Hyeon-Jong Hwang

Cyclic Loading Test for Beam-Column Connections with 600 MPa (87 ksi) Beam Flexural Reinforcing Bars

where α0 is the coefficient related to the location of the plastic hinge of beams (=1.0 to 1.25); αf is the coeffi- cient related to the direction of the beam reinforcing bars; (=0.85 to 1.0); αd is the coefficient related to the ductility of the plastic hinge of beams (=1.0 to 1.2); γ is the coeffi- cient related to inter-story drift when the yield strength of beam reinforcing bars is greater than 300 MPa (43.5 ksi) (γ = 1.53 - 0.29 δc ≤ 1.0); and δc is the inter-story drift ratio expressed as a percentage.

Flexural Test for Prefabricated Composite Columns Using Steel Angle and Reinforcing Bar

PSRC column is a concrete encased steel angle column. In the PSRC column, the steel angles placed at the corner of the cross-section resists bending moment and compression load. The lateral re-bars welded to steel angles resist the column shear and the bond between the steel angle and concrete. In the present study, current design procedures in KBC 2009 were applied to the flexure-compression, shear, and bond design of the PSRC composite column. To verify the validity of the design method and failure mode, simply supported 2/3 scaled PSRC and correlated SRC beams were tested under two point loading. The test parameters were the steel angle ratio and lateral bar spacing. The test results showed that the bending, shear, and bond strengths predicted by KBC 2009 correlated well with the test results. The flexural strength of the PSRC specimens was much greater than that of the SRC specimen with the same steel ratio because the steel angles were placed at the corner of the column section. However, when the bond resistance between the steel angle and concrete was not sufficient, brittle failures such as bond failure of the angle, spalling of cover concrete, and the tensile fracture of lateral re-bar occurred before the development of the yield strength of PSRC composite section. Further, if the weldability and toughness of the steel angle were insufficient, the specimen was failed by the fracture of the steel angle at the weld joint between the angle and lateral bars.

Immediate and Long-Term Deflections of Reinforced Concrete Slabs Affected by Early-Age Loading and Low Temperature

ACI Structural Journal, V. 109, No. 3, May-June 2012. MS No. S-2010-225.R2 received March 4, 2011, and reviewed under Institute publication policies. Copyright

Cyclic Loading Test for Beam-Column Connections of Concrete-Filled U-Shaped Steel Beams and Concrete-Encased Steel Angle Columns

AbstractPrefabricated steel–reinforced concrete angle columns and concrete-filled U-shaped steel beams were recently developed for efficient steel-concrete composite construction. In the present study, seismic details of TSC beam–PSRC column connections were developed, taking into consideration constructability and cost efficiency. A cyclic loading test was performed on the beam-column connections to investigate load-carrying capacity, deformation capacity, failure mode, and energy dissipation capacity. For the test parameters, the connection type (interior or exterior) and the depth of the TSC beams were considered. The test results showed that the deformation and energy dissipation capacities of the specimens satisfied the requirements for intermediate moment frames specified in the AISC standard. Further, the moment-carrying capacities predicted using plastic stress distribution were found to be in agreement with the test results. The joint shear capacities of the specimens were evaluated according to ...

Flexural Test for Steel-Concrete Composite Members Using Prefabricated Steel Angles

In the proposed composite [prefabricated steel-reinforced concrete (PSRC)] column, steel angles located at the corners of the cross section are weld connected with tie bars to provide a bond for the steel angles, shear resistance, and lateral confinement. In this paper, simply supported PSRC specimens were tested to investigate their flexural strength and ductility. For comparison, a conventional concrete-encased H-section specimen was also tested. The test parameters were the steel ratio of the angle section and the spacing of the tie bars. The flexural, shear, and bond strengths of the test specimens correlated well with predictions. The flexural strength and stiffness of the PSRC specimens were significantly greater than those of the conventional composite specimen with the same steel area. However, at large inelastic deformations, the PSRC specimens were vulnerable to the bond failure between the steel angle and concrete and the tensile fracture of the angle at the weld-connection to the tie bars. When the bond strength between the steel angles and concrete was greater than the demand, the PSRC specimens exhibited ductile behavior after flexural yielding.

