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Erection Bracing of Low-Rise Structural Steel Buildings phần 2

Các kháng tải trọng trong quá trình xây dựng trên khung thép được cung cấp bởi một sự kết hợp của công việc lâu dài bổ sung bằng hỗ trợ tạm thời khi cần thiết. Cuộc kháng chiến của cấu trúc vĩnh viễn phát triển như công việc tiến triển. Trong một cấu trúc tự hỗ trợ kháng chiến là hoàn thành khi công việc của người dựng hoàn tất. | the exact effect of the seismic force due to the seismic base shear but must be modified by the following equations taken from ASCE 7 paragraph 9.3.7 in Equation A4-5 E Qe 0.5 AVD and in Equation A4-6 E Qe - 0.5 AVD where E the effect of horizontal and vertical earthquake-induced forces Av the coefficient representing effective peak velocity-related acceleration from ASCE 7 D the effect of dead load D Qe the effect of horizontal seismic earthquake-induced forces The term 0.5 AVD is a corrective term to reconcile the load factors used in the NEHRP requirements and the load factors used in the ASCE 7 LRFD requirements. This correction is described in detail in the Commentary to ASCE 7 which concludes that the correction is made separately .so that the original simplicity of the load combination equations in Sec. 2 is maintained. It is also explained in this paragraph taken from the Commentary to the AISC Seismic Provisions The earthquake load and load effects E in ASCE 7-93 are composed of two parts. E is the sum of the seismic horizontal load effects and one half of Av times the dead load effects. The second part adds an effect simulating vertical accelerations concurrent to the usual horizontal earthquake effects. In forming combinations containing the effects of stability the load factors for the load source D or L which induces the PA effect would be used for the load factor s on the effect of stability. In the authors earlier paper 11 on this topic the following ASD combinations were recommended a. Stability loading b. 0.75 stability loading plus wind loading These combinations reflected the current ASD Specification provision for one-third increases for stresses computed for combinations including wind loading acting alone or in combination with dead and live load. In this Guide the determination of load and resistance is based on the LRFD Specification. Allowable stress design is used only when LRFD procedures are not available or would be inappropriate. 4. .