No abstract

Nowadays prestressed concrete (PSC) bridges have become very common, but there are still many difficulties in predicting their longterm behavior. In order to predict the long-term behavior of PSC bridges, it is possible to use very complex formulas developed by various researchers or numerical analysis through computer, but many engineers are having difficulty in using such methods. Moreover, the accuracy of the prediction result is not satisfactory compared to the effort. On the contrary, the PCI Bridge Design Manual proposes a method that can easily predict the long-term behavior using multipliers. However, this method does not take into account various construction schedules and has some assumptions that are inadequate for the current situation in various girder sections and topping thicknesses. erefore, in this study, new long-time factors were developed by modifying the multipliers of the PCI Bridge Design Manual by a rational manner. is allows prediction of long-term behavior of bridges taking into account various construction schedules and the characteristics of modern girder sections. e prediction results of the long-term camber and deflection of PSC bridges using the proposed multipliers were compared with those using the basic PCI Bridge Design Manual, the improved PCI Bridge Design Manual, KR C-08090 (same as ACI 318-14), and numerical analysis. As a result, the newly proposed method makes possible to predict the long-term behavior at any time after casting, and the accuracy of the prediction is also improved.

Ultra-high-performance concrete (UHPC) is required to develop multifunctional concrete structures such as long-span bridges. During the construction of long-span bridges, girders exhibit significant differences in age because they use different curing days in the precast process. In this study, the performances of UHPC were compared when subjected to long-term storage under various conditions after 3-day steam curing. At 365 days, the compressive strength of steam curing is 197 MPa, moist is 191 MPa, and the air is 169 MPa. Based on these differences, prediction models were proposed for long-term performances. Furthermore, the development characteristics of compressive strength, modulus of elasticity (MOE), and flexural strength until 365 days of age were analyzed under air, moist, and steam conditions. Steam curing exhibited the highest level of strength development while air curing showed the lowest. Flexural strength showed no significant difference depending on age because steel fibers were mixed with UHPC; they significantly contributed to flexural performance. The results would contribute to recognizing differences in strength between members at sites where UHPC is applied and to managing high-quality structures constructed using precast members. These research results are expected to contribute to efficient member production and process management during the construction of large structures such as super-long-span bridges.

The behavior of a slab-column joint subjected to blast loads was studied by numerical analysis using a general-purpose finite element analysis program, LS-DYNA. Under the explosive load, the joint region known as the stress disturbed zone was defined as a region with a scaled distance of 0.1 m/kg1/3 or less through comparison with ConWep’s empirical formula. Displacement and support rotation according to Trinitrotoluene (TNT) weight and scaled distance were investigated by dividing in and out of the joint region. In addition, fracture volume was newly proposed as an evaluation factor for blast-resistant performance, and it was confirmed that the degree of damage to a member due to blast loads was well represented by the fracture volume. Finally, a prediction equation for the blast-resistant performance of the slab-column joint was proposed, and the reliability and accuracy of the equation were verified through additional numerical analysis.

Carbon-based nanomaterials are used in various industrial fields because of their excellent performance. In construction, cementitious composites containing carbon-based materials have the potential to be used for various purposes such as crack detection and deicing. However, carbon-based materials have been experienced difficulties that cannot be easily dispersed in the cementitious composite because of the inherent material characteristic. This study aimed to investigate the possibility of using these carbon-based nanomaterials as construction materials. The structural and electrical performances of cementitious composites were investigated based on carbon-based materials such as Multi-Walled Carbon Nanotube (MWCNT), Single-Walled Carbon Nanotube (SWCNT), Graphene Nanoplatelets (GNP), Conductive Graphite Powder (CGP). In addition, the microstructural analysis was performed through the noncovalent functionalization of carbon-based nanomaterials to examine the dispersibility.