An innovative experimental method to upgrade performance of external weak RC joints using fused steel prop plus sheets

Ali Kheyroddin,Ali Khalili,Ebrahim Emami,Mohammad K. Sharbatdar 국제구조공학회 2016 Steel and Composite Structures, An International J Vol.21 No.2

In this paper, the efficiency and effectiveness of two strengthening methods for upgrading behavior of the two external weak reinforced concrete (RC) beam-column joints were experimentally investigated under cyclic loading. Since two deficient external RC joints with reduced beam height and low strength concrete were strengthened using one-way steel prop and curbs with and without steel revival sheets on the beam. The cyclic performance of these strengthened specimens were compared with two another control external RC beam-column joints, one the standard RC joint that had not two mentioned deficiencies and another had both. Therefore, four halfscale RC joints were tested under cyclic loading.The experimental results showed that these innovative strengthening methods (RC joint with revival sheet specially) surmounted the deficiencies of weak RC joints and upgraded their performance and bearing capacity, stiffness degradation, energy absorption, up to those of standard RC joint. Also, results exhibited that the prop at joint acted as a fuse element due to adding steel revival sheets on the RC beam and showed better behavior than that of the specimen without steel revival sheets. In other words by stiffening of beam, the prop collected all damages due to cyclic loading at itself and acted as the first line of defense and prevented from sever damages at RC joint.

Nonlinear behavior of connections in RCS frames with bracing and steel plate shear wall

Ali Kheyroddin,Saeedeh Ghods,Meissam Nazeryan,Seyed Masoud Mirtaheri,Majid Gholhaki 국제구조공학회 2016 Steel and Composite Structures, An International J Vol.22 No.4

Steel systems composed of Reinforced Concrete column to Steel beam connection (RCS) have been raised as a structural system in the past few years. The optimized combination of steel-concrete structural elements has the advantages of both systems. Through beam and through column connections are two main categories in RCS systems. This study includes finite-element analyses of mentioned connection to investigate the seismic performance of RCS connections. The finite element model using ABAQUS software has been verified with experimental results of a through beam type connection tested in Taiwan in 2005. According to verified finite element model a parametric study has been carried out on five RCS frames with different types of lateral restraint system. The main objective of this study is to investigate the forming of plastic hinges, distribution of stresses, ductility and stiffness of these models. The results of current research showed good performance of composite systems including concrete column-steel beam in combination with steel shear wall and bracing system, are very desirable. The results show that the linear stiffness of models with X bracing and steel shear wall increase remarkably and their ultimate strength increase about three times rather than other RCS frames.

Increasing the flexural capacity of RC beams using partially HPFRCC layers

Ali Hemmati,Ali Kheyroddin,Mohammad K. Sharbatdar 사단법인 한국계산역학회 2015 Computers and Concrete, An International Journal Vol.16 No.4

High Performance Fiber Reinforced Cementitious Composites which are called HPFRCC, include cement matrices with strain hardening response under tension loading. In these composites, the cement mortar with fine aggregates, is reinforced by continuous or random distributed fibers and could be used for various applications including structural fuses and retrofitting of reinforced concrete members etc. In this paper, mechanical properties of HPFRCC materials are reviewed briefly. Moreover, a reinforced concrete beam (experimentally tested by Maalej et al.) is chosen and in different specimens, lower or upper or both parts of that beam are replaced with HPFRCC layers. After modeling of specimens in ABAQUS and calibration of those, mechanical properties of these specimens are investigated with different thicknesses, tensile strengths, tensile strains and compressive bars. Analytical results which are obtained by nonlinear finite analyses show that using HPFRCC layers with different parameters, increase loading capacity and ultimate displacement of these beams compare to RC specimens.

Numerical Investigation of the Progressive Collapse of the Reinforced Concrete Wall-Frame Structures Considering the Soil–Structure Interaction

Seyed Ali Ekrami-Kakhki,Ali Kheyroddin,Alireza Mortezaei 한국콘크리트학회 2023 International Journal of Concrete Structures and M Vol.17 No.4

