15.2. Vertical Loads

For closely spaced identical loads (such as joist loads), it is customary to treat them as a uniformly distributed load rather than as discrete loads, Fig. 15.1.

In structural engineering, when dealing with loads that are closely spaced and identical, such as the loads supported by joists, we often simplify our calculations by treating these loads as a single, evenly distributed load instead of calculating each load separately. This simplification helps in designing and analyzing structures more efficiently.

Think of this like a group of people standing in a line to get on a bus. If everyone stands right next to one another, it’s easier to think about how many people fit on the bus in total rather than counting each individual person. This is similar to how engineers treat these identical loads.

Material

lb=ft2

Ceilings Channel suspended system 1 Acoustical (fiber tile) 1 Floors Steel deck 2-10 Concrete-plain 1 in. 12 Linoleum 1/4 in. 1 Hardwood 4 Roofs Copper or tin 1-5 5 ply felt and gravel 6 Shingles asphalt 3 Clay tiles 9-14 Sheathing wood 3 Insulation 1 in. poured in place 2 Partitions Clay tile 3 in. 17 Clay tile 10 in. 40 Gypsum Block 5 in. 14 Wood studs 2x4 (12-16 in. o.c.) 2 Plaster 1 in. cement 10 Plaster 1 in. gypsum 5 Walls Bricks 4 in. 40 Bricks 12 in. 120 Hollow concrete block (heavy aggregate) 4 in. 30 8 in. 55 12 in. 80 Hollow concrete block (light aggregate) 4 in. 21 8 in. 38 12 in. 55

This section provides a detailed table of the weight of various building materials. The weight is measured in pounds per square foot (lb/ft²). Heavy materials such as bricks and concrete exert a significant vertical load on structures, which engineers need to account for in their designs. For example, a 12-inch brick wall weighs 120 lb/ft², which adds considerable weight to the structure it supports.

Imagine a stack of books. If you have thick textbooks, they weigh a lot, while a few thin magazines weigh much less. Just like the books, different building materials have varying weights, and engineers must choose materials wisely based on how they will support structures.

Material lb=ft2 Timber 40-50 Steel 50-80 Reinforced concrete 100-150

This table gives the average dead load of common materials used in construction. Timber has a dead load of about 40-50 lb/ft², steel ranges from 50-80 lb/ft², and reinforced concrete can weigh between 100-150 lb/ft². These values help engineers understand how much weight a building's structure has to support, known as the 'dead load'.

Consider a backpack. If you fill it with books, it will get heavy quickly, just like how the weight of materials in a building adds up. The heavier the materials (like reinforced concrete), the stronger our backpack (the building) needs to be to carry the load.

Roof snow load vary greatly depending on geographic location and elevation. They range from 20 to 45 psf, Fig. 15.2. Snow loads are always given on the projected length or area on a slope, Fig. 15.3.

Snow loads on roofs can vary significantly based on the region and how high the building is located. For example, roofs in snowy areas might have design snow loads ranging from 20 to as much as 45 pounds per square foot (psf). This measurement is crucial because it helps engineers determine how much snow weight a roof must safely support without collapsing.

Think of a picnic table in winter. If a heavy snowfall covers it, you can imagine how much weight is pressing down on it. Just like we clear snow off our tables to prevent collapses, engineers need to ensure buildings can withstand similar snow loads.

The steeper the roof, the lower the snow retention. For snow loads greater than 20 psf and roof pitches more than 20°, the snow load p may be reduced by p = ((θ - 20) * 0.5) psf (15.2).

On steep roofs, snow doesn't build up as much compared to flat roofs, due to gravity pulling the snow down. Engineers use a formula to calculate how much they can reduce the anticipated snow load based on the steepness of the roof. If a roof has a pitch above 20 degrees and a snow load greater than 20 psf, it can be safely assumed that less snow will stay on the roof.

Imagine a slide at a playground. The steeper the slide, the faster the kids go down and the less likely they'll pile up at the top. This is similar to how snow behaves on a sloped roof compared to a flat one.

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