• Wind and Structures
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• v.11 no.1
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• pp.1-18
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• 2008

Interference effects in five square tall buildings arranged in an L- or T-shaped pattern are investigated in the wind tunnel. Mean and fluctuating shear forces, overturning moments and torsional moment are measured on each building with a force balance mounted at its base. Results are obtained at two values of clear separation between adjacent buildings, at half and a quarter building breadth. It is found that strong interference effect exists on all member buildings, resulting in significant modifications of wind loads as compared with the isolated single building case. Sheltering effect is observed on wind loads acting along the direction of an arm of the "L" or "T" on the inner buildings. However, increase in these wind loads from the isolated single building case is found on the most upwind edge building in the arm when wind blows at a slight oblique angle to the arm. The corner formed by two arms of buildings results in some wind catchment effect leading to increased wind pressure on windward building faces. Interesting interference phenomena such as negative drag force are reported. Interference effects on wind load fluctuations, load spectra and dynamic building responses are also studied and discussed.

• Aerospace Engineering and Technology
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• v.13 no.1
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• pp.10-19
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• 2014

We designed bearingless rotor hub system which replace mechanical hinge/bearing with composite beam component and conducted fatigue analysis for flexbeam and torque tube. Extension/bending/torsional stiffness was calculated from 2D section analysis using VABS and 2D section structure analysis was applied for strain calculation. S-N curve of each composite material was generated using Wohler equation and fatigue analysis was conducted on weakness section which was decided from static structure analysis. CAMRAD II was used for load analysis and load analysis result was applied HELIX/FELIX standard load spectrum to generate bearingless rotor system load spectrum which was used fatigue safe life analysis.

• Composites Research
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• v.29 no.6
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• pp.369-374
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• 2016

In this study, a structural optimal design of 10 MW composite blade was performed using bend-twist coupled(BTC) design concept. Bend-twist coupling of blade means the coupling behavior between the bending and torsional deflections due to the composite lamina with fiber angle biased from the blade longitudinal axis. This can potentially improve the overall performance of composite blade and reduce the dynamic loading. Parametric studies on layup angle, thickness and area of off-axis carbon UD were conducted to find the optimum coupling effect with weight reduction. Comparing the results of fatigue load analysis between conventional model and BTC applied model, the damage equivalent load(DEL) of blade root area were decreased about 3% in BTC model. To verify the BTC effect experimentally, a 1:29 scaled model was fabricated and the torsion at the tip under deflection behavior of blade stiffener model was measured by static load test.

• Computers and Concrete
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• v.20 no.6
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• pp.663-670
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• 2017

The post-tensioned (PT) flat plate slab system is commonly used in practice, and this simple and fast construction method is also considered to be a very efficient method because it can provide excellent deflection and crack control performance under a service load condition and consequently can be advantageous when applying to long-span structures. However, a detailed design guideline for evaluating the lateral behavior of the PT flat plate slab system is not available in current design codes. Thus, typical design methods used for conventional reinforced concrete (RC) flat plate slab structures have inevitably been adopted in practice for the lateral load design of PT flat plate structures. In the authors' previous studies, the unified equivalent frame method (UEFM) was proposed, which considers the combined effect of gravity and lateral loads for the lateral behavior analysis of RC flat plate slab structures. The aim of this study is to extend the concept of the UEFM to the lateral analysis of PT flat plate slab structures. In addition, the stiffness reduction factors of torsional members on interior and exterior equivalent frames were newly introduced considering the effect of post-tensioning. Test results of various PT flat plate slab-column connection specimens were collected from literature, and compared to the analysis results estimated by the extended UEFM.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.2
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• pp.161-168
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• 2015

Horizontally curved bridges are subjected to torsional loads by their vertical dead loads only as well as eccentric loads, which cause negative reactions at supports. In this paper, effects of bridge curvature on vertical reactions at supports are investigated for 48.8 m length simple span steel box girder bridges with elastomeric bearings by varying curvature angle from 0.49 to 1.35 rad. In order to expect magnitude and direction of reactions including possibility of negative reactions, reaction evaluation equations have been analytically developed by separating a superstructure of curved bridge into independent components. Concrete slabs and bottom flanges in steel box section are assumed geometrical annular sectors in area dimension, and top flanges and webs that have very narrow projected areas are assumed geometrical arcs in line dimension. Proposed equations have relatively simple forms and prediction values are on very good agreement with those from finite element analyses by difference of 1% order.

