This thesis investigates the feasibility of using lightweight cold-formed steel (CFS) structures in seismic regions of the world, particularly in Iran. The study considers economic as well as structural issues through comprehensive testing and highly advanced numerical analyses. The study was planned not only to identify the advantages and disadvantages of the system in terms of economic issues but also to complement the current gaps of knowledge in the structural performance characteristics, in order to facilitate the use of this exciting system in earthquake-prone regions. The study is divided into four main parts: experimental, numerical, analytical, and managerial.
A comprehensive literature review was performed as part of this study in order to discover the existing gaps in available knowledge regarding the structural performance of CFS structures. It was found although CFS walls are not new and have been used as non-structural components for many years, their application as main load-bearing structural frames is relatively new, and as a result, appropriate guidelines that address the seismic design of CFS structures have not yet been fully developed. In addition, the lateral design of these systems is not adequately detailed in the available standards of practice.
A series of different CFS shear walls were constructed in order to investigate the lateral behaviour of the walls with different configurations: X-strap bracing, K-bracing, knee bracing, fibre-cement board sheathed walls, and steel sheathed shear walls. The performance of each of the proposed systems was evaluated by experimental tests on full-scale specimens under a particular lateral cyclic loading regime, based on method B of the ASTM E2126-07 standard . For each wall, the hysteretic envelope curve was plotted and different characteristics, such as the Equivalent Energy Elastic-Plastic (EEEP) curve and some important structural behaviour parameters, like R-factor, were evaluated.
Also, non-linear finite element analysis was employed using software, ANSYS , in order to investigate the seismic performance of CFS shear walls. A large-deformation degenerated shell finite element was used to model the CFS sections, and different structural characteristics, including material non-linearity, geometric imperfection, residual stresses and perforations, were taken into account. The numerical models were verified based on the experimental tests. The agreement observed in between the numerical simulations and the test results showed that finite element analysis can be used effectively to predict the ultimate capacity of the CFS shear panels. A particular objective of this study was optimisation of the seismic characteristics of some CFS shear panels and the corresponding dimensions and configurations.
In addition, an analytical differential model of the behaviour of general hysteretic systems considering all of the relevant structural characteristics, including pinching, stiffness degradation, load deterioration, and sliding, was derived and is presented in the following chapters. This model is generated based on Mostaghel’s model , which already includes all of these phenomena except sliding. Thus, an attempt was made to develop the model further, in order to cover the sliding phenomenon. A single-degree-of-freedom model was used to develop the hysteretic model by writing a system of ordinary differential equations. The proposed model captures the key features of the hysteretic cycles of any structure using some measurable system parameters through tests. A few examples of bilinear systems excited by harmonic loads are provided to give realistic descriptions of the force-displacement performance of general hysteretic systems.
Finally, as the construction management part of this thesis, a modified advanced programmatic risk analysis and management model (APRAM) is presented, which is capable of considering all potential risks attached to a project which might occur over the whole project life cycle, including technical and managerial failure risks. The purpose of this is to investigate the feasibility of using CFS structures in the high-seismic regions of Iran; and also to help identify whether the structural improvements which are basically the aims of the other parts of this project are rational when the CFS system is compared to other conventional constructional systems, economically speaking. APRAM is one of the recently developed methods which can be used for risk analysis and management purposes, and considers schedule, cost and quality risks simultaneously. However, this model takes into account only those failure risks which occur during the design and construction stages of the project life cycle. While this can be sufficient for some projects (for example, if the budget required cost the project’s operating life is much less than the budget needed for the construction period), it is not suitable for construction projects, as the costs absorbed during the operating life cycle are considerable. The modified model is demonstrated using a real building project, and shown to be employable as a suitable decision support tool for construction managers.