The Technical File | Groundforce Groundforce Shorco | Technical File Issue 3.0 Box Struts - 4.7m Manhole Box General description Due to their size and specialist nature, the 4.7m manhole box has its own dedicated struts. Both fixed length and incrementally adjustable struts are available. Two types of fixed length unit are available, the original design provides a square box configuration whilst the later design permits varying widths. The incrementally adjustable struts are similar the struts used in the premier trench box but with a different end connection. All types of strut are constructed out of sufficiently large box section steel so that lateral bucking is not a design consideration at the relative small spans involved. Consequently the axial resistance or capacity of these struts is limited by local effects such as shear strength of the 40mm diameter adjustment / connector pins. Fixed length struts (original design) Design Data: Maximum Strut Length (pin to pin) - 2.75m. Note that when assembled this will provide a “square” box configuration. Connection between box panels and struts is by a 605M36T (EN16) 35mm Ø pin. The weight of the fixed strut is 1750kg. Axial Capacity - fixed length struts Allowable axial compressive force = 308.0kN. Allowable axial tensile force = -144.4kN. Fixed length struts (later design) These struts use the premier box fixed length beams fitted with a shoe adaptor pinned on at each end to facilitate the connection to the panel at each end. Data for this type of strut is stated in the table below. Fixed length strut (original design) Fixed length strut (later design) Strut Reference (and length #) Box width (external) (mm) Strut Weight c/w two end adaptors (kg) Allowable axial compressive force (kN) Allowable axial tensile force (kN) Strut B - 614mm 3138 103 +266.0kN with a FOS = 1.6 (as limited by shear in the 40mm pin connections) -266.0kN with a FOS = 1.6 (as limited by shear in the 40mm pin connections) Strut C - 714mm 3238 108 Strut J - 2214mm 4738 188 Strut D - 814mm 3338 113 Strut E - 914mm 3438 119 Strut H - 1714mm 4238 162 Strut F - 1114mm 3638 131 Strut G - 1414mm 3938 146 Strut K - 2714mm 5238 200 Strut L - 3214mm 5738 224 Data table for fixed length struts (later design) # - refers to the overall length of the extension piece 9.5.7