Strongly localized states and giant optical absorption induced by multiple flat-bands in AA-stacked multilayer armchair graphenenanoribbons

We propose an AA-stacked multilayer graphene nanoribbon with two symmetrical armchair edges as a multiple flat-band (FB) material. Using the tight-binding Hamiltonian and Green’s function method, we find that the FBs are complete and merged into many dispersive bands. The FBs cause multiple strongly localized states (SLSs) at the sites of the odd lines in every sublayer and a giant optical absorption (GOA) at energy point 2t, where t is the electronic intralayer hopping energy between two nearest-neighbor sites. By driving an electric field perpendicular to the ribbon plane, the bandgaps of the FBs are tunable. Accordingly, the positions of the SLSs in the energy regime can be shifted. However, the position of the GOA is robust against such field, but its strength exhibits a collapse behavior with a fixed quantization step. On the contrary, by driving an electric field parallel to the ribbon plane, the completeness of FBs is destroyed. Resultantly, the SLSs and GOA are suppressed and even quenched. Therefore, such ribbons may be excellent candidates for the design of the controllable information-transmission and optical-electric nanodevices.

Study on Collapse Resistance of RC Frame under the Corner Column Removal Scenario

The progressive collapse of buildings induces a variety of catastrophic consequences, such as casualties and property loss over the past few decades. The corner column is more prone to abnormal load events compared to the inner column and outer column; thus, it is easier to trigger progressive collapse. By considering the effects of floor slabs and adjacent bays on progressive collapse behavior, the pseudo-static loading method was used to study the progressive collapse test of a 1/3 scaled, one story, 2 × 2-bay cast-in-place reinforced concrete frame substructure under the removal condition of a corner column. The test results show that the flexural deformation principally concentrates upon the components of a directly affected part (DAP), and compressive arch actions are observed in members of the indirectly affected part (IAP). Moreover, the slab adjacent to the removed column and periphery elements contributes great resistance to a progressive collapse.

Alternative Load Path Analysis for Assessing the Geometric Agreement of a Cable-Stayed Bridge with Steel Truss Girders

The geometric agreement, commonly hailed as load-transferring paths withinbridge structures, is significantly crucial to the bridge structural mechanicalperformance, such as capacity, deformation, and collapse behavior. This paperpresents a methodology dependent on alternative load paths to investigate thecollapse behavior of a double-pylon cable-stayed bridge with steel truss girderssubjected to excess vehicle loading. The cable-stayed bridge with steel trussgirders is simplified using a series-parallel load-bearing system. This researchmanifests that the enforced vehicle loading can be transferred to alternativepaths of cable-stayed bridges in different load-structure scenarios. A 3-Dfinite element model is established utilizing computer software ANSYS to explorethe collapse path of cable-stayed bridge with steel truss girders, taking intoaccount chord failure, loss of cables together with corrosion in steel trussgirders. The results show that chord failures in the mid-portion of the mainspan result in brittle damage in truss girders or even sudden bridge collapse. Further,the loss of long cables leads to ductile damage with significant displacement.The corrosion in steel truss girders has a highly slight influence on the collapsebehavior of cable-stayed bridge. The proposed methodology can be reliably usedto assess and determine the vulnerability of cable-stayed bridge with steeltruss girders during their service lifetime, thus preventing structural collapsesin this type of bridge.

PROGRESSIVE COLLAPSE RESISTANCE OF STEEL FRAMED BUILDINGS UNDER EXTREME EVENTS

This paper presents experimental and theoretical investigations on progressive collapse behavior of steel framed structures subjected to an extreme load such as fire, blast and impact. A new capacity-based index is proposed to quantify robustness of structures. An energy-based theoretical model is also proposed to quantify the effect of concrete slabs on collapse resistance of structures. The experimental results show that the dynamic amplification factors of frames subject to impact or blast are much less than the conventional value of 2.0. The collapse process of frames in fire can be either static or dynamic depending on the restraint conditions and load levels. It is necessary to account for the failure time and residual strength of blast-exposed columns for assessing the collapse resistance of structures subject to explosion. Two collapse modes of steel frames under blast or impact are found: connection-induced collapse mode and column-induced collapse mode. In case of fire, a frame may collapse due to either column buckling or pulling-in effect of beams. The energy dissipation from elongation of slab reinforcement and additional resultant moment greatly contribute to the collapse resistance of structures.