Structural Systems

Bay length

A bay length of 7.5 m is used in this chapter because it is the most economical in most PEB applications. However, 9 m bay lengths are gaining popularity and acceptance because longer bays often result in savings to the overall project cost as their use results in lower foundation costs (fewer rigid frames translates into fewer footings). When bay lengths greater than 9 m are required, jack beams or open web joists are used. These permit bay lengths of unto 18 m.

Single Slope Buildings (SS) – are economical in spans that are less than 12 meters. The mist common conditions for using Single Slope Buildings are: Whenever rainwater drainage is required to be along one sidewall of the building only. When a Single Slope Building is added directly adjacent to an existing building and the designer is required to avoid; The creation of a valley condition along the connection of both buildings that will result in an expensive water drainage system. The imposition of additional loads on the columns of the existing building. The imposition of additional loads on the foundations of the existing building. For buildings wider than 12m, it is common to specify a gable roof from economic, as well as aesthetic, considerations. Single Slope buildings may be either Clear Spans or Multi – Spans. Common applications of Single Slope buildings are demountable buildings such as those used for site office s or camp accommodations. These are typically 3.6m wide, 12 m long with a 2.4 m eave height at the lower side.
Multi – Gable Buildings: consist of two or more gable buildings sharing common sidewall columns. Although Multi – gable buildings are commonly used in many regions of the world, Zamil Steel recommends the use of Multi – Span buildings because of the following practical reasons: The valley between gables requires frequent maintenance to prevent accumulation of residue such as sand, etc. that must be frequently removed. Access to valley gutters for cleaning is more cumbersome than accessing eave gutters. This access requires maintenance traffic on the roof, risking sheeting deterioration or damage. Risk of overflow of rain water at valley during periods of extremely heavy rain (especially when the valley gutter between the buildings has not been maintained periodically) In long Multi – Gable buildings, interior downspouts have to be provided inside the buildings with horizontal drain pipes of concrete channels embedded in the concrete along the length of the buildings, under each valley gutter, to carry the water from the roof to an exterior location. The construction of such a water draining system is expensive and risky since blockage of these pipes can cause flooding inside the building. Wind bracing design for Multi – Gable buildings requires the provision of wind bracing members between the interior columns of the buildings. This bracing arrangement restricts interior movement and ease of access across the building. However, Multi – Gable buildings have the advantage of reducing the height of the building ridge (peak) for very wide buildings. Multi – Gable buildings may be either Clear Spans or Multi – Spans.
Low rise buildings: are ideal for offices and other commercial uses, low rise buildings, utilizing the PEB approach, are not only more economical than traditional methods of construction but are often constructed in half the “normal” time especially when complemented with the following subsystems. Interior gypsum board liner Interior gypsum board partitions Central air conditioning ducting Suspended ceiling In addition to speed of constructing and the economy of supply, pre-engineered buildings can be neat and elegant in appearance when accessorized with parapet walls and accented with contrasting trim colors. The most common (and most economical) example of a low-rise steel building is a building with a ground floor + two intermediate floors + roof. The roof of a low-rise building may be flat or sloped. The intermediate floors of low-rise buildings are made of mezzanine systems.