Fatigue of Semi-precast Slabs with Lattice Girders: Fid-Bau Portal

Fatigue of Semi-precast Slabs with Lattice Girders

Wieneke, Katrin / Hegger, Josef

Abstract To satisfy the high degree of prefabrication in construction practice, semi-precast slabs present a flexible and highly efficient alternative to in-situ concrete structures. For the design of semi-precast slabs, the load-bearing capacity of the shear joint must be verified separately. According to Eurocode 2, the shear resistance along the interface is affected by adhesive bond, friction and shear joint reinforcement. To account for the decreasing resistance of the joint under fatigue loads, the shear strength of the interface must be reduced by constant factors. Additionally, the stress range in the steel reinforcement must be verified separately. For semi-precast slabs, lattice girders ensure a safe transport and assembling as well as a sufficient shear capacity of joint and slab. The design of semi-precast slabs follows the general technical approval of the lattice girders which is based on Eurocode 2 with the National Annex of Germany. The use under cyclic loading conditions (e.g.: forklift trucks and traffic loads for bridges) is either limited or excluded. The curved and welded shape of lattice girders confines the design under fatigue loads to a verification of a damage equivalent stress range. The design for multiple cycles with fatigue-strength-curves is excluded. To investigate the load-bearing capacity of shear joints and lattice girders under cyclic loading, fourteen fatigue tests have been conducted at RWTH Aachen University within an AiF research project. The investigated parameters of the test series were roughness of shear joint, slab size, shear reinforcement ratio and concrete strength. To expand the applicability of semi-precast slabs with lattice girders, a number of small-size tests have been performed in order to verify a fatigue-strength-curve for lattice girders. The present paper presents the experimental investigations and proposes a fatigue-strength-curve for lattice girders. The results of the test program are evaluated by the design regulations for shear joint and shear reinforcement based on Eurocode 2 and the general technical approval of the lattice girders.