Seismic performance evaluation of steel arch bridges against major earthquakes. Part 2: simplified verification procedure

The performance‐based philosophy has been accepted as a more reasonable design concept for engineering structures. For this purpose, capacity evaluation and demand prediction procedures for civil engineering structures under earthquake excitations are of great significance. This work presents a displacement‐based seismic performance verification procedure including capacity and seismic demand predictions for steel arch bridges and investigates its applicability. Pushover analyses is employed as a basis in this method to investigate the structure's behaviors. A failure criterion for steel members accounting for the effect of local buckling is involved and an equivalent single‐degree‐of‐freedom (ESDOF) system with a simplified bilinear hysteretic model formulated using pushover analyses results is introduced to estimate the displacement capacity and maximum demand of steel arch bridges under major earthquakes. To check the accuracy of the proposed method, seismic capacities and demands from multi‐degree‐of‐freedom (MDOF) time‐history analyses with Level‐II design earthquake record inputs modeling major earthquakes are used as benchmarks for comparison. By a case study, it is clarified that the proposed prediction procedure can give accurate estimations of displacement capacities and demands of the steel arch bridge in the transverse direction, while insufficient for the longitudinal direction, which confirms the conclusion drawn in other structure types about the applicability of pushover analyses. Copyright © 2004 John Wiley & Sons, Ltd.     

Cyclic analysis and capacity prediction of concrete‐filled steel box columns

Concrete‐filled steel columns have been widely used in civil and architectural constructions throughout the world in recent years. This study is concerned with the cyclic elastoplastic analysis and capacity prediction of concrete‐filled steel columns having thick‐ and thin‐walled stiffened box‐shaped sections. An analytical procedure for determining the ultimate state of the concrete‐filled steel column is proposed based on the fiber analysis technique. Strength and ductility predictions are made by means of a new failure criterion. This is proposed based on the average failure strain of concrete and steel at critical regions. A recently developed monotonic stress–strain relation for confined concrete is modified so that it can be used in the analysis of thin‐ or thick‐walled section columns with stiffeners. A simple cyclic rule is introduced into this model in order to be used in cyclic analysis. Material non‐linearity of steel is represented by the modified two surface model developed at Nagoya University. The predictions are then compared with the existing experimental results and found to exhibit satisfactory agreement. Both small‐ and large‐scaled columns are considered in the comparisons. Copyright © 2001 John Wiley & Sons, Ltd.     

Developing high‐performance aluminum alloy buckling‐restrained braces based on series of low‐cycle fatigue tests

In order to enhance the durability of high‐performance buckling‐restrained braces (BRBs) used in bridge engineering, which are expected to withstand severe earthquakes three times without being replaced, aluminum alloys were employed to manufacture BRBs. A series of low‐cycle fatigue tests, including 18 specimens, were conducted to address the low‐cycle fatigue strength of the aluminum alloy BRB. Test results of all specimens show that stable hysteretic curves were obtained without overall buckling occurrence. Failure mode of the welded aluminum alloy BRB is obviously affected by the ribs' welding under the variable or constant strain amplitude condition. Therefore, another type of aluminum alloy BRB, the bolt‐assembled BRB with or without spot‐welded stoppers, is proposed and tested. Results showed that the low‐cycle fatigue performance of bolt‐assembled BRBs with stoppers improved four to five times compared with welded BRBs. However, the stoppers' spot welding has an adverse effect on the failure mode because the crack, which induced the specimen's failure, initiated from the spot weld toes of the stoppers. Both bolt‐assembled BRBs with and without stoppers can meet the cumulative inelastic deformation requirement proposed for high‐performance BRBs under the constant strain amplitude, not larger than 2%. In addition, under the variable strain amplitude condition, only the bolt‐assembled BRB without stoppers has an excellent cumulative inelastic deformation capacity and sustains two cycles of 2.5% strain amplitude. Finally, recommended Manson–Coffin equations and preliminary cumulative damage formulae for welded and bolt‐assembled BRBs are given as the references of the strain‐based damage evaluation. Copyright © 2011 John Wiley & Sons, Ltd.     

Formation of intermediate-mass black holes as primordial black holes in the inflationary cosmology with running spectral index

Formation of primordial black holes (PBHs) on astrophysical mass scales is a natural consequence of inflationary cosmology, if the primordial perturbation spectrum has a large and negative running of the spectral index as observationally suggested today because double inflation is required to explain it and fluctuations on some astrophysical scales are enhanced in the field-oscillation regime in between. It is argued that PBHs thus produced can serve as intermediate-mass black holes (IMBHs), which act as the observed ultraluminous X-ray sources (ULXs) by choosing appropriate values of the model parameters in their natural ranges. Our scenario can be observationally tested in near future because the mass of PBHs is uniquely determined once we specify the values of the amplitude of the curvature perturbation, spectral index and its running on large scales.     

Multiple generations of forearc mafic–ultramafic rocks in the Timor–Tanimbar ophiolite, eastern Indonesia

We investigated mafic–ultramafic rocks distributed in the Timor–Tanimbar region as a possible modern analogue for the Mediterranean-type ophiolites in the Tethyan system. The geological occurrence suggests that the buoyant subduction of Australian continent uplifted the fragments of newly formed mantle–crust section, which extends to the neighboring preemplaced forearc marginal basins. However, we recognized a large variety of igneous features, which is consistent with the lack of complete succession and the presence of abundant crosscutting structures. All peridotite masses in Timor (Mutis, Atapupu and Dili) are mostly fertile (lherzolitic) in compositions. In addition, we found depleted harzburgite, highly refractory dunite and olivine websterite to occur as minor constituents, which display compositional contrast to those of the lherzolites. Structurally overlying Ocussi volcanics resemble island–arc tholeiite in terms of trace element characteristics, apparently inconsistent with genetic relationship with Timor lherzolite masses. In eastern small islands (Moa and Dai), all types of ophiolitic rocks display varying degrees of island–arc affinities. Cumulate origin of wehrlite and gabbroic rocks in Dai is marked by early crystallization of clinopyroxene and common occurrence of high-calcic plagioclase. Dikes cutting the gabbro sequence have weak island–arc signatures relative to those of Ocussi volcanics. Mildly depleted lherzolite–harzburgite in Moa was intruded by high-Mg andesitic magma, which crystallized hornblende gabbro containing high-Mg orthopyroxene. These petrological and geochemical variations can be best explained by the combination of (1) a temporal change of igneous activity possibly associated with development of forearc basin and (2) the emplacement of spatially different forearc regions in each locality. Unusual occurrence of fertile lherzolite in the forearc setting, generation of high-Mg andesite magmatism, inverted metamorphic grade recorded from associated metamorphic rocks, and formation of marginal basins may be linked to the injection of high-temperature asthenospheric materials into the mantle wedge.     

Simulating the carbon balance of a temperate larch forest under various meteorological conditions

Background  

Changes in the timing of phenological events may cause the annual carbon budget of deciduous forests to change. Therefore, one should take such events into account when evaluating the effects of global warming on deciduous forests. In this article, we report on the results of numerical experiments done with a model that includes a phenological module simulating the timing of bud burst and other phenological events and estimating maximum leaf area index.