Building Structures and Structural Selection (建筑结构与结构选型)
建筑结构与结构选型 asks whether you can choose a sensible system and read the numbers behind it - loads, height limits, seismic detailing - without running a full design. Most questions are selection or ratio questions, not member design.
Loads and combinations
- 永久荷载 partial factor 1.3 where unfavourable, 可变荷载 1.5; characteristic values follow GB 50009.
- Floor 活荷载: 住宅 2.0, 教室 and 办公室 2.5, 走廊/楼梯 2.5–3.5, 商场 3.5 kN/m².
- 基本风压 and 基本雪压 use a 50-year return period for ordinary buildings.
Choosing the system
- 砌体结构: economical multi-storey housing, but capped by 层数 and 高度 limits (7度/0.10g: 7 storeys, 21 m in the GB 50011 table) and by 横墙间距.
- 现浇框架: height limits 60 / 50 / 40 / 35 / 24 m for 6 / 7 / 8(0.2g) / 8(0.3g) / 9度; column size usually governed by 轴压比, not by strength.
- 剪力墙 and 框架-剪力墙 carry the lateral load in tall housing; the wall piers, not the slabs, resist the earthquake.
- Long-span roofs: 网架 or 网壳 for a 60 m gymnasium, 张弦梁 beyond about 100 m, 门式刚架 for 12–36 m factory spans.
Joints
- 伸缩缝 may stop at the foundation; 沉降缝 and 防震缝 must cut through it.
- 框架 防震缝 width: 100 mm up to 15 m height, plus 20 mm per further 4 m at 7度, and corresponding increments at other intensities.
Worked example: simply supported beam, span 6 m, 恒载标准值 15 kN/m, 活载标准值 10 kN/m. Design load q = 1.3×15 + 1.5×10 = 34.5 kN/m; M = ql²/8 = 34.5×36/8 = 155.3 kN·m. Note that using 1.2 and 1.4 - the old values - gives 32.0 kN/m and 144 kN·m, which is the distractor answer.
Traps
- Mixing characteristic and design values in one line.
- Citing 抗震等级 from memory; it depends on 设防烈度, 结构类型 and 高度 together.
- Selecting 砌体 for a building beyond the 层数/高度 table.
- Assuming a 防震缝 that stops at the foundation.