The following text is taken from an article describing the Health and Safety Executive investigation into the toppling o

[answerhappygod]

The Following Text Is Taken From An Article Describing The Health And Safety Executive Investigation Into The Toppling O 1 (172.73 KiB) Viewed 96 times

The following text is taken from an article describing the Health and Safety Executive investigation into the toppling of five wind turbines during unexceptional weather. When Turbines Topple¹ -An investigation into the collapse of five wind turbines has pinpointed design weaknesses and should lead to improved safety standards in the industry. ... The (HSE) inspectors were keen to investigate the integrity of the foundation attachment. The correct assembly involved the preformed steelwork being cast in the concrete base using a series of jig rings to set the pitch circle location of the threaded foundation rods that would protrude from the base. The bottom nuts were then threaded onto all the foundation rods. The nuts at five locations distributed evenly around the pitch circle were screwed higher up, to act as initial points for the tower flange. Concrete Base Grout Foundation rod Top Nut Spacer Tower flange Bottom Nut Figure A2-1 - Foundation design for wind turbine The tower was lowered onto the foundation rods and sat on the five raised nuts. The heights of these nuts were adjusted to level the tower. Spacers and top nuts were partially tightened down to lock the tower flange in place. The remaining bottom nuts were screwed up to the underside of the tower flange and the spacers and top nuts fitted. All the fasteners were then tightened to the specified torque to clamp the tower flange fully. After ... approximately three months, the fasteners were re-tightened and the gap between the tower flange and concrete foundation slab around the fasteners was filled using structural grout. To control the profile of this grout filler, a pair of formwork rings were placed on the inside and around the outside of the joint. PLEASE TURN OVER
According to the report ... it was apparent that the securing rods had all failed at a common point. This was on a plane coincident with the lower face of the bottom nut... the clearance holes around the foundation rods showed no signs of distortion. (a) (b) (c) Explain briefly how bolts of a different specification are typically identified, and any advantages of using a rolled thread compared to a cut thread. (4 marks) Explain carefully how the variable load experienced by the wind turbine should be carried without significant variation of tension in the foundation bolts. (6 marks) What purpose does the spacer perform, and why does the installation procedure include re-tightening before the grout is inserted. Typically what tool would be used for re-tightening the nuts and what factors may influence the final torque reached? (7 marks) (d) If the grout was found to have surface voids, explain the impact this may have on the load capacity of the joint and ultimately explain the failure of the foundation rods. What design changes would you recommend to prevent future failures? (8 marks)