Plastic Hinge Length of RC Columns under the Combined Effect of Near-Fault Vertical and Horizontal Ground Motions

Plastic hinges are an extension of the ductile design concept used in building seismically resistant structures. The formation of a plastic hinge in an RC column in regions that experience inelastic actions depends on the characteristics of the earthquakes as well as the column details. Recordings from recent earthquakes have proved that in the near-fault region of large earthquakes, the vertical component of the near-fault ground motion has exceeded the horizontal, and damage to the structures has been predominantly by these motions. Therefore, this paper focuses on near-fault ground motions that have been recorded within rather 20 km of the causative fault and 936 inelastic time-history analyses have been performed to predict the nonlinear behavior of RC columns subjected to combined effect of near-fault vertical and horizontal ground motions. The effects of some parameters are evaluated analytically by finite element methods and the results are compared with corresponding experimental data. Findings from this study provide a simple expression to estimate plastic hinge length of RC columns subjected to the combined effect of near-fault vertical and horizontal ground motions

Exploring the Tight Asymptotic Bounds of the Trade-off Between Query Anonymity & Communication Cost in Wireless Sensor Network

We address query-anonymity in the context of wireless sensor networks. Query-anonymity is the property that the destination of a client’s query is indistinguishable from other potential destinations. Prior work has established that this is an important issue, and has also pointed out that there appears to be a natural trade-off between query-anonymity and communication-cost. We explore what we call the limits of this trade-off: what is the communication-cost that is sufficient to achieve a certain query-anonymity, and what is the communication-cost that we must necessarily incur to achieve a certain query-anonymity? We adopt an unconditional notion of query-anonymity that we argue has intuitive appeal. We then establish the limits of the trade-off. In particular, we show that in wireless sensor networks which are source-routed, the necessary and sufficient communication-cost for query-anonymity asymptotically smaller than the diameter of the network d is a function of d only, and the necessary and sufficient communication-cost for query-anonymity larger than d is a function of the desired query-anonymity only. Our result applies to any network topology that is an arbitrary connected undirected graph. We validate our analytical insights empirically, via simulations. In summary, our work establishes sound and interesting theoretical results for query-anonymity in wireless sensor networks, and validates them empirically.4 month

Seismic Performance of High-Rise RC Shear Wall Buildings Subjected to Ground Motions with Various Frequency Contents

Construction of tall buildings in societies is rising up for the increased population and limitation in horizontal expansion of cities. Therefore, behavior of these structures against earthquake essentially requires investigation. Recent research has shown that frequency content parameter of an earthquake has remarkable impacts on seismic response of buildings. This study aimed to investigate direct effects of frequency content on high – rise buildings. Thus, six Reinforced Concrete (RC) central core 10, 15, 20, 25, 30, and 35- story buildings were built in open source software OpenSees, and their seismic behavior under seismic records with various frequency contents were investigated. In this research,  non – linear dynamic Time – History was carried out and also behavior of buildings was compared in drift, shear force of stories, and maximum displacement of stories. Results of Time – History analysis showed that low – frequency content records have the highest effects on buildings. Most of the responses of drift and displacement of stories pertained to low – frequency contents in low – rise 10 and 15-story buildings. Although the most shear force of stories was related to low – frequency contents, with increasing height of buildings, shear force of stories increased, too. So that under Kobe Japan record which has the lowest frequency content among all records in this paper. Maximum shear force of stories was 6840 ton in 10-story building, whereas it was 12332 ton in 35- story building

Strengthening of Vulnerable RC Moment Resisting Frames Using Direct Internal Connection of X-Steel Bracing

Non-ductile reinforced concrete frames are commonly found in older buildings in many parts of the world. These structures are designed for gravity loads, have limited lateral strength and ductility, are prone to excessive one-way lateral movement and soft-story mechanism. This paper focuses on the retrofit of an existing reinforced concrete frame, using steel X-braces by direct internal connection method. The main purpose is the analytical study of general behavior and response of large-scale vulnerable frames. An experimental study was used to validate the numerical modelling performed in ABAQUS. Next, the base models were retrofitted with X-braces and four proposed direct internal connection methods. Additionally, in separate parametric studies, the effect of frame-type, bracing cross-section dimensions and gusset plate shape were investigated. The results indicated that the stiffness, bearing capacity and absorbed energy of the reinforced concrete frame by using steel X-braces increases up to 4, 2.3 and 1.5 times, respectively. Moreover, bracing acts like the first defense system against lateral loads, such as structural fuse with its yield, increases the amount of energy dissipation. It also removes the plastic hinges by reducing the ultimate displacement and stress of lateral load in the panel zone

The effect of the operational characteristics of the tractor composite electronic measurement system by the standards of emotion on the performance of chisel plows in a clay loam soil

