• Journal of the Earthquake Engineering Society of Korea
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• v.21 no.1
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• pp.49-57
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• 2017

In order to avoid collapse of bridges in earthquakes bridge piers are generally designed to attain sufficient ductility. This full-ductility design method has merits for securing the seismic safety readily against strong earthquakes but, it has weakness of high cost design because of excessive safety margin. Recently, in many countries with high seismic technologies, the seismic design concept tends to shift from the collapse prevention design to the performance-based one which requires different performance (damage) levels according to the structural importance. In order to establish this performance-based design method the displacement ductility of confined concrete members should be evaluated quantitatively. And the stress-strain model of confined concrete is indispensible in evaluating displacement ductility. In this study, 6 test groups with different lateral reinforcement ratios were prepared. 10 same specimens with circular section for each group were tested to obtain more reliable test results. The characteristic values necessary for composing the stress-strain model were obtained from experiments. Based on these characteristic values the new stress-strain model modifying the Hoshikuma's one has been proposed.

• Computers and Concrete
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• v.16 no.3
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• pp.467-485
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• 2015

This paper presents a comprehensive work on determination of yield base shear coefficient and displacement ductility factor of three to eight story actual reinforced concrete buildings, instead of using generic frames. The building data is provided by a walkdown survey in different locations of the pilot areas. Very detailed three dimensional models of the selected buildings are generated by using the data provided in architectural and reinforcement projects. Capacity curves of the buildings are obtained from nonlinear static pushover analyses and each capacity curve is approximated with a bilinear curve. Characteristic points of capacity curve, the yield base shear capacity, the yield displacement and the ultimate displacement capacity, are determined. The calculated values of the yield base shear coefficients and the displacement ductility factors for directions into consideration are compared by those expected values given in different versions of Turkish Seismic Design Code. Although having sufficient lateral strength capacities, the deformation capacities of these typical mid-rise reinforced concrete buildings are found to be considerably low.

• Structural Engineering and Mechanics
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• v.88 no.2
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• pp.169-178
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• 2023

Lightweight aggregate concrete (LWAC) has various advantages, but it has limitations in ensuring sufficient ductility as structural members such as reinforced concrete (RC) columns due to its low confinement effect of core concrete. In particular, the confinement effect significantly decreases as the axial load increases, but studies on evaluating the ductility of RC columns at high axial loads are very limited. Therefore, this study examined the effects of concrete unit weight on the seismic performance of RC columns subjected to constant axial loads applied with different values for each specimen. The column specimens were classified into all-lightweight aggregate concrete (ALWAC), sand-lightweight aggregate concrete (SLWAC), and normal-weight concrete (NWC). The amount of transverse reinforcement was specified for all the columns to satisfy twice the minimum amount specified in the ACI 318-19 provision. Test results showed that the normalized moment capacity of the columns decreased slightly with the concrete unit weight, whereas the moment capacity of LWAC columns could be conservatively estimated based on the procedure stipulated in ACI 318-19 using an equivalent rectangular stress block. Additionally, by applying the section lamina method, the axial load level corresponding to the balanced failure decreased with the concrete unit weight. The ductility of the columns also decreased with the concrete unit weight, indicating a higher level of decline under a higher axial load level. Thus, the LWAC columns required more transverse reinforcement than their counterpart NWC columns to achieve the same ductility level. Ultimately, in order to achieve high ductility in LWAC columns subjected to an axial load of 0.5, it is recommended to design the transverse reinforcement with twice the minimum amount specified in the ACI 318-19 provision.

• International Journal of High-Rise Buildings
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• v.6 no.3
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• pp.249-259
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• 2017

The use of high-strength steels in construction of highrise and mega building structures can bring about many technological advantages from fabrication to erection. However, key design criteria such as local and lateral stability in current steel design specifications were developed based on tests of ordinary steels which have stress-strain characteristics very different from that of high strength steels. A series of tests on 800 MPa tensile strength steel (HSA800) members are summarized in this paper which were conducted to investigate the appropriateness of extrapolating current ordinary-steel based design criteria to high strength steels. 800 MPa I-shape beam specimens designed according to flange local buckling (FLB) criteria of the AISC Specification developed a sufficient strength for elastic design and a marginal rotation capacity for plastic design. It is shown that, without introducing distinct and significant yield plateau to the stress-strain property of high-strength steel, it is inherently difficult to achieve a high rotation capacity even if all the current stability limits are met. 800 MPa I-shape beam specimens with both low and high warping rigidity exhibited sufficient lateral torsional buckling (LTB) strength. HSA800 short-column specimens with various edge restraint exhibited sufficient local buckling strength under uniform compression and generally outperformed ordinary steel specimens. The experimental P-M strength was much higher than the AISC nominal P-M strength. The measured residual stresses indicated that the impact of residual stress on inelastic buckling of high-strength steel is less. Cyclic seismic test results showed that HSA800 members have the potential to be used as non-ductile members or members with limited ductility demand in seismic load resisting systems. Finally, recent applications of 800 MPa high strength steel to highrise and mega building structures in Korea are briefly presented.

