•Reliability methods drive the assessment of overstrength ratios in Cross Laminated Timber structures.•There is a satisfactory agreement between the experimental lateral response of Cross-Laminated ...Timber panels and the simulations based on the Extended Energy-dependent Generalized Bouc-Wen model.•Given a certain failure probability, the overstrength factor is estimated as the ratio between the failure Peak Ground Acceleration of the ductile and brittle system.•The obtained overstrength ratios range between 1.5 and 2.5.•The obtained overstrength ratios are in accordance with those obtained by other scholars following non-probabilistic approaches.
The ductile collapse mechanisms of structures should be less resistant than the brittle mechanisms to ensure a ductile seismic response: in this way, the ductile mechanisms activate before the brittle ones. This sort of chronological law of collapse is obtained in the design phase by providing a proper ”overstrength” to the brittle mechanisms. The realization of overstrength plays a crucial role in the design, and several studies endeavoured to estimate the best overstrength factors, defined as the ratio between the characteristic load-carrying capacity of the non-ductile element and the characteristic load-carrying capacity of the ductile element. In this paper, the conventional definition of overstrength is discussed and compared to a probabilistic definition based on reliability methods. The probabilistic definition of overstrength drives the assessment of the overstrength factors of Cross-Laminated Timber buildings using a sort of indirect approach. The Extended-Energy dependent generalized Bouc-Wen model is used to estimate the nonlinear seismic response of a set of Cross-Laminated Timber shear walls with different ductility. The results are compared with the existing formulations, attempting to draw correlations possibly useful in the design phase.
•Restraining the notch effect in the dowels significantly increases the connection ductility.•Post-elastic steel properties of the dowels strongly influence the displacement capacity.•Optimized ...detailing combined with an adequate steel allow to reach a high ductility.•Constriction of the dowels in the contact area with the plate has been observed.
According to Eurocode 8 moderate to high dissipative behaviour of timber structures requires sufficient ductility of the critical regions. Earlier experiments on timber connections with slotted-in steel plates and laterally loaded common steel dowels rarely achieved high ductility values. Connections consisting of LVL-C members, dowel-type fasteners with different post-elastic steel properties, full confinement of the timber member and measures to restrain the notch effect were investigated by means of monotonic and cyclic tests with regards to the displacement ductility. The measures taken proved to be effective in enhancing the plastic deformation capacity of the steel dowels to a large extent. However, a new aspect was observed: the constriction of the dowels in the contact area with the plate. The research results provided a better understanding of the factors influencing the behaviour of slotted-in steel plate connection.
•MCMB with the optimal pre-lithiation capacity as negative electrode in LIC.•The capacity design of cathode affects the electrochemical performance of LIC.•The optimal designed capacity of positive ...electrode has been proposed.
Lithium-ion capacitors (LICs) are assembled with activated carbon (AC) cathode and pre-lithiated mesocarbon microbeads (MCMB) anode. The effect of AC cathode capacity design on the electrochemical performance of LIC is investigated by the galvanostatic charging-discharging and electrochemical impedance tests. As the designed capacity of AC positive electrode is lower than 50mAhg−1, the working potential of negative electrode is always in the low and stable plateau, which is conductive to the sufficient utilization and the working potential stability of positive electrode. When the designed capacity of positive electrode is higher than 50mAhg−1, the instability of negative electrode directly causes the reduced utilization and shortened working potential range of the positive electrode, which is responsible for the capacity attenuation and cycle performance deterioration of LIC. The positive electrode capacity design can realize the optimization of electrochemical performance of LIC. LIC50 exhibits the optimal electrochemical performance, high energy density up to 92.3Whkg−1 and power density as high as 5.5kWkg−1 (based on active material mass of two electrodes), excellent capacity retention of 97.0% after 1000 cycles. The power density and cycle performance of LIC can be further improved by reducing the AC positive electrode designed capacity.
•We consider the capacity design of renewable-only islanded microgrid and explicitly pose the problem as a chance-constrained optimization problem, which is solved using a probabilistically robust ...method.•An affine control policy is designed to dispatch battery power under uncertain renewable generation and load. The policy is integrated into the chance-constrained optimization problem.•In order to address conservativeness inherent in the robust method, we develop two approaches to set reshaping that reduce the volume of the robust set, thereby enabling less conservative designs.
Microgrids offer a promising opportunity for achieving greater use of renewable generation. In this paper, we consider optimal capacity design for an islanded microgrid supplied by a wind turbine, solar panel and battery system. The objective is to reduce plant cost while ensuring energy sufficiency, taking into account stochasticity of renewable generation and load. An affine control policy is designed to dispatch battery power under uncertain renewable in-feed and load. The policy is integrated into a stochastic chance-constrained optimization problem, which is solved using a probabilistically robust method. In order to address conservativeness inherent in the robust method, we develop two approaches to set reshaping that reduce the volume of the robust set, thereby enabling less conservative designs.
