Experimental investigation of carbon dioxide trapping due to capillary retention in saline aquifers

Capillary trapping is a physical mechanism by which carbon dioxide (CO₂) is naturally immobilized in the pore spaces of aquifer rocks during geologic carbon sequestration operations, and thus a key aspect of estimating geologic storage potential. Here, we studied capillary trapping of supercritical carbon dioxide (scCO₂), and the effect of initial scCO₂ saturation and flow rate on the storage/trapping potential of Berea sandstone. We performed two‐phase, scCO₂‐brine displacements in two samples, each subject to four sequential drainage–imbibition core‐flooding cycles to quantify end‐point saturations of scCO₂ with the aid of micro‐ and macro‐computed tomography imaging. From these experiments, we found that between 51% and 75% of the initial CO₂ injected can be left behind after the brine injection. We also observed that the initial scCO₂ saturation influenced the residual scCO₂ saturation to a greater extent than the rate of brine injection under the experimental conditions examined. In spite of differences in the experimental conditions tested, as well as those reported in the literature, initial and residual saturations were found to follow a consistent relationship.     

Experimental study of the effect of variation in in‐situ stress on capillary residual trapping during CO2 geo‐sequestration in sandstone reservoirs

During a geo‐sequestration process, CO₂ injection causes an increase in reservoir pore pressure, which in turn decreases the reservoir net effective stress. Changes in effective stress can change all the reservoir and cap‐rock properties including residual saturations. This article presents the results of an experimental work carried out to understand the potential change in the volumes of residually trapped CO₂, while the porous medium tested underwent change in the net effective stress under in‐situ reservoir conditions of pore pressure and temperature. The experimental results obtained show that an initial 1725 psi (11.9 MPa) decrease in the net effective pressure caused 1.4% reduction in the volumes of residually trapped CO₂, while another 1500 psi (10.3 MPa) reduction caused a further 3.2% drop in the residual saturation of CO₂.     

SOME DESIGN PRINCIPLES RELEVANT TO TORSIONAL PHENOMENA IN DUCTILE BUILDINGS

Recent studies provided opportunities to review some of the principles, which have been used in the formulations of internationally accepted code-recommendations relevant to the seismic design of ductile buildings also subjected to torsional phenomena. With the progress of this study, features emerged which are considered to have contributed to a better understanding of structural behaviour. Moreover, the identification of deeply embedded fallacies, relevant to ductile response, suggested the introduction of some changes in seismic design strategies, yet not widely known or appreciated. Reasons for necessary re-interpretations of traditional structural properties, together with illustrative examples, demonstrating applications, rather than set code-type rules, are offered.     

CONCEPT AND DEVELOPMENT OF HYBRID SOLUTIONS FOR SEISMIC RESISTANT BRIDGE SYSTEMS

The development of alternative solutions for precast concrete buildings based on jointed ductile connections has introduced innovative concepts in the design of lateral-load resisting frame and wall systems. Particularly efficient is the hybrid system, where precast elements are connected via post-tensioning techniques and self-centring and energy dissipating properties are adequately combined to achieve the target maximum displacement with negligible residual displacements. In this contribution, the concept of hybrid system is extended to bridges as a viable and efficient solution for an improved seismic performance when compared with monolithic counterparts. Critical discussion on the cyclic behaviour of hybrid systems, highlighting the most significant parameters governing the response, is carried out.

The concept of a flexible seismic design (displacement-based) of hybrid bridge piers and systems is proposed and its reliability confirmed by quasi-static cyclic (push-pull) and nonlinear time-history analyses based on lumped plasticity numerical models.     

Excesses of nationalism: Greco‐Turkish population exchange

This article studies 1923 compulsory population exchange between Greece and Turkey through a case study of its experience in Izmir. It traces the ways the early Republican state engaged in the project of reshaping the population by eliminating the non‐Muslims who were rendered as ‘excesses’ in the spatial and discursive matrices of the nation‐state. Through the experience of the exchange in Izmir, it argues that the process of the accommodation and assimilation of the exchangees played a significant role in shaping the modalities of Turkish nationalism by creating new lines and fissures, further dividing the ‘Muslim brethren’ into ever restrictive constructions of Turkishness. It also underlines that this forced displacement is not just a significant episode in Greek and Turkish histories but that it represents a turning point in the project of nation formation in general.     

北京市居民租赁住房可支付能力及空间分异研究

长期以来，我国租赁住房市场被严重边缘化，“十三五”规划明确提出建立租购并举的住房制度，彰显了让住房回归“居住属性”特征。住房租赁市场成为研究热点，而居民的租赁住房可支付能力是其关键。本文将保障性租赁住房与商品性租赁住房合为一体作为研究对象，从我国住房租赁市场的现状出发，客观评价不同人群的家庭可支配收入、最低非住房消费标准、住房补贴比例等指标，在此基础上定义人均租赁住房可支付能力指数，用于评估不同人群的可支付能力。结合目前的租赁住房市场的供给情况，运用GIS软件分析居民可支付能力的空间特征，分析北京市现有租赁住房与居民租房可支付能力匹配情况，对于合理制定多层次租赁住房市场政策具有参考意义。     

PERFORMANCE-BASED SEISMIC RESPONSE OF FRAME STRUCTURES INCLUDING RESIDUAL DEFORMATIONS. PART II: MULTI-DEGREE OF FREEDOM SYSTEMS

The role of residual deformations when evaluating the performance of multi-storey frame structures subjected to ground motion is investigated in this paper. The limitations of damage indices available in the literature, either based on ductility, energy dissipation or a combination of both, in capturing such a significant aspect of the seismic response of frame structures are discussed. The concept of residual deformations as a critical complementary indicator to cumulative damage, introduced in a companion paper (Part I) for single-degree-of-freedom (SDOF) systems, is herein extended to multi-degree-of-freedom (MDOF) frame systems. The seismic performance of multi-storey frame structures, either representative of new designed or existing structures, is investigated, focusing on the response in terms of residual deformations. Residual deformations are shown to be sensitive to the hysteretic rule adopted, to the system inelastic mechanism as well as to the seismic intensity. The influence of higher modes and P-Δ effects on the final residual deformations is addressed. A combination of maximum drift and residual drift in the format of a performance matrix is used to define the system's global performance levels and is then extended to a framework for an alternative performance-based seismic design and assessment approach.