Do Hyung Lee

A probabilistic capacity spectrum strategy for the reliability analysis of bridge pile shafts considering soil structure interaction

This paper presents a probabilistic capacity spectrum strategy for the reliability analysis of a bridge pile shaft, accounting for uncertainties in design factors in the analysis and the soil-structure interaction (SSI). Monte Carlo simulation method (MCS) is adopted to determine the probabilities of failure by comparing the responses with defined limit states. The analysis considers the soil structure interaction together with the probabilistic application of the capacity spectrum method for different types of limit states. A cast-in-drilledhole (CIDH) extended reinforced concrete pile shaft of a bridge is analysed using the proposed strategy. The results of the analysis show that the SSI can lead to increase or decrease of the structures probability of failure depending on the definition of the limit states.

Estimation of tension force in double hangers by a system identification approach

This article suggests a new technique for the estimation of tension of a double hanger cable system that is often used in a suspension bridge. The considered hanger system consists of the two independent parallel hanger cables tied by a lateral clamp. Measuring natural frequencies of the system, the hanger tension is determined by a frequency-based system identification technique with the aid of a finite element analysis. The proposed technique is able to simultaneously identify the tension, flexural rigidity and axial rigidity of the target hanger cable system. Laboratory experiments show that estimation errors of the proposed approach are less than 3%. For a relatively long hanger system in the field, the estimated results are similar to those evaluated by the existing methods. However, a significant difference is observed in a short hanger cable system.

Extracting Modal Parameters of a Layered Stone Pagoda Using TDD Technique

This work introduces a modal testing and analysis results of the mock-up for a layered stone pagoda. The pagoda has been horizontally excited by an impact hammer. As to the measured acceleration time responses, the first five lower mode shapes and natural frequency are extracted by the TDD technique. It is observed that the time delay of a shear wave occurs through friction surfaces. Such phenomena cannot be described by using the traditional analytical models such as a continuum cantilever beam model or a discrete shear building model. However, the time delay typically affects only the phases of the pagoda system. The frequencies of the pagoda system are not affected by such time delay. It is found in the first time that the layered stone pagoda system has a set of closely placed modes in near of natural frequency. It is believed that such modes are due to the friction characteristics in friction surfaces. Based on the stick-slip friction model, it seems that the one of the closely placed mode can be a self-excited one.

Estimating Longitudinal Elastic Wave Velocity of Bonded PSC Tendon

This study proposes a most effective way to estimate longitudinal elastic wave velocity of bonded PSC tendon. Various longitudinal vibration tests are conducted for bonded prestressed concrete beams with different applied prestress levels. To estimate elastic wave velocity from measured structural responses, the various estimation techniques are examined such as utilization of acceleration time history, velocity time history, reflected acceleration time history, measured frequency, etc. The comparison results show that the utilization of filtered acceleration is most effective way in practice to estimate elastic wave velocity in an impact-echo test.

Seismic Behavior of Concrete Cylinders Reinforced by Outside Lateral Hoops

/ A B S T R A C T /This paper investigates experimentally the confinement effect on concrete. For this purpose, outside lateral reinforcement memb ers made of stainless steel and GFRP were employed. Then, uniaxial compressive tests on concrete cylinders incorporating the members were conducted. A total of 30 cylinder specimens, specifically, 6 unconfined specimens, 12 specimens confined by stainless steel and 12 specimens confined by GFRP, were fabricated. The failure patterns of both unconfined and confined specimens were assessed and discussed based on experimental results. The results proved that the maximum stress and corresponding strains of the cylinders confined using the proposed hoops are increased in comparison with those of the unconfined. This supports that the current work can be u sed for retrofitting concrete members and structures and thus may lead to increased stability of such structures.

A Feasibility Study for Estimating Prestressed Stress on a Steel Wire Using Permeability of Magnetic Flux

This work examines the feasibility for estimating existing tensile stress on a stressed wire using the permeability of magnetic flux. A closed magnetic circuit has been constructed to induce magnetic flux inside a steel wire. With different tension stress levels on a wire, the permeability of magnetic flux on the wire has been measured. Two different experimental case studies have been conducted for the examination of sensitivity of permeability of magnetic flux on the stressed wire. One is a varying-length stress test, and the other is a fixed-length stress test. The results show that the permeability of magnetic flux in the varying-length stress test is inversely proportional to the applied stress, while the permeability in the fixed-length stress test is linearly proportional to the applied stress on the stressed wire. It is thus expected that the permeability of magnetic flux on a wire can be a promising indicator for the inspection of its tensile stress.

Effect of Applied Stress of Unbonded PSC Tendon on Stress Wave Velocity

This study experimentally investigates the effects of applied stress level on the stress wave velocity of unbonded PSC tendon. A set of longitudinal impact-echo tests with respect to several applied prestress levels are conducted for both unbonded prestressed strand and steel wire. The comparison results show that the longitudinal stress wave velocity is linearly proportional to the applied stress level in the case both strand and steel wire. However, the sensitivity of the longitudinal stress wave velocity to the applied stress level is very low. Based on the result of nondimensional analysis, it is postulated that the stress wave velocity is also affected by the tensile strength level.

Estimating Tension Force of Elevator Wire Rope Using Frequency

This study introduces the estimation technique of tension force on elevator wire rope using measured frequencies. The proposed approach estimates tension force of elevator wire rope by appling the measured frequencies into the taut string theory or linear regression technique. Such frequencies are measured by accelerometers attached on elevator wire rope. To validate the proposed approach, the various experimental cases for real elevator wire ropes are conducted. The results reveal that both the taut string theory and the linear regression technique show an error bound of . Thus, in practice, the proposed approach could be used for the estimation of tension force on elevator wire rope.