双向跨交叉层压木材的设计

Mass timber panels are commonly used in single-span floor and roof systems w在这里 support beams or walls are perpendicular to the strong axis spans of the panels. 然而, a unique attribute of cross-laminated timber (CLT) is that panels have structural capacity in both the major and minor strength directions. 次要强度方向的承载力通常小于主要强度方向的承载力, 这使得CLT是正交异性的. 尽管如此, the capacity of CLT in the minor strength direction can be utilized to create a two-way or flat-plate style of construction. 这允许没有支撑梁的框架系统, CLT面板在列之间的两个方向跨度在哪里. 北美最著名的例子之一是 布洛克Commons Tallwood House, a student residence at the University of British Columbia with 17 stories of mass timber over a concrete podium. Designers of the Brock Commons project used 5-ply CLT panels spanning over a grid of columns spaced approximately 9 ft x 13 ft apart.

因为这种结构构型并不常见, 为了对设计充满信心，项目团队承担了几项非凡的任务. 第一个, the engineering team at 快速+ Epp developed a custom CLT layup with the appropriate shear and minor direction bending strengths. The team then worked with researchers at FPInnovations to perform structural testing of the CLT and connections to verify the two-way panel and connection behavior. The column and panel joints were detailed with steel components to directly transfer column axial forces between levels and prevent loading floor panels in compression perpendicular to grain. 关于这一过程的更多信息可以在快速+ Epp网站上找到 在这里.¹

类似的, the 1510年韦伯斯特 project in Oakland uses two-way CLT with structural composite lumber laminations over a grid of columns set 12 ft x 15 ft apart.

A more common structural configuration that uses the two-way strength capacities of CLT is to have panels cantilever in two directions off the corner of a building, 创造无梁屋檐. 另一种是在多户建筑的走廊上使用CLT. 在传统的双层走廊里, 大量的木地板横跨住宅单元，从单元壁面到单元壁面, 平行于走廊. 在走廊上, 一种选择是转动CLT面板，使它们从走廊墙延伸到走廊墙. 然而, 创建更统一的面板布局, 另一种选择是让面板的长方向与走廊平行. 视走廊宽度和小轴强度而定, 有可能实现无梁支撑条件, 从走廊墙到走廊墙的墙板在其小轴上的位置. 在更开放的平面图中类似的配置, 比如办公室, 是在平面图的中心位置有一个点支撑CLT板的柱廊, creating a beamless zone through which MEP trunk lines and fire sprinkler mains can traverse the building without needing to penetrate dropped beams.

当看到双向跨CLT结构, 至少有三个潜在的容量限制可能需要考虑:

1. 面板的抗弯和抗剪能力
2. 支座承载能力
3. 支座处局部冲剪

面板的弯曲和剪切能力 

Manufacturers of CLT panels compliant with ANSI/APA PRG 320: Standard for Performance-Rated Cross-Laminated Timber provide third-party certified flexural and shear strength (and stiffness) of their panels in both the major and minor flatwise bending directions. Design of wood structures in jurisdictions of the International Building Code should generally follow the American Wood Council’s 国家 Design Specification® (NDS®) for Wood Construction. Chapter 10 of the NDS includes provisions to calculate ASD and LRFD design capacities to be compared against the building code-defined loads. 对于双向行为, 然而, the NDS does not address interaction effects between the major strength and minor strength bending and shear checks of CLT panels. 因此，设计师必须基于工程基础来合理化交互效果, 如NDS 2015 C3中描述的.9.2-2. A common design approach in Europe apportions load to the major and minor strength directions based on relative stiffness of the orthogonal layup and then conducts the respective flexural and shear design checks. 第5节描述了欧洲设计中这种常见的实践状态.11 of 交叉层合木结构设计:根据欧洲规范的基本设计和工程原则.²

