• Magazine of the Korean Society of Agricultural Engineers
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• v.44 no.3
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• pp.73-84
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• 2002

Nominal shear strength of concrete beam is the combined strength of concrete shear strength and steel shear strength in current design code. But Torsional moment strength of concrete is neglected in calculation of the nominal torsional moment strength of reinforced concrete beam in current revised code. Tensile stress of concrete strut between cracks is still in effect due to tension stiffening effect. But the tensile stresses of concrete after cracking are neglected in bending and torsion in design. The torsional behavior is similar to the shear behavior in mechanics. Therefore the torsional moment strength of concrete should be concluded to the nominal torsional moment strength of reinforced concrete beam. To verify the validity of the proposed model, the nominal torsional moment strengths according to CEB, two ACI codes(89, 99) and proposed model are compared to experimental torsional strengths of 55 test specimens found in literature. The nominal torsional moment strengths by the proposed model show the best results.

• Computers and Concrete
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• v.29 no.5
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• pp.303-321
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• 2022

The current design equations for predicting the torsional capacity of RC members underestimate the torsional strength of under-reinforced members and overestimate the torsional strength of over-reinforced members. This is because the design equations consider only the yield strength of torsional reinforcement and the cross-sectional properties of members in determining the torsional capacity. This paper presents an analytical model to predict the thickness of shear flow path in RC beams subjected to pure torsion. The analytical model assumes that torsional reinforcement resists torsional moment with a sufficient deformation capacity until concrete fails by crushing. The ACI 318 code is modified by applying analytical results from the proposed model such as the average stress of torsional reinforcement and the effective gross area enclosed by the shear flow path. Comparison of the calculated and observed torsional strengths of existing 129 test beams showed good agreement. Two design variables related to the compressive strength of concrete in the proposed model are approximated for design application. The accuracy of the ACI 318 code for the over-reinforced test beams improved somewhat with the use of the approximations for the average stresses of reinforcements and the effective gross area enclosed by the shear flow path.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.445-448
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• 1999

The minimum shear and torsional reinforcement provisions in ACI 318-95 are still empirical. This paper describes the derivation of a rational approach for minimum shear and torsional reinforcement in beams so as to preclude brittle failure in shear and torsion. This is ensured by specifying that the beam's ultimate capacity of shear and torsion should be greater than its cracking shear and torsion. The formula presented herein for computing minimum shear and torsional reinforcement shows the need for modification of current provision for the minimum shear and torsion reinforcement.

• Journal of the Korea Concrete Institute
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• v.23 no.1
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• pp.57-65
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• 2011

Both shear and torsional moments apply shear stresses on cross-section of a member, which need to be considered in the design. But in the current Korean Building Code, the design equations for shear and torsional moments are expressed in terms of the sectional strength with different units, causing figures to be drawn separately in two axes. If the design equations are expressed in terms of stresses, then the stresses of shear and torsional moments can be added, allowing figures to be drawn in one axis for easy recognition of the design procedure and the final design results. Moreover, the current code's design equations for shear and torsional moments are considered separately with the intention of summing the area of stirrups with respect to unit length for shear moment ($A_{\upsilon}/s$) and torsional moment ($2A_t/s$). Since the size or type of vertical stirrups are predetermined in the design process, the design equations are expressed in terms of the spacing of stirrups rather than the $A_{\upsilon}/s$ and $2A_t/s$ terms, clarifying various design steps and a design process.

• Journal of the Korea Concrete Institute
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• v.14 no.1
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• pp.24-32
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• 2002

The modified compression field theory is already applied in shear problem at some code(AASHTO-1998) partly. Nominal shear strength of concrete beam is sum of the concrete shcar strength and the steel shear strength in the current design code. But Torsional moment strength of concrete is neglected in the calculation of the nominal torsional moment strength of concrete beam In the current revised code. Tensile stress of concrete strut between cracks is still in effect due to tension stiffening effect. But The tensile stresses of concrete after cracking are neglected in bending and torsion In design. The torsional behavior is similar to the shear behavior in mechanics. Therefore the torsional moment strength of concrete should be concluded in the nominal torsional moment strength of reinforced concrete beam. This paper shows that the torsional moment strength of concrete is caused by the average principal tensile stress of concrete. To verify the validity of the proposed model, the nominal torsional moment strengths according to two ACI codes (89, 99) and proposed model are compared to experimental torsional moment strengths of 55 test specimens found in literature. The nominal torsional moment strengths by the proposed model show the best results.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.35 no.5
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• pp.277-286
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• 2022

