Capacity analysis of exterior beam-column reinforced concrete joints using Midas FEA software

. One of the main parts in the planning of reinforced concrete structures lies in the beam column joint (BCJ) connection . The beam-column connection consists of interior, exterior, and knee joints. In this study an analysis has been carried out regarding the behavior of the joints on the exterior of the beam-column joints and look for the capacity of the structural strength of the beam-column using conventional methods. The connection type component will be carried out based on the results of laboratory test results and modifying the connection type based on the data search obtained, then compared with the Midas FEA Software. The results of the analysis of the capacity of beam-column joints based on ASCE 41 and finite elements in the yield condition yield smaller values with a difference of 1.34% - 4%. In the inside hook modification using laboratory and finite element test methods, the difference in capacity values is greater, namely 2.91% - 8.12%. The behavior of the beam-column joints capacity when two U-bar joint shear reinforcement was added did not increase significantly by 2.77% and the behavior of the beam-column joints when four U-bar joint shear reinforcement was added showed a high increase by 95.26%.


Introduction
Connection is the meeting point of one component to another component.Reinforced concrete beam-column joints are in column sections located between beam intersections.Beam-column joints are required to withstand alternating loads that develop the flexural strength of adjacent beams [1].Structural components under different types of loading are based on the design and details of the reinforcement [2].
The function of reinforced concrete beam-column joints is to transfer loads and moments at the ends of the beams to the columns and provide stability to the structural system.Connection types consist of interior joints, exterior joints, and knee joints.Exterior joints in a cyclically loaded frame will be subjected to shear strength of the longitudinal joints.Knee joint is required when restraints in beam reinforcement head along the top face of the joint [3].
Connection deformations are grouped into two parts, namely structures that do not tend to experience large inelastic deformations and do not need to be designed are called non-seismic structures and structures that must be able to accommodate large inelastic deformations are called seismic structures [3].
In this case, the analysis done is the connection reinforcement model HBK which has the largest capacity for receive a lateral force.
With Fig. 1 description regarding beam-column joints, the author wants to discuss connections with reinforced reinforcement models Inside hook and Outside hook using finite element analysis MIDAS FEA.

Current design method
To find the capacity of the exterior beam-column joints, three failure modes are considered as follows: 1. Flexural yielding of beam reinforcement 2. Joint crack failure, and 3. Shear failure of beam reinforcement joints.
The lateral force corresponding to each failure mode can be estimated as follows.

Beam-column joints
The beam-column relationship is a very critical zone in strengthening concrete frame structures where the elements intersect in more than one direction.Structural joints ensure and transfer forces present at the ends of beams.The beam-column connection is an important part of the frame structure that can transfer various types of loads and forces such as moments, shears and torsions in the design process beam-column joints have a major role in resisting lateral loads such as earthquakes, wind and explosions [5].
The internal moment frame restraint system provides rigidity to the structure that can withstand lateral forces.Beam-column connections are rigidly and specifically designed to accommodate bending moments caused by lateral forces.Steel and concrete materials in designing beam and column relationships are the most commonly used to provide flexibility in planning [6].

Exterior joint
Exterior joints have a flow of forces acting to resist oblique cracks and to resist diagonal stresses.For joints with an external configuration, the beams are connected to three or two opposite sides, the width of the beam on the two opposite sides of the connection shall be at least ¾ of the depth of the beam.Configuration of exterior joints on beam joints that do not meet the size requirements, must be evaluated using a γ value for exterior joints, namely 15 [7].
The design criteria for exterior building beamcolumn joints require shear reinforcement to prevent damage from shear cracking.The joints also require transverse reinforcement to prevent buckling of the column longitudinal reinforcement [1].

Structure design capacity
Estimating the failure of a structure based on the maximum load experienced by the structure.The behavior of the structure due to an earthquake will experience deformation depending on the amount of bending deformation, when combined with detailing to find the amount of ductility.Optimal deformation capacity energy dissipation will produce a structure that behaves plastically [8].
Fig. 2 shows the support reactions and internal moments at the joint face in an exterior beam-column connection specimen subjected to a lateral load (P) at the top of the column.Mnb is the nominal flexural strength of the beam and lb is the length of the beam from the center line of the column to the support.The capacity of beam column can be calculated from the moment equilibrium using the following Equations 1-2. (1) Fig. 2. Internal forces and reaction forces acting on exterior beam-column connections [9].
The capacity of the beam-column connection in Equation 1 can be calculated when the beam reaches its yield state and in Equation 2 it can be calculated when the beam has reached its ultimate condition [10].In determining the shear strength capacity of the beamcolumn connection, it can be calculated using the following Equation 3.
Beam-column connections are when confined and the cover at least three-quarters of the common faces.In sales, the effective area (Aj) in Equation 3 can be calculated by adding the effective joint width to the joint height around the reinforcement that produces shear [1].

