Seismic fragility assessment of load‐bearing soft‐brick unreinforced masonry piers

Unreinforced masonry(URM)made with soft bricks comprises a large percentage of the building stock in devel-oping countries.However,the poor performance of URM piers during earthquakes has led to renewed interest in understanding their behavior under lateral loads.Little experimental data is available on the seismic response,analysis,and design of URMs made of soft bricks.In this study,the micro-modeling technique is used to simulate the in-plane behavior of load-bearing,soft-brick URM piers.The parameters required in the constitutive models are obtained from material tests and used to develop a calibrated numerical model of the URM piers.Piers with various aspect ratios subjected to various axial stresses are numerically modeled to obtain monotonic and cyclic responses,and their critical displacement limit states are identified.Changes in the failure modes of masonry piers with variations in the aspect ratio and axial stress are established.Load-bearing piers exhibit three distinct failure modes:bed sliding,diagonal shear cracking,and flexure,depending on the aspect ratio and axial stress.The seismic fragility of each pier failure type is examined using nonlinear time history analyses.The results show that bed-sliding piers collapse at extremely low PGA levels.Piers failing through diagonal shear cracking also fail at low PGA levels.Flexural piers can resist seismic forces up to a slightly higher PGA level and thus are the last to collapse.The results also indicate that the effect of uncertainty in ground motions is more significant than the effect of variability in the masonry pier capacities.

Study on the Microscopic Network Model of PVA Hydrogel Based on the Tensile Behavior

Hydrogel is an emerging material widely used in the biological field.The tensile properties of hydrogel mainly depend on its polymer network,but due to the complex microstructure of the network,some properties of the hydrogel have yet to be qua nt itatively analyzed.In this article,we built a three-dimensional random fiber net work to characterize the micros tructure of a hydrogel.The fibers were simplified as elastic beams,and the cross-links were regarded as"hinges."Combined with the macroscopic experimental results,the influence of the change of fiber length and the relationship between the polymer content and the cross-link density were studied.The model was verified by the quasi-static tensile test results of real PVA hydrogel materials with different fiber contents.The results show that the model can well match the tensile stress-strain curve and tensile strength of the PVA hydrogels with different fiber contents.The change in micros true ture of the fiber network induces nonlinear behaviors,and although the cross-link number increases with the increase in polymer content,the cross-link density(per unit PVA chain length)of the PVA hydrogel slightly decreases as the content increases.

Intermittent and short duration ultrasound in a simulated porous medium

Ultrasound is an unconventional method used to recovery oil,despite the report on the use of this technique,the focus has always been on the continuous application of ultrasound.But the continuous ultrasound has its own limitation of high cost of production and maintenance of equipment because of high energy generated.In this study,the use of short duration,intermittent ultrasound was investigated,and the result compared with the continuous ultrasound.The effect of viscosity and intensity on both intermittent and continuous ultrasound was also investigated.A 2D micro-model placed inside an ultrasonic bath under an ultrasound radiation was used,a stereo microscope with the camera mounted at the top of the micro-model recorded the displacement process.The snapshot of each time interval was used to give the estimate in percentage(%)of the residual oil left in the micro-model.The results show that,short duration and intermittent ultrasound can recover more oil compared with the application using continuous ultrasound and longer duration.Therefore,the use of intermittent ultrasound as a green and cost-effective technique is herein proposed.