Joo Ha Lee

Improving Punching Shear Behavior of Glass Fiber-Reinforced Polymer Reinforced Slabs

This study compares the behavior of slab-column connections reinforced with steel or glass fiber-reinforced polymers (GFRP). The effects of concentrating the reinforcement in the immediate column region and the influence of using steel fiber-reinforced concrete (SFRC) in the slab were also studied. The punching shear capacity, stiffness, ductility, strain distribution, and crack control were investigated. Concentrating the slab reinforcement and the use of SFRC in the slab enhanced the punching behavior of the slabs reinforced with GFRP bars. Predictions using different design guidelines are compared to the experimental results obtained from the FRP reinforced slabs tested in this study and those tested by other researchers. Results show that the GFRP-reinforced slabs have significantly lower punching shear capacities, lower post-cracking stiffness and greater deflections than slabs reinforced with steel reinforcing bars. Concentrating the top mat of flexural reinforcement results in beneficial effects on punching shear strength, postcracking stiffness, and crack control. The presence of 0.5% by volume steel fibers in the concrete significantly improves punching shear capacity and crack control.

Influence of steel fibers and headed bars on the serviceability of high-strength concrete corbels

Vertical loading tests are reported for six double-sided, high-strength concrete corbel specimens. The primary variables of the investigation were the percentage of steel fibers and the anchorage method of the main tension tie. The test results indicated that performance in terms of load-carrying capacities, stiffness, ductility, and crack width was improved, as the steel fibers were added and the percentage of steel fibers was increased. The corbel specimens with headed bars used as the main tension-tie reinforcement showed superior load-carrying capacities, stiffness, and ductility compared with the corbel specimens in which the main tension ties were anchored by welding to the transverse bars. From the test results, it is expected that the load-carrying capacities, serviceability, and durability of high-strength concrete corbels would be improved by using steel fibers and headed bars. Experimental results presented were also compared with various prediction models.

Prediction of Effective Compressive Strength of Column-slab Joint Considering Slab Confinement Effect

In this study, rational prediction models for the effective compressive strengths of high-strength concrete (HSC) interior columns with intervening normal strength concrete (NSC) slabs are developed. A structural analogy between HSC column-NSC slab joint and brick masonry is used to develop the prediction models. In addition, the aspect ratio of slab thickness to column dimension and the surrounding slab confinement effect are considered in the models. The proposed prediction model is verified by comparison with experimental results and various prediction expressions. As a result, the proposed equation provided superior predictions over all of the existing effective strength prediction approaches including KCI structural concrete design code (2012).

A Study on the Slab-Column Joint Reinforcements using Nonlinear Finite Element Analysis

The needs for high-strength concrete is increasing, especially for high-rise buildings. Given the economics and the structural utility of high-strength concrete, structural elements subjected to axial load like concrete columns are the main targets for its application. Unlike columns, slabs do not have to be made of high-strength concrete so that the slab is generally cast with normal-strength concrete in a continuous fashion through the slab-column joint. Consequently, this lower strength concrete joint may result in problems for transmission of column loads through the joint, and moreover the capability of high-strength concrete column cannot be fully used due to the intervening normal-strength concrete slab. Therefore, it is necessary to provide alternative design or construction strategies for the transmission of column loads through slab-column connections. Current design practice recommends three strategies: puddling of high-strength concrete, reinforcing with dowels and spirals, the effective compressive strength of joint. As an active solution, puddling concrete and vertical dowels are the specific interest of this study. To find other effective methods for enhancing the behavior of slab-column joint, high-strength concrete core in the joint and high-strength steels for the column longitudinal bars were added to variables of this numerical analyses. As a result, some alternative reinforcement methods significantly improved the performance of the joints in terms of strength, stiffness, and ductility.