8,996 research outputs found
Behavior of RC beams patch repaired and strengthened with FRP composites : a numerical study
No full textIncludes bibliographical references.Reinforced concrete (RC) beams get deteriorated and become deficient mainly due to corrosion of steel reinforcements, poor maintenance and design, earthquakes and aging. Patch repair and structural strengthening using fiber reinforced polymers (FRP) have been increasingly adopted all over the world as an economical solution to upgrade the load carrying capacity of such beams. However, the failure modes of such repaired and strengthened RC beams are governed by brittle and sudden premature debonding which involves separation of external reinforcement; i.e. FRP and RC beam. Different researchers have used different approaches including experimental, analytical and numerical to investigate the behavior of patch repaired and FRP strengthened RC beams. It is noteworthy that there are no such numerical studies that investigated the effect of patch repair. In this study, a numerical investigation was carried out using the commercial finite elements analysis software ABAQUS with the aim of investigating the overall behavior of RC beams patch repaired and strengthened with FRP plates including the failure mechanisms
Modelling delay and noise in arbitrarily coupled RC trees.
Full text linkClosed-form equations for second-order transfer functions of general arbitrarily coupled resistance-capacitance (RC) trees with multiple drivers are reported. The models allow precise delay and noise calculations for systems of coupled interconnects with guaranteed stability and represent the minimum complexity associated with this class of circuits. Their accuracy is extensively compared against other relevant models and is found to be better or comparable to more expensive models. All results are derived from a theoretical approach, and their physical basis is examined. The simplicity, accuracy, and generality of the models make them suitable for use in early signal integrity analyses of complex systems and incremental physical optimization
Analysis of retrofitted RC beam with fixed end supports against blast loads
No full textCurrently, there are adequate guidelines available for FRP retrofitting RC structures against static and seismic loads. However, there is still limited information on retrofitting RC structures against short-duration dynamic loading effects such as blast loading. Due to the increasing threat of terrorism in recent years, retrofitting of RC structures against blast loading is of paramount importance in structural engineering. In this paper, a dynamic model that is based on single-degree-of-freedom (SDOF) approach is developed for the analysis of the response of retrofitted fixed end supported RC slabs subjected to blast loads. A previously validated layered capacity analysis method is used to determine the yielded and ultimate blast resistant capacity of a cross-section of a RC slab which allows varying strain rates with time along the depth of the member. The corresponding deflections are determined by plastic hinge analysis. To simplify the calculation process, a tri-linear resistance-deflection function which consists of elastic, elasto-plastic and plastic region for fixed end supported RC slabs is converted to an equivalent bilinear function. This developed model can adequately predict the retrofitted members’ response to blast loading. It is then is used to conduct a parametric study to optimise the retrofitting of RC slabs subjected to blast loading by varying the quantity, material type and technique of retrofitting.Chengqing Wu, C. Wu, William Chen, Deric John Oehler
Simultation of pressure impulse diagrams for foam protected RC members
No full textProtection of critical infrastructure against bomb attacks due to the rising threat of terrorism requires more attention. An effective solution to mitigate blast effects on infrastructure is to protect them with foam material cladding. In this paper a load cladding structure interaction model based on finite element approximations developed in a previous study is used to simulate the response of foam protected RC members under blast loads. In the load cladding structure interaction model, the foam cladding layer over the member is modelled as inelastic springs with nonlinear stiffness and a series of springs are connected at each node of the RC member while the RC beam is modelled as small regions referred to as hinges together with large non-hinge regions. Using the coupled load cladding structure interaction model, parametric studies are conducted to generate pressure impulse diagrams for slabs cladded with aluminium foam with various thickness and density. From the pressure impulse diagrams, it can be concluded that aluminium foam is effective in mitigating blast effects on RC members. The derived pressure impulse diagram can be used in preliminary design calculations to ensure a structure is adequately protected using aluminium foam. © 2013 Taylor & Francis Group.C. Wu and H. Sheikhhttp://www.crcpress.com/product/isbn/978041563318
A Compact 10-MHz RC Frequency Reference With a Versatile Temperature Compensation Scheme
