Strength and Stiffness of Metal-Clad Roof Sections

Post-frame timber construction has gained popularity with architects and designers in recent years because of design flexibility and cost effectiveness. Beside [sic] being economically feasible, improved strength and stiffness especially with the utilization of diaphragm action was achieved. The lack of an accurate analytical method to describe the strength and stiffness characteristic of metal-on-wood diaphragms makes full-scale testing necessary for predicting diaphragm behavior. Investigations of eighteen (18) steel panels on lumber framing shear diaphragms were completed. Parameters used in the investigation were five (5) sheet-purlin fasteners patterns; two (2) sheet-to-purlin fasteners with or without the provision of shear connectors placed between purlins; blocking attached to the edge purlin by nails and a combination of nails and bolt; two (2) diaphragm widths, 1.829 m (6 ft) and 2.743 mm (9 ft) with constant purlin spacing and the use of either nails or screws for sheet-purlin fasteners. Testing procedures for this investigation were adopted from guidelines reported by Luttrell (1967). Results showed that an increase in the number of sheet-purlin fasteners would increase diaphragm strength and stiffness considerably. However, the fasteners were most effective when placed on both sides of the ribs, along the seams, on the crest of the seam and on the entire edge of the diaphragm. Sheet-to-sheet fasteners were also found to improve the diaphragm strength and stiffness. Shear connectors placed between purlins combined with sheet-purlin fasteners were found to be very effective in preventing purlin twist and reducing sheet-purlin and purlin-rafter slip. Blocking attached to the edge purlin by a combination of bolts and nails was found to be more effective than just five (5) nails in reinforcing the purlin-rafter connection. However, increasing the width of the diaphragm from 1.829 m (6 ft) to 2.743 m (9 ft) while purlin spacing remained constant decreased the ultimate load capacity by 24% and the stiffness by 16%. Replacing screws with nails as sheet-purlin fasteners resulted in very low stiffness and strength values. An attempt to model metal-on-wood diaphragms using the Davies and Bryan (1982) prediction method did not yield favorable results as compared to the actual values. Although overall results of the prediction method were similar to the actual values, a better prediction method for individual component slip is required for metal-on-wood diaphragms