Dong-Guen Lee

Analysis of shear wall with openings using super elements

The box system that consists of reinforced concrete walls and slabs is adopted for many high-rise apartment buildings recently constructed. In an apartment building, shear walls may have one or more openings for functional reasons. Some researches on the analysis of shear wall with openings were performed, but some restrictions prevent those research results from being applied to the practical analysis and design procedure. It is necessary to use fine mesh finite element models for an accurate analysis of a box system structure with openings. But it would take a significant amount of computational time and memory if the entire building structure were subdivided into a finer mesh. An efficient analysis method that can be used regardless of the number, size and location of openings is proposed in this study. The analysis method uses super elements developed using the matrix condensation technique. Static and dynamic analyses of example structures having various types of openings were performed to verify the efficiency and accuracy of the proposed method. The analyses of example structures demonstrated that the proposed method can be used for the analysis of a shear wall structure with openings. Outstanding accuracy in analysis could be achieved with drastically reduced computational time and memory.

Efficient seismic analysis of high-rise building structures with the effects of floor slabs

Box system structures, composed of only reinforced concrete walls and slabs, have been recently adopted for many high-rise apartment buildings. Commercial software such as ETABS, commonly used for the analysis of high-rise apartment buildings, assumes a rigid diaphragm for floor slabs. The flexural stiffness of slabs is generally ignored in the analysis. This assumption may be reasonable for the analysis of framed structures. In box system structures like apartment buildings, however, the floor slabs may have a significant influence on the lateral response of the structures. If the flexural stiffness of slabs in a box system structure is totally ignored, the lateral stiffness may be significantly underestimated. In reality, the cracked section property of a slab will determine the amount of its flexural stiffness that will be included in the analysis. In order to include the flexural stiffness of slabs, the slab needs to be modeled with plate elements. If the slab is subdivided into many plate elements while keeping each shear wall with a large element (as generally modeled with commercial software), the compatibility condition will not be satisfied at the interface of the slab and the shear wall. To enforce the compatibility condition at the interface, a fictitious beam is introduced. It would cost a significant amount of analysis time and computer memory to model the floor slab with many subdivided plate elements in every floor of a high-rise building. In this study, an efficient method is proposed to analyze high-rise box system structures considering the effects of floor slabs. The proposed method will reduce computational time and memory in the analysis by using the substructuring technique and matrix condensation.

Vertical distribution of equivalent static loads for base isolated building structures

It has been pointed out that the static lateral response procedure for a base isolated structure presented in UBC-97 somewhat overestimates the seismic story force. In this study the UBC-91 and UBC-97 static lateral load procedures for isolated structures are investigated, and a new formula is proposed for the vertical distribution of seismic load. The formula is derived by combining the fundamental mode shape of the isolated structure idealized as two degrees of freedom system and the fundamental mode shape of a fixed-based structure. The seismic story forces resulting from the proposed method are compared with those obtained from dynamic time history analysis and the code procedures. The results show that the proposed method provides conservative results compared with those from dynamic analysis and UBC-91 approach, and produces a more economic solution compared with the UBC-97 static lateral response procedure.

Efficient siesmic analysis of building structures with added viscoelastic dampers

Conventional analysis methods for building structures with added viscoelastic dampers, such as direct integration, complex mode superposition, and modal strain energy method, were compared, and a procedure based on rigid diaphragm assumption and matrix condensation technique was proposed for application in the preliminary analysis and design stages. The results from the various analysis methods with and without the matrix condensation were compared, in view of both accuracy and efficiency. According to the eigenvalue analysis the major vibration modes were mostly preserved after the matrix condensation. It was also found that the matrix condensation technique applied to dynamic analysis of a structure with added viscoelastic dampers provided quite accurate results in significantly reduced time, regardless of the plan shape and the location of the viscoelastic dampers.

Performance Evaluation of Floor Vibration of Biaxial Hollow Slab Subjected to Walking Load

국문 요약 >> 2방향 중공슬래브 시스템은 슬래브 두께가 증가해도 자중은 크게 증가하지 않으면서 솔리드 슬래브에 비해서 휨강성이 크게 저하되지 않는 장점이 있다. 따라서 최근 넓은 바닥판 구조에 대한 수요가 커지면서 2방향 중공슬래브 시스템에 대한 관심이 증가하 고 있다. 그러나 이러한 장스팬 구조의 경우 바닥판 진동의 증가에 의한 사용성에 문제가 발생할 수 있고 특히 2방향 중공슬래브의 경우 기존의 구조시스템과 동적특성이 상이하다. 따라서 본 연구에서는 기존의 라멘조 시스템과 2방향 중공슬래브 시스템의 바닥진동성능을 보행하중을 가하여 검토해 보았다. 본 연구에서는 해석의 효율성을 위하여 2방향 중공슬래브의 동적특성을 정확히 나타낼 수 있는 등가의 플레이트 모델을 사용하여 시간이력해석을 수행하였다. 해석결과를 바탕으로 일본건축학회와 미국표준협회에서 제안하는 진동성능평가 기준을 이용하여 진동성능 평가를 수행한 결과 2방향 중공슬래브가 사무실 수준의 진동성능을 만족하고 있는 것으로 나타났다.

