• Journal of the Korea Concrete Institute
• /
• v.28 no.1
• /
• pp.13-21
• /
• 2016

A hybrid precast concrete beam system with a simple rigid connection was proposed to compensate the limitations and shortcomings of the conventional bolt connection associated with the H-beams embedded into concrete beams. Three beam specimens with fixed both ends were tested under one-point top cyclic loading to explore the effectiveness of the developed hybrid beam system in transferring externally applied flexure to a column. The main parameter considered was the length ($L_s$) of H-beam, which was selected to be $0.25L_I$, $0.5L_I$, and $1.0L_I$, where $L_I$ is the distance from the support to the point of inflection. All beam specimens showed a better displacement ductility ratio than the reinforced concrete beams with the same longitudinal reinforcement index, indicating that the cyclic load-deflection curve and ductility were insignificantly affected by $L_s$. The continuous strain distribution along the beam length and the prediction of the ultimate load based on the collapse mechanism ascertained the structural adequacy of the developed rigid connection.

• Journal of The Korean Astronomical Society
• /
• v.27 no.1
• /
• pp.13-29
• /
• 1994

We have constructed a 3-dim hydrodynamics code called BTSPH. The fluid dynamics part of the code is based on the smoothed particle hydrodynamics (SPH), and for its Poisson solver the binary tree (BT) scheme is employed. We let the smoothing length in the SPH algorithm vary with space and time, so that resolution of the calculation is considerably enhanced over the version of SPH with fixed smoothing length. The binary tree scheme calculates the gravitational force at a point by collecting the monopole forces from neighboring particles and the multipole forces from aggregates of distant particles. The BTSPH is free from geometric constraints, does not rely on grids, and needs arrays of moderate size. With the code we have run the following set of test calculations: one-dim shock tube, adiabatic collapse of an isothermal cloud, small oscillation of an equilibrium polytrope of index 3/2, and tidal encounter of the polytrope and a point mass perturber. Results of the tests confirmed the code performance.

• Journal of the Korea Safety Management & Science
• /
• v.9 no.1
• /
• pp.51-63
• /
• 2007

It is noted that the disaster such as fire, explosion, collapse has been rapidly increased caused by strength deterioration of steel structures at petrochemical plant during fire. In this regard, it is stressed out that the legal requirement for fire proofing for steel structures at petrochemical plant should be carefully reviewed since the current legal requirement such as Industrial Safety & Health Law, Architectural Law has a conflict and different way of approach. In addition, it is our point of view that the present law should be revised to consolidate into single law including engineering design criteria to reflect unreasonable legal requirement. It is further our point of view that the performance certificate for fire proofing like UL-1709, basis of maintenance should be appropriately and reasonably provided in line with global practice.

• Structural Engineering and Mechanics
• /
• v.36 no.5
• /
• pp.529-544
• /
• 2010

Nonlinear equations of structures are generally solved numerically by the iterative solution of linear equations. However, this iterative procedure diverges when the tangent stiffness is ill-conditioned which occurs near limit points. In other words, a major challenge with simple iterative methods is failure caused by a singular or near singular Jacobian matrix. In this paper, using the Newton-Raphson algorithm based on Davidenko's equations, the iterations can traverse the limit point without difficulty. It is argued that the propose algorithm may be both more computationally efficient and more robust compared to the other algorithm when tracing path through severe nonlinearities such as those associated with structural collapse. Two frames are analyzed using the proposed algorithm and the results are compared with the previous methods. The ability of the proposed method, particularly for tracing the limit points, is demonstrated by those numerical examples.

• The Transactions of the Korean Institute of Electrical Engineers
• /
• v.45 no.4
• /
• pp.457-466
• /
• 1996

The Voltage stability problem has recently been dealt with in the literature from various points of view. The diverse theories have been established in voltage stability analysis because of the complicates of power systems and diverse phenomena of voltage collapse. Through rigorous mathematical operations, this paper shows that all the major methods used in static voltage stability, i.e - Jacobian method, voltage sensitivity method, real and reactive power loss sensitivity method and energy function method - have an identical background in theory. The results from the test in sample systems have shown the validity of this verification. (author). refs., figs., tabs.