Nonliniear finite element method
Structural behavior in a case is said to be nonlinear if the strength matrix or load vector depends on the displacements.Changes in material properties, such as plasticity, are included in the nonlinear classification of materials.Configuration changes, such as large deformations and a beam whose elastic properties are included in the geometric nonlinear classification.Loads that cause large deformations in the structure can change the shape and behavior of the structure.When the material stress reaches a certain limit, the material properties will also change [11].Nonlinear analysis ignores the assumption of constant stiffness, which is defined as a change in behavior during the deformation process, and the stiffness matrix will be updated continuously so that the structure converges with an iteration process that requires a long duration of time [7].

Research method
The stages of the methodology and research flow can be seen in Fig. 3. Following are some explanations of the stages of this research method: 1. Conduct literature studies from various sources such as articles, books, scientific journals, and other reliable sources related to research.

Type and number of test object
There are three (3) types of test objects for beam-column connections with each type of stirrups having different variants and dimensions.

Test speciments
Reinforcement in reinforced concrete columns with codes HBK 1, HBK2, HBK 3 using 8D25 longitudinal reinforcement and transverse reinforcement can be seen in Table 2 and Table 3. Beam reinforcement for all test objects is with 7D19 top reinforcement and 4D19 bottom reinforcement.Dimensions of reinforced concrete beam-column connections tested with column height between pinned bearings as high as 3060 mm and beam length between roll bearings as high as 2880 mm.The column dimensions used for reinforced concrete specimens with codes HBK 1, HBK 2, HBK 3 are hc × bc = 350 × 350 mm, and the beam size used for reinforced concrete specimens is bb × hb = 350 × 480mm.The dimensions of the test object can be seen in Fig. 4.

Material strengths
The quality of the concrete used by all codes of specimens is 31.

Structural geometry modeling MIDAS FEA
The relationship between beams and columns modeled in 3 dimensions with details of reinforcement connections as shown in

Result and discussion
The results of the analysis of the yield capacity of the beam-column connections are calculated based on Equation 1.The behavior of the increase in beam column connection capacity can be seen when the behavior of HBK is added 2 U-bar shear reinforcement and 4 U-bar shear reinforcement.The capacity of beamcolumn connections from the results of manual calculations, laboratory reference data and finite element analysis of the MIDAS FEA program will then be compared to one which can be seen in Table 4 and Fig. 7.

Beam-column connection crack pattern
The crack pattern obtained based on the MIDAS FEA finite element testing and laboratory testing on the HBK 1 model without the U-bar joint shear reinforcement can be seen in Fig. 8, which shows an almost identical crack pattern.

Conclusion
1.The capacity of the beam-column connection when it reaches the melting condition based on the results of laboratory tests with the finite element method shows that the biggest difference is 4.54%.2. The capacity of beam-column connections during yield conditions based on manual calculations with laboratory tests produces the largest difference of 4%. 3. The behavior of the beam-column connection capacity when two U-bar joint shear reinforcement was added did not increase significantly by 2.77% and the behavior of the beam-column connection when four U-bar joint shear reinforcement was added showed a high increase by 95.26%.4. The crack pattern based on the results of finite element analysis with laboratory results shows almost the same crack pattern.

2 .
Collect and summarize data from the results of tests that have been carried out by Kim et al. [9].3. Modeling and analysis using the finite element method and Midas FEA software.4. Analyze the data obtained from the Midas FEA software to answer the objectives and formulation of the research problems.5. Make conclusions to answer the objectives and formulation of research problems based on the analysis results obtained from the Midas FEA software.

Table 4 .
Comparison of melting capacity and increase in HBK capacity.
Fig. 7. Graph of laboratory test melting capacity vs MIDAS FEA.