AbstractFor seismic applications in special and intermediate steel moment frames, the design stan... more AbstractFor seismic applications in special and intermediate steel moment frames, the design standard provides a number of prequalified connections. This assumes that the beam frames orthogonally i...
Journal of Structural Engineering-asce, Oct 1, 2003
ABSTRACT Standard construction 2.4 mx 2.4 m woodframe shearwalls were tested using different load... more ABSTRACT Standard construction 2.4 mx 2.4 m woodframe shearwalls were tested using different loading protocols. The CUREE-Caltech protocols, recently developed by Krawinkler in 2001, were compared with other, previously used protocols. The following protocols were considered in the study: monotonic, CUREE-Caltech standard (CUREE), CUREE-Caltech near-fault, sequential phased displacement (SPD), and international standards organization. Findings from the research indicate that loading sequence has a significant influence on shearwall performance. Protocols with a large number of cycles (SPD) tended to produce nail fatigue fractures, which were not nearly as prevalent in protocols with lower numbers of cycles (CUREE). The research clearly showed that the nail fatigue fractures were associated with a large energy demand related to the number of cycles, which resulted in a reduced ultimate strength and deformation capacity. The initial stiffness of the specimens was relatively unaffected by the loading protocol used; however, there was significant variation in the stiffness values obtained depending on the stiffness definition used.
Journal of Structural Engineering-asce, Aug 1, 1994
ABSTRACT Seismic design provisions estimate the maximum roof and story drifts occurring in major ... more ABSTRACT Seismic design provisions estimate the maximum roof and story drifts occurring in major earthquakes by amplifying the drifts computed from elastic analysis at the prescribed design seismic force level with a deflection amplification factor (DAF). A comparison of several seismic design provisions indicated that the deflection amplification factor in both the UBC and NEHRP Recommended Provisions, being equal to 3R(w)/8 and C(d), respectively, is very low and could lead to unconservative drift estimations. An analytical study of the seismic responses of four instrumented buildings confirmed that drifts developed in major earthquakes are much higher than those predicted by the UBC or NEHRP approach. It is recommended that the deflection amplification factor be increased to at least the seismic force reduction factor (R(w) in UBC and R in NEHRP) for estimating maximum drifts. The effects of the ratio between building period and earthquake predominant period, types of yield mechanisms, and structural overstrength on the DAF are also presented.
Journal of Structural Engineering-asce, Aug 1, 2008
ABSTRACT During an earthquake, steel braced frame columns can be subjected to high axial forces c... more ABSTRACT During an earthquake, steel braced frame columns can be subjected to high axial forces combined with inelastic rotation demand resulting from story drift. Cyclic testing of nine full-scale W14 column specimens representing a practical range of flange and web width-to-thickness ratios were subjected to different levels of axial force demand (35, 55, and 75% of nominal axial yield strength) combined with up to 10% story drift. No global buckling was observed in all test specimens. Flange local buckling was the dominant buckling mode. Specimens achieved interstory drift capacities of 0.07-0.09 rad. These large deformation capacities were, in part, achieved due to the delay in flange local buckling resulting from the stabilizing effect provided by the stocky column web of the W14 section specimens. Testing indicated that the ASCE 41 predicted plastic rotation capacities are very conservative. The ASCE 41 criteria do not specify plastic rotation capacity at axial load ratios greater than 0.5; however, tested specimens exhibited significant plastic rotation capacities of approximately 15-25 times the member yield rotation.
Journal of Structural Engineering-asce, Jun 1, 2016
AbstractAISC 358 provides steel connections that are prequalified for use in special and intermed... more AbstractAISC 358 provides steel connections that are prequalified for use in special and intermediate moment frames (SMF and IMF). Implicit in this standard is that the beam and column are orthogonal to each other in the elevation of the frame. To evaluate the effects of a sloped connection considering an angle of deviation from orthogonal of 28°, two reduced beam section (RBS) moment connections with W36×231 beam and W36×302 column were cyclically tested. Although both specimens met the acceptance criteria of AISC 341, brittle fracture of top flange weld soon followed, a failure mode not typical of an RBS connection. Finite-element analysis demonstrated that the strain demand was not symmetric between two flanges. The strain demand at the heel location was higher than that at the opposite flange and increased with the angle of the slope. The AISC 341 welding requirement for steel backing removal, back-gouging, and fillet reinforcing should be linked to the heel and toe locations, not the top and bottom f...
