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プレストレスト二重鋼管コンクリート (WSC) は, 同心円状に二重に配置された鋼管の内側にコンクリートが充填されており中心にはPC鋼棒が配置されている. 内側コンクリートにはプレストレスが導入され引張力には内側コンクリートとPC鋼棒そして外側鋼管が抵抗し, 圧縮力には二重鋼管と外側コンクリートによって拘束された内側コンクリートのみが抵抗する新しい構造形式である. 本論文ではWSCの実用化のために実験及び解析によりWSCの軸方向力に対する力学的特性を明らかにし, 非線形な変形性状をもちながら残留変形を生じないという特徴を生かすためブレース材として用いた場合の動的応答特性を解析的に評価し, 弾塑性振動系及び線形弾性振動系よりも優れた動的応答特性を示すことを明らかにした.

Fatigue tests were carried out for steel-concrete sandwich beams with shear reinforcement. Under fatigue loading, the sandwich beams indicated three failure modes, namely shear compression failure due to crushing of concrete between diagonal cracks and the fatigue fracture of the steel plates either the lower flange plate or the shear reinforcing steel plates. The S-N relationship for the different failure modes is presented. The fatigue strength of the sandwich beams was also predicted by the finite element method. A simple method to predict the strains in the shear reinforcing plates under fatigue loading is presented. A fatigue design proposal for the sandwich beams is also presented.

Fatigue tests were carried out for steel-concrete sandwich beams without shear reinforcement. Observed failure modes and their experimental S-N relationships for this type of beams are presented. The fatigue strength of the sandwich beams was predicted analytically by using the finite element method. The fatigue analysis was based upon reducing the compressive strength, the tensile strength, and the stiffness of the concrete with increasing the number of loading cycles (N) and increasing the stress range (Sr, ). The analytical S-N relationships are compared with the experimental ones. Finally, a design proposal for the sandwich beams under fatigue loading is presented.

水中浮遊式トンネルは, 従来の構造物に比べて大きな動揺を許容することにより, 支持構造物の軽量化, 経済化を図ることを目的としている. したがって, 動揺の予測と制御が極めて重要な構造物であるが, 水中の長大線状構造物としての解析手法が確立されていない上, 我が国沿岸域のような厳しい波浪条件下において, どのような挙動を示すのかを研究した例は少ない. 本論文では, まず断面二次元のモデルにおいて, 基本的な動揺特性の解明を行った後, 動的問題に拡張したモリソン式による比較的簡便な全体解析モデルを提案した. その結果, 水中浮遊式トンネルの基本的な波浪動揺特性が明かになった.

Although actual submerged floating tunnels have not yet been constructed, they are seen as one of the most promising structures for strait crossings. The authors proposed a suitable model for a super-long submerged floating tunnel using the modified Morison's equation even if the phase delay by propagation of earthquake wave should be taken into consideration. As a result of this study, a super-long tunnel of 2km in length were analyzed, and the fundamental characteristics of the response due to earthquakes were obtained.

鉄筋コンクリートスラブの押抜きせん断耐力は, 作用荷重が自由縁に近づくにつれて低下する. 土木学会コンクリート標準示方書では, このような破壊に対して設計断面の長さを減少させることにより考慮している. 本研究は, 相対する二辺が単純支持されたスラブの試験結果を基に, 上記の方法が不十分なものであることを指摘するとともに, 自由縁附近載荷の場合における耐力の評価方法を検討した. その結果, 耐力低下を押抜きせん断に対する設計断面の長さの減少のほかにその単位長さ当たりのせん断強度の減少としてとらえる方法と, 有効幅を用いてはりのせん断耐力として設計する方法を提案した.

本研究において, 非線形有限要素解析による数値実験により連続繊維補強コンクリートはりのせん断耐力評価式を構築した. 本せん断耐力評価式は, はりがせん断圧縮破壊を起こす場合を想定したものであり, その破壊基準を曲げ圧縮域での主応力により規定している. 本評価式は, 曲げ圧縮域でのコンクリートによるせん断力, 曲げ圧縮域と斜めひび割れ域とを結ぶ水平領域でのコンクリートによるせん断力, 斜めひび割れ域でのせん断補強筋が受け持つせん断力およびせん断補強筋以外が受け持つせん断力の和として定義される. 最終的に, 既往の実験結果との比較を行うことにより本評価式の妥当性を確認した.

