Deep excavations require bracing along the wall height to resist lateral earth pressures. Design of a typical straight strut is influenced by self-weight bending stresses acting simultaneously with axial stresses. As length increases beam-column actions and second order effects (P-δ) can significantly reduce the axial load carrying capacity of the strut. Long struts therefore need to be supported intermittently, using “pin-piles”, resulting in additional cost and inefficiencies associated with congestion in the excavation trench. Additionally there can be problems associated with leakage of water in the invert slabs due to penetration in the waterproofing system around the “pin-piles”. Weidlinger Associates has proposed the use of a cambered, or “tuned”, strut [1]. In this design a long span twin I-girder strut is cambered upwards, such that the P-δ effects partially offset the gravity induced bending stresses. This could result in minimized bending stresses and optimal strut axial capacity, minimizing the need for intermediate supports. This paper describes an experimental and analytical research program in which scaled strut models were tested. The deflection and strain of axially loaded struts of varying length and camber were compared to a finite element analysis to verify concept and establish design recommendations.
展开▼
