34322 Weld Filler Metal

Prior to the 1994 Northridge Earthquake, the welds in the welded special moment frame (WSMF) connections were commonly made with the self-shielded flux-cored arc welding (FCAW-S) process using an E70T-4 weld wire. Figure 34.19 shows a plot of CVN versus temperature for deposited weld metal using E70T-4, E70TG-K2 (another FCAW-S filler metal), and ordinary E7018 shielded metal arc welding (SMAW) electrodes. The CVN for E70T-4 is less than 20 J for temperatures up to 40°C [74].

Many of these low-toughness WSMF connections fractured in the earthquake [90]. Figure 34.20 shows a fractured beam flange end and a cross-section. Figure 34.21 shows the crack-like notch created by the backing bar. The fracture surfaces, such as those shown in Figure 34.20, indicate that the fractures originate in the root of the weld, typically at a lack-of-fusion defect adjacent to the backing bar notch

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