Stiffness identification of two- and three-dimensional frames

Four widely used structural system identification methods are presented. Based on Bayesian estimation theory, two new formulae and their derivations are shown. Time domain responses of two frames when subjected to the ground motion of the El Centro earthquake are computed then transformed to the frequency domain. Frequencies and mode shapes of frames are extracted from Fourier spectra. Using these frequencies and mode shapes, a parametric study is conducted, and the system identification methods are compared and discussed. The importance of a prior analytical model on the rate of convergence of the revised parameters is investigated. Recommendations are given regarding the feasibility of each method for more accurate estimation. A model suitable for parameter identification of three-dimensional frames is presented. This model, with different identification methods, is used to estimate the parameters of a two-storey frame.     

An elastoplastic description of frictional destructuration in natural clays and shales

The existence of structuration in natural clays and shales is believed to change their stiffness, yielding, dilatancy and strength characteristics. These constitutive features are widely known to ultimately reunite with those of the reconstituted parent soil upon large straining. However, some experimental results show that such reunification may not occur in isotropic/one-dimensional compression, especially with regard to the critical state friction angle. This peculiar phenomenon has been barely addressed in constitutive models for natural geomaterials. Hence, the present study aims at introducing a structure-dependent critical state friction angle within the subloading yield framework. A new internal variable is introduced in the model of Nakai et al. (Soils Found 51(6):1149–1168, 2011) to capture subtle irreversible degradation of the structured critical state line which also serves as the threshold between contractive and dilatant volume changes. Additionally, a new evolution rule for the proposed destructuration factor is developed by considering important microstructural information revealed by discrete element method simulations. The proposed new modifications not only enhance the model capabilities in predicting bonding effects, but also enrich the classical stress-dilatancy equation by rendering it a function of void ratio, mean stress and the microstructural state. Model simulations of laboratory experimental tests on the Colorado shale as well as Bacinetto clay are presented in order to illustrate the improved predictive capabilities of the new model.     

Late glacial and early Holocene hydroclimate variability in northwest Iran (Talesh Mountains) inferred from chironomid and pollen analysis

We reconstructed the paleohydrologic and climatic history of the Lake Neor region, NW Iran, from the end of the late glacial to the middle Holocene (15,500–7500 cal yr BP). Subfossil chironomid and pollen assemblages in a sediment core from a peatland located south of Lake Neor enabled identification of four main hydrologic phases. The period 15,500–12,700 cal yr BP was characterized by a relatively dry climate with an open landscape, suggested by the abundance of Irano-Turanian steppe plants (e.g. Amaranthaceae, Artemisia and Cousinia). Dominance of several shallow-water and semi-terrestrial chironomid taxa (e.g. Pseudosmittia, Smittia/Parasmittia and Paraphaenocladius/Parametriocnemus) during this period is indicative of lower water tables in the wetland. Between 12,700 and 11,300 cal yr BP, chironomid taxa indicate higher wetland water tables, as suggested by the presence of Zavrelia, Chironomus anthracinus/plumosus-type and Micropsectra, which are inhabitants of open-water, lacustrine areas. The open-steppe vegetation remained dominant in the watershed during this time. Increasing wetland moisture could be explained by: (1) cool summers that reduced the evaporation rate; and/or (2) a decrease in duration of the summer dry season. The period 11,300–8700 cal yr BP was characterized by lower wetland moisture, contemporaneous with a delay in the expansion of deciduous forest, suggesting persistent dry climate conditions throughout the beginning of the Holocene, which may have been related to the intensified seasonality of precipitation. Around 8700 cal yr BP, higher wetland water levels, inferred from chironomids, occurred simultaneously with the onset of regional deciduous forest expansion, probably caused by a shortening of the summer dry period. We concluded that chironomids are appropriate paleoecological proxies to investigate global and local hydrologic variability in the Middle East.     

Permian Calcareous algae from the Khachik Formation at the Ali Bashi Mountains,NW of Iran

Micropaleontological investigations on Permian successions in the NW of Iran based on algae led to the determination of taxa belonging to some families such as Ungdarellaceae (Ungdarella uralica), Gymnocodiaceae (Gymnocodium bellerophontis and Permocalculus sp.), Dasycladales (Mizzia cf. M. yabei), and some microproblematics (Vermiporella nipponica and Pseudovermiporella sodalica). These investigations are mainly focused on the Khachik Formation at the Ali Bashi Mountains. According to the algal community, a lagoon environment is offered for the studied successions.     

