• Smart Structures and Systems
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• v.25 no.5
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• pp.515-530
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• 2020

A new type of pure torsional yielding damper made from steel pipe is proposed and introduced. The damper uses a special mechanism to apply force and therefore applies pure torsion in the damper. Uniform distribution of the shear stress caused by pure torsion resulting in widespread yielding along pipe and consequently dissipating a large amount of energy. The behavior of the damper is investigated analytically and the governing relations are derived. To examine the performance of the proposed damper, four types of the damper are experimentally tested. The results of the tests show the behavior of the system as stable and satisfactory. The behavior characteristics include initial stiffness, yielding load, yielding deformation, and dissipated energy in a cycle of hysteretic behavior. The tests results were compared with the numerical analysis and the derived analytical relations outputs. The comparison shows an acceptable and precise approximation by the analytical outputs for estimation of the proposed damper behavior. Therefore, the relations may be applied to design the braced frame system equipped by the pure torsional yielding damper. An analytical model based on analytical relationships was developed and verified. This model can be used to simulate cyclic behavior of the proposed damper in the dynamic analysis of the structures equipped with the proposed damper. A numerical study was conducted on the performance of an assumed frame with/without proposed damper. Dynamic analysis of the assumed frames for seven earthquake records demonstrate that, equipping moment-resisting frames with the proposed dampers decreases the maximum story drift of these frames with an average reduction of about 50%.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.18 no.2
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• pp.181-190
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• 2005

In the conventional outrigger system, the outriggers are located in the planes of the core walls and this system has disadvantage of obstructing flexibility in the interior layout. But thc facade riggers in the structure uc located In the exterior frames in the direction of the lateral loading. The interaction between the traced frames and facade riggers is through the floor diaphragms adjacent to the chords of the riggers. This paper presents an approximate analysis technique lot preliminary analysis of multiple facade rigger stiffened braced frames in tall buildings subjected to uniformly and triangularly distributed loads as well as a lateral point load at the top of the structure. Comparisons with the results by the program MIDAS for the structural models have shown that this analysis can give reasonably accurate results for highrise braced frames with multiple facade riggers. The method allows a simple procedure for obtaining the optimum level of the facade riggers in addition to a rapid assessment of the influence of the facade riggers on the performance of the highrise structure such as the reduction in lateral deflection at the top and the overturning moment at the base of the braced frame.

• Journal of the Earthquake Engineering Society of Korea
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• v.5 no.6
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• pp.21-27
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• 2001

In this paper, a nonlinear finite element procedure is presented for the dynamic analysis of reinforced concrete shells. A computer program, named RCAHEST(reinforced concrete analysis in higher evaluation system technology), for the analysis of reinforced concrete structures was used. A 4-node flat shell element will drilling rotational stiffness is used for spatial discretization. The layered approach is used to discretize behavior of concrete and reinforcement through the thickness. Material nonlinearity is taken into account by comprising tensile, compressive and shear models of cracked concrete and a model of reinforcing steel. The smeared crack approach is incorporated. Solution of the equations of motion is obtained by numerical integration using Hilber-Hughes-Taylor(HHT) algorithm. The proposed numerical method for the nonlinear dynamic analysis of reinforced concrete shells is verified by comparison with reliable analytical results.

• Journal of the Earthquake Engineering Society of Korea
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• v.6 no.3
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• pp.31-40
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• 2002

The purpose of this study is to investigate the seismic behavior of RC bridge piers and to provide the data for developing improved seismic design criteria. The accuracy and objectivity of the assessment process may be enhanced by the use of sophisticated nonlinear finite element analysis program. A computer program, named RCAHEST(reinforced concrete analysis in higher evaluation system technology), for the analysis of reinforced concrete structures was used. Material nonlinearity is taken into account by comprising tensile, compressive and shear models of cracked concrete and a model of reinforcing steel. The smeared crack approach is incorporated. n boundary plane at which each member with different thickness is connected, local discontinuity in deformation due to the abrupt change in their stiffness can be taken into account by introducing interface element. The effect of number of load reversals with the same displacement amplitude has been also taken into account to model the reinforcing steel and concrete. In the companion paper, the proposed numerical method for seismic damage evaluation of RC bridge piers is verified by comparison with the reliable experimental results.

• Journal of Korean Society of Steel Construction
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• v.29 no.5
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• pp.341-352
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• 2017

Well designed group bolted connections can exhibit excellent ductile behavior through the bearing mechanism until the occurrence of shear rupture in the bolt or in the connecting plate. This excellent ductility can be utilized in favor of economical connection design. In this study, comprehensive tests on single-bolt bearing connections were conducted and analyzed considering bearing boundary conditions. The primary objective was to propose a generalized bearing strength and load-deformation relationship that can be used for designing group-bolted connections. To this end, new bearing strength formula, deformation limits as well as new load-deformation relationship were first proposed. Especially the proposed load-deformation relationship can reflect the stiffness, strength, and geometrical boundary conditions of the joint. The proposed formula and relationship are validated based on test results.

