Application of a novel energy dissipation beam-column connector in precast structures

Abstract

In this study, which is prepared as a master thesis, seismic performance and cyclic loading behavior of four type precast reinforced concrete frames with two different type of moment resisting beam to column connection is investigated comparatively. The first one is the widely used moment resisting connection that is defined as wet connection in TBDY. The second connection type is known as ACPH (Artificial Controllable Plastic Hinge) that is taken as reference study about repleaceable plastic hinge concept. The goal of this connection, known as an replaceable plastic hinge, is to defend reinforced concrete components from earthquake related plastic deformations by keeping them in a specialized connecting section. It will be possible to repair the broken connections after the earthquake so the building can keep on operating normally. Another advantage of the developed method is that it is disassemblable and removable, allowing a completed structure to be dismantled, transported and reassembled when desired. The study is consist of five major sections. In the first section, precast reinforced concrete structures are introduced briefly and most used moment resisting beam to column connections is explained with mentioning advantages and disadvantages of them. Then the precast structure connection types included in the Turkish seismic design code are introduced. Within the scope of the thesis, MAB1 type connection, which is mentioned in Turkish Seismic Code, is used for analytical study. After that, the aim and scope of this thesis and literature review on replaceable hinge conncections are explained. At the end of first section, the paper which is named as "Performance coordination design method applied to replaceable artificial controllable plastic hinge for precast concrete beam-column joints" by Yuan (2022) are explained in more detail. Within the scope of thesis, this paper are chosen as reference for analytical study. An idea of strong joint/weak component structural design is covered by this design philosophy. It is recommended that the ACPH have a lower bending capacity than the end beam to ensure that the damage mechanism and failure mode are stable, regular, and controllable. Moment design of the connection was performed according to the equations given in the reference article. According to the reference article, it is recommended to keep λ below 0.9. When λ value were less than 0.9, This indicated that the ACPH performance was weaker than that of the concrete components, and the structural deformation was mainly concentrated at the ACPH. When λ were about 1, the area of the ACPH hysteresis loop gradually grew. The ACPH and concrete components subjected to loading participated in the structural deformation, and the Z-shape of the hysteresis loops gradually changed to spindle-shaped. The concrete components became a vulnerable section as λ increases. In the second section, first of all, details of ABAQUS software and information about Concrete Damaged Plasticity (CDP) are given. Then, modeling of reference article is performed in ABAQUS software by considering parameters such as model geometries, materials, interactions, loading, boundary conditions and mesh. Then the results are compared with article to show that the model works correctly. In this section details about modeling are as follows; reinforced concrete elements and steel joint elements are modeled within the ABAQUS software. ABAQUS software uses the Concrete Damaged Plasticity (CDP) model, which allows us to take into account nonlinear effects of materials and degradation effects. The geometric shapes for concrete and steel hinge elements are modeled as three-dimensional (3D), deformable, solid and extrusion. Reinforcement Steels are selected as 3D, wire and planar. For the material properties, the concrete model used is the Popovics compressive stress-strain model for concrete by Popovics (1973) and a modified tensile reinforcement model by Nayal and Rasheed (2006) is chosen to represent the tensile stress behavior of concrete. Reinforcement steel and steel hinge elements have inputted to software as a stress-plastic strain. Another important parameter to get the right result is the mesh, C3D8R was selected for concrete materials and ACPH. With this selection, concrete is defined as a 3D element with 8 nodes. For steel reinforcements, T3D2 is selected as a linear 3D material with 2 nodes. In the test setup of the reference article, a design was made for λ=0.3 and an experimental study was performed. Accordingly, in order to calibrate the ABAQUS model, the model was calibrated using this λ value and the hysteresis curves compared. In the third section, frame designs are made to evaluate the characteristics of the ACPH type connection that stand out from other connection types. The frames consist of 4 different type that depends on number of storeys and bays. These are one bay-one storey, one bay-two storeys, two bays-one storey and two bays-two storeys. The column and beam elements to be used in the design are dimensioned. 1.8m column height and 3m beam length were taken because the same dimensions were used in the reference article. However, the frame dimensions are smaller in height and length than the actual field application. The reason is that it is not feasible to analyze with real applications due to reasons such as data storage and analysis time in the analysis performed in ABAQUS software. Therefore, the results obtained should be evaluated accordingly. Beam and column are dimensioned for a total of 4 types of frames. The selected column and beam reinforcement is common for all of them. A force of 15% of the axial load capacity of the column is applied to the top of the column. It is checked that the column is stronger than the beam. After deciding on the properties of the column and beam, moment and shear design for ACPH was performed. The λ value for the design of the frames was 0.45, while the reference article calibration had an λ value of 0.3. In this direction, it