Behavior Of Exterior Beam-column Joints Research Articles

Cyclic behavior of lightweight engineered cementitious composite beam-column joints

This study investigated the behavior of exterior beam-column joints made of engineered cementitious composites (ECC) with varying densities (i.e., ranging from 1740 to 2080 kg/m3) under reversed cyclic loading. In total, six ECC joints were cast using different mixtures detailed as: (a) two normal weight ECC (NWECC) mixtures developed with silica sand (SS) as a filler and either polyvinyl alcohol (PVA) fibers or polypropylene (PP) fibers; (b) two lightweight ECC (LWECC) mixtures developed with lightweight slate sand (SL) as a filler and either PVA fibers or PP fibers; (c) one LWECC mixture developed with PVA fibers and the filler consisting of a combination of SL and powder rubber (PR) in a ratio of 70%:30% (by volume); and (d) one LWECC mixture developed with PVA fibers and the filler consisting of a combination of SL and crumb rubber (CR) in a ratio of 70%:30% (by volume). An additional joint made of conventional lightweight concrete (LWC) with a density of 1850 kg/m3, was tested for comparison. The steel reinforcement details were kept the same on all specimens conforming to the typical design of strong column-weak beam concept. The hysteretic behavior, capacity, stiffness, cracking behavior, ductility, and energy dissipation capacity of all tested joints were assessed. The results indicated that utilizing SL alone helped to successfully develop lightweight joints with a mixture density of less than 1850 kg/m3 and strength-to-weight ratios comparable to those of NWECC. However, these joints exhibited lower ductility and energy dissipation capacity compared to NWECC joints. Using PR or CR with SL appeared to be a more efficient alternative over using SL alone, in constructing LWECC joints with lighter self-weight, higher ductility, and higher energy dissipation capacity. Notably, all LWECC joints demonstrated superior structural performance compared to the LWC joint, even though they were lighter, thus indicating promising potentials of LWECCs for lightweight structures. The results also revealed that in all tested specimens, the PVA fibers exhibited better performance over those with the PP fibers.

Cyclic loading test for shear-deficient reinforced concrete exterior beam-column joints with high-strength bars

The seismic behavior of exterior beam-column joints is significantly affected by the beam rebar yield strength and joint hoop ratio. In the present study, high-strength bars were used for beam longitudinal bars and stirrups in exterior beam-column joints with the joint hoop ratio lower than the requirement of ACI 318–14. In an attempt to distribute the damage from the joint panel toward the beam in the shear deficient exterior beam-column joints, the beam shear resistance was intentionally decreased by removing the beam cross-ties or by using the high-strength beam stirrups at a large spacing. Cyclic loading tests were performed on 9 exterior beam-column joints. The test parameters were the amount of joint hoop bars, the yield strength and diameter of the beam longitudinal bars, the yield strength and spacing of the beam stirrups, and use of beam cross-ties. The test results showed that the seismic performance was improved by increasing the beam flexural damage, preventing a shear failure, through a reduced contribution of the beam stirrups to the shear strength of the beam or weakening the beam by removing the beam cross-ties that increased vulnerability of buckling of the beam longitudinal bars. As the damage concentration was transferred from the joint panel to the weakened beam, the energy dissipation capacity and damping ratio increased by 30% and 54%, respectively. It was found that 33% decrease in the amount of joint hoop bars compared to that of prescribed in ACI 318, equal to one leg of joint stirrup, was enough to change the failure mode from the beam flexural failure to severe joint shear failure. The allowable development length of beam compression bars was discussed to prevent the cover concrete spalling at the back face of the column. Particle image velocimetry (PIV) was conducted to accurately measure the joint shear deformation and the distribution of the local flexural deformation of the beam.

A Review-Behavior of Reinforced Concrete Exterior Beam-Column Connections under Cyclic Loading

In many seismically active regions worldwide, massive reinforced concrete (RC) structures built before the 1970s existed. These older RC buildings, in countries having seismic history, were designed for gravity loads only. Anyway, the beam-column connections influence the structures where the functions of connection shortage by transport the forces like shear, moment, and torsion through the beam to the column. Also, it could behave in a ductile manner to help the structure resist the seismic, as simulate the seismic loading by high and low cyclic loading. Due to the failure of external joints more than the internal beam-column joints, this review focuses on the behavior of exterior beam-column joints under cyclic loading, consequently simulated the behavior under an earthquake and the reinforcement detailed.

Flexural Behavior of Hybrid-Reinforced Concrete Exterior Beam-Column Joints under Static and Cyclic Loads

This study presents an experimental investigation of the flexure behavior of exterior beam-column joints made from hybrid concrete (normal concrete (NC) and reactive powder concrete (RPC)) or hybrid reinforcement (steel and carbon fiber reinforced polymer (CFRP) bars internally or externally by near surface mounted (NSM) technique). Nine hybrid-reinforced concrete beam-column joint specimens under the effect of static or cyclic loading were studied and tested within three test groups. Several variables that affect the behavior of the beam-column joint region are investigated such as: type of loading (static or cyclic), type of hybridization (concrete hybridization or reinforcement hybridization), and area of concrete hybridization. The results showed that using RPC as a replacement concrete at different areas of beam-column joint under static loading improved the ultimate load capacity and first cracking load to about 8–32% and 20–60%, respectively, compared with the reference NC joint with increase in the ductility of about 6–14%. Moreover, using the same technique under cyclic loading condition showed an increase in the ultimate load of about 39%, with improvement in the cumulative ductility of about 12% compared with the reference NC joint. On the other hand, using CFRP bars as (internal or external) hybridization system (33% of main reinforcement) under static loading caused increments of ultimate and first cracking loads of about 11%, 8% and 0%, 30%, respectively compared with the reference steel reinforced joint; while the ductility ratio increased about 36%, 5%, respectively. Moreover, the internal hybrid reinforcement system exhibited a decrease in the ultimate load of about 15% and reduction in the cumulative ductility of about 40% under cyclic loading.

