https://doi.org/10.4334/JKCI.2025.37.3.269

김형기(Hyeong-Ki Kim) ; 권성준(Seung-Jun Kwon)

A fundamental Monte Carlo Simulation (MCS) approach for modeling chloride diffusion was expanded by incorporating both the increase in the diffusion coefficient at elevated temperatures and its associated variability as input parameters. Using this method, the probability of reinforcement corrosion was simulated as a function of exposure duration period and concrete cover depth. Additionally, the durability failure probability was recalculated by considering the time-dependent behavior of the chloride diffusion coefficient and the effects of temperature as the diffusion period increased. The estimated service life was then compared with deterministic durability design results obtained using the LIFE365 program. The comparison showed that lower temperatures andgreater cover depths led to a lower probability of durability failure and extended the projected service life. The probabilistic service life estimation method generally provided more conservative results due to the influence of variability (coefficient of variation) indesign parameters and the adoption of a low target failure probability. However, since LIFE365 adopted a significantly high activation energy for diffusion, the difference between the two approaches decreased with increasing exposure temperature.

https://doi.org/10.4334/JKCI.2025.37.3.277

천성철(Sung-Chul Chun) ; 안성문(Seong-Moon Ahn)

According to KCI 2021 and ACI 318, the strength by anchor reinforcement can replace concrete breakout strength, provided that the development requirements for the reinforcement are met in both directions of the anticipated breakout failure surface. However, due to the limited research on anchor reinforcement, the design codes do not specify upper limits for the diameter, yield strength, or design strength of anchor reinforcement. Previous studies on anchor reinforcement were re-analyzed, and anchor reinforcement design was performed using a Strut-and-tie model. The re-analysis showed that when the development length and placement of anchor reinforcement complied with code provisions, the strengths averaged twice the expected values. Even when cracks formed along the anticipated failure surface, the anchor reinforcement limited crack widening, thus allowing partial preservation of the concrete breakout strength. Furthermore, reinforcement placed outside the effective width defined by the code provisions also contributed to the anchor reinforcement capacity. From the Strut-and-tie model analysis of anchors in tension with anchor reinforcement, it was found that proper placement of anchor reinforcement according to code requirements could achieve more than three times the concrete breakout strength. In addition, the presence of edge reinforcement further enhanced this strength. Because the anchorage conditions for anchor reinforcement are more favorable than those of standard straight or hooked bars specified in design codes, it is anticipated that the strength of anchor reinforcement can be fully realized regardless of its diameter. However, future experimental studies are needed to validate the performance of large-diameter, high-strength anchor reinforcement.

https://doi.org/10.4334/JKCI.2025.37.3.289

양근혁(Keun-Hyeok Yang)

This study determined the mixture proportions for lightweight aggregate concrete (LWAC) with a compressive strength of approximately 60 MPa and a unit weight in the range of 1,500 kg/m3. It then evaluated the improvement in compressive and flexural toughness achieved by adding 0.5 % microsteel fibers by volume to the LWAC mixtures. To meet the performance targets for LWAC, the coarse aggregate content was minimized, resulting in fine aggregate-to-total aggregate volume ratios of 70 % and 75 %, with unit water contents of 120 kg/m3 and 130 kg/m3, respectively. The compressive and flexural toughness indices of the microsteel fiber-reinforced LWAC specimens were assessed in accordance with ASTM C1018 (1997) and ASTM C1609 (2007), respectively. Residual flexural strength was estimated using the fib 2010 Model Code. The test results showed that microsteel fiber reinforcement induced a highly ductile response in high-strength LWAC beams, promoting hardening behavior in the flexural load?deflection and flexural stress?crack mouth opening displacement responses after the initial flexural crack occurred. Consequently, the microsteel fiber-reinforced LWAC specimens exhibited higher flexural toughness indices and residual flexural strengths compared to normal-strength LWAC reinforced with conventional steel fibers, despite the inherently brittle nature associated with a high strength/unit weight ratio.

https://doi.org/10.4334/JKCI.2025.37.3.297

최세진(Se-Jin Choi) ; 이재인(Jae-In Lee) ; 김채영(Chae-Young Kim) ; 김민정(Min-jeong Kim) ; 이호준(Ho-Jun Lee)

Cementless composites are regarded as a potentially advantageous substitute for cement composites, as they have the potential to reduce carbon dioxide emissions in the construction industry by eliminating the use of cement. However, there is a paucity of research on the fire resistance performance of CaO-activated cementless composites. This study compared and analyzed the residual strength and fire resistance performance of conventional cement composites and CaO-activated cementless composites. It was found that the cementless composite exhibited a relatively higher flow rate than the cement composite, while the compressive strength was relatively lower. Following heating, the surface morphology and internal center temperature change of the cementless composites demonstrated superior morphology and internal temperature change compared to the cement composites, indicating enhanced fire resistance performance.

https://doi.org/10.4334/JKCI.2025.37.3.305

정찬서(Chanseo Jung) ; 서유재(Yujae Seo) ; 주현진(Hyunjin Ju)

