عملکرد از پانل های برشی سرد مرصع دیوار تحت بارگذاری یک نواخت و دوره ای: قسمت دوم: تجزیه و تحلیل و مدل سازی و عملکرد عددی

The main components to provide earthquake performance of a light-gauge steel house are the shear walls. Understanding shear wall behaviour and finding suitable hysteretic models is important in order to be able to build realistic finite element models and assess structural performance in case of earthquake. As for any building structure expected to exceed its elastic behaviour-range in case of earthquake, the interaction of design capacity, load bearing capacity and structural ductility will influence the performance. In this paper alternative design methods and hysteretic modeling techniques are presented. Based on tests described in Part I, a numerical equivalent model for hysteretic behavior of wall panels working in shear was built and used in 3D dynamic nonlinear analysis of cold-formed steel framed buildings. Preliminary conclusions refer to the effect of over-strength and ductility upon possible earthquake load reduction in case of light-gauge shear wall structures.

Earthquake performance of a structure depends on large number of parameters. Even if we do not consider the high uncertainties related to the evaluation of earthquake motion characteristics at a given site, the overall behaviour of a structure is influenced by numerous factors related to the behaviour of its structural components, interaction with the soil and interaction with non-structural elements that are usually neglected in design calculations. Undoubtedly, one of the most important parameters to consider for a structure is the actual behaviour characteristics of its structural components. In the case of light-gauge steel houses the primary elements to resist lateral forces (i.e. wind and earthquake) are the wall panels, so the steps towards understanding global response are through assessing wall panel behaviour and then integrating it into the structure. As a first step it is important to find suitable modelling tools for a panel, which is easily integrated into a global structural scheme. Also, it is unavoidable to define the objectives that we are trying to fulfil through design and how it is possible to avoid collapse and limit damage.

Based on experimental results, a simple FE model has been calibrated to be used in earthquake modeling of shear wall-panels in light structures. The model is accurate enough to take into account all the important aspects of the hysteretic behavior under consideration and it is simple enough to be incorporated in more complex structural schemes for full structural modeling. A number of inelastic time-history runs have been performed using different wall panels, acting masses and earthquake records, and the model has been found satisfactory for the purpose of dynamic analysis. Using experimentally determined criteria, three performance levels were associated with corresponding lateral displacement of the panels and ‘partial behaviour’ factors have been identified for the panels based on time-history analysis results. The effect of over-strength is identified to be an important in the post elastic behavior of panels and source of a possible design earthquake-force reduction. The resulting factor (2.2–2.6) harmonizes reasonably with the value 1.5–5 suggested by Gad et al. [12]. The possibility of design force reduction due to ductility and energy dissipation seems to be more limited (1.4–1.6) probably due to low energy dissipation capacity of the hysteretic loops. Some inadequacies in the determination of elastic limit for wall panels with openings have been identified, yielding very low values with the obvious consequences of underestimating their capacity. Even if results are limited to a small number of earthquake records and analysis of simple wall panels has been performed, the similar particularities of behaviour can be expected for entire structures where horizontal force resisting elements of this type are used.