A. Loading diagram and design data
External loading diagram
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Loading diagram of the left joint |
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Design data
External forces: FY; FYs = FY/2.
Dimensional constraints: the square tube 12, 12′, of side h12 and thickness t12, is assembled with the square tube 11, of size h11 and thickness t11 (Ex.6.1).
Operating constraints: temperature T = (−30…40) °C; outdoor working environment with high humidity.
Design constraints: dimensional interchangeability.
B. Choice of material and heat treatment
A weldable material (Annex.M.01), S235 steel according to SR EN 10025-2 (STAS 500/2), was chosen for elements 11, 12 and 12′.
The pin is made of steel for mechanical construction, e.g. E295, E335, E360 (SR EN 10025/2005), or even of a quenching-and-tempering steel C35, C40, C45, etc. (Annex.M.01).
For each material identify: the yield strength σ02; the ultimate tensile strength σr; the allowable shear stress τaf = (0.6…0.8)σat, where σat = σ02/c is the allowable tensile stress, σ02 the yield strength and c = 2…3 the safety factor; and the allowable steel-on-steel crushing stress σas = 60…90 MPa (lower values are adopted for mild steels).
C. Design of the constructive shape
Constructive drawing
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Constructive features and constraints – a headed pin with a groove for a retaining ring is adopted (Annex.ST.09); – the pin passes transversely through both walls of the tubes; – for interchangeability, a standard pin diameter Db is adopted; – the pin holes are placed in the middle of the tube-in-tube joints 11-12, 11-12′.
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D. Calculation model, sizing and checking
Calculation model
The calculation model is similar to the one used for pin joint 5-6 (Sec.4.2).
Sizing
Using calculation window Calc.4.2.1, with F = FYs, ti = t12, te = t11 and σas = 60…80 MPa, 
is determined.
Db > 
is adopted (Annex.ST.09); for technological and handling reasons Db ≥ 8 mm is recommended.
Checking
With window Calc.4.2.2, using F = FYs and the adopted Db, the actual shear stress τf is obtained; it must satisfy τf ≤ τaf, where τaf = 50…70 MPa is the allowable shear stress of the pin material.
E. Design of the constructive-technological shape
Constructive-technological drawing
Recommendations for choosing the dimensions and constructive-technological parameters:
– section dimensions: h11, t11, h12, t12, L11 = Y1, L12 = Y1/2 + L11-12, l = L11-12/2, Db;
– the number of adjustment pin holes, and hence the adjustment travel, is set when drawing the assembly;
– technological operations: milling (the bar ends) and drilling;
– sharp edges are chamfered 1×45°;
– roughness of the surfaces machined by milling (bar ends) and drilling: Ra1 = 6.3 µm or Ra1 = 12.5 µm; Ra2 = 6.3 µm or Ra2 = 12.5 µm.
Recommendations for choosing the dimensions of the joint components:
– pin: d, l (Annex.ST.09);
– retaining ring: d2, s (Annex.ST.13);
– washer for pins: d, d1, h (Annex.ST.11).