Improvements of ground anchors for Better Shelter

Abstract: This report is part of a bachelor’s degree project in solid mechanics at KTH, Stockholm. It is performed by two students on behalf of the social enterprise Better Shelter, which provides shelters for people displaced by war and natural disasters. The scope of the project is to expand Better Shelters product specifications by providing improvements of the shelter earth anchors. This would allow use of the shelter in areas affected by higher wind speeds and thereby help more people in need of temporary housing and shelters. The earth anchors prevent the shelter from uplifting and tilting by taking uplift forces when horizontal wind loads acts on the structure. Two wind models with wind speeds up to 36 m/s were created to find the reaction forces on the anchors resisting the wind load. The wind models were compared with each other to validate the results and find the largest reaction forces on the anchors. Simulations of the anchors were made to analyse occurring stresses due to wind loads. Redesigns of the current earth anchor were made to find improvements of the anchor shape and reduce the stresses on the anchor. Experiments were then performed to analyse the redesigned anchor shapes in practise. The redesign, calculations and computational analyses of the anchors were done using the programs SolidEdge, ANSYS and Matlab. Results showed that redesigning the anchor contact area with the anchor wire reduced the stresses on the anchors drastically. Increasing the wing size of the anchors proved to be successful for preventing anchors from being pulled out of the soil. This allows better use of the current anchor material volume. Experiments also proved that burying the anchor deeper into the soil is an effective way of increasing the resistance from being pulled out of the ground. By reducing the stresses on the anchor, more materials are available for use. This could be explored further and is a suggested as a continuation of this project. The current anchor material is aluminium, and most aluminium alloys can be used with the redesigned ball joint connection to the anchor wire even when wind forces are large.