Jung-Han Yoo

Bio: Jung-Han Yoo is an academic researcher from Seoul National University of Science and Technology. The author has contributed to research in topics: Buckling & Braced frame. The author has an hindex of 8, co-authored 29 publications receiving 259 citations.

Seismic Performance of Pile-Wharf Connections

Abstract: Imports and exports are essential to our economy, but the wharf structures that accommodate this activity are susceptible to earthquake damage Wharves are pile supported structures, and the pile-wharf connection is an essential element of their seismic performance Either precast prestressed concrete piles with moment-resisting connections or steel batter piles are used to provide lateral resistance, but precast concrete piles are more common Little research has been performed on the seismic performance of these precast concrete pile-wharf connections Eight experiments evaluating the seismic performance of moment-resisting precast concrete pile-wharf connections are described The test specimens simulate the wide range of practice presently noted in wharf design These connections tolerate large cyclic inelastic deformations, but they also show significant deterioration in resistance and stiffness Extended pile connections are used when the pile is driven below deck level Precast concrete pile connections are stronger than extended pile sections, but they degrade more quickly Axial load on the pile also increases connection moment capacity but results in greater deterioration in resistance Analysis shows that this degradation in resistance significantly reduces the inelastic pushover resistance and increases the inelastic dynamic response demands of the system

Influence of gusset plate connections and braces on the seismic performance of X-braced frames

Abstract: Braced frames are one of the most economical and efficient seismic resisting systems yet few full-scale tests exist. A recent research project, funded by the National Science Foundation (NSF), seeks to fill this gap by developing high-resolution data of improved seismic resisting braced frame systems. As part of this study, three full-scale, two-story concentrically braced frames in the multi-story X-braced configuration were tested. The experiments examined all levels of system performance, up to and including fracture of multiple braces in the frame. Although the past research suggests very limited ductility of SCBFs with HSS rectangular tubes for braces recent one-story tests with improved gusset plate designs suggest otherwise. The frame designs used AISC SCBF standards and two of these frames designs also employed new concepts developed for gusset plate connection design. Two specimens employed HSS rectangular tubes for bracing, and the third specimen had wide flange braces. Two specimens had rectangular gusset plates and the third had tapered gusset plates. The HSS tubes achieved multiple cycles at maximum story drift ratios greater than 2% before brace fracture with the improved connection design methods. Frames with wide flange braces achieved multiple cycles at maximum story drift greater than 2.5% before brace fracture. Inelastic deformation was distributed between the two stories with the multi-story X-brace configuration and top story loading. Copyright © 2010 John Wiley & Sons, Ltd.

Axial loading tests and FEM analysis of slender square hollow section (SHS) stub columns strengthened with carbon fiber reinforced polymers

Abstract: This paper presents the experimental and analytical results of axially loaded stub columns of slender steel hollow square section (SHS) strengthened with carbon fiber reinforced polymers (CFRP) sheets. The total eight specimens were fabricated and the main parameters were: width-thickness ratio (b/t), the number of CFRP ply, and the CFRP sheet orientation. From the tests, it was observed that two sides would typically buckle outward and the other two sides would buckle inward. A maximum increase of 33% was achieved in axial-load capacity when 3 layers of CFRP were used to wrap HSS columns of b/t=100 transversely. Also, stiffness and was compared between un-retrofitted specimens and retrofitted specimens. To extend and better understand the experimental work, a companion analytical study (FEM study) was conducted. The comparisons between experimental observations and computed results show that the analyses provided good correlation to actual behavior.

Experimental investigation on strength and curling influence of bolted connections in thin-walled carbon steel

Abstract: Experimental studies regarding the influence of curling on the ultimate strength of cold-formed stainless steel bolted connections have been carried out by Kim et al. Basic data and modified equations for predicting the structural behaviors considering strength reduction due to curling through the finite element analysis method have also been suggested by previous researchers. In this paper, single shear bolted connections fabricated with four bolts and thin-walled carbon steel commonly utilized in light-weight structural members were tested to investigate the fracture mechanism and curling influence on the ultimate strength. Main variables for test specimen are plate thicknesses and end distances parallel to the direction of loading. Curling (out-of-plane deformation in the direction of plate thickness) also occurred in thin-walled carbon steel bolted connections with a large end distance and thinner plate like previous cold-formed stainless steel connections. The curling occurrence reduced suddenly the ultimate strength of single shear carbon steel bolted connections and the influence pattern of curling on strength was affected according to the plate thickness and end distance. Current design specifications for block shear strength with the combination of tensile fracture and shear fracture are summarized and the ultimate strengths of test results are compared to the predicted design strengths. AISI (American Iron and Steel Institute) and EC3 (Eurocode 3) made conservative estimates of ultimate strength for thin-walled carbon steel bolted connections with no curling, whereas AIJ (Architectural Institute of Japan) and SSBA(Stainless Steel Building Association) manuals provided a good prediction for ultimate strength and fracture mode. Modified strength equations were recommended respectively for bolted connections with typical block shear fracture considering shear stress factor and severe curling accompanied by strength reduction.

