 1943-5592. ; 17:4, s. 691-699
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Tidskriftsartikel (refereegranskat)abstract
- A general assumption reported in the literature is that the structural response of a stress-laminated-timber (SLT) bridge deck islinear until failure. However, few studies of ultimate-load tests (ULTs) on timber bridges have been reported. A full-scale test of a SLT deck(span, 4.9 m; thickness, 270 mm) was performed to obtain the deformations at various prestress levels as well as at the ultimate-load capacityof such a structure. Prior to the ULT, nondestructive tests (NDT) were performed at three different prestress levels. The load was applied as anaxle load positioned both centrically and eccentrically. The deflections were about 10% larger at a prestress level of 300 kPa compared with aprestress level of 600 and 900 kPa. For applied loads larger than 150–250 kN, the deflection of the deck was nonlinear at certain positions.This was most likely owing to large concentrated shear forces that resulted in interlaminar slip between the laminates. The limit for linearityseems to be dependent on the applied prestress. A prestress of 600 kPa and an eccentrically positioned load was used for the ULT. Failureoccurred at a load level of 900 kN. The existing design codes and new procedures in development may be verified and calibrated against theresults in this paper.
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