Effects of Shore Stiffness and Concrete Cracking on Slab Construction Load I: Theory

Long-term floor deflection caused by excessive construction load became a critical issue for the design of concrete slabs, as a flat plate is becoming popular for tall buildings. To estimate the concrete cracking and deflection of an early age slab, the construction load should be accurately evaluated. The magnitude of construction load acting on a slab is affected by various design parameters. Most of existing methods for estimating construction load addressed only the effects of the construction period per story, material properties of early age concrete, and the number of shored floors. In the present study, in addition to these parameter, the effects of shore stiffness and concrete cracking on construction load were numerically studied. Based on the result, a simplified method for estimating construction load was developed. In the proposed method, the calculation of construction load is divided to two steps: 1)Onset of concrete placement at a top slab. 2)Removal of shoring. At each step, the construction load increment is distributed to the floor slabs according to the ratio of slab stiffness to shore stiffness. The proposed method was compared with existing methods. In a companion paper, the proposed method will be verified by the comparison with the measurements of actual construction loads.

Effects of Shore Stiffness and Concrete Cracking on Slab Construction Load II: Measurements and Comparisons

In a companion paper, a simplified method for the evaluation of the slab construction load was developed. Unlike existing methods, the proposed method includes the effects of shore stiffness and concrete cracking on the construction load. In the present study, construction loads were measured in actual flat-plate slabs. For verification, the measured shore-forces were compared with the predictions by the proposed method and existing methods. Further, the proposed method was applied to a wall-slab structure, and the prediction results were compared with the measurements. The comparison results showed that the proposed method well predicted the construction loads, furthermore it gave better predictions than the existing methods did.

Cyclic Seismic Testing of Composite Concrete-Filled U-Shaped Steel Beam to H-Shaped Column Connections

In this study, the cyclic seismic performance of a concrete-filled U-shaped steel beam to H-shaped steel column connections was experimentally evaluated. The concrete-filled U-shaped steel beams were compositely attached to the concrete floor slab. The test was conducted in two stages. The first testing program was carried out on one-sided moment connections to find the most promising connecting scheme. The strengthening scheme, or welding steel plates to the beam bottom flange with minimized stress concentration, was shown to be the most satisfactory, and it was used in the second-stage test on two full-scale cruciform specimens. Considering the unique constructional nature of the proposed composite connections, the critical limit states such as weld fracture, local buckling, concrete crushing, and rebar buckling were carefully addressed in designing specimens. Test results showed that the connection details and design procedures proposed in this study can successfully control the critical limit states mentioned previously. The proposed connection detail successfully pushed the plastic hinging to the tip of the strengthened zone as intended in design, thus effectively protecting the more vulnerable beam-to-column welded joint. The specimens typically exhibited a maximum story drift capacity of more than 5.5% rad, exceeding the minimum limit of 4% rad required of special moment frames. Four of the five specimens tested in this study eventually failed because of a low-cycle fatigue fracture across the beam bottom flange at a high story drift greater than 5.0% rad.

Seismic Performance of Beam-Column Connections for Special Moment Frame Using 600 MPa Flexural Reinforcement

An experimental study was performed to evaluate the seismic performance of beam-column connections using 600 MPa re-bars for beam flexural reinforcement. Three full scale specimens of interior beam-column connection and two specimens of exterior beam-column connection were tested under cyclic loading. The specimens were designed to satisfy the requirements of Special Moment Frame according to current design code. The structural performance of the specimens with 600 MPa re-bar were compared with that of the specimen with 400 MPa re-bars. The test results showed that bond-slip increased in the beam-column joint. However, the load-carrying capacity, deformation capacity, and energy dissipation capacity of the specimens with 600 MPa re-bar were comparable to those of the specimens with 400 MPa re-bars.

Slab Construction Load Affected by Shore Stiffness and Concrete Cracking

ACI Structural Journal, V. 108, No. 6, November-December 2011. MS No. S-2010-076.R2 received October 8, 2010, and reviewed under Institute publication policies. Copyright