• Earthquakes and Structures
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• v.14 no.4
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• pp.305-312
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• 2018

Significant research efforts were undertaken to evaluate seismic performance of vertically irregular buildings on flat ground. However, there is scarcity of study on seismic performance of buildings on hill slopes. The present study attempts to investigate seismic behaviour of reinforced concrete irregular stepback building frames with different configurations on sloping ground. Based on extensive regression study of free vibration results of four hundred seventeen frames with varying ground slope, number of story and span number, a modification is proposed to the code based empirical fundamental time period estimation formula. The modification to the fundamental time period estimation formula is a simplified function of ground slope and a newly introduced equivalent height parameter to reflect the effect of stiffness and mass irregularity. The derived empirical formula is successfully validated with various combinations of slope and framing configurations of buildings. The correlation between the predicted and the actual time period obtained from the free vibration analysis results are in good agreement. The various statistical parameters e.g., the root mean square error, coefficient of determination, standard average error generally used for validation of such regression equations also ensure the prediction capability of the proposed empirical relation with reasonable accuracy.

• International Journal of Concrete Structures and Materials
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• v.8 no.4
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• pp.289-299
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• 2014

Alkali-activated slag concretes are being extensively researched because of its potential sustainability-related benefits. For such concretes to be implemented in large scale concrete applications such as infrastructural and building elements, it is essential to understand its early and long-term performance characteristics vis-a'-vis conventional ordinary portland cement (OPC) based concretes. This paper presents a comprehensive study of the property and performance features including early-age isothermal calorimetric response, compressive strength development with time, microstructural features such as the pore volume and representative pore size, and accelerated chloride transport resistance of OPC and alkali-activated binder systems. Slag mixtures activated using sodium silicate solution ($SiO_2$-to-$Na_2O$ ratio or $M_s$ of 1-2) to provide a total alkalinity of 0.05 ($Na_2O$-to-binder ratio) are compared with OPC mixtures with and without partial cement replacement with Class F fly ash (20 % by mass) or silica fume (6 % by mass). Major similarities are noted between these binder systems for: (1) calorimetric response with respect to the presence of features even though the locations and peaks vary based on $M_s$, (2) compressive strength and its development, (3) total porosity and pore size, and (4) rapid chloride permeability and non-steady state migration coefficients. Moreover, electrical impedance based circuit models are used to bring out the microstructural features (resistance of the connected pores, and capacitances of the solid phase and pore-solid interface) that are similar in conventional OPC and alkali-activated slag concretes. This study thus demonstrates that performance-equivalent alkali-activated slag systems that are more sustainable from energy and environmental standpoints can be proportioned.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.5
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• pp.148-155
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• 2017

In this study, by using the international standards ISO TS 16774, Part 2 Test method for chemical resistance as a quality control method of injection type repair material used for leakage crack of underground concrete structure, the performance requirement against of chemical environment of underground concrete structures for repair materials was tested. For this testing 3 types for each of the 2 classes of repair materials(synthetic rubber, cement), with a total of 9 types repair materials, were selected and examined. As a result, the test results showed that the smallest performance deterioration by the change in the mass was with the synthetic rubber(RG) type as opposed to the cement type system, showing that the synthetic rubber type had the strongest relative resistance to chemical exposure. Furthermore, it is necessary to investigate the material with high resistance to chemical substances and to examine the material which can increase resistance to sodium hydroxide and sodium chloride in cement system. These results can be used as a basic index for the selection of repair materials with the strongest resistance to chemical environment found in concrete structures. In addition, it is expected that the test results derived in this study can be used as reference data that can be reflected in the quality improvement of the maintenance material to be developed later.

• Composites Research
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• v.12 no.4
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• pp.25-32
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• 1999

A method of calculating the natural frequency corresponding to the first mode of vibration of beams and tower structures, with irregular cross sections and with arbitrary boundary conditions was developed and reported by Kim, D. H. in 1974. In this paper, the result of application of this method to the special orthotropic plates on elastic foundation with free boundaries is presented. Such plates represent the concrete highway slab and hybrid composite pavement on bridges. Any method may be used to obtain the deflection influence surfaces needed for this vibration analysis. Finite difference method is used for this purpose, in this paper. The influence of the modulus of the foundation and the aspect ratio of the plate on the natural frequency is thoroughly studied. The effect of neglecting the mass of the plates on the natural frequency, as the ratio of the point mass/masses to the plate mass increases, is also studied, in deep.

• Geomechanics and Engineering
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• v.9 no.3
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• pp.329-344
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• 2015

Cratering tests in rock are generally carried out to identify its fragmentation characteristics. The test results can be used to estimate the minimum amount of explosives required for the target volume of rock fragmentation. However, it is not easy to perform this type of test due to its high cost and difficulty in securing the test site with the same ground conditions as the site where blasting is to be performed. Consequently, this study investigates the characteristics of rock fragmentation by using the hydrocode in the platform of AUTODYN. The effectiveness of the numerical models adopted are validated against several cratering test results available in the literature, and the effects of rock mass classification and ground formation on crater size are examined. The numerical analysis shows that the dimension of a crater is increased with a decrease in rock quality, and the formation of a crater is highly dependent on a rock of lowest quality in the case of mixed ground. It is expected that the results of the present study can also be applied to the estimation of the level and extent of the damage induced by blasting in concrete structures.

