Portal Cranes are used for load carrying in industrial and transportation sites. They have complex structure with big dimensions and many mechanisms with high security requests. In this work, we will study the influence of load swinging in dynamic behavior of Single girder L- type portal crane, in case of forward motion- travelling with full loading using computer modelling and simulations. Studying the behavior of portal cranes proves to be difficult using physical experimentation and measurement devices. Creating the crane’s computer model and applying simulations is useful method to study dynamic occurrences, which helps explaining the reasons of oscillations, failures and accidents of cranes, and gives conclusions that can be useful for design considerations and safety. The analysis will be concentrated in finding the nature of forces, moments and stresses that acts on crane’s construction and effects the stability, particularly at the start and end of travelling motion. Also, the study will look to find main parameters that contributes on the negative effects of load swinging. For this purpose, we designed “virtual portal crane” using model design and simulation applications. Crane is modeled from standard manufacturer, as a common model of L type portal cranes.