The function of king post in a king post roof truss is A. To support the frame work of the roof B. To receive the ends of principal rafter C. To prevent the walls from spreading outward D. To prevent the tie beam from sagging at its centre

The correct answer is: To prevent the tie beam from sagging at its centre.

A king post roof truss is a type of roof truss that uses a king post to support the weight of the roof. The king post is a vertical member that is located between the ridge beam and the tie beam. The king post helps to prevent the tie beam from sagging at its center.

Option A is incorrect because the king post does not support the framework of the roof. The framework of the roof is supported by the rafters, which are the inclined members that support the roof deck.

Option B is incorrect because the king post does not receive the ends of the principal rafters. The principal rafters are the main rafters that support the roof deck. The ends of the principal rafters are supported by the ridge beam.

Option C is incorrect because the king post does not prevent the walls from spreading outward. The walls are prevented from spreading outward by the tie beam. The tie beam is a horizontal member that is located at the bottom of the roof truss. The tie beam helps to keep the walls from spreading outward by transferring the weight of the roof to the foundation.