• Proceedings of the Korean Geotechical Society Conference
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• 1999.10a
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• pp.209-216
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• 1999

In tunneling and road cuts by blasting, it is of the utmost importance that the remaining rock is of high quality in order to avoid rockfall, rockslides and excessive maintenance work. Therefore, numerous blasting techniques which make use of decoupled charge or shock wave superposition effect have been used to control overbrake. In this paper. some approximate method for the determination of blast load according to the charge condition was introduced at first and, instrumented tests were conducted in small scale transparent material to investigate the shape and amplitude of blast load around the bore hole. Compare to the fully coupled charge, low amplitude of blast load around the bore hole was observed in the decoupled charge and explosion gas pressure was important in the shape of blast load. Therefore, quasi-static behaviour of the crack pattern was shown due to low loading rate.

• Journal of the Earthquake Engineering Society of Korea
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• v.16 no.1
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• pp.13-25
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• 2012

The purpose of this study was to investigate the seismic behavior of hollow circular reinforced concrete bridge columns with confinement steel, and to develop improved seismic design criteria. Three hollow circular columns were tested under a constant axial load and a quasi-static, cyclically reversed horizontal load. The accuracy and objectivity of the assessment process can be enhanced by using a sophisticated nonlinear finite element analysis program. The numerical method used gives a realistic prediction of the seismic performance throughout the loading cycles for the several test specimens investigated. Based on the experimental and analytical results, design recommendations are presented to improve current practice in the design and construction of hollow circular reinforced concrete bridge columns.

• Steel and Composite Structures
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• v.22 no.1
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• pp.45-61
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• 2016

The domestic and foreign scholars conducted many studies on mechanical properties of wave web steel beam and high-strength spiral stirrups confined concrete columns. Based on the previous research work, studies were conducted on the anti-seismic property of the end plate bolt connected wave web steel beam and high-strength spiral stirrups confined concrete column nodes applied with pre-tightening force. Four full-size node test models in two groups were designed for low-cycle repeated loading quasi-static test. Through observation of the stress, distortion, failure process and failure mode of node models, analysis was made on its load-carrying capacity, deformation performance and energy dissipation capacity, and the reliability of the new node was verified. The results showed that: under action of the beam-end stiffener, the plastic hinges on the end of wave web steel beam are displaced outward and played its role of energy dissipation capacity. The study results provided reliable theoretical basis for the engineering application of the new types of nodes.

• Journal of the Earthquake Engineering Society of Korea
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• v.20 no.1
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• pp.21-31
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• 2016

This study investigates the seismic performance of new hollow reinforced concrete (RC) bridge piers with triangular reinforcement details. The developed triangular reinforcement details are economically feasible and rational, and facilitate shorter construction periods. We tested a model of new hollow RC bridge piers with triangular reinforcement details under a constant axial load and a quasi-static, cyclically reversed horizontal load. We used a computer program, Reinforced Concrete Analysis in Higher Evaluation System Technology (RCAHEST), for analysis of RC structures. The used numerical method gives a realistic prediction of seismic performance throughout the loading cycles for several hollow pier specimens investigated. As a result, developed triangular reinforcement details for material quantity reduction was equal to existing reinforcement details in terms of required performance.

• Steel and Composite Structures
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• v.20 no.6
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• pp.1193-1203
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• 2016

This paper focuses on the analytical behavior of modular circular concrete-filled tubular (CFT) column with enhanced bracing details. To design a full-scale bridge pier of multiple circular concrete-filled tubes, numerical analysis was used to evaluate structural performance according to load directivity. In previous research (Ma et al. 2012, Shim et al. 2014), low cycle fatigue failure at bracing joints was observed, so enhanced bracing details to prevent premature failure are proposed in this analysis. The main purpose of this research is to investigate seismic performance for the diagonal direction load without premature failure at the joints when the structure reaches the ultimate load. The ABAQUS finite-element software is used to evaluate experimental performance. A quasi-static loading condition on a modular bridge pier is introduced to investigate structural performance. The results obtained from the analysis are evaluated by comparing with load-displacement responses from experiments. The concrete-filled tubes with enhanced bracing details showed higher energy dissipation capacity and proper performance without connection failure for a diagonal load.

• Steel and Composite Structures
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• v.31 no.2
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• pp.133-148
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• 2019

This paper reports on the energy absorption characteristics of a lattice-web reinforced composite sandwich cylinder (LRCSC) which is composed of glass fiber reinforced polymer (GFRP) face sheets, GFRP lattice webs, polyurethane (PU) foam and ceramsite filler. Quasi-static compression experiments on the LRCSC manufactured by a vacuum assisted resin infusion process (VARIP) were performed to demonstrate the feasibility of the proposed cylinders. Compared with the cylinders without lattice webs, a maximum increase in the ultimate elastic load of the lattice-web reinforced cylinders of approximately 928% can be obtained. Moreover, due to the use of ceramsite filler, the energy absorption was increased by 662%. Several numerical simulations using ANSYS/LS-DYNA were conducted to parametrically investigate the effects of the number of longitudinal lattice webs, the number of transverse lattice webs, and the thickness of the transverse lattice web and GFRP face sheet. The effectiveness and feasibility of the numerical model were verified by a series of experimental results. The numerical results demonstrated that a larger number of thicker transverse lattice webs can significantly enhance the ultimate elastic load and initial stiffness. Moreover, the ultimate elastic load and initial stiffness were hardly affected by the number of longitudinal lattice webs.

