BLDG 1200 – Building Construction 1 Fall 2024SQL

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Fall 2024

BLDG 1200 – Building Construction 1

Lab Exercise – Structural Design Analysis – Worksheet #2

Roof Rafters, Ceiling Joists, Roof Joists & Ridge Beam Exercises

Given:

Conventions:              All exterior dimensions to outside face of wall sheathing

All interior dimensions to centre of walls and beams

Structure:                   Lumber: SPF No. 1 & No.2

Exterior walls: 38x140mm (2x6”) studs with 13mm (1/2”) plywood sheathing Interior walls: 38x89mm (2x4”) studs

Note:                           Include units (all metric) in your answers. If necessary, review the lecture material

for clarifications on span, supported length, end bearing, etc. If necessary, review “Structural Design Analysis – Worksheet #1” .

Part 1 – Roof Rafters & Ceiling Joists

Based on the partial roof plan and partial building section on the next page, provide solutions for the roof rafters and ceiling joists. Choose the smallest lumber size possible at the largest on-centre     spacing that the span tables will allow. Assume the attic space is not accessible by a stairway.

Given:             Project location: Cloverdale, BC                     Dimensions:    A: 9150mm     C: 450mm

Ridge board size:  38x235mm (2x10”)

Total roof span:                                                                                                                                            

From 9.4.2.2. & Division B – Appendix C – Table C-2

Cb:                                                                             

Ss:                                                                               

Sr:                                                                              

Specified Snow Load (S):                                                                                                                            

Roof rafter span:                                                                                                                                         

Roof rafter size & spacing:                                                       @                                            o.c.

Ceiling joist span:                                                                                                                                         

Ceiling joist size & spacing:                                                    @                                           o.c.

Design Reality:  The length of lumber can range, starting at 8’, with 2’ increments up to 24’ . Lengths of   8’ to 16’ are more readily available. Lengths longer than 16’ cost more and are more prone to twisting,    warping and bending. Although the code will permit long spans for ceiling joists, they are not practical to use. Typically, two shorter ceiling joists will be used, supported by an intermediate interior loadbearing  & BLDG 1200 – Building Construction 1 Fall 2024SQL nbsp;wall or drop beam. If an interior loadbearing wall is located at the middle of the floor plan to provide intermediate support for the overlapping ceiling joists, determine the following:

Ceiling joist span:                                                                                                                                         

Ceiling joist size & spacing:                                                    @                                           o.c.

 

Part 2 – Roof Joists & Ridge Beam

Based on the partial roof plan and partial building section on the next page, provide solutions for the roof joists, ridge beam and concentrated point loads.

For the roof joists, choose the smallest lumber size possible at the largest on-centre spacing that the span tables will allow.

For the ridge beam, choose the option that uses the least number of plies.

Given:             Project location: Greenwood, BC                   Dimensions: B: 9150mm         C: 450mm

Span of the Ridge Beam: 2.80m

Total roof span:                                                                                                                                              

From 9.4.2.2. & Division B – Appendix C – Table C-2

Cb:                                                                                           

Ss:                                                                                           

Sr:                                                                                             

Specified Snow Load (S):                                                                                                       

It’s recommended to solve the ridge beam first. Knowing the number of plies (width) for the ridge beam  will help determine the span of the roof joists.

Ridge beam supported length (tributary width)                                                                                              

Ridge beam solution:                                                                                                                                    

Size of P9 point loads (W x End Bearing):                                           X                                            

Roof joist span:                                                                                                                                             

Roof joist size & spacing:                                                                     @                                           o.c