Article and photos by Gregory Havel
Manufactured wood I-joists have been in common use since the 1970s. They are advertised as providing the same or greater strength as dimensional-lumber joists while using less material and being lighter in weight. They are also advertised as being straighter than dimensional lumber and therefore better for level floors and ceilings. These statements about this material are true under normal conditions but not in structure fires.
制造的I-toist的顶部和底弦最初是2 x 4或2 x 3尺寸的木材，每张脸部的凹槽切成一个凹槽，以用胶水连接网络。制造的I-toist的网络最初是胶合板，1/4英寸或3/8英寸（6mm或9mm）厚，具体取决于要支撑的重量。
Photo 1 shows a close-up of the top chords and webs of today’s I-joists, still bundled after delivery to a construction job site. The top and bottom chords are laminated veneer lumber (LVL), like plywood but with the grain in all of the laminates running parallel with the long axis of the joist and cut into dimensional lumber sizes rather than into sheets. The webs are of oriented strand board (OSB), a product made of wood shavings and glue that is pressed into sheets and that is advertised as stronger than plywood. Both LVL and OSB are cured under pressure with heat. The adhesives used to manufacture OSB and LVL, and to assemble I-joists, are usually either urea-formaldehyde or phenolic resins.
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Photo 2 (left) shows I-joists with LVL chords and OSB webs in place on top of a wall framed of 2 x 6s (to provide space for the insulation required by the building code). These I-joists will support the floor of the top half-story of this house, and the gypsum board ceiling of the rooms below. The roof rafters shown are of sawn dimensional lumber. Note that I-joists are sometimes also used for rafters, in place of dimensional lumber, usually with a ridge board of LVL, dimensional lumber, or plywood.
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照片3显示了将支持这所房子一楼的I-toist。请注意，在钢梁顶部的托梁的末端之间的I型连接的短部分没有开火。它们正在阻止I-Joist系统所要求的，并提供侧向支撑，以防止I-Joist扭曲。
（3）
另请注意，在这种构造方法中，所示的一英寸板螺栓固定在钢梁的顶部法兰上很常见。它可以钉住I-toist，以保持其位置。
See also the splice in the web of the I-joist blocking section in the center of photo 3. Since OSB sheets are usually only eight feet long and I-joists can be many times longer, the OSB sheets are trimmed with zigzag or scalloped edges, which are interlocked and glued together when the joists are assembled. Expect to see several of these splices in the web of a long I-joist.
在所有情况下，将胶合板（胶合板或OSB）粘合并钉在托梁的顶部，并涂上地板饰面（地毯或瓷砖）。在所有情况下，石膏板的天花板（通常1/2英寸）都会拧到托梁的底面，除非托架允许在地下室或地窖中暴露于托架。
I-joists can be part of a fire-rated floor-ceiling assembly. In this case, the ceiling will be 5/8-inch Type X gypsum board attached to the joists according to the listing specification in the Underwriters Laboratories Directory, including the number, length, and spacing of the screws. The fire rating is tested with fire only on one side of the floor-ceiling assembly–not inside it. Fire inside a fire-rated assembly, especially of manufactured wood products, will cause it to fail quickly and catastrophically. Since the adhesives used to manufacture I-joists are cured with heat, they can begin to weaken when heated by fire, even though the temperature may not yet be high enough to ignite them.
有关在火灾条件下的锯木材，I-咖啡师和木桁架的行为的详细比较，请查看承销商实验室在线短课程http://www.ul.com/fire/structural.htmlor athttp://www.ul.com/global/eng/pages/offerings/industries/buildingmaterials/fire/structural/structural。在UL测试中，在火灾条件下，制造的木材I-咖啡师要比装有金属远距离板的木桁架更快。
无论使用哪种类型的框架（锯木材，制造的托梁或木桁架）以及任何类型的天花板（无论是否创建火评估的组件），完成后，完成的产品看起来相同：上方的地毯或瓷砖地板，并在下面涂上石膏。如果这座建筑物中有火灾是基于您在建造时所采取的任何笔记的结构的预火计划，那么您将知道可能会为您提供什么方式的唯一方法。
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主题:建筑消防队员,I-Joists
