拘束鋼製せん断パネルの終局耐力と変形性能に関する研究

<p> This paper investigated experimentally the hysteretic behavior of steel panels confined by two pieces of polypropylene plates (hereinafter referred to as PP plates) and bolts, and proposed methods to evaluate ultimate strength and deformation capacity of the confined steel panels. Thirty one 1/2-scale and/or 1/4-scale specimens were made and tested under reversed cyclical lateral loading, with the size, the thickness and the type of steel plates, the thickness of PP plates, and the loading program as main experimental variables.</p><p> Test results have indicated that when confined by PP plates thick enough to prevent the panel from out-of-plane buckling, the steel panels exhibited high lateral resistance and sound energy absorption performance until the drift angle of 0.07 rad without resistance degradation. For the bare steel panels and those confined by thin PP plates, out-of-plane buckling occurred before the drift level of 0.05 rad, but the deformation capacity increased along with the thicknesses of steel plates and PP plates. The specimen having sufficient confinement cracked at the corners of the steel panel at large drift beyond 0.07 rad, and the deformation capacity was independent of the thickness of PP plates. Test results also shown that the loading history might affect the cumulative plastic drift angle at the ultimate state.</p><p> The full plastic moment of the plate section can predict ultimate strength of the steel panels confined by PP plates with sufficient thickness on the safe side, and increasing the yield strength of steels by 10 percent to take into account the effect of strain hardening can enhance accuracy of the theoretical ultimate strength. An equation based on the elastic lateral buckling strength of the steel-PP composite plate was proposed to predict the lateral buckling load of the confined panel without sufficient confinement by PP plates, and gave very good prediction of the measured buckling loads. It is noteworthy that one can determine the minimum thickness of PP plates to prevent the panel from the premature out-of-plane buckling just by letting the lateral resistance (_calQ_bu2), defined by Eq. (3), corresponding to the 10% enhanced full plastic moment, be smaller than the calculated buckling load (_calQ_cr2), defined by Eq. (10).</p><p> Furthermore, the equivalently converted width-thickness ratio ((b/t)_BE, see Eq. (14)) and the balanced (b/t)_BE (=_eq(b/t)_BE, see Eq. (16)) were introduced to evaluate the ultimate accumulative plastic drift angles (γ_u) and the equivalent shear buckling deformation angle (γ_B) of the confined steel panels. Very strong correlations existed between the measured drift angles at ultimate states and the theoretical ones calculated by Eq. (15) and Eq. (20), respectively. The cumulative plastic drift angles at ultimate states of the specimens failing in out-of-plane buckling increased with the decrease of the (d/t)_BE, while those of the specimens failing with crack at the corners of steel plates were almost constant. These observations imply the rationality of the introduced two terms ((b/t)_BE and _eq(b/t)_BE) and the accuracies of the empirical formulae (Eq. (15) and Eq. (20)).</p>