The indices to evaluate the seismic damage level of reinforced concrete underground structures with shear walls were investigated supposing the use of non-linear FEM analysis as the method to calculate dynamic response. Firstly, it was derived that the ratio of the width where principal compressive strain was larger than 1% to the total width correlated with horizontal load capacity degradation based on analytical studies for single walls. To the next, the judgement of reaching maximum load capacity and the classification of the damage level in the post-peak region were illustrated through the damaging width ratio extracted from the follow-up analysis of a shake table test and numerical case studies.
Tensile test of reinforced concrete members with crack repairing under cyclic loading was conducted to clarify their basic characteristics. When the maintained tensile stress of the reinforcing bar during the crack repairing is different, the residual strain of the reinforcing bar at unloading becomes larger according to amplitude of its tensile stress. In case of using the epoxy resin as the repairing material under the larger tensile force, the bond force of the bar near the repaired crack was recovered. When using cement based repairing material instead of epoxy resin, the influence on a strain behavior of the reinforcing bar does not show a large difference. A prediction equation to the residual strain of the reinforcing bar after crack repairing was proposed from maximum strain for the cyclic load hysteresis and the maintained strain of the reinforcing bar at crack repairing. It was shown that, increasing the residual stress at unloading generated the moderate pre-stress force to the reinforcing bar, and thus prolonging the fatigue life of the reinforcing bar by reducing the stress amplitude under the cyclic loading.
This study proposes a novel method of recycling concrete waste by compaction. The advantages of the proposed method are its high production speed and its complete recycling, as we use the aggregate and the cement paste matrix. First, the hardened cement paste (HCP) is examined, crushed, milled, and compacted. The formed compacts showed high strength. Compacts of hardened concrete were prepared after crushing and milling; however, their strength was low. The processes of adding HCP or sludge cakes and performing carbonation treatment were studied, and all treatments were found to be effective in increasing the strength of the compacts.