• Structural Engineering and Mechanics
• /
• v.74 no.2
• /
• pp.267-282
• /
• 2020

The seismic performance and failure modes of the dual system of moment resisting frames and thin steel plate shear walls (TSPSWs) without and with one or two outrigger trusses are studied in this paper. These structural systems were utilized to resist vertical and lateral loads of 40-storey buildings. Detailed Finite element models associated with nonlinear time history analyses were used to examine seismic capacity and plastic mechanism of the buildings. The analyses were performed under increased levels of earthquake intensities. The models with one and two outriggers showed good performance during the maximum considered earthquake (MCE), while the stress of TSPSWs in the model without outrigger reached its ultimate value under this earthquake. The best seismic capacity was in favour of the model with two outriggers, where it is found that increasing the number of outriggers not only gives more reduction in lateral displacement but also reduces stress concentration on thin steel plate shear walls at outrigger floors, which caused the early failure of TSPSWs in model with one outrigger.

• Journal of Korean Society of Steel Construction
• /
• v.20 no.5
• /
• pp.625-632
• /
• 2008

In the companion paper (Model Development), an analytical model estimating the available rotation capacity of fully restrained beam-column connections in special steel moment-resisting frames was proposed. In this paper, two limit states were considered as the connection rotation capacity criteria: (i) strength degradation failure when the strength falls below the nominal plastic strength due to the local buckling of the beam's cross-section and (ii) low-cycle fatigue fracture caused by plastic strain accumulation at the buckled flange after only a few cycles of high-amplitude deformation. A series of analyses are conducted using the proposed model with two limit states under monotonic and cyclic loadings. Beam section geometric parameters, such as flange and web slenderness ratios, varied over the practical ranges of H-shapedbeams to observe their effect on the rotation capacity and low-cycle fatigue life of pre-qualified WUF-W connections.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.10 no.5 s.51
• /
• pp.85-97
• /
• 2006

Capacity design is to guarantee ductile failure of whole bridge system by preventing brittle failure of columns and any other structural elements until the columns develope fully enough plastic deformation capacity. This concept has been explicitly regulated in most bridge design specifications of foreign countries except the current Korea Bridge Design Specifications. In the capacity design, the transformed shear force from flexural overstrength of reinforced concrete column is used as the design lateral shear force for shear design of columns and design of footings and piles. Different calculating methods are adopted by the design specifications, since the variability of material strength and construction circumstances of the local regions should be considered. This paper proposed material overstrength factors by investigating 3,407 reinforcing bar data and 5,405 concrete compressive strength data collected in Korean construction sites. It also proposed calculating procedures for flexural overstrength of reinforced concrete columns using the material overstrength. Finally, overstrength factor was proposed as 1.5 by investigating 1,500 column section data from moment-curvature analysis using the material overstrength.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2010.09a
• /
• pp.3-25
• /
• 2010

The paper deals with two bearing capacity problems of shallow footing under combined loading. The first is a FEM study of shallow strip footing on two-layer clay deposits subjected to a vertical, horizontal and moment combined loading, while the second is a centrifuge study of shallow rectangular footing on dry sand under double eccentricity. The FEM results revealed that the existence of top soft layer sensitively affects more on horizontal and moment capacity than vertical capacity for cases of footing on soft clay overlying stiff clay. Practical design charts are presented to evaluate bearing capacities of footing for various combinations of the ratio of the depth of the upper layer to the footing width and the ratio of undrained strength of the upper layer to that of the lower. The centrifuge tests indicated that current design practice of calculating failure load of rectangular surface footing under double eccentricity underestimates the centrifuge loading test data. This trend is more marked when the eccentricity becomes larger. The decreasing trend in failure load with an increase of double eccentricity is rather uniquely expressed by a single curve, using a newly defined resultant eccentricity and the diagonal length of the footing base.

• International Journal of High-Rise Buildings
• /
• v.3 no.3
• /
• pp.231-241
• /
• 2014

Ductile fracture is one of the most common failure modes of steel beam-to-column connections in moment resisting frames. Most proposed evaluation methods of the plastic deformation capacity of a beam until ductile fracture are based on steel beam tests, where the material's yield strength/ratio, the beam's moment gradient, and loading history are the most important parameters. It is impossible and unpractical to cover all these parameters in real tests. Therefore, a new attempt to evaluate a beam's plastic deformation capacity through analysis is introduced in this paper. Another important issue is about the loading histories. Recent years, the effect on the structural component under long-duration ground motion has drawn great attentions. Steel beams tends to experience a large number of loading cycles with small amplitudes during long-duration earthquakes. However, current research often focuses on the beam's behavior under standard incremental loading protocols recommended by respective countries. In this paper, the plastic deformation capacity of steel beams subjected to long duration ground motions was evaluated through analytical methodology.

• Proceedings of the Earthquake Engineering Society of Korea Conference
• /
• 2005.03a
• /
• pp.308-315
• /
• 2005

The capacity protection is normally related with slenderness effect of the columns, force transfer in connections between columns and adjacent elements, and shear design of columns. It is intends to prevent brittle failure of the structural components of bridges, so that the whole bridge system may show ductile behavior and failure during earthquake events. For bridge systems, this means it is necessary to assess the overstrength capacity of columns prior to proceeding with the design of foundation and superstructure. The objective of this paper is to develop a capacity design approach that applies an overstrength factor for determination of possible maximum shear force in the plastic hinge zone of reinforced concrete bridge columns. In order to estimate and determine overstrength factor, material strength was developed to investigate for actual material strength total 3,407 steel and 5,405 concrete by domestic product. Based on actual material strength, this paper was conducted on moment overstrength factors using moment-curvature analysis program. And also design recommendations for capacity design are presented to revise the annual report, KEERC 2002.

