Tests of the capacity of shear connections consisting of nails in a row placed at distances 7, 10 and 14d, “d” being the cross-sectional dimension of the nail, versus single nail capacities, were executed. The perfo...Tests of the capacity of shear connections consisting of nails in a row placed at distances 7, 10 and 14d, “d” being the cross-sectional dimension of the nail, versus single nail capacities, were executed. The performed tests do support the connotation that no reduction should be required for nails of diameter 2.8 mm or less in a row, provided that nails are spaced sufficiently far apart for wood cracking not to occur. At the ultimate capacity of the joint, all such thin nails in a row will be yielding, having developed plastic hinges, i.e. each single nail will have developed its ultimate capacity. Hence, the ultimate capacity of the connection will be each nail’s capacity times the number of nails in the row. The force pr. nail increases subsequent to the development of a plastic hinge. This is likely due to the axial pullout-force, i.e. the ultimate capacity of a shear connection is higher than the force required for developing plastic hinges in the nails. This additional capacity-reserve may also partly be attributed to the rotational resistance of nails. The number of nails in a row should make insignificant difference in the pr. nail capacity, as long as no wood cracking takes place. Thus, applying elastic theory to nails in a row does not seem relevant. This is in contrast to bolt-connections.展开更多
The object of this research effort was, upon request for evidence from a building contractor, to compare the influence of various amounts and types of fibers on crack widths, using a steel ring mold. Comparisons were ...The object of this research effort was, upon request for evidence from a building contractor, to compare the influence of various amounts and types of fibers on crack widths, using a steel ring mold. Comparisons were made between synthetic fibers (polyolefin) of 48 mm length, hooked-end steel fibers of diameters 0.6 mm and 1.05 mm, both of 50 mm length. 10-liter samples were extracted from concrete ready-mix truck batches at delivery sites, whereupon fibers were mixed into the samples, layer by layer, by applying a drill-mounted mortar mixing device. For each amount of fiber content, 4 rings were cast, and of the plain concrete control samples, 5 rings were cast. After removing the outer steel casting, strain gages were installed on the exposed outer concrete surface. Strain values were continuously logged, and crack developments and crack widths were measured daily. Sufficient data with statistically high significance were obtained to indicate that: A synthetic fiber content of 3 kg/m3 did not decrease crack-widths as compared to the non-fiber concrete samples. Synthetic fiber contents of 5 kg/m3 and higher, did reduce crack widths on par with hooked-end steel fibers in the amounts of 25 kg/m3 and above. Hooked-end steel fibers of aspect ratio 80 are more efficient with regards to crack width reduction, yielding 33% narrower cracks, than hooked-end steel fibers, at equal weight-contents, with aspect ratio 45.展开更多
文摘Tests of the capacity of shear connections consisting of nails in a row placed at distances 7, 10 and 14d, “d” being the cross-sectional dimension of the nail, versus single nail capacities, were executed. The performed tests do support the connotation that no reduction should be required for nails of diameter 2.8 mm or less in a row, provided that nails are spaced sufficiently far apart for wood cracking not to occur. At the ultimate capacity of the joint, all such thin nails in a row will be yielding, having developed plastic hinges, i.e. each single nail will have developed its ultimate capacity. Hence, the ultimate capacity of the connection will be each nail’s capacity times the number of nails in the row. The force pr. nail increases subsequent to the development of a plastic hinge. This is likely due to the axial pullout-force, i.e. the ultimate capacity of a shear connection is higher than the force required for developing plastic hinges in the nails. This additional capacity-reserve may also partly be attributed to the rotational resistance of nails. The number of nails in a row should make insignificant difference in the pr. nail capacity, as long as no wood cracking takes place. Thus, applying elastic theory to nails in a row does not seem relevant. This is in contrast to bolt-connections.
文摘The object of this research effort was, upon request for evidence from a building contractor, to compare the influence of various amounts and types of fibers on crack widths, using a steel ring mold. Comparisons were made between synthetic fibers (polyolefin) of 48 mm length, hooked-end steel fibers of diameters 0.6 mm and 1.05 mm, both of 50 mm length. 10-liter samples were extracted from concrete ready-mix truck batches at delivery sites, whereupon fibers were mixed into the samples, layer by layer, by applying a drill-mounted mortar mixing device. For each amount of fiber content, 4 rings were cast, and of the plain concrete control samples, 5 rings were cast. After removing the outer steel casting, strain gages were installed on the exposed outer concrete surface. Strain values were continuously logged, and crack developments and crack widths were measured daily. Sufficient data with statistically high significance were obtained to indicate that: A synthetic fiber content of 3 kg/m3 did not decrease crack-widths as compared to the non-fiber concrete samples. Synthetic fiber contents of 5 kg/m3 and higher, did reduce crack widths on par with hooked-end steel fibers in the amounts of 25 kg/m3 and above. Hooked-end steel fibers of aspect ratio 80 are more efficient with regards to crack width reduction, yielding 33% narrower cracks, than hooked-end steel fibers, at equal weight-contents, with aspect ratio 45.
