The precast concrete (PC) method allows for simple assembly and disassembly of structures; however, ensuring airtight connections is crucial to prevent energy loss and maintain optimal building performance. This study focuses on the analytical investigation of the shear capacity of precast ultra-high-performance concrete (UHPC) ribs combined with standard concrete PC cladding walls. Five specimens were tested under static loading conditions to evaluate their structural performance and the thermal behavior of the UHPC rib shear keys. Test results indicated that the specimens exhibited remarkable structural performance, with shear capacity approximately three times greater than that of standard concrete. Numerical models were subsequently developed to predict the shear capacity of the shear keys under various loading conditions. A comparison between the experimental results and finite element (FE) models showed a maximum strength difference of less than 10% and a rib displacement error of up to 1.76 mm. These findings demonstrated the efficiency of the FE model for the simulation of the behavior of structures.
This research introduces a novel probabilistic approach to consider the effects of uncertainty parameters during the design and construction process, providing a fresh perspective on the evaluation of the structural performance of reinforced concrete structures. The study, which categorized various random design and construction process variables into three groups, selected a two-story reinforced concrete frame as a prototype and evaluated it using a nonlinear analytical model. The effects of the uncertainty propagations to seismic responses of the prototype RC frame were probabilistically evaluated using non-linear dynamic analyses based on the Monte-Carlo simulation sampling with the Latin hypercube method. The derivation of seismic fragility curves of the RC frame from the probabilistic distributions as the results of uncertainty-propagation and the verification of whether the RC frame can meet the seismic performance objective from a probabilistic point of view represent a novel and significant contribution to the field of structural engineering.
In this research, the concrete breakout strength in tension of cast-in-place anchors (CIP) is experimentally investigated to be used as fundamental data for the seismic fragility analysis of equipment in nuclear power plants. Experimental variables are chosen, such as the embedment depth of the anchor, single/group anchor configurations, diameter of the head plate, and crack width. Monotonic and cyclic loading are applied to all types of specimens. As measured from the experiments, concrete breakout strength in tension is 1.5 to 2 times higher than the expected strengths from concrete capacity design (CCD) method-based model equations. In alignment with the model’s predictions, concrete breakout strength increases with deeper embedment depth, and the strength of group anchors also increases based on the expansion of the projected concrete failure area. This study also explores the effects of head plate diameter and crack width, which are not considered in the model equation. Experimental results show that the diameter of the head plate is not directly correlated to the concrete breakout strength, whereas the crack width is. The presence of cracks, with widths of 0.3 mm and 0.5 mm, leads to reductions of approximately 7% and 17%, respectively, compared to single anchors in non-cracked concrete.
Steel brace is a popular option among seismic rehabilitation methods for school buildings, but it has a weakness in that the section area must be large enough to prevent buckling, so stiffness and strength are highly increased locally, and foundation reinforcing is required. On the contrary, BRB has strength that the steel core may be negligible since buckling is restrained, so the increase of stiffness and strength is insignificant, and foundation reinforcing may not be required. This study compared the effectiveness of both reinforcing methods for the seismic performance of school buildings by conducting both pushover and nonlinear dynamic analyses. Steel brace and BRB reinforcing may not be satisfied by nonlinear dynamic analysis, even by pushover analysis. This result is due to the school buildings' low lateral resistance and high column shear strength ratio. Suppose BRB can be regarded as a general rehabilitation method. In that case, BRB reinforcing is a favorable and economical option for school buildings with low column shear strength ratio since it can better satisfy performance objectives than steel brace by pushover analysis with a small steel core and no foundation reinforcing.
This study investigates the risk reduction effect and identifies the optimal capacity of Multi-barrier Accident Coping Strategy (MACST) facilities for nuclear power plants (NPPs) under seismic hazard. The efficacy of MACST facilities in OPR1000 and APR1400 NPP systems is evaluated by utilizing the Improved Direct Quantification of Fault Tree with Monte Carlo Simulation (I-DQFM) method. The analysis encompasses a parametric study of the seismic capacity of two MACST facilities: the 1.0 MW large-capacity mobile generator and the mobile low-pressure pump. The results demonstrate that the optimal seismic capacity of MACST facilities for both NPP systems is 1.5g, which markedly reduces the probability of core damage. In particular, the core damage risk is reduced by approximately 23% for the OPR1000 system, with the core damage fragility reduced by approximately 72% at 1.0g seismic intensity. For the APR1400 system, the implementation of MACST is observed to reduce the core damage risk by approximately 17% and the core damage fragility by approximately 44% under the same conditions. These results emphasize the significance of integrating MACST facilities to enhance the resilience and safety of NPPs against seismic hazard scenarios, highlighting the necessity for continuous adaptation of safety strategies to address evolving natural threats.
