The aim of this study is to determine the stress intensity factor (SIF) and fatigue lifecycle of load-carrying 6 mm-thick fillet-welded cruciform joints subjected to fatigue loading conditions by means of finite element analysis (FEA). These joints are typical of automotive structures such as the mid-series rear axle of motor trucks which are sensitive to fatigue loading because of their construction and loading conditions. Finite element software was used to develop various cruciform joint models with varying geometrical dimensions, namely the depth of penetration and weld throat length, and simulation and analysis of the crack propagation were performed with 2D and 3D crack simulation software. The effect of the variations in the weld geometry with an induced crack at the weld root and weld toe on fatigue life was determined from the simulation results. The stress intensity factor values and lifecycles determined by the fracture mechanics approach were compared with the simulation results. It was shown that an increase in the depth of weld penetration and the weld size in isosceles triangles fillet weld shape for crack initiated in the weld root can decrease the stress intensity factor (SIF) and intensify the fatigue lifecycle. It was also found that linear misalignment had no significant effect on the SIF and fatigue life of cracks originating from the weld toe.

In this investigation concrete of different compressive strength is exposed to fire for various duration similar to natural fire occurring in buildings. A total of 72 Concrete cubes have been cast from three different concrete mixes then exposed to fire up to 10000C for three different durations (15,30 and 60 minutes) then tested using non- destructive methods like hammer rebound test and Ultra-Sonic Pulse velocity test. Then  the cubes were tested to destruction to measure their compressive strength. The results have shown that the unit weight, compressive strength and actual residual strength decreases with the increase of firing exposure duration similar to concrete exposed to steadily rising temperature. The correlation between the cube compressive strength and RN of the hammer test is very close, however the correlation coefficient of the cube strength with the UPV results is less. Using the combined method of the NDT, the relation between the cube strength and the NDT improves. Equations of relation betweencompressive strength and NDT tests are proposed for use in practice.

In this experimental investigation cement mortar panels reinforced with the different type of meshes were subjected to impact load after exposure to fire. Five groups of sandwich ferrocement panels (400x400x30mm in dimensions) had been cast and exposed to firing temperature up to 700˚C. Then the panels were tested using drop impact loading to measure the energy absorption of the specimens after firing. The variable parameters were type and number of mesh and styrofoam content. The results showed that the impact resistance of all groups of panels was significantly decreased when exposed to fire. Firing had little effect on strain energy for panels having a layer of styrofoam at the center. Different crack types and failure modes were observed due to the variety in number and type of meshes and percentage content of styrofoam. Numbers of blows were increased due to the increase of the number of mesh layers.