![]() ![]() Section 8.3 of ASCE7-16 specifies the following equation for the computation of rain loads on an undeflected roof in the event that the primary drain is blocked: Figure 2.3 depicts a roof and these drainage systems. The primary drain collects water from the roof and directs it to the sewer, while the secondary drain serves as a backup in the event that the primary drain is clogged. The International Code Council requires that roofs with parapets include primary and secondary drains. Therefore, it must be considered when designing a building. Water accumulated on a flat or low-pitch roof during a rainstorm can create a major structural load. ![]() Ponding in roofs occurs when the run off after precipitation is less than the amount of water retained on the roof. This process, which is referred to as ponding, mostly occurs in flat roofs and roofs with pitches of less than 0.25 in/feet. Rain loads are loads due to the accumulated mass of water on a rooftop during a rainstorm or major precipitation. Building live load impact factors, as specified in ASCE/SEI 7-16.Ĭrane support girders and their connections L = length in feet (or meters) of the span-loaded segment to cause maximum stress in the member under consideration.The American Association of State Highway and Transportation Officials (AASHTO) specifies the following expression for the computation of the impact factor for a moving truck load for use in highway bridge design: Some building load impact factors are presented in Table 2.3. In practice, impact loads are considered equal to imposed loads that are incremented by some percentage, called the impact factor. Examples of impact loads are loads from moving vehicles, vibrating machinery, or dropped weights. They cause larger stresses in structural members than those produced by gradually applied loads of the same magnitude. Impact loads are sudden or rapid loads applied on a structure over a relatively short period of time compared with other structural loads. During design, member sizes and weight could change, and the process is repeated until a final member size is obtained that could support the member’s weight and the superimposed loads. The determination of the dead load due to structural members is an iterative process. The recommended weight values of some commonly used materials for structural members are presented in Table 2.1. ![]() Prior to the analysis and design of structures, members are preliminarily sized based on architectural drawings and other relevant documents, and their weights are determined using the information available in most codes and other civil engineering literature. Dead loads also include the loads of fixtures that are permanently attached to the structure. They include the self-weight of structural members, such as walls, plasters, ceilings, floors, beams, columns, and roofs. \)ĭead loads are structural loads of a constant magnitude over time. ![]()
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