Namhee Kim Hong

Computer-supported evaluation for seismic performance of existing buildings

A seismic performance evaluation is one of the highly complicated multi-criteria evaluation problems. This study presents a hierarchy of performance criteria that consists of performance categories such as strength, stiffness, configuration, and age of structures at a higher level while their subcategories considering the capacity of subsystems and components at lower levels mainly focus on the stage of preliminary evaluation. Two methods for determination of performance index are proposed; a simple composition method and a fuzzy inference method. Both methods use weighting factors to represent relative importance of multi-criteria in the determination of performance index. The simple composition method that operates on definite index values and assumes independence between performance criteria is easy to use but difficult to address the cases where complicity and uncertainty are of important problems. The fuzzy inference system uses fuzzy concepts where uncertainties are inherently unavoidable due to insufficient information and engineering assumption and exploits fuzzy rules in the multi-criteria evaluation by replicating heuristic knowledge and experience in logic-based descriptive rules. Moreover, the single performance index obtained by defuzzification enables us to draw a representative and comprehensive seismic performance index from a set of individual performance indexes at multi-levels.

Application of entity-based approach for unified representation of design alternatives for structural design

Abstract To support the design process fully from preliminary to detailed design stages in a natural way, a computer-integrated design system is needed. In early design stages more than one design alternatives are considered as possible solutions. The representation of design alternatives must be uniform and unbiased to be equally treated. In this study, an entity-based approach has been adopted to develop product and process models for representing design alternatives, which is more desirable for top–down design process because it allows high-level abstraction in representing design information and design activities. The entity-based approach has several benefits: (1) a unified representation of design alternatives; (2) a consistent development of product and process models based on the entity-based concepts; and (3) an easy integration of the product and process models. The work toward product and process models for structural design presented in this paper is a useful step toward integrated computer-aided design systems.

Deformation Capacity of Structural Concrete in Disturbed Regions

The design of structural concrete in disturbed regions such as shear critical members with limited ductility should be based on a realistic estimation of the deformation capacity. The deformation capacity of structural concrete, which is mostly controlled by the ultimate compressive strain of concrete regardless of whether the reinforcement yields, is estimated on the construction of bending and translational and rotational failure mechanisms for compression struts. This study presents a novel methodology for estimating the deformation capacity of structural concrete in disturbed regions that is based on the principle of the limit analysis and uses failure mechanisms compatible with strut-and-tie models. The proposed model reasonably estimates the deformation capacity of deep beams and coupling beams relying on diagonal struts for shear transfer that fail due to the crushing of the struts.

Toward a Balanced Heritage Management Plan for Old Stone Bridges Considering the Embedded Cultural Significance

Old stone bridges in Korea are becoming short of safety while their cultural significance is becoming more important. Unlike existing modern bridges requiring strengthening mainly for structural safety, old stone bridges must be treated from both the points of view of historic significance and safety to advocate for the preservation of cultural and engineering landmarks–monuments for the people and communities. Therefore, engineers must balance preservation principles demanding authenticity of materials and visual characteristics with code requiring safety, strength, and stability and historic significance for the maintenance of historic bridges. This article proposes a framework for developing management plans for old stone bridges to consider cultural significance values as decision variables. To verify the concepts proposed in this article, a case study was simulated for the Supyo Bridge management plan, which is under consideration by the office of Seoul Metropolitan cultural heritage.

Hysteretic Behavior of Korean Traditional Wooden Frames

The objective of this paper is to provide basic information on structural behavior of Korea traditional wooden frames under earthquake loading. One of prototype wooden frames for this study was chosen from a designated national treasure in Korea. A series of experimental work were prepared to investigate the behavior and hysteresis characteristics of traditional wooden frames under cyclic lateral loading. Three test specimens of a full scale were performed for cyclic hysteretic behaviors based on one static test specimen as a pilot test. The experimental observation showed stiffness degradations and slips after experiencing initial yield point and the first cycle at a new larger displacement due to inherent gaps in connections between columns and connection parts of beams and a gradual indentation of interfaces under pull and push. Addition of structural components such as an upper beam and clay-filled wall to the basic beam and columns increased the initial stiffness, strength and energy dissipation than those of basic frames. The behaviors of the wooden frames were simulated by DRAIN-2DX program for the dynamic analysis of an entire wooden frame system. Comparison between analysis models and the experimental behaviors showed that the behavior of wooden frames under consideration could be represented by a combination of link and truss elements. The maximum response of a wooden frame system under three earthquakes showed a safe behavior for a potential earthquake.

Shear Strength of UHPFRC Beams Without Stirrups: Fracture Mechanics Approach

Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) has outstanding capacity in post-cracking phase with residual tensile strength and a large tensile strain. The stress redistribution after dispersed crack formation enhances shear strength of UHPFRC I-beams. This paper investigates in-plane shear behavior in the web of UHPFRC I-beams without stirrups of varying shear span ratio and beam depths. And this study proposes a new parameter to relate the stress redistribution capacity at material level and structural performance as structural level in terms of characteristic length. From the test results, all specimens for shear strength were found to fail by critical crack localization in the diagonal crack zones. The tensile behavior of UHPFRC at material level is necessary to understand UHPFRC structural behavior which fails by crack localization. Thereby fracture mechanics approach may lead to more reasonable explanation. Characteristic length representing a hardening tensile behavior of UHPFRC is defined as one of representative parameters for fracture behavior. In this paper the effective length of concrete tension strut in diagonal crack zone is suggested as a characteristic length for structural element with a new brittleness factor. The shear strength equation for UHPFRC beam without stirrup is proposed using the lower bound approach with the brittleness factor based on fracture mechanics.