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.

Seismic Behavior of Frames with Bolted End Plate Connections Rehabilitated by Welded Haunches Under Near- and Far-Fault Earthquakes

Hamid Saberi,Vahid Saberi,Ali Kheyroddin,Mohsen Gerami 한국강구조학회 2019 International Journal of Steel Structures Vol.19 No.2

A retrofi t method for bolted end plate connections is the use of haunches. This method needs no change or replacement of connection components. The optimum selection of rehabilitation parameters like thickness or haunch-beam angle is of great importance for designers. Besides, one of the important factors for designers to select this retrofi t method, is the effi ciency of retrofi tting by haunches and the eff ectiveness of retrofi t parameters on behavior of retrofi tted frames in near- and far-fi eld earthquakes. The results of 2D numerical modeling of the frames shows that rehabilitation of the weak end plate connections using haunch improves the seismic behavior of the weak frame relative to the reference frame with connections designed according to AISC code. For example, the roof displacements are reduced by 8% averagely and the maximum story drifts in near and far-fi eld earthquakes are reduced by 22% and 12% in the rehabilitated frames compared to those of the reference frame. The results of 3D substructure numerical models, after verifi cation by experimental results, showed that the increase of haunch thickness from 12 to 18 mm did not signifi cantly increase the moment capacity and initial rotational stiff ness. However, the pinching in moment-rotation hysteresis is decreased. The increase of haunch angle from 30 to 60 resulted in shift of plastic hinge to haunch internal area and 100% reduction of energy absorption and initial rotational stiff ness compared to those of the reference specimen. Since the change of retrofi t method parameters results in change of stiff ness and natural time period of the structure and the aff ecting parameter on structure dynamic behavior is “the ratio between structure main time frequency to earthquake predominant time period”, the selection of the fi rst haunch thickness with an angle of 30 degree toward the beam that satisfy the requirements of FEMA350 will be economic and optimized.

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 effect of blood contamination on the compressive strength of MTA modified with hydration accelerators

Oloomi, Kaveh,Saberi, Eshaghali,Mokhtari, Hadi,Mokhtari Zonouzi, Hamid Reza,Nosrat, Ali,Nekoofar, Mohammad Hossein,Dummer, Paul Michael Howell The Korean Academy of Conservative Dentistry 2013 Restorative Dentistry & Endodontics Vol.38 No.3

Objectives: This study was performed to evaluate the effect of blood contamination on the compressive strength (CS) of Root MTA (RMTA) modified with Calcium chloride ($CaCl_2$) and Disodium hydrogen phosphate ($Na_2HPO_4$) as setting accelerators over time. Materials and Methods: A total of 110 cylindrical specimens of RMTA were divided into 6 experimental groups as follows: Group1, RMTA; Group 2, RMTA modified with $CaCl_2$ (RMTA-C); Group 3, RMTA modified with $Na_2HPO_4$ (RMTA-N); Group 4, RMTA contaminated with blood; Group 5, RMTA-C contaminated with blood; Group 6, RMTA-N contaminated with blood. The CS of specimens in all groups was evaluated after 3 hr, 24 hr, and 1 wk. In the modified groups (groups 2, 3, 5, and 6) the CS of five specimens per group was also evaluated after 1 hr. Results: Blood contamination significantly reduced the CS of all materials at all time intervals (p < 0.05). After 3 hr, the CS of specimens in the RMTA groups (with and without blood contamination) was significantly lower than those in the RMTA-C and RMTA-N groups (p < 0.05). The CS values were not significantly different at the other time intervals. In all groups, the CS of specimens significantly increased over time (p < 0.05). Conclusions: Blood contamination decreased the CS of both original and accelerated RMTA.

Evaluation of the effect of blood contamination on the compressive strength of MTA modified with hydration accelerators

Kaveh Oloomi,Eshaghali Saberi,Hadi Mokhtari,Hamid Reza Mokhtari Zonouzi,Ali Nosrat,Mohammad Hossein Nekoofar,Paul Michael Howell Dummer 大韓齒科保存學會 2013 Restorative Dentistry & Endodontics Vol.38 No.3

Objectives: This study was performed to evaluate the effect of blood contamination on the compressive strength (CS) of Root MTA (RMTA) modified with Calcium chloride (CaCl2) and Disodium hydrogen phosphate (Na2HPO4) as setting accelerators over time. Materials and Methods: A total of 110 cylindrical specimens of RMTA were divided into 6 experimental groups as follows: Group1, RMTA, Group 2, RMTA modified with CaCl2 (RMTA-C), Group 3, RMTA modified with Na2HPO4 (RMTA-N), Group 4, RMTA contaminated with blood, Group 5, RMTA-C contaminated with blood, Group 6, RMTA-N contaminated with blood. The CS of specimens in all groups was evaluated after 3hr, 24 hr, and 1 wk. In the modified groups (groups 2, 3, 5, and 6) the CS of five specimens per group was also evaluated after 1 hr. Results: Blood contamination significantly reduced the CS of all materials at all time intervals (p < 0.05). After 3hr, the CS of specimens in the RMTA groups (with and without blood contamination)was significantly lower than those in the RMTA-C and RMTA-N groups (p < 0.05). The CS values were not significantly different at the other time intervals. In all groups,the CS of specimens significantly increased over time (p < 0.05). Conclusions: Blood contamination decreased the CS of both original and accelerated RMTA.