鉄筋を複合する木質集成材梁の曲げ耐力に対する荷重継続期間の影響係数

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  • DURATION OF LOAD FACTOR FOR HYBRID TIMBER–STEEL BAR GLULAM BEAM UNDER BENDING LOAD
  • テッキン オ フクゴウ スル モクシツ シュウセイザイリョウ ノ マゲ タイリョク ニ タイスル カジュウ ケイゾク キカン ノ エイキョウ ケイスウ

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 Recently, from view-point of Global Environment, timber, i.e., one of nature-cycle materials, has been tried to be utilized as structural members of large timber buildings in Europe and North America. A representative timber of the members is Cross-laminated timber (CLT), however, CLT structural system very often restricts planning of building because of CLT being plate member. High-stiffness-strength-timber slender beam and column are significantly desired.<br> This study focuses a hybrid glulam timber with steel deformed bar (rebar) and Epoxy resin adhesive. Hybrid timber beams such as this study technique has been researched as we can recognize at several references6)-17). No research, however, on duration of load factor of hybrid timber beam has been conducted.<br> Aim of this study is to reveal duration of load (DOL) factor of the hybrid timber beam under bending load. We conducted short-term loading test and long-term loading test. The short-loading test was conducted to identify maximum loading capacity necessary for stress level in long-term loading test.<br> The result of short-term loading test and its discussion are summarized as follows:<br> (i) The number of specimens of hybrid timber beam and timber beam, which each have same cross-section, was ten. Standard deviation (σhy) of maximum bending capacity of the hybrid timber beams was 41% of that (σw) of the timber beams. Mechanism of the deviation reduction by rebar is worth to be researched furthermore;<br> (ii) Standard deviation of bending moment at rebar yielding of hybrid timber beam is extremely small because same production rebars are used and property of the rebar is stable, whereas that of bending moment capacity of the timber beam is comparatively large because bending strength of timber is more variable;<br> (iii) Bending moment－curvature curve of the hybrid timber beam can be precisely predicted by calculation using Bernoulli-Euler hypothesis and appropriate stress- strain curve of rebar and timber.<br> The result of long-term loading test and its discussion are summarized as follows:<br> (iv) Nearly all of the data of DOL factors of the hybrid timber beams tested were more than value of Madison curve and conventional timber beam, and DOL factor after 50 years of the hybrid timber beam is predicted to exceed DOL factor, i.e. 55%, required by Japan's Building Standards Act;<br> (v) Equation (5) to predict DOL factor curve of the hybrid timber beam has been proposed, which is based on assumption: DOL factor of timber is calculated by Madison curve; all rebars have yielded in fracture of the beam, and; maximum bending moment capacity of the beam is equal to sum of its timber bending moment and its rebar bending moment. The equation predicted approximately experiment data of DOL factor of the hybrid timber beam: the all experiment data ranged within standard deviation (± σhy) of bending moment capacity of the beam in short-term loading to curve by Equation (5) as seen in Fig. 11 (b);<br> (vi) Design methods of check to prevent bond failure around rebar and shear failure of web in the hybrid timber beam are described in order to ensure to fail under bending load. By the method, hybrid timber beam specimen of this experiment has been evaluated not to collapse by the bond failure and the shear failure after 50 years, and DOL factor after 50 years, which is predicted by Equation (5), has been evaluated to demonstrate its ability.

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