This study proposed a shear strength evaluation model for reinforced concrete beams strengthened with fabric reinforced cementitious matrix (FRCM). The proposed model considers the contributions of FRCM to shear strength based on the stiffness ratio between the shear reinforcement and the FRCM fibers. It also incorporates a bond reduction coefficient assuming of bond failure occurs prior to the fibers reaching their maximum tensile strength. The model was validated using specimen data collected from existing experimental studies. In addition, the test results were evaluated using the ACI 549 and ACI 440 guidelines and the outcomes were compared with the predictions of the proposed model. For specimens with shear reinforcement, the mean values of measured shear strength relative to those calculated by the proposed model, ACI 549.4R, and ACI 440.2R were 1.22, 1.22, and 1.15, respectively, with coefficients of variation of 26 %, 29 %, and 31 %. For speciems without shear reinforcement, the meanvalues were 1.59, 1.57, and 1.51, with coefficients of variation of 28 %, 31 %, and 38 %.

https://doi.org/10.4334/JKCI.2025.37.3.317

홍진영(Jinyoung Hong) ; 이태민(Taemin Lee) ; 최하진(Hajin Choi)

This study proposes an ultrasonic measurement technique for monitoring the hardening process of concrete within steel formworks. Unlike conventional methods, the proposed approach offers a non-contact monitoring of concrete hardening inside the formwork. Ultrasonic waves with a frequency of 215 kHz were applied to the outer surface of a 3 mm-thick steel plate, and guided waves transmitted along the steel-concrete interface were measured. To validate the proposed method, both numerical simulations and experimental tests using mock-up specimens were conducted. The results demonstrated that, as the concrete hardened, the guided waves generated in the steel propagated into the concrete, causing noticeable differences in ultrasonic behavior. The analysis revealed that the surface wave velocity of the internal concrete could be monitored with a maximum error of 7.5 % (75 m/s). Further analysis confirmed that optimal measurement conditions were achieved using a minimum of five measurement points, a spacing of 60 mm, and a total measurement length of 240 mm. Future work will focus on the development of specialized measurement equipment for field applications and the testing of large-scale specimens.

https://doi.org/10.4334/JKCI.2025.37.3.327

김선우(Sun-Woo Kim) ; 박완신(Wan-Shin Park) ; 우진석(Jin-Seok Woo) ; 김광현(Kwang-Hyun Kim) ; 이진희(Jin-Hui Lee) ; 윤현도(Hyun-Do Yun)

This study experimentally evaluates the shear performance of CFRP-reinforced concrete shear walls and proposes an appropriate shear strength evaluation method. Three wall specimens were tested under cyclic lateral loading: (1) a CFRP-reinforced shear wall (CCW), (2) a hybrid shear wall with vertical CFRP and horizontal steel reinforcements (CSW), and (3) a conventional steel-reinforced shear wall (SSW). The results indicate that CFRP-reinforced walls exhibited reduced crack propagation but increased crack width, attributed to CFRP’s lower bond strength and lower elastic modulus compared to steel. The CSW specimen showed similar behavior to the SSW but with reduced energy dissipation due to CFRP’s elastic properties. Meanwhile, the CCW specimen displayed pronounced pinching effects, reflecting CFRP’s linear elastic behavior and weak bond characteristics. Additionally, CFRP-reinforced walls exhibited larger tensile strains and higher compression strains than steel-reinforced walls, indicating a different failure mechanism. Comparisons with existing design codes (KDS, ACI 440.11, and CSA S806) revealed that shear strength predictions were conservative, with experimental results exceeding calculated values.

https://doi.org/10.4334/JKCI.2025.37.3.337

정철우(Chul-Woo Chung) ; 노강민(Gang Min Noh) ; 아비츄 미카엘 리에우(Gebremicael Liyew) ; 권성준(Seung-Jun Kwon) ; 장승엽(SeungYup Jang) ; 김형기(Hyeong-Ki Kim)

A series of experimental studies was conducted to reassess the maximum allowable initial chloride content in concrete as specified by relevant standards. Various properties were evaluated, including the slump and air content of fresh concrete, as well as the porosity, strength, elastic modulus, and chloride penetration resistance of hardened concrete, all with varying levels of initial chloride content. In addition, the corrosion risk to reinforcing steel embedded in concrete with varying initial chloride content was evaluated. The experimental results revealed that, in terms of both fresh and hardened concrete properties, initial chloride content up to 0.4 wt.% of the binder had no adverse effects. Furthermore, concrete with initial chloride content ranging from 0 to 0.4 wt.% of the binder exhibited a low risk of reinforcement corrosion.

https://doi.org/10.4334/JKCI.2025.37.3.347

강승범(Seung-Beom Kang) ; 김선희(Sun-Hee Kim) ; 최원창(Wonchang Choi)

In this study, elevated temperature tensile tests were conducted on 13 mm diameter carbon fiber reinforced polymer(CFRP) rebars in accordance with the KS standard, and their tensile properties were analyzed as a function of temperature. The results showed that at 100 °C, tensile strength increased due to the post-curing effect, while after 300 °C, both tensile strength and ultimate strain decreased rapidly due to resin decomposition. It was confirmed that residual resin remained below 250 °C, while at 375 °C, an increasing trend in the elastic modulus was observed as most of the resin was lost. Reliability evaluation showed relatively high consistency under elevated-temperature conditions, except at 250 °C suggesting the need for further research to enhance the applicability and accuracy of the KS standard under such conditions.