No full textThis article presents the design and implementation of a compact CMOS RC frequency reference. It consists of a frequency-locked loop (FLL) that locks the period of a voltage-controlled oscillator (VCO) to the time an RC network takes to charge to a reference voltage. Conventionally, an RC time constant with a near-zero temperature coefficient (TC) is realized by using a trimmed network of resistors with different TCs. In this work, such a network is used to realize a temperature-dependent reference voltage whose TC cancels that of a single-resistor RC time constant. Compared with the conventional approach, which requires resistors with TCs of opposite polarity, the proposed approach can be implemented with resistors with TCs of similar polarity, and so it can be implemented in most CMOS processes. To compensate for RC spread, a trimmed capacitor is used to adjust the nominal frequency. Two prototype chips were made, one based on p- /n-polysilicon resistors and other based on silicided/p-diffusion resistors. Fabricated in a standard 180-nm CMOS technology, the polysilicon-based prototype has an active area of 0.01 mm2 and an absolute inaccuracy of ±2800 ppm from -45 °C to 125 °C with a fixed TC-trim and a one-point frequency trim. After one week of accelerated aging at 150 °C, however, significant drift (5000 ppm) was observed. The diffusion-based prototype exhibits greater inaccuracy (±14 400 ppm) but much less drift (600 ppm).Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic InstrumentationMicroelectronic
Fragmentation from spallation of RC slabs due to airblast loads
No full textTerrorist attacks using improvised explosive devices on reinforced concrete buildings create a rapid release of energy in the form of a shock wave. Most casualties and injuries resulting from such an attack are not caused by the blast itself, but rather by the disintegration and fragmentation of the RC member due to concrete spallation on the opposite side of the member and which is propelled at high velocities depending on the size of the fragments. Therefore, it is important to analyze the size distributions of the concrete fragments from spallation. In this paper, two RC specimens were tested under explosive loading in a blast chamber: the first, a reinforced concrete (RC) specimen; and the second, an identical RC specimen retrofitted with 6 near surface mounted (NSM) carbon fibre reinforced polymer (CFRP) plates on both the top and bottom faces. Both specimens were subjected to the equivalent 2.1 kg of TNT at a standoff distance of 0.6 m, resulting in significant scabbing of the concrete. All fragments resulting from the blast tests were collected and analyzed. A sieve analysis was carried out to investigate the size distributions of the fragments from the two specimens. It was found that the fragment size followed both a Weibull distribution and a Rosin–Rammler–Sperling–Bennet (RRSB) distribution. The distribution of the fragment shape factor was also studied. The fragment shape factors were distributed according to the lognormal distribution. Furthermore, the influence of fragment size distribution on energy density dissipation was evaluated.Chengqing Wu, Ratni Nurwidayatia and Deric John Oehler
Response of shear-deficient reinforced circular RC columns under lateral impact loading
No full textThis paper reports the results of an extensive experimental investigation on the behavior of shear-deficient reinforced circular RC columns under lateral impact loading. First, it provides a brief literature review on studies of the dynamic response induced by vehicle collisions on RC columns highlighting the lack of experimental tests on vertical elements. In this context, a novel facility for testing of vertical elements under lateral impact loading was realized. Two different types of RC columns characterized by different hoop spacing were tested, representing a one-third scaled model of a reinforced circular bridge pier, designed with obsolete design practice with particular reference to non-seismic areas. A total of 10 specimens (5 for each type) were tested under a lateral rigid-hammer impact at different impact velocities (2.25, 3 and 4.5 m/s) and boundary conditions (cantilever and fixed-simply-supported). The impact load was applied at the typical vehicular impact location, i.e. near the base. A description of the impact and reaction forces, of the lateral displacements and accelerations, of the damage development and of the post-impact damage is given. The dynamic response and the observed damage are found to be significantly affected by the column type, the impact velocity and the boundary condition. A brittle shear-type damage was observed, characterized by one main diagonal crack originating from the base of the column to the impact point, revealing the high vulnerability of these structural elements
"Fluid Color" Sigh : A Useful Indicator for Discrimination Between Plemal Thickening and Plemal Effusion
No full textExperimental and numerical study on the behavior of circular RC columns under impact loading
No full textColumns of overpasses are highly exposed to the potential hazard of vehicular collisions. This type of collisions occurred in the past, sometimes with catastrophic consequences. Previous research reported in the literature has explored the dynamic response of RC column under impact loading using both numerical and experimental methods. The majority of the available tests were performed on horizontal elements featuring beam characteristics. In this context, a new facility for the testing of vertical elements featuring the real characteristics of RC columns was realized in the Collision Laboratory of Nanjing Tech University. Four impact tests on cantilever circular RC column were conducted using this facility. The diameter of the column is 330 mm and the height is 1700 mm. The column is a one-third scaled model of a 5.2 m tall RC bridge pier. All the columns have the same configuration of the longitudinal reinforcement bars and two different hoop spacings both representing the case of a low shear reinforced structural element. Impact force, lateral displacements and accelerations were measured. A high-speed camera was adopted to record the evolution of the damage of the RC column during the impact. A brittle shear-type damage was observed characterized by one main diagonal crack located from the rear base of the column to the base of the impact point. Finally, a numerical study was also conducted using LS-DYNA showing a good agreement with the experimental results, especially in the low-velocity impacts. Results highlighted the vulnerability of these structural elements under impact loading
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