Seismic analysis of nonstructural elements

Abstract

Nonstructural failures have accounted for the majority of earthquake damage in several recent earthquakes. Thus, it is critical to raise awareness of potential nonstructural risks, the costly consequences of nonstructural failures, and the opportunities that exist to limit future losses. Non-structural parts of a building have the potential to modify earthquake response of the primary structure in an unplanned way. This can lead to severe structural damage or even collapse. Failure of non-structural components may cause death or injury from: Falling panels, masonry or glass, collapsed ceiling components, falling fittings and fixtures, debris blocking exit ways, etc. The configuration of a building could be called its seismic form. An obvious example of poor seismic configuration is a U or L shaped building on plan, if it is not structurally divided into simply shaped blocks. Such a building may suffer damage in an earthquake because the ‘free’ ends on plan will sway in a different way to the corner section, which is stiffer. Columns on re-entrant corners are particularly prone to damage because of the concentration of forces at such points. Therefore should be avoided in the design: irregular configuration, soft-storey, asymmetrical horizontal bracing, short pillars, etc. so as to properly distribute the stresses. Of course, an important starting point in the study and evaluation of this topic is the consideration and the comparison of several local regulations and their approach to the seismic design of non-structural elements. The reason of the importance of considering and evaluating the possible differences among different approaches to the same problem is clearly understandable. These national regulations represent the expression of the “state of the art” about this topic of a specific country or region of the world. In this project analyzes regulations as: European regulation (Eurocode 8), American regulation (ASCE 7-10), New Zealand regulation (NZS 1170.5), Japan regulation and Spanish Regulation (NCSE-02). Finally we focus on a specific non-structural element such as the facades. Facade systems can be categorized by three main types; infill panels, cladding and a combination of the two. In general, infill panels are constructed within the frame of the structure and cladding facades are attached externally to the primary structure. Each facade system will behave in a particular way when subjected to inter-storey drift. It is important to understand how each facade system behaves in order to determine which parameters are important for the performance based design. How a facade system is connected to the primary structure is the critical aspect in determining the interaction between the two systems. The current practice in seismically active countries such as Japan, USA and New Zealand is to separate the facade system from the frame. For infill panels this is most commonly done using a seismic (or separation) gap between the wall and frame. Similarly to seismic gaps, the interaction between cladding systems and the frame can be minimized using movement connections. These connections commonly consist of a fixed and sliding connection which allows the cladding panels to move and rotate relative to the frame when undergoing seismic excitation. Another possible solution is use of a relative displacement between facade and structure. Facade systems can be integrated with energy dissipative connections that are designed to yield before the facade yields. Finally, having a complete integration of the facade system is often an effective strategy to reduce the drift of a structure because of the additional stiffness provided by the façade. Finally, we analyze a masonry wall brick through a computer application that is based on the finite element method. We analyze a concrete masonry wall (the properties of each masonry wall vary depending on the individual parameters of the masonry and the connection between them) and adjust the model to obtain the stress distribution maps, compare the results with the Spanish regulation (CTE) and to draw conclusions. See as, masonry is a material designed to resist vertical loads, one of the principal factors must be considered in the design is the compressive strength. However, these structures are affected by other actions, such as earthquakes loads, which translate into horizontal forces. This requires considering the shear strength and tensile strength of the masonry.