Civil Engineering Professional Engineer Practice Exam

What is a floor joist specifically designed to resist?

1. Shear forces

2. Compression from above

3. Bending from walking loads

4. Tension

The correct answer is: Bending from walking loads

The correct answer is that a floor joist is specifically designed to resist bending from walking loads. Floor joists are structural members that support the floors of a building and are typically placed in parallel rows to create a framework for the floor. When loads, such as people walking on the floor or furniture placed on it, are applied, they create bending moments in the joists due to the forces acting on them. This bending occurs because the joists are supported at their ends while the loads cause the middle sections to deflect downward. The ability of the joist to resist bending is crucial for maintaining the structural integrity of the floor and providing a safe, stable surface. Proper sizing and material selection of the floor joists ensure they can adequately support expected loads without excessive deflection or failure. While floor joists do also resist other forces, such as shear forces resulting from loads and reactions at their supports, their primary function is indeed to carry bending moments due to lateral loading. Compression and tension forces can also come into play due to unbalanced loads and framing conditions, but the primary resistance that floor joists are designed for is against bending stresses caused by loads applied perpendicular to their length when people walk on the floor.