Building frequency fluctuations from continuous monitoring of ambient vibrations and their relationship to temperature variations

Building frequencies (fundamental and higher modes) are a critical parameter especially in the field of structural health monitoring mainly based on the stability of the structural dynamic parameters of individual building (frequencies, damping and modes shape). One of the most used methods to find out these parameters is based on the use on ambient vibration analysis. In this work, we study the fluctuations over a month period of the fundamental frequencies (transverse and longitudinal) of a 3.5-story RC-building made of 2 identical units connected by a structural joint. Time independent building frequencies is a strong assumption; as illustrated by our experiment showing that over an observation period of a month, building frequencies fluctuate of about 3.5 %. A clear correlation is found between the building frequency fluctuations and temperature variations, with a phase-shift interpreted as the characteristic time of heat diffusion within the walls. This allows: (1) determining the thermal diffusivity of the structure, (2) inferring its relative stiffness variations, and (3) showing that its Young modulus varies linearly with temperature.     

Impact of lateral force-resisting system and design/construction practices on seismic performance and cost of tall buildings in Dubai, UAE

The local design and construction practices in the United Arab Emirates(UAE),together with Dubai’s unique rate of development,warrant special attention to the selection of Lateral Force-Resisting Systems(LFRS).This research proposes four different feasible solutions for the selection of the LFRS for tall buildings and quantifies the impact of these selections on seismic performance and cost.The systems considered are: Steel Special Moment-Resisting Frame(SMRF),Concrete SMRF,Steel Dual System(SMRF with Special Steel Plates Shear Wall,SPSW),and Concrete Dual System(SMRF with Special Concrete Shear Wall,SCSW).The LFRS selection is driven by seismic setup as well as the adopted design and construction practices in Dubai.It is found that the concrete design alternatives are consistently less expensive than their steel counterparts.The steel dual system is expected to have the least damage based on its relatively lesser interstory drifts.However,this preferred performance comes at a higher initial construction cost.Conversely,the steel SMRF system is expected to have the most damage and associated repair cost due to its excessive flexibility.The two concrete alternatives are expected to have relatively moderate damage and repair costs in addition to their lesser initial construction cost.     

Geomorphic response to an active transpressive regime: a case study along the Chaman strike‐slip fault,western Pakistan

The Chaman left‐lateral strike‐slip fault bounds the rigid Indian plate boundary at the western end of the Himalayan‐Tibetan orogen and is marked by contrasting topographic relief. Deformed landforms along the fault provide an excellent record for understanding this actively evolving intra‐continental strike‐slip fault. The geomorphic response of an active transpessional stretch of the Chaman fault was studied using digital elevation model (DEM) data integrated with Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Visible and Near Infrared/Short Wave Infrared (VNIR/SWIR) and images from GeoEye‐1. Geologic and geomorphic mapping helped in reconstructing the Late Quaternary landscape history of this transpessional strand of the Chaman strike‐slip fault and the associated Spinatizha thrust fault in western Pakistan. Topographic analysis of a part of the transpression (the thrust bounded Roghani ridge) revealed northward growth of the Spinatizha fault with the presence of three water gaps and two corresponding wind gaps. Geomorphic indices including stream length‐gradient index, mountain front sinuosity, valley floor width to valley height ratios, and entrenchment of recent alluvial fan deposits were used to define the lateral growth and direction of propagation of the Spinatizha fault. Left‐lateral displacement along Chaman fault and uplift along the Spinatizha fault was defined using topographic analysis of the Roghani ridge and geomorphic mapping of an impressive alluvial fan, the Bostankaul fan. The landforms and structures record slip partitioning along the Indian plate boundary, and account for the convergence resulting from the difference in the Chaman fault azimuth and orientation of the velocity vector of the Indian plate. Copyright © 2012 John Wiley & Sons, Ltd.     

