屋顶结构失效的 7 个原因

屋顶结构损坏的原因

The integrity of each element of a building is critical to its stability. However, no component carries more potential for property damage or personal injury than the roof. A poorly performing foundation or failing exterior cladding can be inconvenient, unsightly, and expensive to repair or replace, but a roof failure can have devastating and long-term consequences.

值得庆幸的是，结构屋顶在没有警告的情况下发生故障的情况极为罕见。几乎总是有迹象表明屋顶的材料、设计、功能或三者都有问题。业主可以通过熟悉这些标志并呼吁保护自己免受昂贵的维修和法律责任的影响 法医工程和建筑科学专家 根据需要指导维修或完全更换屋顶。

按数字建造：建筑物和其他结构的最小设计荷载

鉴于屋顶倒塌或任何类型的结构故障的广泛影响，重要的是要按照当前的行业标准设计、建造建筑物，并在必要时进行维修或加固。这些标准被编入所谓的国际建筑规范 (IBC)，美国土木工程师协会 (ASCE) 在一份名为 标准 7 – 建筑物和其他结构的最小设计载荷.

The guidelines include detailed information on how roofs should be designed to accommodate primarily two different types of loads. The first is called dead load. It includes any static weight that will remain the same for the life of the roof, such as the roof structure itself, ceiling material, roofing material, insulation, mechanical/electrical/plumbing, and rooftop HVAC equipment. The second type are known as live loads. Live loads are variable and temporary forces associated with occurrences like snowfall, people walking on the roof, wind, etc.

在较冷的气候中规划雪荷载是屋顶设计和施工的一个特别重要的方面。 ASCE 标准解决了不同的建筑几何形状和布局如何影响积雪和由此产生的屋顶雪荷载。例如，当护墙围成平屋顶时，它们会积雪，导致沿护墙飘雪。相比之下，弯曲的屋顶或没有护栏的平屋顶允许雪滑或吹走，使其不太容易出现这些问题。不同屋顶高度的存在也可能是一个挑战，因为雪从较高的屋顶落到较低的屋顶，产生大的漂移。为了确保建筑物的结构完整性，这些漂移需要在设计过程中加以考虑。

IBC/ASCE 标准提供了建造屋顶所需的信息，该屋顶将支撑其承受的负载，前提是它得到适当的维护。当屋顶或周围环境的变化没有被识别和解决，并且结构被削弱时，就会出现问题。

结构屋顶故障的常见原因

There are many conditions that can contribute to problems with a roof. Below are seven of the most common causes of roof failures:

1. 劣化和进水

屋顶故障的主要原因之一是水侵入引起的结构部件损坏。定期或持续暴露在水中的木结构可能会受到霉菌和细菌的攻击，最终导致它们分解。金属部件，包括金属桁架板、托梁和屋顶甲板，也会受到生锈和腐蚀的类似影响和削弱。水可以通过多种方式进入屋顶框架，包括失效的带状疱疹或屋顶膜，以及通过内部冷凝。

2、屋顶排水的变化

正向排水对屋顶的健康至关重要。屋顶排水的有害变化的一个例子可能是排水管被碎屑堵塞，导致水在屋顶上积水。在每立方英尺 62.4 磅的情况下，积水的重量会很快增加，并对屋顶和支撑结构造成巨大的压力。

3.附近或相邻建筑物的增加

如果相邻建筑物屋顶表面的某些部分将降雨或融雪洒到旧结构的屋顶上，则旧屋顶可能没有足够大的排水管来适当地容纳径流。降雪在旧屋顶上漂移和积聚方式的变化，或者从一个屋顶落到另一个屋顶的漂移的重量，是破坏性压力的其他来源。

4. 增加保温材料导致的融化和径流变化

业主通常采取的使建筑物更节能的步骤之一是增加隔热层以防止热量通过屋顶散失。不幸的是，在某些情况下，一定量的热量损失是有帮助的，因为它有助于屋顶上降雪的融化和脱落。当该过程被缩减时，尤其是在旧建筑物上，可能会形成危险的堆积物，从而导致屋顶损坏。

5、屋架结构改造不当

当对建筑物中的机械、电气或管道系统进行维修或改进时，有时会以屋顶结构为代价。结构构件可以在其中钻孔、凹口或完全移除以容纳导管、管道或管道系统。这些修改削弱了屋顶结构，导致挠度随着时间的推移而恶化，在极端情况下，会导致屋顶失效。

6、安装过程中对屋架的损坏

另一个导致桁架变弱和屋顶问题的原因是运输或安装过程中的损坏。无论是对木材本身的损坏，还是对用于连接构件的金属板的损坏，这个问题都可能会一直隐藏，直到屋顶承受过大的负载。

7. 固有的设计错误

没有按照使用、位置等适当标准设计的屋顶更容易发生故障。例如，明尼苏达州的屋顶必须能够承受与该州大雪相关的大活荷载。如果错误使用最大预期雪荷载低得多的密西西比州标准，则可能会出现从偏转到完全倒塌的问题。

恶性循环：问题如何结合起来降低屋顶结构性能

Any of the issues listed above can, on its own, cause a roof weakening and ultimately roof failure. However, in most cases, serious problems arise not because of one factor, but due to the compounding of two or more of these issues. For example, a new addition is constructed next to an existing warehouse building. The addition is upwind of the original building, and has a higher roof, resulting in snow drifts forming on the roof of the old building. The weight of the snow drift causes the bar joists supporting the old roof to deflect, which causes ice to form in the roof drains. The roof over the original building collapses when the drift melts but the resulting water cannot drain off the roof due to deflection of the joists and blocked roof drains.

Consequently, performing regular maintenance is essential, as it can uncover small issues before they develop into major problems. And, when an issue is discovered, it is important to have a forensic engineer or building science expert perform a comprehensive inspection. Simply attributing a defect to the most visible or most likely cause can leave other contributing factors undiscovered, resulting in future problems.

从评估到支撑改造：Lerch Bates 能为您做些什么

One of the most important investments building owners can make in preventing deterioration of the roof is having any changes in appearance or function that might be attributable to problems with the roof assessed promptly by a forensic engineer. If the structural analysis reveals that the integrity of the roof has been compromised, there are a number of methods that can be used to secure it and ensure that it meets the current building code and is safe for occupants.

在柱子和屋顶梁上安装护膝是解决梁线不足的一种方法。另一种是通过增加柱来减小梁跨度。您还可以通过添加新成员来加强横梁，使其更宽或更深。在某些情况下，现有梁的问题非常严重，因此拆除和更换是最佳选择。

幸运的是，虽然每个屋顶都是独一无二的，但实际上有一种方法可以解决任何结构问题。

–香农皮尔斯，PE