• Structural Engineering and Mechanics
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• v.51 no.2
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• pp.267-276
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• 2014

Wharfs are essential to shipping and support very large gravity loads on both a short-term and long-term basis which cause quite large seismic internal forces. Therefore, these structures are vulnerable to seismic activities. As they are supported on vertical and/or batter piles, soil-pile interaction effects under earthquake events have a great importance in seismic resistance which is not yet fully understood. Seismic design codes have become more stringent and suggest the use of new design methods, such as Performance Based Design principles. According to Turkish Code for Coastal and Port Structures (TCCS 2008), the interaction between soil and pile should somehow be considered in the nonlinear analysis in an accurate manner. This study aims to explore the lateral load carrying capacity of recently designed wharf structures considering soil-pile interaction effects for different soil conditions. For this purpose, nonlinear structure analysis according to TCCS (2008) has been performed comparing simplified and detailed modeling results.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2001.09a
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• pp.235-242
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• 2001

Inelastic seismic response of steel moment frame structures, which are usually quite gravity load and subject to large displacement under severe earthquake, may be severly influenced by the structure P-Δ effects. The P-Δ effect may have an important impact on the dynamic behavior of the structure in the nonlinear seismic analysis. In multi degree of freedom systems P-Δ effects may significantly affect only a subset of stories or a single story alone. Therefore, a story drift amplification of structure is happened by P-Δeffects and such nonlinear dynamic behaviors are very difficult to evaluate in the structures. In this study, two systems having different design methods of steel moment frame structures are investigated to evaluate the P-Δ effects due to gravity load. The plastic hinge formations, maximum rotational ductility demands, and energy distribution will be compared and evaluated following whether the P-Δ effects are considered or not. And design methods are proposed for the prevention of the instability of structures which due to the P-Δ effects.

• Structural Engineering and Mechanics
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• v.22 no.5
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• pp.575-597
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• 2006

Enhanced three-dimensional finite elements for geometrically nonlinear analysis of cable-supported structures are presented. The cable element, derived by using the concept of an equivalent modulus of elasticity and assuming the deflection curve of a cable as catenary function, is proposed to model the cables. The stability functions for a frame member are modified to obtain a numerically stable solution. Various numerical examples are solved to illustrate the versatility and efficiency of the proposed finite element model. It is shown that the finite elements proposed in this study can be very useful for geometrically nonlinear analysis as well as free vibration analysis of three-dimensional cable-supported structures.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1990.04a
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• pp.59-64
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• 1990

The cable structures undergo large deformation because of its highly flexibility. Therefore, we must take account of its geometric nonlinearity before analysis and find the equiribrated shape of cable structures. To solve these problems, a numerical procedures included nonlinear near theory which is applicable to general cable net, flexible transmission lines and suspended cable roofs, are presented in this paper. Now, this procedures are devided two parts : the one is to obtain the equibrated shape and stress of the cable structures applied uniform load by flexibility iteration method, the other is to analysis the equibrated structures subjected to nodal external forces by nonlinear finite element mothed. Its accuracy and efficiency are found to be comparable to some of other method and, in some aspect, it is mere applicable to cable structures.

• Journal of Korean Association for Spatial Structures
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• v.3 no.1 s.7
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• pp.87-97
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• 2003

The structural system that discreterized from continuous shells is frequently used to make a large space structures. As well these structures show the unstable phenomena when a load level over the limit load, and snap-through and bifurcation are most well known of it. For the collapse mechanism, rise-span ratio, element stiffness and load mode are main factor, which it give an effect to unstable behavior. In our real situation, most structures have semi-rigid joint that has middle characteristic between pin and rigid joint. So the knowledge of semi-rigid joint is very important problem of stable large space structure. And the instability phenemena of framed space structures show a strong non-linearity and very sensitive behavior according to the joint rigidity For this reason In this study, we are investigating to unstable problem of framed structure with semi-rigidity and to grasp the nonlinear instability behavior that make the fundamental collapse mechanism of the large space frame structures with semi-rigid joint, by proposed the numerical analysis method. Using the incremental stiffness matrix in chapter 2, we study instability of space structures.

• Computers and Concrete
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• v.19 no.6
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• pp.689-699
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• 2017

An energy-based approach for determining earthquake safety of reinforced concrete frame structures is presented. The developed approach is based on comparison of plastic energy capacities of the structures with plastic energy demands obtained for selected earthquake records. Plastic energy capacities of the selected reinforced concrete frames are determined graphically by analyzing plastic hinge regions with the developed equations. Seven earthquake records are chosen to perform the nonlinear time history analyses. Earthquake plastic energy demands are determined from nonlinear time history analyses and hysteretic behavior of earthquakes is converted to monotonic behavior by using nonlinear moment-rotation relations of plastic hinges and plastic axial deformations in columns. Earthquake safety of selected reinforced concrete frames is assessed by using plastic energy capacity graphs and earthquake plastic energy demands. The plastic energy dissipation capacities of the frame structures are examined whether these capacities can withstand the plastic energy demands for selected earthquakes or not. The displacements correspond to the mean plastic energy demands are obtained quite close to the displacements determined by using the procedures given in different seismic design codes.

