Assessment: Design of Timber structures
(1) Tension Design
The main roof trusses of a restaurant in Mildura, Victoria will be fabricated from 35 mm thick seasoned Australian hardwood, marked as F14 and bolted together using steel gusset plates. Connections will be at each end of the member. The roof truss will span 12 m, will be 3 m apart and will support purlins, insulations and steel sheet roofing. The bolted connection at each end will use 4 M12 bolts in rows of two bolts. It is also identified that the cross-section of timber chosen must be more than 80 mm deep in order to accommodate the connection.
A tension chord in the trusses has the following unfactored loads: Permanent action 6.5 kN (tension)
Imposed action (construction) 3.0 kN (tension)
Imposed actions- from lights and a/c (fixtures) 2.3 kN Ultimate wind load giving tension in the chord 3.5 kN
It is to be noted here that roof furniture/ fixtures- lighting and air conditioning are considered as permanently acting imposed loads.
a) Find the factored strength limit state load combinations for the design of the chord as a tension member. Consider at least the following combinations:
- Permanent action plus imposed action (construction)
- Permanent action plus imposed action (fixtures)
- Permanent action plus imposed (fixtures) plus ultimate wind load (tension)
b) For the strength limit state, select the appropriate size material from the sizes given in the following Table 1.
(2) Compression Design
You have been asked to design the timber bridge piles at Jenolan (New South Wales) to resist vertical imposed and permanent actions using F17 unseasoned hardwood (which is locally available near bridge site). The piles are 13.5 m long and are effectively pinned at each end. Cross-bracing is provided in the plane perpendicular to traffic flow, at a maximum spacing of
4.5 m.
Assuming the piles are circular and same diameter is used throughout its length, determine the minimum nominal diameter required to resist the following loads per pile:
- Permanent action 60 kN (compression)
- Imposed action (DOL - 5 months) 145 kN (compression)
(3) Bending Design
Calculate the following:
a) Find material constant for beams (ρb) for glulam grade GL12 used with a loading consisting of 0.8 kN/m permanent load and 2.4 kN/m short-term occupancy imposed load.
b) Find the k9 factor for a group of F14 seasoned hardwood floor joists with a spacing of 450 mm and a span of 3.2 m supporting 19 mm plywood flooring.
c) As part of designing a timber beam to support a railway track (Figure a) as it passes over a small drain at Westgate golf club near Melbourne, you are required to calculate the stability factor k12. The only timber you have at your disposal is some new unseasoned visually graded F17 hardwood sleepers 250 × 150 and with following configuration (Figure b). Calculate the stability factor for the configuration (III) of Figure b.
Attachment:- Steel.rar