Wei-Jian Yi

Experimental Study on Progressive Collapse-Resistant Behavior of Reinforced Concrete Frame Structures

This paper demonstrates the feasibility of using a static unloading approach to simulate column loss in investigating the progressive failure of a reinforced concrete frame due to the loss of a lower story column. A four-bay and three-story one-third scale model representing a segment of a larger planar frame structure was tested. A constant vertical load was applied to the top of the middle column by a servo-hydraulic actuator to simulate the gravity load of the upper floors and the failure of the middle column of the first story was simulated by unloading a mechanical jacking system. The frame collapse, defined in this study as the rupture of tension steel bars in the floor beams, occurred at a vertical unloading displacement of 456 mm (18 in.) that corresponds to a beam drift angle of 10.3 degrees. The mechanical behavior of the model frame is analyzed and the redistribution and transition of the load resisting mechanisms is discussed. During the progressive collapse process, the RC frame structure experience 3 distinct phases in its response: elastic, plastic and catenary phases. Findings indicate that the calculated capacity of the frame based on the plastic limit state was approximately 70% of the tested failure capacity if catenary effects are also included. The findings in this study can contribute to the future development of collapse-resistant design methods.

Fatigue Behavior of Reinforced Concrete Beams with Corroded Steel Reinforcement

Corrosion of steel reinforcement is one of the most prevalent degradation mechanisms in reinforced concrete (RC) structures. It may impair structural capacity through the loss of reinforcement cross section, the loss of bond between reinforcement and concrete, cracking, and spalling of the concrete. This study investigates the performance of RC beams with corroded reinforcement under fatigue loading. In addition, the mechanical properties of corroded steel reinforcement in beams after fatigue loading were investigated up to failure. It was found that an increase in the corrosion degree of steel reinforcement decreased the fatigue life of the beams and caused them to collapse in a brittle failure mode. For the same fatigue loading history, the ratio of maximum elongation at rupture to yield strength of the corroded steel decreased with an increase in the fatigue stress magnitude.

Progressive Collapse Performance of RC Flat Plate Frame Structures

AbstractIn collapse-resistant design of structures, understanding primary structural failure-mechanisms and alternative load paths under accidental extreme loads is important. A quasi-static experimental method is used to simulate the sudden loss of a column in a single story concrete flat slab-column structure. In a series of experiments on two identical large-scale models, an interior, exterior, and corner column of the structure were replaced by mechanical jacks during the fabrication of the structure. After application of uniform loads of increasing intensity, the jack representing the lost column was unloaded. In the first model test wherein an interior column was removed, a downward concentrated load was also applied on the upper end of the interior column until the structure collapsed. Elastic behavior, yield-line mechanisms, and compressive and tensile membrane actions in the flat slab-column structure were observed during the collapse tests. The results provide valuable information on the load tr...

Experimental Studies on Confinement Effect of Steel Hoops in Concrete Columns

This experimental study investigates the distribution of stress and strain of a concrete column section under cyclic loads. The seismic behavior of the specimens under different loading paths and axial load levels was examined by testing four reinforced concrete frame column specimens without an effective concrete cover under constant axial compressive and cyclic lateral loading. The hoop strains of lateral reinforcement at different column heights under cyclic loading were attained by attaching strain gages along the hoops. The characteristics of strain distribution in the transverse reinforcement also were studied. Results of the testing in conjunction with the cyclic stress-strain relationship of steel and the confining stress and its distribution around the cross section were evaluated. The effect of the confining force of transverse reinforcement on the ductility demand of columns under cyclic loading also is highlighted. Findings show that both the loading path and the axial load level affect the length of the plastic region. The transverse reinforcement provided confining stress both in the compressive and tensile sections prior to crushing of the concrete. The strains in the transverse reinforcement increase rapidly after it yields, and the peak lateral load is achieved. The lateral strain does not decrease until concrete has spalled after the crushing of the concrete. The asymmetric distribution of the confining stress under combined axial force and cyclic bending suggest that the nature of the confining stress distribution should be considered when calculating the movement-curvature relationship of the section.

Earthquake response of low-rise RC moment frame structures according to energy dissipation ratio of beam-column joints

Abstract Seismic response of RC moment frame structures (particularly, in low-rise buildings) is affected by the inelastic hysteretic response and energy dissipation of beam-column joints. In current earthquake design codes, however, the earthquake response of the structures is evaluated without direct consideration of the energy dissipation of beam-column joints. In the present study, non-linear time history analysis using the energy-based hysteresis model was carried out to investigate the effect of the energy dissipation performances of the beam-column joints on the seismic response of the structures. To demonstrate the applicability of the proposed analysis method, it was applied to existing dynamic test results of RC moment frame structures. On the basis of the proposed method, non-linear time history analysis for six different typed low-rise RC moment frame structures under 14 earthquake records was performed. Design parameters were the energy dissipation ratios of beam-column joints (from pinching behavior to elasto-perfectly plastic behavior), moment frame stories (3, 5, and 9 stories), and moment frame configuration (two and four spans). The analysis results showed that the low energy dissipation of beam-column joints increased the ductility requirement of the low-rise RC moment frame structures.

Shear Mechanisms in Reinforced Concrete Beams under Impact Loading

AbstractA well-instrumented drop-weight test program was developed to investigate shear failure modes of large-scale RC beams under impact loading. Test variables included beam span, transverse rei...

Discussion of “Rotation-Based Shear Failure Model for Lightly Confined RC Columns” by Wassim M. Ghannoum and Jack P. Moehle

Li-Wei Liu; Wei-Jian Yi, Ph.D.; and Yun Zhou, Ph.D. Ph.D. Student, College of Civil Engineering, Hunan Univ., Changsha 410082, P.R. China (corresponding author). E-mail: hnuliuliwei@ yahoo.cn Professor, College of Civil Engineering, Hunan Univ., Changsha 410082, P.R. China. E-mail: wjyi_hnu@163.com Associate Professor, College of Civil Engineering, Hunan Univ., Changsha 410082, P.R. China. E-mail: zhouyun05@gmail.com