In Akita prefecture in Japan, two kinds of wooden erosion]control dams, which are Akita original, have been studied and developed from ‚Q‚O‚O‚P. One of which is all wood type dam composed only wood members and lag screws and another is hybrid dam packed the thinned wood and gravels in the steel flexible frame, and total of thirty dams are already constructed in Akita prefecture as of ‚Q‚O‚P‚P. However, since these dams cost are about two times high than concrete dam, as the next stage of studies and development, the researches of cost reduction type dams are advanced now. In all wood dam the costs of lag screw are six million yen per unit, if it is possible to change the lag screws to the cheap pin as round steel, it seems that the costs of a few million yen per unit can reduce. But it is has been understood that the combined stress occurred at the lag screws, it is difficult to adequately consider the different pins one per one. Therefore, in this study, we tried to the optimum design concerning the arrangements of pins by using FEM that can consider the complex combined stress. First, FEM analyses were carried out for the specimen used all lag screw and used all round steel, and the results as for vertical and horizontal displacements, the maximum quantity of pullout of each pin and the stress occurred at each pin and the wood members are compared. Based on these results, the cost reduction dam where the all lag screw on downstream side except the first tier changed round steels was designed. Finally, we conduct FEM for the cost reduction dam, it was shown that the specimen have safety rate ‚W for the design load.

Key wordsFwooden check dam, FEM, lag screw, optimum design, cost reduction