Local buckling in the stub columns fabricated with HSA800 of high performance steel

Abstract: Recently, high-performance steels have been increasingly used for structural materials in buildings and bridges with the demand for high-rise and long-span of main structures This paper is a series of basic study for the design specification of structural members using new high-performance steel with the material properties of HSA800 (High-performance Steel having tensile strength of 800 MPa for building structures) The steel stub columns of built-up H-section and square hollow section with various width-to-thickness ratios are experimentally planned to investigate the local buckling behaviors and then to check their current design limits The nonlinear three-dimensional finite element models are also constructed to verify the experimental results The present experimental results are seen to closely agree with those from finite element analysis In addition, the verified finite element models are used for extensive parametric studies to check up the applicability of highstrength steel in current design specification

A Beam-Column Joint Model for Simulating the Earthquake Response of Reinforced Concrete Frames

Abstract: .............................................................................................................................iii ACKNOWLEDGMENTS..........................................................................................................iv TABLE OF CONTENTS............................................................................................................v LIST OF FIGURES ..................................................................................................................vii LIST OF TABLES.....................................................................................................................ix

A balanced design procedure for special concentrically braced frame connections

Abstract: Concentrically braced frames (CBFs) are stiff, strong structures that are suitable for resisting large lateral loads. Special CBFs (SCBF) are used for seismic design and are designed and detailed to sustain relatively large inelastic deformations without significant deterioration in resistance. Current AISC Seismic Design Provisions aim to ensure the brace sustains the required inelastic action, but recent research showed that current SCBF design requirements lead to variable seismic performance, unintended failure modes, and limited deformation capacity. To improve the seismic response of SCBFs, a balanced design procedure was proposed. The premise of the design methodology is to balance the primary yield mechanism, brace buckling and yielding, with other, complementary ductile yielding mechanisms, such as gusset plate yielding. This balance process maximizes ductile yielding in the frame thereby maximizing the drift capacity of the frame. Further, the undesirable failure modes are balanced with the yield mechanisms and the preferred failure mode, brace fracture, to ensure that the frame fails in the desired manner. To achieve the objectives of the design methodology namely maximum drift capacity, and adherence to a desired yield and failure hierarchy, rational resistance checks and appropriate balance factors (β factors) are used to balance each yield mechanism and failure mode. These factors were developed, validated, and refined using the measured results from an extensive test program. An SCBF connection design example to illustrate the application of the balanced design method and to demonstrate differences from the current AISC design method is presented in an appendix.

Machine Learning–Based Failure Mode Recognition of Circular Reinforced Concrete Bridge Columns: Comparative Study

Abstract: The prediction of failure mode of columns is critical in deciding the operational and recovery strategies of a bridge after a seismic event. This paper contributes to the critical need of f...

Structural response and continuous strength method design of slender stainless steel cross-sections

Abstract: In current structural stainless steel design codes, local buckling is accounted for through a cross-section classification framework, which is based on an elastic, perfectly-plastic material model, providing consistency with the corresponding treatment of carbon steel cross-sections. Hence, for non-slender cross-sections, the codified design stress is limited to the 0.2% proof stress without considering the pronounced strain hardening exhibited by stainless steels, while for slender cross-sections, the effective width method is employed without considering the beneficial effect of element interaction. Previous comparisons between test results and codified predictions have generally indicated over-conservatism and scatter. This has prompted the development of more efficient design rules, which can reflect better the actual local buckling behaviour and nonlinear material response of stainless steel cross-sections. A deformation-based design approach called the continuous strength method (CSM) has been proposed for the design of stocky cross-sections, which relates the strength of a cross-section to its deformation capacity and employs a bi-linear (elastic, linear hardening) material model to account for strain hardening. In this paper, the scope of the CSM is extended to cover the design of slender stainless steel cross-sections under compression, bending and combined loading, underpinned by and validated against 794 experimental and numerical results. The proposed approach allows for the beneficial effect of element interaction within the cross-section, and is shown to yield a higher level of accuracy and consistency, as well as design efficiency, in the capacity predictions of slender stainless steel cross-sections, compared to the effective width methods employed in the current international design standards. Non-doubly symmetric sections in bending, which may be slender, but still benefit from strain hardening, are also discussed. The reliability of the CSM proposal has been confirmed by means of statistical analyses according to EN 1990, demonstrating its suitability for incorporation into future revisions of international design codes for stainless steel structures.

Modeling of Unreinforced Masonry Infill Walls Considering In-Plane and Out-of-Plane Interaction

Abstract: This paper describes a practical analytical model which can be used for the seismic evaluation of unreinforced masonry (URM) infill walls located within a reinforced concrete (RC) frame. The model, consisting of diagonal beam-column members utilizing fiber-element cross sections, is suitable for use in nonlinear time history analyses. The model considers both the in-plane (IP) and the out-of-plane (OOP) responses of the infill, as well as any chosen convex interaction between IP and OOP capacities. The behaviour is elastoplastic, and limit states may be defined by deformations or ductilities in the two directions. These limit states may be chosen to conform to code guidelines or they may be developed independently by the engineer. The model is composed of elements available in commonly used structural analysis software programs. The performance of the model is shown to be satisfactory for static pushover and dynamic analyses using a single panel structure. The proposed infill model is incorporated into a five-storey RC moment frame building with URM infill walls. It is subjected to 20 sets of ground acceleration time histories at five different levels of spectral acceleration. Collapse of the infill panel is assumed to occur at critical displacement ductilities in the IP and OOP directions with interaction between the ductilities considered. Fragility functions, giving the probability of collapse as a function of spectral acceleration level, are calculated and discussed.