Analysis of Balanced Double Lap Joints with a Bi-Linear Softening Adhesive

The response of a bonded symmetric balanced double lap joint under tensile loading with a bilinear softening adhesive is described with a closed form solution. Since bonded joints in concrete structures undergo softening, a versatile model to describe the response for a wide range of constitutive relationships is needed. A constitutive relationship containing a bi-linear softening law contains such versatility. The solution was investigated for moderate and extreme softening parameters. The solution for extreme softening parameters, exhibited a non-physical behavior, where the size of the stress-free crack decreased for increasing size of fracture process zone. This suggests that in order to fully describe the loading and unloading response, an unloading law should be implemented in the constitutive model. Apart from adhesively bonded metallic joints, the present solution may be used in analysis of cracked concrete disks strengthened with adhesive bonded fiber reinforced polymers (FRP), or in any other structure comparable to a double lap joint with a softening interface. The present constitutive model can be changed to fit any model with the same shape of constitutive relationship, see Figure 1.