• Structural Engineering and Mechanics
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• v.62 no.2
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• pp.209-224
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• 2017

Elevated water tanks are considered as important structures due to its post-earthquake requirements. Elevated water tank on reinforced concrete frame staging is widely used in India. Different response reduction factors depending on ductility of frame members are used in seismic design of frame staging. The study on appropriateness of response reduction factor for reinforced concrete tank staging is sparse in literature. In the present paper a systematic study on estimation of key components of response reduction factors is presented. By considering the various combinations of tank capacity, height of staging, seismic design level and design response reduction factors, forty-eight analytical models are developed and designed using relevant Indian codes. The minimum specified design cross section of column as per Indian code is found to be sufficient to accommodate the design steel. The strength factor and ductility factor are estimated using results of nonlinear static pushover analysis. It was observed that for seismic design category 'high' the strength factor has lesser contribution than ductility factor, whereas, opposite trend is observed for seismic design category 'low'. Further, the effects of staging height and tank capacity on strength and ductility factors for two different seismic design categories are studied. For both seismic design categories, the response reduction factors obtained from the nonlinear static analysis is higher than the code specified response reduction factors. The minimum dimension restriction of column is observed as key parameter in achieving the desired performance of the elevated water tank on frame staging.

• Journal of Korean Association for Spatial Structures
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• v.23 no.1
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• pp.53-60
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• 2023

A bending experiment was conducted to verify the structural performance of the U-flange truss hybrid bean using rebars or steel pipes to reinforce the upper compression zone. As a result of evaluating the bending strength of the truss hybrid beam according to the Structural Design Standard (KDS 14 2020: 2022) by introducing the lattice member as a tensile resistance element, the following conclusions were obtained. Considering the lattice element as a tensile resistance element, the nominal bending strength was increased by 38.57 to 47.90 kN.m. As a result of reviewing the experiment as to whether the flexural member has proper ductility, it was found that it is desirable to place appropriate rebars, steel quality plans, and lateral restraints on the upper and lower parts of the hybrid beam to have sufficient ductility ratio.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2000.10a
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• pp.356-363
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• 2000

The objectives of this study are to investigate seismic performance of spirally reinforced bridge columns and to provide test result for developing improved seismic design criteria. Quasi-static test was conducted for 12 columns of which variables were transverse reinforcement ratio and spacing, longitudinal reinforcement ratio, and axial load level. Sufficient seismic performance was observed from the test for the columns with greater confinement steel amount than the requirement of the Korean Bridge Design Specification. The columns with 0.84% of the confinement steel requirement provided adequate performance under less than 0.2 of axial load level, but showed lower ductility under 0.3 of axial load level. The current provision for the region of confinement steel distribution may be non-conservative under high axial load level, therefore a modified provision is proposed.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2002.03a
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• pp.211-219
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• 2002

This study is performed to investigate the behavior of multi-column piers and to evaluate the seismic performance. In this study, 3 types of scale model piers with 2-column are designed and tested by quasi-static load in both longitudinal and transverse directions. Each type of model consisting of 2 specimens has different reinforcement details in the lap splice of longitudinal bars and amount of transverse reinforcements. This paper reports that the ductility of the model in transverse direction is rather higher than in longitudinal direction because of formation of several plastic hinges and that the ultimate displacement and the energy absorbtion capacity are enhanced by using continuous longitudinal bars instead of lap-splice ones. And it is confirmed that relatively large amount of ductility can be achieved by providing sufficient lap-splice length and transverse reinforcements with end hook even if longitudinal bars are lap spliced in the base of pier.

• Journal of Industrial Technology
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• v.17
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• pp.305-312
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• 1997

Shear connections in steel structures should satisfy dual criteria of shear strength and rotational flexibility and ductility. The connection should be strong enough to transfer the shear reaction of the beam, and should have sufficient rotational flexibility and ductility to rotate easily and supply the end rotation demand of the beam. This paper is concerned with the behavior of double-angle shear connections where the parameters are numbers of high strength bolts, bolt pitch, the length of angle leg, and connection method. An experimental investigation of shear connection was conducted by testing 12 beam-to-column joint specimens. Based on experimental and analytical study, the failure modes are developed and proposed design formulas.

• Journal of the Korea Concrete Institute
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• v.16 no.4 s.82
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• pp.573-579
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• 2004

For the fast construction and replacement of bridges in urban area, a prefabricated bridge system can be an excellent alternative. Details of prefabricated slabs for PSC girders were developed and static tests on shear connections were conducted to propose design equations of the shear connection. Stirrups and stud connectors were used as shear connectors and non-shrink mortar was used for the filling material in shear pockets for shear connectors. Stirrups and studs were fabricated to insert embedded nut-type devices in PSC girders. Shear strength of the shear connection considering chemical bond, friction and mechanical connectors was evaluated and empirical equations were suggested. Due to the mechanical connectors, ultimate slip capacity of the shear connection was sufficient for shear load redistribution, and suggested details of the shear connection showed good performance in terms of strength and ductility.