• Journal of the Korean Geotechnical Society
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• v.21 no.2
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• pp.67-84
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• 2005

This research was conducted to evaluate the effectiveness of reinforcement for nearly saturated soft clay compaction. The effectiveness was investigated by roller compaction test using nearly saturated clay specimens. The nearly saturated condition was obtained by submerging clay in the water for 12 hours. High water content specimens were compacted in plane strain condition by a steel roller. A specimen was compacted by four 5 cm horizontal layers. Specimens were prepared fur both reinforced and unreinforced cases to evaluate the effectiveness of reinforcement. Used reinforcement is a composite consisted of both woven and non-woven geotextile. The composite usually provides drainage and tensile reinforcement to hi인 water-contented clay so that it increases bearing capacity. Therefore, large compaction load can be applied to reinforced clay and it achieves higher density effectively. The reinforcement also increases compaction efficiency because it reduces the ratio between shear and vertical forces during compaction process. The maximum vertical stress on the base of specimen usually decreased with higher compaction thickness. The reinforcement increases soil stiffness under the compaction roller and it initiates stress concentration. As a result, it maintains higher vertical stress level on the base of specimen that provides better compaction characteristics. Based on test results, it can be concluded that the reinforcement is essential to achieve effective compaction on soft clay.

• Journal of the Korean Geotechnical Society
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• v.30 no.12
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• pp.41-49
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• 2014

The 3D numerical analysis is carried out to investigate the settlement behavior of flexible mat foundations subjected to vertical loads. Special attention is given to the improved analytical method (YS-MAT) that reflects the mat flexibility and soil spring coupling effect. The soil model captures the stiffness of the soil springs as well as the shear interaction between the soil springs. The proposed method has been validated by comparing the results with other numerical methods and a field measurement on mat foundation. Through comparative studies, the settlement of the proposed method was in relatively good agreement with those of a field measurement and other numerical methods. The results permit us to estimate the response of the mat foundation subjected to vertical loads that should be taken into account in the combination of mat flexibility and soil continuity characteristics.

• Steel and Composite Structures
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• v.7 no.6
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• pp.457-468
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• 2007

Analytical and experimental investigation on dynamic properties of extra lightweight concrete sandwich beams reinforced with various lay ups of carbon reinforced epoxy polymer composites (CFRP) are discussed. The lightweight concrete used in the core of the sandwich beams was made up of extra lightweight aggregate, Lica. The density of concrete was half of that of the ordinary concrete and its compressive strength was about $100Kg/cm^2$. Two extra lightweight unreinforced (control) beams and six extra lightweight sandwich beams with various lay ups of CFRP were clamped in one end and tested under an impact load. The dimension of the beams without considering any reinforcement was 20 cm ${\times}$ 10 cm ${\times}$ 1.4 m. These were selected to ensure that the effect of shear during the bending test would be minimized. Three other beams, made up of ordinary concrete reinforced with steel bars, were tested in the same conditions. For measuring the damping capacity of sandwich beams three methods, Logarithmic Decrement Analysis (LDA), Hilbert Transform Analysis (HTA) and Moving Block Analysis (MBA) were applied. The first two methods are in time domain and the last one is in frequency domain. A comparison between the damping capacity of the beams obtained from all three methods, shows that the damping capacity of the extra lightweight concrete decreases by adding the composite reinforced layers to the upper and lower sides of the beams, and becomes most similar to the damping of the ordinary beams. Also the results show that the stiffness of the extra lightweight concrete beams increases by adding the composite reinforced layer to their both sides and become similar to the ordinary beams.

• Steel and Composite Structures
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• v.22 no.1
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• pp.141-159
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• 2016

Commonly in steel frames, steel beam and concrete slab are connected together by shear keys to work as a unit member which is called composite beam. When a composite beam is subjected to positive bending, flexural strength and stiffness of the beam can be increased due to "composite action". At the same time despite these advantages, composite action increases the strain at the beam bottom flange and it might affect beam plastic rotation capacity. This paper presents results of study on the rotation capacity of composite beam connected to Rectangular Hollow Section (RHS) column in the steel moment resisting frame buildings. Due to out-of-plane deformation of column flange, moment transfer efficiency of web connection is reduced and this results in reduction of beam plastic rotation capacity. In order to investigate the effects of width-to-thickness ratio (B/t) of RHS column on the rotation capacity of composite beam, cyclic loading tests were conducted on three full scale beam-to-column subassemblies. Detailed study on the different steel beam damages and concrete slab damages are presented. Experimental data showed the importance of this parameter of RHS column on the seismic behavior of composite beams. It is found that occurrence of severe concrete bearing crush at the face of RHS column of specimen with smaller width-to-thickness ratio resulted in considerable reduction on the rate of strain increase in the bottom flange. This behavior resulted in considerable improvement of rotation capacity of this specimen compared with composite and even bare steel beam connected to the RHS column with larger width-to-thickness ratio.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.3
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• pp.855-864
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• 2013

The dynamic characteristics of natural rubber bearings, which are used as isolator, are dependent on the main rubber's dynamic behaviors and nonlinear properties. Rubber materials tend to undergo an aging process under the influence of mechanical or environmental factors, so they inevitably end up facing damage. A main cause of aging like this is known to be oxidization, which occurs through the heat of reaction at high temperatures. Accordingly, in this study an accelerated thermal aging test was carried out in order to compare the characteristic values of the bearings before and after thermal aging occurs. As a result of this experiment, it was found that a thermal aging phenomenon could have some effects on shear stiffness, energy absorption, and equivalent damping coefficients of the bearings. Furthermore, a deterioration in the dynamic properties of the natural rubber bearings caused by the thermal aging was applied to an actual bridge and then the effects of such thermal aging on the seismic performance of the bridge were also compared and analyzed based on numerical analysis. As a result of this analysis, it was found that the changes in the basic properties of the natural rubber bearings caused by the thermal aging bring only a minor effect on the seismic performance of bridges.