EFFECT OF USING HIGHLY CONFINED SHORT LAP-SPLICE REINFORCEMENT ON SEISMIC PERFORMANCE OF EXTERIOR BEAM-COLUMN JOINT

The present paper aims to examine the behavior of exterior beam-column joints with different reinforcement details of their columns: continuous and lap splice longitudinal bars were adopted as design parameter. The experimental program was carried out at the Concrete Research Laboratory at Housing and Building Research Center in Egypt; included three exterior reinforced beam column joints that were tested under the effect of quasi-static cyclic loading. One sample was designed according to the provisions of the current seismic design codes and served as a control sample. Columns of the other two samples were detailed with well confined shorter lap spliced longitudinal reinforcement. The overall behavior of the beam-column joints and conclusions are discussed in this paper.

Cyclic behavior of exterior beam-column joints strengthened with precast slurry infiltrated fibrous concrete laminates

Beam-column joint is an important component of a reinforced concrete (RC) moment resisting frame and should be designed and detailed properly, especially when the frame is subjected to seismic forces. Many of the existing structures located in the seismic prone zone were designed and built on the basics of earlier codes with inadequate ductile reinforcement detailing. At present, even though these structures are not deteriorated, they are structurally inadequate. Hence, it becomes necessary to upgrade these structures using most economical and reliable strengthening techniques. This paper presents the investigations carried out to study the cyclic behavior of exterior beam-column joints strengthened with precast slurry infiltrated fibrous concrete (SIFCON) laminates. A total of 12 specimens corresponding to four test series were cast and tested under cyclic loading to study the load-deformation behavior, ductility associated parameters, ultimate load carrying capacity and failure characteristics. 20 mm thick precast SIFCON laminates were used to strengthen the conventional RC and fiber RC beam-column joints. For laminates, the fiber volume fraction was 9%. The steel fibers used in the study were round crimpled fibers having 0.5 mm diameter with the aspect ratio 60.

Cyclic Response of Exterior Beam-Column Joints with Different Anchorage Methods

This paper presents the cyclic response of six exterior beam-column joints with or without eccentricity to evaluate the use of mechanical anchorages in place of hooked bar anchorages. In high seismic zones, the hooked beam bars often cause steel congestion in a joint at building comers. From previous tests of beam-column joints, the use of mechanical anchorages in place of hooked bar anchorages provides a promising solution for steel congestion, but it has not been verified in eccentric beam-column joints. The presented experimental program demonstrates that eccentric beam-column joints with mechanical anchorages can exhibit satisfactory performance and adequate anchorage capacity for a limiting drift ratio. Extending ACI design methods to cover the use of mechanical anchorages for eccentric beam-column joints is an appropriate code modification. Test results also indicate that the cyclic behavior of exterior beam-column joints can be significantly improved by attaching double mechanical devices on each beam bar within the joint.

The effects of stirrups and the extents of regions used SFRC in exterior beam-column joints

Seven full-scale exterior beam-column joints were produced and tested under reversible cyclic loads to determine. Two of these seven specimens were produced using ordinary reinforced concrete (RC). Steel Fiber Reinforced Concrete (SFRC) was placed in three different regions of the beams of the rest five specimens to determine the extent of the region where SFRC is the most effective. The extent of the region of SFRC was kept constant at the columns of all five specimens. Three of these five specimens which had one stirrup in the joint, were tested to evaluate the effect of the stirrup on the behavior of the beam-column joint together with SFRC. In production of the specimens with SFRC, all special requirements of the Turkish Earthquake Code related to the spacing of hoops were disregarded. Previous researches reported in the literature indicate that the fiber type, the volume content, and the aspect ratio of steel fibers affect the behavior of beam-column joints produced with SFRC. The results of the present investigation show that the behavior of exterior beam-column joints depends on the extent of the region where SFRC is used and the usage of stirrup in the joint, in addition to the parameters listed in the literature.

반복하중을 받는 외부 보-기둥 접합부에서 작은 헤드를 사용한 Headed Bar적용

The applicability of headed bars in exterior beam-column joints under reversed cyclic loading was investigated. A total of ten pullout tests were first performed to examine pullout behavior of headed bars subjected to monotonic and cyclic loading with test variables such as connection type between head and bar stem (weld or no weld), loading methods (monotonic or cyclic loading), and head shape (small or large circular head and square head). Two full-scale beam-column joint tests were then performed to compare the structural behavior of exterior beam-column joints constructed using two different reinforcement details: i.e. standard hooks and headed bars. Both joints were designed following the recommendations of ACI-ASCE Committee 352 for Type 2 performance: i.e. the connection is required to dissipate energy through reversals of deformation into inelastic range. The pullout test results revealed that welded head to the stem did not necessarily result in increased pullout strength when compared to non-welded head. Relatively large circular head resulted in higher peak load than smaller circular and square head. Both beam-column joints with conventional hooks and headed bars behaved similarly in terms of crack development, hysteresis curves, and peak strengths. The joint using the headed bars showed better overall structural performance in terms of ductility, deformation capacity, and energy dissipation. These experimental results demonstrate that the headed bars using relatively small head can be properly designed far use in external beam-column joint.