• Earthquakes and Structures
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• v.17 no.4
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• pp.425-434
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• 2019

The most effective passive vibration control and seismic resistance options in a reinforced concrete (RC) high-rise building (HRB) are the base isolation and the tuned mass damper (TMD) system. Many options, which may be suitable or not for different soil types, with different types of bearing systems, like rubber isolator, friction pendulum isolator and tension/compression isolator, are investigated to resist the base straining actions under five different earthquakes. TMD resists the seismic response, as a control system, by reducing top displacement or the total movement of the structure. Base isolation and TMDs work under seismic load in a different way, so the combination between base isolation and TMDs will reduce the harmful effect of the earthquakes in an effective and systematic way. In this paper, a comprehensive study of the combination of TMDs with three different base-isolator types for three different soil types and under five different earthquakes is conducted. The seismic response results under five different earthquakes of the studied nine RC HRB models (depicted by the top displacement, base shear force and base bending moment) are compared to show the most suitable hybrid passive vibration control system for three different soil types.

• Journal of the Korea Institute of Building Construction
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• v.11 no.4
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• pp.371-378
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• 2011

Concrete is affected by various deterioration factors, such as $CO_2$ and chloride ions from the sea, which cause carbonation and salt attack on concrete. These deterioration phenomena cause steel corrosion in RC structures. Although a great deal of research has been carried out in this area thus far, it is difficult to know the point at which corrosion will occur to a reinforced bar. As the diffusion of deterioration factors depends on the water content in concrete, it is imperative to assess the condition of absorbed water content. A mass measuring method was applied to calculate the absorbed water diffusion coefficient, as well as non-linear finite element method(FEM) analysis. As a result, it was found that W/C and unit water content in concrete mixture affect the diffusion coefficient decision.

• Earthquakes and Structures
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• v.18 no.2
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• pp.263-273
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• 2020

The use of energy concepts in seismic analysis and design of structures requires the understanding of the input energy response of multi-degree-of-freedom (MDOF) systems subjected to strong ground motions. For design purposes and non-time consuming analysis, however, it would be beneficial to associate the input energy response of MDOF systems with those of single-degree-of-freedom (SDOF) systems. In this paper, the theoretical formulation of energy input to MDOF systems is developed on the basis that only a particular portion of the total mass distributed among floor levels is effective in the nth-mode response. The input energy response histories of several reinforced concrete frames subjected to a set of eleven horizontal acceleration histories selected from actual recorded events and scaled in time domain are obtained. The contribution of the fundamental mode to the total input energy response of MDOF frames is demonstrated both graphically and numerically. The input energy of the fundamental mode is found to be a good indicator of the total energy input to two-dimensional regular MDOF structures. The numerical results computed by the proposed formulation are verified with relative input energy time histories directly computed from linear time history analysis. Finally, the elastic input energies are compared with those computed from time history analysis of nonlinear MDOF systems.

• Structural Engineering and Mechanics
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• v.61 no.5
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• pp.663-674
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• 2017

The determination of the fundamental period of vibration of a structure is essential to earthquake design. Current codes provide formulas for the approximate estimation of the fundamental period of earthquake-resistant building systems. These formulas are dependent only on the height of the structure or number of storeys without taking into account the presence of infill walls into the structure, despite the fact that infill walls increase the stiffness and mass of the structure leading to significant changes in the fundamental period. Furthermore, such a formulation is overly conservative and unable to account for structures with geometric irregularities. In this study, which comprises the companion paper of previous published research by the authors, the effect of the vertical geometric irregularities on the fundamental periods of masonry infilled structures has been investigated, through a large set of infilled frame structure cases. Based on these results, an attempt to quantify the reduction of the fundamental period due to the vertical geometric irregularities has been made through a proposal of properly reduction factor.

• Journal of the Korea Institute of Building Construction
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• v.16 no.6
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• pp.561-569
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• 2016

Concrete is cheap, easy to deal with, and the quality is satisfactory. Also, it is one of the easiest materials to get because chemical composition of cement is similar to chemical composition of surface. On the other hand, it is so vulnerable to transform because of weak binding capacity and low binding energy that it produces cracks. Cracks decline durability, usability, safety of structures and damage exterior. In order to decline drying shrinkage crack, this study used shrinkage reducing typed Superplasticizer, which is combination of and water-reducing agent for convenience, different with existing study using AE agent, water-reducing agent, shrinkage reducing agent,. Considering SRS field application possibility, this study planned to mix concrete and mortar generally used in ready-mixed concrete company and did basic experiment depending on a change of SRS content ratio and admixture. Based on the experiment result. It is judged that SRS admixture 2% is proper ratio when Given the intensity and length change. Also mass combination will conduct follow-up studies.