Pendulum and Static Tests of Laminated Wood Sign Supports

摘要

The report describes three pendulum tests and four static tests conducted on box and H-shaped sign supports built up from Micro-Lam. Micro-Lam, is a laminated wood product with the grain in all the wood veneers running in the same direction. Different cutout patterns in the webs of the box and H-sections near the ground were used to improve the breakaway characteristics. The pendulum tests simulated an impact by a lightweight passenger car. The pendulum mass weighed 2250 lbs, was equipped with a crushable nose simulating a pre-1974 Chevrolet Vega, and had an impact speed of 20 mph. The static tests were used to simulate wind loading forces on the sign supports, and the load was increased until the supports failed. The box and H-shaped members hold promise as effective breakaway supports. The change of momentum for the pendulum mass varied from 299 to 573 lb-sec, well below the preferred maximum value of 750 lb-sec. The failure moments at the base of the supports varied from 23,200 to 41,580 ft-lbs in the first three static tests. Design wind load moments were 38,200 ft-lbs; hence, the ultimate strength was low. In Test 4, two horizontal sawcuts were used in the box section webs instead of rectangular cutouts, and the failure moment was 52,900 ft-lbs. This moment should increase for supports embedded in the ground.