约翰·W·米滕多夫（John W. Mittendorf）
The last “Reading A Building” article covered one of the most dangerous types of building construction suppression personnel can encounter on the fireground – fascias. Although any type of construction exposed to fire can present a significant hazard, specific types of construction are capable (and willing) to pose unique hazards. Such is the case with unreinforced masonry construction (URM). Fortunately, this type of construction is often easily recognizable. You can expect buildings of this type to present a specific hazard when exposed to fire – collapse.
Pre 1933
Prior to 1933, brick buildings featured the following characteristics:
- Mortar consisting of sand and lime only;
- A lack of rebar;
- Exterior walls about 13″ thick and tapering vertically upward (reducing in thickness);
- 围绕屋顶周围的栏杆墙（通常是值得注意的高度）；
- Floor and roof joists that were “let” (resting in a cavity) into the exterior walls; and
- Roof and floor joists that were “fire cut” (ends are cut at an angle) so they would pull away from a wall and fall into the interior of a building without collapsing the exterior walls.
在1933年的CA地震发生灾难性的长滩之后，修订了建筑法规，为新的砖石建筑提供了增强的地震安全。同时，很明显，这些建筑物在火灾条件下容易倒塌。结果，针对新的砖石建设实施了以下修订：
- Cement to be used in the mortar;
- Steel rebar to be used;
- 外墙至少为九英寸厚；和
- All joist and rafters to be anchored to exterior walls. This was normally accomplished by bolting a ledger board to a wall and attaching the joist/rafter to the ledger via a metal hanger.
1933年
After the Tehachapi, CA earthquake in 1959, many building codes (applied to masonry construction, and specifically URM construction) were modified (including some retrofits) as follows:
- 沿公共人行道和出口的栏杆顶部的四到六英寸混凝土“帽”；
- 栏杆的高度可能不超过16英寸（包括“帽子”）；
- Rafters and joists had to be anchored to exterior walls with a steel anchor bar or rod.
1971年的塞尔玛（Sylmar），加利福尼亚州的地震进一步强调了对URM建筑物进行其他修改的必要性。这些修改主要是在加利福尼亚州采用的追溯校正，并由加利福尼亚以外的各州进行部分或完全采用。这些修饰主要旨在防止外墙通过以下方式稳定URM建筑物来向外崩溃。
- 将墙壁固定到地板和屋顶系统；和
- Strengthening roof construction (metal straps, etc).
With this brief history of URM modifications, one would think these buildings have been adequately strengthened to withstand the effects of earthquakes – and for our discussion, the effects of fire. However, this isn’t the case. Some of the aforementioned modifications havesignificantly increased崩溃对火场人员的危害。下一篇文章将探讨特定的危害以及如何识别URM建筑物。
约翰·W·米滕多夫（John W.1981年，他被提升为营负责人，在接下来的一年中，他成为了在职培训部门的指挥官。1993年，他在服役30年后从LAFD退休。Mittendorf一直是国家消防研究基金会的成员。他为马里兰州艾米斯堡国家消防学院提供了培训计划；188博金宝体育1加州大学洛杉矶分校；以及英国莫尔顿 - 玛什的英国消188博金宝体育1防学院。他是编辑顾问委员会成员188金宝搏是正规吗和author of the books卡车公司Operations(Fire Engineering, 1998) andFacing the Promotional Interview(Fire Engineering, 2003).