• Journal of Korean Society of Steel Construction
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• v.16 no.1 s.68
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• pp.155-167
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• 2004

In this paper, the inelastic buckling behavior of the beam under uniform bending was investigated using the energy-based method, which can tackle problems in fourth order eigenvalue. The pattern of residual stress was not available to satisfy the I-sections manufactured in Korea. however; therefore, the well-known polynomial and simplified pattern of residual stress was adopted in this study. The inelastic lateral-distortional buckling behavior of the beam with I-sections manufactured in Korea was investigated. The study was then extended to the inelastic lateral-torsional buckling of the beam by minimizing the out-of-plane web distortion. The inelastic lateral-torsional buckling results obtained in this paper were compared with the prediction of allowable bending stress given in the Korean steel designers' manual (1995). Results showed that the importance of inelastic lateral-distortional buckling did not arise for beams under uniform bending. Likewise, the design method in KSDM (1995) was proven to bo too conservative for intermediate and short spans of beams without intermediate bracing.

• Earthquakes and Structures
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• v.9 no.1
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• pp.49-71
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• 2015

The present paper aims at evaluating damage and collapse behavior of low-rise buildings with unidirectional mass irregularities in plan (torsional buildings). In previous earthquake events, such buildings have been exposed to extensive damages and even total collapse in some cases. To investigate the performance and collapse behavior of such buildings from probabilistic points of view, three-dimensional three and six-story reinforced concrete models with unidirectional mass eccentricities ranging from 0% to 30% and designed with modern seismic design code provisions specific to intermediate ductility class were subjected to nonlinear static as well as extensive nonlinear incremental dynamic analysis (IDA) under a set of far-field real ground motions containing 21 two-component records. Performance of each model was then examined by means of calculating conventional seismic design parameters including the response reduction (R), structural overstrength (${\Omega}$) and structural ductility (${\mu}$) factors, calculation of probability distribution of maximum inter-story drift responses in two orthogonal directions and calculation collapse margin ratio (CMR) as an indicator of performance. Results demonstrate that substantial differences exist between the behavior of regular and irregular buildings in terms of lateral load capacity and collapse margin ratio. Also, results indicate that current seismic design parameters could be non-conservative for buildings with high levels of plan eccentricity and such structures do not meet the target "life safety" performance level based on safety margin against collapse. The adverse effects of plan irregularity on collapse safety of structures are more pronounced as the number of stories increases.

• Journal of the Earthquake Engineering Society of Korea
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• v.9 no.3 s.43
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• pp.23-32
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• 2005

Torsional behavior of eccentric structure under seismic leading may cause the stress and/or deformation concentration, which arouse the failure of the structure in an unexpected manner. This study suggests D-R relationship which shows the overall displacement and rotation of the system based on the ultimate displacement capacity of the each lateral load resistant member. Using the suggested D-R relationship and displacement spectrum, the seismic assessment is conducted and verified in comparison with the time history analysis result. Multi-level seismic assessment Is considered which takes multiple seismic hazard levels and respective performance levels into account. Finally, based on the seismic assessment result, seismic rehabilitation process is presented. In this research, two rehabilitation methods are considered. One is done by means of stiffening/strengthening the seismic resistant members, and the other is based on the member ductility. Especially, in the first method, to optimize the rehabilitation result, the rehabilitation problem is modeled as an optimization problem, and solved using BFGS quasi-Newton optimization method.

• Geotechnical Engineering
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• v.11 no.1
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• pp.113-126
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• 1995

Both resonant column (RC) and torsional shear(TS) tests were performed at small to intermediate strain levels to investigate deformational characteristics of cohesive soils. The effects of variables such as strain amplitude, loading frequency, and number of loading cycles were studied. Plasticity index was found to be an important variables in evaluating these effects. Soils tested include undisturbed silts and clays and compacted subgrade soils. At small strains below the elastic threshold, shear modulus is independent of number of loading cycles and strain amplitude. Small strain material damping exists wi th ranges be tween 1.1% and 1.7% for 75 tests. The elastic threshold strain increases as confining pressure and plasticity index increases. Above the cyclic threshold strain, the modulus of cohesive soil decreases with increasing number of cycles while damping ratio is almost independent of number of load cycles. Moduli and damping ratios of cohesive soils obtanined by RC test are higher than those from 75 test because of the frequency effect. Shear modulus of cohesive soil increases linearly as a function of the logarithm of loading frequency.

• Journal of Korean Society of Steel Construction
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• v.15 no.3
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• pp.299-311
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• 2003

This paper presents a finite element procedure to estimate the ultimate strength of space frames considering spread of plasticity. The improved displacement field is introduced based on the inclusion of second-order terms of finite rotations. All the non-linear terms due to bending moment, torsional moment, and axial force are precisely considered. The concept of plastic hinges is introduced and the incremental load/displacement method is applied for elasto-plastic analyses. The initial yield surface is defined based on the residual stress, and the full plastification surface is considered under the combined action of axial forces, bending and torsional moments. The elasto-plastic stiffness matrices are derived using the flow rule and the normality condition of the limit function. Finite element solutions for the ultimate strength of space frames are compared with available solutions and experimental results.