This paper proposes a simplified estimation method for redundancy of steel check dam, and its related design method. The estimation method uses a parameter defined as “elemental index”. The mathematical significance of the elemental index is proved in this paper, from the view point of structural degree of indeterminant. Using typical model of 6 steel check dams, this paper discusses the relationship between the elemental index and structural redundancy. First, each structure is evaluated by the proposed elemental index. Secondly, the effect of elemental index on collapse load is discussed. Thirdly, residual collapse load ratio associated with the structures removed some elements is checked and its relation to respect elemental index is discussed. And, the positive relationship between the residual collapse load ratio and the elemental index is found. Based on above discussion, this paper proposes the modified allowable stress design method, i.e., the allowable stress is reduced for low elemental index structure. The modified design method tends to adapt to the lager section area or section modulus of important members of less elemental index structures, in order to complement the insufficiency of redundancy of structure. In order to evaluate the effect of proposed design method from the view point of upgrading the probability of residual collapse load, two dimensions hazard map for falling gravels and fragility curve for each elemental character are produced, respectively. The probability of an elemental failure is calculated by using both the hazard curve for position of a member and the fragility curve for resistance of a member. Finally, it is found that the proposed method properly upgrading the residual collapse load for low elemental index structure.
Many structures, such as housing, building, bridges etc., were damaged by the Hyogo earthquake in 1995. At that time, it was tried to evaluate seismic resistance of Sabo dam. However, at that time, earthquake observation records for Sabo dam was not exist, so the adequate analysis of seismic resistance could not be carried out. While, recently, many seismic responses of Sabo dams were observed. Thus, we evaluated seismic resistance using two observation records (small and medium earthquakes). At first, we examined the applicability of seismic response analysis to evaluate seismic resistance of Sabo dam. Results showed that the seismic response analysis can explain seismic response characteristics of Sabo dam, although elastic coefficient of ground and damping factor of ground have to be fitted to observation record. Then, we examined effects of size of earthquake on values of these fitted parameters and showed that seismic response characteristics of the Sabo dam on the medium earthquake can be reenacted using parameters which were fitted from observation record of small earthquake. Based on these analyses, it can be thought that at least, the concrete gravity Sabo dam has enough seismic resistance with the earthquake that corresponds to 6 upper of JMA Seismic Intensity.
Wood absorbs and fixes the CO2 from atmosphere in its growth process and suppresses increasing of CO2. Utilization of wood for structures in long-term increases the fixed effect for CO2 further, and it contributes to global warming control. When the thinned wood is used for erosion control structures, the forest thinning will be promoted, the forest improvement advances, and CO2 absorption amount of forest increases. There are thus many benefits to use wood for erosion control structures. However utilization of wood for erosion control structures is limited in the present state of affairs. Challenges to use wood for erosion control structures with summarized recent research progress situation and wood use of future prospects are described.