In conventional construction practices, roof-parapet junction structures inevitably disrupt the insulation installation's continuity, leading to energy loss and thermal bridging. To address this issue, parapet thermal breaks were installed to interrupt the heat flow between the roof and the parapet, effectively preventing thermal bridging and energy loss and thereby reducing overall energy loss in buildings. This study equipped three experimental specimens with the developed parapet thermal breaks to verify their structural performance. These specimens were subjected to unidirectional loading under displacement-controlled conditions. The structural performance of these insulation structures was evaluated by comparing and analyzing the test results with corresponding analytical studies conducted using a finite element analysis program. In addition, five analytical models with varying parameters of the parapet thermal breaks were developed and compared against the baseline model. Consequently, the most efficient shape of the parapet thermal break was determined.
Recently, high-rise residential buildings in Korea have adopted slender shear walls with irregular section shapes, such as T-shape, H-shape, and C-shape. In the seismic design of the slender shear walls, the transverse reinforcement for lateral confinement should be provided in the boundary elements to increase deformation capacity and subsequent ductility. However, in practice, the irregularity of the shear walls is not adequately considered, and the lateral confinement region is calculated for the rectangular wall segments. This study investigated the proper design method for lateral confinement regions using finite element analysis. The lateral confinement region was considered in analysis for two cases: 1) as a typical rectangular wall segment and 2) as an irregular wall. When the irregularity of the walls was considered, the compression zone depth was increased because the vertical reinforcement in the flange was addressed. The effect of lateral confinement design methods on the structural performance of the walls was directly compared under various design parameters, including the length of the flange, concrete compressive strength, vertical rebar layout, axial load ratio, and loading direction. According to the results of the parametric analysis, the peak strength and deformation capacity could be significantly increased when the lateral confinement region was calculated based on irregularly shaped walls, regardless of the design parameters. In addition, the effective compression zone was located within the lateral confinement region. Thus, it is recommended that the lateral confinement region of T-shaped walls is calculated by addressing the irregularity of the walls.
According to the recently revised seismic design standards, seismic design of underground structures is required. Concrete underground outer walls are installed separately from temporary earth retaining walls as permanent underground outer walls. This raises issues of constructability, economy, and space narrowness. Therefore, a steel underground continuous wall is developed to promote construction efficiency, safety, and economy by introducing the off-site construction (OSC) method of underground structures. The steel underground continuous wall will be used as a permanent underground continuous wall along with the temporary earth retaining wall. To this end, it must satisfy structural performance equivalent to or higher than the concrete underground outer wall. The integrity and in-plane shear resistance performance between single panel members must be satisfied to be used as a permanent wall. The interlocking effect through geometric bonding is intended to enhance the bonding effect between these members. Therefore, trapezoidal members were developed, and bending performance tests and analyses of each member were performed to confirm the structural bending performance of these members. The bending performance improvement effect of the combined multiple members was confirmed. As a result, it was confirmed that the integration of members and structural performance was improved due to the interlocking effect of the absence of joints. The seismic design analysis of the demonstration site was performed with these developed members, and it was confirmed that the structural performance was equivalent to or higher than that of the existing RC underground continuous wall. As a result, it was confirmed that the steel underground continuous wall can be used as a permanent underground wall together with the temporary earth retaining wall.
Steel moment frame connections are vital in moment frames designed to resist forces transferred from adjoining beams and columns. The welded unreinforced flange-welded web (WUF-W) connection is one of the pre-qualified connections used for steel special moment frames (SMFs). This study developed drift-based fragility functions for WUF-W connections based on test data of 35 WUF-W connection specimens from ten previous experimental studies. Four different damage states were defined to calculate the fragility: onset of yielding, local buckling, strength loss, and fracture. Fragility functions were derived assuming that lognormal distribution was validated using the Kolmogorov-Smirnov (K-S) test. It was confirmed that fragility functions for WUF-W connections were accurately proposed within a specified confidence interval. The fragility functions proposed in this study exhibit smaller standard deviations compared to FEMA P58, thereby reducing the likelihood of overestimating or underestimating damage at specific drift ratios. Furthermore, these functions remain within the confidence intervals across all damage states, contributing to improved accuracy in damage analysis and loss estimation in performance-based earthquake engineering.