The elastic and inelastic responses obtained from the experimental and analytical results of two RC building structures under the service level earthquake (SLE) and maximum considered earthquake (MCE) in Korea were used to weinvestigate the characteristics of the mechanisms resisting shear and torsional behavior in torsionally unbalanced structures. Equations representing the interactive effect of translational drift and torsional deformation on the shear force and torsional moment were proposed. Because there is no correlation in the behavior between elastic and inelastic forces and strains, the incremental shear forces and incremental torsional moments were analyzed in terms of their corresponding incremental drifts and incremental torsional deformations with respect to the yield, unloading, and reloading phases around the maximum edge-frame drift. In the elastic combination of the two dominant modes, the translational drift mainly contributes to the shear force, whereas the torsional deformation contributes significantly to the overall torsional moment. However, this phenomenon is mostly altered in the inelastic response such that the incremental translational drift contributes to both the incremental shear forces and incremental torsional moments. In addition, the given equation is used to account for all phenomena, such as the reduction in torsional eccentricity, degradation of torsional stiffness, and apparent energy generation in an inelastic response.

• Wind and Structures
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• v.3 no.4
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• pp.279-289
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• 2000

The main purpose of this paper is to demonstrate the necessity of considering wind load combinations even for low-rise buildings. It first discusses the overall quasi-static wind load effects and their combinations to be considered in structural design of low-rise buildings. It was found that the maximum torsional moment closely correlates with the maximum along-wind base shear. It was also found that the instantaneous pressure distribution causing the maximum along-wind base shear was quite similar to that causing the maximum torsional moment, and that this asymmetric pressure pattern simultaneously accompanies considerable across-wind and torsional components. Secondly, the actual wind pressure distributions causing maximum quasi-static internal forces in the structural frames are conditionally sampled and their typical pressure patterns are presented.

• Earthquakes and Structures
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• v.9 no.1
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• pp.145-171
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• 2015

Due to earthquakes, many structures suffered extensive damages that were attributed to the torsional effect caused by mass, stiffness or strength eccentricity. Due to this type of asymmetry torsional moments are generated that are imposed by means of additional shear forces developed at the vertical resisting structural elements of the buildings. Although the torsional effect on the response of reinforced concrete buildings was the subject of extensive research over the last decades, a quantitative index measuring the amplification of the shear forces developed at the vertical resisting elements due to lateral-torsional coupling valid for both elastic and elastoplastic response states is still missing. In this study a reliable index capable of assessing the torsional effect is proposed. The performance of the proposed index is evaluated and its correlation with structural response quantities like displacements, interstorey drift, base torque, shear forces and upper diaphragm's rotation is presented. Torsionally stiff, mass eccentric single-story and multistory structures, subjected to bidirectional excitation, are considered and nonlinear dynamic analyses are performed using natural records selected for three hazard levels. It was found that the proposed index provides reliable prediction of the magnitude of torsional effect for all test examples considered.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.4 s.97
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• pp.499-505
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• 2005

In this paper, a new type of pi+ezoelectric stepping motor is designed, manufactured and tested. This motor is composed of piezoelectric torsional actuator and a pair of one-way clutch bearings. The torsional actuator consists of 16-polygonal tube of piezoceramic that can produce an angular displacement associated with shear mode. One-way clutch bearing converts oscillation of torsional actuator into a continuous stepping rotation. The proposed stepping motor does not require any conversion mechanism for stepping motion like any other motors. In the design process, the shear resonance mode of piezoelectric actuator is analyzed by using a commercial finite element analysis program, and the performance of the fabricated torsional actuator is measured. $0.124^{\circ}$ of maximum angular displacement is measured in square wave excitation on the actuator only. The stepping motor is manufactured by assembling a pair of one-way clutch bearings and the torsional actuator. The maximum rotation speed of 72rpm and the blocking torque of 3.136 mNm are measured at 3540 Hz and 100V/mm. Once the proposed piezoelectric stepping motor is miniaturized, it can be used for many compact and precise moving applications.

• Journal of the Korean Society for Railway
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• v.3 no.1
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• pp.34-41
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• 2000

The analysis of static and dynamic characteristics of reinforced roadbed materials was performed through model and laboratory tests. The strength characteristic of reinforced roadbed materials such as HMS-25 and soil were investigated through the unconfined axial compression test, the model soil box test and the combined resonant column and torsional shear test. The unconfined axial compression strength of HMS-25 shows a steady increasement in strength due to the chemical hardening reaction between HMS-25 and water. The result of model soil box test reveals that railroad roadbed of HMS-25 is better than that of soil in several aspects, such as, bearing capacity and settlement. The combined resonant column and torsional shear test result indicates that shear modulus of HMS-25 and soil increase with the power of 0.5 to the confining pressure and linear relationship to normalized shear modulus and damping ratio.