The evolution of the architecture leaded us to build structures with more complex and stylish shapes. This evolution has created the appearance of new structures with unknown behavior and the necessity of study it. This complex shapes they are not only used for buildings, they are also used for any kind of structures as it could be industrial structures or bridges. Steel structures are some of the most used structures for seismic force resisting systems in the world. Many of industrials structures contain hazardous materials and located in areas with very high seismic risk, any failure in the structure during an earthquake would lead to a big catastrophe. Although some industries have their own seismic design guidelines, most of them use the design codes developed primarily for building structures. This type of seismic design practice is not comparable with the importance of the industrial structure itself. The lack of research in this field, specifically focusing on industrial structures with irregularities is mainly responsible for such ill conditions in seismic design practice. There are still a lot of questions about the behavior of these types of structures waiting to be answered. Some parts of the seismic analysis where studies haven’t been deep in it and some design procedures should be redone for irregular industrial steel structures. Our goals for this thesis are to study the linear and nonlinear behavior of an irregular industrial steel structure, to comment the problems they cause and if the code needs any modification to avoid or reduce this problems. The irregularity used in this structure is a set-back irregularity; this means that the height of the structure is not the same everywhere, so in some parts we will have more stories than in others. We will deeply study the linear analysis, the difference we found in this structure compared with regular ones and which problems does the set-back cause. Nonlinear analysis will be run for our structure and we will go as far as the theory, the technology and the capacity of the computers nowadays allow as to go. We would design a specific industrial steel structure with a vertical irregularity following the American code. Once the design is completed we would apply a particular earthquake in three different directions to observe the reaction of the structure. We would run both analyses, linear and nonlinear in order to get more deeply into its behavior. Once processed the results obtained we would comment if the structure can be designed following the American code for buildings since there is not any specific code or irregular industrial structures and which particular behavior have the irregular structures as ours. With this thesis we are trying to observe the behavior of irregular industrial steel structure, such analysis haven’t been carried out before so we are going profoundly to an unknown area.