In this essay, the progressive collapse resistance of the reinforced concrete wall-frame structures was evaluated with and without considering the soil–structure interaction. The vulnerability of the frames against progressive collapse was investigated with the middle column removal scenario from the first story, based on the sensitivity index. To evaluate the effects of soil–structure interaction, the wall-frame structures along with the soil (hard soil) and foundation were simultaneously modeled in FLAC software and compared with the frames in Seismostruct software. The results showed that the sensitivity index decreased by considering the soil–structure interaction in the wall-frame structures. Afterward, a parametric study of the structures (foundation thickness) and substructures (soil types, soil densities, soil saturation conditions and soil layers) was performed. The results showed that with an increase in thickness of the foundation, the sensitivity index increased, and therefore, the condition of the structure would be more critical against progressive collapse. It was found that high groundwater levels in the subsoil can reduce its bearing capacity and lead to the damage to the structure. In addition, it was determined that by changing the substructure soil type from type 4 (Clay-MC) to type 1 (Rock), the use of layer 1 (SM) and layer 2 (SM-CL/ML (Very hard clay)-SM), and the soils with high density, the condition of the structures is better to prevent progressive collapse.

Evaluation of the Progressive Collapse of the Reinforced Concrete Frames Considering the Soil–Structure Interaction: Parametric Study Based on the Sensitivity Index

Seyed Ali Ekrami Kakhki,Ali Kheyroddin,Alireza Mortezaei 한국콘크리트학회 2022 International Journal of Concrete Structures and M Vol.16 No.5

In this essay, to investigate the progressive collapse of the reinforced concrete (RC) frames, a nonlinear static pushdown analysis was performed with column removal scenarios from the first story. At first, a numerical model was simulated and verified with the experimental model in SeismoStruct software without soil–structure interaction (SSI). Afterward, the foundation, soil, and the RC frame were modeled simultaneously in FLAC software and verified with the numerical model of the SeismoStruct software. Furthermore, the effect of SSI was studied on the progressive collapse of RC frames based on the sensitivity index (SI). The sensitivity index is defined as the ratio of the residual capacity under gravity loading of the structure by removing the column to the value of the undamaged structure. The results showed that by considering SSI, the sensitivity index decreases. Then, a parametric study of the framed structures (thickness of the foundation) and substructures (soil density, soil types, soil layers, and the soil saturation conditions) was performed to evaluate the progressive collapse-resisting capacity based on the sensitivity index. The results showed that by considering SSI, with an increase in the soil density and decrease in the groundwater level, the conditions would be better for preventing progressive collapse. It was also shown that rock and silty sands (SM), compared to other studied soil types, and SM and silty sands—silty clay with low plasticity—silty sands (SM-CL/ML-SM), compared to other studied soil layers, are better for preventing progressive collapse.

Relationships for prediction of backstay effect in tall buildings with core-wall system

Karimi, Mahdi,Kheyroddin, Ali,Shariatmadar, Hashem Techno-Press 2020 Advances in computational design Vol.5 No.1

One of the prevailing structural systems in high-rise buildings is the core-wall system. On the other hand, the existence of one or more underground stories causes the perimeter below-grade walls with the diaphragm of grade level to constitute of a very stiff box. In this case or a similar situation, during the lateral response of a tall building, underground perimeter walls and diaphragms that provide an increased lateral resistance relative to the core wall may introduce a prying action in the core that is called backstay effect. In this case, a rather great force is generated at the diaphragm of the grade-level, acting in a reverse direction to the lateral force on the core-wall system, and thus typically causes a reverse internal shear. In this research, in addition to review of the results of the preceding studies, an improved relationship is proposed for prediction of backstay force. The new proposed relationship takes into account the effect of foundation flexibility and is presented in a non-dimensional form. Furthermore, a specific range of the backstay force to lateral load ratio has been determined. And finally, it is shown that although all suggested formulas are valid in the elastic domain, yet with some changes in the initial considerations, they can be applied to some certain non-linear problems as well.

Experimental Investigation on Flexural Capacity of Reinforced Concrete Beams Strengthened with 3D-Fiberglass, CFRP and GFRP

Mahdi Vahidpour,Ali Kheyroddin,Mahdi Kioumarsi 한국콘크리트학회 2022 International Journal of Concrete Structures and M Vol.16 No.3

The main objective of this study is to investigate the structural performance of reinforced concrete (RC) beam specimens strengthened with 3D-fiberglass as compared with fiber-reinforced polymers (FRP) sheets. For this purpose, six RC beams were fabricated, strengthened, and tested under a four-point bending machine. One of the beams served as the control beam (REF), while the others were strengthened with carbon FRP (RCFRP), glass FRP (RGFRP), 3D-fiberglass and epoxy resin (R3DTR), 3D-fiberglass and epoxy resin extended to the sides (R3DTRB), and 3D-fiberglass and concrete repair (R3DTG). Failure mode, crack development, flexural capacity, ductility, the effectiveness of wrapping configurations, and the performance of epoxy resin in comparison with concrete repairer were studied between various beams. The results attest to the better performance and effectiveness of 3D-fiberglass over FRP in terms of flexural capacity, crack pattern, and ductility. The R3DTR and RGFRP specimens, compared to the control specimen, had the highest and lowest flexural capacity growth, with 19% and 8.4%, respectively. In addition, the failure modes observed in this study were in good agreement with the failure modes present in ACI.440.2R-17. Moreover, finite element (FE) models were proposed to predict the residual capacity of the specimens strengthened with FRP, using Abaqus software.

