• Smart Structures and Systems
• /
• v.4 no.5
• /
• pp.605-628
• /
• 2008

In bridge structures, damage may induce an additional deflection which may naturally contain essential information about the damage. However, inverse mapping from the damage-induced deflection to the actual damage location and severity is generally complex, particularly for statically indeterminate systems. In this paper, a new load concept, called the positive-bending-inspection-load (PBIL) is proposed to construct a simple inverse mapping from the damage-induced deflection to the actual damage location. A PBIL for an inspection region is defined as a load or a system of loads which guarantees the bending moment to be positive in the inspection region. From the theoretical investigations, it was proven that the damage-induced chord-wise deflection (DI-CD) has the maximum value with the abrupt change in its slope at the damage location under a PBIL. Hence, a novel damage localization method is proposed based on the DI-CD under a PBIL. The procedure may be summarized as: (1) identification of the modal flexibility matrices from acceleration measurements, (2) design for a PBIL for an inspection region of interest in a structure, (3) calculation of the chord-wise deflections for the PBIL using the modal flexibility matrices, and (4) damage localization by finding the location with the maximum DI-CD with the abrupt change in its slope within the inspection region. Procedures from (2)-(4) can be repeated for several inspection regions to cover the whole structure complementarily. Numerical verification studies were carried out on a simply supported beam and a three-span continuous beam model. Experimental verification study was also carried out on a two-span continuous beam structure with a steel box-girder. It was found that the proposed method can identify the damage existence and damage location for small damage cases with narrow cuts at the bottom flange.

• Structural Engineering and Mechanics
• /
• v.27 no.5
• /
• pp.625-638
• /
• 2007

The damage detection process may appear difficult to be implemented for truss structures because not all degrees of freedom in the numerical model can be experimentally measured. In this context, the damage locating vector (DLV) method, introduced by Bernal (2002), is a useful approach because it is effective when operating with an arbitrary number of sensors, a truncated modal basis and multiple damage scenarios, while keeping the calculation in a low level. In addition, the present paper also evaluates the noise influence on the accuracy of the DLV method. In order to verify the DLV behavior under different damages intensities and, mainly, in presence of measurement noise, a parametric study had been carried out. Different excitations as well as damage scenarios are numerically tested in a continuous Warren truss structure subjected to five noise levels with a set of limited measurement sensors. Besides this, it is proposed another way to determine the damage locating vectors in the DLV procedure. The idea is to contribute with an alternative option to solve the problem with a more widespread algebraic method. The original formulation via singular value decomposition (SVD) is replaced by a common solution of an eigenvector-eigenvalue problem. The final results show that the DLV method, enhanced with the alternative solution proposed in this paper, was able to correctly locate the damaged bars, using an output-only system identification procedure, even considering small intensities of damage and moderate noise levels.

• Structural Engineering and Mechanics
• /
• v.62 no.6
• /
• pp.709-717
• /
• 2017

This paper develops a two-stage method for structural damage identification by using modal data. First, the Residual Force Vector (RFV) is introduced to detect any potentially damaged elements of structures. Second, data of the frequency domain are used to build up the objective function, and then the Imperialist Competitive Algorithm (ICA) is utilized to estimate damaged extents. ICA is a heuristic algorithm with simple structure, which is easy to be implemented and it is effective to deal with high-dimension nonlinear optimization problem. The advantages of this present method are: (1) Calculation complexity can be decreased greatly after eliminating many intact elements in the first step. (2) Robustness, ICA ensures the robustness of the proposed method. Various damaged cases and different structures are investigated in numerical simulations. From these results, anyone can point out that the present algorithm is effective and robust for structural damage identification and is also better than many other heuristic algorithms.

• Journal of the Korean Geosynthetics Society
• /
• v.6 no.4
• /
• pp.29-37
• /
• 2007

Reduction Factor for Installation Damage required for calculation of design strength of geogrid used in MSEW(mechanically stabilized earth wall) design is usually obtained in the field test simulating real construction condition. However, damages occurred in geogrid during backfill work are influenced by many factors such as polymer types, unit weight per area, backfill construction method and gradation of backfill material and field test considering these factors demands lots of time and costs. In this study, factors affecting installation damage are analyzed and empirical method for evaluating reduction factor for installation damage using maximum particle size in backfill material is suggested.

• Korean Journal of Construction Engineering and Management
• /
• v.8 no.1 s.35
• /
• pp.150-158
• /
• 2007

The delay of construction is one of the most frequent and complicated elements of the claim. And the liquidated damages cause many disputes during the judgement. The liquidated damages should be a compensation for owner's substantial loss, but actually be applied as a damage for breach of contract. These damages are different from owner's loss and give constructors a excessive burden. So we need a more reasonable system than a lump application system. In this study, we make a Improvement System, that based on owner's substantial loss, and suggest the new liquidated damages calculation method.