Cantilevered steel sign structures are widely used for freestanding signs. This type of structure... more Cantilevered steel sign structures are widely used for freestanding signs. This type of structure can be flexible and the connections are vulnerable to fatigue cracking due to wind-induced vibration. Damage and collapses of sign structures due to fatigue and fracture at the sleeve connections have been reported. To investigate the cause of failure at the sleeve connection and to mitigate the problem, case studies on failed sign structures and the associated finite element analyses have been performed. The studies showed that the cracks typically occurred at the toe of the fillet weld connecting the upper pipe to the upper ring with a very high stress concentration. A common practice of strengthening or repairing the joint by welded gussets was not effective in mitigating fatigue cracking. A testing program was developed to evaluate the relative fatigue resistance of the conventional, retrofit, and alternative connection details. The fatigue test results verified that the conventional and gusset-stiffened connection details had a very poor fatigue resistance. The alternative connection details, which used improved weld detail and grout with steel jacket, significantly increased the fatigue life.
AbstractThe instantaneous center of rotation method is presented in the AISC Steel Construction M... more AbstractThe instantaneous center of rotation method is presented in the AISC Steel Construction Manual for the design of eccentrically loaded bolted connections. Tabulated values for normalized str...
AbstractTesting of 21 single-sided partial-joint-penetration (PJP) groove weld specimens was perf... more AbstractTesting of 21 single-sided partial-joint-penetration (PJP) groove weld specimens was performed to evaluate the effects of three parameters: (1) root opening, (2) weld reinforcing profiles, ...
AbstractFor seismic applications in special and intermediate steel moment frames, the design stan... more AbstractFor seismic applications in special and intermediate steel moment frames, the design standard provides a number of prequalified connections. This assumes that the beam frames orthogonally i...
Journal of Structural Engineering-asce, Oct 1, 2003
ABSTRACT Standard construction 2.4 mx 2.4 m woodframe shearwalls were tested using different load... more ABSTRACT Standard construction 2.4 mx 2.4 m woodframe shearwalls were tested using different loading protocols. The CUREE-Caltech protocols, recently developed by Krawinkler in 2001, were compared with other, previously used protocols. The following protocols were considered in the study: monotonic, CUREE-Caltech standard (CUREE), CUREE-Caltech near-fault, sequential phased displacement (SPD), and international standards organization. Findings from the research indicate that loading sequence has a significant influence on shearwall performance. Protocols with a large number of cycles (SPD) tended to produce nail fatigue fractures, which were not nearly as prevalent in protocols with lower numbers of cycles (CUREE). The research clearly showed that the nail fatigue fractures were associated with a large energy demand related to the number of cycles, which resulted in a reduced ultimate strength and deformation capacity. The initial stiffness of the specimens was relatively unaffected by the loading protocol used; however, there was significant variation in the stiffness values obtained depending on the stiffness definition used.
Journal of Structural Engineering-asce, Aug 1, 1994
ABSTRACT Seismic design provisions estimate the maximum roof and story drifts occurring in major ... more ABSTRACT Seismic design provisions estimate the maximum roof and story drifts occurring in major earthquakes by amplifying the drifts computed from elastic analysis at the prescribed design seismic force level with a deflection amplification factor (DAF). A comparison of several seismic design provisions indicated that the deflection amplification factor in both the UBC and NEHRP Recommended Provisions, being equal to 3R(w)/8 and C(d), respectively, is very low and could lead to unconservative drift estimations. An analytical study of the seismic responses of four instrumented buildings confirmed that drifts developed in major earthquakes are much higher than those predicted by the UBC or NEHRP approach. It is recommended that the deflection amplification factor be increased to at least the seismic force reduction factor (R(w) in UBC and R in NEHRP) for estimating maximum drifts. The effects of the ratio between building period and earthquake predominant period, types of yield mechanisms, and structural overstrength on the DAF are also presented.