Seismic Strengthening of Weak Bolted End Plate Connections Using Welded Haunches

Hamid Saberi,Ali Kheyroddin,Mohsen Gerami 한국강구조학회 2017 International Journal of Steel Structures Vol.17 No.2

Bolted steel connections have been frequently used after Northridge earthquake. Among the concerns regarding the poor performance of weak connections is the ability to effectively and economically rehabilitate steel moment connections in existing buildings. Strengthening of these connections without the need for changing or replacing their components is a problem that has been recently considered by engineers. This study develops and experimentally validates an innovative technique for enhancing the seismic performance of steel beam to column moment connections. The use of haunch as a way to rehabilitate end plate bolted connections with weak end plate or bolts is studied constructing 6 experimental specimens of corner connections under SAC (Structural Engineers Association of California) cyclic loading protocol. The results of the study show that this strengthening method improves the cyclic behavior of the weak connections. Besides, it provides specimens with better performance than that of the reference connection designed according to AISC. The moment capacity, initial rotational stiffness and energy dissipation of the rehabilitated connections are averagely higher than those of the reference connection by 25, 10 and 12 percent respectively. Moreover, the failure potential in the connection is reduced because the plastic hinge is kept away from connection region and is transferred to the haunch end. It should be noted that this strengthening method is more efficient for cyclic behavior of a bolted connections with weak end-plate than a bolted connection with weak bolts, since the moment capacity is more increased.

Comparison of Bolted End plate and T-Stub Connections Sensitivity to Bolt Diameter on Cyclic Behavior

Hamid Saberi,Ali Kheyroddin,Mohsen Gerami 한국강구조학회 2014 International Journal of Steel Structures Vol.14 No.3

Considering the construction limitations, proper and correct design of connections is vital and of great importance. At theconstruction stage, it is probable to use a connection bolt with a diameter less than the design assumptions. It can occur dueto an imperfection in construction or even to changes in the function of the building. The unforeseen changes can increase thestructural load, and consequently the moment and shear force demand values. Therefore, the present paper is aimed to examinethe sensitivity of the bolted connections to the diameter of bolts using a numerical method. The results show that bolted T-stubconnections are more sensitive to bolt diameter than end plate connections. Hence, the bolted end plate connections arerecommended where the imperfection in construction or changes in function of the building is probable. Moreover, inconstruction of bolted connections, if changing the number of bolts regarding the constant total cross sectional area isconsidered, it is recommended to use the symmetric arrangement of bolts on each beam flange. In design of connections fora particular frame according to AISC, the moment capacity of T-stub connection is higher than that of end plate connection. However, the total energy absorptions of these connection types are approximately equal.

Evaluation of the seismic performance of off-centre bracing system with ductile element in steel frames

Mohammad Bazzaz,Ali Kheyroddin,Mohammad Ali Kafi,Zahra Andalib 국제구조공학회 2012 Steel and Composite Structures, An International J Vol.12 No.5

In order to evaluate the dynamic behavior of passive energy dissipation system, two steps need to be considered for prediction of structural response in the presence of ductile element in an off-centre bracing system. The first is a detailed analysis of the proposed ductile element and the second is the effect of this ductile element on an off-centre bracing system. The use of ductile bracing system is expanding in steel structures in order to increase the force reduction factor. Therefore, regarding the nonlinear behavior of steel material used in an off-centre bracing systems and using ductile element in OBS bracing systems, the seismic evaluation of the mentioned systems seems to be necessary. This paper aims to study linear and nonlinear behavior of steel frames with off-centre bracing system and ductile element, in order to get the best position of these bracing elements. To achieve this purpose, the modeling has been done with ANSYS software. The optimum eccentricity has been obtained by modeling three steel frames with different eccentricities and evaluating the results of them. The analytical results showed that the model OBS-C with 0.3 eccentricities has higher performance among the models.