Creating Efficient Structural Grids in Mass Timber Buildings

Mass timber products such as cross-laminated timber (CLT), 钉层压木材(NLT)和胶合层压木材(glulam)是一场革命的核心，它正在改变设计师对建筑的看法. 材料选择从来没有像现在这样成为建筑设计师日常工作中不可或缺的一部分. In addition to its sustainability and light carbon footprint, mass timber has benefits that include enhanced aesthetics, 施工速度快，重量轻, 所有这些都会对成本产生积极影响. 然而, to convince building owners and developers that a mass timber solution is viable, the structural design must also be cost competitive. 这需要充分了解材料特性和制造商的能力.

Mass timber is commonly seen in projects such as offices, 学校和高层混合用途建筑, 通常假设结构网格. Intended to meet the need for tenant flexibility, these “default” grids align with the capabilities of materials historically used—i.e.钢筋混凝土. When it comes to laying out a structural grid for mass timber, the square peg/round hole analogy is pertinent. 尽管大量木材解决方案可能在许多有利于钢/混凝土框架的网格上经济地工作, 一些网格修改可能是有价值的. 试图在钢和混凝土网格上强制使用大量木材解决方案可能会导致构件尺寸效率低下，同时否定与制造商能力相关的机会. As such, it is critically important to design a mass timber building 作为一个大型木结构建筑 从一开始. This requires a thorough understanding of how to best lay out the structural grid, 不牺牲空间功能, to optimize member sizes—but there’s more to cost efficiency than column spacing.

The following considerations are based on a post-and-beam frame for occupancies such as offices; however, many also apply to bearing wall-supported systems in other occupancy types.

网格选择

简单地说，大型木结构建筑有两种主要的网格选择:方形和矩形. In deciding which to use, there are a number of factors to consider.

确定有效的网格间距, it is important to understand possible span ranges for mass timber floor panels. 因为它们的重量相对较轻, 这些板的允许跨度通常由振动和挠度而不是弯曲或剪切能力决定. 另外还有面板的振动设计, vibration performance of the framing system as a whole, 包括梁, 应该考虑吗. 下表给出了基于面板尺寸的示例范围，假设有刚性支撑. (每个项目的具体跨度, 加载和支撑条件, as well as manufacturer-specific design properties, should be accounted for when selecting panel thickness.)如欲了解更多有关大型木地板结构设计的详情，请与当地联系 WoodWorks区域总监 或发邮件给WoodWorks帮助台 help@digisourcetech.com. 有关其他信息，请参见 结构 杂志的文章, Cross-Laminated Timber Structural Floor and Roof Design, 钉层压木材:美国.S. 设计施工指南.

根据美国已完工的建筑，方形网格的范围往往在20×20到30×30英尺之间. 虽然在20×20-ft网格中，大块木板可以跨越20英尺的支撑梁之间的距离, 另一种方法是在每个凸间内包括一根中间梁，以减少大质量木地板的跨度. 例如, 20×20-ft网格可以有一个中间梁，所以跨度10英尺的3层CLT地板可以使用. 此场景用于 阿宾娜院子里 office building in Portland, OR (pictured above). 也可以使用较大的方形网格，如28×28或30×30 ft，并带有一个中间梁. 这通常导致使用5层CLT或2×6 NLT地板，跨度14或15英尺. 这个场景用于 粘土创意也是在波特兰(见下图). In general, thinner floor and roof panels may result in lower material costs. 然而, 较低的水平面板成本可能会被较高的梁(也许是柱)成本所抵消, additional intermediate beams also need to be coordinated with MEP systems. As such, a cost analysis for thicker floors and fewer beams vs. thinner floors and more beams may be necessary.

超过30英尺或32英尺跨度的胶合木梁开始需要相当大(深)的梁. 这是可以做到的，但经济和净空问题可能会超过更长的跨度带来的好处. The image below illustrates several square grid options and associated member sizes.

Rectangular grids are usually in the 12×20-ft to 20×32-ft range. 与矩形网格的主要区别是中间梁往往不被使用, often simplifying the approach to accommodating MEP. 较窄的网格尺寸通常基于地板的跨度能力(见上面的跨度范围表)。. The larger grid dimension is based primarily on programmatic layout, while taking into account economical spans for glulam. Projects that have used this scenario include the 第一科技联邦信用合作社 in Hillsboro, OR, which used a 12×32-ft grid with 5-1/2-in. CLT面板横跨12英尺，和 东大会堂111号 in Des Moines, IA, which used a 20×25-ft grid with 2×8-ft DLT panels spanning 20 ft. 两个项目如下图所示.

There are several reasons to eliminate the intermediate beam, but the one often cited by design teams is easier MEP coordination. 因为在大多数木结构建筑中，需要在天花板侧暴露大量的木地板, 在管道系统方面有一些创造性, sprinkler lines and other MEP services are accommodated is required. 有关此主题的更多信息，请阅读本文 向专家请教 Q&A. 如果没有中间光束, 主要的MEP干线可以围绕一个中央走廊运行，支线延伸到每个海湾. 这种方法的一个好处是，没有中间梁意味着没有或很少穿透胶合木檩条或梁来协调, 减少, 设计, 等.

制造商的输入

在选择网格尺寸时，另一个重要的考虑因素是制造商的能力. 大多数获得PRG-320性能等级交叉层压木材标准认证的北美CLT制造商能够生产8至12英尺宽，40至60英尺长的面板. Minimizing the amount of waste from each panel is key to maximizing efficiency. 例如, a grid with 20-ft increments could be very efficient; it could use 40-ft-long panels or 60-ft-long panels (if the manufacturer is capable of producing those sizes). 另一方面, 一个24英尺的网格可能没有那么高效，因为它要么需要48英尺长的面板(对于双跨度)，要么从40英尺长的面板上剪下16英尺. Both options increase waste and reduce efficiency. 在考虑特别长的面板时，还应考虑卡车运输物流.

阿肯色大学 Adohi大厅 student residence hall project in Fayetteville, AR utilized a 20-ft grid increment for a 60-ft-wide building. The CLT manufacturer provided 40-ft-long panels, 因此使用一个全长和一个半长面板来实现整个60英尺的建筑宽度. Because each half-length panel was simply a full-length panel 减少 in half, 效率高，浪费少.

虽然制造商的能力不同, it is possible to create grids that are efficient for several manufacturers. 大型木结构建筑设计的一个重要步骤是与制造商协商，以确定最有效的面板布局. Most North American mass timber manufacturers are WoodWorks 国家 Partners. Information on each can be found by clicking the logos on 这个网页.