INTRODUCTION AND LITERATURE REVIEW
1.2 LITERATURE REVIEW
1.2.1 Experimental studies on RC beam-column joints and connections
The first experimental study on RC beam-column joint was conducted in the United States by Hanson and Connor [1967]. In their study seven exterior beam-column joints were tested under simulated cyclic earthquake loading. Performance of these specimens including moment capacities at first yield of reinforcements, ultimate moment and ductility of the assemblies, maximum beam deflection and anchorage bond stresses of beam reinforcements were reported. The authors concluded that properly designed cast- in-situ RC frames could resist severe earthquakes without loss of strength and moderate earthquakes without damage. These tests became the standard reference for subsequent investigations.
Megget and Park [1971] reported experimental investigation on the behaviour of exterior RC beam-column joints subjected to seismic loading with a low column axial load. Three specimens were designed using different methods, which were tested under the same cyclic loading in their investigation. The authors found that the joints of the specimens were not adequately reinforced against large shear stresses at inelastic loading conditions.
Scribner and Wight [1980] investigated the strength decay in RC beam-column joints under load reversals. Eight half-scale and six full-scale RC exterior beam-column connections were tested in order to study the effect of intermediate longitudinal reinforcement on shear deterioration of flexural members subjected to repeated type of loading. Some specimen contained only vertical web reinforcement while some contained intermediate vertical reinforcement along with vertical web reinforcement. Specimens were tested under displacement-controlled cyclic loading. The authors concluded that severe loss of strength and energy dissipation was observed for the members which were subjected to high shear stress. It was also concluded that the increase in size of vertical ties increased the energy dissipation capacity along with damage at a concentrated location, while longitudinal intermediate bars was capable of spreading the damage throughout the beam plastic hinge region.
Durrani and Wight [1985] reported results of an experimental investigation on the performance of an interior beam-column joint under earthquake-type loading, which had less joint reinforcement than recommended by ACI-ASCE Committee 352. They concluded that the joint shear stress had a pronounced effect on the behavior at large ductility levels and the joint hoop reinforcement. Some guidelines were suggested to simplify the design of joints.
Shah et al. [1987] reported the effects of loading rates on the performance of RC beam- column joints. Small scale joints designed as per ACI codal provisions were tested under
two cyclic loading rates of 0.025 Hz and 1.0Hz. The author concluded that at the faster rate the maximum load carrying capacity of the specimens was higher. Further, the faster rate of loading caused greater damage and produced more localized cracks than that at slower rate. Thus, it was indicated that the rate effect is related to the transfer of forces between reinforcing bars and concrete.
Abdel-Fattah and Wight [1987] studied the relocating of plastic hinging zones for earthquake-resistant design of RC buildings. In their investigation, twelve full-size interior beam-column connections were tested under cyclic loads. In addition to the main reinforcement in beam, intermediate longitudinal reinforcing bars were passed through the joint and were extended up to a specific length away from the column face in beam.
The aim of the research was to relocate the potential beam plastic hinges away from the column face by the addition of these intermediate longitudinal bars. Three basic modes of failure including joint shear failure, localized beam hinging zone and distributed beam hinging were observed in their tests. The authors concluded that the performance of extra reinforcement in the joint could help in successfully relocating the plastic hinge away from the column face.
Ehsani and Alameddine [1991] investigated the behaviour of corner joints constructed with high-strength concrete. Twelve specimens were tested in their study in order to examine the recommendations of ACI-ASCE Committee 352 on the design of high- strength ductile moment resisting beam-column joints. The authors showed that the recommendations which were developed for normal strength concrete could not be applied to high-strength concrete frame. They presented new requirements such as allowable joint shear stress and joint confinement for ductile design of RC beam-column joints.
Tsonos et al. [1994] tested fourteen exterior joints to study the effect of variable axial loading in comparison to constant axial loading. The main variables for the study were the axial load, ratio of column flexural capacity to that of the beam, the joint shear stress level and the amount of transverse reinforcement in the joint. The authors concluded that the increased axial load lead to major deterioration of the joints.
Chutarat and Aboutaha [2003] investigated a solution for relocating potential beam plastic hinge zones by the use of headed bars in the exterior RC joints. Four large-scale beam- column connections, with and without headed bars, were tested under quasi-static cyclic lateral loads. The results showed that straight-headed bars could relocate beam potential plastic hinge regions very effectively.
Murty et al. [2003] tested twelve half-scale exterior beam-column joints under displacement-controlled cyclic loading to study the effectiveness of anchorages of longitudinal beam bars and the transverse reinforcement in the joint core. Four different reinforcement details for anchorage into the column for beam longitudinal bars were followed. The authors concluded that out of all the different joint reinforcement detailing investigated, the performance of the joint constructed following ACI standard hook was the best and it was easy to construct as well.
Joshi et al. [2005] tested four full scale exterior precast beam-column joint under cyclic loading in order to identify a suitable technique for connecting precast beam and column components. Following two different types connection techniques, precast and monolithic specimens were cast. Out of two types of detailing, one was done by the provisions of Indian standard code while the other was cast by using single U bar as top and bottom reinforcement of beam. The column was placed horizontally and beam was placed vertically in the test set up. The axial movement of the column was restrained by providing stiff supports fixed to the strong floor by steel studs. The ends of the column
were supported on rollers equidistant from the beam centre. The authors concluded that the performance of the monolithic specimen with U bar detailing was better than all other types of joints used in their study.
Nie et al. [2008] tested six beam-column joints comprising of three interior and three corner joints for proposing a new connection system for concrete filled steel tube composite column and RC beams. According to the new system, the column was encased by a steel tube. The tube was cut at the beam-column joint and the steel reinforcing bar in the RC beam was kept continuous at the floor level in which concrete was confined by multiple lateral hoops in the joint region. The specimens were tested under cyclic loading.
The authors concluded that the new connection was capable of dissipating enough energy in addition to showing a good performance from ductility aspect.
Li and Kulkarni [2010] carried out an experimental and numerical investigation on RC wide beam-column joints subjected to seismic loads. It was concluded that wide beam- column joints when designed with suitable parameters would perform quite well in carrying the horizontal lateral loads. Moreover, due to the larger section of the wide beam, the shear stresses in the beam transverse reinforcement were very low and therefore, the requirement of beam shear reinforcement might be relaxed.
Choudhury [2010] tested beam-column connections with three typical deficiencies and three geometrically similar specimens of full scale, two-third scale and one-third scale sizes. All specimens were subjected to slow cyclic loading test. The performances of the connections in each category were evaluated in terms of displacement ductility, cumulative energy per unit volume, cumulative energy dissipation, variation of stress with deflection etc. The study was aimed at to explore the existence of size effect and it was observed that the size effect in RC beam-column connection followed closely the law
The literature survey revealed that the test on beam-column joints and connections were initiated as early as 1967. Since then, other research studies were carried out to improve the performance for beam-column joints and connections. Experimental studies were conducted on both exterior and interior joints/connections on full scaled as well as scaled down specimens. Quasi static loading were used by many researchers to simulate the seismic actions. These frequencies are however substantially lower than those corresponding to the frequencies of actual seismic excitations. Characteristic of loading such as number of repeated loading cycle of displacement, frequency of excitation and the level of excitation plays a vital role in the behavior of the joints and connections.
However, very little informations were reported on the performance of beam-column