LABORATORY INVESTIGATION TO DETERMINE STATIC AND REPEATED LOAD STRENGTH OF FULL-SIZE SOUTHERN PINE GLUED LAMINATED STRINGERS
This report contains the analysis of data recorded during the laboratory investigation of 24 full size southern pine glued laminated stringers at the Association of American Railroads Research Center and a description of certain physical properties as determined by the Forest Products Laboratory at Madison, Wisconsin. The purpose of the investigation was to determine the static and repeated load strength of the stringers and the effect of load placement. The stringers were loaded in increments of the shear design load with the load points that were 4 ft-8 in. apart and with the first load point at 1-1/2d, 2-1/4d and 3d from center line of bearing. Design load was that load which produced an allowable design shear stress of 180 psi. The following observations may be made from the recorded data: 1. The three stringers tested statically at load points 1-1/2d, 2-1/4d, and 3d failed at 5.34, 4.71, 3.72 shear design increments. Failure was in bearing for 1-1/2d and 2-1/4d loading; and tension for 3d loading. The deflection and flexural strains were linear up to failure. Pending failure was not noticeable and it occurred quite rapidly 2. Four stringers which did not fail after 2,000,000 cycles of repeated loading were later tested statically. One stringer was tested at 1-1/2d, one at 2-1/4d, and two at 3d loading. The shear design increments were 5.04, 4.41, and 3.83 respectively. The stringer at 1-1/2d and the two at 3d did not fail since the capacity of the loading jack was reached first. At 2-1/4d the stringer failed in horizontal shear. 3. Five stringers were tested under repeated loads positioned at 1-1/2d. Of the two stringers loaded at 2.13 times shear design load, one did not fail and one failed at 882,000 cycles because of a knot within the lamination. One stringer was subjected to a shear stress design load ratio of 2.33 and it did not fail. Another stringer was subjected to a shear design load of 2.72 and failed in bearing at 1,365,000 cycles. The final stringer was subjected to 3.11 shear design load and it failed in horizontal shear at 666,200 cycles. 4. Seven stringers were tested under repeated loads positioned at 2-1/4d. One stringer was tested at a shear design load 2.18 or 25,500 lbs per load point and it did not fail. Another stringer subjected to the same shear load ratio failed in horizontal shear after only 417,000 cycles of repeated loading. Failure was attributed to a knot.
Chicago, IL United States 60616
- Publication Date: 1964-12
- Features: Figures; Photos; Tables;
- Pagination: 16 p.
- TRT Terms: Bridges; Failure; Fatigue tests; Laminated wood; Stresses; Stringers; Wooden bridges
- Old TRIS Terms: Bridge stresses; Glued laminated bridge stringers
- Subject Areas: Bridges and other structures; Railroads;
- Accession Number: 00095708
- Record Type: Publication
- Source Agency: Association of American Railroads
- Report/Paper Numbers: ER-52
- Files: TRIS
- Created Date: Jul 15 1976 12:00AM