•Pendulum impact loading tests for PC columns.•A novel pendulum test facility to maintain axial compression force.•The effect of column base connection types on the impact resistance.
In the present ...study, pendulum impact loading tests were performed to investigate the lateral impact resistance of precast concrete (PC) columns with various column base connections. To maintain axial compression force during the impact process and subsequent collapse, a set of specially designed loading facility with solid counterweights was proposed. The test parameters included three PC columns using grouted sleeve connection (PC1), lap splice in grout-filled hole connection (PC2), and bolt connection (PC3), and a cast-in-place concrete (RC) column as a counterpart specimen. The dynamic responses including the damage mode, crack development process, impact force–time history, deflection-time history, strain–time history, and acceleration-time history were investigated. Further, the energy dissipation and stress wave transmission law of the specimen were analyzed. The test results showed that semi-rigid boundary conditions of PC columns decreased the column damage, but the lateral deformation increased, indicating relatively low impact resistance. The mechanical performance of each PC connection method was also discussed.
•Quasi-static cyclic test was conducted on the self-centring connection after fire exposure.•Post-fire seismic behaviour changed significantly in geometric conditions and deformation ...mechanism.•Energy dissipation was postponed and weakened while self-centring capacity was completely damaged.•Finite-element analysis reappeared post-fire response after calibrating the highest temperature field.•Post-fire repair was simulated in sequence and practical suggestions were proposed based on effects.
Fire hazard is regarded as a significant threat to structural systems, not only the resistance during the fire should be concerned but the post-fire assessment of structural performance is also of great importance. The post-fire seismic behaviour is the key metric for evaluating the residual performance of structures mainly serving seismic demands. However, limited research considers whether the self-centring system, one of the seismic-resilient structures, can still resist seismic loadings after fire exposure. Based on that, this study mainly aims to investigate the post-fire seismic response of a self-centring system with buckling-restrained plates and pre-stressed bars. A sequence of the fire exposure and the post-fire cyclic test was conducted on the cross-shaped specimen, and hysteretic behaviour after air-cooling was analysed and compared with the regular seismic response. Results showed that fire exposure not only significantly influences the geometric conditions of the self-centring system, but also completely transforms the original deformation mechanism. Pre-stressed bars were expanded and stretched during the fire so that could not provide self-centring capacity in post-fire conditions, while the energy dissipation of buckling-restrained plates was postponed and weakened because of the slippage at bolted connections. Compared with the regular seismic behaviour, the post-fire hysteretic response appeared sliding and pinching effect rather than the flag-shaped, with a much lower load-carrying capacity and extremely larger residual deformation. To improve the post-fire seismic resistance, the numerical model was established first to reappear the experimental response by the heat transfer analysis and post-fire static analysis, and then extended to simulate the post-fire repair in proposed strategies. According to the repair effect, it is suggested that the high-strength bolts should be replaced with pre-load, and the bars are required at least to provide additional stiffness and re-tensioned if necessary. The findings reveal the considerable influence of fire exposure on the seismic performance of the self-centring system, and highlight the importance of improving residual resistance of seismic-resilient structural systems in post-fire scenarios.
High‐efficiency organic solar cells (OSCs) largely rely on polymer donors. Herein, we report a new building block BNT and a relevant polymer PBNT‐BDD featuring B‐N covalent bond for application in ...OSCs. The BNT unit is synthesized in only 3 steps, leading to the facile synthesis of PBNT‐BDD. When blended with a nonfullerene acceptor Y6‐BO, PBNT‐BDD afforded a power conversion efficiency (PCE) of 16.1 % in an OSC, comparable to the benzo1,2‐b:4,5‐b′dithiophene (BDT)‐based counterpart. The nonradiative recombination energy loss of 0.19 eV was afforded by PBNT‐BDD. PBNT‐BDD also exhibited weak crystallinity and appropriate miscibility with Y6‐BO, benefitting of morphological stability. The singlet–triplet gap (ΔEST) of PBNT‐BDD is as low as 0.15 eV, which is much lower than those of common organic semiconductors (≥0.6 eV). As a result, the triplet state of PBNT‐BDD is higher than the charge transfer (CT) state, which would suppress the recombination via triplet state effectively.
An easily synthesized building block BNT and a relevant polymer PBNT‐BDD featuring B‐N covalent bond were synthesized for application in solar cells. The polymer offered a power conversion efficiency of 16.1 %, a nonradiative recombination energy loss of 0.19 eV, and a singlet‐triplet gap as low as 0.15 eV, demonstrating the promising prospect of B‐N‐containing materials in organic photovoltaics.