https://doi.org/10.4334/JKCI.2025.37.3.355

이현호(Hyun-Ho Lee)

In this study, the hysteretic behavior of a steel rod damper designed for application in coupling beams was evaluated based on findings from previous research. The steel rod damper features detailing to prevent lateral deformation, and four specimens were manufactured with varying numbers of steel rods. Loading was applied in accordance with inter-story drift ratios. The experimental results indicated that as the number of steel bars in the damper increased, the maximum strength also increased, but not in direct proportion to the number of dampers. In terms of the failure mode, the damper functioned effectively up to a displacement of 73 mm before reaching final failure.

https://doi.org/10.4334/JKCI.2025.37.3.363

채경훈(Kyoung-Hun Chae) ; 안영승(Yeong-Seung An) ; 박태원(Tae-Won Park) ; 허무원(Moo-Won Heo)

In this study, an experimental investigation was conducted to evaluate the seismic performance of torque-controlled expansion anchors with improved structural details, including modified sleeves and heads. The seismic performance was evaluated according to established evaluation guidelines by conducting repeated force application tests and residual strength tests, following the concrete design method and simulated seismic tension procedures specified in the Example Book (KCI-M-24-018). None of the anchors were damaged or broken during the repeated loading tests. In the residual strength tests, the average residual tensile strength of all anchors was found to be greater than or equal to the evaluation criteria. The final failure mode was identified as concrete breakout, which was judged to have contributed to the anchors’ high seismic tensile resistance by effectively countering the effects of cracking and repeated loading. In addition, when comparing the experimental value (NTest) with the design value (NKDS) according to the domestic anchor design standard, it was confirmed that the strength was about 1.36 times and 1.43 times higher. These findings confirm that torque-controlled expansion anchors with improved structural details exhibit excellent seismic performance and can be effectively applied in structures requiring seismic design considerations.

https://doi.org/10.4334/JKCI.2025.37.3.371

이원준(Won-Jun Lee) ; 이득행(Dueckhang Lee) ; 김민수(Min-Su Kim) ; 심희영(Hee-Young Shim)

As modern buildings continue to increase in span length and story height, the application of precast concrete (PC) systems has become prevalent in the construction industry. PC members are manufactured in factory environments and subsequently assembled on-site, resulting in structural systems that inherently incorporate discrete connections and joints. These connections and joints play a critical role in the seismic performance of PC shear wall systems, as they govern the transfer of forces and the overall structural integrity under seismic loading. To ensure adequate seismic performance, precast connections and joints at wall-to-wall and wall-to-foundation interfaces should be designed to have sufficient overstrength and seismic details to achieve composite action and energy dissipation. In particular, PC shear walls require extensive joint detailing to address the combined effects of in-plane shear forces and flexural moments. This study newly introduced a group-coupling method for PC shear wall systems and subsequently presents a simplified flexural strength model by utilizing the G-factor. To validate the proposed approach, three full-scale PC coupled shear wall specimens were fabricated and tested under reversed cyclic loadings. It appeared that the proposed approach with G factor can simplify the design process by achieving a target level of composite action in group-coupled precast shear wall systems.

https://doi.org/10.4334/JKCI.2025.37.3.381

우진석(Jin-Seok Woo) ; 윤현도(Hyun-Do Yun) ; 김선우(Sun-Woo Kim) ; 박완신(Wan-Shin Park) ; 최원창(Won-Chang Choi) ; 서수연(Soo-Yeon Seo)

This study developed a strain-detecting cementitious composite (FBMC) sensor by incorporating Fe-modified biochar and multi-walled carbon nanotubes (MWCNTs), and evaluated its applicability to real structures by embedding it in a concrete shear wall subjected to cyclic lateral loading. The sensing performance of the structural member’s deformation and damage level was quantitatively assessed through comparison with a commercial strain gauge. MWCNTs, added at 1 % by cement weight, were uniformly dispersed using ultrasonic treatment to form a conductive network within the matrix. Under cyclic compressive loading, the sensor’s performance was analyzed based on fractional change in resistance (FCR), response linearity, and gauge factor(GF). The FBMC sensor exhibited superior cyclic response stability and sensing precision (R²=0.913) compared to a sensor using only Fe-modified biochar (FBC). In the shear wall experiment, the FBMC sensor was embedded in the boundary region, and its FCR response was compared with vertical reinforcement strain, damage index (DI), and energy dissipation coefficient (η). The results showed that the sensor exhibited a peak FCR response at a drift ratio of 1.7 %, securing a wider damage-sensing range than the vertical reinforcement. Furthermore, strong correlations with DI and η confirmed the sensor’s quantitative ability to track structural damage progression. The FBMC sensor maintained high sensitivity and response stability under cyclic loading, demonstrating its suitability for real-time structural health monitoring. However, signal degradation due to disconnection of the conductive network after sensor cracking was observed.