冷間プレス成形角形鋼管柱の局部座屈による耐力劣化挙動の解析モデル

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  • NUMERICAL MODEL FOR DETERIORATION BEHAVIOR CAUSED BY LOCAL BUCKLING OF COLD PRESS-FORMED SQUARE HOLLOW SECTION COLUMNS
  • レイカン プレス セイケイ カクガタ コウカン チュウ ノ キョクブザクツ ニ ヨル タイリョク レッカ キョドウ ノ カイセキ モデル

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<p> 1. Introduction</p><p> Under quite strong ground motion, complete collapse of steel moment frames may occur because of strength deterioration by fracture and/or buckling of steel members. To simulate deterioration behavior of square hollow section (SHS) columns, which are most used in Japan, is the most important for revealing complete collapse behavior of steel moment frames. In relevant studies, multi-spring model (MS model) is often adopted for complete collapse analysis because it can achieve high accuracy result at low computational cost. In this paper, procedure to build up MS-model for cold press-formed SHS, which has not been dealt in past researches, is proposed.</p><p> 2. Outline of multi-spring model</p><p> MS model consists of an elastic bar element and multi-spring elements, as shown in Fig. 1. The multi-spring element is a component of some uniaxial springs inserted between two rigid plates. Force-deformation relationship of the uniaxial spring is modeled in consideration of following regulations;</p><p> 1) Some differences of material properties between flat area and corner area of SHS exist.</p><p> 2) On hysteresis curves after local buckling occurring, stiffness during unloading becomes smaller than elastic stiffness and slip behavior occurs.</p><p> 3) Plastic deformation of uniaxial spring is transformed from longitudinal plastic strain in plastic region or local buckling region in consideration of equivalence of plastic dissipation energy.</p><p> 3. Formularization of stress-strain relationships of stub-columns under axial force</p><p> In order to clarify stress-strain relationships after local buckling of stub columns occurring, finite element method (FEM) analysis of stub columns is conducted under only axial force. Analysis parameters are width-to-thickness ratio, length-to-width ratio and cyclic loading protocols. Based on observation regarding stress-strain relationships under monotonic compression axial force and under cyclic axial force, several parameters to define approximated stress-strain relationships, as shown in Fig. 7 and 11, are formulated.</p><p> 4. Transformation for force-deformation relationships of uniaxial springs of MS model</p><p> In order to transform for force-deformation relationships of uniaxial springs from stress-strain relationships as represented in Chapter 3, the following configurations should be considered.</p><p> 1) Longitudinal strength at the end of column is larger than the strength under uniaxial stress because of constraint of circumstance strain of the column due to weld.</p><p> 2) Strength of uniaxial spring of MS model is amplified from the defined stress at local buckling region, based on bending moment distribution.</p><p> 3) Plastic deformation of uniaxial spring of MS model is obtained as to correspond plastic dissipation energy in the entire either plastic region or local buckling region with that of MS model.</p><p> 5. Verification of validity of proposed MS model</p><p> In order to confirm accuracy of the proposed MS model, analysis results by MS model are compared with analysis results by FEM or test results in the past research. Most of results by MS model agree well with FEM results and test results, unless width-to-thickness ratio is small.</p><p> 6. Conclusions</p><p> As a result, it is clarified that the proposed MS-model is valid for simulating deterioration behavior of cold press- formed SHS column due to local buckling. In the further study, MS-model should be modified to adapt for other kind of SHS columns.</p>

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