Basics of Structural Design Load Calculations | One-Way Vs Two-Way Slab

Summary

This video focuses on the fundamentals of calculating structural design loads, with an emphasis on gravity loads. It explains the different types of loads, such as dead loads, superimposed dead loads, and live loads, and their importance in structural design. The video walks through examples on how to calculate these loads, especially for concrete slabs, and how to distribute them across beams and columns for an economical design. Additionally, it highlights key concepts like one-way and two-way slabs and concludes by encouraging viewers to engage with the content for more detailed insights.

Takeaways

• 🏗️ Structural engineers must carefully consider and assign design loads for accurate and economical designs.
• ⚖️ Design loads directly influence the weight, reinforcement, and size of structural members.
• 📚 This video focuses on calculating structural design loads and understanding basic load paths.
• 🏢 The main loads in a structure include Dead Loads, Superimposed Dead Loads (SDL), and Live Loads.
• 🧮 Dead Load is the self-weight of the structure and can be calculated by multiplying the unit weight of the material by its thickness.
• 🧱 Superimposed Dead Load includes interior walls, floor finishes, ceilings, and MEP systems, calculated similarly to Dead Load.
• 🚶‍♂️ Live Loads account for movable items like furniture, equipment, and occupants, varying based on building use.
• 📖 Codes like ASCE 7-16 provide minimum live load values based on the type of structure or occupancy.
• 🔄 The load distribution in slabs depends on whether it’s a one-way or two-way slab, affecting how loads are carried by beams.
• ✍️ To apply service loads in design, structural engineers multiply by ULS factors: 1.2 for Dead Loads and 1.6 for Live Loads.

Q & A

Question 1: What are the types of loads a structure typically carries?

A structure typically carries gravity loads and resists horizontal or lateral loads. The main gravity loads include Dead Load (self-weight), Super-imposed Dead Load (SDL), and Live Loads (movable loads).

Question 2: How is the Dead Load of a structure calculated?

The Dead Load is calculated by multiplying the density or unit weight of the material by its thickness. For example, for a concrete slab of 0.25m thick with a unit weight of 25 kN/m3, the Dead Load is 6.25 kN/m2.

Question 3: What does Super-imposed Dead Load (SDL) include?

The Super-imposed Dead Load includes partition or interior walls, floor screed, floor finish, ceiling loads, facade and internal cladding, and MEP (Mechanical, Electrical, Plumbing) pipes and fixtures.

Question 4: What are Live Loads and how are they determined?

Live Loads are movable loads such as equipment, movable partitions, furniture, and occupants. The magnitude of Live Loads depends on the type of building or occupancy, and the minimum requirements are specified in relevant codes and standards, like ASCE 7-16.

Question 5: How do one-way and two-way slabs differ in load distribution?

A one-way slab transfers loads in one direction, typically to two opposite edges, while a two-way slab transfers loads in two directions and is supported on all four sides.

Question 6: How do you determine if a slab is one-way or two-way?

A slab is considered one-way if the ratio of the longer span to the shorter span is greater than 2.0. If the ratio is less than or equal to 2.0, it is classified as a two-way slab.

Question 7: What is the procedure for distributing loads on a two-way slab?

For a two-way slab, draw an isosceles triangle in the shorter direction and a trapezoid in the longer direction to visualize how loads are transferred to the supporting beams. The loads are distributed proportionally to these areas.

Question 8: How do you calculate the load distribution on beams?

To calculate load distribution on beams, calculate the area of the slab adjacent to each beam (triangle, trapezoid, or rectangle) and multiply it by the Dead Load, Super-imposed Dead Load, and Live Load. Divide the result by the length of the beam to get the uniformly distributed load in kN/m.

Question 9: What load factors are used for Ultimate Limit State (ULS) design?

For ULS design, the load factors are 1.2 for Dead Loads and 1.6 for Live Loads. These factors are applied to the service loads to ensure safety under extreme conditions.

Question 10: How are loads transferred from the slab to the foundation in a structure?

The loads carried by the slab are transferred to the perimeter beams, which distribute the loads to the columns. The columns transfer the load to the footing, which then transfers it to the underlying soil.