This study investigates the failure mechanisms and strength of plate-tube-connected circular steel arches. The upper and lower chord of the arch are joined by a series of uniformly distributed steel ...plates in a radial direction. The chord of the arch mainly bears bending moment, shear force and axial force. The connecting plates mainly resist bending moment, so its failure mechanisms and strength design are different from the traditional truss arch with diagonal tubes and web-opening arches. In this paper, the finite element (FE) software ABAQUS is used to study the in-plane failure mechanism and stability bearing capacity of planar plate-tube-connected circular steel arches, which is subjected to full-span uniform radial load (FSURL), full-span uniform vertical load (FSUVL) and half-span uniform vertical load (HSUVL). The elastic buckling load formula of two-hinged plate-tube-connected circular steel arches is proposed under FSURL.. Also, the limited condition of avoiding local buckling is also proposed under FSURL. The stability bearing capacity design formula of the arch under FSURL is proposed. Studies have shown that under FSURL, the arch will be subjected to global elastoplastic failure, and the upper chord will exhibit a full-section yield at the scope of 1/4 L span and the lower chord will exhibit a full-section yield at the scope of 3/4 L span. Under F(H)SUVL, the global failure mode may occur. The global failure stability bearing capacity design formulas of the arch under FSUVL and HSUVL are also proposed. The FE results are in good agreement with these formulas. Finally, the design suggestions of plate-tube-connected circular steel arches are proposed.
The hourly cooperation of production units and storage units in integrated energy system (IES) improves its performance on energy generation and supply, but increases the complexity in the capacity ...design. Conventional methods are flawed in terms of inappropriate operation mode and inaccurate performance evaluation. To improve the reliability of IES design, this research adopts operation trajectory prediction, energy dispatch schedule, and real time correction into operation mode, as well as annual continuous active dispatch optimization into capacity design method. IES components are divided into production unit, storage unit, and backup units. The proposed operation mode operates storage units actively to shift peak demand and resist uncertainty. The proposed design method optimizes both the capacity and cooperation of all units through an annual continuous operation, which improves the stability and reliability of the system performance. Compared with conventional methods, IES designed by the proposed method reduces energy consumption by 2.22%, annual cost by 1.40%, and carbon emission by 3.87%. In addition, this IES presents stability and robustness under different renewable energy and customer demand uncertainties. The proposed operation mode and design method contribute to accurate and speedy optimization, and provide reliable suggestions and feedbacks for IES investment and management.
•Storage units are operated actively to shift peak demand and resist uncertainty.•Both capacity and cooperation of production units and storage units are optimized.•Stability and reliability of performance are improved in operation and design.•Accurate reference and feedback are provided for IES investment and management.
Summary
This paper presents a procedure for seismic design of reinforced concrete structures, in which performance objectives are formulated in terms of maximum accepted mean annual frequency (MAF) ...of exceedance, for multiple limit states. The procedure is explicitly probabilistic and uses Cornell's like closed‐form equations for the MAFs. A gradient‐based constrained optimization technique is used for obtaining values of structural design variables (members' section size and reinforcement) satisfying multiple objectives in terms of risk levels. The method is practically feasible even for real‐sized structures thanks to the adoption of adaptive equivalent linear models where element‐by‐element stiffness reduction is performed (2 linear analyses per intensity level). General geometric and capacity design constraints are duly accounted for. The procedure is applied to a 15‐storey plane frame building, and validation is conducted against results in terms of drift profiles and MAF of exceedance, obtained by multiple‐stripe analysis with records selected to match conditional spectra. Results show that the method is suitable for performance‐based seismic design of RC structures with explicit targets in terms of desired risk levels.
This paper is a companion to “Displacement-Based Method of Analysis for Regular Reinforced-Concrete Wall Buildings: Application to a Full-Scale 7-Story Building Slice Tested at UC–San Diego” and ...presents key results obtained from a full-scale 7-story reinforced concrete building slice built and tested on the George E. Brown Jr. Network for Earthquake Engineering Simulation Large Outdoor High-Performance Shake Table at the University of California, San Diego. The building was tested in two phases. This paper discusses the main test results obtained during Phase I of the experimental program. In this phase, the building had a rectangular load-bearing wall acting as the main lateral force–resisting element. The building was subjected to four historical California input ground motions, including the strong-intensity near-fault Sylmar record, which induced significant nonlinear response. The test addressed the dynamic response of the building, including the interaction between the walls, the slabs, and the gravity system as well as four issues relevant to construction optimization: (1) reduction in the longitudinal reinforcement; (2) use of a single curtain of reinforcement to transfer shear; (3) constrain of plasticity in the first level of the wall using capacity design; and (4) use of resistance-welded reinforcement in the boundary elements of the first level of the walls. The building responded very satisfactorily to the ground motions reproduced by the shake table and met all performance objectives. The effects of kinematic system overstrength and higher modes of response in the experimental response were important; this verified to a large extent the displacement-based method of analysis presented in the companion paper.
