The part of the building structure, typically below grade, upon which all other construction is built is known as:

horizontal structural member that supports a floor. Beams are typically wood, cold formed metal framing or steel.

Joists

Horizontal timbers, beams or bars supporting a floor.

two charges are fixed in place on the x-axis as shown. the charge at x = 0 is negative and has magnitude q = 2 μcoulombs (1 μcoulomb = 10-6 coulombs). the charge at x = d, (d = +12 cm), is positive and has magnitude q = 4 μcoulombs. find a point x = xo along the x-axis at which the electric field is zero.