is possible that the hysteresis curve behavior may change as the λ value increases. As a result, 8 frames including 4 ACPH and 4 wet connection type frames were modeled in ABAQUS software. As ABAQUS element geometry and material model creation parts are discussed in section 2, the same method is used in this section. In the Step module, 3 different procedures will be applied for each frame analysis. Within the scope of this thesis, these procedures are "frequency" for period calculation, "dynamic implicit" for nonlinear dynamic analysis and "static general" for cyclic displacement loading. After the solution steps are determined, the desired data is selected from the "Edit Field Output" section to select which data will be in the solution outputs. The outputs for frequency analyses is frequency of frames. The outputs for dynamic analyses are base shear, DAMAGEC, DAMAGET, SDEG, PE and S. The outputs for cyclic analyses are base shear and roof displacement. After that, it is selected how the elements that we combine in the assembly section will establish a connection on the surfaces they come into contact with each other. In the other section, loading states and boundary conditions of the models are defined. For frequency analysis, all column bottom surfaces should be defined as fixed. In case of earthquake, the direction in which the acceleration is applied should be left free. Earthquake accelerations are applied to the column bottom surfaces and the nonlinear dynamic analysis steps are completed by applying gravity loading to the whole model. To complete modeling of frame, mesh system is created in the elements. C3D8R was selected for concrete materials and ACPH. With this selection, concrete and ACPH are defined as a 3D element with 8 nodes. For Steel Reinforcements, T3D2 is selected as a linear 3D material with 2 nodes. Another issue mentioned in this section is the selection of the earthquake record to be applied to the frames. The selected earthquake record belongs to the Maraş Earthquake. However, in order to save analysis time, accelerations between 70th and 80th seconds, which is the region where the acceleration reaches peak value in the earthquake record, are selected for analysis. The selected earthquake record exceeded the value of the spectrum used in the design of the frames. This made it possible to see the frame damages more clearly in the seismic analysis. For the cyclic load analysis, a loading reaching a drift rate of 5.6% is applied to the frames. In the fourth section which is the dicussion section, the frames mentioned in section 3 were subjected to earthquake recording and cyclic displacement loading. Then their seismic performances were examined and discussed. As a result of frequency analyses, period changes of the frames are calculated. It is seen that an increase in period was observed in all frames thanks to ACPH. Among the frame types, it is observed that increase in the storey number affected the period change more than increase in the bay number. As a result of dynamic implicit analyses, base shear vs time, compressive damage, tension damage, SDEG (scalar stiffness degredation), PE (plastic strain) and S (von mises stress) are evaluated. When base shear results is investigated, a decrease was observed in all frames thanks to ACPH. As in the period change, the highest effect was observed in the increase in the number of storeys. Another outcome for base shear is the use of ACPH reduces the base shear carried by the middle column proportionally and provides a more balanced distribution with the other columns. For other analysis results, the following can be said that damage occurred at the column base of both RC and ACPH frames during the earthquake. Plastic hinges were formed on the column bottom surfaces of all frames due to damage. Therefore, plastic hinges at the bottom of the columns should be investigated as a separate study subject. Regarding the damage to the beams, in RC frames, damage occurred in the region of the beams close to the column face. In the two bays case, damages also occurred in the beam-column joint region in the middle of the frames. In ACPH frames, the damage to the beams was concentrated on the energy dissipation plate region of the ACPH, which significantly reduced the damage to the reinforced concrete elements. The use of ACPH will contribute to achieving undamaged middle beams, which is one of the philosophies of the use of the replaceable connection. Lastly, ductility and structural system behavior coefficient were evaluated by looking at the cyclic analysis results. Within the scope of this thesis,the yield displacement was obtained by balancing the assumed bilinear shape. For the ultimate displacement, the ultimate displacement can be obtained from the point where the maximum base shear capacity usually decreases by 10% or 20%, assuming that it corresponds to the point where the compressive stress in concrete or the fracture or buckling of the transverse reinforcement in any structural element occurs. However, for ultimate displacement in this thesis, the maximum base shear capacity was not reduced, and the ultimate displacement is matched with the maximum base shear capacity. It is recommended to evaluate the results to be obtained in this direction. Because it was preferred to stay on the safe side regarding the semi-rigid or rigidity of the connection.According to the results the effect of ACPH on ductility in frame 1B2S is 47.5% on average and in frame 2B2S it is 57.3% on average. it was concluded that a value between 3.90 and 4.52 should be used for the behavioral coefficient (R) of the structural system for this type of joint. As a result of this analytical study, the use of replaceable joints in precast structures are investigated in different types of frames and comparative data are presented. Based on the data, the use of replaceable joints in precast structures minimized the damage to the structural members after the earthquake. It is shown that it will increase the ductility of the structure and a suggestion is made for the behavior coefficient of the structural system.