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가설 설정
- ∙ The cross sectional area of HSS shall be at least 1 percent of the total composite cross section.
- ∙ The maximum diameter-thickness ratio for a circular HSS filled with concrete shall be equal to 0.15E/Fy .
제안 방법
- The purpose of this research is two-fold. First, it examines the monotonic and cyclic behavior of CFT beam-columns subjected to combined axial and moment loading in an attempt to estimate both the maximum strength and ductility for doubly-symmetric and axisymmetric composite cross sections. From these studies it can be shown that ultimate capacities for rectangular/circular CFT beam-columns can be estimated with reasonable accuracy using the simplified axial and moment (P-M) interaction formulas provided by 2005 AISC Specification for composite systems.
- In so far as the frame designs are concerned, those are governed by the Seismic Provisions (Seismic Provisions, 2005) Four potential classes of Composite Moment Frame (C-MF) are identified in the Part II of the Seismic Provisions (Seismic Provisions, 2005) as shown in Table 3. For this study, composite special moment frames (C-SMF), the most ductile system, were selected for the design of several trial low-rise moment frames. Five-story buildings with long bays (36ft.
- From these studies it can be shown that ultimate capacities for rectangular/circular CFT beam-columns can be estimated with reasonable accuracy using the simplified axial and moment (P-M) interaction formulas provided by 2005 AISC Specification for composite systems. Second, based on the analytical study of CFT crosssectional strength and ductility, advanced computational simulations are carried out on a series of five story composite moment resisting frames. The primary aim of this portion of the study is to develop preliminary damage assessment metrics for low-rise, composite frames designed to the 2005 Seismic Provisions when subjected to large seismic loads.
- The 2005 AISC Specification endorses the use of the full plastic stress distribution to calculate cross-sectional strength. The calculations are based on the assumption of linear strain across the section height and perfectly elasto-plastic behavior. The nominal strength is estimated by assuming that the steel has reached its yield stress under either tension or compression and that the concrete has reached its crushing strength under only compression as shown in Fig.
- The case studies in this paper comprise both element (composite CFT cross section) analyses and frame analyses. The numerical experiments are performed using a nonlinear structural analysis program, OPENSEES v.
- The cross-sectional analyses include both circular and rectangular concrete-filled steel tubes (CCFT or RCFT). The cross-sectional specimens were subjected to simulations that first applied an axial load and then monotonically increased the bending moments while holding the axial load constant. The simulations utilized fiber models consisting of steel and concrete two-dimensional fiber elements available in OPENSEES (Mazzoni et al.
- Two primary indices were used to quantify expected performance. The first, which was used for the static and linear dynamic analysis, will be labeled the elastic strength ratio (ESR) and compares the bending plus axial load ratio generated from the frame analyses to that provided by the section selected in the design process. The second, which will be used for the non-linear dynamic analysis, is the inelastic curvature ductility ratio (ICDR) and compares the required rotational ductility given by the frame analysis with the yield ductility predicted by the cross-section one.
- Design provisions based on the full plastic behavior of composite members and systems are particularly useful in limit state calculations for both non-seismic and seismic resistant design. The new USA code provisions for composite construction-namely, the American Institute of Steel Construction 2005 Specification for Structural Steel Buildings (AISC Specification, 2005) and the Seismic Provisions for Structural Steel Buildings (Seismic Provision, 2005)-present designers with new guidance on the analysis and design of composite columns and frames. The current AISC Specification for composite columns are appropriate for predicting the ultimate capacity of CFT beam-columns corresponding based on a simplified full plastic stress distribution.
- Second, based on the analytical study of CFT crosssectional strength and ductility, advanced computational simulations are carried out on a series of five story composite moment resisting frames. The primary aim of this portion of the study is to develop preliminary damage assessment metrics for low-rise, composite frames designed to the 2005 Seismic Provisions when subjected to large seismic loads.
- 3. The test model was subjected to various levels for the axial force, roughly corresponding to the axial load levels of the five interpolation points given by the code provisions. The axial load as applied first and then the moment was increased.
- The two dimensional composite moment resisting frames designed for this study were first evaluated using an equivalent static lateral load procedure (pushover) and then using both linear and non-linear dynamic analysis for a ground motion taken from the 1994 Northridge earthquake. For the non-linear dynamic analysis, geometric non-linearities were included in the formulation.
- The initial P-M interaction curves were formulated using monotonic fiber analyses. These studies verified that the simplified P-M interaction formulas from 2005 AISC Specification are able to accurately predict the capacity of the CFT beam-columns. In the second part of these analyses, the envelopes of the cyclic moment-curvature responses generated from the fiber models were compared and calibrated with those of monotonic moment-curvature response.
이론/모형
- Fixed joint conditions were assumed at all connections. All analyses utilized the Newton-Raphson iteration algorithm to ensure equilibrium at each time step. Static analyses were conducted using load a control method, while dynamic analysis was performed by implicit integration using the NewmarkBeta constant acceleration method.
- First, it examines the monotonic and cyclic behavior of CFT beam-columns subjected to combined axial and moment loading in an attempt to estimate both the maximum strength and ductility for doubly-symmetric and axisymmetric composite cross sections. From these studies it can be shown that ultimate capacities for rectangular/circular CFT beam-columns can be estimated with reasonable accuracy using the simplified axial and moment (P-M) interaction formulas provided by 2005 AISC Specification for composite systems. Second, based on the analytical study of CFT crosssectional strength and ductility, advanced computational simulations are carried out on a series of five story composite moment resisting frames.
- All analyses utilized the Newton-Raphson iteration algorithm to ensure equilibrium at each time step. Static analyses were conducted using load a control method, while dynamic analysis was performed by implicit integration using the NewmarkBeta constant acceleration method. For the dynamic analysis, the structural damping ratio was assumed to be 0.
- The case studies in this paper comprise both element (composite CFT cross section) analyses and frame analyses. The numerical experiments are performed using a nonlinear structural analysis program, OPENSEES v.1.7.2 (Mazzoni et al., 2005). The cross-sectional analyses include both circular and rectangular concrete-filled steel tubes (CCFT or RCFT).
- The numerical experiments were performed by the OPENSEES program with all members modeled as nonlinear beam-column elements with discrete fiber sections. Fixed joint conditions were assumed at all connections.
- The cross-sectional specimens were subjected to simulations that first applied an axial load and then monotonically increased the bending moments while holding the axial load constant. The simulations utilized fiber models consisting of steel and concrete two-dimensional fiber elements available in OPENSEES (Mazzoni et al., 2005). Simulations included both monotonic and cyclic analyses.
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