SWAT-based hydrological modelling of tropical land-use scenarios

Abstract

The Hulu Langat basin, a strategic watershed in Malaysia, has in recent decades been exposed to extensive changes in land-use and consequently hydrological conditions. In this work, the impact of Land Use and Cover Change (LUCC) on hydrological conditions (water discharge and sediment load) of the basin were investigated using the Soil and Water Assessment Tool (SWAT). Four land-use scenarios were defined for land-use change impact analysis, i.e. past, present (baseline), future and water conservation planning. The land-use maps, dated 1984, 1990, 1997 and 2002, were defined as the past scenarios for LUCC impact analysis. The present scenario was defined based on the 2006 land-use map. The 2020 land-use map was simulated using a cellular automata-Markov model and defined as the future scenario. Water conservation scenarios were produced based on guidelines published by Malaysia’s Department of Town and Country Planning and Department of Environment. Model calibration and uncertainty analysis was performed using the Sequential Uncertainty Fitting (SUFI-2) algorithm. The model robustness for water discharge simulation for the period 1997–2008 was good. However, due to uncertainties, mainly resulting from intense urban development in the basin, its robustness for sediment load simulation was only acceptable for the calibration period 1997–2004. The optimized model was run using different land-use maps over the periods 1997–2008 and 1997–2004 for water discharge and sediment load estimation, respectively. In comparison to the baseline scenario, SWAT simulation using the past and conservative scenarios showed significant reduction in monthly direct runoff and monthly sediment load, while SWAT simulation based on the future scenario showed significant increase in monthly direct runoff, monthly sediment load and groundwater recharge.

Editor D. Koutsoyiannis; Associate editor C. Perrin     

Monitoring of wastewater percolation in unsaturated sandy soil using geoelectrical measurements at Gabal el Asfar farm,northeast Cairo,Egypt

The use of wastewater for irrigation in sandy soil increases the pollution risk of the soil and may infiltrate to the shallow groundwater aquifer. In such environment, some important parameters need to be obtained for monitoring the wastewater in the unsaturated zone over the aquifer. These parameters include clay content, heterogeneities of the upper soils, depth to the aquifer and the variations of groundwater quality. In the present work, the efficiency of DC resistivity method in forms of 1-D and 2-D measurements was studied for wastewater monitoring in the Gabal el Asfar farm, northeast of Cairo, Egypt. Forty-one Schlumberger soundings (VES) were performed then followed by three pole-dipole 2-D profiles along some considered regions within the area. The resistivity measurements were integrated with the boreholes, hydrogeological and hydrochemical (surface and groundwater samples) information to draw a clear picture for the subsurface conditions. The obtained results were presented as cross sections and 3-D visualization to trace the clay intercalations within the unsaturated zone. In addition, a vulnerability map was created using the obtained results from 1-D Schlumberger survey and confirmed with the 2-D resistivity profiling. The obtained results have shown that the 2-D resistivity imaging technique is a powerful tool for mapping the small-scale variability within the unsaturated zone and the wastewater infiltration. However, limitations of resistivity techniques were observed in the area with limited resistivity contrast such as thin clay layers with brackish water background. Under that condition, the measured pattern of resistivity distributions depends on the applied electrode array, electrode spacing and using the available geological information during the inversion process.     

Scaling property of regional floods in New South Wales Australia

Regional flood frequency analysis (RFFA) is often used in hydrology to estimate flood quantiles when there is a limitation of at-site recorded flood data. One of the commonly used RFFA methods is the index flood method, which is based on the assumptions that a region satisfies criterion of simple scaling and it can be treated homogeneous. Another RFFA method is quantile regression technique where prediction equations are developed for flood quantiles of interest as function of catchment characteristics. In this paper, the scaling property of regional floods in New South Wales (NSW) State in Australia is investigated. The results indicate that the annual maximum floods in NSW satisfy a simple scaling assumption. The application of a heterogeneity test, however, reveals that NSW flood data set does not satisfy the criteria for a homogeneous region. Finally, a set of prediction equations are developed for NSW using quantile regression technique; an independent test shows that these equations can provide reasonably accurate design flood estimates with a median relative error of about 27%.     

