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    Analysis of Thermal Environmental Effects on Precast, Prestressed Concrete Bridge Girders: Temperature Differentials and Thermal Deformations
    (Multi-Science Publ Co Ltd, 2012) Lee, Jong-Han; Kalkan, Ilker
    AASHTO specifications provide vertical thermal gradients for the thermal design of precast, prestressed concrete bridge girders. However, the thermal behavior of the girders pertains to not only vertical thermal movement but also lateral thermal movement. Thus, a one-year experimental and analytical study was conducted on a prestressed concrete BT-1600 girder segment to investigate both the vertical and lateral thermal gradients with variations in environmental conditions. The vertical thermal gradients were compared using current AASHTO recommendations. In addition, this study evaluated the lateral thermal gradients, which are not provided in the specifications, to propose a second-order curve. To determine the magnitudes of the thermal gradients in different environmental conditions, this study has developed equations that calculate the maximum vertical and lateral temperature differentials from daily climatic information. Results of the study showed that the predicted temperature differentials provided good agreement with the measured values. Finally, thermal deformations induced by the vertical and lateral thermal gradients were evaluated using an analytical method derived from one-dimensional beam theory.
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    Effect of shrinkage restraint on deflections of reinforced self-compacting concrete beams
    (Korean Society Of Civil Engineers-Ksce, 2013) Kalkan, Ilker; Lee, Jong-Han
    This paper presents the results of a study aimed at investigating the effects of restrained shrinkage on the in-plane deflection behavior of reinforced beams cast with self-compacting concrete. The load-deflection data from the tests on two sets of heavily-reinforced concrete beams were analyzed. The first set of beams was made with self-compacting concrete while conventionally vibrated concrete with shrinkage reducing admixture was used in the second set. It was found out that the first set underwent shrinkage cracking at early ages and this cracking caused the member responses of the beams to be closer to the fully-cracked response at the initial stages of loading. The second set of beams was found to have initial responses approximate to the uncracked response and the maximum shrinkage restraint stresses were calculated to be in the order of 20-40% of the modulus of rupture of concrete. The maximum shrinkage-induced restraint stress expressions of the AS 3600-2001, AS 3600-2009, EC2, and CSA A23.3-04 codes were found to underestimate the restraint stresses developed in the first set, yet the estimates from code solutions were in closer agreement with the experimental values in the second set.
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    Experimental and Analytical Investigation of Lateral-Torsional Buckling of RC Beams with Geometric Imperfections
    (Trans Tech Publications Ltd, 2014) Lee, Jong-Han; Kalkan, Ilker
    The design of reinforced concrete beams has usually focused on the ultimate flexural capacity and disregarded the lateral stability of the beams. However, the development of high-strength concrete and the implementation of new construction techniques increase the use of longer and deeper concrete beams, which makes the lateral instability a primary concern of failure in concrete bridges. In particular, the lateral stability should be more taken into consideration in the construction and erection phases due to inadequate lateral supports. Thus, an experimental study was carried out to evaluate the lateral torsional buckling of reinforced concrete beams with initial geometric imperfections. The lateral flexural and torsional rigidity expressions, which could account for the flexural, torsional, and shrinkage cracking of concrete, the contribution of longitudinal and shear reinforcement, and the nonlinearity of materials, were proposed for rectangular reinforced concrete beams. Finally, this study proposed an analytical formula to estimate the buckling loads of initially imperfect reinforced concrete beams. The estimates of the study showed close agreement with the experimental values.
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    Rollover instability of precast girders subjected to wind load
    (Ice Publishing, 2017) Lee, Jong-Han; Kalkan, Ilker; Lee, Jong-Jae; Cheung, Jin-Hwan
    The use of longer and deeper precast concrete girders has created concern regarding their rollover instability, particularly during construction. Current design and construction specifications do not provide any specific guidelines that can be used to evaluate the rollover instability of a girder. Therefore, analytical and simplified numerical studies were performed to evaluate the critical wind load, lateral displacement and rotational angle that would induce rollover instability of a girder supported on an elastomeric bearing pad. The influence of the length and section properties of the girder on rollover instability was also investigated. The analytical method proposed in this study can be effectively used for evaluating the lateral behaviour and rollover instability of bridge girders and can also provide management values for securing the lateral stability of girders. The paper also provides a worked problem for a long-span typical European girder to determine critical values with application of the proposed method.
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    Seismic performance of R/C structures under vertical ground motion
    (Techno-Press, 2017) Bas, Selcuk; Lee, Jong-Han; Sevinc, Mukadder; Kalkan, Ilker
    The effects of the vertical component of a ground motion on the earthquake performances of semi-ductile high-rise R/C structures were investigated in the present study. Linear and non-linear time-history analyses were conducted on an existing in-service R/C building for the loading scenarios including and excluding the vertical component of the ground motion. The ratio of the vertical peak acceleration to the horizontal peak acceleration (V/H) of the ground motion was adopted as the main parameter of the study. Three different near-source earthquake records with varying V/H ratio were used in the analyses. The linear time-history analyses indicated that the incorporation of the vertical component of a ground motion into analyses greatly influences the vertical deflections of a structure and the overturning moments at its base. The lateral deflections, the angles of rotation and the base shear forces were influenced to a lesser extent. Considering the key indicators of vertical deflection and overturning moments determined from the linear time-history analysis, the non-linear analyses revealed that the changes in the forces and deformations of the structure with the inclusion of the vertical ground motion are resisted by the shear-walls. The performances and damage states of the beams were not affected by the vertical ground motion. The vertical ground motion component of earthquakes is markedly concluded to be considered for design and damage estimation of the vertical load-bearing elements of the shear-walls and columns.