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Computer Aided Civil and Infrastructure Engineering

With the rapid development of flexible wearable electronics, a piezoresistive sensor with low detection limit and wide strain sensing range turns out to be a great challenge for its application in this field. Here, a cracked cellulose nanofibril/silver nanowire (CA) layer-coated polyurethane (PU) sponge was acquired through a simple dip-coating process followed by precompression treatment. The electrical conductivity and mechanical property of the conductive CA@PU sponge could be effectively tuned through changing the dip-coating number. As a piezoresistive sensor, the sponge exhibited the capability of detecting both small and large motions over a wide compression strain range of 0–80%. Based on the “crack effect”, the sensor possessed a detection limit as low as 0.2% and the gauge factor [GF, GF = (ΔR/R0)/e, where ΔR, R0, and e represent the instantaneous resistance change, original resistance, and strain applied, respectively] was as high as 26.07 in the strain range of 0–0.6%. Moreover, the “contact e...

Ultrasensitive and Highly Compressible Piezoresistive Sensor Based on Polyurethane Sponge Coated with a Cracked Cellulose Nanofibril/Silver Nanowire Layer.

On social suffering

For thirty years Ben Kiernan has been deeply involved in the study of genocide and crimes against humanity. He has played a key role in unearthing confidential documentation of the atrocities committed by the Khmer Rouge. His writings have transformed our understanding not only of twentieth-century Cambodia but also of the historical phenomenon of genocide. This new book--the first global history of genocide and extermination from ancient times--is among his most important achievements. Kiernan examines outbreaks of mass violence from the classical era to the present, focusing on worldwide colonial exterminations and twentieth-century case studies including the Armenian genocide, the Nazi Holocaust, Stalin's mass murders, and the Cambodian and Rwandan genocides. He identifies connections, patterns, and features that in nearly every case gave early warning of the catastrophe to come: racism or religious prejudice, territorial expansionism, and cults of antiquity and agrarianism. The ideologies that have motivated perpetrators of mass killings in the past persist in our new century, says Kiernan. He urges that we heed the rich historical evidence with its telltale signs for predicting and preventing future genocides.

Ben Kiernan, “Blood and Soil: A World History of Genocide and Extermination from Sparta to Darfur”

Scour effects on the response of laterally loaded piles considering stress history of sand

Scour is a process of soil erosion, which can occur around the foundations of bridges or offshore structures through the action of flowing water; it can, therefore, reduce the capacity of the foundations and sometimes lead to the failure of structures. During an analysis of scour effects on laterally loaded piles, scour hole geometry is often ignored. Instead, scour effects are considered by simply removing the whole soil layer to the scour depth. However, a scour hole has not only depth, but also width and a slope. At present, the widely used p-y method for analyzing laterally loaded piles cannot consider three-dimensional scour hole dimensions. For this reason, a simplified method was developed herein for the analysis of laterally loaded piles in sand under a scour condition. The p-y curves in this method were based on a wedge type of failure. The effects of the scour hole dimensions on the response of laterally loaded piles in sand were evaluated using this simplified method. The computed resul...

Analysis of Laterally Loaded Piles in Sand Considering Scour Hole Dimensions

Analysis of laterally loaded piles in soft clay considering scour-hole dimensions

This paper presents a novel large-area strain sensing technology for monitoring fatigue cracks in steel bridges. The technology is based on a soft elastomeric capacitor (SEC), which serves as a flexible and large-area strain gauge. Previous experiments have verified the SEC's capability to monitor low-cycle fatigue cracks experiencing large plastic deformation and large crack opening. Here an investigation into further extending the SEC's capability for long-term monitoring of fatigue cracks in steel bridges subject to traffic loading, which experience smaller crack openings. It is proposed that the peak-to-peak amplitude (pk–pk amplitude) of the sensor's capacitance measurement as the indicator of crack growth to achieve robustness against capacitance drift during long-term monitoring. Then a robust crack monitoring algorithm is developed to reliably identify the level of pk–pk amplitudes through frequency analysis, from which a crack growth index (CGI) is obtained for monitoring fatigue crack growth under various loading conditions. To generate representative fatigue cracks in a laboratory, loading protocols were designed based on constant ranges of stress intensity to limit plastic deformations at the crack tip. A series of small-scale fatigue tests were performed under the designed loading protocols with various stress intensity ratios. Test results under the realistic fatigue crack conditions demonstrated the proposed crack monitoring algorithm can generate robust CGIs which are positively correlated with crack lengths and independent from loading conditions.

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1154&context=ccee_pubs

A large-area strain sensing technology for monitoring fatigue cracks in steel bridges

Scour can remove soils around bridge foundations and result in reduced bridge capacity. Because most bridge failures have been associated with scour events, it is important to evaluate scour effects on bridge safety. In practice, an evaluation of the performance of bridge piles under scoured conditions is usually achieved by simply removing soils from around the piles while possible changes in stress history of the remaining soils are ignored. In reality, the remaining soils undergo an unloading process when scour removes soils from above the remaining soils. This process increases the overconsolidation ratios of the remaining soils. In this study, the stress history of soft clay was considered in the analysis of laterally loaded piles using the p-y method. To account for the stress history effect, the conventional p-y curves for the soft clay were modified to evaluate the undrained responses of the laterally loaded piles at different scour depths. A case study was used to compare the computed res...

Caroline Bennett

Papers

Scour effects on the response of laterally loaded piles considering stress history of sand

Analysis of Laterally Loaded Piles in Sand Considering Scour Hole Dimensions

Analysis of laterally loaded piles in soft clay considering scour-hole dimensions

A large-area strain sensing technology for monitoring fatigue cracks in steel bridges

Behavior of Laterally Loaded Piles under Scour Conditions Considering the Stress History of Undrained Soft Clay