Characterization of phosphoric acid- and lime-stabilized tropical lateritic clay

The effect of calcium-based stabilizers such as lime on the geotechnical properties of tropical soils has been reported by many researchers. However, the amount of literature available on the micro-structural, molecular, and leaching characteristics of lime and in particular phosphoric acid-stabilized lateritic clays has been limited. This research was carried out in an attempt to identify the time-dependent soil-chemical reactions. In addition, the possible mechanisms that contributed to the stabilization process were discussed in the light of various spectroscopic and microscopic techniques such as X-ray diffractometry (XRD), energy-dispersive X-ray spectrometry (EDAX), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance spectroscopy (NMR) etc. Based on the results it was found that in lime-treated samples, the coating action of free iron oxides on clay particles imposed inhibitive effects on the dissolution of clay alumina. On the other hand, in phosphoric acid-stabilized soil, due to the increase in solubility of metal oxides and also the subsequent release of clay alumina the formation of cementitious compounds were more feasible. From engineering point of view, the phosphoric acid-stabilized lateritic soil showed the highest degree of improvement with an approximately threefold strength increase in comparison with the natural soil over an 8-month curing period.     

Structural control of El Sela granites and associated uranium deposits, Southern Eastern Desert, Egypt

The El Sela area is a part of the basement complex of the Eastern Desert of Egypt and the Pan-African Shield. The area comprises outcrops of dismembered ophiolites thrust over arc volcano-sedimentary sequence and intruded by different syn- to post-tectonic granitoids. Structural analysis of the area enabled the separation and definition of four structural episodes: (E1) folding–thrusting episode associated with the cratonization of the arc/inter-arc rock association and the intrusion of the syntectonic (Older) granites. (E2) Upright folding episode associated with the compression and shortening to the ENE–WSW direction which is different from the NNW–SSE shortening direction during E1; at the end of E2, late tectonic granites were intruded. (E3) Post-tectonic granitic intrusion episode: two mica granite and granitic dikes were intruded during this episode. (E4) Fracturing, faulting, and post-granitic dike extrusion episodes caused different faults that took place after cratonization until the present. There are three generations of folds during ductile deformation (E1 and E2). The F2 folds are nearly coaxial (along ENE–WSW trend) with the F1 folds. The F3 folding is displayed by folds generally trending NNW–SSE. Therefore, the ENE–WSW and NNW–SSE trends can considered as preexisting discontinuities and mechanical anisotropy of the crust in the following structure episodes. Brittle deformation (E3 and E4) reveals the importance of those trends which control the multi-injections and many alteration features in the study area. During reactivation, a simple shear parallel to the inherited ductile fabrics was responsible for the development of mineralized structures along the ENE–WSW and NNW–SSE trends. So they can be considered as paleochannel trends for deep-seated structures and can act as a good trap for uranium and/or other mineral resources. Most of the uranium anomalies are delineated along ENE–WSW and NNW–SSE shear zones where quartz-bearing veins bounded the lamprophyre dike and microgranites and dissected them in relation to the successive fracturation and brecciation corresponding to the repeated rejuvenation of the structures. Therefore, the structural controls of the uranium mineralizations in the El Sela area appear to be related to the interaction between inherited ductile fabrics and overprinting brittle structures.     

Hydrogeophysical study for additional groundwater supplies in El Heiz Area, Southern part of El Bahariya Oasis, Western Desert, Egypt

El Bahariya Oasis is a part of the great groundwater reservoir of the Western Desert of Egypt. The different stratigraphic units, the water-bearing zones, aquifer potentiality conditions, and the favorable locations for drilling new wells were evaluated by carrying out 24 Schlumberger vertical electrical soundings (VESs), along with the data of some wells drilled in the near vicinity of the measuring sites. The results of the interpreted field data revealed the presence of ten distinctive subsurface geoelectric layers; a thin surface, dry loose sand and gravel, sandy clay and shale interclations, saturated coarse sand layer, shale and clay, and saturated fine sandstone and saturated coarse sandstone. The aquifer is a multilayer aquifer with different thicknesses represented by the fourth, sixth, eighth, and tenth geoelectric layers. Results also revealed that the thicknesses of the water-bearing horizons increase towards the east direction, consequently the aquifer potentiality increases. Therefore, the best production well locations are in that direction. Depth to water starts from 40 m at VES no. 14 and increases gradually toward the east to reach 66 m at VES no. 5. Hydrogeochemical analysis of two groundwater samples taken from Ein El Ezza and well no. 2 showed that groundwater in the study area is suitable for agricultural purposes but not for human consumption due to the high iron content. Recommendations concerning site selection for drilling new productive groundwater wells are given.