This paper is dedicated on the phenomenon of jet quenching and its quantitative description at SNN=5.02TeV. Data from collision events with an isolated leading photon, pTγ>40GeV, associate jets with ...pTjet>30GeV, are plotted as a function of centrality; result is then matched to reference function in p-p events at the same level of energy to infer some model for parton energy loss in PbPb collisions. The main motivation for this paper is to overcome the difficulties of comparing the theoretical models and experimental data, which are linked with a hypothetical equation for energy loss.
The nanofluid, composed of kerosene and tantalum and nickel nanoparticles, is propagating through a porous, elastic surface. The kerosene base fluid is incompressible and electrically conducting. The ...energy equation for this nanofluid is formulated taking into account the viscous dissipation. The mathematical modeling is performed with the help of a similarity transformation. The developed governing equations are numerically solved using the shooting technique and the Matlab software. The physical behavior of different parameters in the model is discussed through tabular and graphical forms. The present results are also compared to past results. The results indicate that the flow propagates faster for higher values of Darcy number and Tantalum nanoparticles and that the magnetic field opposes the fluid motion. Also that the thermal boundary layer decreases in the presence of Tantalum and Nickel nanoparticles.
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•A re-centering energy-dissipation brace with a pendulum (REBP) is proposed.•The REBP can dissipate energy by friction and re-center the structure once unloaded.•Five REBPs with ...different cable tensions are subjected to cyclic loading tests.•The cable pretension has significant effects on the seismic behaviors of the REBP.•A hysteretic model and design formulas for the REBP are proposed and validated.
In this study, a re-centering energy-dissipation brace with a pendulum (REBP) is proposed for high-rise structures. The REBP can consume energy by friction under the action of a horizontal external load, and then re-center the structure by means of cable pretension after removing the load. Through the lever action of the pendulum, the deformation capability of the REBP is significantly amplified with the small deformation of the cables, and can satisfy the inter-story drift requirement for a severe earthquake. The REBP is optimized from a prestressed re-centering energy-dissipation brace (PTSEB) previously proposed by the authors. In particular, the T-shaped pendulum in the PTSEB is replaced by a truss pendulum. The pendulum-wing, vertical bar, and diagonal bars form a truss with high strength. This increases the initial stiffness and energy consumption capability of the REBP, and decreases the weight of the REBP. Two semicircle rollers are set on the top and bottom of the blocker to facilitate its rotation. An hysteretic model and design formulas are proposed for the REBP. Through cyclic testing and a finite element (FE) analysis of REBPs with five different cable pretensions, the cyclic behaviors of the REBP and the influences of cable pretension on the energy consumption, re-centering, stiffness, friction, and cable tension are determined. The results indicate that the REBP has good energy consumption and a good re-centering capability. An increase in cable pretension leads to an increases in the friction between the blocker and pendulum-wing, energy consumption capability, and stiffness.
Abstract
Magnetic reconnection is invoked as one of the primary mechanisms to produce energetic particles. We employ large-scale 3D particle-in-cell simulations of reconnection in magnetically ...dominated (
σ
= 10) pair plasmas to study the energization physics of high-energy particles. We identify an acceleration mechanism that only operates in 3D. For weak guide fields, 3D plasmoids/flux ropes extend along the
z
-direction of the electric current for a length comparable to their cross-sectional radius. Unlike in 2D simulations, where particles are buried in plasmoids, in 3D we find that a fraction of particles with
γ
≳ 3
σ
can escape from plasmoids by moving along
z
, and so they can experience the large-scale fields in the upstream region. These “free” particles preferentially move in
z
along Speiser-like orbits sampling both sides of the layer and are accelerated linearly in time—their Lorentz factor scales as
γ
∝
t
, in contrast to
γ
∝
t
in 2D. The energy gain rate approaches ∼
eE
rec
c
, where
E
rec
≃ 0.1
B
0
is the reconnection electric field and
B
0
the upstream magnetic field. The spectrum of free particles is hard,
dN
free
/
d
γ
∝
γ
−
1.5
, contains ∼20% of the dissipated magnetic energy independently of domain size, and extends up to a cutoff energy scaling linearly with box size. Our results demonstrate that relativistic reconnection in GRB and AGN jets may be a promising mechanism for generating ultra-high-energy cosmic rays.
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