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Behavior of Bolted Circular Flange Connections Subject to Tensile Loading
Yail J. Kim,Murty K. S. Madugula 한국강구조학회 2010 International Journal of Steel Structures Vol.10 No.1
This paper presents the tensile behavior of bolted circular flange connections that represent typical connectivity of leg members in a steel guyed lattice communication tower. A total of twelve specimens have been tested to failure under increasing monotonic tension. Each test specimen consists of a pair of circular flange plates (Φ178 mm), where each plate is welded to a solid circular bar. The flanges are bolted back-to-back using two high-strength bolts located 180o apart. The focus of the experiment includes the development of gaps between the upper and lower flanges connected with ASTM A325 bolts (Φ16mm), increase in bolt forces, and prying action. The development of gaps between the flanges is significantly influenced by the size of leg members. The increase in the bolt force at failure is approximately 40%, relative to the initial preload of 110kN. The maximum prying force is observed at the preload level and the prying force decreases gradually as the flanges are further loaded, indicating a complete separation of the upper and lower flanges. The widely used T-stub design equations conservatively predict the behavior of bolted circular flange connections. The proposed predictive equations agree well with the test data, especially near the failure of the bolts.
Multiscale Modeling of Concrete in Anchorage Region of Post-Tensioned NSM CFRP
Kim, Yail J.,Ji, Yongcheng,Chang, Wei-Tze,Kang, Jae-Yoon,Park, Jong-Sup,Jung, Woo-Tai American Concrete Institute 2016 ACI structural journal Vol.113 No.6
<P>This paper presents a multiscale modeling approach to understand the behavior of anchorage concrete in prestressed concrete bridge girders strengthened with post-tensioned near-surfacemounted (NSM) carbon fiber-reinforced polymer (CFRP) strips. The macroscale, mesoscale, and microscale responses of the concrete are represented by continuum finite element, discrete-object physics, and analytical representative element models, respectively. Domain decomposition and integration are implemented in accordance with an information-passing mechanism. The post-tensioned NSM CFRP results in macroscale strain softening near the anchorage and it also causes a regional net strain increase responsible for macroscale and microscale damage. The existence of a rapid crack-propagation phase is ascertained in the anchorage concrete from a mesoscale standpoint, which influences stress transfer from the anchor bolt to the contiguous concrete. The microscale damage of the concrete rapidly propagates when mechanical distress is applied due to post-tensioning the NSM CFRP and stabilizes with a decrease in stress transfer from the cementitious binder to aggregate inclusion in the representative element. The concept of effective stress is proposed to link the macroscale and microscale responses of the anchorage concrete.</P>
Recent Advances in Ultra-high Performance Concrete
Kim, Yail J. Korean Recycled Construction Resources Institute 2013 한국건설순환자원학회 논문집 Vol.1 No.3
This paper presents a comprehensive review of recent advances in ultra-high performance concrete (UHPC). Fundamental characteristics of UHPC are elaborated with focus on its material constituents, mixing, and formulation procedures. Use of state-of-the-art materials such as carbon nanotubes or nano-silica is discussed as well, whose inclusion may enhance the performance of UHPC. The review evaluates supplementary treatment methods (e.g., pressuring curing) and identifies applicable standard test methods for determining the properties and behavior of UHPC. Site implementation is provided to link laboratory research with full-scale application. Research needs are suggested to further develop UHPC technologies from technical and socio-economical perspectives.
Kim, Yail J.,Kang, Jae-Yoon,Park, Jong-Sup,Jung, Woo-Tai American Society of Civil Engineers 2016 Journal of bridge engineering Vol.21 No.1
<P>This paper presents the effect of corrosion damage on the service response of prestressed concrete bridge girders strengthened with posttensioned near-surface-mounted (NSM) carbon fiber-reinforced polymer (CFRP) strips. Three-dimensional finite-element modeling, validated against experimental data, is conducted to deterministically study the static and dynamic behavior of the girders subjected to chloride-induced corrosion for a period of 100 years. With an increase in corrosion damage, the efficacy of the posttensioned NSM CFRP augments from a serviceability perspective. Modal analysis identifies critical regions along the girder where strain localization occurs at certain dynamic excitation frequencies. The unstrengthened girders are more reactive to dynamic responses than their strengthened counterparts; however, both exhibit similar ride quality. Corrosion damage significantly decreases the equivalent flexural rigidity of the decrepit girders up to 30% relative to that of the control girders. The level of damage and the extent of the total potential for the strengthened girders are correlated with the magnitude of their fundamental frequencies. (c) 2015 American Society of Civil Engineers.</P>
Composite Strips with Various Anchor Systems for Retrofitting Concrete Beams
Isamu Yoshitake,Yail J. Kim,Keiyu Yumikura,Yoichi Mimura 한국콘크리트학회 2011 International Journal of Concrete Structures and M Vol.5 No.1
This paper presents the performance of anchor systems for reinforced concrete beams retrofitted with carbon fiber reinforced polymer (CFRP) strips. Nine simply-supported beams are tested with various anchor systems such as steel hooks, steel plates with anchor bolts, CFRP anchor plates, and near-surface mounted (NSM) CFRP strip. The effects of these anchors on the behavior of the retrofitted beams are discussed, including load-carrying capacity, failure modes, and ductility characteristics. Test results indicate that end-anchorage is an important parameter when a CFRP-retrofit design is conducted. Mechanical bolts and NSM CRFP anchors are recommended.
Composite Strips with Various Anchor Systems for Retrofitting Concrete Beams
Yoshitake, Isamu,Yumikura, Keiyu,Mimura, Yoichi,Kim, Yail-J. Korea Concrete Institute 2011 International Journal of Concrete Structures and M Vol.5 No.1
This paper presents the performance of anchor systems for reinforced concrete beams retrofitted with carbon fiber reinforced polymer (CFRP) strips. Nine simply-supported beams are tested with various anchor systems such as steel hooks, steel plates with anchor bolts, CFRP anchor plates, and near-surface mounted (NSM) CFRP strip. The effects of these anchors on the behavior of the retrofitted beams are discussed, including load-carrying capacity, failure modes, and ductility characteristics. Test results indicate that end-anchorage is an important parameter when a CFRP-retrofit design is conducted. Mechanical bolts and NSM CRFP anchors are recommended.