• Wind and Structures
• /
• v.38 no.6
• /
• pp.445-459
• /
• 2024

To model the aeroelasticity in vortex-induced vibrations (VIV) of slender tubular towers, this paper presents an approach where the aerodynamic damping distribution along the height of the structure is calculated not only as a function of the normalized lateral oscillation but also considering the local incoming wind velocity ratio to the critical velocity (velocity ratio). The three-dimensionality of aerodynamic damping depending on the tower's displacement and the velocity ratio has been observed in recent studies. A contour map model of aerodynamic damping is generated based on the forced vibration tests. A sectional calculation procedure based on the spectral method is developed by defining the aerodynamic damping locally at each increment of height. The proposed contour map model of aerodynamic damping and the sectional calculation procedure are validated with full-scale measurement data sets of a rotorless wind turbine tower, where good agreement between the prediction and measured values is obtained. The prediction of cross-wind response of the wind turbine tower is performed over a range of wind speeds which allows the estimation of resulting fatigue damage. The proposed model gives more realistic prediction in comparison to the approach included in current standards.

• Journal of the Society of Naval Architects of Korea
• /
• v.55 no.3
• /
• pp.274-280
• /
• 2018

This paper deals with the calculation of vulnerable areas of critical components required for the assessment of naval ship's vulnerability. Taking into account the effectiveness of threatening weapons, the probability density function of damage was used to assess vulnerable areas or vulnerabilities of critical components. It is shown that the vulnerable area of critical component can be simply computed from the damage function. Considering the weapon effectiveness of fragmentation and explosion on the target, both Carleton Damage Function and Rectangular Cookie Cutter Function representing the probability of damage are applied to the vulnerable area assessment. Carleton damage function is utilized to describe the weapon-target interaction in the vulnerability analyses. A problem of blast effect against an assumed naval ship is chosen as a case study. Vulnerability is evaluated by applying the suggested method to the equipments arranged in the engine room of the virtual ship.

• Journal of the Korean Society of Safety
• /
• v.35 no.1
• /
• pp.97-106
• /
• 2020

The objective of this paper is to suggest a new quantification method for multi-unit probabilistic safety assessment (PSA) that removes the overestimation error caused by the existing delete-term approximation (DTA) based quantification method. So far, for the actual plant PSA model quantification, a fault tree with negates have been solved by the DTA method. It is well known that the DTA method induces overestimated core damage frequency (CDF) of nuclear power plant (NPP). If a PSA fault tree has negates and non-rare events, the overestimation in CDF drastically increases. Since multi-unit seismic PSA model has plant level negates and many non-rare events in the fault tree, it should be very carefully quantified in order to avoid CDF overestimation. Multi-unit PSA fault tree has normal gates and negates that represent each NPP status. The NPP status means core damage or non-core damage state of individual NPPs. The non-core damage state of a NPP is modeled in the fault tree by using a negate (a NOT gate). Authors reviewed and compared (1) quantification methods that generate exact or approximate Boolean solutions from a fault tree, (2) DTA method generating approximate Boolean solution by solving negates in a fault tree, and (3) probability calculation methods from the Boolean solutions generated by exact quantification methods or DTA method. Based on the review and comparison, a new intersection removal by probability (IRBP) method is suggested in this study for the multi-unit PSA. If the IRBP method is adopted, multi-unit PSA fault tree can be quantified without the overestimation error that is caused by the direct application of DTA method. That is, the extremely overestimated CDF can be avoided and accurate CDF can be calculated by using the IRBP method. The accuracy of the IRBP method was validated by simple multi-unit PSA models. The necessity of the IRBP method was demonstrated by the actual plant multi-unit seismic PSA models.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.15 no.1
• /
• pp.21-32
• /
• 2003

In this study, the reliability design method developed by Hanzawa et al. in 1996 for calculation of the expected damage to armor blocks of a horizontally composite breakwater is extended to take into account the variability in wave direction such as directional spreading of waves, obliquity of the design principal wave direction from the shore-normal direction, and its variation about the design value. To calculate the transformation of random directional waves. the model developed by Kweon et al. in 1997 is used instead of Goda's model, which was developed in 1975 for unidirectional random waves normally incident to a straight coast with parallel depth contours and has been used by Hanzawa et al. It was found that the variability in wave direction had great influence on the computed expected damage to armor blocks. The previous design, which disregarded wave directionality, could either overestimate or underestimate the expected damage by a factor of two depending on water depth and seabed slope, if the assumption of the present study that the stability formula for breakwater armor blocks proposed for normal incidence can be used for obliquely incident waves is valid.

• Journal of Advanced Marine Engineering and Technology
• /
• v.29 no.7
• /
• pp.785-794
• /
• 2005

Modern ship hulls of large oil carriers and container carrers have become more flexible with scantling optimization and increase in ship length. On the other hand. as the demand for power has increased with the ship size. shaft diameters have become larger and stiffer. Consequently. the alignment of the propulsion system has become more sensitive to hull girder deflections. resulting in difficulties in analyzing the alignment and conducting the alignment procedure. Accordingly. the frequency of shaft alignment related bearing damages has increased significantly in recent years. The alignment related damages are mostly attributed to inadequate analyses. changes in the design of the vessel. shipyards' practices in conducting the alignment. and a lack of well defined analytical criteria. The hull deflections should be considered at the design stage to minimize the bearing damage caused by hull deflection. Hull deflections can be estimated by analytical approach and reverse calculation using the measured data. The hull girder deflection analysis using the reverse calculation will be introduced in this paper.