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Träs skjuvhållfasthet och limträbalkars tvärkraftskapacitet - Provningar och beräkningar

Odén, Johan and Anderson, Daniel (2009) VSM820
Structural Mechanics
Civil Engineering (M.Sc.Eng.)
Abstract
Following changes on a European level, there are plans to also in Sweden reduce the characteristic value of shear strength of glued-laminated timber. In Sweden, a decrease of approximately 30% from a characteristic value of 4.0 MPa (for glulam L40) to 2.5 or 3.0 MPa is planned. This would mean that wood would lose competitiveness against other construction materials such as steel and concrete.

The objective of this work was primarily to, through calculations and shear tests, try to clarify whether a reduction in the characteristic value is justified. The tests included the shear capacity of standard shear strength test specimens and tests of shearing force capacity in glulam beams.

The European standard method for determining shear... (More)
Following changes on a European level, there are plans to also in Sweden reduce the characteristic value of shear strength of glued-laminated timber. In Sweden, a decrease of approximately 30% from a characteristic value of 4.0 MPa (for glulam L40) to 2.5 or 3.0 MPa is planned. This would mean that wood would lose competitiveness against other construction materials such as steel and concrete.

The objective of this work was primarily to, through calculations and shear tests, try to clarify whether a reduction in the characteristic value is justified. The tests included the shear capacity of standard shear strength test specimens and tests of shearing force capacity in glulam beams.

The European standard method for determining shear strength of wood is denoted EN408. This method uses glue to attach the load plates of steel onto the test specimen. In this work, two modified test methods have been evaluated: "EN408-skruv" and "EN408-krycka." These alternatives were chosen in order to avoid the risk of fracture in the glue joints and to achieve more pure state of shear stress. In total, 16 material tests were performed. These consisted of specimens of rectangular and I-shaped cross sections of glued laminated wood, L40, and resulted, respectively, in mean shear strengths of 4.2 MPa and 7.1 MPa. The width of the rectangular cross section was 115 mm. The I-section was manufactured by milling the rectangular cross section, and had a web width of 55 mm.

Measurements and calculations of the shearing force capacity of beams were performed to investigate the influence of cross-sectional shape (rectangular and I- cross- section), compressive or tensile stress perpendicular to the beam, an overhang and the effect of bending moment at the middle support in a continuous beam with three supports. The results showed for the rectangular section a mean shear strength of 4.6 MPa and for the Icross-section 6.1 MPa. Normal stress perpendicular to the beam had, as well as an overhang, little or no impact. The shearing force capacity at a middle support was increased by about 20%. Each test series included only 4 nominally equal specimens. However, with an assumption that the characteristic five percent fractile is 0.67 times the mean value, the reduction of the characteristic value from 4.0 MPa to about 3.0 MPa may be justified for the rectangular cross section, but not for a beam with an I- cross- section. (Less)
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author
Odén, Johan and Anderson, Daniel
supervisor
organization
course
VSM820
year
type
H3 - Professional qualifications (4 Years - )
subject
report number
TVSM-5159
ISSN
0281-6679
language
Swedish
id
3566913
date added to LUP
2013-08-02 11:34:58
date last changed
2013-10-07 12:49:57
@misc{3566913,
  abstract     = {Following changes on a European level, there are plans to also in Sweden reduce the characteristic value of shear strength of glued-laminated timber. In Sweden, a decrease of approximately 30% from a characteristic value of 4.0 MPa (for glulam L40) to 2.5 or 3.0 MPa is planned. This would mean that wood would lose competitiveness against other construction materials such as steel and concrete. 

The objective of this work was primarily to, through calculations and shear tests, try to clarify whether a reduction in the characteristic value is justified. The tests included the shear capacity of standard shear strength test specimens and tests of shearing force capacity in glulam beams.
 
The European standard method for determining shear strength of wood is denoted EN408. This method uses glue to attach the load plates of steel onto the test specimen. In this work, two modified test methods have been evaluated: "EN408-skruv" and "EN408-krycka." These alternatives were chosen in order to avoid the risk of fracture in the glue joints and to achieve more pure state of shear stress. In total, 16 material tests were performed. These consisted of specimens of rectangular and I-shaped cross sections of glued laminated wood, L40, and resulted, respectively, in mean shear strengths of 4.2 MPa and 7.1 MPa. The width of the rectangular cross section was 115 mm. The I-section was manufactured by milling the rectangular cross section, and had a web width of 55 mm.

Measurements and calculations of the shearing force capacity of beams were performed to investigate the influence of cross-sectional shape (rectangular and I- cross- section), compressive or tensile stress perpendicular to the beam, an overhang and the effect of bending moment at the middle support in a continuous beam with three supports. The results showed for the rectangular section a mean shear strength of 4.6 MPa and for the Icross-section 6.1 MPa. Normal stress perpendicular to the beam had, as well as an overhang, little or no impact. The shearing force capacity at a middle support was increased by about 20%. Each test series included only 4 nominally equal specimens. However, with an assumption that the characteristic five percent fractile is 0.67 times the mean value, the reduction of the characteristic value from 4.0 MPa to about 3.0 MPa may be justified for the rectangular cross section, but not for a beam with an I- cross- section.},
  author       = {Odén, Johan and Anderson, Daniel},
  issn         = {0281-6679},
  language     = {swe},
  note         = {Student Paper},
  title        = {Träs skjuvhållfasthet och limträbalkars tvärkraftskapacitet - Provningar och beräkningar},
  year         = {2009},
}