3.2.3 Lateral Support Beams Prevent Beam Buckling

Figure 3.9 Drawing of Column 79 and girder A2001 seated beam connection shown in Figure 821 of the NIST report.

Figure 3.10 Figure 8-23 of the NIST report showing NIST’s finite element analysis of the Column 79 and girder A2001 seated beam connection.

3.2.3 Lateral Support Beams Prevent Beam Buckling

Figures 3.11, 3.12, 3.13, and 3.14 show our evaluation of NIST’s preliminary hypothesis, which NIST used to determine whether the shear studs on the floor beams would fail when the

floor system was heated. The NIST report posits that beam G3005 buckled because its thermal expansion was restrained by girder A2001. Our analysis found that this can only happen when the three lateral support beams S3007, G3007, and K3007 spanning from beam G3005 to the north exterior wall are not included in the model. While these short beams are observed in some of the figures in the NIST report, they are missing from the model(s) used in the thermal and structural analyses shown in the report. It is important to realize that the lateral support beams have a significant effect and therefore should not have been omitted from the model(s). In addition, the NIST report describes the response of beam G3005 based on the wrong size beam. Erection drawing E12/13 (Frankel Steel Limited, 1985) shows a W21x44 for G3005 and a W24x55 for the four adjacent beams (K3004, C3004, B3004, and A3004). The erection drawing shows G3005 framing into the wind girder. However, the NIST report shows analysis results for G3005 based on a W24x55, not a W21x44. Further, the NIST report results were based on a modeling error in that this beam framed into an exterior girder, not an exterior column (see Figures 3.11 and 3.14).

Figure 3.11 UAF ABAQUS analysis shows beam G3005 does not buckle when braced by lateral support beams S3007, G3007 and K3007 (Frankel Steel Limited, 1985).

Figure 3.12 Figure 8-22 in the NIST report shows model for girder A2001 and five beams to the east of it with no lateral bracing for beam G3005 (NIST, 2008, NCSTAR 1-9, Vol. 1, Page 350).

Five

Figure 3.13 Figure 8-27 of the NIST report shows results of a finite element analysis where lateral support beams connecting to G3005 were not included (NIST, 2008, NCSTAR 1-9, Vol. 1, Page 354).

W21x44; G3005 w/o bracing

Figure 3.14 UAF analysis of the W21x44 G3005 with no lateral support beams included.

When the NIST constraints are followed, our analysis showed that beams D3004 and K3004 would have also buckled (see Figures 3.11 to 3.14). The NIST results were based upon erroneously selected boundary conditions, wherein NIST assumed the east exterior wall was extremely stiff and acted as a fixed restraint against thermal movements. As discussed previously, this was not the case. Figure 3.14 above shows that girder A2001 was restrained by the Column 79 side plate. As a result of girder A2001 being restrained, beams D3004 and K3004 are buckling. In addition, girder A2002 is being pushed to the east along with Column 79 by girder A2015 from the west. The beams adjacent to beams D3004 and K3004 do not buckle and therefore no full floor collapse would be expected.