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Tham khảo tài liệu 'structural steel designers handbook part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | LATERAL-FORCE DESIGN 9.21 FIGURE 9.11 Photograph of crack through the column flange and into the column web or panel zone of connection. of these buildings collapsed and there was no loss of life but the economic loss was considerable. This unexpected damage has caused a new evaluation of the design of moment frame connections through the SAC Steel Project. SAC is a joint venture of SEAOC ATC Applied Technology Council and CUREE California Universities for Research in Earthquake Engineering and the joint venture is funded by FEMA. This work is still in progress but it is clearly leading structural engineers in new directions in the design of special steel moment frame buildings. The work shows that great ductility is possible but it also shows that the engineer must exercise great care in the selection and design of members and connections. The requirements that are evolving for special moment frames are briefly summarized in Art. 9.7.1. Concentric braced frames defined in Art. 9.4 economically provide much larger strength and stiffness than moment-resisting frames with the same amount of steel. There are a wide range of bracing configurations and considerable variations in structural performance may result from these different configurations. Figure 9.12 shows some concentric bracing configurations. The braces which provide the bulk of the stiffness in concentrically braced frames attract very large compressive and tensile forces during an earthquake. As a result compressive buckling of the braces often dominates the behavior of these frames. The pinched cyclic force-deflection behavior shown in Fig. 9.9b commonly results and failure of braces may be quite dramatic. Therefore concentrically braced frames are regarded as stiffer stronger but less ductile than steel moment-resisting frames. In recent years research has shown that concentrically braced frames can sustain relatively large inelastic deformation without failure if greater care is used in the design and