支座承载能力  

NDS Chapter 10 includes design provisions for the bearing capacity of CLT panels loaded on the CLT panel face. CLT面板的基本参考设计应力为垂直于纹理的压缩， F_c⟂，是基于本构木材在面板. These values are sometimes omitted in third-party CLT product evaluation reports aside from references to the species group and grade of lumber used in the CLT. 在这种情况下, the perpendicular-to-grain reference design stress may be obtained from the NDS Supplement for the species and grade of lumber in the surface layer of the CLT or from the manufacturer. 在WoodWorks的表3中可以找到列上支持CLT的示例连接细节 大型木材连接索引.³ T在这里 are reinforcing detailing strategies that have been used to strengthen the face bearing capacity of CLT panels. 但在国家安全局的管辖范围之外, such reinforcing strategies use fully-threaded self-tapping screws to distribute stresses into the CLT panel. 使用示例请参见 SDCF木材- cf作为压缩加固材料.⁴

支座处局部冲孔剪切

在双向CLT面板的支持, 支撑点周边的抗剪能力有待验证. 这种检查是使用参考平面剪切能力V进行的_s,0 和V_s,90 根据ANSI/APA PRG 320开发. 虽然在NDS中没有明确提到, Bogensperger等人开发了一种欧洲方法. (2016).⁵ A controlling perimeter line is found by projecting into the panel from the edge of the support at 35 degrees from vertical to the center of the panel. The shear capacity of the panel around this perimeter line is then checked against the applied design loads. 更多关于冲孔剪切研究的最新信息可以在Slotsboom等人的文章中找到. (2023).⁶ 和Shahnewaz等人. (2023).⁷

由于双向弯曲相互作用的影响和冲孔剪切没有明确地涵盖, 应采用谨慎的工程设计. 该方法的可接受性由设计师自行决定, 建立官方, 和管辖. 直到设计方法与美国标准一致.S. 制定并验证了CLT冲剪标准, 建议以试验结果为依据进行冲剪设计验证, 由合格专家进行同行评审, 或两个.

双向弯曲性能建模与分析

A robust method to evaluate CLT panels for two-way bending behavior is though finite element method (FEM) plate analysis of the CLT and support system coupled with experimental validation of the model. 虽然有很多方法可以通过结构分析包来做到这一点, 重要的是要记住，CLT不是各向同性板, meaning that flexural and shear stiffness is different in the major and minor strength axis of the panel and these properties can very across and within manufacturers. 足够的有限元分析软件包需要支持正交各向异性板分析, 理想情况下，在“厚板分析”中使用Mindlin板分析或类似的剪切效应. 这样的建模可以在WoodWorks的 U.S. 大质量木地板振动设计指南.⁸

¹ 快速+ Epp. 点支持的CLT测试.

² Wallner-Novak, M.科佩尔胡贝尔，J.波克，K. proHolz奥地利. (2014). 交叉层合木结构设计:根据欧洲规范的基本设计和工程原则.

³ 木制品-木制品委员会. (2021). 大量木材连接的木工指数.

⁴ 辛普森强关系. (2023). 技术工程公报:SCDF木材- cf作为压缩钢筋.

⁵ Bogensperger T.约翰斯蒂尔，R.奥古斯丁，M. (2016). Concentrated Load Introduction in CLT Elements Perpendicular to Plane – Experimental and Numerical Investigations. 世界木材工程会议. 奥地利的维也纳.

⁶ Slotsboom C.迪克夫，C.杰克逊，R。. (2023). 点支CLT板冲剪设计方法比较. 世界木材工程会议. 挪威奥斯陆.

⁷ 马里兰州Shahnewaz.迪克夫，C.甘加利，H.斯洛布恩，C.谭，M.杰克逊，R。.波波夫斯基，M.坦纳特，T. (2023). 点支CLT板的试验研究:第一阶段:滚动抗剪强度. 世界木材工程会议. 挪威奥斯陆.

⁸ Breneman,年代.齐默尔曼，R.格伯，A.艾普，L.迪克夫，C.泰勒，A.W .洛斯比.麦克唐纳，E.斯洛布恩，C.麦卡琴，J.维舍尔，R. 木制品-木制品委员会. (2023). U.S. 大质量木地板振动设计指南.