•Yielding of serially arranged ductile connections does not occur systematically.•Steel commonly used in timber connections shows unfavourable characteristics.•Using steel with favourable ...post-elastic characteristics enables serial yielding.•Steel with favourable post-elastic characteristics also increases the resistance.•Optimized steel quality could lead to a reassessment of some design principles.
In the seismic design of structures according to the dissipative structural behaviour, the connection ductility is crucial in order to ensure the desired level of energy dissipation of the overall structure. Therefore, in case of ductile zones composed of dowel-type fasteners arranged in series, it is important to ensure that all the fasteners can fully develop their energy dissipation capacity by plastic deformations. However, when different types of connections made of two symmetrical and serially arranged assemblies of dowel-type fasteners are tested, it often appears that only few fasteners fully work in the plastic region while most of the remaining ones exhibit very low yielding.
Looking at the causes of this dysfunction, a possible explanation is due to the fact that the rules for the seismic design of dissipative zones in timber structures given in international codes and used in common practice often make reference only to the steel quality of the dowel-type fasteners specifying a minimum tensile strength or sometime, like is the case of the current version of Eurocode 8, only to maximum values of the dowel-type fastener diameter and of the thickness of the connected timber or wood-based members. Also, the research conducted so far about the ductile behaviour of serially arranged connections was not focused on the post-elastic properties of steel. However, for the seismic design of ductile zones of other materials, such as for example is the case of reinforced concrete walls, post-elastic characteristics of steel are required for the reinforcing bars, in order to achieve the desired dissipative behaviour.
Inspired by this fact, timber connections composed of serially arranged dowels made of steel grades with different hardening ratio and elongation at maximum tensile stress were fabricated and tested. The purpose of this work is to understand if the use of steel with significant post-elastic properties may help to solve the problem of limited yielding in serially arranged dowel-type connections.
The tested specimens were composed of two symmetrical timber members made of Glulam and LVL connected to two 6 mm thick slotted-in steel plates by means of 9 steel dowels with a diameter of 6.0 mm, which were subjected to monotonic and cyclic tests carried out by implementing dowels made of steel with favourable post-elastic properties.
The results showed that the simultaneous yielding of two serially arranged dowelled assemblies is possible, although not fully. Moreover, assuming as reference the steel grade with the lowest post-elastic properties, the connection ductility and strength measured through monotonic and cyclic tests increased by about 30% for the steel grades with the highest hardening ratio and elongation at maximum tensile stress, whereas the displacement at maximum strength was about five times higher.
In addition, it was found that confinement of the timber members and shaping of holes were crucial in order to avoid undesired and premature brittle failures and to increase the connection strength and ductility.
The results obtained may be useful in order to bring a reassessment of the code requirements regarding the steel properties of ductile connections as well as of certain principles of dimensioning and detailing.
In recent years, the distributed photovoltaic battery (PVB) system is developing rapidly. To fully utilize photovoltaic production and increase the penetration of renewable energy, battery storage in ...distributed photovoltaic systems becomes essential. Despite plenty of studies dedicated to the capacity design and system control strategies under different work conditions, few research pay attention to the sophisticated battery storage aging problem and its effect on the system performance. This paper develops a five-parameter photovoltaic model and the electrochemical lithium battery model for the PVB system considering the residential load uncertainty in the distributed photovoltaic system. The battery and system performance under different capacity design and operation strategies are discussed. The results show that the oversize of the battery capacity design contributes to the capacity loss, leading to the increasement of levelized cost of storage, and the capacity design of 6, 8, 10 kWh under 100 %, 80 %, 70 % state of charge (SOC) charging limit is recommended in this case. Under the 100 % SOC limit, the battery capacity declines by 22 %–28 % annually, which is much higher than the limit of 80 % and 70 %. Meanwhile, the battery lifetime based on recommended capacity design can be improved further by 8.6 %, 4.0 % and 2.0 % with controlling the battery charge rate. Besides, a comparison between the electrochemical and traditional battery models is conducted, demonstrating that both models present a high consistency in system energy flow, while the traditional battery model lacks the internal electrochemical aging mechanism. The electrochemical battery model gives out a more precise battery aging result and reveals the different performances under varied control strategies.
•A precise PVB system model, including the 5p PV model and the electrochemical lithium battery model, is established in this research.•The effect of the different battery control strategies on the performance of the PVB system and battery is investigated.•The recommended capacity design in this case under different control strategy is proposed.•A comparison between traditional battery model and electrochemical battery model is conducted.
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