Investigation and comparison of some techniques in asymmetrically retrofitting of steel frame connections

Document Type : Original Article

Authors

1 civil engineering faculty, Semnan university, Semnan, Iran

2 Associate Professor, Faculty of Civil Engineering, Semnan University, Semnan, Iran

Abstract

The presence of concrete slab in steel framing frame structures always makes retrofitting problems difficult. On the other hand, most of damages reported from Northridge earthquake (1994) has focused on the bottom flange of the beam. Therefore, in order to reduce the cost of retrofit, this operation can be done only at the bottom flange of the beam. In other words, by defining and applying a ductile fuse in the beam, by weakening the bottom flange of the bottom, it is possible to reduce the concentration of tension in the near-weld regions in connection and fracture failure in these areas. In this paper, a steel frame connection was analyzed numerically and after ensuring the modeling accuracy, it was under rehabilitation. Retrofit techniques have been made on the bottom flange of the beam. Two general "cut-off" and "heat" methods were considered to weaken the beam. In this research, incomplete penetration of the weld was placed in the bottom flange connection to the column as a deficiency in the joint. The modeling results showed that the connection with incomplete weld, underwent 4/4%, suffering a deflection in the weld area in the flange. In the specimens which were retrofitted asymmetrically, the possibility of brittle fracture in the weld region was decreased due to relocation of the plastic hinge in the weakened area of the beam. In the method of reducing the bottom flange, lateral buckling led to sudden decrease in flexural strength at 2.5 % inter story drift. In the heat-induction method accompanied with steel annealing, the out of buckling occurred at 5% drift. The retrofitted connection with this method showed a post elastic displacements of 3% and could be expected to be suitable for special moment frames.

Keywords

Main Subjects


[1] SAC Hinge Venture. (2000). cyclic response of RBS moment connections: loading sequence and lateral bracing effects. Rep. No. SAC/BD-00/22.
[2] FEMA-350, Federal Emergency Management Agency. (2000). Recommended seismic design criteria for new steel moment frame buildings. Washington DC
[3] Shen, J., Kitjasateanphun, T., Srivanich, W. (2000). Seismic performance of steel moment frames with reduced beam sections. Engineering Structures, 22(8), 968–983.
[4] Atashzaban, A., Hajirasouliha, I., Jazany, R. A., and Izadinia, M. (2015). Optimum drilled flange moment resisting connections for seismic regions. Journal of Constructional Steel Research, 112, 325-338.
[5] Roudsari, M. T., and Moradi, S. H. (2018). Experimental and Numerical Assessment of Reduced IPE Beam Sections Connections with Box-Stiffener. International Journal of Steel Structures, 18(1), 255-263.
[6] Saleh, A. Mirghaderi, S. R., Zahrai, S.M. (2016). Cyclic testing of tubular web RBS connections in deep beams. Journal of Constructional Steel Research, 117(3), 214–226.
[7] Ohsaki, M. Tagawa, H., Pan, P. (2009). Shape optimization of reduced beam section under cyclic loads. Journal of Constructional Steel Research, 65(7), 1511–1519.
[8] Sang, W. H, Ki-Hoon M., Seong-Hoon H., Bozidar S. (2012). Rotation capacities of reduced beam section with bolted web (RBS-B) connections. Journal of Constructional Steel Research, 70(1), 256–263.
[9] Hedayat, A., Murude C. (2009). Post-Northridge connection with modified beam end configuration to enhance strength and ductility. Journal of Constructional Steel Research, 65(7), 1413-1430
[10]Keunyeong, O. (2015). Seismic performance evaluation of weak axis column-tree moment connections with reduced beam section. Journal of Constructional Steel Research, 105(1), 28-38.
[11] Fema 547, Federal Emergency Management Agency. (2006). Techniques for the Seismic Rehabilitation of Existing Buildings. Washington DC.
[12] Civjan, M., Engelhardt, D. and Gross, J. (2000). Retrofit of Pre-Northridge Moment-Resisting Connections. Journal of Structural Engineering, 4(3), 445- 452.
[13] Brandon, Chi. Uang, Ch. and Chen, A. (2006). Seismic rehabilitation of pre-Northridge steel moment connections: A case study. Journal of Constructional Steel Research, 62(8), 783-792.
[14] Civjan, A., Engelhardt, M. D. (2001) .Slab effects in SMRF retrofit connection tests. Journal of structural engineering, 127 (3), 230-237.
[15] Morrison, M., Schweizer, D. Tasnim, H.. (2015). an innovative seismic performance enhancement technique for steel building moment resisting connections. Journal of Constructional Steel Research, 109(2), 34–46.
[16] ABAQUS/PRE. (1997). Users manual. Hibbit, Karlsson and Sorensen Inc.
[17] FEMA-355D, Federal Emergency Management Agency. (2000). State of the art report on connection performance. Washington DC.
[18] Azuma, K., Kurobane, Y., & Makino, Y. (2000). Cyclic testing of beam-to-column connections with weld defects and assessment of safety of numerically modeled connections from brittle fracture. Engineering Structures, 22(12), 1596-1608.