本論文では, 道路橋示方書の算式に基づく慣用の解法を用いて計算したコンクリートのクリープ・乾燥収縮によるプレストレス力減少量と断面力移行量を段階的積分法による結果と比較することによって, 鋼材による変形の拘束およびコンクリートの遅れ弾性歪みによる影響が適切に評価されているかを調べた. そして, 構造系が変化するPC構造物の設計においてこれらの影響を総合的に評価するための算式を提案し, これをPC連結T桁に適用した結果を示して, その妥当性についての考察を行った.

本研究では, 非線形有限要素解析により連続繊維補強コンクリートはりのせん断耐荷性状の検討を行い, 実験結果と比較することによりその有用性を確認した. さらに, ひび割れ面における作用せん断力に対する抵抗力は圧縮域での分担せん断力と斜めひび割れ域での分担せん断力により構成されるものと考え, これらの分担力およびはりのせん断耐力が, 主筋およびせん断補強筋の弾性係数の大きさ, 降伏強度の大きさによりどのように異なるのか定性的に明らかにした.

Submerged floating tunnels, which consist of buoyant tubes and tension legs, have been expected as one of the most prospective structures for deep-water crossings in the future. In this paper, their dynamic responses due to wave forces were reported. The dynamic motions of submerged floating tunnels were analyzed by a two-dimensional model based on the potential theory. In order to realize their fundamental characteristics, various arrangements of tension legs were taken into consideration as well as the tube weights and water depths. Consequently, the wave forces and displacements were generalized with the natural frequencies.

The uniaxial tensile tests of Reinforced Concrete elements with Carbon Fiber Sheet (RCC) are conducted to clarify the basic mechanical characteristics which affect the tension stiffness of RCC. This paper mainly presents the difference between RCC and ordinary reinforced concrete (RC) member in the load carrying capacity, the average crack spacing, stress and/or strain distributions of steel and the average stress - strain relationship of concrete. Crack spacing of RCC becomes smaller between 35% and 60% of that in RC as the amount of Carbon Fiber Sheet (CFS) increases. The strain distributions of steel in RCC before and after the yielding of steel differ from those in RC. The tension stiffness developed by the bond action of CFS increases as the amount of CFS increases but that of steel becomes less. With the steel and CFS contributions combined, the tension stiffness of concrete as a whole generally becomes greater than that in RC. There is, however, a case in which tension stiffness of concrete in RCC decreases more than that in RC, because the average bond stress of steel rapidly decreases after the yielding of steel.

To examine the confinement effects of rectangular ties in reinforced concrete columns, 18 short tied columns are tested. The variables are the tie spacing, the amount and the yield strength of lateral steel, the tie configuration, and the amount and the distribution of longitudinal steel. Based on the test results, the stress-strain curves of confined core concrete are obtained and the results are compared with some models proposed by other researchers. It is concluded that these models have the limit of application to the test results. A new model is then proposed. The relationships between the test results and the calculated results are satisfactory. In this paper the effects of the strain rates and the ratio of area of the core bounded by the perimeter tie to the gross area on confinements, are also discussed through the comparison with other researchers' test data.

For calculating the deformation of reinforced concrete members under working load, it is important to estimate the tensile resistance of concrete after cracking. The authors has previously demonstrated the method for generally applying the Branson's approach to reinforced concrete members subjected to combined bending and axial force. However, it has been impossible to calculate strain by using the method.In this paper, based on the extension of the Branson's approach, method for calculating mean steel strain in reinforced concrete members is studied, and it is found that an expression of the same type as the transition of centroidal axis location can be used also for the transition of neutral axis location in the effective section. By comparing test results with calculated results, it is concluded that the method is satisfactory.

The purpose of this study is to investigate the fatigue strength of reinforced concrete slabs failing by punching shear. A total of 108 slabs were tested under constant or combined cyclic loads. The results of the tests show that the number of loading cycles to failure has a logarithmic normal distribution and the fatigue strength for one million cycles is about 55 % of the ultimate strength, and that Miner's hypothesis is applicable to the punching failure. Finally, the design equation of fatigue punching strengths is proposed.

The purpose of this study is to examine the confinement effects of supplementary ties in reinforced concrete columns. 16 short tied columns are tested. The supplementary ties used have 180° hooks at both ends or at one end. In the two test specimens the tie with 180° hooks at both ends are engaged with longitudinal steel bars and in the other test specimens the ties are engaged with a perimeter tie. The test specimens are subjected to monotonic and cyclic loading. Based on the test results, the stress-strain curves of confined core concrete are obtained and the results are compared with the model which has been proposed by the authors. It is concluded that the authors' model on the stress-strain curves of confined core concrete is valid for the confinement effects of supplementary ties.