• The Transactions of the Korean Institute of Electrical Engineers A
• /
• v.48 no.8
• /
• pp.958-964
• /
• 1999

The distance in load parameter space to the closest saddle node bifurcation (CSNB) point provides the worst case power margin to voltage instability and the left eigenvector at CSNB identifies the most effective direction to steer the system to maximize voltage stability under contingency. This paper presents an improved direct method for computing CSNB: the order of nonlinear systems equations is reduced to about twice of the size of load flow equations in contrast to about three-times in Dobson's direct method; the initial guess for the direct method is computed efficiently and robustly by combined use of continuation power flow, a pair of multiple load flow solution with Lagrange interpolation. It is also shown that voltage stability may be enhanced significantly with shift of generations in the direction of the left eigenvector at CSNB.

• Proceedings of the KIEE Conference
• /
• 2003.11a
• /
• pp.255-258
• /
• 2003

In this paper there are different methods used to study the voltage stability, such as the P-V curve method. Jacobian method and the voltage collapse proximity indicator(L-index) method. The P-V curve method is to check operating margin from the maximum operating point. The Jacobian method is to check the eigenvalue or the minimum singular value of the load flow Jacobian matrix. If the power system is unstable, one of the eigenvalues, at least, has crossed the imaginary axis. The L-index method is to quantify how to close a particular operating point. This paper describes these methods to select the best location of FACTS and demonstrate the effectiveness of STATCOM of voltage stability on the IEEE 9-bus system.

• Proceedings of the KIEE Conference
• /
• 1996.11a
• /
• pp.80-83
• /
• 1996

This paper develops a method for reliably estimating an UEP(Unstable Equilibrium Point) which is located in the direction of SEP(Stable Equilibrium Point)'s moving as system load is getting heavy. As power systems are getting loaded heavily, the SEP which is an operable solution, and the UEP which is occurring voltage collapse, are moving toward each other linearly. The estimated UEP is used as a good initial guess for the real UEP. The proposed method is tested by 3 bus system and Stagg 5 bus system. It is demonstrated that the proposed method is very useful for assessing system voltage stability in the case of heavy loaded power system. The result solutions are often used in conjunction with energy methods and the stability margin.

• Steel and Composite Structures
• /
• v.25 no.2
• /
• pp.217-229
• /
• 2017

The effect of column loss location on the structural response of steel moment resisting frames (MRF) is investigated in this study. A series of nonlinear static and dynamic analyses were performed to determine the resistance of a generic frame to an arbitrary column loss and detect the structural members that are susceptible to failure progression beyond that point. Both force-controlled and deformation-controlled actions based on UFC 4-023-03 and ASCE/SEI 41-06 were implemented to define the acceptance criteria for nine APM cases defined in this study. Results revealed that the structural resistance against an arbitrary column loss in the top story is at least 80% smaller than that of the bottom story. In addition, it was found that the dynamic increase factor (DIF) at the failure point is at most 1.13.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.30 no.6 s.249
• /
• pp.653-661
• /
• 2006

Metallic sandwich plates with various inner cores have important new features with not only ultra-light material characteristics and load bearing function but also multifunctional characteristics. Because of production possibility on the large scale and a good geometric precision, sandwich plates with inner dimpled shell structure from a single material have advantages as compared with other solid sandwich plates. Inner dimpled shell structures can be fabricated with press or roll forming process, and then bonded with two face sheets by multi-point resistance welding or adhesive bonding. Elasto-plastic bending behavior of sandwich plates have been predicted analytically and measured. The measurements have shown that elastic perfectly plastic approximation can be conveniently employed with less than 10% error in elastic stiffness, collapse load, and energy absorption. The dominant collapse modes are face buckling and bonding failure after yielding. Sandwich plates with inner dimpled shell structure can absorb more energy than other types of sandwich plates during the bending behavior.