Design and full‐scale experimental evaluation of a seismically endurant steel buckling‐restrained brace system

This paper presents the results of 12 full‐scale tests on buckling‐restrained brace (BRB) specimens. A simple‐to‐fabricate all‐steel encasing joined by high‐strength bolts was used as the buckling‐restrainer mechanism. Steel BRBs offer significant energy dissipation capability through nondeteriorating inelastic response of an internal ductile core. However, seismic performance of BRBs is characterized by interaction between several factors. In this experimental study, the effects of core‐restrainer interfacial condition, gap size, loading history, bolt spacing, and restraining capacity are evaluated. A simple hinge detail is introduced at the brace ends to reduce the flexural demand on the framing components. Tested specimens with bare steel contact surfaces exhibited satisfactory performance under the American Institute of Steel Construction qualification test protocol. The BRBs with friction‐control self‐adhesive polymer liners and a graphite‐based dry lubricant displayed larger cumulative inelastic ductility under large‐amplitude cyclic loading, exceeding current code minimum requirements. The BRB system is also examined under repeated fast‐rate seismic deformation history. This system showed significant ductility capacity and remarkable endurance under dynamic loading. Furthermore, performance is qualified under long‐duration loading history from subduction zone's megathrust type of earthquake. Predictable and stable performance of the proposed hinge detail was confirmed by the test results. Internally imposed normal thrust on the restrainer is measured using series of instrumented bolts. Weak‐ and strong‐axis buckling responses of the core are examined. Higher post‐yield stiffness was achieved when the latter governed, which could be advantageous to the overall seismic response of braced frames incorporating BRBs.     

A review of flood damage analysis for a building structure and contents

Natural Hazards - As a natural hazard, flood can cause a significant damage to buildings. Buildings are one of the important components of an economy which are providing the necessary space for...     

Dynamic response of double beam rested on stochastic foundation under harmonic moving load

This paper deals with the dynamic response of infinite double Euler–Bernoulli beam supported by elastic foundation with stochastic stiffness subjected to an oscillating moving load, which is the first research in relevant literature review. In this matter, equations of motion for double beam are formulated in a moving frame of reference. Moreover, by employing the first order perturbation theory and calculating contour integration, the response of double beam is obtained analytically and validated by a stochastic finite element model. Sensitivity analyses on the various parameters of closed form solution such as velocity, load frequency, coefficient of variation of soil foundation and rail and slab bending stiffness show the significant effect of load frequency on the dynamic response of the doubled beam. From practical point of view, the obtained results of the present study can be utilized efficiently in analysis and design of slab track systems. Copyright © 2013 John Wiley & Sons, Ltd.     

Rocking vibration of a rigid circular disc in a transversely isotropic full‐space

In this paper, forced rocking vibration of a rigid circular disc placed in a transversely isotropic full‐space, where the axis of material symmetry of the full‐space is normal to the surface of the plate, is analytically investigated. Because of using the Fourier series and Hankel integral transforms, the mixed boundary‐value problem is transformed into two separate pairs of integral equations called dual integral equations. The dual integral equations involved in this paper are reduced to Fredholm integral equations of the second kind. With the aid of contour integration, the governing integral equation is numerically evaluated in the general dynamic case. The reduced static case of the dual integral equations is solved analytically and the vertical displacement, the contact pressure and the static impedance/compliance function are explicitly determined, and it is shown that the pressure in between the plate and the full‐space and the compliance function reduced for isotropic half‐space are identical to the previously published solutions. The dynamic contact pressure in between the disc and the space and also the related impedance function are numerically evaluated in general dynamic case and illustrated. It is shown that the singularity exists in the contact pressure at the edge of the disc is the same as the static case. To show the effect of material anisotropy, the numerical evaluations are given for some different transversely isotropic materials and compared. Copyright © 2010 John Wiley & Sons, Ltd.