Journal of Structural Engineering-asce, Aug 1, 2008
ABSTRACT During an earthquake, steel braced frame columns can be subjected to high axial forces c... more ABSTRACT During an earthquake, steel braced frame columns can be subjected to high axial forces combined with inelastic rotation demand resulting from story drift. Cyclic testing of nine full-scale W14 column specimens representing a practical range of flange and web width-to-thickness ratios were subjected to different levels of axial force demand (35, 55, and 75% of nominal axial yield strength) combined with up to 10% story drift. No global buckling was observed in all test specimens. Flange local buckling was the dominant buckling mode. Specimens achieved interstory drift capacities of 0.07-0.09 rad. These large deformation capacities were, in part, achieved due to the delay in flange local buckling resulting from the stabilizing effect provided by the stocky column web of the W14 section specimens. Testing indicated that the ASCE 41 predicted plastic rotation capacities are very conservative. The ASCE 41 criteria do not specify plastic rotation capacity at axial load ratios greater than 0.5; however, tested specimens exhibited significant plastic rotation capacities of approximately 15-25 times the member yield rotation.
Journal of Structural Engineering-asce, Jun 1, 2016
AbstractAISC 358 provides steel connections that are prequalified for use in special and intermed... more AbstractAISC 358 provides steel connections that are prequalified for use in special and intermediate moment frames (SMF and IMF). Implicit in this standard is that the beam and column are orthogonal to each other in the elevation of the frame. To evaluate the effects of a sloped connection considering an angle of deviation from orthogonal of 28°, two reduced beam section (RBS) moment connections with W36×231 beam and W36×302 column were cyclically tested. Although both specimens met the acceptance criteria of AISC 341, brittle fracture of top flange weld soon followed, a failure mode not typical of an RBS connection. Finite-element analysis demonstrated that the strain demand was not symmetric between two flanges. The strain demand at the heel location was higher than that at the opposite flange and increased with the angle of the slope. The AISC 341 welding requirement for steel backing removal, back-gouging, and fillet reinforcing should be linked to the heel and toe locations, not the top and bottom f...
Cantilevered steel sign structures are widely used for freestanding signs. This type of structure... more Cantilevered steel sign structures are widely used for freestanding signs. This type of structure can be flexible and the connections are vulnerable to fatigue cracking due to wind-induced vibration. Damage and collapses of sign structures due to fatigue and fracture at the sleeve connections have been reported. To investigate the cause of failure at the sleeve connection and to mitigate the problem, case studies on failed sign structures and the associated finite element analyses have been performed. The studies showed that the cracks typically occurred at the toe of the fillet weld connecting the upper pipe to the upper ring with a very high stress concentration. A common practice of strengthening or repairing the joint by welded gussets was not effective in mitigating fatigue cracking. A testing program was developed to evaluate the relative fatigue resistance of the conventional, retrofit, and alternative connection details. The fatigue test results verified that the conventional and gusset-stiffened connection details had a very poor fatigue resistance. The alternative connection details, which used improved weld detail and grout with steel jacket, significantly increased the fatigue life.
AbstractThe instantaneous center of rotation method is presented in the AISC Steel Construction M... more AbstractThe instantaneous center of rotation method is presented in the AISC Steel Construction Manual for the design of eccentrically loaded bolted connections. Tabulated values for normalized str...
AbstractTesting of 21 single-sided partial-joint-penetration (PJP) groove weld specimens was perf... more AbstractTesting of 21 single-sided partial-joint-penetration (PJP) groove weld specimens was performed to evaluate the effects of three parameters: (1) root opening, (2) weld reinforcing profiles, ...
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