Seismic response assessment of rocking systems using single degree-of-freedom oscillators

A new modeling for the seismic response assessment of free-standing, rigid or flexible, pure rocking systems is presented. The proposed modeling is based on equivalent single degree-of-freedom (SDOF) oscillators that can be implemented with common engineering software or user-made structural analysis codes. The SDOF models adopted use beam elements that are connected to a nonlinear rotational spring with negative stiffness that describes the self-centering capacity of the rocking member. The loss of energy at impact is treated with an “event-based” approach consistent with Housner's theory. Different variations pertinent to rigid blocks are first presented, and then the concept is extended to the flexible case. The implementation of the method requires some minor programming skills, while thanks to the versatility of the finite element method, it is capable to handle a variety of rocking problems. This is demonstrated with two applications: (a) a vertically restrained block equipped with an elastic tendon and (b) a rigid block coupled with an elastic SDOF oscillator. The accuracy and the efficiency of the proposed modeling is demonstrated using simple wavelets and historical ground motion records.     

Extensional tectonics in Mt Parnon (Peloponnesus,Greece)

Peloponnesus in the south-western part of the Aegean is formed by a heterogeneous pile of alpine thrust sheets that was reworked by normal faulting from Upper Miocene to recent times. Upper Miocene–Lower Pliocene extension in Mt Parnon was accommodated by several mappable brittle detachment faults that exhibit a top-to-the-NE-ENE sense of shear. The hanging wall of the detachments comprises a number of highly tilted fault blocks containing abundant evidence of intense internal deformation by normal faulting and layer-parallel shearing contemporaneous with faulting. These fault blocks are remnants of a cohesive extensional block that slipped to the NE-ENE and broke up along high-angle normal faults that sole into or are cut by the detachments. The largest part of this block is located at the eastern edge of the metamorphic core forming the hanging wall of East Parnon high-angle normal fault that excised part of the aforementioned detachments. The lowermost metamorphic Unit of the nappe-pile does not seem to be affected by the previous extensional episode. Upper plate reconstruction shows that various units of the nappe-pile were affected by high-angle normal faults that linked to detachment faults in the weaker layers. Since the Middle-Upper Pliocene further exhumation of the metamorphic rocks has resulted in the formation of high-angle normal faults overprinting Neogene extensional structures and cut the entire nappe-pile. This new fault system tilted the earlier extensional structures and produced a NE-SW coaxial deformation of Mt Parnon.     

Which policy instruments attract foreign direct investments in renewable energy?

Reducing GHG emissions and mitigating climate change would require significant investments in renewable energy technologies. Foreign direct investments (FDI) in renewable energy (RE) have increased over the last years, contributing to the diffusion of RE globally. In the field of climate policy, there are multiple policy instruments aimed at attracting investments in renewable energy. This article aims to map the FDI flows globally including source and destination countries. Furthermore, the article investigates which policy instruments attract more FDI in RE sectors such as solar, wind and biomass, based on an econometric analysis of 137 Organisation for Economic Co-operation and Development (OECD) and non-OECD countries. The results show that Feed in Tariffs (FIT) followed by Fiscal Measures (FM), such as tax incentives and Renewable Portfolio Standards (RPS), are the most significant policy instrument that attract FDI in the RE sector globally. Regarding carbon pricing instruments, based on our analysis, carbon tax proved to be correlated with high attraction of FDI in OECD countries, whereas Emissions Trading Schemes (ETS) proved to be correlated with high attraction of FDI mainly in non-OECD countries.

Key policy insights

• Feed in Tariffs is the most significant policy instrument that attracts FDI in the Renewable Energy sector globally.

• Fiscal Measures (FM), such as tax incentives, show a significant and positive impact on renewable energy projects by foreign investors, and particularly on solar energy.

• Carbon pricing instruments, such as carbon taxation and emissions trading, proved to attract FDI in OECD and non-OECD countries respectively.

• Public investments, such as government funds for renewable energy projects, proved not as attractive to foreign private investors, perhaps because public funds are not perceived as stable in the long run.

     

Modeling of rocking frames under seismic loading

A novel modeling approach for the seismic response assessment of rocking frames is presented. Rocking frames are systems with columns that are allowed to fully, or partially, uplift. Despite the apparent lack of a mechanism to resist lateral forces, they have a remarkable capacity against earthquake loading. Rocking frames are found in old structures, for example, ancient monuments, but it is also a promising design concept for modern structures such as bridges or buildings. The proposed modeling can be implemented in a general-purpose structural analysis software, avoiding the difficulties that come with the need of formulating and solving specifically tailored differential equations, or the use of detailed computational models. Different configurations of a rocking portal frame problem are examined. The model is based on rigid, or flexible, beam elements that describe the members of the frame. Negative-stiffness rotational springs are smartly positioned at the rocking interfaces in order to simulate the rocking restoring moment, while the mass and the rotational moment of inertia are considered either lumped or distributed. Both the cases of rigid and flexible piers/columns are discussed, while it is shown that frames with restrained columns can be considered in a straightforward manner. A simple alternative based on an equivalent oscillator that follows the generalized rocking equation of motion is also investigated. The efficiency and the accuracy of the proposed modeling is demonstrated with the aid of carefully chosen case studies.