• Earthquakes and Structures
• /
• v.8 no.3
• /
• pp.591-617
• /
• 2015

Standards for seismic assessment and retrofitting of buildings provide deformation limit states for structural members and connections. However, in order to perform fully consistent performance-based seismic analyses of soil-structure systems; deformation limit states must also be available for foundations that are vulnerable to nonlinear actions. Because such limit states have never been established in the past, a laboratory testing program was conducted to study the rotational capacity of small-scale foundation models under combined axial load and moment. Fourteen displacement-controlled monotonic and cyclic tests were performed using a cohesionless soil contained in a $2.0{\times}2.0{\times}1.2m$ container box. It was found that the foundation models exhibited a stable hysteretic behavior for imposed rotations exceeding 0.06 rad and that the measured foundation moment capacity complied well with Meyerhof's equivalent width concept. Simplified code-based soil-structure analyses of an 8-story building under an array of strong ground motions were also conducted to preliminary evaluate the implication of finite rotational capacity of vulnerable foundations. It was found that for the same soil as that of the experimental program foundations would have a deformation capacity that far exceeds the imposed rotational demands under the lateral load resisting members so yielding of the soil may constitute a reliable source of energy dissipation for the system.

• Steel and Composite Structures
• /
• v.10 no.4
• /
• pp.361-371
• /
• 2010

Enhancement in the seismic buckling capacity of steel tanks caused by the addition of fiber reinforced polymers (FRP) retrofit layers attached to the outer walls of the steel tank is investigated. Three-dimensional non-linear finite element modeling is utilized to perform such analysis considering non linear material properties and non-linear large deformation large strain analysis. FRP composites which possess high stiffness and high failure strength are used to reduce the steel hoop stress and consequently improve the tank capacity. A number of tanks with varying dimensions and shell thicknesses are examined using FRP composites added in symmetric layers attached to the outer surface of the steel shell. The FRP shows its effectiveness in carrying part of the hoop stresses along with the steel before steel yielding. Following steel yielding, the FRP restrains the outward bulging of the tank and continues to resist higher hoop stresses. The percentage improvement in the ultimate base moment capacity of the tank due to the addition of more FRP layers is shown to be as high as 60% for some tanks. The percentage of increase in the tank moment capacity is shown to be dependent on the ratio of the shell thickness to the tank radius (t/R). Finally a new methodology has been explained to calculate the location of Elephant foot buckling and consequently the best location of FRP application.

• Structural Engineering and Mechanics
• /
• v.87 no.2
• /
• pp.151-164
• /
• 2023

The latest earthquake's costly repairs and economic disruption were brought on by excessive residual drift. Self-centering systems are one of the most efficient ways in the current generation of seismic resistance system to get rid of and reduce residual drift. The mechanics and behavior of the self-centering system in response to seismic forces were impacted by a number of important factors. The amount of post-tensioning (PT) force, which is often employed for the standing posture after an earthquake, is the first important component. The energy dissipater element is another one that has a significant impact on how the self-centering system behaves. Using the damper as a replaceable and affordable tool and fuse in self-centering frames has been recommended to boost energy absorption and dampening of structural systems during earthquakes. In this research, the self-centering steel moment frame connections are equipped with cushion flexural dampers (CFDs) as an energy dissipator system to increase energy absorption, post-yielding stiffness, and ease replacement after an earthquake. Also, it has been carefully considered how to reduce permanent deformations in the self-centering steel moment frames exposed to seismic loads while maintaining adequate stiffness, strength, and ductility. After confirming the FE model's findings with an earlier experimental PT connection, the behavior of the self-centering connection using CFD has been surveyed in this study. The FE modeling takes into account strands preloading as well as geometric and material nonlinearities. In addition to contact and sliding phenomena, gap opening and closing actions are included in the models. According to the findings, self-centering moment-resisting frames (SF-MRF) combined with CFD enhance post-yielding stiffness and energy absorption with the least amount of permeant deformation in a certain CFD thickness. The obtained findings demonstrate that the effective energy dissipation ratio (β), is increased to 0.25% while also lowering the residual drift to less than 0.5%. Also, this enhancement in the self-centering connection with CFD's seismic performance was attained with a respectable moment capacity to beam plastic moment capacity ratio.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2006.05a
• /
• pp.190-193
• /
• 2006

The definition of the Dual system is that the total seismic force resistance is to be provided by the combination of the moment frame and the shear walls or braced frames in proportion to their stiffness and the moment frame shall be capable of resisting at least 25% of the design force in Korean Building Code 2005 (KBC 2005). But, the definition of moment frame is ambiguous whether the moment frame include the imaginary columns in the shear wall (Case I) or include only the columns outside the shear wall (Case II). 60-story RC building was designed as dual system for Case I and Case II, and the required strength and reinforcement are compared. Moment and axial capacity of the shear wall of Case II decreased about 5% due to the absence of the column in the shear wall. The requirement of upper and bottom reinforcement of slab in Case II increased 13% and 40%, respectively, when compared to those of Case I. The required longitudinal reinforcement in columns for Case II is about 1.5 times larger than that of Case I.