Baik-Soon Cho

Behavior of Reinforced Concrete Columns Confined by New Steel-Jacketing Method

Jacketing can be an effective way to improve the performance of the lap-spliced region of reinforced concrete (RC) columns. This paper introduces a new steel-jacketing method for RC columns that uses external pressure to attach the steel jackets to the column surface. The advantage of this method is that it does not require the application of grout between the steel jackets and the concrete surface to attach them together. Experimental tests of twelve concrete cylinders and four RC columns are performed to assess the effectiveness of the proposed method. Both single-layered and double-layered jackets are tested. The newly jacketed cylinders show good results in terms of increasing the compressive strength and ductility compared to plain cylinders. The double-layered jackets are estimated to show equal performance to that of a single steel jacket with the same thickness. The proposed steel-jacketing method increased the ductility of lap-spliced RC columns. The double-layered jacket appeared to perform better in terms of increasing ductility and energy dissipation capacity than the single-layered jacket.

Recovery stress of shape memory alloy wires induced by hydration heat of concrete in reinforced concrete beams

The goal of this study is to investigate the prestressing effect of shape memory alloy bars in reinforced concrete beams; bars are prestressed by external force or recovery stress due to shape memory effect. The shape memory alloy bars are heated by hydration heat of concrete during curing to induce the shape memory effect. To achieve this goal, this study conducts bending tests of concrete beams reinforced by shape memory alloy bars as well as those reinforced by steel bars. The beams with shape memory alloy bars with recovery stress show the same or slightly larger flexural strength than those with shape memory alloy bars prestressed with external force. Thus, this study indicates that the recovery stress of shape memory alloy bars plays the same role as the prestressing force, and that the shape memory effect can be induced by hydration heat of concrete instead of heating by electronic resistance.

Inducing recovery stress of NiTiNb SMA wires using heat of hydration for confining concrete

This study suggests the utilization of heat of hydration of concrete to activate the shape memory effect (SME) of shape memory alloy (SMA) wires embedded in concrete and produce recovery and residual stress on the wires. This method is more convenient than the previous electronic resistance heating. For the purpose, this study prepares NiTiNb SMA wires that show appropriate temperature window for the use of heat of hydration. Axial compressive tests of concrete cylinders confined by the NiTiNb SMA wire jackets are used to prove that the utilization of heat of hydration is valid to generate recovery and residual stress in the SMA wires. The confined cylinders show increased peak strengths and much larger failure strains than those of the plain concrete. The general behavior of the SMA wire-confined specimens in this study is similar to that of specimens heated by electronic heating jacket. Also, this study explains two examples for the utilization of heat of hydration for the SME in reinforced concrete beams and columns.

Probabilistic seismic performance assessment of lap-spliced RC columns retrofitted by steel wrapping jackets

In this study, the seismic fragility curves of two reinforced concrete (RC) columns that were lap-spliced at the bottom and retrofitted with steel wrapping jackets were generated. Their seismic performance was probabilistically assessed in comparison to that of lap-spliced or continuous reinforcement RC columns. This study used two types of steel wrapping jackets, a full jacket and a split jacket. Analytical models of the four types of columns were developed based on the experimental results of the columns using OpenSEES, which is effective in conducting nonlinear time history analyses. A suite of ten artificial ground motions, modified from recorded ground motions, was used to perform nonlinear time history analyses of the analytical models with scaling of the peak ground acceleration from 0.1 g to 1.0 g in increments of 0.1 g. The steel wrapping jackets did not increase the medians for yield (slight damage state) of the lap-spiced column and did not exceed the corresponding median of the continuous reinforcement column. However, the two steel jackets increased the medians for failure by 1.872 and 2.017 times, respectively, and exceeded the corresponding median of the continuous reinforcement column by 11.8% and 20.5%, respectively.

Evaluation on Bending Moment of Bridge Approach Slabs under Vehicle Load Considering Soil Settlement

The bridge approach slabs (BAS) to provide a transitional roadway between a roadway pavement and a bridge structure have not performed adequately due to various factors. The current Korean Roadway Design Guidelines treat the BAS as a simply supported beam with 70% of the span length and do not consider settlement and void development underneath the slab. To investigate the effect of soil settlements on the bending moment of BAS, a beam on elastic support (BAS-ES) was used in the present study. The parameters used in this study were span length, washout length, washout location, and soil modulus. It was shown from the parametric study that washout regions closer to the midspan exhibit maximum moment in the slab. Since voids under the BAS have typically been observed to be closer to bridge abutments, the springs from the abutment were removed to simulate settlement and void development in the model. The design moments based on AASHTO LRFD Bridge Design Specifications were compared to those of Korean Standard Specifications for Highway Bridge and Design Trucks for Highway Bridges. Even if the design moment from BAS-ES was used to incorporate the effect of the potential washout, significant savings could still be achieved compared to the current BAS design.