• Journal of Korean Association for Spatial Structures
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• v.17 no.1
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• pp.31-40
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• 2017

The objective of this study is to analysis the mechanical characteristics and nonlinear behaviors on the geometric nonlinear behavior of a cable spoke wheel roof system for long span lightweight roof structures. The weight of a cable spoke wheel roof dramatically can reduce and the cable roof system can easily make the required rigidity and shape by the sag ratio and pretension forces. Determining the pretension and initial sag of cable roof system is essential in a design process and the shape of roof is changed by pretension. The nonlinear behavior of flexible cable system has greatly an affect on the sag and pretension. This paper will be carried out analyzing and comparing the tensile forces and deflection of a cable spoke wheel system for the large span retractable roof, and analyzed to deflections and tensile forces by the post height of center hub. The double arrangement of a spoke wheel system with reverse curvature works more effectively as a load bearing system, the pretension can easily increase the structural stiffness. The cable truss system can carry vertical load in up and downward direction, and act effectively as load bearing elements.

• Smart Structures and Systems
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• v.24 no.2
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• pp.209-221
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• 2019

The classical Kalman filter (KF) provides a practical and efficient way for state estimation. It is, however, not applicable when the external excitations applied to the structures are unknown. Moreover, it is known the classical KF is only suitable for linear systems and can't handle the nonlinear cases. The aim of this paper is to extend the classical KF approach to circumvent the aforementioned limitations for the joint estimation of structural states and the unknown inputs. On the basis of the scheme of the classical KF, analytical recursive solution of an improved KF approach is derived and presented. A revised form of observation equation is obtained basing on a projection matrix. The structural states and the unknown inputs are then simultaneously estimated with limited measurements in linear or nonlinear systems. The efficiency and accuracy of the proposed approach is verified via a five-story shear building, a simply supported beam, and three sorts of nonlinear hysteretic structures. The shaking table tests of a five-story building structure are also employed for the validation of the robustness of the proposed approach. Numerical and experimental results show that the proposed approach can not only satisfactorily estimate structural states, but also identify unknown loadings with acceptable accuracy for both linear and nonlinear systems.

• Journal of Korean Association for Spatial Structures
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• v.21 no.4
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• pp.49-56
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• 2021

This study aims to develop a form-finding algorithm for a single-layered pneumatic membrane. The initial shape of this pneumatic membrane, which is an air-supported type pneumatic membrane, is to find a state in which a given initial tension and internal pneumatic pressure are in equilibrium. The algorithm developed to satisfy these conditions is that a nonlinear optimization problem based on the force method considering the deformed shape is formulated, and, it's able to find the shape by iteratively repeating the process of obtaining a solution of the governing equations. An computational technique based on the Gauss-Newton method was used as a method for obtaining solutions of nonlinear equations. In order to verify the validity of the proposed form-finding algorithm, a single-curvature pneumatic membrane example and a double-curvature air pneumatic membrane example were adopted, respectively. In the results of these examples, it was possible to well observe the step-by-step convergence process of the shape of the pneumatic membrane, and it was also possible to confirm the change in shape according to the air pressure. In addition, the calculation results of the shape and internal force after deformation due to initial tension, air pressure, and self-weight were obtained.

• Earthquakes and Structures
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• v.12 no.1
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• pp.135-144
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• 2017

Near-fault ground motions are characterized by high values of the ratio between the peak of vertical and horizontal ground accelerations, which can significantly affect the nonlinear response of a base-isolated structure. To check the effectiveness of different base-isolation systems for retrofitting a r.c. framed structure located in a near-fault area, a numerical investigation is carried out analyzing the nonlinear dynamic response of the fixed-base and isolated structures. For this purpose, a six-storey r.c. framed building is supposed to be retrofitted by insertion of an isolation system at the base for attaining performance levels imposed by current Italian code in a high-risk seismic zone. In particular, elastomeric (e.g., high-damping-laminated-rubber bearings, HDLRBs) and friction (e.g., steel-PTFE sliding bearings, SBs, or friction pendulum bearings, FPBs) isolators are considered, with reference to three cases of base isolation: HDLRBs acting alone (i.e., EBI structures); in-parallel combination of HDLRBs and SBs (i.e., EFBI structures); FPBs acting alone (i.e., FPBI structures). Different values of the stiffness ratio, defined as the ratio between the vertical and horizontal stiffnesses of the HDLRBs, sliding ratio, defined as the global sliding force divided by the maximum sliding force of the SBs, and in-plan distribution of friction coefficient for the FPs are investigated. The EBI, EFBI and FPBI base-isolation systems are designed assuming the same values of the fundamental vibration period and equivalent viscous damping ratio. The nonlinear dynamic analysis is carried out with reference to near-fault earthquakes, selected and scaled on the design hypotheses adopted for the test structures.