• Geomechanics and Engineering
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• v.24 no.1
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• pp.15-28
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• 2021

Digging well foundation has been widely used in railway bridges due to its good economy and reliability. In other instances, bridges with digging well foundation still have damage risks during earthquakes. However, there is still a lack of knowledge of lateral behavior of digging well foundation considering the soil-foundation interaction. In this study, scaled models of bridge pier-digging well foundation system are constructed for quasi-static test to investigate their lateral behaviors. The failure mechanism and responses of the soil-foundation-pier interaction system are analyzed. The testing results indicate that the digging foundations tend to rotate as a rigid body under cyclic lateral load. Moreover, the depth-width ratio of digging well foundation has a significant influence on the failure mode of the interaction system, especially on the distribution of foundation displacement and the failure of pier. The energy dissipation capacity of the interaction system is discussed by using index of the equivalent viscous damping ratio. The damping varies with the depth-width ratio changing. The equivalent stiffness of soil-digging well foundation-pier interaction system decreases with the increase of loading displacement in a nonlinear manner. The absolute values of the interaction system stiffness are significantly influenced by the depth-width ratio of the foundation.

• Smart Structures and Systems
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• v.32 no.6
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• pp.371-382
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• 2023

Box girder bridges are now widely used in bridge construction, and it is necessary to perform load rating regularly to evaluate the load capacity of box girder bridges. Load testing is a common measure for load rating. However, the bridge must be loaded by many trucks under different loading conditions, which is time-consuming and laborious. To solve this problem, this paper proposes a load rating method for box girder bridges based on rapid moving loads testing. The method includes three steps. First, the quasi-influence factors of the bridge are obtained by crossing the bridge with rapidly moving loads, and the structural modal parameters are simultaneously obtained from the dynamic data to supplement. Second, an objective function is constructed, consisting of the quasi-influence factors at several measurement points and structural modal parameters. The finite element model for load rating is then updated based on the Rosenbrock method. Third, on this basis, a load rating method is proposed using the updated model. The load rating method proposed in this paper can considerably reduce the time duration of traditional static load testing and effectively utilize the dynamic and static properties of box girder bridges to obtain an accurate finite element model. The load capacity obtained based on the updated model can avoid the inconsistency of the evaluation results for the different structural members using the adjustment factors specified in codes.

• Earthquakes and Structures
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• v.2 no.3
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• pp.233-256
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• 2011

This paper investigates the applicability of newly developed Cu-Al-Mn shape memory alloy (SMA) bars to retrofitting of historical masonry constructions by performing quasi-static tests of half-scale brick walls subjected to cyclic out-of-plane flexure. Problems associated with conventional steel reinforcing bars lie in pinching, or degradation of stiffness and strength under cyclic loading, and in their inability to restrain residual deformations in structures during and after intense earthquakes. This paper attempts to resolve the problems by applying newly developed Cu-Al-Mn SMA bars, characterized by large recovery strain, low material cost, and high machinability, as partial replacements for steel bars. Three types of brick wall specimens, unreinforced, steel reinforced, and SMA reinforced specimens are prepared. The specimens are subjected to quasi-static cyclic loading up to rotation angle enough to cause yielding of reinforcing bars. Corresponding nonlinear finite element models are developed to simulate the experimental observations. It was found from the experimental and numerical results that both the steel reinforced and SMA reinforced specimens showed substantial increment in strength and ductility as compared to the unreinforced specimen. The steel reinforced specimen showed pinching and significant residual elongation in reinforcing bars while the SMA reinforced specimen did not. Both the experimental and numerical observations demonstrate the superiority of Cu-Al-Mn SMA bars to conventional steel reinforcing bars in retrofitting historical masonry constructions.

• Structural Engineering and Mechanics
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• v.39 no.3
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• pp.427-447
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• 2011

The progressive collapse phenomenon is generally regarded as dynamic. Due to the impracticality of nonlinear dynamic computations for practitioners, an interest arises for the development of equivalent static pushover procedures. The present paper proposes a methodology to identify such a procedure for sudden column removals, using energetic evaluations to determine the pushover loads to apply. In a dynamic context, equality between the cumulated external and internal works indicates a vanishing kinetic energy. If such a state is reached, the structure is sometimes assumed able to withstand the column removal. Approximations of these works can be estimated using a static computation, leading to an estimate of the displacements at the zero kinetic energy configuration. In comparison with other available procedures based on such criteria, the present contribution identifies loading patterns to associate with the zero-kinetic energy criterion to avoid a single-degree-of-freedom idealisation. A parametric study over a family of regular steel structures of varying sizes uses non-linear dynamic computations to assess the proposed pushover loading pattern for the cases of central and lateral ground floor column failure. The identified quasi-static loading schemes are shown to allow detecting nearly all dynamically detected plastic hinges, so that the various beams are provided with sufficient resistance during the design process. A proper accuracy is obtained for the plastic rotations of the most plastified hinges almost independently of the design parameters (loads, geometry, robustness), indicating that the methodology could be extended to provide estimates of the required ductility for the beams, columns, and beam-column connections.