An equivalent model for the seismic analysis of high-rise shear wall apartments

Currently in the country, the necessity of seismic analyses is increasing due to the increase of demand and interest in seismic design. Especially, shear wall apartments are constructed mostly for a residental building so seismic analyses for the apartment are actively executed. For the seismic analysis of the shear wall apartment, it may be not efficient in time and effort to model the entire structure by a finite element mesh. Therefore, an equivalent model is needed to simulate the dynamic behavior of the structure by decreasing the number of degrees of freedom. In this study, a method to form an equivalent model that is simple and easy to use was proposed utilizing effective mass coefficient that is highly correlated to mode shape of the structure. This equivalent model was obtained by replacing a shear wall structure with an equivalent frame structure having beams and columns. This model can be used very effectively when excessive seismic analyses are necessary in a short period because it can be operated in any commercial program and reduce the analysis time. Also, it can model floor slabs so it can represent the actual behavior of shear wall apartments. Furthermore, it is very excellent since it can represent the asymmetry of the structure.

Evaluation of Seismic Behavior for RC Moment Resisting Frame with Masonry Infill Walls

Masonry infill walls are frequently used as interior partitions and exterior walls in low- or middle- rise RC buildings. In the design and assessment of buildings, the infill walls are usually treated as non-structural elements and they are ignored in analytical models because they are assumed to be beneficial to the structural responses. Therefore, their influences on the structural response are ignored. In the case of buildings constructed in the USA in highly seismic regions, infill walls have a lower strength and stiffness than the boundary frames or they are separated from the boundary frames. Thus, the previously mentioned assumptions may be reasonable. However, these systems are not usually employed in most other countries. Therefore, the differences in the seismic behaviors of RC buildings with/without masonry infill walls, which are ignored in structural design, need to be investigated. In this study, structural analyses were performed for a masonry infilled low-rise RC moment-resisting frame. The infill walls were modeled as equivalent diagonal struts. The seismic behaviors of the RC moment-resisting frame with/without masonry infill walls were evaluated. From the analytical results, masonry infill walls can increase the global strength and stiffness of a structure. Consequently, the interstory drift ratio will decrease but seismic forces applied to the structure will increase more than the design seismic load because the natural period of the structure decreases. Partial damage of the infill walls by the floor causes vertical irregularity of the strength and stiffness.

Seismic Design of Structures in Low Seismicity Regions

Seismic design codes are developed mainly based on the observation of the behavior of structures in the high seismicity regions where structures may experience significant amount of inelastic deformations and major earthquakes may result in structural damages in a vast area. Therefore, seismic loads are reduced in current design codes for building structures using response modification factors which depend on the ductility capacity and overstrength of a structural system. However, structures in low seismicity regions, subjected to a minor earthquake, will behave almost elastically because of the larger overstrength of structures in low seismicity regions such as Korea. Structures in low seismicity regions may have longer periods since they are designed to smaller seismic loads and main target of design will be minor or moderate earthquakes occurring nearby. Ground accelerations recorded at stations near the epicenter may have somewhat different response spectra from those of distant station records. Therefore, it is necessary to verify if the seismic design methods based on high seismicity would he applicable to low seismicity regions. In this study, the adequacy of design spectra, period estimation and response modification factors are discussed for the seismic design in low seismicity regions. The response modification factors are verified based on the ductility and overstrength of building structures estimated from the farce-displacement relationship. For the same response modification factor, the ductility demand in low seismicity regions may be smaller than that of high seismicity regions because the overstrength of structures may be larger in low seismicity regions. The ductility demands in example structures designed to UBC97 for high, moderate and low seismicity regions were compared. Demands of plastic rotation in connections were much lower in low seismicity regions compared to those of high seismicity regions when the structures are designed with the same response modification factor. Therefore, in low seismicity regions, it would be not required to use connection details with large ductility capacity even for structures designed with a large response modification factor.

Development of Efficient Seismic Analysis Model using 3D Rigid-body for Wall-Frame Structures with an Eccentric Core

In a shear wall-frame structural system, the structural response is determined by the interaction between the shear wall in bending mode and the frame in shear mode. In order to effectively consider these characteristics of a shear wall-frame structure, the simplified numerical model using the T-shape rigid body was suggested in the previous study. Based on the previously proposed model, an efficient numerical model for a wall-frame structure with an eccentric core has been proposed in this study. To this end, the previously proposed 2D model is extended to the 3D model and it is enhanced by considering torsion effects. As a result, the enhanced model can be applied to the analysis of a wall-frame structure with an eccentric core as well as a centric core.

Development of Efficient Seismic Analysis Model using 2D T-Shape Rigid-body for Wall-Frame Structures with a Central Core

Abstract In this study, an efficient analytical model for the dynamic analysis of tall buildings with a shear wall-frame structural system has been proposed. A shear wall-frame structural system usually consists of a core wall showing flexural behavior and a frame presenting shear behavior. Therefore, the deformed shape of the shear wall-frame structural system is shown by the combination of flexural mode and shear mode. These characteristics should be considered when an efficient analytical model is developed. To this end, the effect of shear wall and frame on the dynamic behavior of a tall building with a dual system has been separately investigated. In this study, the structural characteristics of a separated individual shear wall model and the frame model without shear wall has been evaluated. In order to consider the effect of the shear wall in the frame model without shear wall, a rigid body was used instead of the shear wall. Each equivalent model for the separated shear wall part and frame part has been independently developed and two equivalent models were then combined to create an efficient analytical model for tall buildings with a shear wall-frame structural system. In order to verify the efficiency and accuracy of the proposed method, time history analyses of tall buildings with a shear wall-frame system were performed. Based on analytical results, it has been confirmed that the proposed method can provide accurate results, requiring significantly reduced computational time and memory