Homework 4 November 8, 2017 A 20.420 pitched roof below with trusses placed at 9

Question

Homework 4 November 8, 2017 A 20.420 pitched roof below with trusses placed at 9ft on center over the length of 63' has rafters 10x10. If the king post (10x12) is placed at the middle of the main beam (12x12) with queen post (10x12) placed equally over the main beam and that the fascia board (2x4), collar beam (10x8) and ridge board (4x4) are part of the framework, a. Find the linear feet of lumber needed to construct the roof. b. Find the total amount of lumber needed for the roofing framework. c. If the roof is to be covered with shingles over the rafter region and that waterproofing 1. (3marks) (5marks) membrane is placed before laying shingles to protect from weather, find the area covered by the waterproofing cover and the number of covers and shingles needed if each is shingle is 1.5'by 2.5' and the membrane/cover is sold in 100 square feet pieces. (4marks) d. If the a 5'x6' ceiling material is places just below the main beam and that it consists of 4x4 joists placed at 5' on center over the length of 63' which are placed over support girders (at 5' on center over the 27 length,(6x6) Determine the amount of joists and girders used for the ceiling support (5 marks) The total number of ceiling material needed a. b. (3 marks) Ridge ing post Collar (tie) beam fter Main beam Queen post Roof section 1.68 Fascia board 27 63 Floor plan

Explanation / Answer

Purlin spacing is important because the load coming on each purlin depends on the purlin spacing. The reason being , the load on each purlin = area load* tributary area of each purlin; tributary area of purlin = purlin span * spacing of purlin

Hence, the load on each purlin is a function of the purlin spacing.

Since purlins collect the lod from the roofing material and transfers to the truss, the joints at which the loads are applied is again a function of the positioning of the purlins and hence spacing of spacing comes into picture here as well. i agree, that the total load on the truss will remain the same irrespective of the spacing of the purlins. However, the spacial distribution of the purlins changes the spactial distribution of the loads on the truss which affects the truss and truss member analysis and forces.

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