A microcontroller based instrumentation package was designed, developed and mounted on an 81 kW Massey Ferguson 399 (MF-399) tractor. This package continuously measures and monitors various performance parameters of the tractor and implement. These parameters were: actual forward speed, theoretical forward speed, slip, fuel consumption and implement draft. The package comprised of four components: power supply, transducers, data acquisition, and display unit. Power was taken from the tractor battery. The data acquisition system was capable of scanning the data at 0.1 s intervals. The system performed well during the field operations and the results obtained showed that the accuracies of the transducers were acceptable

Experimental Study on the Effect of Fibers on Engineered Cementitious Composite Short Square Columns

Recent earthquakes severely damaged short columns due to high lateral stiffness and low ductility. Some conditions, such as reductions in the heights of some columns compared to others on the same floor, deep beams, partially buried basements, and non-structural walls, cause short column effects. The prominent characteristics of engineered cementitious composites (ECCs) reinforced with polyvinyl alcohol (PVA) fibers – including their high tensile strength, micro and multiple cracks, energy dissipation, high ductility, and strain hardening – lead to improved seismic performance and economic efficiency in structure elements. In this study, 11 ECC columns with different fiber fractions (0–1.5%) and aspect ratios (3–7), as well as one conventional concrete column, were tested and evaluated. The results showed that increasing fiber friction and shear aspect ratio increased the length of the plastic hinge zone and ductility by at least 50% and 100%, respectively. Furthermore, the failure mode changed from brittle shear to ductile shear

Mesh dependency phenomenon in the nonlinear behavior of RC members under the blast loading

اگرچه داده‌های آزمایشگاهی اطلاعات ارزشمندی را در خصوص رفتار اعضای بتن‌آرمه و پاسخ پسماند آنها ارائه می‌دهند، اما این آزمایشات چه به صورت مقیاس‌شده و چه در مقیاس واقعی از یک سو پرهزینه و وقت‌گیر بوده و از سوی دیگر، روندهای ارائه‌شده در طراحی و بررسی رفتار اعضا تحت اثر انفجار در دسترس نمی‌باشد. در حال حاضر، با استفاده از روش تحلیل اجزاء محدود غیرخطی، با یک زمان و هزینه کمتر، می‌توان پاسخ کامل اعضای بتن‌آرمه را تحت هرگونه شرایط بارگذاری از جمله انفجار بدست آورد. ظرفیت باربری یک عضو بتن‌آرمه وابسته به اندازه المان و نوع مش‌بندی گفته می‌شود هنگامی که مقادیر تخمینی وابسته به اندازه عضو باشند. در حقیقت وابستگی مقدار بار گسیختگی به اندازه المان به آزاد شدن انرژی الاستیک ذخیره‌شده به سبب انتشار ترک که نهایتا منجر به گسیختگی برشی تیر بتن‌آرمه می‌گردد، نسبت داده می‌شود. هدف اصلی این تحقیق بررسی اثر اندازه المان در تحلیل غیرخطی اعضای بتن‌آرمه و دستیابی به پاسخ این سئوال می‌باشد که رفتار اعضای بتن‌آرمه تحت اثر انفجار آیا وابسته به اثرات ابعاد المان می‌باشد یا خیر. این هدف با مقایسه مقادیر آزمایشگاهی و نتایج مدلسازی عددی و پیش‌بینی‌شده دنبال می‌شود. نتایج حاصل از تحلیل‌ها نشان می‌دهند که اجزاء مربعی منجر به نتایج نزدیک‌تر به واقعیت می‌شوند. بطور مثال، شبکه‌بندی مربعی با 7 درصد خطا در مقاومت نهایی و شکل‌پذیری در قیاس با نمونه آزمایشگاهی نزدیک‌ترین پاسخها را ارائه نموده است. همچنین بررسی در مورد ابعاد بهینه شبکه بیانگر آن است که یک اندازه مشخصه 25 میلیمتر برای اعضای بتن‌آرمه، مناسب‌ترین گزینه است

The effect of moment redistribution on the stability of reinforced concrete moment resisting frame buildings under the ground motion

In recent years some studies have been done on the moment rredistribution in buildings and new methods offered for calculating of redistribution. Observations demonstrated that the combination of moment and shear force is important in analysis of reinforced concrete structures. But little research is done about the effect of redistribution by using moding in software. In order to study the effect of moment redistribution on the stability of RC moment resisting frame structures, four buildings with 4, 7, 10 and 13 story have been considered. In these models, the nonlinear behavior of elements (beam and column) is considered by the use of interaction PMM hinges. The average plastic rotation was calculated by performing pushover analysis and storing stiffness matrix for 5 points and then the buckling coefficients were obtained by conducting buckling analysis. By the use of modal analysis natural frequency was calculated and it was attempted to be related the average plastic rotation with the buckling coefficients and the natural frequency.   It could be concluded that increase in the plastic rotation reduce the buckling coefficients to about 96% which this amount of reduction is related to the average plastic rotation. Moreover, the buildings experience instability state when the average plastic rotation reached to 0.006 radian