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Requirements for Blocking/Bracing in Light-Frame Walls

涵盖结构和防火用途及其要求, including acceptable bracing for wood studs in their weak axis.

用于轻型框架墙结构的木螺柱可能需要水平方向的阻塞,原因有很多,包括在剪切板边缘的阻塞, fire blocking, and buckling restraint when subject to axial loads.

Structural Blocking Purposes

Blocking to Reduce Stud Slenderness Ratio
Section 3.7.1.美国木材委员会国家木结构设计规范(NDS)第4条规定,螺柱的长细比在使用条件下不得超过50,在施工期间不得超过75. 这意味着最大允许弱轴不支撑长度为2倍标称木螺柱是6 ' -3″(50 x1.5″) for in-service conditions or 9′-4.5″ (75x 1.5″) in under-construction conditions. However, 这并不一定意味着在这些间距处需要在螺柱之间使用实木阻塞,以便考虑螺柱在其弱轴上得到充分支撑. 内外木墙结构通常包括多层木结构板(胶合板或OSB)和/或石膏墙板. 一般做法是将这些护套产品及其与木螺柱的附件视为足够的弱轴螺柱支撑, 这表明,在螺柱之间不需要实木阻隔的情况下,可以满足NDS长细比. However, under construction, 这是常见的内部承重墙,是支持建筑负荷从上面,但还没有安装他们的石膏板饰面. In these conditions, wood blocking may be necessary for taller walls.

在一些内墙中存在一个独特的条件是交错的螺柱墙组件, where 2×4 wood studs are installed on 2×6 top and bottom plates, with the studs alternating from one edge of the plates to the other. This wall condition provides excellent acoustical performance.

However, in this case, only the outer faces of the studs are in contact with the sheathing and/or gypsum coverings; the interior faces of the studs are unbraced. NDS 2015 Appendix A.11.3 indicates that bracing on only one face of the studs is adequate:

当轻型框架结构的钉墙至少有一侧被充分护套时, the depth, rather than breadth of the stud, 在计算损失率时,应被允许作为最小的尺寸. 护套应根据经验证明能提供横向支撑,并应适当紧固.

Similarly, NDS 2015图3F显示了仅在螺柱/柱的一面支撑基础上的无支撑柱长度. NDS 2015 Commentary C.3.6.7 further states:

在确定护套或包覆轻型框架墙体系统的轴向承载能力时,使用螺柱深度作为计算长细比的最小尺寸是一种长期的做法. Experience has shown that wood structural panels, fiberboard, hardboard, gypsum board, 或其他护套材料提供足够的横向支持,跨其厚度的螺柱当适当紧固. 

此外,考虑木螺柱在弱轴上的长细比极限, the buckling capacity of load bearing studs should also be considered. This is accounted for in the column stability factor per NDS Section

虽然规范没有规定最小阻塞/支撑能力,以抑制这种弱轴屈曲, common practice is that any of the sheathing systems mentioned above, with standard fastener schedules, or solid wood blocking between the studs, has adequate capacity to resist weak axis buckling.

Shear panel edges

When using wood-frame shear walls, it is common to design the walls as blocked, 从而显著高于无堵塞剪力墙的允许抗剪能力. When designed as blocked, all shear panel edges must fasten to a common framing member; these common framing members are usually vertically-oriented studs and horizontally-oriented blocking between studs. Section 4.3.美国木材委员会的《皇冠2登录welcome》(SDPWS)第6条规定了这些挡块构件的要求 WoodWorks Ask an Expert post 讨论剪切板边块的大小和方向的选择.

Fire Blocking Purposes

The International Building Code (IBC)有防火要求,旨在限制火焰的蔓延, 烟雾和气体在可燃的隐蔽空间,如木框架墙腔. These requirements, contained in IBC 2015 Section 718.2.2, 说明在垂直的天花板和地板上需要防火隔断,水平的间隔不超过10英尺. Additionally, IBC Section 718.2.3要求水平和垂直空间之间的连接使用防火屏障,以防止火焰通过, smoke and gases from walls to connecting floors and vice versa. 在传统的轻框架木结构中,墙壁和天花板饰面安装在与其相关的框架构件上, and where platform-frame construction is used, the top plates of the walls will function as the fire blocking. This concept is confirmed in the code commentary to IBC Section 718.2.3. However, in situations such as balloon-frame walls or dropped soffit ceilings, additional fire blocking in the wall may be necessary. See the image below for an example of this from the 2015 IBC commentary.

Source: International Building Code Commentary

Finally, 值得注意的是,该规范允许使用一些产品作为防火屏障. In addition to solid 2x nominal wood members, other options include a double layer of 1x nominal wood, particleboard, gypsum board and others as outlined in IBC Section 718.2.1.